CN108479759B - Visible light response type lanthanum-doped bismuth tungstate catalyst and preparation method thereof - Google Patents
Visible light response type lanthanum-doped bismuth tungstate catalyst and preparation method thereof Download PDFInfo
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- 229910052797 bismuth Inorganic materials 0.000 title claims abstract description 43
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/24—Chromium, molybdenum or tungsten
- B01J23/31—Chromium, molybdenum or tungsten combined with bismuth
-
- B01J35/39—
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/30—Treatment of water, waste water, or sewage by irradiation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/30—Organic compounds
- C02F2101/38—Organic compounds containing nitrogen
Abstract
The invention provides a visible light response type lanthanum-doped bismuth tungstate catalyst and a preparation method thereof, belonging to the technical field of photocatalysis3)3·5H2O), lanthanum chloride (LaCI)3·7H2O), sodium tungstate (Na)2WO4·2H2O) in glycol to prepare a precipitate through solvothermal reaction, and then washing and drying the precipitate to prepare the lanthanum-doped bismuth tungstate catalyst, wherein the lanthanum doping proportion in the lanthanum-doped bismuth tungstate catalyst is 2-10 wt%. La-Bi2WO6The catalyst has good photocatalytic performance, and can be used for photocatalytic degradation of organic pollutants, especially antibiotic pollutants. When the doping proportion of La is 5%, La-Bi2WO6The photocatalytic effect of (2) is the best. Under the simulated solar light irradiation condition of a 300W xenon lamp, the removal rate of the catalyst to tetracycline with the initial concentration of 30mg/L is as high as 96.25%.
Description
Technical Field
The invention relates to a catalyst and a preparation method thereof, in particular to a visible light response type lanthanum-doped bismuth tungstate catalyst suitable for sewage treatment and a preparation method thereof, belonging to the technical field of photocatalysis.
Background
In recent years, the abuse of antibiotic compounds has led to different courses not only in water but also in soil and sedimentsDetection of degree of residue[1]. Antibiotic compounds generally have a short degradation half-life compared to POPs. However, the antibiotic pollutants are called as 'false' persistent pollutants because the substances are continuously supplemented to the environment due to the mass use of the substances in the animal husbandry and the aquaculture industry, and the antibiotic pollutants can achieve a 'persistent' accumulation effect in the environment[2-3]。
The current research on the actual degradation technology of the tetracycline wastewater at home and abroad is not very mature[4,5]Therefore, the research and development of new treatment technologies and the use of simple and efficient methods to obviously improve the degradation effect of tetracycline antibiotics are becoming research hotspots at home and abroad at present. The current conventional antibiotic removal method is a biological treatment method[6]Physical adsorption method[7]Chemical treatment methods, and the like. The chemical treatment method includes a general chemical treatment method and advanced chemical oxidation techniques (AOPs). Compared with a biological treatment method, the method has the defects that the operation period is long, the biological poisoning phenomenon is easy to occur, the physical adsorption method only realizes the separation of the tetracycline substances and can not achieve the purpose of removing and degrading, the common chemical treatment method has higher investment cost and is easy to cause secondary pollution, and the like, and the advanced oxidation technology is widely accepted as a suitable method for removing the antibiotic pollutants by a simple and flexible process method and environmental friendliness without generating secondary pollution. The photocatalytic oxidation technology is one of advanced oxidation technologies, and semiconductor photocatalysts are used for generating free radical substances with strong oxidizing property under the illumination condition to thoroughly oxidize and remove pollutants difficult to degrade in wastewater. Therefore, the photocatalysis technology as a new advanced oxidation technology has wide prospect and research significance in the aspect of tetracycline wastewater treatment[8]。
The photocatalysis technology originates from the end of the 70 th 20 th century and is an emerging sewage treatment technology taking oxidation-reduction reaction as a principle. The photocatalyst usually uses some special semiconductor materials to completely oxidize and decompose some complex refractory toxic substances into CO under normal conditions2、H2O and the like, and has low price compared with the traditional physical sewage treatment methodLow cost, low requirement for reaction condition, no harm to reaction product and no secondary pollution[9]。
Modifying the bismuth tungstate semiconductor photocatalyst, introducing defects by codoping rare earth elements and enabling non-metal elements to enter crystal lattices to replace O. Can generate synergistic effect, reduce the forbidden bandwidth of the semiconductor photocatalyst and simultaneously reduce the recombination rate of photo-generated electrons and holes, thereby greatly improving the photocatalytic activity of the catalyst[10-12]。
The modified bismuth tungstate photocatalyst is added into the antibiotic drug tetracycline hydrochloride for reaction under the drive of visible light by using a photocatalysis technology, so that the tetracycline can be finally mineralized into CO2、H2O、NH4 +Etc. to thereby enable effective removal of contaminants[13]. Therefore, the method has wide prospect for treating the tetracycline wastewater by adopting the photocatalysis technology, and provides a certain theoretical basis for the treatment of the wastewater polluted by the high-concentration antibiotic compounds.
Bismuth tungstate (Bi)2WO6) Is a perovskite type oxide having a chemical formula represented by WO6And (Bi)2O2)2+The formed sandwich-shaped perovskite-like lamellar structure. Bi2WO6Has a forbidden band width of only 2.69eV, can absorb visible light more effectively, and is Bi2WO6The special sandwich configuration and the photoelectric characteristic make the water pollution control have certain prospect. Bi2WO6Albeit with TiO2Compared with the prior art, the method widens the response interval of visible light, but the recombination rate of photo-generated electrons and holes is still very high, and the photocatalytic effect is still not ideal enough. Therefore, the modification, further reduction of the band gap width, and reduction of the recombination rate of the photo-generated electrons and holes become the research hotspots of the current novel bismuth-based photocatalyst.
The existing methods for modifying a semiconductor photocatalyst to improve and enhance the photocatalytic performance of the semiconductor photocatalyst comprise metal element/nonmetal element doping, surface deposition of metal or metal oxide, semiconductor compounding and the like, and the forbidden bandwidth can be effectively reduced through modification, so that the edge of an absorption band is red-shiftedAnd further reduces the recombination rate of the photogenerated carriers. In the research, rare earth metal lanthanum is adopted to dope semiconductor photocatalyst bismuth tungstate to prepare La-Bi2WO6The visible light is responsive to the photocatalyst. The main reasons for improving the activity of the photocatalyst by doping the rare earth lanthanum element can be summarized as the following points:
the lanthanide rare earth element has a special and active 4f electron layer structure, which is very beneficial to the transition of electrons and the formation of new energy level, and the effect of red shift of the absorption band edge of the photocatalyst can be achieved by doping the rare earth metal element and bismuth tungstate. The doping of the rare earth elements can cause lattice distortion of bismuth tungstate, so that lattice defects are generated, a new intermediate energy level, namely a doping energy level, appears between the original conduction band energy level and the original valence band energy level, the forbidden bandwidth is narrowed, the transition of electrons is facilitated, and the response degree of the catalyst to visible light is improved.
Secondly, the generation of lattice defects becomes a capture center of a photon-generated carrier, and the recombination of photon-generated electron-hole pairs is effectively inhibited, so that the photocatalytic reaction can be continuously carried out.
The doping of rare earth elements inhibits the growth of bismuth tungstate crystals, so that the grain size is reduced, the specific surface area of catalyst particles is effectively increased, the migration rate of photon-generated carriers is greatly improved, and the utilization rate of visible light by the catalyst is also enhanced[14]。
Research shows that the rare earth element ions have certain oxygen storage capacity, oxygen is stored when the oxygen concentration in the reaction solution is high, and oxygen is released when the oxygen concentration is too low. The oxygen adsorbed on the surface of the catalyst is the main photo-generated electron capture agent and can react with photo-generated electrons to generate peroxide O2 -Inhibiting recombination of photo-generated electrons and holes[15]。
Therefore, Bi is doped by using the rare earth lanthanum element doping method2WO6The photocatalyst is modified to increase Bi2WO6The potential of photocatalytic activity has certain environmental significance on the high-efficiency treatment of tetracycline wastewater and the practical application of a photocatalytic technology.
[1] The photochemical behaviour of antibiotics in water environment [ J ] Chinese science: chemistry 2010(2): 124-.
[2] Ja\29815, Hodgkin-Sharp, Sun Jianxian, et al. pharmaceuticals and personal care products in the environment [ J ] chemical evolution, 2009(z1):389-399.
[3]Watkinson AJ,Murby E J,Kolpin D W,et al.The occurrence of antibiotics in an urban watershed:from wastewater to drinking water.[J].Science of the Total Environment,2009,407(8):2711-23.
[4]Zhengpei, Qin \261212@ carbon nanotube adsorption for removing tetracycline hydrochloride [ J]Environmental engineering report, 2015,9(8): 3615-.
[5]Lu Chung Yu, Guanwei province, Pengyixin, etc. TiO2Research on ion exchange modification of nanotubes and photocatalytic removal of tetracycline from water [ J]Journal of university of chemical industry (Nature science edition), Beijing 2015,42(1):81-86.
[6] Study on the adsorption rule and mechanism of tetracycline antibiotics on activated sludge [ D ]. southern opening university, 2014.
[7]Ahmed M B,Zhou J L,Ngo H H,et al.Adsorptive removal of antibiotics from water and wastewater:Progress and challenges[J].Science of the Total Environment,2015,532:112-126.
[8]Yahiaoui I,Aissani-Benissad F,Fourcade F,et al.Removal of tetracycline hydrochloride from water based on direct anodic oxidation(Pb/PbO2,electrode)coupled to activated sludge culture[J].Chemical Engineering Journal,2013,221(2):418-425.
[9]Kubacka A,
M,
G.Advanced nanoarchitectures for solar photocatalytic applications.[J].Chemical Reviews,2016,112(3):1555-614.
[10]Wang bright, plum, Dongliang, etc3+Doping with Bi2WO6Preparation of photocatalystPreparation and photocatalytic Performance Studies [ J]The university of Guangxi university journal science edition 2014(6) 1378-1384.
[11]Zhoudu, Dongying, Sun Hongjie, etc. F/Ce doped Bi2WO6Visible light photocatalytic oxidation of methyl orange [ J ]]Water resources and Water engineering journal, 2016,27(1):54-58.
[12]Wang D,Shen H,Li G,et al.La and F co-doped Bi2MoO6architectures with enhanced photocatalytic performance via synergistic effect[J].Rsc Advances,2016,6(75).
[13]Cool in clock and Bi2WO6Preparation of visible-light-based photocatalyst and research on degradation of tetracycline wastewater in continuous flow reactor [ D]Jilin university, 2016.
[14] Chenjianhua, Wangxiang, Zhang peixin, etc. research on ion doping of nano titanium dioxide powder [ J ]. proceedings of Guangxi university (Nature science edition), 2005,30(1):44-50.
[15]Houting red rare earth doped nano TiO2Study of Structure and electronic Properties of (1) [ D]University of Sichuan, 2006.
Disclosure of Invention
Aiming at the problem that the efficiency of treating antibiotic wastewater by using a single bismuth tungstate photocatalyst is low at present, the invention provides a visible light response type lanthanum-doped bismuth tungstate catalyst by using the special property of rare earth lanthanum element so as to improve the removal efficiency of visible light catalysis technology on antibiotics in water, and in addition, the invention also provides a preparation method of the catalyst.
In order to solve the technical problems, the invention is realized by the following technical scheme:
a lanthanum-doped bismuth tungstate catalyst with visible light response is prepared from bismuth nitrate (Bi (NO)3)3·5H2O), lanthanum chloride (LaCI)3·7H2O), sodium tungstate (Na)2WO4·2H2O) is subjected to high-temperature high-pressure reaction in ethylene glycol to prepare a precipitate, and then the precipitate is washed and dried to prepare the lanthanum-doped bismuth tungstate catalyst, wherein the lanthanum doping proportion in the lanthanum-doped bismuth tungstate catalyst is 2-10 wt%.
Preferably, the molar ratio of the bismuth nitrate to the lanthanum chloride to the sodium tungstate is 1 (0.04-0.2) to 2.
A preparation method of a visible light response type lanthanum-doped bismuth tungstate catalyst comprises the following steps:
s1, mixing bismuth nitrate (Bi (NO)3)3·5H2O) is dissolved in ethylene glycol while lanthanum chloride (LacI) is added3·7H2O) adding the mixture into the solution, and magnetically stirring until the mixture is completely dissolved to obtain a solution A;
s2, adding sodium tungstate (Na) into a beaker2WO4·2H2O) is dissolved in Ethylene Glycol (EG) to obtain a solution B, and the solution B is magnetically stirred until the solution B is completely dissolved;
s3, slowly pouring the solution B into the solution A, continuously stirring for 1.0-2.0h by using a magnetic stirrer to uniformly mix the solution, transferring the solution into a high-pressure reaction kettle to react completely, and naturally cooling to room temperature;
s4, pouring out the upper liquid after the catalyst powder is completely settled after the kettle is opened, repeatedly cleaning the upper liquid by using a cleaning liquid mixed by ethanol and water according to the volume ratio of 1:1, finally removing the supernatant, drying the bottom catalyst in an oven, grinding the catalyst into fine powder by using an agate mortar, and obtaining the finished product of the lanthanum-doped bismuth tungstate catalyst (La-Bi)2WO6)。
Preferably, the molar ratio of bismuth nitrate, lanthanum chloride and sodium tungstate in the step S1 is 1 (0.04-0.2): 2.
Calculating mass according to the mass mol and the relative molecular mass of the substance, and dividing by the mass of the bismuth tungstate to obtain the mass fraction of 2-10 wt%.
Preferably, the temperature in the high-pressure reaction kettle in the step S3 is 160-180 ℃, and the reaction time is 16-24 h. The pressure in the high-temperature high-pressure reaction kettle is difficult to detect, the pressure is measured by temperature, and the higher the temperature is, the higher the pressure is. In the closed high-temperature high-pressure reaction vessel, the pressure at which the above temperature is reached is the pressure required in the present invention.
Preferably, the number of washing times in the step S4 is 3-5, and the temperature in the oven is 50-80 ℃.
Compared with the prior art, the invention has the following technical effects:
(1) the invention adoptsOne-step solvothermal method for preparing La-Bi by using ethylene glycol as solvent2WO6The catalyst has simple preparation process, does not need to adjust the pH value of the solution, has mild preparation conditions, does not influence the crystalline phase structure of bismuth tungstate after the rare earth lanthanum is doped, and the La-Bi prepared by the invention2WO6The catalyst has high crystallinity and uniform appearance.
(2) La-Bi prepared by the invention2WO6The catalyst has good photocatalytic performance, and can be used for photocatalytic degradation of organic pollutants, especially antibiotic pollutants. When the La doping ratio is 5 wt%, La-Bi2WO6The photocatalytic effect of (2) is the best. Under the simulated sunlight irradiation condition of a 300W xenon lamp, the removal rate of the catalyst to tetracycline with the initial concentration of 30mg/L is as high as 96.25 percent, which is higher than that of Bi undoped with La2WO6The catalyst degradation rate (88.92%) was increased by 7.33%.
(3) La-Bi prepared by the invention2WO6The catalyst has good stability, and after 4 times of repeated experiments, the removal rate of the tetracycline by the catalyst is still 90.44%. The catalyst has wide application prospect in the aspect of treating organic pollutants in water.
Drawings
FIG. 1 shows La-Bi2WO6XRD patterns of the series of catalysts; wherein (a): 0% of La-Bi2WO6；(b)：2％La-Bi2WO6；(c)：5％La-Bi2WO6；(d)：10％La-Bi2WO6；
FIG. 2 is a scanning electron microscope observation of the microscopic morphology and particle distribution of a catalyst sample; wherein (a) is pure Bi2WO6Scanning an electron microscope image; (b) is La-Bi2WO6Scanning an electron microscope image;
FIG. 3 shows 5% La-Bi2WO6A spectrum of the catalyst;
FIG. 4 shows 5% La-Bi2WO6Transmission electron micrographs of the catalyst; wherein, (a) the structure diagram of the surface of the transmission electron microscope (the inset is an electron diffraction diagram) and (b) the diagram of the high-resolution transmission electron microscope;
FIG. 5 shows La-Bi2WO6Ultraviolet-visible diffuse reflectance absorption spectrum (UV-Vis); wherein, (a) a UV-Vis spectrum; (b) absorption band edge diagrams;
FIG. 6 shows La-Bi2WO6Infrared spectrograms of a series of catalysts;
FIG. 7 shows 5% La-Bi2WO6XPS spectra analysis plots; wherein (a): a full map; (b) the method comprises the following steps Bi4 f; (c) the method comprises the following steps W4 f; (d) the method comprises the following steps O1 s; (e) the method comprises the following steps La3 d;
FIG. 8 shows La-Bi2WO6The degradation effect of the catalyst on the tetracycline is shown; (a) carrying out photocatalytic degradation on tetracycline hydrochloride curves by using photocatalysts with different doping ratios; (b) adsorption curves of the photocatalysts with different doping proportions on tetracycline hydrochloride are shown;
FIG. 9 shows 5% La-Bi2WO6Repeated experimental curves for the catalyst.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides a visible light response type lanthanum-doped bismuth tungstate catalyst, which aims at the problem that the efficiency of the existing single bismuth tungstate photocatalyst in treating antibiotic wastewater is low.
Visible light response type lanthanum-doped bismuth tungstate (La-Bi)2WO6) The catalyst is prepared by a solvothermal method, and the specific method comprises the following steps: 4mmol (1.9393g) of bismuth nitrate (Bi (NO)3)3·5H2O) was dissolved in 40mL of ethylene glycol while varying the proportions of lanthanum chloride (LaCI)3·7H2O) was added to the above liquid to obtain a solution a-1 (0.0149 g ═ 0.04mmol) added lanthanum chloride, a-2 (0.0371 g ═ 0.1mmol added lanthanum chloride), a-3 (0.0743 g ═ 0.2mmol added lanthanum chloride), and magnetically stirred for 1h to total solution; 2mmol (0.6596g) of sodium tungstate (Na) were added in a 100mL beaker2WO4·2H2O), dissolving into 30mL of Ethylene Glycol (EG) to obtain 5 parts of the same solution B, and magnetically stirring for 1h until the solution B is completely dissolved; slowly pouring the solution B into the solutions A-1, A-2 and A-3, stirring with a magnetic stirrer for 30min to mix the solutions uniformly, transferring into a 100mL high-pressure reaction kettle, and reactingReacting for 16-24h at 160-180 ℃, and naturally cooling to room temperature. After the kettle is opened, pouring out the upper liquid after the catalyst powder is completely settled, and repeatedly cleaning for 3-5 times, each time for 30min, by using a cleaning solution with the mixing ratio of ethanol to water being 1: 1. Finally, removing the supernatant, drying the bottom catalyst in a baking oven at 50-80 ℃, grinding the catalyst into fine powder by using an agate mortar, and obtaining the finished product La-Bi2WO6The La doping proportion of the series catalysts is respectively 2 wt%, 5 wt% and 10 wt%.
In addition, bismuth tungstate (Bi) is prepared2WO6) The catalyst is used as a comparison, and the preparation method comprises the following steps:
4mmol (1.9393g) of bismuth nitrate (Bi (NO)3)3·5H2O) is dissolved in 40mL of glycol to obtain a solution A, and the solution A is magnetically stirred for 1 hour; 2mmol (0.6596g) of sodium tungstate (Na) was added in a 100mL beaker2WO4·2H2O) is dissolved in 30mL of Ethylene Glycol (EG) to obtain a solution B, and the solution B is magnetically stirred for 1 hour; slowly pouring the solution B into the solution A, stirring for 30min by using a magnetic stirrer to uniformly mix the solution, transferring the solution into a high-pressure reaction kettle with an inner container measuring range of 100mL, reacting for 20h at 160 ℃, and naturally cooling to room temperature. After the kettle is opened, pouring out the upper liquid after the catalyst powder is completely settled, and repeatedly cleaning for 3-5 times (30 min each time) by using a cleaning solution with the mixing ratio of ethanol to water being 1:1 under magnetic stirring. Finally, removing supernatant fluid, drying the bottom catalyst in a 60 ℃ oven, grinding the catalyst into fine powder by using an agate mortar, and obtaining the bismuth tungstate (Bi)2WO6) A catalyst.
The invention sets different doping ratios, determines the doping ratio of the photocatalyst with the best activity by carrying out a photocatalytic degradation experiment, simultaneously carries out characteristic tests such as XRD, SEM, TEM and the like, and observes the internal structure and the light absorption characteristic of the material. Different initial experimental conditions are changed, and the influence of different conditions on the photocatalytic effect is researched, so that the optimal reaction condition of photocatalytic degradation is determined, and the research on the doped visible light reaction catalyst is completed.
La-Bi2WO6Catalyst and Bi2WO6Characterization test results analysis of
1. XRD analysis
XRD was used to examine the crystal composition and structure changes of the catalysts with different doping ratios, as shown in fig. 1.
From FIG. 1, it can be seen that pure Bi2WO6The characteristic diffraction peak (lanthanum doping ratio is 0%) is consistent with standard PDF card #73-2020, and the peak intensity is higher, thus the prepared catalyst has better crystallinity and complete crystal form. Characteristic diffraction peak and pure Bi of catalyst with same La doping amount2WO6Basically, the intensity of the diffraction peak is gradually weakened with the increase of the La doping amount, and the crystal plane is shifted to the direction of 2 theta increase. This is because the doping of rare earth elements suppresses the grain growth, decreases the unit cell volume, and increases the specific surface area. La3+Has an ionic radius of 0.103nm, and Bi3+The ionic radii of (A) and (B) are the same, which indicates that La3+Substituted Bi3+Is not the main reason for the smaller grains. The reason why the crystal grains are reduced and the crystallinity is reduced is that the doping of the rare earth lanthanum inhibits the formation of bismuth tungstate crystal nucleus, the crystal cells generate defects and generate crystal lattice distortion, and the crystal cells cannot form a complete crystal structure but exist in microcrystal or amorphous small particles.
2. SEM analysis
The microscopic morphology and particle distribution of the catalyst sample observed by a scanning electron microscope are shown in FIG. 2.
FIG. 2(a) shows Bi at a magnification of 40000 times2WO6Scanning electron microscope images show that the prepared catalyst presents a uniform distribution state of particle spheres, and the generation of large particles agglomerated inside is probably related to the adhesion and agglomeration of the dispersed catalyst after the catalyst is subjected to ultrasonic pretreatment and then is dripped on a silicon wafer for too many times. Careful observation of each catalyst particle revealed a plate-like structure with a matte surface. FIG. 2(b) is a 5% La-Bi magnification of 40000 times2WO6The scanning electron microscope image shows that the catalyst particles doped with 5% of La element are finer, and the distribution is more uniform and dispersed. But still exhibit a flaky particle spherical structure with a matte surface.
In addition, 5% of La-Bi was passed2WO6Energy spectrum diagram (fig. 3)Can see that La element is successfully doped into Bi2WO6In the catalyst. Bi2WO6The main constituent elements of (1) are C, O, Si, W, Bi and Au, wherein the Si element comes from a silicon wafer for bearing a catalyst sample during scanning, the C and O elements can be used for preparing ethylene glycol in the catalyst by a solvothermal method, and the Au is introduced by gold spraying during a scanning electron microscope. 5% La-Bi2WO6The energy spectrum of the alloy is added with La element, which shows that La-Bi2WO6The preparation is successful.
3. TEM analysis
Pure Bi was selected from all samples2WO6、5％La-Bi2WO6Two samples were the subjects and were subjected to TEM analysis as shown in figure 4.
FIG. 4(a) shows 5% of La-Bi2WO6The surface structure diagram of the transmission electron microscope (the inset is an electron diffraction diagram), and the particle of the prepared catalyst sample is uniformly dispersed and presents a particle structure with the particle size of 10nm-20 nm. The ring structure of the diffraction spots in the figure may indicate that the catalyst sample is of a polycrystalline structure. It is evident from the high resolution TEM image of FIG. 4(b) that there are two different lattice fringes with different extension directions, which are measured by using Digital Micrograph software to show the fringe spacing of 0.315nm and 0.272nm, corresponding to Bi respectively2WO6The (131) and (200) planes of (A) and (B) correspond to XRD diffraction peaks.
4. UV-Vis analysis
The band structure is an important factor influencing the activity of the catalyst, and ultraviolet spectrum analysis is carried out on the catalysts with different La doping ratios as shown in FIG. 5.
FIG. 5 shows La-Bi2WO6Ultraviolet-visible diffuse reflectance absorption spectrum (UV-Vis). As can be seen from FIG. 5(a), the prepared catalyst has a certain light absorption amount in the visible light region (> 400nm range) and the light absorption capacity is 5% La-Bi2WO6Maximum, 10% La-Bi2WO6And minimum. The obvious red shift of the light absorption edge can be seen after doping rare earth elements in bismuth tungstate, and La-Bi2WO6Absorption of visible light in sunlightThe yield and utilization rate is obviously improved. In fig. 5(b), the absorption band edge wavelengths of the photocatalysts with the doping proportions of 0%, 2%, 5% and 10% La are 386nm, 412nm, 415nm and 420nm in sequence by cutting lines on the light absorption curves with different doping proportions by a tangent method, and the forbidden band widths (band gap widths) of the catalysts with the doping proportions are 2.98eV, 2.95eV, 2.84eV and 3.01eV in sequence according to the calculation formula of the intrinsic absorption wavelength of the conductor material shown in the following formula (1). With the increase of La doping amount, the forbidden bandwidth of the prepared semiconductor photocatalyst becomes lower, and the response degree to visible light is increased, but when the doping ratio is larger than a certain value, the forbidden bandwidth does not decrease but increases with the continuous increase of the doping ratio, and the response degree to visible light is also reduced. The best doping proportion of the prepared catalyst with the photocatalytic performance of 5 percent La-Bi can be obtained from an ultraviolet-visible diffuse reflection absorption spectrogram2WO6。
λg＝1240/ΔEg (1)
In formula 1, a long wavelength limit λgUnit of (d) is nm; delta EgThe unit is eV.
5. FT-IR analysis
Infrared spectroscopic analysis of the catalyst sample was performed to determine the chemical bond structure present therein, as shown in fig. 6.
FIG. 6 shows La-Bi of different doping ratios2WO6Infrared spectrum (FT-IR) of the catalyst. At 3500cm-1、1590cm-1There is an absorption peak of bending vibration of-OH (O-H) because the catalyst sample absorbs moisture in the air when exposed to the air. At 1380cm-1The absorption peak is caused by N-O bending vibration, which is due to NO contained in the raw material for preparing the catalyst3-Is present. It is evident from the figure that the main absorption zone of the catalyst sample is located at 400-1000cm-1Meanwhile, the absorption peak in the low band is mainly formed by Bi-O, W-O, W-O-W bending vibration. However, we can also see that when the La doping ratio is too high by 10%, the absorption peak of the catalyst at the low band is not already significant.
6. XPS analysis
In the XPS analysis, the elemental species of each substance in the product can be qualitatively analyzed in terms of the position where the electron binding energy is present, and the surface composition of the sample is measured, that is, the valence of the element is determined.
XPS survey spectra can be used to preliminarily determine the chemical composition of the surface of the sample being tested. We can detect all or most of the elements in one measurement by a full spectrum scan of the sample. In order to obtain the accurate position of the binding energy, identify the chemical state of the element, and perform narrow-area high-resolution fine scanning on the element to be identified.
FIG. 7 shows 5% La-Bi2WO6The X photoelectron spectrum of the catalyst, (a) the full spectrum (b) Bi4f (C) W4f (d) O1s (e) La3d, and it can be seen from fig. 7(a) that the catalyst sample mainly contains elements of Bi, W, O, La, wherein C1s with the binding energy of 284.6eV in the sample mainly comes from the hydrocarbon pollutants carried by the apparatus itself. FIG. 7(b) shows that there are two distinct characteristic peaks in the XPS plot of Bi4f, namely Bi4f with binding energy of 159.1e V7/2The orbital peak and the Bi4f5/2 orbital peak at 164.3eV, which are the same as the peak positions reported in a large number of literatures, demonstrate 5% La-Bi2WO6Bi ions in the sample exist in a +3 valence state. FIG. 7(c) is an XPS analysis of sample W4f showing that electron binding energies appear at 35.2eV and 37.5e V corresponding to the inner shell electrons of W4f5/2 and W4f7/2, indicating that the valence of W is +6, as reported in the literature. Fig. 7(e) shows that a characteristic peak of electron binding energy appears at 284.6eV of the La3d orbital, corresponding to the presence of the +3 valent La element. Further description of La3+Into Bi2WO6In the crystal lattice, the photocatalytic reaction performance of the catalyst is improved. The asymmetric peaks in the O1s spectrum in FIG. 7(d) indicate the presence of two combined states of oxygen at the sample surface. The peak fitting result shows that the peak with the binding energy of 530.4eV is Bi2WO6Lattice oxygen (Olatt) in the crystal is derived from Bi-O bonds and W-O bonds. The peak at a binding energy of 531.8eV is attributed to adsorbed oxygen (Oads) at the surface of the sample.
Determination of La doping ratio
With tetracycline hydrochloride as a target pollutant, a degradation experiment of photocatalysts with different La doping ratios was performed under a 450W xenon lamp light source, and the corresponding adsorption performance investigation was completed as shown in FIG. 8.
It can be seen from fig. 8(a) that the catalyst activity doped with the rare earth La element is improved compared with bismuth tungstate. When the reaction time is 180min (the lamp is turned on for 150min), the removal rate of bismuth tungstate to tetracycline with the concentration of 30mg/L is only 88.92%, and the 2% La-Bi2WO6The removal rate of (a) was 90.73%, and 5% of La-Bi2WO6The removal rate of the catalyst is up to 96.25, 10 percent of La-Bi2WO6Again reducing the removal rate to 92.06%. Thus indicating the presence of the optimum doping ratio for the rare earth La. When the doping ratio is lower than the optimum doping ratio, the photocatalyst fails to generate enough traps to capture photogenerated carriers, and thus electron-hole pairs are not effectively separated to fail to achieve the optimum catalytic performance. When the optimal doping ratio is reached, the electron-hole separation reaches the optimal degree, and the photocatalysis effect is the best. However, as the doping amount is further increased, Bi is added2WO6The thickness of the surface electron cloud (charge layer) is reduced, only the transmission depth of ultraviolet light can be consistent with the thickness of the charge layer, the separation level of electron-hole pairs is reduced, and the photocatalytic performance of the photocatalyst is reduced. There is an optimum doping ratio.
As can be seen from the observation of FIG. 8(b), the adsorption saturation time of different catalysts is about 30min, and the concentration level of tetracycline is almost unchanged during the period of 30min-180 min. From the adsorption curve, the adsorption performance of the La-Bi with the height of 10 percent can be seen2WO6＞5％La-Bi2WO6＞2％La-Bi2WO6＞Bi2WO6。
Catalyst stability study
For the prepared 5% La-Bi2WO6The evaluation of the photocatalytic stability performance of the catalyst is shown in fig. 9.
FIG. 9 is a graph showing the stability of the catalyst, from which it can be seen that 5% La-Bi was produced2WO6The catalyst shows better stability in the repeated experimental process of 4 times of tetracycline (30mg/L) degradation. From the figure, it is observed that the adsorption level of tetracycline is obviously reduced when the catalyst is reused, but the reverse reaction is generated in the process of photocatalytic degradationThe phenomenon that the removal rate is gradually reduced at the same time is reflected. This is probably because the catalyst was simply stirred and washed with ethanol each time, and then dried and then subjected to the degradation test again. Therefore, incomplete cleaning process directly affects the adsorption performance of the prepared catalyst, and further, the adsorption amount and the removal rate of tetracycline are reduced. The tetracycline removal (90.44%) decreased slightly after 4 catalyst degradation experiments compared to 1 st (96.60%), which was also related to the loss of catalyst fines during the experiment. After weighing, 0.041g of catalyst remained after the 4 th degradation compared to 0.05g of the initial charge, with a loss of about 18%. In conclusion, the La-Bi prepared in this example2WO6The composite catalyst has stable photocatalytic activity under visible light conditions.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (6)
1. A visible light response type lanthanum-doped bismuth tungstate catalyst is characterized in that a precipitate is prepared by high-temperature and high-pressure reaction of bismuth nitrate, lanthanum chloride and sodium tungstate in ethylene glycol, and then the precipitate is washed and dried to prepare the lanthanum-doped bismuth tungstate catalyst, wherein the lanthanum doping proportion in the lanthanum-doped bismuth tungstate catalyst is 2-10 wt%;
the lanthanum-doped bismuth tungstate catalyst is prepared by the following method:
s1, dissolving bismuth nitrate in ethylene glycol, adding lanthanum chloride into the solution, and magnetically stirring until the lanthanum chloride is completely dissolved to obtain a solution A;
s2, dissolving sodium tungstate into ethylene glycol by using a beaker to obtain a solution B, and magnetically stirring until the solution B is completely dissolved;
s3, slowly pouring the solution B into the solution A, continuously stirring the solution by using a magnetic stirrer to uniformly mix the solution, transferring the solution into a high-pressure reaction kettle to completely react, and naturally cooling the solution to room temperature;
and S4, opening the kettle, pouring out the upper liquid after the catalyst powder is completely settled, repeatedly cleaning the upper liquid by using a cleaning liquid mixed by ethanol and water according to the volume ratio of 1:1, finally removing the supernatant, drying the bottom catalyst in an oven, and grinding the catalyst into fine powder by using an agate mortar to obtain the finished product lanthanum-doped bismuth tungstate catalyst.
2. The lanthanum-doped bismuth tungstate catalyst of claim 1, wherein the molar ratio of bismuth nitrate to lanthanum chloride to sodium tungstate is 1: 0.04-0.2: 2.
3. A preparation method of a visible light response type lanthanum-doped bismuth tungstate catalyst is characterized by comprising the following steps:
s1, dissolving bismuth nitrate in ethylene glycol, adding lanthanum chloride into the solution, and magnetically stirring until the lanthanum chloride is completely dissolved to obtain a solution A;
s2, dissolving sodium tungstate into ethylene glycol by using a beaker to obtain a solution B, and magnetically stirring until the solution B is completely dissolved;
s3, slowly pouring the solution B into the solution A, continuously stirring the solution by using a magnetic stirrer to uniformly mix the solution, transferring the solution into a high-pressure reaction kettle to completely react, and naturally cooling the solution to room temperature;
and S4, opening the kettle, pouring out the upper liquid after the catalyst powder is completely settled, repeatedly cleaning the upper liquid by using a cleaning liquid mixed by ethanol and water according to the volume ratio of 1:1, finally removing the supernatant, drying the bottom catalyst in an oven, and grinding the catalyst into fine powder by using an agate mortar to obtain the finished product lanthanum-doped bismuth tungstate catalyst.
4. The method for preparing a lanthanum-doped bismuth tungstate catalyst as claimed in claim 3, wherein the molar ratio of bismuth nitrate to lanthanum chloride to sodium tungstate in step S1 is 1: 0.04-0.2: 2.
5. The preparation method of the lanthanum-doped bismuth tungstate catalyst as claimed in claim 3, wherein the temperature in the high-pressure reaction kettle in the step S3 is 160-180 ℃, and the reaction time is 16-24 h.
6. The preparation method of the lanthanum-doped bismuth tungstate catalyst as claimed in claim 3, wherein the number of times of cleaning in the step S4 is 3-5, and the temperature in the oven is 50-80 ℃.
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| CN112007633A (en) * | 2020-09-15 | 2020-12-01 | 西北矿冶研究院 | La/Bi2WO6Preparation method and application of photocatalyst |
| CN113231099B (en) * | 2021-05-21 | 2022-05-17 | 吉林大学 | Preparation and application of Z-type polypyrrole-bismuth tungstate photocatalyst |
| CN113769779B (en) * | 2021-08-16 | 2023-12-29 | 中化学朗正环保科技有限公司 | Photocatalyst for treating sewage containing amine organic matters, and preparation method and application thereof |
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