阅读说明：本技术 F、S、Zr、Al共掺杂TiO2光催化剂的制备及太阳光催化降解丙烯腈工业废水效能 (F. S, Zr and Al codoped TiO2Preparation of photocatalyst and efficiency of catalytic degradation of acrylonitrile industrial wastewater by sunlight ) 是由 欧阳峰 李翰良 刘典 于 2019-01-10 设计创作，主要内容包括：本发明涉及模拟及自然太阳光下条件照射下光催化降解丙烯腈实际废水COD满足国家排放标准的F、S、Zr、Al共掺杂改性二氧化钛复合氧化物催化剂的其制备方法。本发明首先提供了优化溶胶凝胶法F掺杂的TiO<Sub>2</Sub>催化剂制备方法基础上,即利用五水硝酸锆和硫脲作为前驱体进行S、Zr、Al共掺杂。F、S、Zr、Al共掺杂改性后的TiO<Sub>2</Sub>催化剂协同作用优势明显,催化剂的光响应范围拓宽,样品表面的酸性位点强度大,硅胶的加入所形成凸凹不平的表观形貌和孔结构造成的光散射,有利于光吸收,这对光催化活性的提高起了重要的作用,其中,Zr、Al的添加使得整个催化剂体系稳定性明显提高。最适宜的Ti、F、S、Zr、Al的比例为1∶0.5-5％∶1-10％∶0.1-2％,适宜的煅烧温度和煅烧时间分别为350-500℃和1-3h。该催化剂重复4次,COD仍可从约89降至42mg/L以下。(The invention relates to a preparation method of an F, S, Zr and Al co-doped modified titanium dioxide composite oxide catalyst for photocatalytic degradation of COD (chemical oxygen demand) of acrylonitrile actual wastewater under the conditions of simulation and natural sunlight, wherein the COD meets the national emission standard. The invention firstly provides an optimized sol-gel method F-doped TiO 2 Based on the catalyst preparation method, zirconium nitrate pentahydrate and thiourea are used as precursors to carry out S, Zr and Al co-doping. F. S, Zr and Al codoped modified TiO 2 The synergistic effect of the catalyst has obvious advantages, the photoresponse range of the catalyst is widened, the strength of acid sites on the surface of a sample is high, the uneven appearance and the pore structure formed by adding the silica gel cause light scattering, the light absorption is facilitated, and the improvement of the photocatalytic activity plays a roleThe optimum ratio of Ti, F, S, Zr and Al is 1: 0.5-5%: 1-10%: 0.1-2%, the appropriate calcination temperature and calcination time are 350-500 deg.C and 1-3h respectively, the catalyst can still reduce COD from about 89 to below 42 mg/L after 4 times of repetition.)

1. The composite oxide photocatalyst for degrading acrylonitrile waste water is prepared with silica gel of 100-mesh and 200-mesh as dispersant, hydrofluoric acid, zirconium nitrate pentahydrate, aluminum nitrate and thiourea as dopant precursor, and fluorine, sulfur, zirconium and aluminum co-doped for modification to obtain TiO with stable structure₂A catalyst.

2. The method for preparing a composite oxide catalyst according to claim 1, comprising the steps of:

step 1, dropwise adding 2-8m L of butyl titanate into 10-16m L of absolute ethyl alcohol, and mixing to obtain a clear solution, namely solution A.

And 2, sequentially adding 12-32m L of absolute ethyl alcohol, 2.3-5.3m L of glacial acetic acid, 15-35mg of thiourea, 429-449mg of zirconium nitrate pentahydrate, 13-18mg of aluminum nitrate, 0.2L-1.5 m L of hydrofluoric acid and 0.4-1.9m L of deionized water into a 150m L beaker, and carrying out ultrasonic treatment for 2min to obtain a solution B.

And 3, dropwise adding the solution B into the solution A, stirring for 1-3h in a sealed manner, opening and sealing, continuously stirring to form uniform water-like sol, continuously stirring for a period of time until oily sol is formed, and then adding 100-mesh 200-mesh silica gel until gel is formed.

And 4, aging the gel for about 8-12 hours at room temperature (20-30 ℃), drying the gel for several hours in a drying oven at 70-90 ℃, uniformly grinding the obtained dry powdery catalyst precursor by using an agate mortar, and finally calcining the obtained product for 1-3 hours in a tubular furnace at 350-500 ℃ to obtain the modified silica gel-supported TiO doped with the four elements₂A catalyst.

3. The method according to claim 2, wherein the fluorine precursor is a commercially available 40% aqueous hydrogen fluoride solution, the sulfur precursor is prepared from analytically pure thiourea, the zirconium precursor is analytically pure zirconium nitrate pentahydrate, and the aluminum precursor is analytically pure aluminum nitrate nonahydrate.

4. F element is used as a doping main body, S, Zr and Al element precursors with different contents are doped, and the proportion is properly adjusted (F: S: Zr: Al is 1: 0.5-5%: 1-10%: 0.1-2%).

5. The preparation method according to claim 2, wherein the method for efficiently photocatalytic degradation of acrylonitrile actual wastewater by the catalyst is characterized in that the co-doping of F, S, Zr and Al improves the acidity strength, light absorption capability and stability of the catalyst surface, and particularly, the addition of silica gel forms uneven appearance and light scattering caused by pore structure, which is beneficial to light absorption and plays an important role in improving the photocatalytic activity.

Technical Field

The invention relates to a composite oxide catalyst for photocatalytic degradation of actual acrylonitrile wastewater, in particular to a photocatalyst for photocatalytic degradation of acrylonitrile industrial wastewater in a water phase, which is prepared by dispersing fluorine, sulfur, zirconium and aluminum codoped modified titanium dioxide in silica gel and a preparation method thereof, and belongs to the technical field of environmental protection.

Background

Acrylonitrile (acrylonitrile, CH)₂CH-CN, abbreviated as AN) acrylonitrile is AN important raw material (ABS) resin for producing acrylic fiber, nitrile rubber, acrylamide, acrylonitrile-butadiene styrene. Global acrylonitrile production capacity exceeds 500 million tons per year. China and the united states are the largest two acrylonitrile producing countries in the world. Unfortunately, current acrylonitrile production processes produce at least one ton of wastewater when producing one ton of acrylonitrile. More seriously, the acrylonitrile production wastewater is composed of a large amount of highly toxic compounds, and the acrylonitrile wastewater not only destroys an aqueous ecosystem, but also has great harm to human health. However, the use of acrylonitrile is inevitable for a short time due to the great demand for acrylonitrile on the market, and a plan for effectively treating acrylonitrile waste water is urgently required. At present, the treatment of acrylonitrile mainly comprises adsorption, incineration, recovery, activated sludge and the like. The method has the advantages of high cost, insufficient removal and harsh working conditions, and is difficult to effectively control the pollution of the acrylonitrile wastewater. The most difficult contaminant to treat in acrylonitrile wastewater is polymer. It is mainly derived from low molecular polymers or copolymers of nitriles. These polymers are usually present in water in colloidal or dissolved form, are difficult to hydrolyze and are used by microorganisms, and cannot be practically removed. Acrylonitrile waste water is generally considered the most difficult organic waste water to treat.

The photocatalyst oxidation is that the catalyst is irradiated by light, absorbs light energy, generates electron transition and generates electron spaceThe hole pairs directly carry out oxidation reduction on the pollutants adsorbed on the surface to generate hydroxyl radicals with strong oxidizing property to oxidize the pollutants. Solar energy is one of the best alternative energy sources due to its abundant resources and low carbon production. At present, great progress has been made in the research and development of solar energy utilization systems, and the most studied semiconductor catalytic material is TiO₂In the ultraviolet range of 300nm to 390nm, TiO₂The photocatalytic activity of the TiO-based photocatalyst is very high, and the TiO-based photocatalyst can still keep very high photocatalytic activity after being recycled for many times₂Can completely mineralize the target pollutant into water and carbon dioxide, does not cause secondary pollution to the environment, and in addition, TiO₂Has great stability in the aspects of chemistry, thermodynamics, mechanical properties and the like, so the method is widely applied to the field of environmental purification.

TiO₂The photocatalytic activity of (A) can be improved by adding silica gel to increase its specific surface area. In recent years, various reports have been made on the manner of supporting titanium dioxide, for example, TiO supported on activated carbon₂Molecular sieve supported TiO₂Glass bead-supported TiO₂TiO supported on silica₂. The mineralization capability of the catalyst to the degradation pollutants can be improved by utilizing the adsorption characteristic of the carrier. The activity of the supported catalyst is greatly improved compared with that of the unsupported titanium dioxide, because a synergistic effect can be formed between the titanium dioxide and the carrier. Wherein, the silicon dioxide has good adsorption performance and larger specific surface area. TiO supported on silica₂The catalyst has the advantages of thermal stability and mechanical stability of silicon dioxide, is transparent, and can reduce light scattering, thereby effectively improving the degradation performance of the catalyst. Adding SiO₂Can effectively control TiO₂The crystal particles grow, the agglomeration phenomenon of the catalyst is effectively inhibited, and the catalyst obtains smaller particle size and higher specific surface area. TiO supported on silica gel₂It also undergoes interfacial diffusion with silicon dioxide to form Si-O-Ti bonds. The formation of Si-O-Ti bond can inhibit anatase type TiO₂Rutile type TiO₂And (4) converting. Golden brightness, etcPeople find that the nano titanium dioxide can effectively degrade acrylonitrile in the water in an open reactor under the condition of sufficient and stable illumination. Pang D.D et al found that F-doped SiO using HF as the F source₂Supported TiO₂The composite photocatalyst shows the highest activity of degrading acrylonitrile. In situ infrared and NH₃The results of TPD show that F-doping increases SiO₂Supported TiO₂The surface acid position number and the acid strength of the composite photocatalyst. When the molar ratio of HF to Ti is 1: 1 and TiO₂When the load is 36%, under the irradiation of simulated sunlight, the removal rate of acrylonitrile can reach 66% in 6 min.

Improvement of TiO by doping modification of non-metal elements₂One advantage of activity is the ability to extend TiO₂The visible light catalytic activity does not affect the catalytic activity of the catalyst ultraviolet light. Semi-conductive TiO₂Medium metal ion Ti⁴⁺The d orbital energy level of (a) determines the energy level of its conduction band, while the energy level of the valence band is determined by the non-metal ion O^2-Is determined by the p orbital level of. The modification of the valence band is generally performed because the space for increasing the potential of the valence band is larger than the space for decreasing the potential of the conduction band, and the valence band is relatively easy to realize. Compared with the 2p orbital of O, non-metallic elements such as B, C, N and S have higher energy p orbitals, and after the elements replace O atoms, the valence band potential of the semiconductor titanium dioxide is improved to a certain extent, thereby reducing the semiconductor TiO₂The forbidden band width of (c). However, theoretically, only when the radius of the non-metal element ion is very close to that of the O ion, the non-metal element ion can replace the TiO₂Oxygen ions in the crystal lattice of (1). Thus, the non-metallic elements studied by scientists are mainly distributed around the oxygen element, such as C, N, S, B and the halogen element. The fluorine atom has a smaller diameter than the oxygen atom, and therefore, theoretically, the fluorine atom can replace the oxygen atom in titanium oxide. Modification of TiO by doping with a large amount of fluorine₂In the study (2), fluorine may be substituted for TiO₂Oxygen ions in the crystal lattice can also be adsorbed on TiO₂The surface of the particles. With nitrogen-doped TiO₂Different, fluorine-doped modified TiO₂The light absorption edge of the catalyst is not significantly altered because of the 2 of fluorinepotential ratio of p orbital TiO₂The valence band potential of (2) is low. Researchers have synthesized anatase type TiO by hydrothermal method₂The visible photocatalytic activity of the catalyst was very high, the authors found that TiO was doped with fluorine₂Then, part of Ti⁴⁺Conversion to Ti³⁺Oxygen vacancies are formed, and oxygen molecules on the surface of the catalyst are captured to generate superoxide radicals, so that the activity of the catalyst is improved. In addition, F is doped with TiO₂Can also increase TiO₂The surface acidity of (2). F-doped TiO₂Then, L ewis and Bronsted acid sites appear on the surface of the sample, and L ewis and Bronsted acid sites are good adsorption centers of oxygen molecules and molecules with lone pair electrons, so that F doping can effectively improve the degradation activity of the organic matters with the lone pair electrons.

Another way to effectively increase the catalytic and activity is to increase the number of surface acid sites. It has been demonstrated that photocatalytic activity increases with an increase in the number of acid sites on the surface of the catalyst. Cui et al 1995 reported that TiO could be doped by metal oxides₂To increase its surface acidity and photocatalytic activity. Wang et al 2006 reported that there was an amorphous TiO₂And sulfur compound at high temperature to synthesize sulfur-doped TiO₂And the photocatalyst can be prepared by using the photocatalyst with acid sites. However, few reports have been made on the photocatalytic degradation of acrylonitrile using acidic and highly stable catalysts.

On one hand, the Zr is doped into TiO2 crystal lattice, and the overall stability is improved because Zr is very stable. On the other hand, Zr also influences the growth direction of Ti during the crystal growth process to form force, so that the stability of the crystal structure is improved, and the Zr also has the function of fixing fluorine. Al has both of the above two effects, and the former has a stronger effect.

Disclosure of Invention

The photocatalysis process is carried out in actual acrylonitrile wastewater, and because various interference ions exist in the actual wastewater, and organic matters and inorganic components are very complex, in order to solve the problems, the invention aims to provide the high-efficiency reusable photocatalyst for photocatalytic degradation of the actual acrylonitrile wastewater, 100-plus-200-mesh silicon dioxide is used as a dispersing agent, and hydrogen fluoride, zirconium nitrate, aluminum nitrate and thiourea are used as doping precursors to prepare the catalyst with the mesoporous structure and the large specific surface area, the composite doping of F, S in the catalyst improves the acid strength and the light absorption capacity of the surface of the catalyst, so that the photocatalytic activity and the anti-interference capacity are improved, and the doping of Zr and Al greatly improves the overall durability of the catalyst.

The invention also aims to provide a preparation method of the catalyst for the sunlight catalytic degradation of the actual acrylonitrile wastewater, and the silica gel-supported fluorine, sulfur, zirconium and aluminum-doped titanium dioxide composite oxide catalyst is prepared by a sol-gel method.

The inventor of the invention discovers that F is doped with TiO through research₂The catalyst shows excellent effect on the actual wastewater degradation of acrylonitrile, and the dark adsorption amount of the catalyst compared with that of organic matters is P25 TiO₂The method also has a relatively large improvement, and analysis shows that an adsorption effect exists between the acid center on the surface of the catalyst and the lone pair of electrons in the organic matter of the acrylonitrile wastewater.

In order to further improve the photocatalytic activity of the catalyst, the composite oxide catalyst provided by the invention adopts fluorine, sulfur and zirconium codoping. In the preparation process by using a sol-gel method, hydrogen fluoride, zirconium nitrate pentahydrate, aluminum nitrate and thiourea solution are added into a catalyst as a doping precursor, and then the mixture is calcined at high temperature to form the fluorine-doped catalyst, which has more surface acid sites, and the addition of silica gel forms uneven apparent morphology and light scattering caused by a pore structure, so that the light absorption is facilitated, the important effect on the improvement of the photocatalytic activity is achieved, and the photocatalytic activity can be greatly improved. Especially, the addition of Zr and Al greatly improves the stability of the catalyst.

The invention also provides a preparation method of the composite oxide photocatalyst, which comprises the following steps:

dropwise adding 2-8ml of butyl titanate into 10-16m L of absolute ethyl alcohol, and mixing to obtain a clear solution, namely solution A.

12-32m L of absolute ethyl alcohol, 2.3-5.3m L of glacial acetic acid, 15-35mg of thiourea, 449mg of 429-449mg of zirconium nitrate pentahydrate, 13-18mg of aluminum nitrate, 0.2-1.5m L of hydrofluoric acid and 0.4-1.9m L of deionized water are sequentially added into a 150m L beaker, and the solution B is obtained after 2min of ultrasonic treatment.

And dropwise adding the solution B into the solution A, sealing and stirring for 1-3h, opening and sealing, continuously stirring to form uniform water-like sol, continuously stirring for a period of time until oily sol is formed, and then adding 100-mesh and 200-mesh silica gel until gel is formed.

Aging the gel for about 8-12h at room temperature (20-30 ℃), drying in a drying oven at 70-130 ℃, uniformly grinding the obtained dry powdery catalyst precursor, and finally calcining for 1-3h in a tubular furnace at 350-500 ℃. Thus obtaining the doped modified SiO₂Dispersed TiO₂/SiO₂A catalyst. The composition ratio of Ti to F to S to Zr to Al is 1 to 0.5-5 to 1-10 to 0.1-2.

The TEM results (left panel) show the catalyst as particles of about 30nm in diameter, and the enlarged right panel more clearly shows that these particles are made up of seemingly smaller agglomerates of particles, with square particles present.

F. S, Zr and Al codoped modified TiO₂/SiO₂The activity evaluation of the photocatalyst selects organic pollutants in the actual acrylonitrile wastewater as target degradation products.

From the research comparison and practical application angles, two light sources, namely a 350w AHD350 type spherical xenon lamp and a sunlight, are respectively selected to treat the acrylonitrile practical wastewater.

Drawings

FIG. 1 shows F-S-Zr-Al-TiO₂/SiO₂TEM images of the samples.

FIG. 2 shows the use of F-S-Zr-Al-TiO₂/SiO₂The COD of the actual acrylonitrile wastewater treated by the catalyst through four reactions (three times of recovery and activation) is along the change curve of the simulated solar illumination time.

FIG. 3 shows the use of F-S-Zr-Al-TiO₂/SiO₂The COD of the actual acrylonitrile wastewater treated by the catalyst for the first time is along the curve of the change of simulation and natural illumination time.

Detailed Description

The following examples are provided to illustrate the present invention and to demonstrate the advantageous effects thereof, but should not be construed as limiting the scope of the invention in any way.

Method for evaluating catalyst activity:

the method specifically comprises the steps of selecting low-concentration acrylonitrile actual wastewater as a target degradation product for activity evaluation of a photocatalyst, pouring 150m L actual wastewater into a quartz reactor, adding 300mg of the photocatalyst, sealing the reactor, stirring in the dark for 35min to achieve adsorption and desorption balance, turning on a xenon lamp to start illumination, selecting a 350w AHD350 spherical xenon lamp light source as the light source, and taking two groups of 4m L wastewater suspensions as parallel samples in 2h, 6h, 10h and 14h in the illumination process.

The detection method comprises the steps of measuring COD by using a Union L H-5B-3B (V8) type COD rapid measuring instrument, measuring the COD error within +/-10%, and measuring the COD of a sample by filtering the sample by using a filter membrane with the aperture of 0.45 mu m immediately after sampling, wherein the value is the COD corresponding to the time.

Along with the prolonging of the illumination time, the COD in the catalyst and the solution is decreased according to a curve shown in figure 2, after 14 hours of irradiation, the COD in the solution is decreased from 89 to about 25 mg/L, and after 4 times of reaction, the COD still can reach about 42 mg/L, so that the basic complete degradation of organic matters and the good stability of the catalyst are demonstrated.

In the same way, the actual waste water of acrylonitrile is degraded to COD of about 50 mg/L by sufficient sunlight reaction.