CN101798126A - Method for treating industrial waste water by means of photoelectrocatalysis - Google Patents

Abstract

The invention provides a method for treating industrial waste water by photoelectrocatalytic chemical oxidation or reduction, which belongs to the field of environmental protection, that is, a highly ordered titanium-based _TiO2 nanotube array film prepared by a titanium anodic oxidation method is used as a photoanode or Photocathode, with high-purity graphite as the counter electrode, degrades the organic matter or heavy metal ions of industrial wastewater into H ₂ O and CO ₂ , low-priced metal ions or metal elements when connected to an external circuit and under light radiation. The advantage of the present invention is that the catalyst photoanode adopted is a highly ordered array film perpendicular to the titanium substrate that is self-assembled by anodic oxidation, which not only overcomes the poor bonding force of the photoanode of the powder-loaded film in the past, the easy falling off and the gradual attenuation of catalytic efficiency defects, and can directly use sunlight by doping and modifying the array film, which is an energy-saving, high-efficiency, high-selectivity, clean, low-cost treatment of a single (dyes such as paper mills, organic wastewater from printing and dyeing plants, or heavy metals) Advanced technology for ions such as electroplating plant chromium-containing wastewater) or composite wastewater.

Description

A kind of photoelectrocatalytic treatment method of industrial waste water

technical field

The invention belongs to the field of industrial waste water treatment in terms of environmental protection and treatment. The highly ordered _TiO2 nanotube array film prepared by titanium anodic oxidation is used as the photoelectrode material, and the high-purity graphite or base metal material is used as the counter electrode. Under the action of 0-3V DC bias and under the irradiation of sunlight or simulated sunlight, The organic matter in the dye or pesticide wastewater is completely mineralized into H ₂ O and CO ₂ at the anode, and the heavy metal ions are reduced to low-valent ions or metal elements. This technology combines the advantages of electrocatalysis and photocatalysis, through the rapid transport of photogenerated electrons by the external circuit and the cathode migration of photogenerated holes assisted by the electric field, the separation of photogenerated electron-hole pairs is accelerated, and the possibility of their recombination is reduced, which can significantly improve Catalytic efficiency is an energy-saving, high-efficiency, high-selectivity, clean, low-cost treatment of a single (dye such as organic wastewater from paper mills, printing and dyeing factories, pharmaceutical factories, etc., or heavy metal ions such as chromium-containing wastewater from electroplating plants, and mercury from metallurgical factories. wastewater, etc.) or advanced technologies for complex wastewater.

Background technique

The bandgap energy of _TiO2 is 3.2eV (anatase type), which is equivalent to photon energy with a wavelength of 387.5nm. When TiO ₂ is irradiated by ultraviolet light with a wavelength less than 387.5nm, the electrons in the valence band transition to the conduction band, thereby generating photogenerated electron (e ^- )-hole (h ⁺ ) pairs. The generated h ⁺ oxidized with O ₂ and H ₂ O molecules adsorbed on the surface of TiO ₂ particles to generate O ₂ ^- and ·OH radicals, respectively. The two active substances, O ₂ ^- and ·OH, have extremely strong oxidizing ability to complete the oxidative decomposition reaction, especially the ·OH group, which has an energy as high as 501KJ/mol, while CC, CH, NC, CO, The bond energies of OH and NH bonds are 347KJ.mol ^-1 , 414KJ.mol ^-1 , 305KJ.mol ^-1 , 351KJ.mol ^-1 , 464KJ.mol ^-1 , 388KJ.mol ^-1 . Much lower energy. Therefore, many kinds of gaseous organic pollutants can be rapidly decomposed by photocatalytic oxidation process, including aliphatic hydrocarbons, alcohols, aldehydes, ketones, halogenated hydrocarbons, aromatics, mercaptans and heteroatom organic compounds, NO _x , SO _{x ,} etc., US Environmental Protection The Bureau announced that 114 organic substances in nine categories have been confirmed to be treated by photocatalytic oxidation. The use of photocatalytic oxidation to treat domestic water can avoid carcinogenic by-products such as chloroform or bromate produced by conventional chlorination or ozone treatment, achieve the purpose of deep mineralization, and show the superiority of photocatalytic oxidation treatment. This method is especially suitable for the treatment of toxic organic substances that cannot or are difficult to biodegrade.

Photogenerated electrons have a strong reducing ability, and heavy metal ions in water can be reduced by accepting electrons on the surface of titanium dioxide. For example, Cr ⁶⁺ is highly carcinogenic, and its toxicity is 100 times higher than that of Cr ³⁺ . In the Cr ⁶⁺ -TiO ₂ system ^[29-32] , photogenerated electrons are captured by Ti ⁴⁺ to generate Ti ³⁺ , and the photocatalytic reduction of Cr ⁶⁺ is mainly indirect reduction of electrons obtained from Ti ³⁺ ; this method It can also be used for comprehensive recovery of valuable metals in low-concentration aqueous solutions of some precious metals or photocatalytic reduction for anticorrosion. It can also be used for photocatalytic oxidation/reduction synergistic systems to simultaneously remove heavy metal ions and organic pollutants in water, such as Cr and Ag containing metal ions. , Au, Cd, Cu, Hg, Ni and Pt, etc., as well as organic matter methanol, formic acid, salicylic acid, EDTA, phenol and nitrobenzene, etc. for photocatalytic oxidation/reduction treatment of wastewater.

As early as 1976, Japanese scholar Carey et al. carried out research on TiO ₂ photocatalytic degradation of various organic substances in water. Under light conditions, TiO ₂ was used as a catalyst to non-selectively oxidize and completely mineralize various organic substances; the following year Frank studied the photocatalytic degradation of various photocatalysts, such as TiO ₂ , ZnO, CdS, WO ₃ , Fe ₂ O ₃ , pollutants including CN ^- , SO ₃ ^2-, etc. 10 ^-6 mol.d ^-1 .cm ^-2 . Due to the non-toxicity, low cost, and excellent acid and alkali resistance and photochemical corrosion of titanium dioxide, the photocatalytic degradation of pollutants in water by _TiO2 has been a hot topic in environmental governance for more than 30 years. The focus of its research is mainly The energy band structure of TiO ₂ is adjusted by modification techniques such as doping, surface deposition, and compound semiconductor, so that its photoresponse wavelength is extended to the visible light region, so as to utilize clean sunlight and increase the quantum yield. However, most researches use ultrafine or nanometer TiO ₂ powder as photocatalyst, which makes the separation, recovery and recycling of the catalyst quite difficult, and it is impossible to obtain a wide range of industrial applications. Therefore, research in recent years has turned to nano-TiO ₂ powder immobilization, and glass, ceramics, metals, resins, molecular sieves, activated carbon, silica gel or porous materials have all been studied as nano-TiO ₂ powder carrier materials. However, the powder of this solid-supported catalyst will fall off after being used for a period of time, and its photocatalytic effect will gradually decline with the prolongation of the use time. Until 1999, Zwilling et al. used a high-purity titanium sheet as an anode and a platinum sheet as a counter electrode in an HF aqueous electrolyte, and used an anodic oxidation method to prepare a highly ordered TiO ₂ nanotube array film with an orientation perpendicular to the titanium matrix. The ordered porous structure material is not only a carrier, but also a catalyst, which solves the problems of poor binding force after the powder is loaded and difficult recovery and recycling of the powder catalyst. Compared with powder photocatalysts, the _TiO2 nanotube array has a larger specific surface area, and its highly ordered arrangement perpendicular to the surface provides a fast path for the transmission of photogenerated electrons, which can effectively reduce the photogenerated charge carrier. The recombination in the processes of capture, separation, transfer, etc., thus significantly improving the quantum yield of the photocatalytic process, has brought new hope for the application of photocatalytic technology in environmental governance. The research work during this period mainly focused on the formation mechanism, morphology control and modification treatment to expand the photoresponse wavelength to the visible light region. Many scholars at home and abroad have carried out fruitful research work in this regard. At present, through the tailoring of electrochemical conditions, the parameters of the tube length, tube diameter, distribution, and wall thickness of the TiO ₂ nanotube array can be effectively controlled, and titanium-based TiO ₂ nanotube array materials for photoelectrocatalytic treatment of wastewater can be prepared. It is used as a photoelectrode material for photoelectric catalytic treatment of wastewater, and it is used for the treatment of organic or inorganic and their composite wastewater in industrial wastewater.

Contents of the invention

The object of the present invention is to provide a method for photoelectrocatalytic treatment of organic or inorganic pollutants in industrial wastewater, which combines the advantages of photocatalysis and catalysis, and uses highly ordered titanium dioxide nanotube arrays perpendicular to the titanium substrate as photoelectrodes , and can directly use clean and cheap sunlight to decompose it into harmless substances. It is suitable for the treatment of heavy metal ion wastewater in dyestuffs, pharmaceuticals, electroplating and metallurgical factories. Advanced technology for industrial wastewater.

The invention adopts a photoelectric catalysis method to treat organic or inorganic pollutants in industrial waste water, and the specific process is as follows: (1) preparing highly ordered titanium dioxide nanotube arrays perpendicular to the titanium substrate by an anodic oxidation method. The industrial pure titanium sheet (>99%) is used as the starting material, followed by mechanical grinding, chemical polishing, and ultrasonic cleaning, with it as the anode, graphite, nickel sheet, platinum or platinum-plated sheet as the cathode, and an inorganic aqueous solution containing fluorine Or an organic solution such as C ₃ H ₈ O ₃ , (CH ₃ ) ₂ CHOH is the electrolyte solution, and the concentration of the fluorine-containing solution used, such as HF, NH ₄ F, NaF or KF, is 0.2 to 1.0 wt%. The voltage is 20-60V, the temperature is 5-20°C, and the time is 0.5-6h. The titanium dioxide film obtained after anodic oxidation is amorphous, and it is transformed into pure anatase after crystallization heat treatment at 500°C for 2h in an air atmosphere. Mineral phase; (2) The anatase-type ordered titanium dioxide nanotube array prepared in (1) is used as a photoelectrode, graphite or iron or base metal is used as a counter electrode, simulated sunlight (350W Xe lamp) is used as a light source, and the bias voltage is 0~3V, photocatalytically degrades organic or inorganic pollutants in industrial wastewater into harmless substances, such as completely decomposing organic matter into H ₂ O and CO ₂ , and reducing high-priced heavy metal ions to low-valent states or metal elements.

The present invention has the following main advantages: (1) The highly ordered _TiO2 nanotube array thin film is used as the photoanode material in photoelectrocatalysis, which serves as the dual function of carrier and catalyst, and solves the difficulty of recycling and solidification of the suspension catalyst system in the past. Supported nano-TiO ₂ powder is easy to fall off, and its ordered structure and large specific surface area not only provide more active reaction centers for photocatalysis, but also provide a fast way for the transfer of photogenerated electrons and holes. channels, and the separation process is accelerated with the help of an external electric field, which can effectively avoid the recombination of photogenerated electron-hole pairs and improve the catalytic activity; Photocatalytic treatment of wastewater using sunlight; (3) Compared with conventional physical chemical or biochemical methods, the process is short and does not produce secondary pollutants or form physical transfer of pollutants; (4) The reaction conditions are mild, The process is environmentally friendly, and the operation and control are extremely simple. Its continuous treatment process is expected to be used for the treatment of wastewater with large volume, large composition changes and complexity, and difficult biochemical treatment, so as to achieve the process goals of low cost, high efficiency, energy saving and environmental protection. It is understood that the current cost of treating dye wastewater is usually more than 10 yuan/ ^m3 , and the cost will drop to ^about 4 yuan/m3 (for low- and medium-concentration wastewater) by using photoelectric catalysis. With photocatalysis, the cost may be further reduced.

XRD analysis shows that the TiO ₂ nanotube array prepared by this method is anatase. FE-SEM analysis shows that the titanium dioxide nanotube arrays prepared by the fluorine-containing aqueous electrolyte solution are highly ordered and arranged vertically to the titanium substrate, the tube length is 300-800nm, the tube inner diameter is 100-300nm, and the wall thickness is 20-40nm; The TiO ₂ nanotube array prepared with fluorine-containing organic electrolyte solution also grows perpendicular to the titanium substrate, and the tube length, tube diameter, and wall thickness are 0.8-20 μm, 80-150 nm, and 15-25 nm, respectively. Under the irradiation of simulated sunlight (350WXe lamp), the photoelectric catalytic oxidation degradation of methylene blue, ammonia nitrogen wastewater or the reduction of hexavalent chromium ion aqueous solution or the degradation of composite wastewater containing methylene blue and hexavalent chromium ions, this method has a high degradation ability. The methylene blue and hexavalent chromium ions in the wastewater can be completely degraded within 2 to 3 hours.

Description of drawings

Figure 1 Photocatalytic oxidation of methylene blue solution (initial concentration 10mg/L), (a) 0V bias, (b) +1V bias

Figure 2 Photocatalytic reduction of hexavalent chromium ion solution results (initial concentration 20mg/L), (a) 0V bias, (b) +1V bias

Figure 3 The results of photoelectric catalysis, air stripping, catalysis + air stripping treatment of ammonia nitrogen wastewater, (a) catalysis + air stripping, (b) air stripping, (c) photoelectric catalysis

Figure 4 Photocatalytic treatment of composite wastewater of methylene blue and hexavalent chromium ions, (a) degradation of hexavalent chromium ions; (b) degradation of methylene blue

Figure 5 XRD pictures of _TiO2 nanotube arrays prepared by this method, (a) before heat treatment (b) 500 ° C, after 2h heat treatment

Fig. 6 FE-SEM photo of _TiO2 nanotube arrays vegetated with fluorine-containing aqueous electrolyte solution in this method

Fig. 7 FE-SEM photo of _TiO2 nanotube arrays vegetated with fluorine-containing organic solution electrolyte solution in this method

Detailed ways

Example 1:

Using pure titanium sheet (99.6%) as the starting material, it is mechanically polished, chemically polished, and ultrasonically cleaned in sequence as the anode, high-purity graphite sheet as the cathode, and 0.5wt% HF aqueous solution as the electrolyte. The constant pressure oxidation condition is: 20V, 30min , 10±2°C; heat treatment conditions: 500°C, 120min. The TiO _nanotube array prepared under this condition is used as a photoelectrode, and the high-purity graphite is used as a counter electrode, or hexavalent chromium ions, which can be completely degraded in about 3 hours by the method of the present invention.

Example 2:

Using pure titanium sheet (99.6%) as the starting material, after mechanical grinding, chemical polishing, and ultrasonic cleaning, the anode is used as the anode, and the high-purity graphite sheet is used as the cathode. 0.2wt% HF + 0.3wt% NH ₄ F + C ₃ H ₈ O ₃ The organic solution is the electrolyte, and the constant pressure oxidation condition is: 50V, 6h, 10±2°C; the heat treatment condition: 500°C, 120min. Using the TiO ₂ nanotube array prepared under this condition as a photoelectrode, high-purity graphite as a counter electrode, and adding 0.05M Na ₂ SO ₄ , the results of photoelectric catalytic treatment of ammonia nitrogen wastewater are shown in Figure 3. Test conditions: bias +1.0V , temperature 30±5° C., air flow rate 250 ml/min (for 200 ml solution), N initial concentration 100 mg/L, pH=11 (adjusted with 10% NaOH solution). It can be seen from Fig. 3 that under the condition of photoelectric catalysis and simultaneous stripping, the method of the present invention also has a strong degradation ability for extremely difficult-to-treat ammonia nitrogen wastewater, and the degradation rate in 3 hours can reach more than 95%.

Example 3:

Using pure titanium sheet (99.6%) as the starting material, after mechanical grinding, chemical polishing, and ultrasonic cleaning, the anode is used as the anode, and the high-purity graphite sheet is used as the cathode. 0.2wt% HF + 0.3wt% NH ₄ F + C ₃ H ₈ O ₃ The organic solution is the electrolyte, and the constant pressure oxidation condition is: 50V, 6h, 10±2°C; the heat treatment condition: 500°C, 120min. Using the _TiO2 nanotube array prepared under this condition as the photoelectrode, and the high-purity graphite as the counter electrode, the experimental results of the photoelectrocatalytic treatment of the composite wastewater of methylene blue and hexavalent chromium ions are shown in Figure 4. Obviously, for the hexavalent chromium ion, it can be completely degraded in about 40 minutes by the method of the present invention. For methylene blue, the 2h degradation rate can reach 76.49%.

Claims (5)

1. the method for a treating industrial waste water by means of photoelectrocatalysis, it is characterized in that: with the industrially pure titanium sheet (＞99%) after mechanical grinding, chemical rightenning, ultrasonic cleaning successively is anode, graphite, nickel sheet, platinum or platinum plating sheet are negative electrode, fluorine-containing inorganic aqueous solution such as HF, NH ₄F, NaF, KF, or fluorine-containing organic solution such as C ₃H ₈O ₃, (CH ₃) ₂CHOH and HF, NH ₄F, NaF, KF are electrolyte solution, handle with anode oxidation method, obtain unformed titanium deoxid film, and after heat treatment making its crystallization is the titania nanotube oldered array film of pure anatase octahedrite phase; Zhi Bei TiO in this way ₂Nano-tube array is the optoelectronic pole in the treating industrial waste water by means of photoelectrocatalysis process, and graphite or iron or base metal are counter electrode, and at the connection external circuit and under sunlight or simulated solar optical radiation, organism is H in the photoelectrocatalysioxidization oxidization trade effluent ₂O and CO ₂, or heavy metal ion is lower valency ion or metal simple-substance in the photoelectrocatalysis reduction trade effluent, or the compound wastewater of while degradation of organic substances and heavy metal ion.

2. method according to claim 1 is characterized in that: anodic oxidation prepares fluorine-containing inorganic or aqueous organopolysiloxane HF, the NH that the high-sequential nano-tube array is adopted ₄The concentration of F, NaF, KF is 0.2～1.0wt%, is C as electrolytical organic solvent ₃H ₈O ₃, (CH ₃) ₂The organic reagent of CHOH or other hydroxyl.

3. method according to claim 1 is characterized in that: the voltage of anode oxidation process is 20～60V, and temperature is 5～20 ℃, and the time is 0.5～6h.

4. method according to claim 1 is characterized in that: the unformed TiO that anodic oxidation obtains ₂The heat of crystallization treatment temp that nano-tube array changes Detitanium-ore-type into is 400～600 ℃, and the time is 1～3h, can keep nano-tube array high-sequential structure under this condition.

5. method according to claim 1 is characterized in that: bias voltage is 0～3V in the photoelectrocatalysis processing waste water process, and the light source that is adopted is simulated solar irradiation or directly utilizes sunlight.

Images