Method of synthesizing vanadium carbide and layered double hydroxide-based composites for solar hydrogen production
12390799 ยท 2025-08-19
Assignee
Inventors
Cpc classification
B01J35/33
PERFORMING OPERATIONS; TRANSPORTING
B01J37/084
PERFORMING OPERATIONS; TRANSPORTING
B01J37/10
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J27/00
PERFORMING OPERATIONS; TRANSPORTING
B01J35/33
PERFORMING OPERATIONS; TRANSPORTING
B01J37/03
PERFORMING OPERATIONS; TRANSPORTING
B01J37/10
PERFORMING OPERATIONS; TRANSPORTING
B01J37/34
PERFORMING OPERATIONS; TRANSPORTING
Abstract
There is disclosed a method of constructing a layered double hydroxide (LDH) material comprising selected metal ions, and employing metallic vanadium carbide (V.sub.2C) for promoting conductive properties of the LDH material, wherein the layered LDH material is a trimetallic LDH material. The trimetallic LDH material comprises selected Ni.sup.2+, Co.sup.2+, and A.sup.3+ metal ions with its cationic configuration for improving photocatalytic properties of the LDH material, wherein trimetallic nickel-cobalt-aluminium layered double hydroxide (Ni.sub.xCo.sub.yAl.sub.z LDH) and vanadium carbide MXene (V.sub.2C)-based composite is coupled with a graphitic carbon nitride (g-C.sub.3N.sub.4) nanosheet, to form a hybrid-junction photocatalyst. Also disclosed is a layered structure of vanadium carbide (V.sub.2C) MXenes, comprising trimetallic nickel-cobalt-aluminium layered double hydroxide (Ni.sub.xCo.sub.yAl.sub.z LDH) and vanadium carbide MXene (V.sub.2C) coupled with graphitic carbon nitride (g-C.sub.3N.sub.4), forming a Ni.sub.xCo.sub.yAl.sub.z LDH/g-C.sub.3N.sub.4 hybrid-junction photocatalyst.
Claims
1. A method of constructing a hybrid-junction photocatalyst, wherein the hybrid-junction photocatalyst comprises a composite of a layered double hydroxide (LDH) material comprising selected metal ions, and vanadium carbide MXene (V.sub.2C) for promoting conductive properties of the LDH material, wherein the layered LDH material is a trimetallic LDH material comprising nickel-cobalt aluminum layered double hydroxide, wherein the method comprises coupling the trimetallic nickel-cobalt-aluminium layered double hydroxide (Ni.sub.xCo.sub.yAl.sub.z LDH) and vanadium carbide MXene (V.sub.2C)-based composite with a graphitic carbon nitride (g-C.sub.3N.sub.4) nanosheet, to form the hybrid-junction photocatalyst.
2. The method of claim 1, wherein the layered LDH material exhibits a hexagonal nanoplates structure.
3. The method of claim 1, wherein the trimetallic LDH material comprises selected Ni.sup.2+, Co.sup.2+, and Al.sup.3+ metal ions with its cationic configuration for improving photocatalytic properties of the LDH material.
4. The method of claim 1, wherein the formed hybrid-junction photocatalyst is a Ni.sub.xCo.sub.yAl.sub.z LDH/g-C.sub.3N.sub.4 hybrid-junction photocatalyst.
5. The method of claim 1, wherein the g-C.sub.3N.sub.4 nanosheet is synthesized via thermal polymerization of melamine.
6. The method of claim 1, wherein the vanadium carbide MXene (V.sub.2C) is is synthesized through selective etching with hydrogen fluoride acid.
7. The method of claim 1, wherein the trimetallic LDH material is prepared through co-precipitation-assisted hydrothermal treatment, incorporating highly active transition metals.
8. The method of claim 7, the highly active transition metals being Ni, Co, and Al, with the regulation of the cationic composition at a controlled layer charge density.
9. The method of claim 1, wherein construction of the trimetallic LDH material in S-scheme heterojunction is further done, leading to a hybrid junction comprising a combination of S-scheme heterojunction and a Schottky-junction system.
10. The method of claim 9 wherein enhanced photocatalytic hydrogen production is conducted through the construction of the S-scheme heterojunction system for electron transfer.
11. The method of claim 1, wherein the hybrid-junction photocatalyst is used for converting water into solar hydrogen.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other aspects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
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DETAILED DESCRIPTION OF THE INVENTION
(32) The aspects of the proposed portable and direct solar thermal desalination system according to the present invention will be described in conjunction with
(33) The present invention proposes the synthesis of a self-assembled V.sub.2C-based binary and ternary composite, in particular, trimetallic nickel-cobalt-aluminium layered double hydroxide (Ni.sub.xCo.sub.yAl.sub.z LDH) and vanadium carbide MXene (V.sub.2C) coupled with graphitic carbon nitride (g-C.sub.3N.sub.4) to form a Ni.sub.xCo.sub.yAl.sub.z LDH/g-C.sub.3N.sub.4 hybrid-junction photocatalyst. In an embodiment of the present invention, a 2D layered structure of vanadium carbide (2D V.sub.2C) MXenes with a hollow porous structure is synthesized through a simple approach and coupled with a novel trimetallic aluminium nickel cobalt and layered hydroxide (AlNiCo-LDH). The invention aims at an enhanced photocatalytic hydrogen production conducted through the construction of an S-scheme heterojunction system for electron transfer.
(34) In an embodiment of the invention, the construction of trimetallic LDH consists of selected Ni.sup.2+, Co.sup.2+, and Al.sup.3+ metal ions with its cationic configuration improves the photocatalytic properties of the single LDH material while the employment of metallic V.sub.2C to promote the conductive properties. The g-C.sub.3N.sub.4 nanosheet is synthesized via the thermal polymerization of melamine, while V.sub.2C is synthesized through selective etching with hydrogen fluoride acid. Trimetallic carbonate-intercalated trimetallic LDH is prepared through co-precipitation-assisted hydrothermal treatment, incorporating highly active transition metals (Ni, Co, and Al) with the regulation of the cationic composition at a controlled layer charge density.
(35) Vanadium carbide (V.sub.2C) MXene, a transition metal, exhibits significant potential as an innovative cocatalyst to enhance photocatalytic efficiency. It can achieve efficient charge carrier separation owing to higher conductivity, abundant active sites, and higher light absorbance properties. V.sub.2C MXene is thinner than other MXene families, offering them a large specific surface area for photonic absorption, favoring the photocatalytic process. Positive enhancement in the photocatalytic activity through the employment of LDH-based catalysts, composed of a trimetallic combination of Ni, Co, and Al metal cations, have been attributed to their excellent conductive metal species and highly active transitional metal elements. The compositional flexibility of divalent and trivalent metal cations in the brucite layer enhances its functionality in the photocatalysis process. The optimization of their electronic structure is attained by tuning the chemical composition of the cations and anionic identity in the interlayer gallery of LDH. Integrating photoactive metal cations into the brucite layer of LDH generates a visible-active photocatalyst and Ni/Co metals ratios enhances the structure and morphology for a higher photocatalytic efficiency.
(36) In an embodiment of the invention, the investigation of photocatalytic hydrogen production is conducted through the construction of an S-scheme heterojunction electron transfer system. The interfacial Schottky junction with the distinct architectural structure of binary multilayered V.sub.2C supported on g-C.sub.3N.sub.4 offers photocatalytic enhancement to 4.23-fold higher than single g-C.sub.3N.sub.4, with 360 mol g.sup.1 h.sup.1 maximal H.sub.2 production. Comparative analysis on the effects of the etching time of vanadium aluminium carbide (V.sub.2AlC) precursor on the structural development of V.sub.2C reveals that HF etching of V.sub.2C for 24 h results in a well-defined layered structure with promoted photocatalytic efficiency. A comparative study on the atomic ratio of carbonate intercalated trimetallic LDHs (Ni.sub.xCo.sub.yAl.sub.z) suggests that cationic regulation into Ni.sub.1Co.sub.1Al.sub.1 LDH significantly enhances the optical properties and physical attributes of the LDH material, resulting in the highest H.sub.2 yield. The S-scheme charge transfer in binary Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 augments the photocatalytic activity up to 254 mol g.sup.1 h.sup.1 with 5.08- and 2.98-times improvement than single Ni.sub.1Co.sub.1Al.sub.1 LDH and g-C.sub.3N.sub.4, respectively. The construction of ternary g-C.sub.3N.sub.4/V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH proffers the best H.sub.2 yield of up to 474 mol g.sup.1 h.sup.1, almost twice the enhancement of its binary counterparts. The improvement in the photocatalytic activity of the ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 is influenced by several factors, such as efficient charge transfer owing to the synergy of S-scheme and Schottky barrier, morphological compatibility, and excellent photophysical properties.
(37) According to the invention, it proposes the construction of trimetallic LDH in S-scheme heterojunction and explores the intercorrelation between the cationic. In an embodiment of the invention, the co-effect of tuning the cationic ratio between divalent (Ni+Co) and trivalent (Al) metal relative to the layer charge density on the photophysical properties of the LDH is analysed. The significance of the di- and trivalent cations on the reaction activity ascertains the intercorrelation of the cationic effects on the LDH properties. An optimal ratio of 2% NiCoAl-LDH with gCN is found to be highly active under visible irradiation with befitting band gap energies for maximal photon absorption. Besides, a well formation of Ni.sub.1Co.sub.1Al.sub.1 LDH nanoplatelet structures with good dispersion onto the planar structure of gCN offers maximal exposure of active sites for efficient solar to hydrogen conversion. In another embodiment of the invention, the photocatalytic stability is examined to investigate the structural and chemical stability of 2D/2D NiCoAl/gCN under continual reaction activity.
(38) In an embodiment of the invention, S-scheme heterojunction of 2D/2D 2NiCoAlCN is designed by finely adjusting the cationic composition of M.sup.2+/M.sup.3+ in Ni.sub.xCo.sub.yAl.sub.z LDH relative to its layer charge density. The cationic ratio of Ni.sub.xCo.sub.yAl.sub.z LDH is varied at different layer charge densities (x: 0.25, 0.33, 0.5) and its photocatalytic effects is analysed. The optimal cationic ratio of Ni.sub.1Co.sub.1Al.sub.1 LDH in 10-2NiCoAlCN nanohybrid, with a layer charge density (x) of 0.33, exhibits the highest hydrogen production rate of 254 mol g.sup.1 h.sup.1 which is two- and four-times enhancement than pure gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH. S-scheme electron transfer mechanism plays a pivotal role in facilitating an efficient electron-hole transport within the 2NiCoAlCN, which promote the oxidizability and reducibility in the nanohybrids for enhancing the overall redox activity. In an embodiment of the invention, the cationic effects suggest an enhanced interaction between the metal hydroxides layer and adsorbed molecules in 2NiCoAlCN, which augment its photocatalytic activity. The adjustment of the cationic ratio and charge density has a notable influence on the electronic properties of the LDH, as evidenced by variations in the band gap value. In an embodiment, Ni.sub.1Co.sub.1Al.sub.1 LDH (E.sub.BG: 2.21 eV) and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH (EBG: 2.84 eV) exhibit narrower band gaps, enabling them to be active under visible irradiation. In contrast, Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH displays a larger band gap value of 3.04 eV. The narrower band gaps of Ni.sub.1Co.sub.1Al.sub.1 LDH and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH contribute to their enhanced performance, allowing for better utilization of visible light for photocatalytic processes. In the morphological perspective, Ni.sub.1Co.sub.1Al.sub.1 LDH sample exhibited a prominent nanoplate structure with well-defined edges, indicating the formation of a stable hydrotalcite structure with higher crystallinity. In another embodiment of the invention, larger crystallite size obtained in Ni.sub.1Co.sub.1Al.sub.1 LDH (9.07 nm) with enhanced S.sub.BET of 115.75 m.sup.2/g increase the surface-active sites and improve its photonic absorption. In contrast, the Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH sample with a lower cationic ratio displayed aggregated, coalesced, and smaller nanoplates attributing to a lower specific surface area (S.sub.BET) of 95 m.sup.2/g for Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH. A higher layer charge density of Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH (x: 0.5) may lead to the formation of non-pure LDH phases, as evidenced by its poor crystallinity and visible inactivation.
(39) The present invention also proposes a method to construct 2D V.sub.2C MXene with 3D/2D binary AlNiCo-LDH/g-CN/V.sub.2C composite with higher efficiency and stability for converting water into solar hydrogen/green hydrogen production. The 2D V.sub.2CTx helps to optimize solar energy usage, allowing for an increased semiconductor sensitivity and helping to optimize solar hydrogen generation. This new sensitizer may be used in conjunction with a variety of semiconductors, layered structure LDHs and graphitic carbon nitrides, to maximize the use of solar energy and increase hydrogen generation.
(40) In an embodiment of the present invention, an experimental setup is developed for the synthesis of Ni.sub.xCo.sub.yAl.sub.z LDH. Ni.sub.xCo.sub.yAl.sub.z LDH is synthesized through co-precipitation-assisted hydrothermal treatment, as illustrated in
(41) In an embodiment of the present invention, an experimental setup is developed for the synthesis of V.sub.2CTx MXene. Vanadium aluminium carbide (V.sub.2AlC>98%) undergoes wet chemical etching to yield 2D structured vanadium carbide (V.sub.2CTx) MXenes, as shown in
(42) In an embodiment of the present invention, the composite of V.sub.2C/g-C.sub.3N.sub.4 is prepared via a physical mixing method, as demonstrated in
(43) In an embodiment of the present invention, Ni.sub.xCo.sub.yAl.sub.z-LDH/g-C.sub.3N.sub.4 composite (xNiCoAlCN) with different mass ratios is prepared using the physical mixing method, The schematic illustration for the composite preparation is demonstrated in
(44) In an embodiment of the present invention, the preparation of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 composite is conducted using the physical mixing method followed by the sonication technique.
(45) In an embodiment of the invention, the photocatalytic hydrogen production experiments are carried out in a liquid slurry photoreactor system equipped with a 35 W HID Xe Lamp (k=420 nm) and an intensity of 20 mW cm.sup.2 as a visible source. In particular, 0.1 g of the photocatalyst is dispersed into the mixture solution of 95 mL distilled water with 5 mL (5%) vol of methanol as a sacrificial agent under continuous stirring. Nitrogen (N.sub.2) serves as a carrier gas and is supplied to the reactor system for cleaning out the system before the reaction starts to remove any impurities. The sampling bag is purged with N.sub.2 to ensure no residual H.sub.2 gas from previous experiments. The reaction starts when the lamp is turned on, and N.sub.2 gas is let flow continuously at a flow rate of 15 mL min.sup.1. The reaction is carried out for a duration of 4 h, and the concentration of H.sub.2 (ppm) collected in the sampling bag is measured every 1 h of the reaction using a gas analyzer (for eg; Brotie Model 100). Pure catalysts such as g-C.sub.3N.sub.4, V.sub.2AlC, V.sub.2C, NiCoAl LDH, the binary composite of V.sub.2C/g-C.sub.3N.sub.4, NiCoAl LDH/g-C.sub.3N.sub.4, and the ternary composite of V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 are characterized by XRD, Raman, FTIR, FESEM, EDX, TEM, UV-Vis, PL, M-S, and XPS to investigate their structural crystallinity, chemical composition and structure, optoelectronic properties, and surface morphology.
(46) XRD analysis is performed to authenticate the crystal structure and mineralogy of the prepared samples. The XRD patterns of, V.sub.2AlC, and V.sub.2C at different etching times, are shown in
(47) In XRD analysis of NiCoAl LDH/g-C.sub.3N.sub.4, apparent peaks observed in
(48) Conversely, smaller basal spacing is observed (c=22.63 ) at the optimum cationic ratio of Ni.sub.1Co.sub.1Al.sub.1 LDH with a layer charge density of x=0.33. A higher charge density promotes a stronger electrostatic interaction between the metal hydroxides layer and adsorbed molecules, which could also affect the structural stability and significantly impact the photocatalytic performances. Notably, fine-tuning the cationic ratio relative to charge density can also adjust the band gap energy of the LDH material, which can be reflected from the tauc plot. However, excessive charge density could limit the water adsorption and restrict the interlayer space through the sandwiching effect of the carbonate anions. A slight decrease in the cell parameter a with a progressive increase of the divalent metal ions can be attributed to the variation in the ionic radius of divalent, Co (0.7 ), Ni (0.7 ) and trivalent Al (0.53 ), in the octahedral framework of NiCoAl LDH, also attributing to the repulsion of Al.sup.3+ corroborating the amorphous substitution.
(49) The crystallite sizes of the NiCoAl LDH at different cationic ratio is calculated based on Scherrer calculation with regards to the full-width-at-half-maximum (FWHM) of (003) reflections, following the trend of Ni.sub.1Co.sub.1Al.sub.1 LDH (9.07 nm)>Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH (6.82 nm), Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH (6.39 nm). A larger crystallite size is obtained at an optimum ratio of Ni.sub.1Co.sub.1Al.sub.1 LDH, influencing the changes in the electronic structure and bonding, resulting in a larger surface area exposure and an increase in the surface active sites corresponding to an enhanced solar absorption response. Smaller crystallite sizes are noticed when altering the cationic ratio to Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH can be due to the impurity formation affecting the crystal growth. The gradual increase in the Al.sup.3+ substitution to that of Ni.sup.2+, Co.sup.2+, which increases with the charge density, may potentially cause structural distortions and the formation of unstable LDH. Relevantly, tuning the cationic composition to optimal charges density (0.2<x<0.33) is crucial to avoid the formation of unwanted phases and ensure high purity of LDH material. Previous works highlighted the significant changes in the structural stability, crystallinity, and phase purity upon cationic tuning with ideal M.sup.2+/M.sup.3+ to be 2-4. The possible formation of other phases is not evident in the XRD data due to the small quantity of the formed products. However, a gradual decrease in the intensity peak from the XRD data with respect to a significant decrease in the divalent cationic ratio (Ni.sup.2+ and Co.sup.2+), elucidating poor crystallinity of the material and can be due to the formation of additional phases which impede their catalytic activity. The intense peak is noticed in Ni.sub.1Co.sub.1Al.sub.1 LDH and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH, signifying that both exhibit good crystallinity in favor of highly active Ni.sup.2+ and Co.sup.2. Additionally, as depicted in
(50) The successful construction of a ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 composite is confirmed through phase identification of each constituent material.
(51) Raman analysis is performed to analyze the vibrational states of the materials through the observation of wavenumber shifts in the Raman spectra. The Raman shift for the V.sub.2C, and V.sub.2AlC are depicted in
(52) The peaks are observed to disappear after the HF treatment, indicating the removal of the Al element. Whereas the appearance of the new peaks at 144, 195, 283, 405, 626, 688, and 988 cm.sup.1 explicates the successful formation of V.sub.2C. The peak observed at 283 cm.sup.1 is attributed to the formation of the space interval of V.sub.2C ascertains the difference in the structure from bulk V.sub.2AlC. The formation of termination groups is affirmed through the appearance of several new peaks. The peak observed at 144 cm.sup.1 confirms the creation of O-terminated V.sub.2C, while the peaks at 283 and 405 cm.sup.1 are ascribed to F and OH terminations. The approximate peak at 626 cm.sup.1 indicatively corresponds to mixed heterogeneous termination groups (F, O, OH) based on the conducted study. For the composite of V.sub.2C/g-C.sub.3N.sub.4, all the characteristic peaks of both g-C.sub.3N.sub.4 and V.sub.2C are present, indicating a successful fabrication of the nanocomposite.
(53) The Raman spectra of NiCoAl LDH at different cationic compositions, g-C.sub.3N.sub.4, and composite Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4, are presented in
(54) Raman spectra for the ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 composite are depicted in
(55) In an embodiment of the invention, the Fourier Transform Infrared Spectroscopy (FTIR) spectra are performed to further affirm the chemical phases of NiCoAl LDH at different cationic ratios, as depicted in
(56) In an embodiment of the present invention, the morphology and structure of the materials are investigated by using Field Emission Scanning Electron Microscope (FESEM) analysis. The morphological structure of V.sub.2AlC and V.sub.2C at different etching times is analysed. The morphology of V.sub.2AlC exhibits larger bulk particles. Treating V.sub.2AlC with HF successfully generates an exfoliated structure of V.sub.2C, as reported in the previous literature. The V.sub.2C is as-prepared at different etching times and morphology is analysed. Treating V.sub.2AlC at 49% of HF concentration for 12 h does not achieve a complete exfoliation and can not etch out the aluminum layers. Nevertheless, a noticeable degree of exfoliation can be observed, although it does not form a multilayered structure. The compact structure of V.sub.2C-12 can result in the inefficient transmission of charges on its surfaces, impeding the photocatalytic reaction. Increasing the etching time up to 24 h reveals a perfect structure exfoliation. This results in the formation of a well-defined multilayered structure, indicating the successful removal of aluminum from V.sub.2AlC to form V.sub.2C. An apparent formation of a broader interval layer facilitates the effective incorporation of multi-structured materials. Meanwhile, extending the HF etching of V.sub.2AlC to 48 h induces defects in the V.sub.2C structure, as evident from the formation of cheese-like morphology. A long etching period may effectively remove the Al layer from V.sub.2AlC but can result in the formation of an ill-defined structure which could negatively impact the photocatalytic activity. The structural defects formed in V.sub.2C-48 can act as centers for charge recombination, leading to a decrease in photocatalytic efficiency. Therefore, fine-tuning the etching parameters is crucial to achieve an optimized V.sub.2C structure with a well-defined multilayer structure while avoiding the over-etching of V.sub.2C.
(57) LDH exhibits the typical 2D hexagonal nanoplates structure. Generally, pure NiCoAl LDH exhibits a considerably smaller nanoscale size than other LDH types. This can be attributed to the incorporation of Al, which have a smaller cationic radius as compared to other metal cations, thereby leading to an increase in the lattice parameter. Notably, distinct differences in the morphological structure of NiCoAl LDH can be discerned in different cationic compositions. The morphological development of LDH at different cationic ratios can significantly impact the photocatalytic properties and performance efficiency. Specifically, lower cationic ratio Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH exhibits highly aggregated and smaller nanoplate sizes that coalesce. The nanoplate structure appears to be ill-defined and is more reminiscent of GD nanoparticles rather than well-defined nanoplates. Higher surface energy in Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH, due to its smaller particle sizes, results in structural clustering, reducing its surface area and limiting the availability of reaction-active sites. This is consistent with the BET surface area (SBET) analysis, where Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH exhibit the lowest S.sub.BET of 95 m.sup.2/g, followed by Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH and Ni.sub.1Co.sub.1Al.sub.1 LDH with S.sub.BET of 108.57 and 115.75 m.sup.2/g, respectively. Additionally, the non-definite nanoplates shape with the additional formation of smaller particulate structures can be attributed to the potential formation of some oxide/hydroxide phases, leading to the unstable construction of LDH. This is due to higher charges density (x=0.5) causing unwanted formation of other phases, resulting in low purity of LDH material as ascribed by previous studies. Nevertheless, fine-tuning the cationic ratio relative to the layer charge density allows for a well-constructed LDH structure. A prominent nanoplate structure can be observed at the optimal ratio (Ni.sub.1Co.sub.1Al.sub.1 LDH) with more definitive edges indicating a profound hydrotalcite formation. The proper formation of LDH facilitates improved contact formation with other materials, thereby aiding in the construction of material interfaces in heterojunction systems. Besides, a higher surface-to-volume ratio exhibited by Ni.sub.1Co.sub.1Al.sub.1 LDH permits better light utilization which could expedite the photocatalytic activity. Meanwhile, increasing the cationic ratio degenerates the hydrotalcite structure. The planar nanoplate has become disoriented, and folding within the structure has occurred. The structural disorientation may result in poor reactant diffusion t the active sites, resulting in decreased catalytic efficiency. Controlled morphology through cationic regulation is a significant step towards achieving highly efficient LDH materials, as it can notably influence photocatalytic performances.
(58) Pure g-C.sub.3N.sub.4 structure exhibits a typical 2D stacked sheet, which displays an evident asymmetrical folding pattern leading to a reduced surface area exposure. V.sub.2C/g-C.sub.3N.sub.4 composites display a sheet-on-layer morphology at 24 h of V.sub.2C HF etching. The large interval gap aids the insertion of g-C.sub.3N.sub.4 sheets sandwiched between the vanadium-containing layer of V.sub.2C. This can significantly be observed from the shifting of XRD peak at (106) V.sub.2C towards a lower angle, indicating layer expansion in the nanocomposite. Besides, the 2D planar orientation of V.sub.2C offers an effective platform for the attachment of g-C.sub.3N.sub.4, which indicatively reduce the aggregation in the g-C.sub.3N.sub.4 sheets. FESEM analysis of the Ni1Co1Al LDH/g-C.sub.3N.sub.4 composite reveals the attachment of smaller-sized LDH nanoplates onto the aggregated sheets of g-C.sub.3N.sub.4, forming a 2D/2D morphological nanocomposite. The larger planar structure of g-C.sub.3N.sub.4 facilitates the attachment of LDH nanoplates, resulting in an intimate interface contact and abundant surface-active sites. FESEM image analysis depicts the construction of ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 nanocomposite. An evident layered V.sub.2C with the attachment of g-C.sub.3N.sub.4 near its intervals gap can be observed at 1 m scale image. Larger lateral sizes of V.sub.2C endow them as a perfect supporting platform for NiCoAl LDH/g-C.sub.3N.sub.4. It is difficult to visually observe NiCoAl LDH at this scale due to its very small structural sizes. However, the well-distributed presence of NiCoAl LDH can be clearly observed at 500 nm, signifying the successful construction of the ternary composite. It is evident that a higher proportion of g-C.sub.3N.sub.4 efficiently stacks onto V.sub.2C surfaces, whereby smaller NiCoAl LDH nanoplates can be observed to be well dispersed on the g-C.sub.3N.sub.4 surfaces. The combination of 2D structures with different morphological sizes has been shown to enhance photocatalytic activity. NiCoAl LDH exhibits comparatively smaller sizes and diameters than other ternary LDH structures, influencing its optical properties and photo-absorption capabilities, likely due to the electron confinement-due sizes. Well-dispersed Ni1Co1Al LDH with the synergy of g-C.sub.3N.sub.4 and V.sub.2C as a stabilization platform to reduce the aggregation of the nanoplates, improve light absorption activity and hasten the redox performances. In addition, the nanosized Ni1Co1Al LDH creates a short diffusion channel for electron migration to undergo a reduction reaction. The distinct features of ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4, characterized by its 2D/2D/2D morphology at different structural sizes, facilitate excellent contact formation, which aids in constructing a multi-hybrid heterojunction photocatalyst.
(59) EDX mapping and elemental composition analysis of the ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 confirms that all the elements of C, N, Ni, Co, Al, V, and O are uniformly distributed in V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4. The elemental mapping of V and C discloses the even dispersion of V.sub.2C in the nanocomposite. Additionally, the elemental mapping of N reveals the integration of g-C.sub.3N.sub.4 onto the planar V.sub.2C structure. The homogeneous distribution of elemental Ni, Co, and A confirms the successful anchoring of NiCoAl LDH onto the composite. Notably, the sonication process effectively promotes the complete coverage of small NiCoAl LDH particles onto the binary V.sub.2C/g-C.sub.3N.sub.4 composite in all areas. This confirms the successful integration of morphologically tuned 2D/2D/2D V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4.
(60) The detailed structure of binary V.sub.2C/g-C.sub.3N.sub.4, NiCoAl LDH/g-C.sub.3N.sub.4, and ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 with their crystallographic interface are investigated by using Transmission Electron Microscopy (TEM) analysis. The TEM image of pure V.sub.2C is analysed with a calculated lattice spacing of 0.22 nm, corresponding to (103) crystal plane. The multilayered structure of V.sub.2C with the distribution of g-C.sub.3N.sub.4 sheets verifies their close interface interaction. The d-spacing of g-C.sub.3N.sub.4 and V.sub.2C is calculated to be 0.31 nm and 0.22 nm, assigned to the (002) plane of g-C.sub.3N.sub.4 and (103) V.sub.2C, respectively. The internal structure and the morphology of NiCoAl LDH and NiCoAl LDH/g-C.sub.3N.sub.4 with their heterojunction formation shows that pure NiCoAl LDH exhibits a small nanoplate-like structure. A more detailed view of TEM image analysis at higher magnification, reveals the inherent hexagonal nanoplate structure of the material, consistent with observations made through FESEM imaging. Meanwhile, in TEM images of NiCoAl LDH/g-C.sub.3N.sub.4, two different structures are observed to coincide, where a smaller, darker sheets-like plate is stacked onto a larger transparent sheet, suggesting the successful stacking of NiCoAl LDH onto g-C.sub.3N.sub.4. Larger g-C.sub.3N.sub.4 sheets which serve as a supporting platform for the attachment of smaller NiCoAl LDH nanoplates, promote an intimate contact formation between both semiconductors. The lattice fringe calculated at 0.26 nm is accredited to (012) plane of pure NiCoAl LDH. The labeled structure of both NiCoAl LDH and g-C.sub.3N.sub.4 further demonstrates that both are well incorporated, forming stable heterogenous nanohybrids. From the TEM images of ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4, it can be noticed that the successful construction of the ternary heterojunction composite with intimate interaction is achieved with a distinct grain boundary region formed between V.sub.2C, NiCoAl LDH, and g-C.sub.3N.sub.4.
(61) UV-Vis diffuse reflectance spectra (DRS) are performed to attain a clear understanding of the light absorption properties of the as-prepared samples. The optical properties and the electronic charge transfer path of NiCoAl LDH at different cationic ratios are explored through UV-Vis diffuse reflectance at the range of 200-800 nm, as depicted in
(62) The absorption spectra of pure V.sub.2C, g-C.sub.3N.sub.4, Ni.sub.1Co.sub.1Al.sub.1 LDH, binary V.sub.2C/g-C.sub.3N.sub.4, binary NiCoAl LDH/g-C.sub.3N.sub.4, and ternary V.sub.2C/Ni1Co1Al LDH/g-C.sub.3N.sub.4 are depicted in
(63) Intriguingly, Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH, Ni.sub.1Co.sub.1Al.sub.1 LDH, and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH exhibit different values of band gap energies, as tabulated in Table 2. The compositional ratio and the dominancy of each metal cation in the NiCoAl LDH framework are found to affect the band gap energies. Nevertheless, all NiCoAl LDH exhibit three different band gap values owing to their multifacet band structure, also ascribed to the presence of diversified electronic transitions within the LDH framework. The energy gap of Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH, Ni.sub.1Co.sub.1Al.sub.1 LDH, and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH is measured to be 2.26 (E.sub.g1), 3.04 (E.sub.g2), 3.93 (E.sub.g3), 1.69 (E.sub.g1), 2.21 (E.sub.g2), 2.85 (E.sub.g3), 2.25 (E.sub.g1), 2.84 (E.sub.g2), 3.31 (E.sub.g3), respectively. Apparently, E.sub.g1 and E.sub.g2 are attributed to the d-d transition of Ni.sup.2+(d.sup.8), and Co.sup.2+ (d.sup.7) in the octahedral coordination, while E.sub.g3 is accredited to the LMCT in the MO.sub.6 octahedra. Based on the photocatalytic consideration with respect to band potential and correlation with the performance efficiency, E.sub.g2 is selected to befit NiCoAl LDH to propel the photocatalytic process. In this context, a narrower E.sub.g1 value results in fast recombination of photogenerated charges, while a larger E.sub.g3 value obstructs the maximal visible-light absorption. Comparative analysis on the E.sub.g value of different M.sup.2+/M.sup.3+ discloses that the band gap value of trimetallic NiCoAl LDH can be modified through fine-control of the cationic compositional ratio. In this finding, under-developed Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH exhibits the largest band gap energy, which impedes their light-harvesting performance, aligning with the lower photocatalytic activity. Besides, the structure is denoted to be smaller in size, which is highly influential to the resulting band gap energy as it is suggested that the widening in the band spaces arising from the increase in the lattice parameters as the diameter gets smaller. The transition towards the visible spectrum with increasing the compositional ratio at optimal Ni.sub.1Co.sub.1Al.sub.1 LDH results in the narrowing of the band gap energy, which enhances the light-harvesting and reflects the higher hydrogen yield obtained, in comparison with Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH.
E.sub.g=(hv).sup.1/n(1)
E.sub.g=VBCB(2)
CB=XE0.5E.sub.g(3)
(64) TABLE-US-00001 TABLE 2 Band gap energies of Ni.sub.xCo.sub.yAl.sub.z LDH at different compositional ratios Layer Structural formula M.sup.II/M.sup.III charge [M.sub.1x.sup.z+M.sub.x.sup.3+(OH).sub.z].sup.x+ molar density Band gap Samples (A.sub.x/n.sup.n) .Math. yH.sub.2O ratio (x) energy (eV) Ni.sub.0.5Co.sub.0.5Al.sub.1 Ni.sup.2+ .sub.0.25Co.sup.2+ .sub.0.25Al.sup.3+ .sub.0.5 1 0.5 Eg.sub.1 2.26 LDH LDH Eg.sub.2 3.04 Eg.sub.3 3.93 Ni.sub.1Co.sub.1Al.sub.1 Ni.sup.2+ .sub.0.33Co.sup.2+ .sub.0.34Al.sup.3+.sub.0.33 2 0.33 Eg.sub.1 1.69 LDH LDH Eg.sub.2 2.21 Eg.sub.3 2.85 Ni.sub.1.5Co.sub.1.5Al.sub.1 Ni.sup.2+ .sub.0.38Co.sup.2+ .sub.0.37Al.sup.3+ .sub.0.25 3 0.25 Eg.sub.1 2.25 LDH LDH Eg.sub.2 2.84 Eg.sub.3 3.31
(65) In an embodiment of the invention, Photoluminescence (PL) analysis is conducted to evaluate the carrier separation efficiency and its effect on photocatalytic activity. The emission intensity denotes the degree of separation efficiency of the photoinduced charges pair. The PL spectra are measured based on the energy released in heat and fluorescence once the recombination of charges occurs within the material. The intense spectral intensity denotes a higher recombination of charges, indicating a higher energy released. Comparatively, weaker peak spectra signify enhanced carrier separation with regard to lower charge recombination and longer carrier lifetime. From the PL analysis of V.sub.2C, g-C.sub.3N.sub.4, and V.sub.2C/g-C.sub.3N.sub.4, (set) V.sub.2C, it can be observed that pure g-C.sub.3N.sub.4 exhibits a higher intensity peak which denotes severe carriers' recombination and lower separation efficiency. However, a lower intensity peak noticed in V.sub.2C is due to their metallic properties, which are unable to generate electron-hole pairs, thereby recording no charge recombination. Meanwhile, the addition of V.sub.2C observed a decrease in the intensity peak, explaining an enhancement in the carrier dynamics. Significantly, the formation of an electrostatic potential barrier at the g-C.sub.3N.sub.4-V.sub.2C interface owing to the electron sinking effects by V.sub.2C impedes the recombination of photogenerated charges. The redistribution of charges causes e- to be confined at V.sub.2C sites while h+ to be accumulated at the VB of g-C.sub.3N.sub.4, leading to efficient separation. PL spectra of NiCoAl LDH/g-C.sub.3N.sub.4 is analysed. The spectral of NiCoAl LDH, as displayed in
(66)
(67) The determination of flat band potential (E.sub.FB) of g-C.sub.3N.sub.4 and Ni.sub.1Co.sub.1Al.sub.1 LDH is estimated from the Mott-Schottky plot. The positive slope observed from the Mott-Schottky plot of g-C.sub.3N.sub.4 indicates its classification as an n-type semiconductor, while the negative slope observed in NiCoAl LDH indicates a p-type semiconductor. The E.sub.FB of g-C.sub.3N.sub.4 and NiCoAl LDH is calculated by the extrapolation of the Mott-Schottky plots at the x-axis, which is found to be 1.26 and +0.42 eV (vs. Ag/AgCl), respectively. By means of the Ag/AgCl to NHE conversion equation (E.sub.FB (NHE)=E.sub.FB (Ag/AgC.sub.1)+0.197), the E.sub.FB is estimated to be 1.06 and +0.62 eV (vs. NHE). Specifically, the E.sub.FB of the n-type semiconductor is more positive at approximately 0.2 eV of the E.sub.CB, resulting in a calculated E.sub.CB of g-C.sub.3N.sub.4 to be 1.26 eV (vs. NHE). Meanwhile, the E.sub.FB of p-type semiconductors is more negative by 0.2 eV than its E.sub.VB. Thereby, the calculated E.sub.VB of NiCoAl LDH is +0.82 eV (vs NHE).
(68) The influence of V.sub.2C on the interfacial features of well-structured V.sub.2C/g-C.sub.3N.sub.4 with the valence information of the surface species is investigated through X-ray Photoelectron spectroscopy (XPS) analysis with a calibration basis of C1 s at a binding energy of 284.6 eV. The detailed high-resolution spectrum of C 1s, N 1s, O 1s, and V 2p are obtained. XPS analysis of the C is region reveals the deconvolution of two peaks spectrum of V.sub.2C/g-C.sub.3N.sub.4 at 284.6 and 287.9 eV, respectively. The binding energy peak at 284.6 eV is accredited to the sp.sup.2 carbon (C-C) bond, while the peak at 287.9 eV is assigned to the NCN coordination of g-C.sub.3N.sub.4. The N 1s spectrum is deconvoluted into three binding energy peaks. Binding energy peaks presence at 397.8 and 398.4 eV is ascribed from the bond formation of sp.sup.2 CN in the s-triazine ring, whereas peak presence at 400.3 eV corresponds to the bonding of the sp.sup.2-hybridized aromatic N, C atom with the amino functional group NH forming NC3 (ternary nitrogen). Significantly, the shifting in the binding energies of C is and N is of V.sub.2C/g-C.sub.3N.sub.4 nanocomposite towards lower binding energies than in pure g-C.sub.3N.sub.4 indicates a strong electronic interaction between V.sub.2C and g-C.sub.3N.sub.4. The apparent changes in the binding peaks further affirms that the introduction of V.sub.2C leads to an increase in the donor density attributing to an improved photocatalytic reaction. The negative shift of the CNC signal by 0.7 eV describes the bond formation through the chemical reaction of electron-rich g-C.sub.3N.sub.4 with electron-deficient V.sub.2C. This drives the electron migration from the electron-rich area towards low concentration, further signifying the electronic transfer between g-C.sub.3N.sub.4 and V.sub.2C, reflecting the Schottky junction formation. Besides, the electronic transfer leaves the N sites with more positive charges, enabling hole accumulation. The deconvolution of O is spectra of pure g-C.sub.3N.sub.4, which appears at 531.9, and 533.1 eV, demonstrates the surface adsorbed oxygen and the presence of oxygen defects in the structure. The binding energy peak at approximately 530.9 eV of V.sub.2C/g-C.sub.3N.sub.4 is assigned to the CV(OH), based on the previous studies, describing the formation of the OH termination group of the V.sub.2C, which is consistent with the Raman results. On the other hand, XPS analysis reveals deconvoluted peaks spectra of V 2p of V.sub.2C/g-C.sub.3N.sub.4. Peak spectra at 512.2 and 518.0 eV are ascribed to the V.sup.2+ 2p.sup.3/2 and V.sup.2+ 2p.sup.1/2 signifying the presence of V.sup.2+, ascribing to the synergy of unreacted V.sub.2AlC and the formation of V-C. Meanwhile, the peak positioned at 515.0 and 523.0 eV is assigned to the V.sup.4+ 2p.sup.3/2 and V.sup.4+ 2p.sup.1/2, respectively, which can be attributed to the formation of vanadium oxide on the V.sub.2C surface.
(69) XPS measurements are performed to investigate the surface chemical composition, the elemental states, and binding structures of pure g-C.sub.3N.sub.4, Ni.sub.1Co.sub.1Al.sub.1 LDH, and Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4, as illustrated in
(70) The presence of distinct oxygen peaks of LDH corroborates the formation of carbonate anion in the interlayer of Ni.sub.1Co.sub.1Al.sub.1 LDH. The shifts observed in the binding energy peaks of the nanohybrids, in comparison to pure Ni.sub.1Co.sub.1Al.sub.1 LDH and g-C.sub.3N.sub.4, indicate changes in the electron density surrounding the materials. Specifically, a positive shift in the binding energies of the Ni 2p, Co 2p, and Al 2p in the Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 as compared to pure Ni.sub.1Co.sub.1Al.sub.1 LDH implying the increase in the electron density within the nanohybrids due to interfacial contact with g-C.sub.3N.sub.4, suggesting that Ni.sub.1Co.sub.1Al.sub.1 LDH as an electron-deficient counterpart. In contrast, the binding energy observed in C is and N is elements of the nanohybrids demonstrates negative shifts, thereby suggesting an interfacial electron transfer from electron-rich g-C.sub.3N.sub.4 to electron-deficient Ni.sub.1Co.sub.1Al.sub.1 LDH. This also serves as a strong indicator that Ni.sub.1Co.sub.1Al.sub.1 LDH functions as a reducing catalyst, playing a pivotal role in driving the photoreduction reaction.
(71) The phase and elemental states analysis of ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 with the binding energy of C, N, V, O, Ni, Co, and A1 has been illustrated in
(72) The presence of Ni.sup.2+ in the nanocomposite can be affirmed from the Ni 2p spectra observed in
(73) The analysis of the characterization techniques for g-C.sub.3N.sub.4, V.sub.2C, and Ni.sub.1Co.sub.1Al.sub.1 LDH, along with their binary and ternary composites and their findings are as follows: The XRD, Raman, and FTIR analysis confirms the successful preparation of single g-C.sub.3N.sub.4, V.sub.2C, and NiCoAl LDH, along with their binary and ternary composites. The successful conversion of V.sub.2AlC to V.sub.2C at different etching times is confirmed by XRD analysis. All the peaks observed in the etched V.sub.2C samples correspond to V.sub.2C, indicating the completion of the conversion process. Higher layer charge density in Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH results in poor crystallinity in the LDH structure due to the possible formation of impurity phases. Meanwhile, XRD analysis reveals Ni.sub.1Co.sub.1Al.sub.1 LDH exhibits a good crystallinity structure with larger crystallite sizes owing to well-formed crystals. Analysis of FESEM reveals that g-C.sub.3N.sub.4 exhibited a typical 2D stacked sheet, which displays an evident asymmetrical folding pattern. Meanwhile, V.sub.2C at 24 h of etching time reveals a well-defined 2D multilayer structure with a higher degree of exfoliation. The construction of smaller 2D nanoplates with less aggregated structure is achieved at the optimal composition of Ni.sub.1Co.sub.1Al.sub.1 LDH. Successful construction of the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 composite is observed, with an evident attachment of g-C.sub.3N.sub.4 sheets onto V.sub.2C surfaces and well-dispersed NiCoAl LDH nanoplates on the g-C.sub.3N.sub.4 surfaces. The EDX analysis further affirms its construction with a uniform distribution of Ni, Co, Al, V, O, C, and N elements observed in the V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite. In addition, the interface construction of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 is confirmed by TEM through IFFT analysis. The UV-Vis analysis reveals the absorption of spectra of V.sub.2C, NiCoAl LDH, and g-C.sub.3N.sub.4. Significantly, g-C.sub.3N.sub.4 depicts a semiconductor-like absorption in the blue region of the visible spectrum. The absorption intensity is apparent at the visible region in the optimal compositional ratio of Ni.sub.1Co.sub.1Al.sub.1 LDH and is red-shifted compared to Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH. The cationic composition of NiCoAl LDH is found to exert a substantial influence on the electronic properties, as evidenced by the tunable band gap value. Meanwhile, V.sub.2C displays a full-spectrum absorption owing to its metallic properties. PL analysis reveals that ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 exhibits facile charge separation with a low recombination rate of photogenerated charges compared to binary V.sub.2C/g-C.sub.3N.sub.4 and Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 owing to the construction of its hybrid-junction. XPS analysis suggests the successful fabrication of the nanocomposite and its chemical composition.
(74) In another embodiment of the invention, photocatalytic Hydrogen production and photocatalytic performance of xNiCoAlCN is evaluated to gain a clear understanding of the ratio effects of metal cations incorporated into Ni.sub.xCo.sub.yAl.sub.z LDH on photoredox activity. The hydrogen generation rate is found to be the highest with the integration of Ni.sub.1Co.sub.1Al.sub.1 LDH, followed by Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH and Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH, as depicted in
(75) Notably, a reduction in the amount of divalent Ni and Co cations in Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH constrains solar absorption capability and photon utilization. This finding demonstrates that the transition metal cations of Ni and Co serve a pivotal role in augmenting photonic absorption capacity. Thereby, a reduced amount would result in lower photocatalytic efficiency. Studies reported that the dominance of Co in the LDH framework is responsible for the favorable improvement in optical performance owing to their catalytically active properties and excellent work function. On the other hand, the dominancy of Ni is noticed to shift the absorption spectrum towards the visible range. The difference in the catalytic behavior observed by Ni.sub.0.5Co.sub.0.5Al.sub.i LDH-based composite is due to their poor solar absorption performance and larger band gap value, which can be discerned from the UV-Vis and tauc plot analysis. Besides, the formation of impurity phases with a reduction in their crystallinity structure will likely obstruct their photocatalytic activity. Additionally, the presence of an excess of divalent cations, as seen in 3NiCoAlCN, may create recombination centers that promote the recombination of photoexcited electron-hole pairs. This recombination process can hinder the overall photocatalytic activity of the material. Therefore, fine-tuning the cationic ratio in regard to their charge density is significant to ensure a stable formation of LDH structure and mitigate the dominance of specific metal cations.
(76) Photocatalytic hydrogen production over different LDH loading is evaluated and presented in
(77) The effects of sacrificial reagents on the photocatalytic activity of 2NiCoAlCN nanocomposite are demonstrated in
(78) In an embodiment of the present invention, the consistency and the photocatalytic stability of 2NiCoAlCN under visible irradiation are further explored, to appraise their photochemical efficiency and recyclability for industrial application. The photostability evaluation is conducted in consecutive cycles with TEOA as a sacrificial electron donor. In specific, the reaction activity is performed in a 5 vol. % TEOA-water mixture with 0.1 g loading of 2NiCoAlCN, and the reaction is carried out under visible irradiation for a total of 4 h per cyclic run. The concentration of hydrogen production per cyclic run is measured every 1 h and is recorded. The system is let to rest and continuously flowed with nitrogen for a minimum of 1 h to cool down and clean out the system from the residual hydrogen and impurities. The second cyclic run proceeded after 1 h with the same TEOA-water mixture and 2NiCoAlCN catalyst, following the same experimental procedures from the first cycle and is continued for the third and fourth cycles. The photocatalytic activity test over consecutive cycles revealed a stable and gradual hydrogen yield for 4 cyclic runs without any glimpse of decline, explicating the robustness of 2NiCoAlCN. Interestingly, an evident increase in the hydrogen yield is observed with apparent improvement in the third cycle, evincing 1.35 times catalytic improvement over the second cycle. The photocatalytic enhancement can be reasoned due to the activation of LDH surface upon continuous light exposure maintaining their robust catalytic activity over a longer duration. Besides, a highly stable structure of 2D/2D 2NiCoAlCN with its efficient charge transfer hampers the photodecomposition of the gCN by hampering hole accumulation. In previous study, we performed the stability test of nickel-incorporated gCN in both methanol and TEOA as a sacrificial reagent. Interestingly, gCN shown to be highly stable in TEOA-water mixture compared to in methanol-water mixture. The stability of the catalyst is observed to decrease over multiple cycles in a methanol-water environment, indicating its poor reusability as a catalyst. This may be attributed to the effectiveness and compatibility of TEOA as a hole scavenger compared to methanol when gCN is used as a catalyst. Furthermore, previous literature suggests that the decomposition of gCN may occur when it is exposed to prolonged light irradiation. This photodecomposition can be induced by the accumulation of holes on the gCN surface, which reduces the bonding energy of CN in gCN and leads to the breaking of its heptazine units in the presence of reactive oxygen species. Therefore, the employment of Ni.sub.1Co.sub.1Al.sub.1 LDH to construct the S-scheme transfer system hinders the accumulation of holes at the gCN counterpart, and the use of TEOA as an effective hole scavenger promotes stable photocatalytic performance over four cycles. In addition, a uniform distribution of Ni.sub.1Co.sub.1Al.sub.1 LDH nanoplatelets onto gCN is beneficial for the full coverage of photon energy prolong their reaction activity over the cyclic hours.
(79) In another embodiment of the invention, the spent catalyst is analyzed by using XPS to examine the changes in the elemental states and chemical stability. A comparison in the XPS binding energy for C, N, O, Ni, Co, and Al elements in fresh 2NiCoAlCN and spent-2NiCoAlCN is made. Calibration of the binding energy of C 1s is done at 284.6 eV. The C is spectra of the spent-2NiCoAlCN still maintain the same elemental states as in the fresh samples, and no chemical shifting is observed. The observed increase in spectral intensity for the NCN bond at 288.1 eV, in comparison to the C-C/CC bond at 284.3 eV, in the spent-2NiCoAlCN can be reasonably attributed to the interaction with TEOA, which contains an amine-rich group. This interaction can lead to modification in the electronic structure and chemical environment of the nitrogen-containing species. Non-apparent shifting in the binding energy of N 1s is observed for CNC, (N(C)3), and CNH of g-C.sub.3N.sub.4. However, the increase of the electronegativity in the spent catalyst might be due to its interaction with TEOA. The analysis of the binding energies peak for both C is and N is in the spent-2NiCoAlCN indicates no phase change or apparent chemical decomposition observed. The finding suggests that g-C.sub.3N.sub.4 maintains its intact structure even after undergoing four cycles of continuous photoreaction. This structural stability can be attributed to the stronger interfacial contact between g-C.sub.3N.sub.4 and Ni.sub.1Co.sub.1Al.sub.1 LDH, which effectively prevents the accumulation of holes that could otherwise trigger the breaking of the g-C.sub.3N.sub.4 structure. Besides, no indication of structural alterations is observed in g-C.sub.3N.sub.4, explaining the continual hydrogen production.
(80) To analyze the chemical changes in Ni.sub.1Co.sub.1Al.sub.1 LDH, the binding energies of Ni 2p, Co 2p, Al 2p, and O 1s are examined. The characteristic peaks in the Ni 2p spectra of spent-2NiCoAlCN, exhibited a weaker peak at a lower energy region 850.1 eV, suggesting the formation of Ni0. The formation of metallic nickel likely contributes to the increase in photoactivity observed during the cyclic hour. On the other hand, changes in the binding energies for Co 2p, might suggest oxidation in the Co element in the nanocomposite might occur. Nevertheless, the peak of Al 2p in both spent, and fresh samples shows no significant changes. Apparently, the shifting in the binding energies can be attributed to the ligand effects from triethanolamine (TEOA), which could lead to changes in electron density. The increase in the spectral intensity of the MO bond at 528.9 eV in O is of spent-2NiCoAlCN with respect to M-OH can be attributed to the formation of CoO. Despite this formation, Ni.sub.1Co.sub.1Al.sub.1 LDH demonstrates no structural degeneration and maintains good chemical stability, contributing to excellent photoreaction stability. In addition, FESEM analysis is performed on spent-2NiCoAlCN to assess its structural stability after 4 consecutive cycles. Interestingly, the composite exhibits an intact structure and no structural deformation is observed in the nanocomposite. In a closed-up FESEM image, the LDH nanoplatelet is clearly demonstrated to be evenly distributed on the gCN, with no degeneration of LDH structure which reflects its superior photocatalytic stability. This finding emphasizes the significance of the structural morphology in influencing the photocatalytic stability of semiconductors. Therefore, it is crucial to develop robust semiconductor composites that can withstand continuous solar-driven reactions in a slurry system.
(81) Further analysis using FTIR on both fresh and spent samples provides insights into the structural and chemical changes that occur during the photocatalytic reaction. The FTIR spectra of fresh/spent-2NiCoAlCN is obtained for analysis. Broader peak in the range of 2800-3600 cm.sup.1 is corresponding to surface adsorbed water molecules and stretching vibration of the amino group (NH) of gCN. Meanwhile, the presence of CN heterocycles of gCN can be observed in the presence of peak at the range of 1020-1700 cm.sup.1. A sharp peak at around 805 cm.sup.1 is attributed to the vibrational modes of the heptazine unit of gCN. Additionally, it is challenging to identify the structural units of Ni.sub.1Co.sub.1Al.sub.1 LDH possibly due to the higher proportion of gCN in the nanocomposite and the overlapping of the peaks. Nevertheless, the structural stability of 2NiCoAlCN can still be assessed since there are no new peaks appearing, and the peak structure remains unchanged, indicating the absence of new species. Besides, no obvious reduction in the peak intensity, specifically for the CN heterocycles and the heptazine units og gCN, further confirms the higher stability of the nanocomposite.
(82) The photocatalytic electron-hole transfer process adheres to the S-scheme mechanism. The Tauc plot analysis is employed to determine the band gap values of pure gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH, which are measured to be 2.9 eV and 2.21 eV, respectively. Additionally, the Mott-Schottky plot is utilized to calculate the E.sub.CB and E.sub.VB of pure gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH, respectively. For pure gCN, the E.sub.CB is determined to be 1.26 eV, and their E.sub.VB value is calculated to be 1.64 eV in reference to E.sub.VB=E.sub.CB+E.sub.BG. Correspondingly, the E.sub.VB value for pure Ni.sub.1Co.sub.1Al.sub.1 LDH determined from Mott-Schottky is +0.82 eV, while the E.sub.CB value is calculated to be 1.4 eV. The transformations of the electron density on the 2NiCoAlCN are identified based on the shifting of the binding energies in the XPS analysis. The negative shift in the binding energy of the nanohybrid with respect to the gCN suggests the reduction in the electron density, highlighting gCN as a higher electron-density region. Meanwhile, the shifting of 2NiCoAlCN towards a higher-energy region when compared to pure Ni.sub.1Co.sub.1Al.sub.1 LDH suggests the electron transfer from gCN to Ni.sub.1Co.sub.1Al.sub.1 LDH. The interface contacts between gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH lead to the formation of a weaker internal electric field, which promotes electron migration. According to Equation (4) to (5), the absorption of photons with an energy equal to or greater than the bandgap of the semiconductor photocatalysts led to the formation of electron-hole pairs. The diffusion of electrons from Ni.sub.1Co.sub.1Al.sub.1 LDH to gCN, once in contact, leads to the creation of electron accumulation and depletion layers near the interface of gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH, causing the surface of gCN to be negatively-charged while Ni.sub.1Co.sub.1Al.sub.1 LDH to be positively-charged. The formation of an internal electric field directing from Ni.sub.1Co.sub.1Al.sub.1 LDH to g-CN hastens the inversed transfer of electrons from g-CN to Ni.sub.1Co.sub.1Al.sub.1 LDH, which is consistent with the XPS analysis. The alignment in the Fermi level in the heterojunction system led to the band structure bending, resulting in the downward and upward shifting in the energy level, which facilitate the electron transfer in the S-scheme route. The distinct S-scheme transfer routes offer the eradication of unused electrons and holes at the CB of gCN and VB of Ni.sub.1Co.sub.1Al.sub.1 LDH through electron-hole Coulombic attraction. Therefore, the electrons and holes with strong redox capability are reserved, which explains the observed enhancement in the photocatalytic activity of 2NiCoAlCN nanohybrids.
(83) Besides, the S-scheme mechanism proffers excellent charge transfer pathways and effectively restrained the recombination of photogenerated charges, which is confirmed by the observed decrease in the intensity peak through PL analysis of 2NiCoAlCN nanohybrids. From Equation (6), preserved holes with stronger oxidative capability will undergo an oxidation reaction to generate protons (H+) and oxygen (O2). Some of the holes will be trapped and oxidized by TEOA to generate H.sub.2, explaining the increase in the hydrogen yield from the stability results (Equation (7)). Meanwhile, from Equation (8), the preserved electrons at the CB of Ni.sub.1Co.sub.1Al.sub.1 LDH, which has a stronger reducing capability, will undergo a reduction reaction with protons to generate hydrogen.
gCN+hv.fwdarw.e.sup.h.sup.+(4)
gCN(e.sup.)+NiCoAl(h.sup.+).fwdarw.e.sup.+h.sup.+(5)
H.sub.2O+2h.sup.+.fwdarw.O.sub.2+2H.sup.+(6)
C.sub.6H.sub.15NO.sub.3+12H.sub.2O.fwdarw.6CO.sub.2+19H.sub.2+HNO.sub.3(7)
2H.sup.++2e.sup..fwdarw.H.sub.2(8)
Thus, construction of an S-scheme electron transfer mechanism with the promotion of oxidizability and reducibility creates efficient electron-hole transport, improves charges lifetime, and enhances the catalytic reaction in 2NiCoAlCN nanohybrids. In addition, the cationic effects suggest an enhanced interaction between the metal hydroxides layer and adsorbed molecules in 2NiCoAlCN, which augment its photocatalytic activity.
(84) In an embodiment of the present invention, the photocatalytic performance of ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 and operating parameters evaluation are conducted. Significantly, the photocatalytic performance is first assessed by investigating the effects of V.sub.2C in the ternary catalyst system. The photocatalytic activity is initially conducted at 0.1 g of catalyst loading with 5 vol. % of TEOA concentration and 4 h of visible irradiation. The photocatalytic evaluation is continued by varying the TEOA at different concentrations. The optimal TEOA concentration determined from this variation is then utilized in the subsequent photocatalytic test to assess the loading of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4. Finally, the photocatalytic stability is evaluated, and the analysis of the spent catalyst is performed. The influence of V.sub.2C in the ternary catalyst system of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 is investigated, and the rate of hydrogen yield relative to V.sub.2C loading is demonstrated in
(85) The impact of Triethanolamine (TEOA) concentration on photocatalytic hydrogen production is investigated by varying the TEOA-water concentration at (vol. %: 5, 10, 15, and 20). The photocatalytic reaction is conducted using 0.1 g of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 for a 4 h reaction under visible-light irradiation. The resulting photocatalytic hydrogen yield is depicted in
(86) The effects of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 loading and its photocatalytic hydrogen yield is analysed. Optimizing the composite loading is crucial for achieving optimal photocatalytic hydrogen production. The photocatalytic activity is conducted at 10 vol. % TEOA-water concentration for 4 h reaction time. The effects of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 loading and its photocatalytic hydrogen yield are depicted in
(87) The photocatalytic stability and consistency of the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite is evaluated in 5 vol. % of TEOA-water sacrificial reagents with 0.1 g of catalyst loading. The photocatalytic reaction is conducted in a slurry photocatalytic reactor, with a total irradiation time of 4 hours for each cycle. The stability and consistency are evaluated over a total of 6 cycles of reaction activity. The experimental procedure for the ternary composite is the same as that of the binary composite. Specifically, the reaction is conducted under continuous visible-light exposure in a cyclic manner. After each cycle, the system is allowed to rest for 1 h while continuously flowing N.sub.2 gas to eliminate any residual hydrogen in the system. Subsequently, the next cyclic reaction started, and hydrogen generation is evaluated at hourly intervals. The photocatalytic stability result observes a notable increase in hydrogen production across the cyclic hour. Significantly, ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite exhibits remarkable and robust photocatalytic activity without any drop in performance. An impressive photocatalytic robustness is attributed to the distinct structure of the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite. Significantly, the effectiveness of TEOA as a sacrificial electron donor and hole scavenger offers a substantial enhancement in the structural stability of V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4. As observed in the binary V.sub.2C/g-C.sub.3N.sub.4, the presence of holes could foster the degradation kinetics resulting in the bond breaking of heptazine units in g-C.sub.3N.sub.4. Significantly, maintaining the chemical stability of the nanocomposite is of great importance, specifically in g-C.sub.3N.sub.4, as it serves as the primary catalyst, contributing the highest proportion within the nanocomposite. TEOA, which is highly compatible with g-C.sub.3N.sub.4, effectively scavenges unused holes and avoids its accumulation on g-C.sub.3N.sub.4 surfaces. In addition, the construction of a multi-hybrid heterojunction system with synergistic effects of S-scheme and Schottky junction improves the charge transfer activity in the ternary nanocomposite. This construction effectively eliminates the accumulation of unused electron-hole pairs, thereby preserving the structural stability of the material. The observed improvement in the photocatalytic performance over the 6 cyclic runs is likely to be attributed form the formation of metallic nickel, Ni.sup.0, as determined by XPS analysis on the spent-V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4. The formation of Ni.sup.0 synergistically promotes light utilization owing to its plasmonic properties and facilitates rapid photoredox reaction.
(88) For spent catalyst analysis, the comparison is made of FTIR analysis between fresh- and spent catalyst. The FTIR spectra of spent-V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 still exhibit the same functional composition as the fresh sample, signifying excellent structural stability even after 6 reaction cycles under visible-light irradiation. Significantly, a narrow peak at 805 cm.sup.1 is attributed to the vibrational modes of the tri-s-triazine unit of g-C.sub.3N.sub.4. Interestingly, there is no reduction in the peak intensity, which indicates the preservation of the intact structure of tri-s-triazine of g-C.sub.3N.sub.4. In addition, the CN heterocycles in both fresh and spent samples exhibit no changes in the peak, indicating higher structural stability. The preservation of both tri-s-triazine and CN heterocycles in g-C.sub.3N.sub.4 indicates the absence of structural decomposition. This positively suggests the ability of the ternary composite to retain its functional composition and catalytic performance during cyclic hours. Nevertheless, there is a slight reduction in the absorption band of NH functional. This can be due to the strong attachment of TEOA molecules on the g-C.sub.3N.sub.4 surface, which may partially block the light absorption of certain functional groups. Despite this reduction, the intact structure of tri-s-triazine and CN heterocycles in g-C.sub.3N.sub.4 demonstrates its excellent structural stability signifying its significance in photocatalytic hydrogen production under prolonged cyclic activity. XPS analysis is employed to investigate the chemical stability of the spent-V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 after 6 reaction cycles under visible irradiation, the binding energy of elements C, N, O, Ni, Co, Al, and V is compared with the fresh catalyst. The chemical stability of g-C.sub.3N.sub.4 in the nanocomposite can be observed from the states of the XPS peak in C is and N Is.
(89) On the other hand, no apparent peak shifting is observed for Co 2p and Al 2p, which strongly suggests higher chemical stability exhibited by the Ni.sub.1Co.sub.1Al.sub.1 LDH, thus contributing to a highly stable heterojunction system. Besides, the binding peak in O is of spent-V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 shows a significant peak shifting which is likely due to the ligand effects by TEOA which results in the change in the electronegativity. An increase in the ratio intensity of M-OH to M-O in the spent catalyst compared to the fresh sample signifies the attachment of TEOA molecules onto the catalyst surface. Significantly, during the photocatalytic reaction, the hydroxyl groups of TEOA are likely to be adsorbed on the catalyst surface and attached to the metal centers on the surface. Meanwhile, the presence of peak spectra at 512.1 and 517.6 eV in spent-V 2p, is attributed to the formation of the V-C bond, corroborates the presence of V.sub.2C and their good interaction with g-C.sub.3N.sub.4 and NiCoAl LDH. The decrease in the intensity peak ratio at 514.7 and 521.5 eV, associated with vanadium oxide formation, denotes a highly stable structure and good oxidation stability of the nanocomposite.
(90) In an embodiment of the invention, a photocatalytic electron transfer mechanism for both the binary and ternary composites is proposed, supported by a series of characterization analyses and experimental evaluations. In addition, the mechanism of hydrogen production in V.sub.2C/g-C.sub.3N.sub.4, Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4, and V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 is proposed to obtain a further understanding on the photocatalytic redox activity. Schottky junction is constructed in V.sub.2C/g-C.sub.3N.sub.4 nanocomposite The photocatalysis process is a process that converts light into chemical energy through photon absorption and carrier generation. The basic principles of photocatalysis involve five principal steps: (1) light utilization by primary photocatalyst, (2) the generation of photocarriers, (3) excitation of the photogenerated electrons, (4) photoredox reaction, and (5) carriers recombination. In general, when the incident light with an energy equal to or greater than the bandgap of the semiconductor photocatalyst strikes the surfaces, the photon absorption results in the generation of electron-hole pairs at VB of the semiconductor material. The photogenerated electrons will undergo an excitation process to CB, separating from holes. The photoredox reaction will occur where the reduction reaction takes place at the CB of the semiconductor, while the oxidation reaction for protons generation will happen at the VB of the semiconductor. For a thermodynamically stable chemical reaction, the generic rule is to ensure that the reductive band potentials and conduction band minimum (CBM) to be more negative than the reduction potential of water, H.sup.+/H.sub.2 (0.41 eV vs NHE at pH 7). On the other hand, the oxidative band potential and the valence band minimum (VBM) are designated to be more positive than the oxidation potential of water, O.sub.2/H.sub.2O (+0.82 eV vs NHE at pH 7). Besides, the band gap energy is designed to be higher than 1.23 eV. Disregarding the generic rules of water splitting will retard the overall photocatalytic process. Therefore, the selection of the main semiconductor material that can fully harvest solar irradiation is essential to ensure an efficient photocatalytic reaction. the photocatalytic hydrogen mechanism of V.sub.2C/g-C.sub.3N.sub.4, is hypothesized based on the characterizations and experimental results. The chemical reaction for the photocatalytic mechanism is depicted in Equations (9-12), which demonstrates the basic mechanism of water splitting in the generation of hydrogen.
g-C.sub.3N.sub.4+hv.fwdarw.e.sup.+h.sup.+(9)
g-C.sub.3N.sub.4(e.sup.)+V.sub.2C.fwdarw.V.sub.2C(e.sup.)(10)
H.sub.2O+2h.sup.+.fwdarw.O.sub.2+2H.sup.+(11)
2H.sup.++2.sup.e.fwdarw.H.sub.2(12)
Based on the characterization analyses and experimental evaluations, the possible mechanism and behavior of the charge transfer in the Schottky junction system is proposed. The VB of g-C.sub.3N.sub.4 is measured from the VB-XPS to be +1.64 eV which is consistent with the calculation from the Tauc plot. From the E.sub.g=E.sub.VBE.sub.CB, the CB of g-C.sub.3N.sub.4 is estimated to be 1.26 eV. Additionally, UV-Vis and PL analysis characterizations reveals the inability of V.sub.2C to generate electrons and holes as no absorption peak is observed from the UV-Vis, while a lower intensity peak from PL analysis indicates no electron-hole recombination. These findings elucidate the possible formation of a metal-semiconductor charge transfer mechanism where g-C.sub.3N.sub.4 is the main photocatalyst responsible for the electron-hole pairs generation, while V.sub.2C functions as a metallic conductor to expedite the photoreaction. Specifically, the electrons and holes are generated at the VB of g-C.sub.3N.sub.4 after exposure to visible light. The photogenerated charges then undergo charge separation where electrons are excited to the CB while holes remain at the VB of g-C.sub.3N.sub.4 as depicted in Equation (9). The negative shift of C is and N is in V.sub.2C/g-C.sub.3N.sub.4 observed from XPS analysis further explains the electron transfer from electron-rich g-C.sub.3N.sub.4 towards electron-deficient V.sub.2C. Additionally, the lower work function in g-C.sub.3N.sub.4 (4.3 eV) than in V.sub.2C (5.7 eV) aids the transfer of photogenerated electrons to the V.sub.2C, such as shown in Equation (10). The difference in the work function and the band alignment at the g-C.sub.3N.sub.4V.sub.2C junction generates a built-in internal electric field that functions as an electron trapping center. Therefore, the merit of having a higher metallic electrical conductivity of V.sub.2C as a co-catalyst is to hinder charge recombination. The creation of the Schottky interface junction, causing charges redistribution, prevents the backward flow of the electrons at V.sub.2C from returning to g-C.sub.3N.sub.4 and recombining with holes. Therefore, more electrons are available at the reduction sites to undergo reaction with protons and generate hydrogen, which is one of the contributing factors for the enhanced hydrogen production after adding V.sub.2C, which can be seen from the PL peak depression in the nanocomposite. The facile transfer of electrons upon the introduction of V.sub.2C corroborates an effective formation of the metal-semiconductor interface junction. In Equation (11-12), the holes at VB undergo an oxidation reaction with water to generate protons and oxygen, while electrons undergo a reduction reaction with protons to produce hydrogen. Faster recombination rates of electrons and holes denote reduced efficiency as fewer available electrons and holes can carry out redox reactions. The recombination of charges once occurs when the excited electrons lose energy in the form of unproductive heat.
(91) The S-scheme formation in NiCoAl LDH/g-C.sub.3N.sub.4 nanocomposite is analysed. The photocatalytic electron-hole transfer process adheres to the S-scheme mechanism, which is postulated based on Mott-Schottky, Tauc Plot, PL, and XPS analysis. The Tauc plot analysis is employed to determine the band gap values of pure g-C.sub.3N.sub.4 and NiCoAl LDH, which are measured to be 2.95 eV and 2.21 eV, respectively. Additionally, the Mott-Schottky plot is utilized to calculate the E.sub.CB and E.sub.VB of pure g-C.sub.3N.sub.4 and NiCoAl LDH, respectively. For pure g-C.sub.3N.sub.4, the E.sub.CB is determined to be 1.26 eV, and their E.sub.VB value is calculated to be 1.64 eV in reference to E.sub.VB=E.sub.CB+E.sub.BG. Correspondingly, the E.sub.VB value for pure NiCoAl LDH determined from Mott-Schottky is +1.10 eV, while the E.sub.CB value is calculated to be 1.4 eV. The transformations of the electron density on the NiCoAl LDH/g-C.sub.3N.sub.4 are identified based on the shifting of the binding energies in the XPS analysis. The negative shift in the binding energy of the nanohybrid with respect to the g-C.sub.3N.sub.4 suggests the reduction in the electron density, highlighting g-C.sub.3N.sub.4 as a higher electron-density region. Meanwhile, the shifting of Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 towards a higher-energy region when compared to pure Ni.sub.1Co.sub.1Al.sub.1 LDH suggests the electron transfer from g-C.sub.3N.sub.4 to Ni.sub.1Co.sub.1Al.sub.1 LDH. The interface contacts between g-C.sub.3N.sub.4 and Ni.sub.1Co.sub.1Al.sub.1 LDH lead to the formation of a weaker internal electric field, which promotes electron migration.
(92) As depicted in
g-C.sub.3N.sub.4+hv.fwdarw.e.sup.+h.sup.+(13)
g-C.sub.3N.sub.4(e.sup.)+NiCoAl LDH(h.sup.+).fwdarw.e.sup.+h.sup.+(14)
H.sub.2O+2h.sup.+.fwdarw.O.sub.2+2H.sup.+(15)
C.sub.6H.sub.15NO.sub.3+12H.sub.2O.fwdarw.6CO.sub.2+19H.sub.2+HNO.sub.3(16)
2H.sup.++2e.sup..fwdarw.H.sub.2(17)
(93) In another embodiment of the invention, hybrid-junction formation in ternary V.sub.2C/NiCoAl LDH/g-C.sub.3N.sub.4 nanocomposite is analysed. The photocatalytic electron transfer in the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite is proposed and postulated based on various experimental analyses, primarily Mott-Schottky and tauc plot analyses, which is to determine the electronic band structure and energy level of the materials. The behavior of electronic transfer in the binary heterojunction is investigated through XPS analysis, which also helps ascertain the transfer pathway in the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 nanocomposite. Analysis such as PL is employed to examine the recombination and carrier dynamics in the binary and ternary heterojunction. Therefore, a hybrid junction consisting of a combination of S-scheme heterojunction and Schottky-junction system is proposed, as depicted in
(94) The shifting in the binding energy of the XPS spectrum affirmed the transfer pathway across the system. The transfer mechanism is evaluated based on the binary nanocomposite counterpart to investigate the electron transfer behavior between the co-catalyst and metal co-catalyst. The negative shifting in the binding energy of C is and N is peak of binary Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 in comparison to pristine g-C.sub.3N.sub.4 suggests a reduction in the electron density of the binary composite. This results in the flow of electrons from the higher density region of g-C.sub.3N.sub.4 to a lower density region of Ni.sub.1Co.sub.1Al.sub.1 LDH, explaining the behavior of charge transfer in the binary heterojunction. The interfacial contact between the materials generates the inversed electric field pointing from Ni.sub.1Co.sub.1Al.sub.1 LDH to g-C.sub.3N.sub.4, along with Coulombic force interaction, to accelerate the electron transmission across the semiconductor. The interface contact between Ni.sub.1Co.sub.1Al.sub.1 LDH and g-C.sub.3N.sub.4 leads to the alignment in the Fermi level, resulting in the band edge bending and creation of electron-rich (g-C.sub.3N.sub.4) and deficient (Ni.sub.1Co.sub.1Al.sub.1 LDH) with a built-in electric field, which promotes the interfacial recombination of unused electron-hole pairs. Therefore, the S-scheme offers a reservation of electrons with stronger reducing capability at Ni.sub.1Co.sub.1Al.sub.1 LDH counterpart, hastening the photoredox reaction.
(95) The construction of a ternary composite with the addition of V.sub.2C as a metal co-catalyst enhances the electronic transfer and hampers charge recombination. Particularly, V.sub.2C serves as electron sinking through the creation of the Schottky barrier. The interfacial contact between metallic V.sub.2C and Ni.sub.1Co.sub.1Al.sub.1 LDH results in rapid migration of electrons from semiconducting Ni.sub.1Co.sub.1Al.sub.1 LDH to metallic V.sub.2C, owing to the difference in the Fermi level energy of both materials. The formation of a potential barrier traps the electrons in the V.sub.2C region, which prevents the reversed injection of electrons back to semiconducting Ni.sub.1Co.sub.1Al.sub.1 LDH. This preserves more electrons with a stronger reduction capability to undergo photoredox reaction, thereby improving photocatalytic activity. The merit of the hybrid-junction system in the ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 can be reflected from the depression of PL spectra, corroborating the notable enhancement in the carrier separation compared to the binary structures. Improvement in the charge transport system with lower transfer resistance further explicates the contribution of a hybrid-junction system for photocatalytic enhancement.
(96) Charge Transfer Mechanism Across the Semiconductor
g-C.sub.3N.sub.4+hv.fwdarw.e.sup.+h+(18)
NiCoAl LDH+hv.fwdarw.e.sup.+h.sup.+(19)
g-C.sub.3N.sub.4(e.sup.+h.sup.+).fwdarw.g-C.sub.3N.sub.4(h.sup.+)(20)
NiCoAl LDH(e.sup.+h.sup.+).fwdarw.NiCoAl LDH(e.sup.)(21)
NiCoAl LDH(e.sup.)+V.sub.2C.fwdarw.V.sub.2C(e.sup.)(22)
Oxidation Reaction of H.sub.2O
H.sub.2O+2h.sup.+.fwdarw.O.sub.2+2H+(23)
Reduction Reaction for Hydrogen Conversion
2H.sup.++2e.sup..fwdarw.H.sub.2(24)
Oxidation Reaction of TEOA
C.sub.6H.sub.15NO.sub.3+12H.sub.2O.fwdarw.6CO.sub.2+19H.sub.2+HNO.sub.3(25)
(97) The basic mechanism of photocatalytic hydrogen conversion in ternary V.sub.2C/Ni.sub.1Co.sub.1Al.sub.1 LDH/g-C.sub.3N.sub.4 is presented in Equations (18-25) ascertained from the experimental evaluation and characterization analyses. The photocatalytic electron transfer mechanism starts with photonic absorption by Ni.sub.1Co.sub.1Al.sub.1 LDH and g-C.sub.3N.sub.4, resulting in carrier generation and separation as demonstrated in Equations (18-19). The electronic redistribution affirmed by binding energy shift led to the accumulation of holes at the g-C.sub.3N.sub.4 and electrons at Ni.sub.1Co.sub.1Al.sub.1 LDH, as presented in Equations (20-21). The formation of the potential barrier by V.sub.2C results in the trapping of electrons, as depicted in Equation (22). Equations (23-24) explains the photoredox reaction by holes at the VB of g-C.sub.3N.sub.4 and accumulated electrons at the V.sub.2C surface, explicating the hydrogen conversion. The introduction of TEOA serves as a hole scavenger to hamper the photodecomposition of g-C.sub.3N.sub.4 while contributing to more production of hydrogen through TEOA oxidation, as depicted in Equation (25).
(98) According to the invention, S-scheme heterojunction of 2D/2D 2NiCoAlCN is designed by finely adjusting the cationic composition of M.sup.2+/M.sup.3+ in Ni.sub.xCo.sub.yAl.sub.z LDH relative to its layer charge density. The cationic ratio of Ni.sub.xCo.sub.yAl.sub.z LDH is varied at different layer charge densities (x: 0.25, 0.33, 0.5) and its photocatalytic effects is analysed. The optimal cationic ratio of Ni.sub.1Co.sub.1Al.sub.1 LDH in 10-2NiCoAlCN nanohybrid, with a layer charge density (x) of 0.33, exhibits the highest hydrogen production rate of 254 mol g.sup.1 h.sup.1 which is two- and four-times enhancement than pure gCN and Ni.sub.1Co.sub.1Al.sub.1 LDH. S-scheme electron transfer mechanism plays a pivotal role in facilitating an efficient electron-hole transport within the 2NiCoAlCN, which promote the oxidizability and reducibility in the nanohybrids for enhancing the overall redox activity. In an embodiment of the invention, the cationic effects suggest an enhanced interaction between the metal hydroxides layer and adsorbed molecules in 2NiCoAlCN, which augment its photocatalytic activity. The adjustment of the cationic ratio and charge density has a notable influence on the electronic properties of the LDH, as evidenced by variations in the band gap value. In an embodiment, Ni.sub.1Co.sub.1Al.sub.1 LDH (E.sub.BG: 2.21 eV) and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH (EBG: 2.84 eV) exhibit narrower band gaps, enabling them to be active under visible irradiation. In contrast, Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH displays a larger band gap value of 3.04 eV. The narrower band gaps of Ni.sub.1Co.sub.1Al.sub.1 LDH and Ni.sub.1.5Co.sub.1.5Al.sub.1 LDH contribute to their enhanced performance, allowing for better utilization of visible light for photocatalytic processes. In the morphological perspective, Ni.sub.1Co.sub.1Al.sub.1 LDH sample exhibited a prominent nanoplate structure with well-defined edges, indicating the formation of a stable hydrotalcite structure with higher crystallinity. In another embodiment of the invention, larger crystallite size obtained in Ni.sub.1Co.sub.1Al.sub.1 LDH (9.07 nm) with enhanced S.sub.BET of 115.75 m.sup.2/g increase the surface-active sites and improve its photonic absorption. In contrast, the Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH sample with a lower cationic ratio displayed aggregated, coalesced, and smaller nanoplates attributing to a lower specific surface area (S.sub.BET) of 95 m.sup.2/g for Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH. A higher layer charge density of Ni.sub.0.5Co.sub.0.5Al.sub.1 LDH (x: 0.5) may lead to the formation of non-pure LDH phases, as evidenced by its poor crystallinity and visible inactivation. The present invention serves for purpose of developing S-scheme LDH-based materials and improving the photocatalytic effects of trimetallic LDH structures.
(99) Benefits of the proposed hybrid-junction composite system in accordance with the present invention include the proposed system optimizing solar energy usage, allowing for an increased semiconductor sensitivity and helping to optimize solar hydrogen generation. This new sensitizer may be used in conjunction with a variety of semiconductors, layered structure LADHs and graphitic carbon nitrides, to maximize the use of solar energy and increase hydrogen generation.
(100) Many changes, modifications, variations and other uses and applications of the subject invention will become apparent to those skilled in the art after considering this specification and the accompanying drawings, which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications, which do not depart from the spirit and scope of the invention, are deemed to be covered by the invention, which is to be limited only by the claims, which follow.