Preparation method and application of supported photocatalyst

Abstract

The present invention discloses a method for preparing a supported photocatalyst by laser induced electrodeposition technology. The method described prepares a supported photocatalyst BiOX / FTO by combining laser irradiation technology with electrochemical deposition technology, wherein X includes Cl, Br, and I; due to the characteristics of localized deposition of the technology, the obtained catalyst has the characteristics of adjustable morphology and high specific surface area. Under the irradiation of visible light, the removal efficiency of the photocatalyst BiOBr / FTO‑0.25mm for rhodamine B can reach up to 98.1% within 60 minutes. After 5 cycles, the removal rate of rhodamine B can still reach 54.6%. The present invention makes it easy to recycle and reuse the catalyst by loading it, thereby improving its industrial application value.

Description

Technical Field

[0001] The invention relates to a catalyst for sewage treatment, and relates to a preparation method and application of a supported photocatalyst which can effectively degrade pollutants and is easy to recycle without causing secondary pollution. Background Art

[0002] At present, most of the research on photocatalysts is based on small-scale operations at the laboratory scale, and only a few papers involve industrial applications. Although the photocatalytic efficiency at the laboratory scale is quite impressive, there are many limitations to the system operating under actual conditions. For example, particle suspensions are usually used to evaluate the activity of photocatalysts at the laboratory scale, but suspension reactors are difficult to meet the requirements of industrial-scale applications. This is because suspension reactors are difficult to receive enough sunlight and need to be regularly updated during operation. More importantly, powdered photocatalysts need to be recycled, otherwise secondary pollution will occur. The recovery of the catalyst needs to be achieved through gravity precipitation and induced coagulation, which is bound to increase costs and often has poor recovery effects. Fixing the catalyst on a carrier allows the catalyst to be quickly separated from the reaction system, so it is easy to recover, filter and recycle. In addition, it is also beneficial to solve the problems of poor stability and easy deactivation of powdered catalysts. Therefore, fixing the particle photocatalyst to a specific substrate is a feasible method to achieve large-scale application of photocatalysts.

[0003] Currently reported loading methods include dip coating, electrospraying, magnetron sputtering, and chemical vapor deposition. However, the photocatalysts prepared by these methods often have small specific surface areas and insufficient contact with reactants, which leads to relatively low photocatalytic efficiency. Laser-enhanced electrodeposition technology combines high-energy laser action with electrochemical action, using the high energy density of lasers to accelerate metal ion reduction, strengthen the electrodeposition reaction process, and increase deposition rate and local selectivity. The deposition process has a high degree of regional selectivity, making the prepared photocatalyst morphology controllable and having a high specific surface area. Summary of the invention

[0004] In order to facilitate the recycling of photocatalysts without causing secondary pollution and at the same time improve the activity of photocatalysts, the present invention uses laser induced electrodeposition technology to prepare a supported photocatalyst BiOX(Cl, Br, I) / FTO with FTO conductive glass as the substrate, which can degrade pollutants under the action of visible light and can be effectively recycled afterwards.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A method for preparing a supported photocatalyst, wherein the photocatalyst is BiOX / FTO; wherein X is selected from one or more of Cl, Br, and I; KX(Cl, Br, I) aqueous solution, Bi(NO3)3·5H2O aqueous solution, and ethanol solution of p-benzoquinone are used as electrolytes, and Nd:YAG laser and pulse signal generator are used in a deposition device for deposition.

[0007] In the present invention, the deposition equipment in the preparation method comprises: a computer, a Nd:YAG laser, a pulse signal generator, a reflector, a focusing mirror, a platinum wire anode, a FTO conductive glass cathode, an electrolytic cell, a mobile working platform and a motion control card.

[0008] In the present invention, the power density, single pulse energy and frequency of the Nd:YAG laser are set by a computer, the laser emits laser light, and then the laser light is focused on the platinum wire anode in the electrolytic cell by a reflector and a focusing mirror; the electrodeposition solution is irradiated by the laser to generate high temperature and high pressure plasma, and turbulence and micro-area stirring effects are generated in the irradiated area; at the same time, the pulse signal generator applies voltage to the platinum wire anode and the FTO conductive glass cathode for electrodeposition; under the dual effects of laser and electrochemistry, the deposition speed is greatly improved. The position of the FTO conductive glass cathode is adjusted by a computer and a motion control card, and the deposition position moves accordingly.

[0009] Therefore, a deposited thin film can be produced by this device.

[0010] In the present invention, the electrolyte in the electrolytic cell comprises 300-500 mL of a 0.02-0.1 mol / L KX(Cl, Br, I) aqueous solution, 300-500 mL of a 0.02-0.1 mol / L Bi(NO3)3·5H2O aqueous solution, and 60-100 mL of a 0.04-0.2 mol / L p-benzoquinone ethanol solution.

[0011] In the present invention, the preparation method of the deposition electrolyte solution comprises the following steps: firstly, a KX aqueous solution is prepared and adjusted to pH=1.0-2.0 with nitric acid; Bi(NO3)3·5H2O is added to the solution and stirred until it is completely dissolved; finally, p-benzoquinone is dissolved in ethanol and mixed with the above solution to prepare an electrolyte solution.

[0012] In the present invention, the power density of the Nd:YAG laser is 200-500 kW / cm 2 ; Single pulse energy is 0.1~1.0mJ; frequency is 2~10Hz.

[0013] In the present invention, the diameter of the platinum wire is 0.05-0.1 mm; the current density of the electrodeposition is 0.5-1.5 mA / cm 2 .

[0014] In a specific embodiment, the method comprises the following steps: placing a platinum wire above the cathode workpiece and coinciding with the position of the laser spot emitted by the Nd:YAG laser, and the gap between the tip of the platinum wire and the upper surface of the FTO conductive glass cathode workpiece is 20 to 40 μm. During deposition, the workbench is controlled by a computer to move in a straight line in a two-dimensional direction, and moves to the next row after each row is deposited, with a row spacing of 0.1 to 0.5 mm; the movement speed is 0.1 to 0.5 mm / s; after the electrodeposition is completed, the FTO is removed; the electrolyte on the surface of the conductive glass is washed with distilled water and alcohol, and dried at 40 to 60°C for 5 to 10 minutes.

[0015] On the other hand, the present invention also provides a supported photocatalyst prepared by the above method.

[0016] Finally, the present invention also provides an application of the supported photocatalyst in degrading pollutants, and the application comprises the following steps:

[0017] The prepared photocatalyst film is placed in a solution containing pollutants, and the pollutants are photodegraded under the irradiation of sunlight or an external light source. After the degradation is completed, it is taken out in time, cleaned and dried, and then used again.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Laser-induced electrodeposition technology combines laser technology with electrodeposition technology. When the electrodeposition solution is irradiated by laser, high-temperature and high-pressure plasma is generated, which produces obvious turbulence and micro-area stirring effects in the irradiated area, thereby greatly improving the deposition rate. Therefore, compared with conventional electrodeposition technology, metal deposition in this technology usually only occurs in the laser irradiation area, which makes the deposition process highly regionally selective, so that photocatalyst materials with controllable morphology and high specific surface area can be obtained.

[0020] 2. The photocatalytic coating prepared by the present invention has good visible light catalytic ability, and because it is loaded on FTO conductive glass, it is easy to recycle and can be reused without causing secondary pollution, thereby improving the industrial utilization value of the photocatalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the equipment for preparing BiOX / FTO photocatalyst by laser induced electrodeposition DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0023] The raw materials and their sources are as follows:

[0024] Bi(NO3)3·5H2O (analytical grade) was from Guangdong Guanghua Technology Co., Ltd., KCl (analytical grade) and KBr (analytical grade) were from Tianjin Yongchen Fine Chemical Co., Ltd., KI (analytical grade) was from Zhengzhou Paini Chemical Reagent Factory, p-Benzoquinone (analytical grade) was from Tianjin Fuchen Chemical Reagent Factory, ethanol (analytical grade) was from Chengdu Jinshan Chemical Reagent Co., Ltd., and rhodamine B (analytical grade) was from Tianjin Jinbei Fine Chemical Co., Ltd.

[0025] Embodiment 1:

[0026] Preparation of supported photocatalyst BiOCl / FTO-0.1mm

[0027] Preparation of deposition electrolyte solution: First, prepare 500 mL of KCl aqueous solution with a concentration of 0.02 mol / L and adjust the pH to 1.0 with nitric acid. Add 500 mL of 0.02 mol / L Bi(NO3)3·5H2O to the aqueous solution and stir until completely dissolved. Dissolve 100 mL of 0.04 mol / L p-benzoquinone in ethanol.

[0028] The main equipment used in laser induced electrodeposition includes: laser irradiation and electrochemical deposition. The laser irradiation equipment uses Nd:YAG laser with a power density of 200kW / cm 2 ; Single pulse energy is 0.1mJ; frequency is 2Hz. The electrodeposition equipment uses a pulse signal generator, with a platinum wire with a diameter of 0.05mm as the anode and a 30×20mm FTO conductive glass as the cathode. The current density is 0.5mA / cm 2 Under the conditions of constant current deposition, FTO conductive glass was used.

[0029] The anode is placed above the cathode workpiece and coincides with the position of the laser spot. The gap between the tip of the platinum wire and the upper surface of the cathode workpiece is 20μm and remains unchanged. During deposition, the worktable is controlled by a computer to move in a straight line in the two-dimensional direction. After each row is deposited, it moves to the next row. The spacing between each row is 0.1mm. The movement speed is 0.1mm / s.

[0030] After the deposition is completed, the FTO is removed. The electrolyte on the surface of the conductive glass is washed with distilled water and alcohol, and dried at 40°C for 10 minutes.

[0031] Embodiment 2:

[0032] Preparation of supported photocatalyst BiOBr / FTO-0.25mm

[0033] Preparation of deposition electrolyte solution: First, prepare 400 mL of KBr aqueous solution with a concentration of 0.05 mol / L and adjust the pH to 1.5 with nitric acid. Add 400 mL of 0.05 mol / L Bi(NO3)3·5H2O to the aqueous solution and stir until completely dissolved. Dissolve 80 mL of 0.1 mol / L p-benzoquinone in ethanol in the above solution.

[0034] The main equipment used in laser induced electrodeposition includes laser irradiation and electrochemical deposition. The laser irradiation equipment uses Nd:YAG laser with a power density of 350kW / cm 2 ; Single pulse energy is 0.5mJ; frequency is 5Hz. The electrodeposition equipment uses a pulse signal generator, with a platinum wire with a diameter of 0.08mm as the anode and a 30×20mm FTO conductive glass as the cathode. The current density is 1.0mA / cm 2 Under the conditions of constant current deposition, FTO conductive glass was used.

[0035] The anode is placed above the cathode workpiece and coincides with the position of the laser spot. The gap between the tip of the platinum wire and the upper surface of the cathode workpiece is 30μm and remains unchanged. During deposition, the worktable is controlled by a computer to move in a straight line in the two-dimensional direction. After each row is deposited, it moves to the next row. The spacing between each row is 0.25mm. The movement speed is 0.3mm / s.

[0036] After the deposition, the FTO was removed. The electrolyte on the surface of the conductive glass was washed with distilled water and alcohol, and dried at 50°C for 8 minutes.

[0037] Embodiment 3:

[0038] Preparation of supported photocatalyst BiOI / FTO-0.5mm

[0039] Preparation of deposition electrolyte solution: First, prepare 300 mL of KI aqueous solution with a concentration of 0.1 mol / L and adjust the pH to 2.0 with nitric acid. Add 300 mL of 0.1 mol / L Bi(NO3)3·5H2O to the aqueous solution and stir until completely dissolved. Dissolve 60 mL of 0.2 mol / L p-benzoquinone in ethanol in the above solution.

[0040] The main equipment used in laser induced electrodeposition includes: laser irradiation and electrochemical deposition. The laser irradiation equipment uses Nd:YAG laser with a power density of 500kW / cm 2 ; Single pulse energy is 1.0mJ; frequency is 10Hz. The electrodeposition equipment uses a pulse signal generator, with a platinum wire with a diameter of 0.1mm as the anode and a 30×20mm FTO conductive glass as the cathode. The current density is 1.5mA / cm 2Under the conditions of constant current deposition, FTO conductive glass was used.

[0041] The anode is placed above the cathode workpiece and coincides with the position of the laser spot. The gap between the tip of the platinum wire and the upper surface of the cathode workpiece is 40μm and remains unchanged. During deposition, the worktable is controlled by a computer to move in a straight line in the two-dimensional direction. After each row is deposited, it moves to the next row. The spacing between each row is 0.5mm. The movement speed is 0.5mm / s.

[0042] After the deposition is completed, the FTO is removed. The electrolyte on the surface of the conductive glass is washed off with distilled water and alcohol, and dried at 60°C for 5 minutes.

[0043] Comparative Example 1: Preparation of supported TiO2 photocatalyst by hydrothermal method

[0044] In order to compare with the existing loading methods, TiO2 / FTO loaded photocatalyst was prepared by hydrothermal method. The main operation steps are as follows: First, FTO conductive glass was cut into 30mm×20mm and ultrasonically cleaned in ethanol for 30min to remove surface contaminants. Equal volumes of concentrated hydrochloric acid and deionized water (35mL each) were mixed and stirred, and then a certain amount of tetrabutyl titanate was added to the mixed solution, and the mixture was stirred continuously until the mixture became clear and transparent. Two pieces of FTO were placed at a certain angle in a polytetrafluoroethylene liner with a volume of 50mL, with the conductive surface facing down. Finally, the high-pressure reactor containing the mixed solution and FTO was placed in an oven for hydrothermal reaction for a period of time. After the reaction, the sample was rinsed alternately with ethanol and deionized water three times, and then dried in air.

[0045] Comparative Example 2: Preparation of TiO2 nanotube arrays by anodization

[0046] In order to compare with the currently available loading methods, titanium foil (purity of 99.6%) was cut into sheets (30mm×20mm×0.2mm) and then ultrasonically washed in deionized water before use. Titanium foil was used as the anode, while platinum was used as the cathode. The distance between the anode and the cathode was 20mm. The anodization experiment was carried out at 40°C in an ethylene glycol solution containing 0.25wt% NH4F and 20wt% H2O at a voltage of 40V for 3h. During the experiment, a magnetic stirrer was used to stir the solution. After anodization, the product was rinsed in deionized water, dried, and then calcined at 460°C for 2h. Finally, highly ordered titanium dioxide nanotube arrays (TiO2NTs) were obtained.

[0047] Comparative Example 3: Preparation of BiOBr / FTO (EC) photocatalyst thin film by electrodeposition

[0048] Preparation of deposition electrolyte solution: First, prepare 300-500 mL of KBr aqueous solution with a concentration of 0.05 mol / L, and adjust the pH to 1.5 with nitric acid. Add 300-500 mL of 0.05 mol / L Bi(NO3)3·5H2O to the aqueous solution and stir until completely dissolved.

[0049] The electrodeposition equipment uses a pulse signal generator, a platinum wire with a diameter of 0.08 mm as the anode, and a 30×20 mm FTO conductive glass as the cathode. The current density is 1.0 mA / cm 2 Under the conditions of constant current deposition, FTO conductive glass was used.

[0050] The anode is placed above the cathode workpiece, and the gap between the tip of the platinum wire and the upper surface of the cathode workpiece is 30μm, and it always remains unchanged. During deposition, the worktable is controlled by a computer to move in a straight line in the two-dimensional direction first, and moves to the next row after each row is deposited. The spacing between each row is 0.25mm. The movement speed is 0.3mm / s.

[0051] After the electrodeposition is completed, the FTO is removed. The electrolyte on the surface of the conductive glass is washed with distilled water and alcohol, and dried at 50°C for 8 minutes.

[0052] Application Example 1: Testing Method for Photocatalyst Removal of Rhodamine B

[0053] Take one piece of each of the photocatalyst films prepared in Examples 1 to 3 and Comparative Examples 1 to 3, place the sample in a photocatalytic reactor containing 100 mL of a 20 mg / L Rhodamine B solution, and stir the reactor in the dark for 10 minutes. Then expose the suspension to visible light and stir continuously, collect 2 mL of the suspension every 15 minutes, and measure the concentration of the pollutant with an ultraviolet spectrophotometer. The total test time is 1 hour, and finally calculate the removal rate of Rhodamine B. The calculation formula is as follows:

[0054] Rhodamine B removal rate = (C0-C t ) / C0×100%

[0055] Where C0 is the initial concentration of rhodamine B, C t is the concentration of rhodamine B at time t

[0056] This application example compares the photodegradation activity of BiOBr / FTO-0.1mm, BiOBr / FTO-0.25mm, BiOBr / FTO-0.5mm, TiO2 / FTO, TiO2 NTs and BiOBr / FTO (EC) photocatalysts for Rhodamine B. Table 1 shows the efficiency (%) of different photocatalysts in degrading Rhodamine B solution at different time periods. The results show that the supported photocatalyst BiOBr / FTO-0.25mm has the highest photocatalytic activity. After 60 minutes of irradiation, the removal rate of Rhodamine B can reach 98.6%. The above results prove that compared with the current mainstream loading technology, the photocatalyst prepared by this method is more active, and the arrangement and morphology of the photocatalyst on the FTO conductive film have a significant impact on the photocatalytic activity.

[0057] Table 1 Efficiency of photocatalysts with different loadings in degrading Rhodamine B solution (%)

[0058]

[0059]

[0060] Application Example 2: Testing of the Cyclic Performance of Photocatalyst BiOBr / FTO-0.5mm

[0061] This application example tests the cyclic performance of BiOBr / FTO-0.5mm photocatalytic film. Table 2 shows the efficiency (%) of photocatalyst degradation of Rhodamine B solution under different number of cycles. The results show that the photocatalytic activity of the sample gradually decreases with the increase of the number of cycles. After 5 cycles, the removal rate of Rhodamine B can still reach 54.6%. The above results prove that the photocatalyst prepared by this method has relatively excellent cyclic performance, can be effectively recovered and reused, avoids secondary pollution, and has certain value for industrial applications.

[0062] Table 2 Efficiency of photocatalyst degradation of Rhodamine B solution at different cycle times (%)

[0063] 0min 15min 30min 45min 60min First cycle 0.0 35.5 64.8 95.7 98.6 Second cycle 0.0 25.4 55.5 75.9 88.9 3rd cycle 0.0 18.1 32.2 54.1 72.5 4th cycle 0.0 11.5 25.9 40.0 64.4 5th cycle 0.0 10.2 22.4 35.0 54.6

[0064] Application Example 3: Cyclic performance testing of TiO2 / FTO, TiO2 NTs and BiOBr / FTO (EC)

[0065] This application example tests the cyclic performance of TiO2 / FTO, TiO2 NTs and BiOBr / FTO(EC) films. Table 3 shows the efficiency of photocatalyst degradation of Rhodamine B solution after 5 cycles. The results show that after 5 cycles, the removal rates of Rhodamine B by TiO2 / FTO, TiO2NTs and BiOBr / FTO(EC) are 11.8%, 1.1% and 3.1%, respectively. The above results prove that the photocatalyst prepared by laser induced electrodeposition has better cyclic performance.

[0066] Table 3 Efficiency of photocatalyst degradation of Rhodamine B solution at different cycle times (%)

[0067] 0min 15min 30min 45min 60min <![CDATA[TiO2 / FTO]]> 0.0 2.6 4.8 9.8 11.8 <![CDATA[TiO2 NTs]]> 0.0 1.2 1.3 1.0 1.1 BiOBr / FTO(EC) 0.0 2.2 2.7 3.0 3.1

Claims

1. A method for preparing a supported photocatalyst, wherein the photocatalyst is BiOX / FTO; KX aqueous solution, Bi(NO3)3·5H2O aqueous solution and ethanol solution of p-benzoquinone are used as electrolytes, and Nd:YAG laser and pulse signal generator are used in a deposition device for deposition; wherein X is selected from one of Cl, Br and I, and the deposition method comprises the following steps: the power density, single pulse energy and frequency of the Nd:YAG laser are set by a computer, the laser emits laser light, which is then focused on the platinum wire anode in the electrolytic cell by a reflector and a focusing mirror; the electrodeposition solution is irradiated by laser to generate high-temperature and high-pressure plasma, and turbulence and micro-area stirring effects are generated in the irradiated area; at the same time, the pulse signal generator applies voltage to the platinum wire anode and the FTO conductive glass cathode for electrodeposition; deposition is carried out under the dual action of laser and electrochemistry, the position of the FTO conductive glass cathode is adjusted by a computer and a motion control card, and the deposition position moves accordingly, and the power density of the Nd:YAG laser is 200-500kW / cm 2 ; Single pulse energy is 0.1-1.0 mJ; frequency is 2-10 Hz; and / or, the diameter of the platinum wire is 0.05-0.1 mm, and the current density of the electrodeposition is 0.5-1.5 mA / cm 2 .

2. The preparation method according to claim 1, characterized in that The deposition equipment comprises: a computer, a Nd:YAG laser, a pulse signal generator, a reflector, a focusing mirror, a platinum wire anode, a FTO conductive glass cathode, an electrolytic cell, a mobile working platform and a motion control card.

3. The preparation method according to claim 1, characterized in that: The electrolyte comprises 300-500 mL of a KX aqueous solution with a concentration of 0.02-0.1 mol / L, 300-500 mL of a Bi(NO3)3·5H2O aqueous solution with a concentration of 0.02-0.1 mol / L, and 60-100 mL of an ethanol solution of p-benzoquinone with a concentration of 0.04-0.2 mol / L.

4. The preparation method according to claim 3, characterized in that: The preparation method of the deposition electrolyte solution comprises the following steps: firstly preparing a KX aqueous solution and adjusting the pH to 1.0-2.0 with nitric acid; adding Bi(NO3)3·5H2O to the solution and stirring until it is completely dissolved; finally, dissolving p-benzoquinone in ethanol and mixing it with the above solution to prepare an electrolyte solution.

5. The preparation method according to any one of claims 1 to 4, characterized in that: During deposition, the platinum wire is placed above the cathode workpiece and coincides with the position of the laser spot emitted by the Nd:YAG laser, and the gap between the tip of the platinum wire and the upper surface of the FTO conductive glass cathode workpiece is 20 to 40 μm.

6. The preparation method according to any one of claims 1 to 4, characterized in that: The workbench is controlled by a computer to move in a straight line in two dimensions. After each row is deposited, it moves to the next row. The spacing between rows is 0.1 to 0.5 mm. The movement speed is 0.1 to 0.5 mm / s.

7. A supported photocatalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the supported photocatalyst prepared by the preparation method according to any one of claims 1 to 6 or the supported photocatalyst according to claim 7 in degrading pollutants, the use comprising the following steps: The prepared photocatalyst film is placed in a solution containing pollutants, and the pollutants are photodegraded under the irradiation of sunlight or an external light source. After the degradation is completed, it is taken out in time, cleaned and dried, and then used again.

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