Optimization of photocatalytic hydrogen generation using aqueous bio-alcohols and plasmonic metals deposited on semiconductor composite nanofibers

Abstract

The present invention combines the advantages of fabrication of semiconductor heterostructure (Ag.sub.3PO.sub.4WO.sub.3) with plasmonic metals (Pt and Ag) with optical interference to optimize the visible light photo response of plasmonic metals deposited semiconductor (PtAg/Ag.sub.3PO.sub.4WO.sub.3) for visible light assisted H.sub.2 generation utilizing the aqueous bio-alcohols. Crystalline Ag.sub.3PO.sub.4 and WO.sub.3 nanofibers were synthesized by microwave and electrospinning methods. Three different WO.sub.3 nanofibers composition (5, 10 and 15 wt. %) were used to obtain Ag.sub.3PO.sub.4/WO.sub.3 nanocomposite heterostructures, which are effective visible light active photo catalysts. Further, a simple, enviro-friendly, and cost-effective biogenic synthesis method have been achieved using Salvia officinalis extract to decorate Pt and Ag metal nanoparticles on the surface of Ag.sub.3PO.sub.4WO.sub.3 composites. Presence of bioactive agents in the extract are responsible for the Pt and Ag.sub.3PO.sub.4 reduction and for prevention of the Pt nanoparticles from aggregation in aqueous medium.

Claims

1. Crystalline Ag.sub.3PO.sub.4WO.sub.3 composite nanofibers comprising 5 to 15 wt. % WO.sub.3, wherein the composite nanofibers are visible light active photo catalysts.

2. The composite nanofibers of claim 1, produced by a process comprising the steps of: a) synthesizing crystalline Ag.sub.3PO.sub.4 powder via microwave synthesis method; b) synthesizing crystalline WO.sub.3 nanofibers via electrospinning method; and c) dispersing the crystalline Ag.sub.3PO.sub.4 and the crystalline WO.sub.3 in a solution of alcohol and water and synthesizing Ag.sub.3PO.sub.4/WO.sub.3 composite nanofibers via ultrasonication homogenization.

3. The composite nanofibers of claim 1, further comprising metal nanoparticles on a surface of the composite nanofibers.

4. The composite nanofibers of claim 3, wherein the metal nanoparticles are decorated with a plant extract comprising bioactive agents capable of preventing the metal nanoparticles from aggregating in an aqueous medium and/or capable of reducing the metal nanoparticles.

5. The composite nanofibers of claim 4, wherein the plant extract is derived from Salvia officinalis.

6. The composite nanofibers of claim 5, wherein the metal nanoparticles comprise Pt and/or Ag metals.

7. The composite nanofibers of claim 6, wherein the composite nanofibers have: i) a lower band gap relative to WO.sub.3 and/or AgP; ii) a higher surface area relative to WO.sub.3 and/or AgP; and/or iii) improved photocatalytic activity for H.sub.2 production from bioethanol relative to WO.sub.3 and/or AgP.

8. A process for making crystalline Ag.sub.3PO.sub.4WO.sub.3 composite nanofibers, the process comprising the steps of: a) synthesizing crystalline Ag.sub.3PO.sub.4 powder via microwave synthesis; b) synthesizing crystalline WO.sub.3 nanofibers via electrospinning; and c) dispersing the crystalline Ag.sub.3PO.sub.4 and the crystalline WO.sub.3 in a solution of alcohol and water and synthesizing Ag.sub.3PO.sub.4/WO.sub.3 composite nanofibers via ultrasonication homogenization; wherein the composite nanofibers comprise 5 to 15 wt. % WO.sub.3 and are visible light active photo catalysts.

9. The process of claim 8, further wherein the composite nanofibers comprise metal nanoparticles on a surface of the composite nanofibers.

10. The process of claim 9, wherein the metal nanoparticles are decorated with a plant extract comprising bioactive agents capable of preventing the metal nanoparticles from aggregating in an aqueous medium and/or capable of reducing the metal nanoparticles.

11. The process of claim 10, wherein the plant extract is derived from Salvia officinalis.

12. The process of claim 11, wherein the metal nanoparticles comprise Pt and/or Ag metals.

13. The process of claim 12, wherein the composite nanofibers have: i) a lower band gap relative to WO.sub.3 and/or AgP; ii) a higher surface area relative to WO.sub.3 and/or AgP; and/or iii) improved photocatalytic activity for H.sub.2 production from bioethanol relative to WO.sub.3 and/or AgP.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Having thus described the subject matter of the present invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

(2) FIGS. 1A-1F show photocatalytic reforming functionality data for synthesized catalysts: A) Influence of reaction time; B) Influence of bioethanol concentration; C) Influence of pH; D) Influence of mass of catalyst; E) Influence of reaction temperature; and F) Recyclability of PtAg/AgPWO.sub.3 (2) catalyst.

(3) FIGS. 2A-2B show XRD patterns of: A) bare Ag.sub.3PO.sub.4WO.sub.3; and B) Pt decorated Ag.sub.3PO.sub.4WO.sub.3 nanocomposites.

(4) FIGS. 3A-3F show SEM images of the synthesized samples: A) AgP; B) PtAg/AgP; C) PtAg/WO.sub.3; D) PtAg/AgPW-1; E) PtAg/AgPW-2; and F) PtAg/AgPW-3.

(5) FIG. 4 shows FT-IR spectra of Pt deposited: a) AgP; b) AgPW-1; c) AgPW-2; d) AgPW-3; and e) WO.sub.3.

(6) FIGS. 5A and 5B show DR UV-vis spectra of the samples: A) AgP, WO.sub.3, AgPW-1, AgPW-2, AgPW-3; and B) PtAgP, PtWO.sub.3, PtAg/AgPW-1, PtAg/AgPW-2, PtAg/AgPW-3

(7) FIGS. 6A-6J show Tauc plots to determine the band gap energy of photocatalysts: A) AgP; B) PtAgP; C) WO.sub.3; D) PtWO.sub.3; E) AgPW-1; F) PtAgPW-1; G) AgPW-2; H) PtAgPW2; I) AgPW-3; and J) PtAgPW-3.

(8) FIG. 7 shows a schematic representation of photo reforming of ethanol over synthesized PtAg/AgPWO.sub.3 catalyst.

(9) FIGS. 8A-8F show deconvoluted XPS spectra of the representative bulk and Pt deposited: A) AgP; B) PtAgP; C) WO.sub.3; D) PtWO.sub.3; E) AgPW-3; and F) PtAgPW-3.

DETAILED DESCRIPTION

(10) The subject matter of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the subject matter of the present invention are shown. Like numbers refer to like elements throughout. The subject matter of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Indeed, many modifications and other embodiments of the subject matter of the present invention set forth herein will come to mind to one skilled in the art to which the subject matter of the present invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. All illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention. Therefore, it is to be understood that the subject matter of the present invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

(11) Optimization of Photocatalytic Hydrogen Generation Using Aqueous Bio-Alcohols and Plasmonic Metals Deposited on Semiconductor Composite Nanofibers

(12) The present invention combines the advantages of fabrication of semiconductor heterostructure (Ag.sub.3PO.sub.4WO.sub.3) with plasmonic metals (Pt and Ag) with optical interference to optimize the visible light photo response of plasmonic metals deposited semiconductor (PtAg/Ag.sub.3PO.sub.4WO.sub.3) for visible light assisted H.sub.2 generation utilizing the aqueous bio-alcohols.

(13) Crystalline Ag.sub.3PO.sub.4 and WO.sub.3 nanofibers were synthesized by microwave and electrospinning methods. Three different WO.sub.3 nanofibers composition (5, 10 and 15 wt. %) were used to obtain Ag.sub.3PO.sub.4/WO.sub.3 nanocomposite heterostructures, which are effective visible light active photo catalysts. Further, a simple, enviro-friendly, and cost-effective biogenic synthesis method have been achieved using Salvia officinalis extract to decorate Pt and Ag metal nanoparticles on the surface of Ag.sub.3PO.sub.4WO.sub.3 composites. Presence of bioactive agents in the extract are responsible for the Pt and Ag.sub.3PO.sub.4 reduction and for prevention of the Pt nanoparticles from aggregation in aqueous medium. Various analytical techniques such as XRD, SEM, FT-IR, DR UV-vis, XPS and N.sub.2-physisorption were utilized to characterize the synthesized photocatalysts. The band gap energy values were decreased after decoration of Pt and Ag metal nanoparticles over Ag.sub.3PO.sub.4WO.sub.3 nanocomposites. The Pt and Ag metal nanoparticles decorated Ag.sub.3PO.sub.4WO.sub.3 (10 wt %) nanocomposite exhibited highest photo catalytic activity for H.sub.2 production from bioethanol due to possession of unique physico-chemical properties low band gap and surface area. In addition, presence of plasmonic nanoparticles assisted for the efficient electron trap to decrease the e.sup.-h-F recombination rate to enhance the hydrogen production.

(14) Accordingly, in one embodiment, the invention relates to crystalline Ag.sub.3PO.sub.4WO.sub.3 composite nanofibers comprising 5 to 15 wt. % WO.sub.3, wherein the composite nanofibers are visible light active photo catalysts. In some embodiments, the composite nanofibers are produced by a process comprising the steps of: a) synthesizing crystalline Ag.sub.3PO.sub.4 powder via microwave synthesis method; b) synthesizing crystalline WO.sub.3 nanofibers via electrospinning method; and c) dispersing the crystalline Ag.sub.3PO.sub.4 and the crystalline WO.sub.3 in a solution of alcohol and water and synthesizing Ag.sub.3PO.sub.4/WO.sub.3 composite nanofibers via ultrasonication homogenization.
In some embodiments, the composite nanofibers further comprise metal nanoparticles on a surface of the composite nanofibers. In other embodiments, the metal nanoparticles are decorated with a plant extract comprising bioactive agents capable of preventing the metal nanoparticles from aggregating in an aqueous medium and/or capable of reducing the metal nanoparticles, particularly wherein the plant extract is derived from Salvia officinalis. In other embodiments, the metal nanoparticles comprise Pt and/or Ag metals. In further embodiments, the composite nanofibers have: i) a lower band gap relative to WO.sub.3 and/or AgP; ii) a higher surface area relative to WO.sub.3 and/or AgP; and/or iii) improved photocatalytic activity for H.sub.2 production from bioethanol relative to WO.sub.3 and/or AgP.

(15) In still further embodiments, a process is provided for making crystalline Ag.sub.3PO.sub.4WO.sub.3 composite nanofibers, the process comprising the steps of: a) synthesizing crystalline Ag.sub.3PO.sub.4 powder via microwave synthesis method; b) synthesizing crystalline WO.sub.3 nanofibers via electrospinning method; and c) dispersing the crystalline Ag.sub.3PO.sub.4 and the crystalline WO.sub.3 in a solution of alcohol and water and synthesizing Ag.sub.3PO.sub.4/WO.sub.3 composite nanofibers via ultrasonication homogenization;
wherein the composite nanofibers comprise 5 to 15 wt. % WO.sub.3 and are visible light active photo catalysts. In some embodiments, the composite nanofibers further comprise metal nanoparticles on a surface of the composite nanofibers. In other embodiments, the metal nanoparticles are decorated with a plant extract comprising bioactive agents capable of preventing the metal nanoparticles from aggregating in an aqueous medium and/or capable of reducing the metal nanoparticles, particularly wherein the plant extract is derived from Salvia officinalis. In other embodiments, the metal nanoparticles comprise Pt and/or Ag metals. In further embodiments, the composite nanofibers have: i) a lower band gap relative to WO.sub.3 and/or AgP; ii) a higher surface area relative to WO.sub.3 and/or AgP; and/or iii) improved photocatalytic activity for H.sub.2 production from bioethanol relative to WO.sub.3 and/or AgP.

EXAMPLES

Materials and Methods

(16) Preparation of Nanocomposite Samples

(17) Synthesis of crystalline Ag.sub.3PO.sub.4 by microwave synthesis method: To synthesize crystalline Ag.sub.3PO.sub.4 powder, 0.1 M aqueous solution of (NH.sub.4).sub.2HPO.sub.4 was slowly added to aqueous AgNO.sub.3 solution (0.15 M), then the pH of the contents was adjusted to 10 by adding the NH.sub.4OH solution to obtain a precipitate. Then, the formed precipitate was transferred into a specially designed polymer vessel with temperature and pressure-controlled sensors. The vessel was then subjected to microwave irradiation (power between 150 and 300 W) to maintain 140 C. for 30 min by using Microwave lab station (Ethos, Milestone). After the microwave treatment, the obtained material was washed with water and ethanol and dried at 80 C. for 3 h.

(18) Synthesis of WO.sub.3 nanofibers by electrospinning method: To synthesize the WO.sub.3 nanofibers, polymethylmethacrylate (PMMA, MW=120,000) and tungsten hexachloride solutions were used as precursors. First, the PMMA was dissolved in chloroform and tungsten hexachloride was dissolved in 2-methoxyethanol and then the two solutions were mixed at 50 C. under stirring for 20 minutes under ultrasonication. The WO.sub.3 nanofibers were grown onto a silicon substrate using electrospinning device at room temperature. The solution was taken in a syringe that is positioned in the Plexiglas box and raised from a metallic support. The needle of syringe is connected to the positive electrode of the high voltage power supply. The substrate is placed on a metallic support and is grounded. The applied voltage was varied from 17 kV to 20 kV and a 15 cm distance was maintained from needle to substrate. After deposition, the sample was calcined at 500 C. to remove the PMMA and to crystallize the WO.sub.3 nanofibers.

(19) Preparation of Ag.sub.3PO.sub.4/WO.sub.3 nanocomposites: The Ag.sub.3PO.sub.4/WO.sub.3 nanocomposites were synthesized by following a simple ultrasonication homogenization method. For the synthesis, 100 mg of WO.sub.3 was dispersed in 25 mL of ethyl alcohol and water (75:25 vol %) by sonication for 30 min. Then calculated amount of Ag.sub.3PO.sub.4 powder was added next to the dispersion and again subjected to sonication for 30 min. The resulting dispersion was heated in an electric oven at 100 C. until the complete evaporation of solvent. During the preparation, x weight percentage of WO.sub.3 (x=5, 10 and 15 wt. %) was added to the Ag.sub.3PO.sub.4 dispersion and the obtained composites were named accordingly as AgPW-1, AgPW-2, and AgPW-3 respectively.

(20) Pt and Ag-decorated Ag.sub.3PO.sub.4WO.sub.3 nanomaterials by green extract method: In the beginning, 20 g of clean leaves of Salvia officinalis (commonly known as Sage) were washed, dried and grinded well. Then, the grounded leaves were boiled in 100 mL of double distilled water for 30 minutes and the aqueous extract was obtained by vacuum filtration. The obtained extract was used to decorate the Pt nanoparticles over Ag.sub.3PO.sub.4WO.sub.3 nanocomposites. Calculated amount of H.sub.2PtCl.sub.6.Math.6H.sub.2O corresponding to 1.0 wt. % of Pt was dissolved in 90 mL of double distilled water and then 10 mL of plant extract solution was added for the reduction of Pt nanoparticles under constant stirring. Finally, calculated amount of Ag.sub.3PO.sub.4WO.sub.3 nanocomposite powder was added and stirred for 1 h, then the excess water was removed by centrifugation. The obtained Pt and Ag metals decorated Ag.sub.3PO.sub.4WO.sub.3 nanocomposites were dried at 100 C. and calcined at 300 C.

(21) Characterization of Synthesized Nanomaterials

(22) The elemental composition of the synthesized materials was determined by using ICP-AES, Optima 7300DV (PerkinElmer) instrument. The XRD patterns of the powders were collected by using PANalytical XpertPro diffractometer. The crystallite size of obtained materials was determined by applying the Debye-Scherer equation. The TEM analysis of the samples was carried out using JEOL 2100HT microscope operated at 200 kV, with images collected on a Gatan digital camera. The laser Raman spectral analysis of the samples was carried out using Bruker Equinox 55 FT-IR spectrometer equipped with an FRA106/S FT-Raman module and a liquid nitrogen cooled Ge detector using the 1064-nm line of a Nd:YAG laser with an output laser power of 200 mW. The X-ray photoelectron spectra of the samples were collected using Thermo-Scientific Escalab 250 Xi XPS instrument with Al K X-rays having a spot size of 650 mm. The peak shift due to charge compensation was corrected using the binding energy of C1s peak. The data was acquired using pass energy of 100 eV, dwell time 200 ms with a step size of 0.1 eV and 10-30 scans. The quantitative determination of the Pt active sites over the catalysts using CO pulse chemisorption measurements using laboratory made equipment. Prior to analysis, known amount of the sample (100 mg) was reduced at 250 C. under H.sub.2 flow (40 mL min.sup.1) for 60 min and then cooled to 25 C. under the flow of helium gas. Then, the CO pulse injection was conducted in a flow of helium gas stream. The metal dispersion was evaluated from the amount of CO consumption (assuming CO/Pt=1). The textural properties of the samples were obtained from the N.sub.2-physisorption experiments, which were conducted using Quantachrome ASiQ adsorption system. Optical properties were measured by Thermo-Scientific evolution UV-vis spectrophotometer equipped with an integrating sphere in the wavelength range of 200-800 nm to measure the reflectance spectra of samples. Band gap energy values of all the samples were calculated using Kubelka-Munk method. The Kubelka-Munk factor (K) was determined by following equation; K=(1R).sup.2/2R, where R is the % reflectance. The wavelengths (nm) were translated into energies (E) and a plot was drawn between (K*E).sup.0.5 and E to obtain a curve. The bandgap energy (eV) was obtained as the intersection point of the two slopes in the curve

(23) Photocatalytic Reforming of Bioethanol to Hydrogen

(24) Photocatalytic reactions were conducted in the liquid phase in a Pyrex flask under an argon atmosphere. The catalyst (150 mg) was dispersed by stirring at 500 rpm in 120 mL of a 20 vol % ethanolic aqueous solution at 25 C. for 30 min in the dark to equilibrate any adsorption processes and ensure a uniform catalyst suspension. The reactor was then evacuated and irradiated by a 300 W Xe lamp providing a flux of approximately 125 mW.Math.cm.sup.2 in the reaction zone for 1 h. Evolved gases flowing into the gas chromatograph sample loop through a closed gas circulation and the product analysis for H.sub.2 was carried out by using a Varian 3300 gas chromatograph with a thermal conductivity detector and a 2 m MS 13 column.

Results and Discussion

(25) Photocatalytic Reforming Activity

(26) The photocatalytic reforming functionality of as prepared Ag.sub.3PO.sub.4, WO.sub.3, AgPWO.sub.3 composites and PtAg decorated Ag.sub.3PO.sub.4, WO.sub.3 nanofibers, AgPWO.sub.3 composite catalysts was tested by determining the hydrogen production from the aqueous ethanol solution. Different reaction parameters such as reaction time, methanol concentration, weight of the catalyst, pH of reactants mixture and reaction temperature were studied to optimize the reaction conditions. The obtained photocatalytic activity results are depicted in FIG. 1. The photocatalytic activity results are clearly demonstrating that Pt and Ag decorated AgPWO.sub.3 composites are superior catalysts compared to AgPWO.sub.3 composites. In case of PtAg/AgPWO.sub.3 samples, the Pt and Ag nanoparticles accepts the photogenerated electrons from CB of AgP to extend the lifetime of the charge carrier. The time on stream analysis was performed for all the synthesized catalysts, and the results are shown in FIG. 1 (A). The figure shows the amount of hydrogen produced under optimized reaction conditions over all the samples. The highest amount of hydrogen was produced after 12 hours of reaction in the samples and PtAg/AgPWO.sub.3 (2) catalyst sample exhibited the highest activity among the synthesized samples. After 12 hours of reaction, the activity of catalysts has not decreased considerably.

(27) When the reactant feed contained only water without ethanol, the H.sub.2 evolution is negligible, however H.sub.2 production increased with increase of vol % of ethanol and reached to the maximum at 20 vol. % in case of all the synthesized AgPWO.sub.3 composites samples [FIG. 1(B)]. However, further increase of vol % of ethanol above 20 vol. % did not showed any significant change in H.sub.2 production. It is observed that both PtAg decorated and pure AgPWO.sub.3 composites samples showed similar behavior although the WO.sub.3 content is different. Decoration of Pt and Ag nanoparticles resulted considerable improvement in the H.sub.2 production in the samples with different WO.sub.3 composition. The previous studies indicated that with increase of vol % of ethanol increases, a greater number of ethanol molecules adsorbs on the semiconductor surface blocking the visible light to reach to ethanol molecules, resulting decrease in the photocatalytic reformation of ethanol to H.sub.2. Thus, an optimum ethanol concentration is existed for the AgPWO.sub.3 composites. The obtained data indicating that bulk AgPWO.sub.3-2 and PtAg decorated AgPWO.sub.3-2 composite samples showed highest activity, 3250 mol g.sup.1 and 4010 mol g.sup.1 respectively.

(28) It was reported that electrostatic interactions between the photocatalyst surface and the reactants play an important role in photocatalytic activity. To study the influence of pH of the ethanol and water solution on the catalyst performance, different aqueous ethanol solutions with pH between 1 and 11 were prepared and used to photocatalytic experiments. The obtained results are plotted in FIG. 1. (C). The results indicating that tested catalysts exhibited better performance when the solutions pH is around 7.0 as the pH at the point of zero charge (pHpzc) of Ag.sub.3PO.sub.4 is 6.65. It is interesting to note that pzc for WO.sub.3 is around pH 2.5, however the major constituent of the synthesized photocatalysts is Ag.sub.3PO.sub.4 and therefore it is not expected any deviation from the suitable pH of solution to obtained highest photocatalytic activity. It was previously observed that the catalysts produced high amount of hydrogen production at neutral pH. It was also observed that change of pH of the solution (acidic or basic) altered the hydrogen production rates significantly. Similar results were observed in case of bulk AgPWO.sub.3 and PtAg decorated AgPWO.sub.3 composite samples. The OH groups on the surface of AgPWO.sub.3 composite enables the adsorption of ethanol molecules via hydrogen bonding [26]. The synthesized PtAg decorated AgPWO.sub.3 composites consists of particles with specific polyhedral and nanofiber morphology exhibited superior photo reforming activity due to presence of more surface OH species and relatively high surface area (characterization results). Previously, it was reported that reformation of alcohols progress stepwise, involving formation of intermediate compounds [27]. In acidic solution, the rate of conversion of CH.sub.3CH.sub.2OH to CH.sub.3CHO (FIG. 7) is low, which could hinder the formation of hydrogen production as CH.sub.3CHO could easily convert into another carbonyl compounds. On other hand, in basic solution, CH.sub.3COOH could be oxidized to form CO 2 due to deprotonation. In addition, the pH could affect the surface functional groups [28]. It is known that Ag.sub.3PO.sub.4 is normally amphoteric and WO.sub.3 is acidic in nature. The change in pH of the aqueous ethanol solution results change in the surface acidity-basicity characteristics of AgPWO.sub.3 composite, which influence the ethanol adsorption. In basic solution, the negatively charged semiconductor surface resulted lower the rate of H.sub.2 production due to interaction between ethanol and AgPWO.sub.3 is lower [29].

(29) FIG. 1 (D) shows influence of catalyst amount on the photocatalytic reformation of ethanol to hydrogen over synthesized AgPWO.sub.3 catalysts using 20 vol. % ethanol solution at pH=7.0. The hydrogen production enhanced gradually with increase of catalyst weight from 50 to 150 mg, however, increase of catalyst weight to 200 mg have not resulted further increase in hydrogen production; a stabilized activity was observed. The observed results indicated that 150 mg is the optimum catalyst weight to obtain the best photocatalytic reforming performance; this is probably because of number of catalytically active sites exposed to reacting ethanol molecules have not changed, when the catalyst amount is beyond 150 mg. It is also possible that the light energy may not be able to reach to the active sites as increase in light scattering could occur because of catalyst weight increase. Slight decrease of surface area was also observed due to accumulation of catalyst particles when the catalyst amount is more than optimum [30].

(30) Further, we also studied the role of reaction temperature on the photocatalytic ethanol reforming activity of the catalysts between 25 C. and 85 C. [FIG. 1(E)]. As shown in the figure, increase in hydrogen production was observed with increase of reaction temperature from 25 C. to 85 C. in case of all the tested catalysts. We previously investigated PtTiO.sub.2 anatase nanocomposite catalysts for photocatalytic hydrogen production using aqueous methanol solution and we noticed that the quantum yield is proportional to the reaction temperature [31]; as it has a great influence over the quantum yield, most probably because of the thermal activation of products desorption. The observed results for synthesized PtAg/AgPWO.sub.3 catalysts are similar to our previous studies. We have not tested the photo reforming of bioethanol beyond 85 C., since there is possibility for the decrease of ethanol adsorption on surface of the catalyst above 85 C.

(31) The stability of photocatalyst under actual reaction conditions is a crucial factor in development of catalyst for any photocatalytic process because the catalysts generally undergo photo-corrosion during to catalytic tests. The stability of the PtAg decorated AgPWO.sub.3 composite catalysts was also studied. To study the reusability of the synthesized PtAg/AgPWO.sub.3 catalysts, we filtered the catalyst after the first cycle of the reaction, washed, dried, and thermally treated at 90 C. for 1 h and used the catalyst for next cycle of the reaction. The recycled catalyst was reused for five cycles The FIG. 1(F) shows the photocatalytic reforming activity of most active catalyst [PtAg/AgPWO.sub.3 (2)]. The PtAg/AgPWO.sub.3 (2) catalyst showed photocatalytic performance for hydrogen production without significant decline in photo reformation activity. The photostability of PtAg/AgPWO.sub.3 (2) catalyst is probably due to the structural stability and high resistance to photo-corrosion under studied reaction conditions.

(32) Characterization

(33) The phase purity and crystal structure of synthesized bare and Pt deposited WO.sub.3, Ag.sub.3PO.sub.4 and AgPWO.sub.3 nanocomposites were determined using powder XRD analysis. As shown in the FIG. 2, the characteristic XRD reflections for the body-centered cubic structure of Ag.sub.3PO.sub.4 [JCPDS No. 06-0505], while the reflections observed for WO.sub.3 sample could be assigned to the orthorhombic WO.sub.3 crystalline structure [JCPDS No. 20-1324].

(34) There are no additional reflections observed in the XRD patterns of AgPWO.sub.3 nanocomposites except for the characteristic reflections of Ag.sub.3PO.sub.4 and WO.sub.3 crystal structures (FIG. 2A). It could be observed in the figure that with increase of WO.sub.3 weight percent in AgPWO.sub.3 nanocomposites, the intensities of WO.sub.3 reflections increased, while the intensities of Ag.sub.3PO.sub.4 reflections gradually decreased. After Pt deposition, the crystal structure of WO.sub.3 was not changed, however the reflections due to bcc structure Ag.sub.3PO.sub.4 were almost disappeared and reflections due to face-centered cubic Ag metal particles were appeared in case of bare Ag.sub.3PO.sub.4 and AgPWO.sub.3 nanocomposite samples. The transformation of Ag.sub.3PO.sub.4 structure during Pt deposition is mainly due to presence of different phytochemicals in Salvia officinalis extract. It was previously reported that aqueous extract of Salvia officinalis contains several types of phytochemicals such as glycosidic forms of apigenin, luteolin and scutellarin and could effectively reduce the metal precursors into metal particles [32]. It is interesting to note that no reflections due to Pt nanoparticles were observed in all Pt deposited samples. This is possibly due to low Pt loading and high dispersion of small size Pt crystallites. The disappearance of reflections due to Ag.sub.3PO.sub.4 structure and appearance of Ag metal particles indicating that the aqueous Salvia officinalis extract effectively reducing the Ag.sub.3PO.sub.4 into Ag metal particles. It is clear that the aqueous extract of Salvia officinalis could not be able to reduce the WO.sub.3 particles, as all samples shows the presence of reflections due to WO.sub.3 phase.

(35) The morphology of the synthesized samples was investigated using SEM analysis. The obtained SEM images of the representative samples are shown in FIG. 3. The SEM image of bare Ag.sub.3PO.sub.4 sample composed of irregular polyhedral crystals with average size of 100-120 nm. The image of sample clearly showing that the surface of Ag.sub.3PO.sub.4 crystals is clean, and it is indicating that Ag.sub.3PO.sub.4 is not yielding any small Ag metal nanoparticles. After Pt deposition, the sample possessed the same morphology however, the existence of much smaller nanoparticles with size of 20-25 nm on the surface of Ag.sub.3PO.sub.4 crystals. As compared to pure Ag.sub.3PO.sub.4 crystals, these small nanoparticles could be the reduced Ag and Pt, nanoparticles. The XRD analysis have not shown presence of reflections due to Pt nanoparticles, therefore most of those are Ag nanoparticles. The SEM images of Pt deposited WO.sub.3 nanofibers and Ag.sub.3PO.sub.4WO.sub.3 composites exhibiting the presence of WO.sub.3 nanofibers. The presence of both polyhedral shaped Ag.sub.3PO.sub.4 and WO.sub.3 nanofibers in the composite samples indicates that the composite formed heterojunction successfully and still inherited the morphology of Ag.sub.3PO.sub.4 and WO.sub.3 components. However, the surface of both Ag.sub.3PO.sub.4 and WO.sub.3 are covered by randomly distributed small nanoparticles.

(36) The FT-IR spectra of the Pt deposited synthesized samples are shown in FIG. 4. The spectra of all samples show a broad and strong IR absorption peak around 3400 cm.sup.1 which could be assigned to OH stretching vibration. And the two peaks at 1380 and 1660 cm.sup.1 are due to HOH bending vibration H.sub.2O molecules [35]. The bare Ag.sub.3PO.sub.4 exhibited the absorption peaks at 551 cm.sup.1, 862 cm.sup.1 and 1020 cm.sup.1 which could be assigned to OPO bending, POP symmetric and asymmetric stretching vibrations respectively [36]. On other hand, the bare WO.sub.3 nanofibers sample shows the IR absorption peaks in the region of 600-900 cm.sup.1 originates from the WOW bridging vibrations [37]. The peaks at 965 cm.sup.1 and 750 cm.sup.1 are attributed to the vibrations of WO bond and stretching of the bridging oxygen OWO, respectively. All the representative absorption peaks of Ag.sub.3PO.sub.4 and WO.sub.3 can be observed in the spectra of the Ag.sub.3PO.sub.4WO.sub.3 composite samples. The observed results revealing the above analyses endorse the coordination environment of W and P did not change significantly during the coupling process of WO.sub.3 and Ag.sub.3PO.sub.4.

(37) The UV-vis light absorption properties of pure and PtAg decorated AgP and WO.sub.3 samples were analyzed by DR UV-vis spectroscopy measurements and the results are presented in FIG. 5. The UV-vis absorption spectra of pure AgP and WO.sub.3 samples shows that they can absorb both UV and visible light. It is also clear from FIG. 6 that that these samples possessed the band gap energy of 2.5 eV and 2.34 eV respectively. Interestingly, the AgPWO.sub.3 composites exhibited more visible light compared to UV light, as prominent absorption peaks were appeared in the visible region. The lowest band gap energy was observed in case of the sample with 10 wt. % WO.sub.3 content (AgPWO.sub.3-2). It is interesting to note that PtAg metals decorated AgPWO.sub.3 samples exhibit marked absorption enhancement in the visible light region, which can be attributed to the surface plasmon resonance (SPR) of Pt and Ag metal nanoparticles formed on the surface of AgPWO.sub.3 composite. The enhancement in light absorption for M/Ag.sub.3PO.sub.4 may also support the successful deposition of noble metal nanoparticles on the surface of Ag.sub.3PO.sub.4.

(38) TABLE-US-00001 TABLE 1 Textural properties of the samples obtained from N.sub.2-physisorption experiments. BET Pore Pore surface area volume diameter S. No. Catalyst (m.sup.2g.sup.1) (cm.sup.3g.sup.1) () 1 AgP 12.5 0.082 30.4 2 Pt-Ag/AgP 9.6 0.044 29.1 3 WO.sub.3 35.3 0.071 26.4 4 Pt-Ag/WO.sub.3 13.4 0.026 26.0 5 AgP-WO.sub.3(2) 23.8 0.028 28.1 6 Pt-Ag/AgP-WO.sub.3 (2) 6.8 0.018 25.6

(39) The textural properties of the samples are obtained from the N.sub.2 physisorption experiments and the BET surface area pore volume and pore diameter of the samples are provided in Table 1. The S BET values of pure AgP and WO.sub.3 samples are 12.5 and 35.3 m.sup.2 g.sup.1, respectively, these observed values are much high compared to reported in the literature. This is possibly due to the different preparation conditions used in the present research. The composites of AgP and WO.sub.3 exhibited the higher surface area than pure AgP and lower than WO.sub.3. However, with increase of WO.sub.3 content, an increase surface area, pore volume was observed.

(40) The band gap energy measurements of the synthesized materials indicated that the pure WO.sub.3 and AgP samples exhibited bandgap of 2.56 eV and 2.02 eV respectively, while band gap was slightly reduced for the AgPWO.sub.3 composites; thus, the e.sup.-h+ pairs could be generated on the surface of AgP, WO.sub.3 and AgPWO.sub.3 composites under visible light irradiation. It was observed that the AgPWO.sub.3 composites exhibited excellent photocatalytic activity for hydrogen production and considerably higher than pure AgP and WO.sub.3 catalysts under identical reaction conditions. As expected, the photocatalytic reforming activities of bulk and Pt and Ag decorated AgPWO.sub.3 composites with different weight percent of WO.sub.3 are higher compared to non-decorated composites. The pure AgP has conduction band (CB) and valency band (VB) values of and 2.62 eV, respectively. Under the visible light irradiation, e.sup.-h.sup.+ pairs are generated on the surfaces of both AgP and WO.sub.3. The lower catalytic activity of WO.sub.3 compared to AgP is mainly due to the more positive CB potential of WO.sub.3, as well as its less absorption of visible light. It was previously reported that the increase in photocatalytic activity of AgPWO.sub.3 composites is mainly due to the highly effective separation of photogenerated e.sup.-h.sup.+ pairs. Under visible light irradiation, the photogenerated e.sup. transfer from VB to the CB of WO.sub.3 and then migrate to the VB of AgP to combine with h.sup.+. Therefore, the photo-induced e.sup. and h.sup.+ of AgP are separated effectively, and the photogenerated e.sup. are unceasingly moved to the CB interface of AgP. Thus, a greater number of e.sup. are gathered on the CB interface of AgP, and more h+ are accumulated in the VB interface of WO.sub.3. It was well reported that the noble metal nanoparticles act as an efficient electron trap in order to decrease the e.sup.-h+ recombination rate upon photoexcitation. The adsorbed ethanol molecule converted into the aldehyde after photoenergy absorption as shown in FIG. 7.

(41) The XPS analysis is a well-known technique to analyze the surface chemical state of the elements presented in the synthesized materials. FIGS. 8A-8F show the deconvoluted XPS spectra for representative bulk and Pt deposited AgP, WO.sub.3, AgPWO.sub.3 samples. The Ag.sub.3d XPS spectra of all the samples exhibited peaks attributed to Ag.sub.3d.sub.5/2 and Ag.sub.3d.sub.3/2, which were fitted to two independent contributions corresponding to Ag.sup.0 and Ag.sup.+ species [38].

(42) The peaks appeared at 373.5 eV and 367.4 eV could be attributed to Ag.sup.0 species, while the peaks at 373.0 eV and 366.7 eV are assigned to Ag.sup.+ ions for pure Ag.sub.3PO.sub.4 sample [39]. The binding energies of these peaks were shifted slightly in case of composite samples, which could be attributed to the interaction between Ag.sub.3PO.sub.4 and WO.sub.3 phases. The deconvolution of P 2p spectra of the samples reveals the phosphorous existed in three different states on the surface in case of all the samples. The samples exhibited peaks in the range of 131.7-133.2 eV for PO, POAg and POH species [40]. The bulk WO.sub.3 nanofibers sample exhibited two major contributions corresponding to W 4f.sub.5/2 and W 4f.sub.7/2 at 36.5 eV and 34.5 eV, which is indicating that the most W species are in +6 oxidation state [41]. However, the binding energies of major W 4f.sub.5/2 and W 4f.sub.7/2 contributions are appeared at 37.2 eV and 35.2 eV in case of AgPWO.sub.3 composite and Pt deposited AgPWO.sub.3 samples. The shift in the binding energies to a high position is possibly due to the interaction between WO.sub.3 and Ag.sub.3PO.sub.4 or Ag species and they are not simply a physical mixture but composited with each other. Similar results were previously observed by the other researchers [42-43].

(43) It is clear from the figure that the O1s spectra are different for bulk WO.sub.3, Ag.sub.3PO.sub.4, and AgPWO.sub.3 composites. The O1s peak in WO.sub.3 can be deconvoluted into two contributions. The major peak at 529.3 eV originated from the WO bond in the WO.sub.3 lattice and the small intensity peak at 530.3 eV corresponding to OH groups, originated from water molecules [44]. On other hand, the bulk Ag.sub.3PO.sub.4 sample exhibited three deconvoluted O1s peaks at 533.2 eV, 531.9 eV, 529.8 eV which could be assigned to oxygen atoms for POH, POAg and PO species respectively. In addition, it is observed that the O1s spectra for the AgPWO.sub.3 composites and Pt deposited samples are consistent with WO.sub.3 and Ag.sub.3PO.sub.4, which also revealing the composition of WO.sub.3 with Ag.sub.3PO.sub.4.

(44) The deconvoluted Pt 4f spectra for Pt deposited samples also presented in the FIG. 7. It is possible to distinguish the difference between the surface Pt (0), Pt (II) and Pt (IV) species presented in samples based on the binding energies of the peaks [45]. Presence of XPS peaks at 72.1 eV, 74.1 eV and 76.1 eV indicating that the PtAgP sample composed of both metal and oxidized Pt (Pt.sup.2+& Pt.sup.4+) species [46]. Similar peaks were observed in case of PtWO.sub.3 and PtAgPWO.sub.3 samples, however peaks were observed at higher binding energies, which indicates that the interaction of Pt is different with WO.sub.3 and AgPWO.sub.3 composite compared with bulk AgP. The intensity of peaks corresponding to surface species is different, therefore determination of the concentration of surface species different.

(45) The surface Ag/P, O/Ag, and O/P atomic ratios for the samples were calculated using the XPS data. The Ag/P atomic ratio for AgP sample is 2.39 is more compared to PtAgP (2.35). The Ag/P atomic ratio in PtAgPWO.sub.3 composite is around 2.44 stayed higher compared to the PtAgP indicating that the PtAgPWO.sub.3 has a higher content of Ag.sup.0. The O/Ag atomic ratio in AgPWO.sub.3 sample is lower than that of AgP and WO.sub.3 samples indicating that the oxygen deficiency is more in case of AgPWO.sub.3. In addition, the ratio of O/P after Pt deposition decreased from 3.03 in AgPWO.sub.3 to 2.95 in PtAgPWO.sub.3. The generation of Ag.sup.0 and Pt.sup.0 could have resulted the oxygen vacancy, which could enhance photocatalytic performance of the materials [47].

General Definitions

(46) Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term including should be read as mean including, without limitation or the like; the term example is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as conventional, traditional, standard, known and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future Likewise, a group of items linked with the conjunction and should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as and/or unless expressly stated otherwise. Similarly, a group of items linked with the conjunction or should not be read as requiring mutual exclusivity among that group, but rather should also be read as and/or unless expressly stated otherwise. Furthermore, although item, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as one or more, at least, but not limited to or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.

(47) For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing amounts, sizes, dimensions, proportions, shapes, formulations, parameters, percentages, quantities, characteristics, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term about even though the term about may not expressly appear with the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are not and need not be exact, but may be approximate and/or larger or smaller as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art depending on the desired properties sought to be obtained by the subject matter of the present invention. For example, the term about, when referring to a value can be meant to encompass variations of, in some embodiments 100%, in some embodiments 50%, in some embodiments 20%, in some embodiments 10%, in some embodiments 5%, in some embodiments 1%, in some embodiments 0.5%, and in some embodiments 0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.

(48) Further, the term about when used in connection with one or more numbers or numerical ranges, should be understood to refer to all such numbers, including all numbers in a range and modifies that range by extending the boundaries above and below the numerical values set forth. The recitation of numerical ranges by endpoints includes all numbers, e.g., whole integers, including fractions thereof, subsumed within that range (for example, the recitation of 1 to 5 includes 1, 2, 3, 4, and 5, as well as fractions thereof, e.g., 1.5, 2.25, 3.75, 4.1, and the like) and any range within that range.

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(50) All publications, patent applications, patents, and other references mentioned in the specification are indicative of the level of those skilled in the art to which the presently disclosed subject matter pertains. All publications, patent applications, patents, and other references are herein incorporated by reference to the same extent as if each individual publication, patent application, patent, and other reference was specifically and individually indicated to be incorporated by reference. It will be understood that, although a number of patent applications, patents, and other references are referred to herein, such reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art.

(51) Although the foregoing subject matter has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be understood by those skilled in the art that certain changes and modifications can be practiced within the scope of the appended claims.