Abstract
The disclosure provides a TiO.sub.2-CQDs nanoflower photocatalyst, a photocatalytic thin film and an application, belonging to a technical field of photocatalyst for food processing. The TiO.sub.2-CQDs nanoflower photocatalyst includes TiO.sub.2 and CQDs doped with TiO.sub.2. the CQDs is derived from aloe extract. According to the disclosure, the extract obtained from natural aloe is used as a carbon source to provide CQDs, and TiO.sub.2 is modified to obtain the nanoflower photocatalyst and the photocatalytic thin film for catalytic degradation of polycyclic aromatic hydrocarbons (PAHs).
Claims
1. A TiO.sub.2-CQDs nanoflower photocatalyst, comprising TiO.sub.2 and CQDs doped with TiO.sub.2. the CQDs is derived from aloe extract.
2. The photocatalyst according to claim 1, wherein a crystal structure of TiO.sub.2 is selected from one of anatase, rutile and brookite, or a mixed phase of any two crystal forms or a mixed phase of three crystal forms; and/or, in terms of a total mass of the TiO.sub.2-CQDs nanoflower photocatalyst, a mass content of CQDs is 10-50 wt %; and/or, in the TiO.sub.2-CQDs nanoflower photocatalyst, a particle size of CQDs is 1.5-2.5 nm; and/or, an ultraviolet absorption band of the TiO.sub.2-CQDs nanoflower photocatalyst is 200-420 nm; and/or, an energy band gap of the TiO.sub.2-CQDs nanoflower photocatalyst is 2.8-3.1 eV; and/or, a degradation rate of the TiO.sub.2-CQDs nanoflower photocatalyst is 0.1-0.2 min.sup.1; and/or, typical peak values of the TiO.sub.2-CQDs nanoflower photocatalyst are 25.3, 37.7, 48.0, 53.8, 55.0, 62.6, 27.4, 36.1, 41.2, 44.1 and 56.6.
3. A preparation method of the TiO.sub.2-CQDs nanoflower photocatalyst, comprising following steps: 1) providing TiO.sub.2 nanoflowers; 2) performing microwave reaction on the aqueous solution or aqueous suspension of the purchased aloe extract, and performing post-treatment to obtain CQDs; and 3) mixing the solution or suspension containing TiO.sub.2 nanoflowers with the solution or suspension containing CQDs, stirring at 100-500 r/min for 1-5 h, and drying and sintering to obtain the TiO.sub.2-CQDs nanoflower photocatalyst.
4. The preparation method of the TiO.sub.2-CQDs nanoflower photocatalyst according to claim 3, comprising at least one of following technical features: a) in the step 1), Pluronic(R)F-127, acetic acid and hydrogen chloride (HCl) are dissolved in tetrahydrofuran, tetrabutyl titanate is added under stirring, dissolved in alcohol solvent after aging, and glycerol is added, and after reflux reaction for 6-24 h, TiO.sub.2 nanoflowers are obtained through cleaning, drying and sintering; b) in the step 2), the conditions of microwave reaction are as follows: irradiating the aqueous solution or suspension of aloe for 10-60 min under the microwave condition of 400-800 W; c) in the step 2), the post-treatment comprises centrifugation to obtain the CQDs precursor, followed by drying the CQDs precursor at a temperature between 70-90 C. to obtain the CQDs; d) in the step 3), the drying temperature is 80-100 C.; e) in the step 3), drying is carried out under vacuum condition; f) in the step 3), the sintering temperature is 500-650 C.; and g) in terms of the total mass of TiO.sub.2-CQDs nanoflower photocatalyst, a mass content of CQDs is 10-50 wt %.
5. The preparation method of the TiO.sub.2-CQDs nanoflower photocatalyst according to claim 4, wherein in the technical feature a), a mass ratio of Pluronic (R) F-127, tetrahydrofuran, acetic acid, HCl and tetrabutyl titanate is 5-6:60-80:5-8:6-10:1-5; a ratio of the aged colloidal substance mass, the alcohol solvent volume and the glycerol volume is 1-5:10-40:5-15.
6. A photocatalytic thin film, comprising the TiO.sub.2-CQDs nanoflower photocatalyst according to claim 1 or the TiO.sub.2-CQDs nanoflower photocatalyst prepared by the preparation method.
7. The photocatalytic thin film according to claim 6, wherein the content of TiO.sub.2-CQDs nanoflower photocatalyst is 0.1-5 wt % in terms of solvent mass; and/or, the photocatalytic thin film further includes a film material; and/or the photocatalytic thin film further includes a plasticizer.
8. The photocatalytic thin film according to claim 7, wherein the film material is selected from sodium alginate or water-soluble polymer. and the plasticizer is glutaraldehyde; in terms of a total mass of the photocatalytic thin film, the content of plasticizer is 10-30 wt %.
9. An application of the TiO.sub.2-CQDs nanoflower photocatalyst according to claim 1, or the TiO.sub.2-CQDs nanoflower photocatalyst prepared by the preparation method, or the photocatalytic thin film in controlling PAHs.
10. The application according to claim 9, wherein an application in controlling PAHs in smoked food and an application in controlling PAHs in smoked environment; and PAHs are B(a)P.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a schematic diagram showing a preparation route of TiO.sub.2-CQDs nanoflower photocatalyst in Embodiment 1 of the present disclosure.
[0036] FIG. 2A is a TiO.sub.2-CQDs Energy-Filtered Transmission Electron Microscopy (EFTEM) image in Embodiment 1 of the present disclosure.
[0037] FIG. 2B is a partial enlarged view 1 of the TiO.sub.2-CQDs EFTEM image in Embodiment 1 of the present disclosure.
[0038] FIG. 2C is a partial enlarged view 2 of the TiO.sub.2-CQDs EFTEM image in Embodiment 1 of the present disclosure.
[0039] FIG. 2D is a TiO.sub.2-CQDs EFTEM lattice energy image in Embodiment 1 of the present disclosure.
[0040] FIG. 2E is an EFTEM image of CQDs in Embodiment 1 of the present disclosure.
[0041] FIG. 2F is an element spectrum of Ti in Embodiment 1 of the present disclosure.
[0042] FIG. 2G is an element spectrum of O in Embodiment 1 of the present disclosure.
[0043] FIG. 2H is an element spectrum of C in Embodiment 1 of the present disclosure.
[0044] FIG. 2I is an element spectrum of N in Embodiment 1 of the present disclosure.
[0045] FIG. 2J is an Energy Dispersive X-Ray Spectroscopy (EDX) diagram of elements in Embodiment 1 of the present disclosure.
[0046] FIG. 3A is an X-Ray Diffraction (XRD) spectrum of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0047] FIG. 3B is an X-ray photoelectron spectroscopy (XPS) survey spectrum of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0048] FIG. 3C is a Carbon 1s (C1s) spectrogram of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0049] FIG. 3D is a Titanium 2p (Ti2p) spectrogram of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0050] FIG. 3E is an Oxygen 1s (O1s) spectrogram of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0051] FIG. 3F is a Nitrogen 1s (N1s) spectrogram of TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0052] FIG. 3G is a Fourier Transform Infrared Spectroscopy (FTIR) related to TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0053] FIG. 4A is an Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis) related to TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0054] FIG. 4B is a an energy band gap diagram related to TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0055] FIG. 4C is a Photoluminescence (PL) spectrogram related to TiO.sub.2-CQDs and TiO.sub.2 in Embodiment 1 of the present disclosure.
[0056] FIG. 4D is a thermogravimetric analysis diagram of TiO.sub.2-CQDs in Embodiment 1 of the present disclosure.
[0057] FIG. 4E is a thermogravimetric analysis diagram of TiO.sub.2 in Embodiment 1 of the present disclosure.
[0058] FIG. 5A is an electron paramagnetic resonance (EPR) spectrum of oxygen vacancy in Embodiment 1 of the present disclosure.
[0059] FIG. 5B is an EPR spectrum of DMPO-.Math.OH in Embodiment 1 of the present disclosure.
[0060] FIG. 5C is an EPR spectrum of DMPO-.Math.O.sub.2.sup. in Embodiment 1 of the present disclosure.
[0061] FIG. 5D is an EPR spectrum of TE; MPO-h+ in Embodiment 1 of the present disclosure.
[0062] FIG. 5E is an impedance test diagram of photocatalyst in Embodiment 1 of the present disclosure.
[0063] FIG. 5F is a current intensity test diagram of the photocatalyst Embodiment 1 of the present disclosure.
[0064] FIG. 6A is an application test diagram of photocatalytic degradation of B(a)P.
[0065] FIG. 6B shows an application linear first-order model of the photocatalytic degradation of B(a)P.
[0066] FIG. 6C is a photocatalytic degradation diagram of B(a)P with a free radical scavenger.
[0067] FIG. 6D is a linear first-order model of the photocatalytic degradation of B(a)P with the free radical scavenger.
[0068] FIG. 6E shows a contribution of active ingredients to the degradation of B(a)P.
[0069] FIG. 6F shows a reusability test on the photocatalyst.
[0070] FIG. 7A shows Langmuir and Freundlich adsorption curves of Embodiment 2.
[0071] FIG. 7B shows pseudo first-order dynamics of Embodiment 2.
[0072] FIG. 7C shows pseudo second-order dynamics of Embodiment 2.
[0073] FIG. 7D shows an intra-particle diffusion of Embodiment 2.
[0074] FIG. 8A shows a film containing nanomaterials at varying concentrations in Embodiment 2 of the present disclosure.
[0075] FIG. 8B is a sampling schematic diagram.
[0076] FIG. 8C is an application test diagram of PM.sub.2.5-B(a)P.
[0077] FIG. 8D shows the disclosure test diagram of B(a)P in sausage.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0078] The embodiments of the present disclosure are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. The disclosure can also be implemented or applied by other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the disclosure.
[0079] It should be noted that the experimental methods in the following examples are all conventional methods unless otherwise specified. The materials and reagents used in the following examples can be obtained from commercial sources unless otherwise specified. The process equipment or devices not specified in the following examples are all conventional in this field.
[0080] The experiments used for testing in the disclosure are as follows:
[0081] 1) Sausage production: removing fat and tendons from fresh pork leg, respectively crushing lean meat and fat, and mixing lean meat and fat according to the ratio of (2:8, w/w), marinating the minced meat with 2% salt, and putting the marinated meat into sausage casings; suspending sausages wrapped with composite starch film in a smoking furnace, and using apple wood for smoking at 90 C. for 4 h; for untreated group, directly exposing sausages to the smoking furnace, and setting three replicates in each group.
[0082] 2) Determination of B(a)P: adding a sausage sample (5 g) into 10 mL n-hexane, performing ultrasonic treatment for 30 min (repeated twice), and putting the supernatant of the two extracts into a 50 mL centrifuge tube; then activating respectively the B(a)P extraction column with 5 mL dichloromethane and 5 mL n-hexane; pouring the extracted supernatant into the extraction column for sample injection, then washing with 5 mL n-hexane and collecting with 5 mL dichloromethane; carrying out nitrogen blowing on the collected eluent, and adding 1 mL acetonitrile for redissolution, and then detecting by High-Performance Liquid Chromatography (HPLC)-Fluorescence Detector (FLD). The smoked composite starch film (about 3 g) is extracted with n-hexane after cutting, and the treatment process is the same as above.
[0083] HPLC-FID conditions: a) chromatographic column: C18, column length 250 mm, inner diameter 4.6 mm, particle size 5 m; b) mobile phase: acetonitrile+water=88+12; c) flow rate: 1.0 mL/min; d) fluorescence detector: excitation wavelength 384 nm, emission wavelength 406 nm; c) column temperature: 35 C. and f) sample volume: 20 L.
3) Photocatalytic Experiment
[0084] Taking B(a)P with strong stability as the research object, the degradation reaction is carried out in a photocatalytic reactor built in the laboratory. 0.05 g of TiO.sub.2-CQDs nanoflower photocatalyst is added to the B(a)P standard sample (20 mL) with a concentration of 20 g/L. In the process of photodegradation experiment, ultraviolet light is placed in the center of the reactor. The ultraviolet lamp is turned on at 25 C., and samples are taken every 5 min for 30 min. The level of B(a)P is detected by HPLC-FLD.
[00001]
[0085] C0 and Ct are the concentrations (g/L) of B(a)P at the beginning of the reaction and at t reaction time, respectively.
4) Particulate Matter Collection
[0086] Photocatalytic degradation of PM.sub.2.5-B(a)P during wood combustion is studied on a laboratory platform. Wood is burned in the container, and the generated smoke is connected to the inhalable particulate matter discharge device and the ultraviolet catalytic oxidation device in turn. Inhalable particulate matter is collected by JCH-120F inhalable particulate matter sampler (Qingdao, China) and Ahlstrom-Munksjo quartz fiber fiber filter paper (Finland), and inhalable particulate matter with diameter less than 2.5 m is collected by PM.sub.2.5 splitter. The sampling space is about 10 m5 m, and the sampling time is 6 h at the flow rate of 100 L/min under the conditions of 25 C. and relative humidity of 40%. After sampling, the quartz fiber filter paper is wrapped with aluminum foil and is storef at 20 C. The calculation formula of PM.sub.2.5-B(a)P is as follows:
[00002]
[0087] : environmental PM.sub.2.5-B(a)P, ng/m.sup.3.
[0088] t: measured concentration of B(a)P, ng/mL.
[0089] V: concentration volume of the sample, mL.
[0090] Va: total volume, m.sup.3.
[0091] DF: dilution factor.
Embodiment 1
[0092] Referring to FIG. 1, a synthesis method of TiO.sub.2-CQDs nanoflower photocatalyst, specifically:
1) Preparation of A/R-TiO.SUB.2 .Nanoflowers
[0093] Placing 60 mL of tetrahydrofuran (THF) in a beaker, and then adding 4 g Pluronic(R)F-127, 6.4 mL acetic acid (>99%) and 8 mL HCl (38%) in turn; dropwise adding 4 mL tetrabutyl titanate with continuous stirring (300 r/min), and then aging at 50 C. for 6-8 h; dissolving the aged colloidal substance (4 g) in 20 mL ethanol, then adding 10 mL glycerol for a reflux of 12 h at 110 C.; drying the precipitate after ethanol cleaning at 80 C., and then sintering at 550 C. to obtain A/R-TiO.sub.2 nanoflowers.
[0094] Dropwise adding 4 mL tetrabutyl titanate with continuous stirring (300 r/min), and then aging at 50 C. for 6-8 h; dissolving the obtained colloidal substance in ethanol, then adding 10 mL glycerol for a reflux of 12 h at 110 C.; drying the precipitate after cleaning at 80 C., and then sintering at 550 C. to obtain A/R-TiO.sub.2 nanoflowers.
2) Synthesis of CQDs from Sloe Extract
[0095] Putting different quality aloe extracts (purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) into a volumetric flask, and adding 20 mL deionized water; putting aloe extracts with different qualities into the volumetric flask, and then adding 20 mL of deionized water; fully stirring the solution, then irradiating with 600 W microwave for 20 min, cooling and centrifuging at a speed of 10000 g/min; after centrifugation, drying at 80 C. to obtain brown CQDs.
3) Synthesis of TiO.SUB.2.-CQDs Nanoflower Photocatalyst
[0096] Dispersing 1 g A/R-TiO.sub.2 nanoflowers synthesized by hydrothermal method in ethanol, dispersing the CQDs in water, and then the CQDs solution dropwise adding into the A/R-TiO.sub.2 nanoflower solution at a stirring speed of 300 r/min for 2 h; then centrifuging the product, washing the product with ethanol three times and drying the product in vacuum at 100 C.; then sintering the product at 550 C. to obtain TiO.sub.2-CQDs nanoflower photocatalyst. TiO.sub.2-CQDs nanoflower photocatalysts prepared from 100 mg, 250 mg and 500 mg aloe extract are named as TiO.sub.2-CQDs-1, TiO.sub.2-CQDs-2 and TiO.sub.2-CQDs-3 respectively.
Characterizations of TiO.SUB.2.-CQDs Nanoflower Photocatalyst
1) Photocatalyst Characterization
[0097] EFTEM images show the internal structure and crystal lattice of TiO.sub.2-CQDs-2 nanoflower photocatalyst. As shown in FIG. 2A, FIG. 2B and FIG. 2C, the prepared TiO.sub.2 has obvious nanoflower structure, which indicates that the crystal growth of TiO.sub.2 occurs under strong acid conditions, rather than the accumulation of small nano-sheets. The edge of the nanoflower increase the contact area of the photocatalyst. The lattice fringe spacing is an important index in substances that reflect the morphological characteristics of catalytic materials. The lattice fringes of each photocatalytic material are clearly displayed (FIG. 2D), and a lattice fringe spacing of 0.352 nm is observed in the TiO.sub.2-CQDs, and is in correspondence with a plane (101) of anatase-TiO.sub.2. a characteristic lattice fringe spacing of 0.321 nm is observed in the TiO.sub.2-CQDs, aligning with a plane (110) of rutile-TiO.sub.2, while a spacing of 0.263 nm is attributed to a plane (100) of the CQDs. In addition, CQDs presents CQD morphology with different particle sizes (FIG. 2E), and the particle size is about 1.5-2.5 nm. The close contact between CQDs and TiO.sub.2 nanoflowers promoted the charge transfer during the photocatalytic reaction. As shown in FIG. 2F, FIG. 2G, FIG. 2H, FIG. 2I and FIG. 2J, Ti, O, C and N are completely detected in the TiO.sub.2-CQDs nanocomposite, which further proved the successful preparation and structural characteristics of the TiO.sub.2-CQDs photocatalyst.
2) Structural Characterization
[0098] The crystal structure of the prepared materials is determined by XRD. As shown in FIG. 3A, TiO.sub.2-CQDs nanoflower photocatalyst has good crystallinity. The peak value of TiO.sub.2-CQDs can be obtained according to PDF No. 99-0008 and PDF No. 99-0090. Obviously, the typical peaks at 25.3, 37.7, 48.0, 53.8, 55.0 and 62.6 are different from those at planes (101), (004), (200), (105), (201) and (200) of anatase TiO.sub.2, respectively. The typical peaks at 27.4, 36.1, 41.2, 44.1 and 56.6 are consistent with those at planes (110), (101), (111), (210), (211) and (220) of rutile TiO.sub.2, respectively. XRD analysis shows that TiO.sub.2 is a composite of anatase and rutile, and no other impurities are detected, which indicates that TiO.sub.2-CQDs has high purity without interference from other substances. TiO.sub.2-CQDs has no obvious CQDs characteristic peak, which is attributed to the very small and disordered crystal structure TiO.sub.2-CQDs, resulting in its XRD pattern showing extensive background scattering and lacking clear characteristic peak.
[0099] XPS is used to analyze the elemental composition and chemical state of the surface of photocatalyst samples, and FIG. 3B shows the detailed information of Ti2p, O1s, N1s and C1s of TiO.sub.2-CQDs. As shown in FIG. 2C, the fitting peaks at 288.5 eV, 286.4 eV, 284.8 eV in C1s orbit of TiO.sub.2-CQDs represent CO, CN and CC bonds respectively. The recombination of CQDs leads to the obvious vibration of C Is orbital peak of TiO.sub.2-CQDs, especially the CC bond. The two characteristic peaks at 464.5 CV and 458.9 eV in FIG. 3D are Ti.sup.3+ 2p1/2 and Ti.sup.3+ 2p3/2, respectively, indicating that Ti.sup.3+ is formed in the composite TiO.sub.2-CQDs. Previous studies have shown that oxygen vacancies in photocatalytic materials will lead to the generation of unpaired electrons or Ti.sup.3+ centers, which will induce the charge transfer rate of TiO.sub.2 electrons or holes. The existence of defects in rutile TiO.sub.2 should contribute to the formation of Ti.sup.3+ during the photocatalytic reaction. Surface defects (i.e. hydroxyl groups) make the valence band top of rutile TiO.sub.2 move up, thus enhancing the photocatalytic activity. Rutile TiO.sub.2 is confirmed by XRD results. The O1s spectral fitting peak of TiO.sub.2-CQDs has two deconvolution peaks at 531.7e V and 530.1 eV, corresponding to lattice oxygen atom and TiO respectively. Therefore, compared with TiO.sub.2, TiO.sub.2-CQDs produces more oxygen vacancies, and the existence of oxygen vacancies stimulates the generation of active oxygen (FIG. 3E). The obvious fitting peaks of N1s spectrum (FIG. 3F) at 399.3 eV and 399.9 eV represent nitride and metal oxynitride, respectively. Nitrogen doping effectively induces charge delocalization, reduces work function, changes the mechanism of electron transport and catalytic reaction, and effectively enhances the catalytic activity and selectivity of CQDs. With the addition of CQDs, the binding energy of C, Ti and O is shifted to the direction of low binding energy, proving that the interaction between CQDs and TiO.sub.2 is close.
[0100] The FTIR spectrum of the photocatalyst is shown in FIG. 3G, and the tensile vibration of 3300 cm.sup.1 represents the tensile vibration of OH. There are OH characteristic vibration peaks in TiO.sub.2 and TiO.sub.2-CQDs, and the vibration of TiO.sub.2-CQDs is more obvious. The vibration with the characteristic peak of TiO.sub.2-CQDs at 1611 cm.sup.1 is attributed to the stretching vibration of NH. At the same time, the stretching peak at 1428 cm.sup.1 represents the vibration of CC, and 1025 cm.sup.1 is due to the stretching vibration of COC. Previous studies have shown that when these oxygen-containing groups absorb energy, the electrons in their molecules will be excited to a high-energy state, forming an excited state. The excited state makes molecules have different chemical properties and reactivity.
3) Optical Characteristics
[0101] Referring to FIG. 4A, FIG. 4B and FIG. 4C, FIG. 4A shows that TiO.sub.2 shows a wide absorption band under the ultraviolet light with the wavelength of 200-400 nm, and the absorption of TiO.sub.2-CQDs shifts to the high frequency region, indicating that the recombination of CQDs enhances the ultraviolet absorption and makes a redshift of the TiO.sub.2 absorption peak. Further, Eg is estimated according to the intercept of the curve tangent in the photon energy relationship diagram. Eg refers to the minimum energy required for electrons in photocatalyst materials to transition from valence band to conduction band, and is an important parameter for evaluating the light absorption and photocatalytic activity of photocatalyst. The results show that the an energy band gap of TiO.sub.2 decreases from 3.24 eV to 2.91 eV with the addition of CQDs (FIG. 4B), which may be caused by the introduction of a new energy state at the molecular orbital interface of TiO.sub.2-CQDs. Photoluminescence (PL) refers to the light phenomenon that a substance emits after being excited by light. PL spectrum vibration indicates the recombination ability of photo-generated electron-hole pairs. As shown in FIG. 4C, TiO.sub.2 shows a broad luminescence peak around 360-440 nm, with a central peak around 410 nm. This shows that the photo-generated carriers recombine seriously and the photocatalytic oxidation reaction is not easy to occur. However, the luminescence intensity of TiO.sub.2-CQDs is greatly reduced, and the doping of CQDs makes the photogenerated electrons of TiO.sub.2 migrate in time, and the recombination of electron pairs is inhibited in time. Therefore, it can be inferred that TiO.sub.2 composite CQDs significantly promoted the charge separation process.
[0102] FIG. 4D and FIG. 4E show the thermogravimetric curves (TGA) of TiO.sub.2 and TiO.sub.2-CQDs. Both of the two photocatalysts show different degrees of mass change at 25-500 C., which is related to the evaporation of water on the surface of the sample. The mass loss at the initial stage of 25-200 C. is attributed to the volatilization of adsorbed water, and the mass loss of TiO.sub.2 and TiO.sub.2-CQDs is 15.4% and 4.7% respectively. Further, the second mass loss occurred at 200-300 C., and the loss at this stage is small, which may be mainly due to the decomposition of oxygen-containing groups in TiO.sub.2. The loss of TiO.sub.2-CQDs at 300-500 C. is higher than that of TiO.sub.2, and TiO.sub.2-CQDs shows obvious stability at 300-500 C. The loss in the third stage may be related to the dehydration of OH group. Generally speaking, the decomposition temperature of TiO.sub.2-CQDs composite is higher, which indicates that there are chemical bond changes between the composite of TiO.sub.2-CQDs and the original metal material, which enhances the intermolecular force and the high temperature resistance of the composite.
4) Photocatalytic Activity
[0103] Referring to FIGS. 5A-5D, electron spin resonance (ESR) technology is applied to test the active substances produced by TiO.sub.2-CQDs under ultraviolet irradiation. Oxygen vacancies can introduce local electronic state oxygen vacancies into the band gap of materials and also play a role in the catalytic process. As shown in FIG. 5A, there is no obvious signal of oxygen vacancy under dark conditions, and TiO.sub.2-CQDs shows obvious oxygen vacancy after ultraviolet irradiation. This is due to the fact that dopants occupy the position of oxygen atoms in the crystal lattice, thus increasing the number of oxygen vacancies and improving the electron transport ability and light absorption characteristics. The results of FIG. 5B and FIG. 5C show that obvious DMPO-.Math.OH and DMPO-.Math.O.sub.2.sup. adducts are observed in both TiO.sub.2 and TiO.sub.2-CQDs after illumination, indicating that .Math.OH and .Math.O.sub.2.sup. free radicals exist in the photocatalytic system. Compared with pure TiO.sub.2, the .Math.OH and .Math.O.sub.2.sup. free radical signals of CQDs composite samples are stronger. CQDs can absorb light energy and excite electrons, making them jump to conduction band, thus forming active electrons and participating in oxygen reduction reaction. These active electrons can combine with oxygen molecules to generate reactive oxygen species such as .Math.OH and .Math.O.sub.2.sup.. The signal intensity of TEMPO-h.sup.+ is detected in FIG. 5D. The signal intensity is obvious under dark conditions, and the signal is obviously weakened after ultraviolet irradiation.
[0104] Impedance is a parameter that describes the resistance and admittance of a circuit to AC electrical signals. The radius of the electrode arc of TiO.sub.2-CQDs is smaller than that of TiO.sub.2, which indicates that the AV-doped photocatalyst has lower interfacial resistance and inhibits the recombination of carriers (FIG. 5E). The measurement of photocurrent can be used to evaluate the current intensity of photocatalytic materials. The results of FIG. 5F show that the photocurrent intensity of TiO.sub.2-CQDs is the strongest, and the oxygen-rich structure enhances the light absorption. The doping of CQDs introduces additional free electrons or holes into semiconductor materials, increases the carrier concentration and promotes the separation efficiency of electrons and holes.
5) Degradation of B(a)P
[0105] In order to study the degradation of B(a)P by CQDs, the degradation of B(a)P standard solution by different catalysts is studied under ultraviolet irradiation. As shown in FIG. 6A, the effect of single ultraviolet irradiation on B(a)P is negligible. Different catalysts were equilibrated in the dark for 20 min. Compared with TiO.sub.2, TiO.sub.2-CQDs nanoflowers showed more obvious photodegradation ability, and B(a)P irradiated for 30 min and 20 g/L is completely degraded. In the UV-bonded TiO.sub.2-CQDs-2 nanoflower system, the same concentration of B(a)P can be rapidly degraded under light conditions, and it can be completely degraded within 15 min. This is mainly because the three-dimensional structure of TiO.sub.2-CQDs nanoflowers provides a highly reactive surface.
[0106] The degradation rates of different catalysts were calculated by first-order kinetic equation. The results of FIG. 6B show that TiO.sub.2-CQDs-2 shows the most significant photocatalytic rate (k=0.198 min.sup.1), and the degradation rates of TiO.sub.2-CQDs-1 and TiO.sub.2-CQDs-3 are 0.119 min.sup.1 and 0.105 min.sup.1. The photocatalytic efficiency of single ultraviolet irradiation is the lowest (K=0.002 min.sup.1). The experimental results show that the photocatalytic effect of photocatalyst on B(a)P is closely related to the doping density of CQDs. The photocatalyst activity is determined by the active site of photocatalyst and ultraviolet light penetration, and the reaction site is insufficient when the concentration of photocatalyst is low. Of course, the loading of high dose CQDs may produce shielding effect and light reflection to weaken the light absorption inside the reaction medium, so too low or too high catalyst dose will reduce the catalytic activity of photocatalyst.
[0107] The species and concentration of active species produced by TiO.sub.2-CQDs play an important role in the photocatalytic degradation of B(a)P. Therefore, in order to further explore and analyze the mechanism of photocatalytic degradation of B(a)P by TiO.sub.2-CQDs, p-benzoquinone (BQ), isopropanol (IPA) and ammonium oxalate (AO) are selected as quenchers to capture .Math.O.sub.2.sup., .Math.OH and h.sup.+ respectively. As shown in FIG. 6C and FIG. 6D, the rate of degradation of B(a)P by TiO.sub.2-CQDs decreased obviously after adding the trapping agent, especially when BQ is used as the trapping agent. Further, through (1-3), the contribution ability of different active free radicals to the degradation of B(a)P is obtained. FIG. 6E shows that the contribution ability of .Math.O.sub.2.sup., .Math.OH and h+ is 86.21%, 73.40% and 83.73% respectively. FIG. 6F shows that TiO.sub.2-CQDs still has stable recycling performance after four times of recycling.
[00003]
[0108] R.sub..Math.OH: contribution rate (%); K.sub..Math.OH: the reaction rate after adding .Math.OH scavenger (min.sup.1); K.sub.B(a)P: the degradation reaction rate of K.sub.B(a)P: B(a)P(min.sup.1).
Embodiment 2
Preparation of Photocatalytic Thin Films
[0109] Adding 3-5% (w/v) sodium alginate (SA) into 100 mL of ultra-pure water and mixing thoroughly for 10-30 min on a magnetic stirrer at 300-800 rpm, adding 10-20% (w/v) glutaraldehyde as plasticizer, fully stirring to prepare SA solution, adding TiO.sub.2-CQDs in the SA solution and continuously stirring for 1 h; then, removing the bubbles in the SA solution by ultrasonic wave for 30 min; finally, pouring the SA solution into a Teflon plate and drying at 50 C. for 8 h. The films with different mass of TiO.sub.2-CQDs (0.5%, 1% and 2%, w/w) are named as 0.5% TCF, 1% TCF and 2% TCF respectively.
[0110] Characterization of film adsorption kinetics: The Langmuir adsorption model examines the formation of a unilayer adsorbate on the adsorbent's surface, typically employed to characterize the adsorption process at saturation. The Freundlich adsorption model, characterized as a multi-layer adsorption model, the adsorptive molecules are arranged in a multi-layered configuration upon the adsorbent surface. The presence of interactive forces among the adsorptive molecules is well-suited for characterizing non-ideal behaviors observed within the adsorption process. Langmuir and Freundlich adsorption models show the potential adsorption mechanism of TiO.sub.2-CQDs photocatalytic thin film for B(a)P. As shown in FIGS. 7A-7D and Table 1, TiO.sub.2-CQDs is closer to the Langmuir model, indicating that B(a)P is adsorbed on TiO.sub.2-CQDs film in the form of monolayer (FIG. 7A). In the Freundlich adsorption model, the value of 1/n is greater than 1, signifying that B(a)P molecules are capable of establishing robust chemical adsorption bonds with the TiO.sub.2-CQDs membrane. The relationship between the adsorption capacity of TiO.sub.2-CQDs membrane for B(a)P and the contact time of the adsorbent is investigated, and the pseudo-first-order, pseudo-second-order and intra-particle diffusion models are used for fitting (FIG. 7B and FIG. 7C). The findings demonstrate that the adsorption rate of TiO.sub.2-CQDs thin films experiences an initial upsurge, attributable to the abundance of adsorption sites. The pseudo first-order model (R.sup.2=0.991) and pseudo second-order model (R.sup.2=0.981) fit the adsorption data of TiO.sub.2-CQDs thin films well. The results of intra-particle diffusion model indicate that the adsorption process is multi-staged, K.sub.1>K.sub.2>K.sub.3, demonstrating that film diffusion is the primary driving force for adsorption (FIG. 7D).
TABLE-US-00001 TABLE 1 Adsorption isotherm and kinetic simulation of TCF film R.sup.2 q k TiO.sub.2-CQDs Langmuir 0.971 31.38 0.309 R.sup.2 k n Freundlich 0.918 26.84 0.553 R.sup.2 a b Pseud-first 0.991 3.37 0.061 order Pseud-second 0.981 8.34 0.222 order Inter-particle R.sub.1.sup.2 = 0.999 C.sub.1 = 0.68 K.sub.1 = 0.488 R.sub.2.sup.2 = 0.997 C.sub.2 = 0.37 K.sub.2 = 0.432 R.sub.3.sup.2 = 0.954 C.sub.2 = 2.57 K.sub.2 = 0.056
Application of TCF Film
[0111] Evaluation of adsorption and photodegradation ability of TCF film for PM.sub.2.5-B(a)P in smog environment. FIG. 8A and FIG. 8B show the situation of sampling film (SF) and SF+TCF film during the collection of particulate matter. The results indicate that during the 10-hour collection process, the presence of TCF leads to a 69.8% reduction in PM.sub.2.5-B(a)P (FIG. 8C). This demonstrates that the TCF film is effective in mitigating the atmospheric emissions of PM.sub.2.5-B(a)P in practical applications. Motivated by the remarkable adsorptive and photodegradative performance of TCF film against PM.sub.2.5 pollutants in smog, an assessment of the film's capacity to degrade B(a)P within smoked sausage is conducted. As shown in FIG. 8D, the B(a)P in the untreated sausage is 3.26 g/kg, and the single ultraviolet ray can reduce the B(a)P in the sausage, but the inhibition ability is much lower than that in other groups. The combination of 0.5% TCF, 1% TCF and 2% TCF with ultraviolet rays can reduce B(a)P in sausages by 70.9%, 56.1% and 49.7% respectively. Excessive photocatalyst can reduce the ability of light to penetrate the material by reducing the transmittance of the gel and increasing the absorption and scattering of light.
[0112] The embodiments described above serve to illustrate the principle and efficacy of the present disclosure, but they are not intended to be limiting. Skilled artisans in the field can easily make modifications or alterations to these embodiments without deviating from the spirit and scope of the present disclosure. Consequently, any adaptations or modifications that are deemed equivalent by individuals with ordinary skill in the art, and that do not stray from the inventive concepts and principles set forth in this disclosure, should be considered within the ambit of the claims of the present disclosure.
