CATALYST FOR PHOTOCATALYTIC REACTION FOR THE PRODUCTION OF HYDROGEN BY HYDROLYSIS AND PREPARATION METHOD THEREOF

Abstract

The present invention is a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis and a preparation method thereof. A preparation method of a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis, comprising: after dispersing the ZnO nanorods into a solvent, adding TiCl.sub.4 and water, followed by hydrothermal treatment, washing and drying to obtain a ZnO@TiO.sub.2(B) nanoflower catalyst, i.e. the catalyst. According to the present invention, a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis and a preparation method thereof, embedding ZnO nanocrystals into a TiO.sub.2(B) lattice can improve the stability of photocatalytic hydrogen production.

Claims

1. A preparation method of a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis, wherein, the preparation method comprises: after dispersing ZnO nanorods into a solvent, adding TiC14 and water, followed by hydrothermal treatment, washing and drying to obtain a ZnO@Ti02(B) nanoflower catalyst, i.e. the catalyst.

2. The preparation method of claim 1, wherein the solvent is ethylene glycol; deionized water and absolute ethanol are used in the washing process for washing.

3. The preparation method of claim 1, wherein the temperature of the hydrothermal treatment is 140-160°C., and the time is 3.5-4.5 h; the drying temperature is 55-65°C., and the drying time is 20-24 h.

4. The preparation method of claim 1, wherein the temperature of the hydrothermal treatment is 150°C., and the time is 4 h; the drying temperature is 60°C., and the drying time is 24 h.

5. The preparation method of claim 1, wherein the molar ratio of Zn and Ti in the catalyst is 1:1-6.

6. The preparation method of claim 1, wherein the ZnO nanorods are synthesized by electrodeposition method.

7. The preparation method of claim 6, wherein the synthesis process of the ZnO nanorods is: subjecting an aqueous solution containing zinc nitrate and urotropine to electrodeposition treatment in a quartz electrolytic cell at 90°C., followed by centrifugation, washing, and drying to obtain the ZnO nanorods

8. The preparation method of claim 7, wherein the molar concentrations of zinc nitrate and urotropine are 0.04-0.06 mol/L and 0.04-0.06 mol/L respectively; in the electrodeposition process, a CFs, a platinum plate and a saturated calomel electrode (SCE) are used as a working electrode, a counter electrode and a reference electrode, respectively; the voltage on the working electrode is −1.1 v, and the reaction time is 2 h; the drying is performed at 60°C. under vacuum.

9. The preparation method of claim 8, wherein the molar concentrations of zinc nitrate and urotropine are 0.05 mol/L and 0.05 mol/L respectively; prior to the electrodeposition process, sonicating the CFs in acetone, deionized water, and ethanol, respectively.

10. A catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis, wherein the catalyst is prepared by the preparation method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a scanning electron micrograph of the nanoflower of Example 5, the scale of the figure is 100 nm;

[0029] FIG. 2 shows an N.sub.2 adsorption-desorption isotherm of the synthesized samples of Examples 1-7;

[0030] FIG. 3 shows the yield of hydrogen production from photocatalytic decomposition of water from the synthesized samples of Examples 1-7;

[0031] FIG. 4 shows the rate of hydrogen production from photocatalytic decomposition of water from the synthesized samples of Examples 1-7;

[0032] FIG. 5 shows the cycle stability of hydrogen production from photocatalytic decomposition of water of Example 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to further illustrate a catalyst for a hydrolysis-to-hydrogen photocatalytic reaction and a preparation method thereof according to the present invention, and achieve the intended purpose of the present invention, a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis and a preparation method thereof according to the present invention, and specific embodiments, structures, features and effects thereof will be described in detail with reference to preferred embodiments. In the following description, various references to “one embodiment” or “an embodiment” are not necessarily to the same embodiment. Furthermore, the particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner. A catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis and a method for preparing the same according to the present invention will now be described in further detail with reference to specific examples.

[0034] Acid leaching method provides a new method. First, ZnO is an amphoteric oxide, offering the possibility to achieve a bulk phase of the lattice-embedded material. By electrodeposition, the present invention will synthesize high crystallinity ZnO nanorods with broader advantages over commercially available ZnO nanoparticles. The nucleation growth of TiO.sub.2(B) is accompanied by the corrosion of ZnO by taking advantage of the characteristic of TiCl.sub.4 hydrolysis that the environment of the hydrolysis process is acidic. By controlling the input of ZnO, incomplete lattice scission of ZnO nanorods can occur during this process. Finally, the lattice of ZnO will be embedded in the lattice of TiO.sub.2(B). The low bulk density unit structure of TiO.sub.2(B) may be key to the synthesis of lattice-embedded ZnO@TiO.sub.2(B) nanoflowers. In this system, since ZnO has a similar energy band as TiO.sub.2(B), the energy band level of ZnO will match well with TiO.sub.2(B) and form Type II heterojunction stably.

[0035] The technical solution of the present invention is:

[0036] A preparation method of a catalyst for a photocatalytic reaction for the production of hydrogen by hydrolysis, comprising: after dispersing ZnO nanorods into a solvent, adding TiCl.sub.4 and water, followed by hydrothermal treatment, washing and drying to obtain a ZnO@TiO.sub.2(B) nanoflower catalyst, i.e. the catalyst.

[0037] Preferably, the solvent is ethylene glycol;

[0038] deionized water and absolute ethanol are used in the washing process for washing.

[0039] Preferably, the temperature of the hydrothermal treatment is 140-160° C., and the time is 3.5-4.5 h; the drying temperature is 55-65° C., and the drying time is 20-24 h.

[0040] Preferably, the temperature of the hydrothermal treatment is 150° C., and the time is 4 h;

[0041] the drying temperature is 60° C., and the drying time is 24 h.

[0042] Preferably, the molar ratio of Zn and Ti in the catalyst is 1:1-6.

[0043] Preferably, the ZnO nanorods were synthesized by electrodeposition method.

[0044] Further preferably, the synthesis process of the ZnO nanorods is: subjecting an aqueous solution containing zinc nitrate and urotropine to electrodeposition treatment in a quartz electrolytic cell at 90° C., followed by centrifugation, washing, and drying to obtain the ZnO nanorods.

[0045] Further preferably, the molar concentrations of zinc nitrate and urotropine are 0.04-0.06 mol/L and 0.04-0.06 mol/L respectively;

[0046] in the electrodeposition process, a CFs, a platinum plate and a saturated calomel electrode (SCE) are used as a working electrode, a counter electrode and a reference electrode, respectively; the voltage on the working electrode is −1.1 v, and the reaction time is 2 h;

[0047] the drying was performed at 60° C. under vacuum.

[0048] Further preferably, the molar concentrations of zinc nitrate and urotropine are 0.05 mol/L and 0.05 mol/L respectively;

[0049] prior to the electrodeposition process, sonicating the CFs in acetone, deionized water, and ethanol, respectively.

[0050] In the following examples, the experimental methods used are conventional unless otherwise specified, and the reagents, materials and the like used may be purchased from chemical reagent companies.

Example 1

[0051] The TiO.sub.2(B) synthesis procedure was as follows:

[0052] 9 ml of ethylene glycol was transferred into an 80 mL Teflon-lined stainless steel autoclave.

[0053] Then, 0.3 mL TiCl.sub.4 was gradually dropped into the suspension at room temperature until no HCl gas was formed at room temperature. Thereafter, an equal volume of deionized water was added to the mixture. The sealed autoclave was heated in an oven at 150° C. for 4 h.

[0054] Finally, the resulting TiO.sub.2(B) nanoflower product was collected by centrifugation, washed with deionized water and absolute ethanol, and dried in a vacuum oven at 60° C. for 24 h.

[0055] The specific surface area of TiO.sub.2(B) nanoflowers was 395.574 m.sup.2/g, and the photocatalytic hydrogen production rate was 0.482 mmol/g/h.

Example 2

[0056] the molar ratio of Zn:Ti in catalyst was 1:1 and the synthesis procedure was as follows:

[0057] (1) Preparation of ZnO Nanorods:

[0058] the electrodeposition was performed in a quartz electrolytic cell containing a mixed aqueous solution of 0.05 mol/L Zn(NO.sub.3).sub.2 and 0.05 mol/L urotropine, and the quartz electrolytic cell was placed in a water bath environment at 90° C. for electrodeposition.

[0059] The white product was then collected by centrifugation, washed several times with deionized water and absolute ethanol, and dried at 60° C. overnight to give ZnO nanorods.

[0060] wherein, in electrodeposition preparation method, CFs, platinum plate and saturated calomel electrode (SCE) were used as working electrode, counter electrode and reference electrode, respectively; The voltage on the working electrode was −1.1 v and the reaction time was 2 h.

[0061] Prior to preparation of CFs working electrode, CFs shall be respectively placed in acetone, deionized water and ethanol for ultrasonic treatment.

[0062] (2) Preparation of Nanoflowers:

[0063] in a typical synthesis procedure, after dispersing 222.2 mg ZnO nanorods in 9 ml ethylene glycol for 15 min by sonication, the homogeneous ZnO suspension was transferred to an 80 mL Teflon-lined stainless steel autoclave.

[0064] Then, 0.3 mL TiCl.sub.4 was gradually dropped into the suspension at room temperature until no HCl gas was formed at room temperature. Thereafter, an equal volume of deionized water was added to the mixture. The sealed autoclave was heated in an oven at 150° C. for 4 h.

[0065] Finally, the obtained nanoflower product from Zn:Ti of 1:1 was collected by centrifugation, washed with deionized water and absolute ethanol, and dried in a vacuum oven at 60° C. for 24 h.

[0066] As determined, the nano flower having a molar ratio of Zn:Ti of 1:1 has a specific surface area of 344.024 m.sup.2/g and a photocatalytic hydrogen generation rate of 0.944 mmol/g/h.

Example 3

[0067] the molar ratio of Zn:Ti in catalyst was 1:2 and the synthesis procedure was the same as in Example 2, except that:

[0068] 0.6 mL TiCl.sub.4 was weighed and gradually dripped into 18 ml ethylene glycol suspension.

[0069] As determined, the nano flower having a molar ratio of Zn:Ti of 1:2 has a specific surface area of 352.465 m.sup.2/g and a photocatalytic hydrogen generation rate of 1.064 mmol/g/h.

Example 4

[0070] the molar ratio of Zn:Ti in catalyst was 1:3 and the synthesis procedure was the same as in Example 2, except that:

[0071] 0.9 mL TiCl.sub.4 was weighed and gradually dripped into 27 ml ethylene glycol suspension.

[0072] As determined, the nano flower having a molar ratio of Zn:Ti of 1:3 has a specific surface area of 369.583 m.sup.2/g and a photocatalytic hydrogen generation rate of 1.315 mmol/g/h.

Example 5

[0073] the molar ratio of Zn:Ti in catalyst was 1:4 and the synthesis procedure was the same as in Example 2, except that:

[0074] 1.2 mL TiCl.sub.4 was weighed and gradually dripped into 36 ml ethylene glycol suspension.

[0075] As determined, the nano flower having a molar ratio of Zn:Ti of 1:4 has a specific surface area of 379.411 m.sup.2/g and a photocatalytic hydrogen generation rate of 1.695 mmol/g/h, after 36 h of cyclic stability test, the sample stability was stable above 90%.

[0076] A scanning electron micrograph of the nano flower prepared in the example is shown in FIG. 1. Scanning electron micrographs (FIG. 1) reveal the microstructure of nanoflowers as the molar ratio of Zn:Ti being 1:4 in synthesized material. The dissolution of ZnO embedded the fragmented ZnO nanocrystals into the TiO.sub.2(B) lattice to produce ZnO@TiO.sub.2(B) nanoflowers.

[0077] The cycle stability of hydrogen production from the photocatalytic decomposition of water of the nanoflower prepared in this example is shown in FIG. 5. This result further confirms the stability and reusability of nanoflowers with the molar ratio of Zn:Ti of 1:4, and the embedding method of ZnO improves the photoetching phenomenon of ZnO itself, also benefiting from the high stability of the composite.

Example 6

[0078] the molar ratio of Zn:Ti in catalyst was 1:5 and the synthesis procedure was the same as in Example 2, except that:

[0079] 1.5 mL TiCl.sub.4 was weighed and gradually dripped into 45 ml ethylene glycol suspension.

[0080] As determined, the nano flower having a molar ratio of Zn:Ti of 1:5 has a specific surface area of 380.157 m.sup.2/g and a photocatalytic hydrogen generation rate of 0.824 mmol/g/h.

Example 7

[0081] the molar ratio of Zn:Ti in catalyst was 1:6 and the synthesis procedure was the same as in Example 2, except that:

[0082] 1.8 mL TiCl.sub.4 was weighed and gradually dripped into 54 ml ethylene glycol suspension.

[0083] As determined, the nano flower having a molar ratio of Zn:Ti of 1:6 has a specific surface area of 394.475 m.sup.2/g and a photocatalytic hydrogen generation rate of 0.771 mmol/g/h.

[0084] Experimental Tests:

[0085] (1) Mesoporous Structure:

[0086] FIG. 2 shows the N.sub.2 adsorption-desorption isotherm of the synthesized samples of Examples 1-7. Above the particle surface adsorption studies, we measured the specific surface area of the samples using a QDS-MP-30 specific surface area analyzer. By analyzing the N.sub.2 adsorption-desorption isotherms of the synthesized samples, all samples showed a type IV isotherm with a H3 hysteresis loop, which means that there is some mesoporous structure in these samples. After ZnO loading, the specific surface area of ZnO@TiO.sub.2(B) samples tended to decrease, and then the specific surface area of BET decreased from 395.574 m.sup.2/g to 344.024 m.sup.2/g with the further increase of ZnO loading, which could be attributed to the occupation of nucleation sites on the surface of TiO.sub.2(B) nanoplatelets by fragmented ZnO nanocrystals. The composite samples all showed an isotherm similar to that of TiO.sub.2(B) nanoflowers, indicating that ZnO embedded in the lattice of TiO.sub.2(B) nanoflowers had little effect on the mesoporous structure.

[0087] (2) Catalyst Performance:

[0088] FIG. 3 shows the yield of hydrogen production from photocatalytic decomposition of water from the synthesized samples of Examples 1-7;

[0089] FIG. 4 shows the rate of hydrogen production from photocatalytic decomposition of water from the synthesized samples of Examples 1-7.

[0090] The test methods are as follows: photocatalytic decomposition of water was performed in a closed glass gas circulation system (LabSolar III AG, Beijing Perfectlight Technology Co., Ltd.). A 300 w xenon lamp (PLS-SEX300C, Beijing Perfectlight Technology Co., Ltd.) was selected as the light source. 50 mg of the catalyst was added into a reactor, 16 mL of deionized water, 4 mL of a mixed solution of 0.1 M Na.sub.2S and 0.1 M Na.sub.2SO.sub.3 was added, ultrasonic dispersion was performed on 30 min, loaded into a catalytic system, vacuum was pulled to −0.1 MPa, and after adsorption for 1 h in a dark reaction, a photocatalytic reaction was started. During the photocatalytic reaction, the temperature of the reaction solution was maintained at 5° C. by the flow of cooling water. Gas components were analyzed using a 5 molecular sieve column (gas chromatograph (GC-7900, Fuli)). The gas chromatograph was equipped with a thermal conductivity detector (TCD) and high purity argon (99.999%) as carrier gas. Hydrogen production was calculated from retention time and peak area calibrated with standard H.sub.2 gas.

[0091] As shown in FIGS. 3 and 4, pure TiO.sub.2(B) showed very weak hydrogen evolution under simulated sunlight irradiation (0.482 mmol/g/h), indicating that it is inert as a photocatalyst. With the increase of ZnO content, the properties of the composites were improved significantly, and then decreased gradually until the molar ratio of Zn to Ti was 1:4. Nanoflows with a molar ratio of Zn to Ti of 1:4 showed the best photocatalytic hydrogen production performance of 1.695 mmol/g/h, which was 3.5 times higher than that of TiO.sub.2(B). This is due to the formation of a heterojunction between ZnO and TiO.sub.2(B), charge carrier transfer and separation in the ZnO@TiO.sub.2(B) composite being faster than in TiO.sub.2(B). The significant improvement in photocatalytic performance can be attributed to the formation of heterojunction contacts between the embedded ZnO and TiO.sub.2(B) nanoplatelets, which can enhance charge transport and inhibit the recombination process.

[0092] It can be seen from the examples of the present invention that the high photocatalytic performance of ZnO@TiO.sub.2(B) nanoflowers can be attributed to the hierarchical structure on the nanometer scale, the large specific surface area. In addition, the heterogeneous interface in the ZnO@TiO.sub.2(B) nanoflower phase exhibits the energy band structure of type II heterojunction, further enhancing the photocatalytic performance. Overall, the lattice-embedded ZnO@TiO.sub.2(B) nanoflowers solve the problem of poor stability caused by the easy collapse of the TiO.sub.2(B) composite structure. At the same time, the uniform distribution of heterogeneous interface in ZnO@TiO.sub.2(B) nanoflowers makes full use of heterogeneous interface and improves the efficiency of electron-hole separation. This study provides a new design idea for heterojunction composite photocatalyst.

[0093] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.