CN101913678B - Photoelectrocatalytic device and method for reducing heavy metal ions using same - Google Patents

Abstract

The invention discloses a photoelectric catalytic device and a method for using the photoelectric catalytic device to reduce heavy metal ions. The photoelectrocatalytic device of the present invention comprises power supply, _TiO photoanode, counter electrode, liquid container, reaction solution, magnetic stirrer, magnetic stirrer and light source; Conductive high-activity TiO ₂ nanotubes, the counter electrode uses acid-resistant metal sheets (networks) with high surface area that can provide more reactive sites, such as titanium sheets (networks), platinum sheets (networks), etc. When the area of the photoanode is constant, the larger the area of the counter electrode within a certain range, the higher the activity of the photoelectrocatalytic system. The present invention combines the TiO _nanotube anode with high specific surface area, photoelectric catalysis technology, and high surface area cathode to propose a method that can efficiently degrade highly toxic heavy metal polluted wastewater such as Cr(VI), which has high practicality Value and application prospect, easy to promote and use.

Description

A photoelectrocatalytic device and method for reducing heavy metal ions using the device

technical field

The invention belongs to the field of environmental chemical industry, and in particular relates to a photoelectric catalytic device and a method for using the photoelectric catalytic device to reduce heavy metal ions.

Background technique

Photocatalysis, as a technology to effectively suppress the recombination of photogenerated electron-hole pairs in semiconductors, has attracted extensive attention of researchers in recent years. At present, photoelectrocatalytic technology mainly utilizes the oxidation ability of photogenerated holes, and is widely used in the oxidation treatment of organic pollutants in wastewater. Huijun Zhao et al. used porous TiO ₂ thin films to photoelectrocatalytically degrade a series of organic substances, such as methanol, glucose, p-chlorophenol, phthalic acid, etc., and can achieve complete mineralization (Huijun Zhao*, Dianlu Jiang, Shanqing Zhang, William Wen Photoelectrocatalytic Oxidation of organic compounds at nanoporous TiO ₂ electrodes in a thin-layer photoelectrochemical cell, Journal of Catalysis 250(2007) 102-109). Chinese patent application number _: 200610117583.1 discloses "method for photoelectric catalytic oxidation of organic matter by ultraviolet light". Phosphate or phosphate buffer solution with a phosphorus element concentration of 0.1-2.8 mol/l is used as an electrolyte to carry out photoelectric catalytic oxidation of organic matter by ultraviolet light. However, there are very few studies on the application of photoelectrocatalytic technology to the reduction of heavy metal ions in wastewater by using the reduction ability of photogenerated electrons.

Contents of the invention

The object of the present invention is to provide a photoelectrocatalytic device and a method for photocatalytically reducing heavy metal ions using the device.

The photoelectrocatalytic device provided by the present invention comprises a power supply, a TiO photoanode, a counter electrode, a liquid container, a reaction solution, a _magnetic stirrer, a magnetic stirrer and a light source; wherein the TiO _photoanode is a _TiO nanotube An array film photoanode, the counter electrode is an acid-resistant metal sheet or an acid-resistant metal mesh.

The length of the TiO ₂ nanotubes in the TiO ₂ nanotube array film can be 100nm-1 μm, the inner diameter can be 20-200nm, and the tube wall thickness can be 5-50nm.

The counter electrode can specifically be a titanium sheet, a titanium mesh, a platinum sheet or a platinum mesh.

The area ratio of the TiO ₂ photoanode to the counter electrode may be 10-0.1:1, preferably 4-1:1.

The power supply is a DC power supply with a voltage of 0.5-5V; the light source can be an ultraviolet lamp.

In the electrophotocatalytic device provided by the present invention, the light source is arranged around the liquid container, the liquid container is arranged on a magnetic stirrer, the reaction liquid and the magnetic stirrer are arranged in the liquid container, the Both the _TiO2 photoanode and the counter electrode were set in the reaction solution.

TiO used in the present invention _nanotube array film photoanode can be prepared according to the following method:

(1) The Ti sheet was ultrasonically cleaned in acetone, ethanol, and deionized water in sequence, and then polished for 30 seconds in a mixed solution with a molar ratio of HF:HNO ₃ :H ₂ O=1:(2~5):(5~20) processing, rinsed with deionized water, and dried;

(2) In a 0.3-0.5% HF solution with a mass concentration of 0.3-0.5%, the Ti sheet is used as an anode, the Pt electrode is used as a cathode, and anodized at a voltage of 15-30V for 10-60min to obtain a _TiO2 nanotube array film;

(3) The TiO ₂ nanotube array film is ultrasonically cleaned with deionized water, dried in the air, and calcined at 350-550° C. for 0.5-3 hours in an air atmosphere to obtain a TiO ₂ nanotube array film photoanode.

The method for the photoelectric catalytic reduction of heavy metal ions provided by the present invention is to place the solution containing heavy metal ions in the photoelectric catalytic device provided by the present invention, use organic matter as a hole capture agent and inorganic salt as an electrolyte, and treat the solution containing heavy metal ions The solution undergoes a photocatalytic reduction reaction.

The heavy metal ion can be selected from at least one of the following ions: Cr(VI), Hg(II), Pb(II) and Cu(II); the pH value of the solution containing the heavy metal ion is 1-4, and the heavy metal ion The concentration of ions is 0-2mmol/L, but not including 0mmol/L.

The hole trapping agent can specifically be citric acid, 4-chlorophenol, rhodamine B or methylene blue; in the reaction solution of the photoelectric catalytic reduction reaction, the concentration of citric acid and 4-chlorophenol is 0.01-5mmol/L , the concentration of rhodamine B and methylene blue is 0-0.1mmol/L.

The electrolyte may specifically be NaCl, Na ₂ SO ₄ or NaClO ₄ , and the concentration of the electrolyte in the reaction solution of the photoelectric catalytic reduction reaction is 0˜1 mol/L.

The present invention combines a _TiO2 nanotube anode with a high specific surface area, a photoelectric catalysis technology, and a cathode with a high surface area, and proposes a method capable of efficiently degrading waste water polluted by highly toxic heavy metals such as Cr(VI).

The present invention adopts the above technical scheme and has the following advantages: 1. The TiO ₂ nanotube array film has a higher specific surface area than the general TiO ₂ film, and its tubular structure is conducive to electron conduction and shows higher activity. 2. Applying a bias voltage can transfer the electrons generated on the photoanode to the cathode to promote the separation of electron-hole pairs. 3. Since the heavy metal reduction reaction occurs at the counter electrode, a large-area counter electrode is used to provide more adsorption sites and reduction reaction active sites for metal ions, which greatly improves the degradation rate of heavy metals such as Cr(VI). 4. The reaction device of the present invention has good stability, and the activity is still high after repeated use. 5. The method proposed by the present invention is simple, cheap, efficient and stable, and can be applied to the rapid and thorough treatment of heavy metal wastewater such as high-concentration Cr(VI), has high practical value and application prospect, and is easy to popularize and use.

Description of drawings

Fig. 1 is a schematic structural view of the photoelectrocatalytic device of the present invention.

Fig. 2 is a curve of the degradation conversion rate of Cr(VI) changing with time when the method of the present invention and the existing photocatalytic method are used to degrade Cr(VI).

Fig. 3 is a curve of the degradation conversion rate of Cr(VI) changing with time when the photocatalytic degradation of Cr(VI) is performed with different anode and different cathode areas.

Fig. 4 is the photocatalytic degradation activity curve of different concentrations of Cr(VI) using the device of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The invention combines _TiO2 nanotubes with photoelectric catalysis technology, and adopts large-area Ti mesh or Pt mesh as a counter electrode for the reduction of heavy metal ions such as Cr(VI). By applying a bias voltage, the electrons are guided to a large-area counter electrode, and the reduction reaction occurs with the heavy metal ions fully adsorbed on the surface of the counter electrode, so as to fully separate electron-hole pairs, effectively utilize electrons and efficiently degrade Cr(VI) ions. Effect.

As shown in Figure 1, the photoelectric reaction device provided by the present invention is made up of 9 parts: light source 1, quartz liquid cup 2, _TiO photoanode 3, counter electrode 4, reaction solution 5, stirrer 6, magnetic stirring bar 7. Power supply 8 and multimeter 9. What light source 1 adopts is ultraviolet lamp, is arranged around quartz liquid cup 2, and quartz liquid cup 2 is arranged on magnetic stirrer 6, and electrolytic solution 5 and magneton are all arranged in quartz liquid cup 2, photoanode 3 and The counter electrodes 4 are both disposed in the electrolytic solution 5 .

The photoanode 3 is a TiO ₂ nanotube array film photoanode, wherein the length of the TiO ₂ nanotubes can be 100nm-1 μm, the inner diameter can be 20-200nm, and the tube wall thickness can be 5-50nm. The counter electrode 4 can be an acid-resistant metal sheet (net), such as a titanium sheet (net), a platinum sheet (net), and the like. The reaction solution 5 is a solution containing heavy metal ions such as Cr(VI) at a certain pH, the concentration is 0-2 mmol/L, and the pH value is 1-4; it contains organic matter as a hole-scavenging agent and inorganic salt as an electrolyte. The hole trapping agent is selected from any one of citric acid, 4-chlorophenol, rhodamine B and methylene blue. The concentration of citric acid and 4-chlorophenol is 0.01-5mmol/L, and the concentration of rhodamine B and methylene blue is 0-0.1mmol/L. The electrolyte is selected from any one of NaCl, Na ₂ SO ₄ and NaClO ₄ , and the used concentration is 0˜1 mol/L. Both the magnetic stirrer and the magnetic stirrer 6 can be purchased from the market, and the two are used together to stir the reaction solution to ensure uniform solution concentration in the reaction system. The power supply 7 is a DC power supply with a voltage range of 0.5-5V. Multimeter 8 is used to detect the electric current in the reaction process.

The preparation method of the photoanode 3 in the photoelectrocatalytic device provided by the present invention comprises the following steps:

(1) Cut the Ti sheets purchased from the market into rectangles of a certain size, ultrasonically clean them in acetone, ethanol, and deionized water in sequence, and then adjust the molar ratio HF:HNO ₃ : _{H 2} O=1:(2~5): (5-20) in a mixed solution for polishing for 30s, rinsed with deionized water, and dried.

(2) In 0.3-0.5wt% HF solution, with Ti sheet as anode and Pt electrode as cathode, 15-30V anodic oxidation for 10-60min to obtain TiO ₂ nanotube array film.

(3) The obtained TiO ₂ nanotubes were ultrasonically cleaned with deionized water, dried in the air, and calcined at 450° C. for 1 h in an air atmosphere to obtain a thin-film photoanode of TiO ₂ nanotube arrays with a certain thickness.

The preparation method of the counter electrode 4 in the photoelectrocatalytic device provided by the present invention is as follows: cut the Ti mesh purchased in the market into a rectangle of a certain size, ultrasonically clean it in acetone, ethanol, and deionized water successively, and then wash it in HF:HNO ₃ :H ₂ O=1:3:16 mixed solution and polished for 30s, rinsed with deionized water, and dried to obtain a Ti mesh counter electrode.

Embodiment 1, utilize photoelectrocatalytic device of the present invention to degrade Cr (VI)

The photocatalytic device used is shown in Figure 1. The device adopts the _TiO2 nanotube array film as the photoanode, wherein the length of the _TiO2 nanotube is 248nm, the Ti network is the counter electrode, and the area ratio of the photoanode and the counter electrode is 1:1. The initial concentration of Cr(VI) in the reaction system was 0.34mmol/L, and the reaction conditions were: pH 2.5, citric acid 0.5mmol/L, NaCl 1mol/L, voltage 1.5V. The concentration of Cr(VI) was detected by UV-Vis spectrophotometer. And take electrocatalytic method, photolysis method and photocatalytic method respectively to degrade the activity of Cr(VI) as contrast, compare the photocatalytic method of the present invention and the degradation efficiency of Cr(VI) of above-mentioned three kinds of methods.

The results are shown in Figure 2. Each curve in Fig. 2 represents the change curve of the degradation conversion rate of Cr(VI) over time, the abscissa represents time, and the ordinate represents the degradation efficiency of Cr(VI). Curve a represents electrocatalysis, curve b represents photolysis, curve c represents photocatalysis, and curve d represents photocatalysis. In the system of the present invention, there is no degradation of Cr(VI) under the voltage of 1.5V by the electrocatalysis method, and part of the Cr(VI) undergoes photolysis after 2 hours of light by the photolysis method. Comparing the degradation rates of c and d, it can be seen that applying a bias voltage can significantly accelerate the degradation of Cr(VI), and its zero-order reaction rate constant is 7.2 times that of photocatalysis. The photoelectric synergistic effect is remarkable, and the initial concentration of 0.34mmol/ Cr(VI) of L.

Embodiment 2, investigate the impact of Ti network area on the photoelectrocatalytic degradation Cr (VI) system

The photocatalytic device used is shown in Figure 1. The device adopts the TiO ₂ nanotube array film as the photoanode, wherein the length of the TiO ₂ nanotube is 248nm; the Ti mesh is the counter electrode, and the area of the photoanode is 60*52mm ² . The reaction conditions are the same as in Example 1.

The effect of Ti grids with different areas on the electrode on the photocatalytic degradation of Cr(VI) system was compared, and the results are shown in Figure 3.

It can be seen from Fig. 3 that when a TiO ₂ nanotube array film with a certain area (60*52mm ² ) is used as the photoanode, the larger the area of the counter electrode is within the range of the area ratio of the photoanode to the counter electrode in the range of 4-1:1 , the higher the photocatalytic activity is, it reaches the maximum when the Ti mesh area is 60*52mm ² . This is because the large-area Ti network counter electrode can provide enough active sites for Cr(VI) to be fully adsorbed on its surface and further undergo reduction reactions with photogenerated electrons. However, when the area of the fixed counter electrode is 60*52mm ² and the photoanode is replaced by a dense TiO ₂ /ITO film, its activity is much lower than that of the TiO ₂ nanotube array film photoanode. It can be seen that in the photocatalytic reduction of Cr(VI) system, the efficient degradation of Cr(VI) can be achieved by using the TiO ₂ photoanode with excellent photoelectron separation and conductivity properties and the Ti mesh counter electrode with high surface area.

Embodiment 3, comparison is with TiO _Nanotube array thin film is photoanode and with _TiO Compact thin film is the influence of photoanode on photocatalytic degradation Cr (VI) system

The photocatalytic device used is shown in Figure 1. The device uses a TiO ₂ nanotube array film as a photoanode, wherein the length of the TiO ₂ nanotube is 248nm; or a TiO ₂ dense film (expressed as TiO ₂ /ITO, prepared by a sol-gel method, on an ITO substrate by pulling Obtained by the method, the thickness is 160nm) is the photoanode, the Ti mesh is the counter electrode, and the area of the counter electrode is 60*52mm ² . The reaction conditions are the same as in Example 1.

The activity of photocatalytic degradation of Cr(VI) was compared between TiO ₂ nanotubes and TiO ₂ dense films, and the results are shown in Figure 3.

It can be seen from Figure 3 that when the area of the fixed counter electrode is 60*52mm ² , the photoanode is replaced by a dense TiO ₂ /ITO film, and its activity of degrading Cr(VI) is much lower than that of TiO ₂ nanotube array light anode. It can be seen that in the photocatalytic reduction of Cr(VI) system, the efficient degradation of Cr(VI) can be achieved by using the TiO ₂ photoanode with excellent photoelectron separation and conductivity properties and the Ti mesh counter electrode with high surface area.

Embodiment 4, utilizing the photoelectrocatalytic device of the present invention to degrade different concentrations of Cr(VI)

The photocatalytic device used is shown in Figure 1. The device adopts the TiO ₂ nanotube array film as the photoanode, wherein the length of the TiO ₂ nanotube is 248nm; the Ti mesh is the counter electrode, the area of the photoanode is 60*52mm ² , and the area of the counter electrode is 60*52mm ² . The reaction conditions are the same as in Example 1.

The photocatalytic degradation activities of different concentrations of Cr(VI) were compared, and the results are shown in Figure 4.

It can be seen from Figure 4 that increasing the concentration of Cr(VI) reduces the photocatalytic degradation rate. Because under the condition of high concentration, the mass transfer of the reduction product has certain limitations. In addition, the amount of TiO ₂ loaded on the photoanode is certain, and it is difficult to meet the degradation of high concentration of Cr(VI). When reducing high-concentration Cr(VI) wastewater, the area of photoanode and photocathode can be appropriately increased to obtain a good photocatalytic degradation effect. In this research example, when the photoanode and the counter electrode area are both 60*52mm ² , the appropriate initial concentration of Cr(VI) is 0.19-0.58mmol/L.

Claims (8)

1. the method for a photoelectrocatalysis reducing heavy metal ion is that the solution that will contain heavy metal ion places photoelectrocatalysidevice device, with organism as hole trapping agents, inorganic salt as ionogen, the solution that contains heavy metal ion is carried out the photoelectrocatalysis reduction reaction;

Described photoelectrocatalysidevice device comprises power supply, TiO ₂The light anode, to electrode, liquid container, reaction soln, magnetic stir bar, magnetic stirring apparatus and light source, it is characterized in that: described TiO ₂The light anode is TiO ₂Nano-pipe array thin film light anode, described is titanium sheet or titanium net to electrode; Described TiO ₂The area of light anode be 4-1:1 to the Area Ratio of electrode.

2. method according to claim 1, it is characterized in that: described heavy metal ion is selected from following at least a ion: Cr (VI), Hg (II), Pb (II) and Cu (II); The described pH value that contains the solution of heavy metal ion is 1-4, and the concentration of heavy metal ion is 0-2mmol/L, but does not comprise 0mmol/L.

3. method according to claim 1 and 2, it is characterized in that: described hole trapping agents is citric acid, 4-chlorophenol, rhodamine B or methylene blue; In the reaction solution of described photoelectrocatalysis reduction reaction, the working concentration of citric acid and 4-chlorophenol is 0.01～5mmol/L, and the working concentration of rhodamine B and methylene blue is 0～0.1mmol/L, but does not comprise 0mmol/L.

4. method according to claim 1 and 2, it is characterized in that: described ionogen is NaCl, Na ₂SO ₄Or NaClO ₄Electrolytical working concentration described in the reaction solution of described photoelectrocatalysis reduction reaction is 0～1mol/L, but does not comprise 0mol/L.

5. method according to claim 1 and 2 is characterized in that: in the described photoelectrocatalysidevice device, and described TiO ₂TiO in the nano-pipe array thin film ₂The length of nanotube is 100nm～1 μ m, and internal diameter is 20～200nm, and thickness of pipe is 5～50nm.

6. method according to claim 1 and 2 is characterized in that: described TiO ₂Nano-pipe array thin film light anode prepares by the following method:

(1) the Ti sheet is cleaned at acetone, ethanol, deionized water for ultrasonic successively, then by HF, HNO ₃And H ₂Polishing 30s processes in the mixing solutions that O forms, and deionized water rinsing dries; Wherein, HF, HNO in the described mixing solutions ₃And H ₂The mol ratio of O is followed successively by 1:(2～5): (5～20);

(2) be in the 0.3-0.5%HF solution in mass concentration, as anode, the Pt electrode is as negative electrode with the Ti sheet, and anodic oxidation 10-60min obtains TiO under the 15-30V voltage ₂Nano-pipe array thin film;

(3) with TiO ₂Nano-pipe array thin film deionized water ultrasonic cleaning is dried, and 350～550 ℃ of roasting 0.5～3h obtain TiO in the air atmosphere ₂Nano-pipe array thin film light anode.

7. method according to claim 1 and 2, it is characterized in that: described power supply is direct supply, its voltage is 0.5-5V; Described light source is ultraviolet lamp.

8. method according to claim 1 and 2, it is characterized in that: described light source is arranged on around the liquid container, and described liquid container is arranged on the magnetic stirring apparatus, and described reaction solution and magnetic stir bar are arranged in the liquid container, described TiO ₂Light anode and electrode all is arranged in the reaction solution.

Images