TWI692375B - The preparing method of a material for photocatalytic hydrogen production and oxytetracycline catalyst and the application thereof - Google Patents

Abstract

The present invention provides a method for preparing a kind of photocatalyst, Cu-CdS composite. This catalyst can be used for photocatalytic hydrogen production and photodegradation of oxytetracycline. This present invention includes a hydrothermal method for CdS preparation and a photodeposition method for Cu-CdS synthesis. The high efficiency of hydrogen production and oxytetracycline degradation shows that this material has very good application prospect.

Description

Manufacturing method and application of material capable of simultaneously producing hydrogen by photocatalysis and degrading epoxytetracycline

The invention discloses a manufacturing method and application of a material capable of simultaneously producing hydrogen by photocatalysis and degrading epoxytetracycline.

In recent years, the increasing energy demand, the gradual depletion of fossil energy and the environmental problems caused by the use of traditional energy sources have further promoted the research boom on clean and renewable alternative energy sources. Among alternative energy sources, hydrogen energy has the characteristics of high energy density and environmental friendliness, which has aroused widespread concern worldwide. At present, the main methods of producing hydrogen include the use of natural gas, petroleum, coal and other fossil fuels, and then the production of hydrogen by thermochemical methods, the production of hydrogen by electrolytic water, and the production of hydrogen by biochemical decomposition of biomass. From a technical and economic perspective, the use of solar energy photocatalytic decomposition of water to produce hydrogen is one of the cleanest and most economical and practical technologies. It is also an ideal way to fundamentally solve the problems of energy shortage and environmental pollution.

Oxytetracycline is a tetracycline antibiotic, widely used in human medical treatment, animal husbandry, fishery, etc. Due to the antibacterial properties of antibiotics, traditional biological treatment cannot clean the wastewater containing antibiotics, so the discharge of antibiotics is a serious threat to the environment and human health.

Faced with the above two problems of energy shortage and serious antibiotic pollution, it is very urgent to find new energy sources and deal with antibiotics. If you can provide a method to solve the above problems at the same time, it is a major technology for improving human life.

In view of this, the present invention uses copper with higher photocatalytic activity to synthesize and modify sulfide-containing compounds, and synthesize copper-chromium sulfide composite materials by hydrothermal method and photodeposition method. Then, through hydrogen production and OTC degradation, the oxidation and reduction properties of copper-chromium sulfide composites were evaluated. Through electrochemical experiments, this experiment confirmed that the Cu-CdS electrode can generate current, and can simultaneously degrade OTC and generate hydrogen in a self-made double-slot device, which can maximize the use of resources and simultaneously solve energy shortages and antibiotic pollution in water Environmental issues.

The biggest difference from the previous case is that the photocatalyst in the general patent can only produce hydrogen or remove antibiotics, but in addition to the efficient hydrogen production and degradation of OTC in a single tank, this patent can also use electron movement and light in H-type double tanks. Catalysis achieves the goal of simultaneously producing hydrogen and degrading OTC.

This patent uses Cu-CdS composite materials to simultaneously degrade OTC and hydrogen production in a self-made double tank device. The Cu-CdS nanocomposites with different copper contents were synthesized by photodeposition, and sodium sulfide and sodium sulfite solutions were used as sacrificial agents to explore the hydrogen production activity under ultraviolet light; the copper loading and materials are shown in the examples The effects of dose, light intensity and sacrificial agent concentration, and IC were used to analyze the ions in the solution before and after the reaction; after the adsorption of oxytetracycline (OTC) to saturation, the degradation was carried out under ultraviolet and visible light. Including the effect of Cu loading, catalyst dosage, reaction temperature, pH and initial OTC concentration, by adding inhibitors to the reaction solution and EPR experiment to explore what is OTC oxidizing substance. In addition, through electrochemical experiments (CV, LSV, EIS, etc.), it can be confirmed that the Cu-CdS electrode can generate current, and can simultaneously degrade OTC and generate hydrogen in a self-made double-slot device.

The invention provides a manufacturing method of a material capable of performing photocatalytic hydrogen production and degradation of epoxytetracycline at the same time, which comprises the following steps of preparing chromium sulfide by hydrothermal method and preparing by photodeposition method:

(a) Prepare chromium sulfide by hydrothermal method, dissolve hydrated chromium nitrate ((Cd(NO 3) 3·4H 2 O) in monoisopropanol, and stir vigorously to form a homogeneous mixture;

(b) Take a sodium sulfide (Na2S) aqueous solution dropwise into the aforementioned homogeneous mixture, and transfer the aqueous solution to an autoclave and heat in a hot furnace;

(c) Cool to room temperature to obtain a yellow solid product, wash the aforementioned product with deionized water and ethanol, and dry it;

(d) Disperse the aforementioned chromium sulfide (CdS) in the aforementioned ethanol solution and stir vigorously to form a homogeneous suspension mixture;

(e) Move the aforementioned homogeneous suspension mixture in step (d) to a quartz photoreactor, and add the hydrated copper nitrate and deionized water to the aforementioned homogeneous suspension mixture; and

(f) The homogeneous suspension mixture in the previous step (e) was continuously stirred under nitrogen bubbling and irradiated with light, cooled to room temperature, the solution was filtered and washed with deionized water, and dried in a vacuum oven at high temperature to obtain a Copper-chromium sulfide (Cu-CdS) composite material.

The present invention further provides a method for simultaneous photocatalytic hydrogen production and degradation of epoxytetracycline, which includes the following steps:

(a) Using a copper-chromium sulfide (Cu-CdS) composite material, placing an epoxy tetracycline in a cylindrical reactor for photodegradation; and

(b) The aforementioned photodegradation reaction is shielded from external light and irradiated with a UV lamp, and the aforementioned composite material of step (a) is stirred with a magnetic stirrer.

Preferably, in the copper-chromium sulfide composite material, the content of copper is 1% to 8%.

Preferably, the light irradiation intensity is 0.97 mW cm-2 to 3.88 mW cm-2.

Preferably, the concentration of the aforementioned epoxytetracycline is 5 mg L-1 to 40 mg L-1.

Preferably, the aforementioned composite material is stirred in the dark for 30 minutes before UV irradiation.

Preferably, the photocatalyst is dispersed in an aqueous solution containing sodium sulfide (Na 2 S) and sodium sulfite (Na 2 SO 3) as a sacrificial agent.

Preferably, the concentration of the sacrificial agent is sodium sulfide (Na 2 S)/sodium sulfite (Na 2 SO 3) from 0.05M/0.05M to 0.4M/0.4M.

Preferably, during the reaction, a magnetic stirrer is used to keep the photocatalyst suspended, and purged with nitrogen to completely degas to completely remove oxygen at atmospheric pressure, and irradiated with a high-pressure mercury vapor lamp to periodically collect the gas.

Preferably, the aforementioned photodegradation reaction is performed in a single tank or in an H-shaped double tank.

Example 1: Preparation of chromium sulfide:

In this example, chromium sulfide nanoparticles were prepared by hydrothermal method. In this method, 4.2 g of (Cd(NO 3)3·4H 2 O was dissolved in 100 mL of isopropanol and stirred vigorously for 45 minutes to form a homogeneous mixture Then, a sodium sulfide (Na 2 S) aqueous solution (100 mL, 0.136 M) was added dropwise to the above solution. The resulting solution mixture was transferred to a 250 mL Teflon autoclave and placed in a 160° C. heating furnace for 48 hours. After hydrothermal treatment, the autoclave was normally cooled to room temperature to obtain a yellow solid product; then the product was washed several times with deionized (DI) water and ethanol to remove impurities, and then dried at 60°C for 12 hours.

Example 2: Preparation of copper-chromium sulfide (Cu-CdS) composite material:

[式1] In this embodiment, the copper is modified by a light deposition method to ensure that the copper is completely deposited; in the light deposition reaction, an ethylene glycol reducing agent is used. A certain proportion of CdS was dispersed in 20.0 mL of ethylene glycol solution and stirred vigorously to form a homogeneous suspension mixture. After mixing, the solution was stirred for 2 hours and then transferred to a 1000mL cylindrical quartz photoreactor, in which an 8W high-pressure mercury (Hg) steam lamp (Phillips, maximum wavelength 254nm) enclosed in a quartz inner tube. A predetermined amount of Cu(NO 3) 2 ·3H 2 O and 600 mL of deionized water were added to the above solution. The weight percentage of Cu deposited on the catalyst is calculated by the concentration of the Cu(NO 3) 2·3H 2 O solution, which is expressed by the weight percentage of Cu in the photocatalyst [Equation 1]. The weight percentage of Cu deposited on the catalyst is recorded as x%Cu-CdS (x = 1,2,4,8), and a schematic diagram of Cu-CdS preparation is shown in FIG. 1. Weight percentage (%) =

[Formula 1]

The aforementioned mixture was continuously stirred under nitrogen bubbling and irradiated with light for 12 hours, and then the aforementioned solution was cooled to room temperature. Finally, the resulting solution was filtered and washed with deionized water and dried in a vacuum oven at 80°C for 6 hours.

Embodiment 3: Photocatalytic hydrogen production and hydrogen production efficiency under various parameters:

In this example, a photocatalytic reaction was carried out in a quartz reaction cell connected to a closed gas circulation and evacuation system, and 20 mg of photocatalyst was dispersed in 200 mL of an aqueous solution containing sodium sulfide (Na 2 S) and sodium sulfite (Na 2 SO 3) as a sacrifice Agent. In addition, during the reaction, a magnetic stirrer at the bottom of the reactor was used to keep the photocatalyst suspended. It was then thoroughly degassed by purging with nitrogen (10 mL min -1) for 30 minutes to completely remove oxygen at atmospheric pressure, and irradiated with a high-pressure mercury vapor lamp (Phillips, 8W maximum wavelength 254 nm). Collect the gas regularly and analyze the amount of H2 produced by a gas chromatograph (GC) equipped with an MS-5A column (2 m stainless steel column filled with 5Å molecular sieve) nitrogen carrier (flow rate 30 mL min) -1) And thermal conductivity detector (GC-TCD, Perkin Elmer, Clarus 580).

表1、各項參數下的產氫效率 In order to analyze the efficiency of photocatalytic hydrogen production under various conditions at room temperature, some parameters were changed in this example, including copper content, catalyst dosage, sodium sulfite/sodium sulfide concentration, light intensity, cycle time, and various parameters for hydrogen generation are listed in in FIG. 1.

Table 1. Hydrogen production efficiency under various parameters

In addition, in order to analyze the concentration of sulfate ion (SO42-) in the solution, ion chromatography (IC, Metrohm, X-00120218) was used.

Example 4: Degradation of tetracycline antibiotics (OTC):

表2、OTC降解及各項參數 Antibiotic (oxytetracycline, OTC for short) is photodegraded in a cylindrical reactor with a diameter of 7 cm and a height of 40 cm, and is shielded from external light throughout. Use a UV lamp (254nm, 0.97mW cm-2; Sparxic, APUV-12F) as a single light source; use a magnetic stirrer to continuously stir 1L of the solution at 100rpm; use hydrogen chloride and sodium hydroxide to adjust the easy pH value; the temperature is circulated by constant temperature water器控制。 Device control. In this embodiment, the copper content, the initial antibiotic concentration, the reaction temperature, the amount of catalyst, and the pH value are used to evaluate the effect of operating factors on the photodegradation performance. To ensure the adsorption equilibrium in the photocatalytic degradation experiment, the solution was stirred in the dark for 30 minutes before irradiation. After turning on the lamp, samples were collected at a predetermined time and filtered with a filter membrane (0.2 μm) before analysis. Three samples were detected at each collection time to reduce error deviation. Table 2 lists the parameters of OTC degradation in this example.

Table 2. OTC degradation and various parameters

[式2] Calculation of light irradiation efficiency: In order to quantify the performance and stability of the catalyst, the following formula [Formula 2] is used to evaluate the degradation ability of the photocatalyst. 2 Q =

[Form 2]

Among them, Q represents the degradation ability of the material, CO represents the initial concentration of OTC, η represents the degradation efficiency, and D represents the dose of the material.

Embodiment 5: Optical absorption characteristics:

F(R) = (1 - R)2/2R  [式3] A series of copper-chromium sulfide samples with different copper loadings were evaluated for optical absorption efficiency. The results are shown in Figure 2. Using Kulbeka-Munk function theory (Vanga et al., 2016), the Eg values of all synthetic catalysts were studied based on UV-vis diffuse reflectance spectroscopy (UV-vis/DRS). The calculated Eg value and absorption edge are obtained as follows [Equation 3].

F(R) = (1-R)2/2R [Formula 3]

Where h is the Planck constant (4.135×10-15), ν is the vibration frequency, R is the percentage reflectance, Eg is the band gap energy, A is the proportional constant, and c is the speed of light (3×108) m s-1 ) And λ are absorption edge values.

表3、從UV-vis / DRS測量獲得的帶隙能量 The Eg of the photocatalyst is calculated by plotting the relationship between [F(R)·hν] 1/2 and hν(eV). The line tangent to the inflection point of the drawn curve is extrapolated to [F(R)·hν] 1/2 = 0 to obtain the value of Eg, which is listed in Table 3 with the absorption edge.

Table 3. Band gap energy obtained from UV-vis/DRS measurement

Figure 2 and Table 3 describe the absorption edge of pure chromium sulfide (CdS) at about 570 nm, and the band gap of CdS is 2.18 eV, which is almost consistent with previous studies (Su et al., 2017). As the copper (Cu) content increases from 1% to 4%, the Eg value sequentially moves from 2.18 eV to 1.59 eV, and then when the copper content increases to 8%, the Eg value increases to 1.89 eV. Therefore, as the copper content increases from 1% to 4%, the absorption edge shifts to longer wavelengths. The narrow band gap means that the maximum absorption edge is more related to visible light. The improved absorption capacity can be attributed to the deposited copper, which indicates an enhanced interaction between chromium sulfide and copper, and the narrowing of the band gap is beneficial to improve the photocatalytic OTC removal efficiency. Therefore, the optimal copper content under visible light response is 4%.

Example 6: Effect of copper content on hydrogen production efficiency:

This example discusses the effect of different copper content on the photocatalytic hydrogen production efficiency. As shown in Figure 3, with different Cu content, the rate of photocatalytic hydrogen production gradually increased from 5.23 mm h-1 g-1 to 24.55 mmol h-1 g-1. The best photocatalytic performance is 1% copper-chromium sulfide, which is 4.7 times that of chromium sulfide nanoparticles. It is worth mentioning that the highest specific surface area (41.1 m2 g-1) leads to the largest hydrogen production rate (24.55 mmol h-1 g-1). The total amount of hydrogen produced is mainly determined by the amount of excited e- in the reduced water at the water/photocatalyst interface (refer to Chen et al., 2010). Therefore, a high content of copper can act as a charge recombination center, resulting in a reduction in photocatalytic activity .

Example 7: Effect of copper content on OTC photodegradation efficiency:

In this example, an OTC adsorption catalyst experiment was performed. Basically, the adsorption equilibrium can be reached after 30 minutes, so 30 minutes is selected as the time to avoid light adsorption. The effect of copper content on photocatalytic OTC degradation is shown in Figure 4. Bare chromium sulfide without copper loading showed the worst removal efficiency of 43%, indicating that chromium sulfide has poor photocatalytic activity. When the copper content is increased from 1% to 4%, the improvement in the photocatalytic OTC degradation efficiency is due to the increase in the degree of effective photo-induced e- and transfer of the CB of the chromium sulfide to the copper particles. This phenomenon can reduce the possibility of e-/h+ recombination and increase the rate of photocatalytic hydrogen production (Hakamizadeh et al., 2014) (Su et al., 2015).

Conversely, when the copper content is higher than 4%, OTC removal efficiency decreases due to the growth and agglomeration of copper particles on the surface of chromium sulfide. This process corresponds to a lower light absorption intensity and leads to a lower OTC photocatalytic degradation efficiency of the 8% copper-chromium sulfide composite. Therefore, according to the single factor experiment, the optimal copper content is 4%, which may also be related to UV-vis/DRS analysis.

Example 8: Effect of cycle time on hydrogen production efficiency:

In order to study the feasibility of reusable materials, in this example, uncoated copper materials and the optimal hydrogen production catalyst 1% copper-chromium sulfide were selected as experimental materials to test the recycling performance. When the dose is 0.05g L-1, every 4 hours as a cycle, the results are shown in Figure 4, the light source is two 8W 254nm mercury lamps for 16 hours.

Figure 4 shows that the hydrogen production of chromium sulfide is significantly reduced from 22.12 to 10.39 mmol g-1, and after 4 cycles (16 hours), the reduction is about 53%. Photocorrosion is considered to be the main cause and leads to poor stability of photocatalysts, especially metal sulfide photocatalysts (Chen et al., 2010). According to previous experiments, chromium sulfide is not stable for photocatalytic hydrogen production. Sulfur ions (S2-) in chromium sulfide instead of water pass light-induced h + auto-oxidation in VB of chromium sulfide. The photo-induced corrosion reaction is shown in [Formula 3].

Conversely, the hydrogen production efficiency of 1% copper-chromium sulfide decreased slightly from 55 to 50 mmol g-1 (about 10% reduction) after 16 hours of the test. The reason for the reduced hydrogen production performance may be that the active sites on the surface of the material are affected by the sacrificial agent ions. In addition, due to prolonged contact with the sacrificial agent solution, the number of active sites decreases, which leads to a decrease in the rate of hydrogen production. The experimental results show that the copper-loaded composite material has strong resistance and can be recycled to increase economic value.

CdS + 2h+ → Cd2+ + S [Form 4]

In summary, the present invention utilizes copper-chromium sulfide (Cu-CdS) composite materials to simultaneously degrade OTC and hydrogen production in a self-made double tank device. Cu-CdS nanocomposites with different copper contents were synthesized by photodeposition, and sodium sulfide and sodium sulfite solutions were used as sacrificial agents to explore the hydrogen production activity under ultraviolet light; the copper loading and material dose were discussed in the experiment , The intensity of light and the concentration of sacrificial agent, and IC was used to analyze the ions in the solution before and after the reaction; after the adsorption of oxytetracycline (OTC) to saturation, the degradation was carried out under ultraviolet light and visible light. The effects of Cu loading, catalyst dosage, reaction temperature, pH and initial OTC concentration were investigated by adding inhibitors to the reaction solution and EPR experiments to explore what oxidizes OTC. In addition, through electrochemical experiments (CV, LSV, EIS, etc.), it can be confirmed that the Cu-CdS electrode can generate current, and can simultaneously degrade OTC and generate hydrogen in a self-made double-slot device.

The results of the hydrogen production experiment show that the catalyst has the highest hydrogen production activity when the copper loading is 1% (mass fraction), the hydrogen production rate can reach 24.9 mmol h-1 g-1, and the hydrogen production rate is exhausted after four cycles of experiment Decrease by 10%; the degradation experiment results show that the catalyst has the highest OTC degradation activity when the copper loading is 4% (mass fraction), and the degradation efficiency can reach 90% within 180 min. The degradation is mainly due to the oxidation of O2 ▪- and h+. Through electrochemical experiments, it was confirmed that the Cu-CdS electrode can generate current, and can simultaneously degrade OTC and generate hydrogen in a self-made double-slot device, which can maximize resource utilization, and can simultaneously solve the energy shortage and the environment of antibiotic pollution in water. issue.

Although the above embodiments disclose specific examples of the present invention, they are not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention belongs, without departing from the principle and spirit of the present invention, should Various changes and modifications can be made to it, so the scope of protection of the present invention shall be defined by the scope of the accompanying patent application.

1: Quartz reactor 2: UV light source 3: circulating water 4: Magnetic stirrer 5: Nitrogen bottle

1 is a schematic diagram of the preparation device of the copper-chromium sulfide composite material of the present invention; 2 is a graph of optical absorption efficiency results of a series of copper-chromium sulfide samples with different copper loadings according to the present invention; Figure 3 is the effect of different copper content on the photocatalytic hydrogen production efficiency in the copper-chromium sulfide composite material of the present invention; 4 is the effect of copper content on the photodegradation efficiency of OTC in the copper-chromium sulfide composite material of the present invention; and Figure 5 shows the effect of cycle time on hydrogen production efficiency in the copper-chromium sulfide composite material of the present invention.

1: Quartz reactor

2: UV light source

3: circulating water

4: Magnetic stirrer

5: Nitrogen bottle

Claims (4)

A method for manufacturing materials capable of simultaneously producing hydrogen by photocatalysis and degrading epoxytetracycline, which comprises preparing chromium sulfide by hydrothermal method and preparing the following steps by photodeposition method: (a) preparing chromium sulfide by hydrothermal method and hydrating Chromium nitrate ((Cd(NO 3)3.4H 2 O) is dissolved in isopropanol and vigorously stirred to form a homogeneous mixture; (b) A sodium sulfide (Na2S) aqueous solution is added dropwise to the aforementioned homogeneous mixture, and Transfer the aqueous solution to an autoclave and heat in a hot furnace; (c) Cool to room temperature to obtain a yellow solid product, wash the aforementioned product with deionized water and ethanol, and dry it; (d) Remove the aforementioned chromium sulfide (CdS) dispersed in the aforementioned ethanol solution and vigorously stirred to form a homogeneous suspension mixture; (e) moved the aforementioned homogeneous suspension mixture in step (d) to a quartz photoreactor, added with hydrated copper nitrate and deionized water In the aforementioned homogeneous suspension mixture; and (f) The homogeneous suspension mixture in the aforementioned step (e) is continuously stirred under nitrogen bubbling and irradiated with light, cooled to room temperature, the solution is filtered and washed with deionized water, and at a high temperature at Dry in a vacuum oven to obtain a copper-chromium sulfide (Cu-CdS) composite material; wherein, the preparation of the aforementioned chromium sulfide is 4.2 g of (Cd(NO 3)3.4H 2 O dissolved in 100 mL of isopropanol and Stir to form the aforementioned homogeneous mixture, and then add the aforementioned sodium sulfide aqueous solution (100 mL, 0.136M) dropwise to the aforementioned homogeneous mixture and place in a 160° C. hot furnace for 48 hours. After hydrothermal treatment, cool the autoclave to At room temperature, the aforementioned yellow solid product was obtained, and the product was washed several times with deionized water and ethanol to remove impurities, and then dried at 60°C for 12 hours; the aforementioned copper-chromium sulfide preparation system dispersed a certain proportion of CdS in 20.0 mL of ethyl acetate Diol solution and stir to form the aforementioned uniform suspension The mixture, after mixing, is transferred to a cylindrical quartz photoreactor, in which an 8W high-pressure mercury (Hg) vapor lamp (Phillips, maximum wavelength 254nm) enclosed in a quartz inner tube, a predetermined amount of Cu(NO 3) 2. 3H 2 O and 600 mL of deionized water are added to the above solution, and the weight percentage of Cu deposited on the catalyst is calculated by the concentration of the Cu(NO 3)2.3H 2 O solution, expressed by the weight percentage of Cu in the photocatalyst, deposited in The weight percentage content of Cu on the catalyst is 1% to 8%, the aforementioned mixture is continuously stirred under nitrogen bubbling and irradiated with light for 12 hours, and then the aforementioned solution is cooled to room temperature. Finally, the resulting solution is filtered and washed with deionized water And dried in a vacuum oven at 80 ℃ for 6 hours. A method for simultaneous photocatalytic hydrogen production and degradation of epoxytetracycline, which includes the following steps: (a) Using a copper-chromium sulfide (Cu-CdS) composite material, placing an epoxytetracycline in a cylindrical reactor Photodegradation reaction; and (b) shielding the aforementioned photodegradation reaction from external light, irradiating with UV lamp, and stirring the aforementioned composite material of step (a) with a magnetic stirrer; wherein, the aforementioned copper-chromium sulfide composite material , The weight percentage content of copper is 1% to 8%; wherein the aforementioned light irradiation intensity is 0.97mW cm-2 to 3.88mW cm-2; wherein the concentration of the aforementioned epoxytetracycline is 5mg L-1 to 40mg L-1; wherein Stir the aforementioned composite materials in the dark for 30 minutes before UV irradiation; wherein, the photocatalyst is dispersed in an aqueous solution containing sodium sulfide (Na 2 S) and sodium sulfite (Na 2 SO 3) as a sacrificial agent; wherein the aforementioned sacrificial agent The concentration of sodium sulfide (Na 2 S)/sodium sulfite (Na 2 SO 3) is 0.05M/0.05M to 0.4M/0.4M. The method of simultaneous photocatalytic hydrogen production and degradation of epoxytetracycline as described in claim 2, wherein during the reaction, a magnetic stirrer is used to keep the photocatalyst suspended and purged with nitrogen to completely degas Oxygen is completely removed at atmospheric pressure and irradiated with a high-pressure mercury vapor lamp to collect the gas regularly. The method of simultaneous photocatalytic hydrogen production and degradation of epoxytetracycline as described in claim 2, wherein the photodegradation reaction is carried out in a single tank or in an H-shaped double tank.

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