CN108970601B - Photocatalytic coating with zinc oxide/titanium dioxide heterostructure and preparation method and application thereof - Google Patents

Photocatalytic coating with zinc oxide/titanium dioxide heterostructure and preparation method and application thereof Download PDF

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CN108970601B
CN108970601B CN201810745174.9A CN201810745174A CN108970601B CN 108970601 B CN108970601 B CN 108970601B CN 201810745174 A CN201810745174 A CN 201810745174A CN 108970601 B CN108970601 B CN 108970601B
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谌宽
黄晶
付耀耀
翟梦娇
龚永锋
刘奕
李华
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Ningbo Institute of Material Technology and Engineering of CAS
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Abstract

The invention discloses a ZnO/TiO-based composite material2The photocatalytic coating with the heterostructure and the preparation method thereof are characterized in that the photocatalytic coating comprises a ZnO cluster formed by stacking nanometer ZnO grains with the diameter of 10-50 nm and nanometer TiO embedded in the ZnO cluster2Particles; the ZnO cluster is of a cluster structure, has a loose porous structure and has a diameter of 3-30 mu m. The photocatalytic coating is prepared by a thermal spraying process in one step, and the shape and the microscopic size of the product are controllable. The photocatalytic coating disclosed by the invention has strong binding force with a substrate, has a larger spectral absorption range, and obviously improves the efficiency of photocatalytic degradation of pollutants such as organic dyes.

Description

Photocatalytic coating with zinc oxide/titanium dioxide heterostructure and preparation method and application thereof
Technical Field
The invention relates to the technical field of photocatalytic materials, in particular to a photocatalytic coating with a zinc oxide/titanium dioxide heterostructure as well as a preparation method and application thereof.
Background
Although the earth surface is covered with nearly 70% of water, fresh water resources account for only 2.8%, 75% of the water stored in polar glaciers and the like is removed, the amount of fresh water available to human beings is still less than 1% of the total amount of water on earth, and these precious water resources have been polluted and wasted for a long time, and many drinking water purification technologies and sewage treatment technologies have been developed successively. Among the purification methods, the photocatalytic technology has important application prospects as a method which can utilize solar energy to drive catalytic reaction, has high efficiency, low energy consumption, wide application range and deep oxidation capability.
Among them, titanium dioxide (TiO)2) The titanium dioxide is a wide-bandgap semiconductor which is most widely applied, has the advantages of no toxicity, high catalytic activity, strong oxidizing capability, low price and easy obtaining, and the like, but the titanium dioxide has a relatively wide band gap (Eg 3.2eV) and only responds to the irradiation of ultraviolet wavelength light, and the generated electron-hole pair is easy to recombine, thereby influencing the catalytic activity and limiting the practical application of the titanium dioxide.
Zinc oxide (ZnO) is a direct semiconductor material (3.37eV) with band gap close to titanium dioxide, has higher exciton binding energy, and is commonly used as a photoelectric catalytic material. ZnO with TiO2Similar energy band structure and physical properties, but also has some characteristics which titanium dioxide does not have, such as higher quantum yield and higher electron mobility, which is very beneficial to improve the photocatalytic activity. ZnO and TiO2If quantum-sized contact exists in an interface region, a nano Schottky junction can be formed, the separation efficiency of photon-generated carriers can be effectively increased, the recombination of the photon-generated carriers is inhibited, the stability of the photocatalytic material is improved, the spectral absorption range can be expanded through the coupling and synergistic effects of the nano Schottky junction and the photocatalytic material, and the utilization rate of visible light is increased.
Wangwangxiaxia etc. (Wangwangxia, Sun Chenghua, Huxiujie, Chenping, Zhongshun, two-step method for synthesizing ZnO/TiO)2Heterostructure, materials engineering, 2008, 10. ) Adopts an electrospinning and hydrothermal two-step method to prepare ZnO/TiO2Heterostructure, first of all TiO prepared by electrospinning2Thin film fibers and then hydrothermally on TiO2ZnO structure grows on the thin film fiber. The preparation method needs multiple steps, has complex process and high requirement on equipment, and is not suitable for large-scale film formation.
Stifled state jun, etc. (stifled state jun, wang yan, hupeguan, liuhong, Liu bell, wang yan, ZnO @ TiO)2Preparation and characterization of a surface heterostructure of a nanobelt, rare metal, 12 months 2009) by a hydrothermal method and a subsequent heat treatment methodThen assembling a zinc oxide nano structure on the surface of the titanium oxide nano belt by a liquid phase synthesis method to prepare ZnO @ TiO nano belt2A nanoribbon surface heterostructure. The product obtained is characterized by being TiO2The surface of the nano-belt is assembled with ZnO nano-flower and TiO2The width of the nanobelt is 50-200 nm, the length of the nanobelt reaches dozens of microns, and petals of about 200nm grow on the 500 nm-long bone bracts of the ZnO nanoflower. The preparation method obtains self-assembled TiO2ZnO nanostructure, but is only suitable for small-range preparation, and the controllability of reaction conditions is poor.
Thus, it is desired to realize a composition having ZnO/TiO2The large-scale production and application of the photocatalytic coating with the heterostructure urgently needs to develop a photocatalytic coating with more excellent photocatalytic performance and a novel structure and a coating preparation technology which has low cost, high film-forming quality, large scale and suitability for industrial production.
Disclosure of Invention
The invention discloses a ZnO/TiO with a novel structure2The photocatalytic coating with the heterostructure has strong binding force with a substrate, has a larger spectral absorption range, and obviously improves the efficiency of photocatalytic degradation of pollutants such as organic dyes. The invention also discloses a preparation process of the photocatalytic coating, the photocatalytic coating is prepared in one step by adopting a thermal spraying process, and the product appearance and the microscopic size are controllable.
The specific technical scheme is as follows:
ZnO/TiO-containing material2The photocatalytic coating with the heterostructure comprises a ZnO stack cluster formed by stacking nanometer ZnO crystal grains with the diameter of 10-50 nm and nanometer TiO embedded in the ZnO stack cluster2Particles;
the ZnO cluster is of a cluster structure, has a loose porous structure and has a diameter of 3-30 mu m.
In the photocatalytic coating, ZnO and TiO2The mass ratio of (A) to (B) is 5-20: 1; the TiO is2Containing at least anatase type nano TiO2。
The thickness of the photocatalytic coating is 1-20 mu m, and the surface roughness is Ra0.2-2 mu m.
Further, through Tauc model fitting calculation, the approximate band gap width of the photocatalytic coating is 2.80-3.01 eV.
By comparing pure ZnO samples (3.11eV) with pure TiO2The approximate band gap width data of the (P25) sample (3.15eV) shows that the approximate band gap width of the photocatalytic coating prepared by the invention is obviously reduced, and the ZnO/TiO formed in the photocatalytic coating is proved2A heterostructure.
The invention also discloses the ZnO/TiO-containing material2The preparation method of the heterostructure photocatalytic coating comprises the following steps:
(1) preparing a zinc salt solution by using absolute ethyl alcohol-water as a solvent, adjusting the pH value of the zinc salt solution to 4-6, and adding a surfactant and nano titanium dioxide particles to obtain a spraying raw material;
(2) depositing the spraying raw material on the surface of a substrate by liquid material thermal spraying to obtain the ZnO/TiO2A photocatalytic coating of heterostructures.
The invention adopts the thermal spraying process, preferably the plasma spraying process, and uses the nano TiO2The precursor suspension of the zinc salt solution mixed with particles is used as a spraying raw material, and the chemical reaction of the raw material in the spraying process is utilized and deposited on a substrate, so that the ZnO/TiO with controllable morphology and microscopic size and the like of the product prepared by a one-step method is realized2A photocatalytic coating of heterostructures.
In general, the nano powder cannot be directly prepared by coating spraying, which is mainly because the nano particles have small particle size and light weight, are easy to agglomerate in the spraying process to block a powder feeding pipe, and have small acceleration kinetic energy, so that the nano powder is difficult to deposit into a coating on a base material; in addition, the nano powder has large specific surface area and high powder activity, and the grain size of the particles is easy to grow and lose the original nano characteristic in the spraying process. In order to overcome the difficulties, the invention adopts the suspension prepared from the nano powder to replace the traditional feeding mode for liquid-phase thermal spraying, thereby avoiding the problems of small particle size, light weight, easy agglomeration in the spraying process, blockage of a powder feeding pipe and the like in the traditional thermal spraying process. Meanwhile, the solvent has good protection effect on the nano particles in the spraying process of the liquid-phase thermal spraying process, and the problems of growth of the grain size of the nano particles, phase change at high temperature and the like are avoided.
Specifically, the zinc salt solution is used as a raw material for coating preparation, and the nano powder preparation and the coating preparation are integrated, so that a complicated flow in the nano powder preparation process is avoided, and the growth and the loss of nano powder crystal grains in the traditional thermal spraying process are avoided. Since the selectivity of titanium salts to solvents is different from that of zinc salts, direct solution-form complexation is difficult to achieve, and mesophases are easily formed. To further obtain ZnO/TiO with micro-nano structure2The invention further improves the atomization process of liquid materials by directly doping titanium dioxide nano particles in a zinc salt solution, improves the bonding strength of a coating and a substrate, simultaneously, the fused or semi-fused titanium dioxide particles are uniformly coated in the ZnO nano particles, effectively realizes the compounding of two wide-bandgap semiconductor materials, and the prepared photocatalytic coating is of a porous structure and has a certain heterojunction, thereby generating a coupling synergistic effect and being expected to obviously improve the photocatalytic activity of the composite coating. Further, characteristic parameters such as the morphology, the phase composition fraction and the like of the final coating are effectively controlled by controlling parameters such as the solid content of titanium dioxide nanoparticles in the spraying raw material, the concentration of a zinc salt solution, the mass ratio of a surfactant, the spraying power and the like. In the step (1), the step (c),
preferably:
in the solvent, the volume ratio of absolute ethyl alcohol to water is 1-4: 1;
the zinc salt in the zinc salt solution is at least one selected from zinc nitrate, zinc acetate and zinc chloride;
the concentration of the zinc salt solution is 0.1-1 mol/L.
Preferably:
the surfactant is selected from at least one of polyethylene glycol, polyethyleneimine, ammonium citrate and polyacrylic acid;
the mass percentage of the surfactant is 5-20% of the mass of the nano titanium dioxide in the spraying raw material.
The mass ratio of the zinc salt to the nano titanium dioxide particles is 5-100: 1.
further preferably, the concentration of the zinc salt solution is 0.5mol/L, and the mass ratio of the zinc salt to the nano titanium dioxide particles is 13.75-55.75: 1.
in the step (2):
preferably:
the substrate is selected from alumina, 45 steel, 316L stainless steel, polished silicon wafers or glass slides, and the substrate is pretreated before use;
the liquid material thermal spraying comprises liquid material atomization and thermal spraying.
In the process of liquid material thermal spraying, spraying raw materials, namely liquid materials, are firstly atomized into fine fog drops through an atomizing nozzle on a spray gun, then enter high-temperature high-speed flame flow for thermal spraying, and form fine solid particles through a series of physical and chemical reactions such as volatilization and combustion of a solvent in the fog drops, precipitation and decomposition of a solute and the like, and the fine solid particles are deposited on the surface of a substrate to form a coating.
Preferably, the process conditions for atomizing the liquid material are as follows: the diameter of the liquid material nozzle is
Figure RE-GDA0001836683360000051
The flow rate of the liquid material is 50-150 mL/min, and the angle formed by the liquid material and the flame flow is 90 degrees.
In the invention, the liquid material flow plays a key role in the formation of a heterojunction in the finally prepared photocatalytic film, and experiments show that when the liquid material flow exceeds the optimized range, a heterostructure cannot be obtained, and the secondary atomization and heating process of the liquid material and flame flow can be weakened by smaller flow, so that the generation and crystallization of ZnO are influenced.
Preferably, the thermal spraying is plasma spraying, and oxygen vacancy defects and ZnO-TiO formed under the condition of plasma high-temperature quenching2The heterostructure narrows the band gap, enlarges the spectrum absorption range and simultaneously reduces the recombination of photon-generated carriers, thereby improving the capability of the coating for degrading pollutants such as organic dye by photocatalysis.
The plasma spraying process parameters are as follows:
the current is 500-700A, the voltage is 45-60V, the spraying distance is 60-100 mm, the moving speed of the plasma spray gun is 200-600 mm/s, and the spraying times of the coating are 1-10 times.
Further preferably, the flow rate of the liquid material is 100-120 mL/min, and the ZnO/TiO prepared by combining the optimized raw material ratio and the plasma spraying process within the flow rate range of the liquid material2The approximate band gap width of the photocatalytic coating of the heterostructure is 2.88-2.93 eV.
The invention also discloses the ZnO/TiO-containing material2The application of the photocatalytic coating with the heterostructure in the field of photocatalytic degradation of organic pollutants.
Compared with the prior art, the invention has the following advantages:
the invention adopts a thermal spraying process, takes nano titanium dioxide powder and zinc salt solution as raw materials to prepare spraying raw materials, strictly controls the flow of the liquid materials, optimizes other thermal spraying process parameters, and prepares ZnO/TiO with micro-nano structure by a one-step method2A photocatalytic coating of heterostructure which effectively realizes ZnO and TiO2The coupling and synergistic effect of the two wide-bandgap semiconductor materials has a larger spectral absorption range, and the efficiency of photocatalytic degradation of pollutants such as organic dyes is remarkably improved. Furthermore, the morphology and the microscopic size of the photocatalytic coating can be effectively regulated and controlled by accurately regulating and controlling the parameters of the thermal spraying process.
Drawings
FIG. 1 shows a ZnO/TiO doped film of the present invention2A flow chart for preparing a photocatalytic coating of a heterostructure;
FIG. 2 is an XRD pattern of the photocatalytic coatings prepared in examples 1 to 5, respectively, and an XRD pattern of the coatings prepared in comparative examples 1 to 3, respectively, is given as a comparison;
FIG. 3 is a low-magnification (5000-magnification) SEM micro-topography of the photocatalytic coatings respectively prepared in examples 1-5 and comparative example 3, which correspond to (a) - (f) in sequence;
FIG. 4 is a high power (100000 times) SEM microtopography (a) and a cross-sectional SEM microtopography (b) of the photocatalytic coating prepared in example 3;
FIG. 5 is a graph showing the diffuse reflection absorption spectra of the photocatalytic coatings prepared in examples 1 to 5 in the UV-visible range, and the diffuse reflection absorption spectra of the coatings prepared in comparative examples 1 to 3 are shown as a comparison;
FIG. 6 is a Tauc model curve of the diffuse reflection absorption spectra of the photocatalytic coatings prepared in examples 1-5, respectively, and curves of the coatings prepared in comparative examples 1-3, respectively, are given for comparison.
Detailed Description
The present invention is described in further detail below with reference to the drawings and examples, and it should be noted that the following examples are intended to facilitate understanding of the present invention and are not intended to limit the present invention in any way.
Example 1
In this example, the substrate material was selected to be 316L stainless steel sheet with a thickness of about 2mm, ZnO/TiO on the substrate2The thickness of the composite coating is about 5 μm, wherein the TiO2The mass ratio of the coating to ZnO is 1:20, the coating is a loose surface formed by stacking and coating ZnO crystal grains and P25 particles, the loose surface is of a bulk structure, the diameter is 3-30 mu m, and the size range of the ZnO crystal grains is 10-50 nm. In this example, P25 is used as a raw material, and after a plasma spraying process, titanium dioxide particles are uniformly dispersed in the coating and are accompanied by a small amount of submicron-sized particles obtained by heat fusion sintering. ZnO/TiO of the composite micro-nano structure2The preparation flow of the coating is shown in fig. 1, and the specific preparation method is as follows:
1. firstly, commercial Zn (CH)3COO)2·2H2Adding O into a solvent with the volume ratio of absolute ethyl alcohol to deionized water, stirring uniformly to prepare a 0.5mol/L zinc acetate solution, adjusting the pH value of the zinc acetate solution to about 6 by using glacial acetic acid, clarifying the solution, adding a surfactant polyethylene glycol (PEG400) accounting for 0.09 wt% of the mass of the zinc salt into the zinc acetate solution, stirring uniformly to obtain a mixed solution, and mixing with Zn (CH)3COO)2·2H2Adding nano titanium dioxide powder (P25) with the O mass ratio of 1.8 wt% into the mixed solution, carrying out ultrasonic dispersion for 5min, and carrying out magnetic stirring for 0.5h to obtain suspension, namely the spraying raw material;
2. cleaning a stainless steel substrate by using acetone, absolute ethyl alcohol and deionized water in sequence, carrying out sand blasting treatment by using 60-mesh brown corundum sand, roughening the surface, wherein the pressure of compressed air is about 0.7MPa, and finally blowing off the surface of the substrate by using compressed air;
3. adopting an external feeding mode of a plasma spray gun, and a certain amount of liquid material passes through the peristaltic pump
Figure RE-GDA0001836683360000071
And the nozzle is vertically fed into the root of the flame flow. The liquid material is atomized, broken, evaporated, concentrated, precipitated, sintered, melted and solidified under the action of plasma flame flow at high temperature and high speed, and a coating with the thickness of about 5 mu m is formed on the surface of a substrate. Wherein, the plasma spraying gun has the following spraying parameters: the current is 500A, the voltage is 50V, the flow rate of the spraying liquid material is 100mL/min, the spraying distance is 80mm, the transverse speed of the plasma gun is 400mm/s, and the spraying times of the coating are 3 times.
Comparative example 1
This comparative example did not add titanium dioxide nanoparticles and surfactant in preparing the spray raw material, i.e., only 0.5mol/L of Zn (CH)3COO)2The solution is used as a raw material for spraying, and the steps 2-3 are completely the same as those in the embodiment 1.
Example 2
In this example, the substrate material was selected to be 316L stainless steel sheet with a thickness of about 2mm, ZnO/TiO on the substrate2The thickness of the composite coating is about 5 μm, wherein the TiO2The mass ratio of the coating to ZnO is 1:10, the coating is a loose surface formed by stacking and coating ZnO crystal grains and P25 particles, and the size range of the ZnO crystal grains is 10-50 nm. ZnO/TiO of the composite micro-nano structure2The preparation method comprises the following steps:
1. firstly, commercial Zn (CH)3COO)2·2H2Adding O into a solvent with the volume ratio of absolute ethyl alcohol to deionized water, stirring uniformly to prepare a 0.5mol/L zinc acetate solution, adjusting the pH value of the solution to about 6 by using glacial acetic acid, clarifying the solution, adding a surfactant polyethylene glycol (PEG400) accounting for 0.18 wt% of the mass of the zinc salt into the solution, stirring uniformly, and mixing with Zn (CH)3COO)2·2H2Nano titanium dioxide with O mass ratio of 3.6 wt%Powder (P25) added to Zn (CH)3COO)2·2H2Performing ultrasonic dispersion for 5min in the O solution, and performing magnetic stirring for 0.5h to obtain a suspension, namely the spraying raw material;
2. cleaning a stainless steel substrate by using acetone, absolute ethyl alcohol and deionized water in sequence, carrying out sand blasting treatment by using 60-mesh brown corundum sand, roughening the surface, wherein the pressure of compressed air is about 0.7MPa, and finally blowing off the surface of the substrate by using compressed air;
3. adopting an external feeding mode of a plasma spray gun, and a certain amount of liquid material passes through the peristaltic pump
Figure RE-GDA0001836683360000081
And the nozzle is vertically fed into the root of the flame flow. The liquid material is atomized, broken, evaporated, concentrated, precipitated, sintered, melted and solidified under the action of plasma flame flow at high temperature and high speed, and a coating with the thickness of about 5 mu m is formed on the surface of a substrate. Wherein, the plasma spraying gun has the following spraying parameters: the current is 500A, the voltage is 50V, the flow rate of the spraying liquid is 120mL/min, the spraying distance is 80mm, the transverse speed of the plasma gun is 400mm/s, and the spraying times of the coating are 3 times.
Example 3:
in this example, the substrate was selected to be a 316L stainless steel sheet with a thickness of about 2mm, ZnO/TiO on the body2The thickness of the composite coating is about 5 μm, wherein the TiO2The mass ratio of the coating to ZnO is 1:5, the coating is a loose surface formed by stacking and coating ZnO crystal grains and P25 particles, and the size range of the ZnO crystal grains is 10-50 nm. ZnO/TiO of the composite micro-nano structure2The preparation method comprises the following steps:
1. firstly, commercial Zn (CH)3COO)2·2H2Adding O into a solvent with the volume ratio of absolute ethyl alcohol to deionized water, stirring uniformly to prepare a 0.5mol/L zinc acetate solution, adjusting the pH value of the solution to 6 by using glacial acetic acid, clarifying the solution, adding a surfactant polyethylene glycol (PEG400) accounting for 0.36 wt% of the mass of the zinc salt into the solution, stirring uniformly, and mixing with Zn (CH)3COO)2·2H2Nano titanium dioxide powder (P25) with O mass ratio of 7.2 wt% is added to Zn (CH)3COO)2·2H2In the O solution, ultrasonically dispersing for 5min, and magnetically stirring for 0.5h to obtain a suspension;
2. cleaning a stainless steel substrate by using acetone, absolute ethyl alcohol and deionized water in sequence, carrying out sand blasting treatment by using 60-mesh brown corundum sand, roughening the surface, wherein the pressure of compressed air is about 0.7MPa, and finally blowing off the surface of the substrate by using compressed air;
3. adopting an external feeding mode of a plasma spray gun, and a certain amount of liquid material passes through the peristaltic pump
Figure RE-GDA0001836683360000091
And the nozzle is vertically fed into the root of the flame flow. The liquid material is atomized, broken, evaporated, concentrated, precipitated, sintered, melted and solidified under the action of plasma flame flow at high temperature and high speed, and a coating with the thickness of about 5 mu m is formed on the surface of a substrate. Wherein, the plasma spraying gun has the following spraying parameters: the current is 500A, the voltage is 50V, the flow rate of the spraying liquid material is 100mL/min, the spraying distance is 80mm, the transverse speed of the plasma gun is 400mm/s, and the spraying times of the coating are 3 times.
Comparative example 2
In this comparative example, step 1, a mixed solvent of absolute ethyl alcohol and deionized water in equal volume ratio was prepared, but only zinc acetate was not added, i.e., a suspension of nano-titanium dioxide powder (P25) with the same solid content was prepared as a liquid material. Steps 2 to 3 are the same as those in example 3.
Comparative example 3
In the comparative example, step 1, a mixed solvent of absolute ethyl alcohol and deionized water in the same volume ratio is prepared, and a suspension of nano zinc oxide powder (with a particle diameter of 30 +/-10 nm) and nano titanium dioxide powder (P25) in the same mass ratio is prepared as a liquid material, wherein the solid content in the suspension is 40 g/L. Steps 2 to 3 are the same as those in example 3.
Example 4
The preparation process flow is completely the same as that in example 3, except that the flow rate of the spraying liquid material in the step 3 is replaced by 50 mL/min.
Example 5
The preparation process flow is completely the same as that in example 3, except that the flow rate of the spraying liquid material in the step 3 is replaced by 150 mL/min.
The products prepared in the above embodiments are subjected to phase analysis, microscopic morphology observation and coating surface element distribution test, and the test method and results are as follows:
1. phase analysis: and (4) flatly placing the coating sample to be flush with the sample stage, and detecting the crystal structure of the coating sample by using an X-ray diffractometer.
Examples 1, 2, 3, 4, 5 in comparison, the spray coating produced TiO products containing predominantly anatase and rutile phases2And wurtzite phase ZnO, and an austenite phase of a stainless steel matrix occurs due to a small coating thickness. The anatase to rutile phase ratio was increased to a different extent than the coating prepared directly from the P25 suspension spray (comparative example 2). With the increase of the content of the titanium dioxide, the proportion of the anatase phase in the coating gradually increases and then decreases. For the direct spray coating of a mixed suspension of zinc oxide and titanium dioxide (comparative example 3), new TiZn appeared2O4And (4) phase(s). Also in example 4 new TiZn appeared2O4Phase and the titanium dioxide in the coating is less crystalline. In example 5, although TiZn did not appear2O4The phases, but the titanium dioxide in the coating is likewise less crystalline and the proportion of anatase phase is drastically reduced compared to examples 1, 2 and 3. As shown in fig. 2, it can be calculated by the scherrer equation that the size of ZnO particles in each coating layer is not significantly changed, and the average grain size is about 20 nm.
2. And (3) microstructure analysis: and (3) taking a coating sample, fixing the coating sample on a sample table by using conductive adhesive, spraying Au, and observing the microstructure of the coating surface or section by using a field emission scanning electron microscope.
As can be seen from FIGS. 3(a) - (e), the surface morphology of the coating is in a cauliflower structure typical of a solution spray coating, i.e. the nano ZnO clusters are in a cluster structure and have certain loose pores, but the cauliflower contains a small amount of TiO2Spherical particles, unmelted TiO being visible in the area of the coating portion2Agglomerated and as the titanium dioxide content increased, the proportion of spherical particles increased. From the high power image of the graph (a) in FIG. 4, it can be known that the diameter of nano zinc oxide is very small, about 10 to 50nm, and in ZnOIn the middle of the granule, a small amount of TiO is mixed2Spherical particles. For the vertical structure of the coating, it can be seen from the graph (b) in fig. 4 that the coating is formed by stacking nanoparticles, and there is a certain porosity between layers.
As can be seen in FIG. 3(f), in the coating, TiO2The spherical particles are in an agglomerated state of large particles and cannot be uniformly dispersed among the nano ZnO clusters.
3. Coating spectral absorption curve: taking a coating sample, fixing the coating sample on a sample rack, and coating with BaSO4And testing the absorbance of the coating with the wavelength within the range of 200-800nm as a blank, and obtaining the approximate band gap width of the coating according to the fitting calculation of the Tauc model.
As can be seen from FIG. 5, in the ultraviolet region having a wavelength of less than 400nm, ZnO/TiO2The absorption curve of the composite coating (examples 1-5) is close to that of the ZnO coating sprayed by the solution precursor and higher than that of the P25 coating sample; in the visible light wave band with the wavelength of more than 400nm, ZnO/TiO2The composite coating absorption curve is close to the P25 coating sample and higher than the ZnO coating sample. ZnO/TiO 22Compared with a single component sample, the absorption line of the composite coating shows a red shift trend of the absorption edge. As can be further seen from FIG. 6 and Table 1 below, ZnO/TiO2The band gap width of the composite coating sample is within the range of 2.88-3.01 eV, and is obviously smaller than that of a ZnO sample (3.11eV), a P25 sample (3.15eV) and ZnO and TiO with single components2The suspension sample was mixed (3.17 eV). For the coating of example 4, the lower liquid flow rate is not good for coating deposition on the one hand, and the higher unit heat input is easy to generate second phase reaction on the other hand, is not good for ZnO/TiO2The formation of heterostructures is also responsible for their high bandgap values (3.01 eV). For the coating of the embodiment 5, the higher liquid material flow rate leads the liquid to jet and disturb the plasma arc flame in the spraying process, on one hand, the uniformity of the coating is reduced, and on the other hand, a large proportion of liquid material is directly mixed into the coating without the action of a heat source, thereby influencing the integral structure of the coating. Comparative example 3 larger band gap values illustrate ZnO and TiO2Mechanical mixing of the nanoparticles does not result in a uniform distribution of the nanoparticles, the TiO being incorporated2The nanoparticles are extremely easy to exist in the form of submicron-sized aggregates in the suspension (see (f) in FIG. 3), and are also easy to be dispersed in the suspensionSintering reaction occurs to generate a second phase, and no heterojunction is formed.
Table 1 below shows the band gap values calculated from the Tauc model curve of the diffuse reflection absorption spectrum of each coating in fig. 6.
TABLE 1
Figure RE-GDA0001836683360000121

Claims (6)

1. ZnO/TiO-containing material2The preparation method of the photocatalytic coating with the heterostructure is characterized in that the photocatalytic coating comprises a ZnO cluster formed by stacking nanometer ZnO grains with the diameter of 10-50 nm and nanometer TiO embedded in the ZnO cluster2Particles; in the photocatalytic coating, ZnO and TiO2The mass ratio of (A) to (B) is 5-20: 1;
the ZnO cluster is of a bulk structure and has a loose porous structure, and the diameter of the ZnO cluster is 3-30 mu m;
through Tauc model fitting calculation, the band gap width of the photocatalytic coating is 2.88-3.01 eV;
the preparation method of the photocatalytic coating comprises the following steps:
(1) preparing a zinc salt solution by using absolute ethyl alcohol-water as a solvent, adjusting the pH value of the zinc salt solution to 4-6, and adding a surfactant and nano titanium dioxide to obtain a spraying raw material;
(2) depositing the spraying raw material on the surface of a substrate by liquid material thermal spraying to obtain the ZnO/TiO2A heterostructure photocatalytic coating;
the zinc salt in the zinc salt solution is at least one selected from zinc nitrate, zinc acetate and zinc chloride;
the mass ratio of the zinc salt to the nano titanium dioxide is 5-100: 1;
the liquid material thermal spraying comprises liquid material atomization and thermal spraying, wherein the flow rate of the liquid material during the liquid material atomization is 100-120 mL/min.
2. The composition of claim 1 having ZnO/TiO2The preparation method of the heterostructure photocatalytic coating is characterized in that in the step (1):
in the solvent, the volume ratio of absolute ethyl alcohol to water is 1-4: 1;
the concentration of the zinc salt solution is 0.1-1 mol/L.
3. The composition of claim 1 having ZnO/TiO2The preparation method of the heterostructure photocatalytic coating is characterized in that in the step (1):
the surfactant is selected from at least one of polyethylene glycol, polyethyleneimine, ammonium citrate and polyacrylic acid;
the mass percentage of the surfactant is 5-20% of the mass of the nano titanium dioxide in the spraying raw material.
4. The composition of claim 1 having ZnO/TiO2The preparation method of the heterostructure photocatalytic coating is characterized in that in the step (2):
the substrate is selected from alumina, 45 steel, 316L stainless steel, polished silicon wafers or glass slides, and the substrate is pretreated before use.
5. The composition of claim 1 having ZnO/TiO2The preparation method of the photocatalytic coating with the heterostructure is characterized in that the technological conditions of liquid atomization are as follows: the diameter of the liquid material nozzle is phi 0.2-0.5 mm, and the angle formed by the liquid material and the flame flow is 90 degrees;
the thermal spraying is plasma spraying, and the technological parameters are as follows:
the current is 500-700A, the voltage is 45-60V, the spraying distance is 60-100 mm, the moving speed of the plasma spray gun is 200-600 mm/s, and the spraying times of the coating are 1-10 times.
6. ZnO/TiO compound obtained by the preparation method of claim 12The application of the photocatalytic coating with the heterostructure in the field of photocatalytic degradation of organic pollutants.
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