CN113617364B

CN113617364B - Preparation method and application of Ag/ZnO/CdS composite photocatalyst

Info

Publication number: CN113617364B
Application number: CN202110917170.6A
Authority: CN
Inventors: 常娜; 谢锋; 王海涛; 贾彦军; 邵伟; 赵晓旭; 张昊
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2021-08-12
Filing date: 2021-08-12
Publication date: 2023-07-25
Anticipated expiration: 2041-08-12
Also published as: CN113617364A

Abstract

The invention belongs to the field of nano material preparation and environmental protection, and discloses a preparation method of a composite photocatalyst Ag/ZnO/CdS. The method comprises the following steps: 1) Cadmium salt, sulfide and polyvinylpyrrolidone react under the high-temperature condition to prepare hexagonal crystal phase CdS crystals; 2) Respectively dissolving sodium hydroxide and zinc acetate into absolute ethyl alcohol, and mixing to obtain ZnO sol; 3) Respectively dissolving zinc nitrate and hexamethylenetetramine into deionized water, and mixing to obtain a ZnO solution; 4) Dispersing CdS crystals into ZnO sol, carrying out water bath reaction in ZnO solution to obtain a dispersion liquid containing ZnO/CdS, and obtaining ZnO/CdS after centrifugation, water washing and drying; 5) And dispersing ZnO/CdS powder in triethanolamine water solution, adding silver nitrate solution, and stirring under the irradiation of a light source to obtain the composite photocatalyst Ag/ZnO/CdS. The preparation method has the advantages of mild conditions, simple materials, uniform particles of the composite photocatalyst, strong stability, high photocatalytic activity, excellent antibacterial performance and good application prospect.

Description

Preparation method and application of Ag/ZnO/CdS composite photocatalyst

Technical Field

The invention relates to the field of preparation of semiconductor photocatalyst materials, in particular to a preparation method of a nano composite photocatalyst Ag/ZnO/CdS, a composite photocatalyst prepared by the preparation method and application of the composite photocatalyst in photocatalytic degradation of organic matters and antibiosis.

Background

With the rapid development of economy, environmental pollution, especially water pollution, is increasingly becoming a problem. The removal of soluble organic pollutants in polluted water and the sterilization and disinfection treatment are important and necessary links in the water resource regeneration and resource utilization process. As a novel environment-friendly technology capable of directly utilizing solar energy to realize the functions of energy conversion, pollutant degradation, sterilization, disinfection and the like, the semiconductor photocatalysis technology has very wide development and application prospect. In general, a photocatalytic reaction uses a semiconductor as a catalyst, and electrons in a valence band of the semiconductor can be transferred to a conduction band of a high energy level under an illumination condition (i.e., light is used as energy). Holes (h) ⁺ ) Transition electrons in conduction band (e ^- ) Superoxide anion radical (O) derived therefrom ₂ ^- ) The hydroxyl radical (OH) can be used as an active species to enable the organic pollutants to undergo oxidation-reduction reaction and mineralization decomposition, so that the effects of reducing and removing the organic pollutants are realized. Furthermore, superoxide anion radical (. O) ₂ ^- ) Hydroxyl free radicals (OH) are taken as two most common reactive oxygen species (reactive oxygen species, ROS), can penetrate the cell membrane of bacteria, damage fatty acid chains, enzymes and DNA in the bacterial cells, inactivate and die the cells, and finally achieve the effect of killing the bacteria.

At present, the design of the novel photocatalyst mainly surrounds two ideas: firstly, the minimum energy (namely band gap energy, also called forbidden band width) required by the electron conduction band transition of the semiconductor valence band is reduced, and the reduction of the band gap energy can make the semiconductor photocatalyst more fully use sunlight (mainly visible light with the occupation ratio of about 46 percent) to realize the electron transition and complete the oxidation-reduction reaction; second, increasing the potential of the conduction band and the valence band, and promoting the conversion of the valence band holes and conduction band electrons into super-electronsOxygen anion free radical and hydroxyl free radical to achieve better oxidation-reduction effect and sterilization effect. Wherein water or hydroxyl ions (H ₂ O/OH ^- ) The potential required for conversion to OH should be higher than 1.99V, dissolving oxygen (O) ₂ ) Conversion to O ₂ ^- The required potential should be higher than-0.33V.

As a semiconductor photocatalytic material which has been developed earlier, znO has many incomparable advantages such as good conductivity, photoelectrochemical properties, lower biotoxicity, higher chemical stability, thermal stability and the like, so that ZnO exhibits good application prospects in the field of photoelectrocatalysis. The band gap energy of ZnO material is higher, about 3.3V, the valence band potential is about 2.9V, the conduction band potential is about-0.4V, which are respectively higher than (H ₂ O/. OH) and (O ₂ /·O ₂ ^- ) Therefore, two active oxygen groups can be simultaneously generated, and the promotion of photocatalytic activity and sterilization performance is promoted. But on the other hand, since the band gap energy is higher than 2.9V (critical band gap energy excited by visible light), znO can realize a photocatalytic reaction only under the condition of ultraviolet light illumination, i.e., the valence band electrons of ZnO are difficult to excite to the conduction band under the condition of visible light illumination. The ultraviolet light accounts for only 5% of the total wavelength of sunlight, so that the sunlight is not fully utilized, and the development of the ZnO photocatalytic material is limited by the problem.

CdS, which is a semiconductor material with a low band gap energy (2.4 eV), is often used as a photoactive material to promote absorption of visible light. Since the band gap energy of CdS is lower than 2.9V, it can generate photo-generated electrons and holes under the irradiation of visible light, and induce the photocatalytic reaction to occur and proceed, which is a significant advantage of CdS materials. The CdS conduction band potential is about-0.6V, higher than (O ₂ /·O ₂ ^- ) But, since the valence band potential thereof is about 1.8V, is lower than (H ₂ O/. OH), so CdS can only produce. O ₂ ^- The active oxygen groups can not generate OH active oxygen groups, which is unfavorable for improving the photocatalytic activity and the sterilization performance to a certain extent.

The two examples above demonstrate that a single component lightThe contradictory problems faced in the catalyst design and preparation process are: the reduction of the band gap energy can improve the utilization rate of visible light, but the potential of a conduction band and a valence band is too low to simultaneously generate O ₂ ^- And an active oxygen group such as OH; conversely, increasing the conduction and valence band potentials can produce more reactive oxygen groups, but the band gap energy increases accordingly. How to coordinate the contradiction between the band gap energy and the conduction and valence band potentials, and simultaneously, the band gap energy of the material is reduced while the higher conduction and valence band potentials are maintained, so that the research direction is very challenging.

The preparation of binary or multi-component composite photocatalytic materials is an effective approach to solve the above problems. At present, a specific method is adopted to prepare a composite photocatalytic material from ZnO and CdS. In addition, examples of preparing ZnO, cdS, noble metal ternary composite photocatalytic materials have also been reported based on Surface Plasmon Resonance (SPR) effect of noble metals such as gold (Au), silver (Ag), platinum (Pt), etc., to enhance the absorption of visible light and electron transfer properties. However, in the prior reports, most of ZnO nanorods are prepared first, then CdS nanocrystals are attached or embedded on the surfaces of the ZnO nanorods, namely, cdS is located on a shell layer or an outer layer, light absorption and photocatalysis reactions are mainly carried out through CdS, and the ZnO on the inner layer only plays a role in electron transfer. This strategy can solve the problem of too high band gap energy, but too low a CdS valence band potential does not produce O ₂ ^- The problem of CdS is not solved, and meanwhile, cdS nano crystals are also fallen off when CdS is positioned on the outer layer of the composite material, and the problem of biotoxicity caused by dispersing or dissolving Cd ions in water is not ignored. However, examples of preparing CdS into crystals with a certain structural morphology and attaching ZnO nanorods to the CdS surface have been hardly reported. The strategy adopted by the invention is that CdS is prepared into submicron crystals, the submicron crystals are positioned on a core layer, znO materials are coated on the surface of the CdS, on one hand, the leakage of the CdS is reduced by increasing the particle size of the CdS and coating of the ZnO, on the other hand, the bandgap energy of the composite photocatalyst is reduced by utilizing the light absorption characteristic of the core layer CdS, and meanwhile, the generation of active oxygen species is promoted by utilizing the high valence band and conduction band potential of the surface layer ZnO, so that the photocatalysis is enhancedSterilization performance. Finally, the visible light absorption performance and the electron transfer performance of the surface ZnO are further enhanced by the SPR effect of Ag attached to the surface of ZnO, so that the better photocatalytic degradation efficiency and the better antibacterial performance are achieved under the condition of simulating sunlight.

Disclosure of Invention

[ technical problem ]

The preparation process of the photocatalyst is faced with the contradiction between the reduction of band gap energy, the improvement of light utilization rate and the improvement of conduction band and valence band potential to generate more active oxygen groups, namely the improvement of the conduction band and valence band potential is faced with the problem of the increase of band gap energy. Aiming at the existing problems, a preparation method of an Ag/ZnO/CdS composite photocatalyst is provided, namely, cdS is prepared into submicron crystals, znO nano rods are coated on the surface of the CdS, and finally Ag is attached to ZnO. The advantages are mainly that: first, reducing the leakage of CdS by increasing the particle size of CdS and coating ZnO; secondly, by utilizing the light absorption characteristic of the nuclear layer CdS, the band gap energy of the composite photocatalyst is reduced, and the absorption of light energy is enhanced; thirdly, the generation of Reactive Oxygen Species (ROS) is promoted by utilizing higher valence band and conduction band potentials of ZnO of a shell layer, so that the promotion of photocatalytic activity and sterilization performance is realized; fourth, the visible light absorption performance and the electron transfer performance of the surface ZnO are further enhanced through the SPR effect of Ag attached to the surface ZnO, and finally, the better photocatalytic reaction activity and the better antibacterial performance are achieved under the condition of simulating sunlight.

Technical scheme

In order to achieve the above object, according to one embodiment of the present invention, there is provided a method for preparing a composite photocatalyst ZnO/CdS/Ag.

In a first aspect, the preparation method of the Ag/ZnO/CdS composite photocatalyst provided by the application adopts the following technical scheme:

the preparation method of the Ag/ZnO/CdS composite photocatalyst comprises the following steps:

(1) Respectively dissolving cadmium salt, sulfide and polyvinylpyrrolidone in deionized water, and reacting for several hours under the high-temperature condition to prepare hexagonal crystal phase CdS crystals;

(2) Preparing ZnO sol: dissolving sodium hydroxide into absolute ethyl alcohol to obtain a solution A, dissolving zinc acetate into absolute ethyl alcohol to obtain a solution B, and then mixing the solution A and the solution B to obtain ZnO sol;

(3) Preparing ZnO solution: zinc nitrate is dissolved in deionized water to obtain a solution C, hexamethylenetetramine is dissolved in the deionized water to obtain a solution D, and then the solution C and the solution D are mixed to obtain a ZnO solution;

(4) Dispersing CdS crystals into ZnO sol, carrying out water bath reaction in ZnO solution to obtain a dispersion liquid containing ZnO/CdS, and centrifuging, washing and drying to obtain ZnO/CdS;

(5) Dispersing ZnO/CdS powder in an aqueous solution of triethanolamine, then adding a silver nitrate solution, and stirring under the irradiation of a xenon lamp light source to obtain a composite photocatalyst Ag/ZnO/CdS;

by adopting the technical scheme, the preparation method adopts submicron CdS as a core layer, disperses the submicron CdS in ZnO sol and a solution for water bath reaction to prepare ZnO/CdS, and inlays nano Ag on the surface of ZnO by adopting a photo-reduction method to prepare the composite photocatalyst Ag/ZnO/CdS. According to the preparation method, cdS is located in the core layer, the particle size of the CdS is increased, leakage of the CdS can be effectively reduced, meanwhile, the light absorption characteristic of the CdS can be utilized, and the band gap energy of the composite photocatalyst is reduced. The ZnO nano rod is positioned on the shell layer, and the high valence band and conduction band potential of the ZnO nano rod can be utilized to promote the generation of active oxygen species, so that the photocatalytic degradation efficiency and the sterilization performance are greatly enhanced. According to the preparation method, nano Ag is inlaid on the surface of the shell ZnO, so that the light absorption performance and the electron transfer performance of the composite material can be further enhanced, and higher photocatalytic degradation efficiency and sterilization performance can be obtained.

In summary, three materials are reasonably designed and set to be specific weight percentages, and meanwhile, the reaction conditions are controlled within a specific range, so that the prepared composite photocatalyst has high photocatalytic activity and high photocatalytic sterilization performance, breaks through the contradiction problem between the band gap energy and the valence band of the photocatalyst, gives consideration to the low band gap energy, high conduction band and high valence band potential, and has good application prospect.

In the step (1), the cadmium salt can be selected from any one of cadmium nitrate, cadmium chloride or cadmium sulfate, preferably cadmium nitrate; the concentration of the cadmium salt is 50-200 mmol/L, preferably 100mmol/L; the sulfide is selected from one of thiourea or thioacetamide, and is preferably thiourea; the molar ratio of the cadmium salt to the sulfide is 6:1 to 1:6, and is preferably 300mmol/L; the mass concentration of the polyvinylpyrrolidone is 4-8 g/L, preferably 6g/L; the reaction temperature is 100-300 ℃, preferably 200 ℃; the reaction time is 1 to 10 hours, preferably 5 hours.

In the step (2), the concentration ratio of the sodium hydroxide to the zinc acetate is 4:1 to 1:1, preferably 3:1; the volume ratio is 1:5 to 3:5, preferably 2:5.

In the step (3), the molar ratio of zinc nitrate to hexamethylenetetramine in the ZnO solution is 3:1 to 1:6, preferably 1:1.

In the step (4), the dispersion concentration of the CdS crystal in the ZnO sol is 0.005-0.3 g/mL, preferably 0.03g/L; the water bath reaction temperature is 90-100 ℃, preferably 95 ℃; the reaction time is 6 to 12 hours, preferably 7 hours.

In the step (5), the ZnO/CdS dispersion liquid is a mixed liquid of water and triethanolamine, and the volume ratio is 5:1 to 1:1, preferably 4:1; the mass concentration of the ZnO/CdS dispersion liquid is 1g/L to 3g/L, preferably 2g/L; the AgNO ₃ The mass ratio of ZnO/CdS is 1:100 to 1:20, preferably 1:33; the AgNO ₃ The concentration of the aqueous solution is 7 to 9mol/L, preferably 8.88mol/L; the xenon lamp irradiation time is 45-60 minutes, preferably 60 minutes.

According to the embodiment of the invention, the preparation method and the prepared composite photocatalyst Ag/ZnO/CdS are applied to degradation of methylene blue in water and photocatalysis sterilization.

Material source

Cadmium nitrate, cadmium chloride, cadmium sulfate, thiourea, thioacetamide, zinc nitrate, zinc acetate, absolute ethyl alcohol, triethanolamine, silver nitrate (AgNO) ₃ ) Aggregation ofVinyl Pyrrolidone (PVP), sodium hydroxide (NaOH) and hexamethylenetetramine are all analytically pure and purchased from national pharmaceutical chemicals Co.

[ advantageous effects ]

Aiming at the contradiction problem faced by single-component photocatalyst, namely that the reduction of band gap energy can improve the utilization rate of visible light, but the potential of conduction band and valence band is too low to simultaneously generate O ₂ ^- And active oxygen groups such as OH, the potential of a conduction band and a valence band can be increased to generate more active oxygen groups, but the band gap energy can be increased along with the potential of the conduction band and the valence band, which contradicts the potential of the conduction band and the valence band, and the potential of the conduction band and the valence band, in contrast to the conventional preparation thought (namely, the CdS is coated with ZnO), the composite photocatalytic material of the ZnO coated with the CdS is designed and prepared, and the nano silver is adopted to modify the ZnO nano rod, so that the following beneficial effects are generated:

preparing CdS into submicron crystals, positioning the submicron crystals on a core layer, coating ZnO materials on the surface of the CdS, on one hand, reducing the leakage of the CdS by increasing the particle size of the CdS and coating ZnO, on the other hand, reducing the band gap energy of the composite photocatalyst by utilizing the light absorption characteristic of the core layer CdS, and simultaneously, promoting the generation of active oxygen species by utilizing the high valence band and conduction band potential of the surface ZnO, and enhancing the photocatalytic and sterilization performances. Finally, the visible light absorption performance and the electron transfer performance of the surface ZnO are further enhanced by the SPR effect of Ag attached to the surface of ZnO, and the separation effect of electrons and holes is enhanced. So as to achieve the most excellent photocatalytic degradation efficiency and photocatalytic antibacterial performance under the condition of simulating sunlight. Meanwhile, the Ag/ZnO/CdS prepared by the method has stable structure, and the operation process is simple and feasible, so that the method is an efficient and low-waste green environment-friendly technology.

Description of the drawings:

FIG. 1A is a schematic illustration of an Ag/ZnO/CdS composite photocatalyst prepared according to the scheme described in example 1;

FIG. 2A is a schematic diagram of an Ag/ZnO/CdS composite photocatalyst prepared according to the scheme described in example 2;

FIG. 3A-C composite photocatalyst of Ag/ZnO/CdS prepared according to the scheme described in example 4;

FIG. 4 CdS crystals prepared according to the scheme described in example 5;

FIG. 5 CdS crystals prepared according to the scheme described in example 6;

FIG. 6A ZnO nanorods prepared according to the scheme described in example 7;

FIG. 7 is a ZnO nano-rod prepared according to the scheme described in example 8;

FIG. 8A-B-C composite photocatalyst prepared by the scheme described in example 9;

FIG. 9A-B composite photocatalyst of Ag/ZnO/CdS prepared according to the scheme described in example 10;

FIG. 10A-C is a schematic illustration of an Ag/ZnO/CdS composite photocatalyst prepared according to the scheme described in example 12;

FIG. 11A-C is a schematic illustration of an Ag/ZnO/CdS composite photocatalyst prepared according to the scheme described in example 13;

FIG. 12 is a CdS crystal prepared according to the scheme described in comparative example 1;

FIG. 13 is a ZnO nano-rod prepared according to the scheme described in comparative example 2;

FIG. 14 is a ZnO/CdS composite photocatalyst prepared according to the scheme described in comparative example 3;

FIG. 15 is a CdS/ZnO composite photocatalyst prepared according to the scheme described in comparative example 4;

FIG. 16 is a schematic diagram of a Ag/CdS/ZnO composite photocatalyst prepared according to the scheme described in comparative example 5;

FIG. 17 is a ZnO/Ag/CdS composite photocatalyst prepared according to the scheme described in comparative example 6;

FIG. 18 XRD patterns of the photocatalysts prepared in accordance with the schemes described in example 1 and comparative examples 1-3;

FIG. 19 is a graph of the impedance spectrum and the photoelectric flow of the photocatalyst prepared according to the scheme described in example 1 and comparative examples 1-3;

FIG. 20 is a graph showing fluorescence spectra of the photocatalysts prepared in the schemes described in example 1 and comparative examples 1-3;

FIG. 21 is a graph showing active species capture under light conditions for Ag/ZnO/CdS prepared according to the scheme described in example 1.

Detailed Description

In order that the present invention may be more clearly understood by those skilled in the art, the following description will be made in detail with reference to examples, but it should be understood that the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited thereto.

< example >

Example 1:

the preparation method of the composite photocatalyst Ag/ZnO/CdS comprises the following steps:

(1) Preparing CdS crystals: dissolving 0.005mol of cadmium nitrate and 0.015mol of thiourea in 50mL of deionized water, stirring for 1 hour, adding 0.3g of polyvinylpyrrolidone powder, continuously stirring for 30 minutes until the solution is clear, transferring the solution into a reaction kettle, and reacting for 5 hours at a constant temperature of 200 ℃;

(2) Preparing ZnO sol: dissolving 0.6mmol of sodium hydroxide solution into 20mL of absolute ethyl alcohol, uniformly stirring to obtain solution A, dissolving 0.5mmol of zinc acetate into 50mL of absolute ethyl alcohol, stirring to obtain solution B, mixing the solution A and the solution B, stirring for 2 hours at 60 ℃ to obtain ZnO sol, and standing for 12 hours for later use;

(3) Preparing ZnO solution: dissolving 0.01mol of zinc nitrate and 0.01mol of hexamethylenetetramine in 100mL of deionized water, and uniformly stirring for the subsequent step;

(4) Preparation of ZnO/CdS: dispersing 0.3g of CdS crystal in 10mL of ZnO sol, fully stirring for 30 minutes to enable ZnO crystal seeds to be adsorbed on the surfaces of the CdS crystal, transferring the dispersion liquid into 100mL of ZnO solution, carrying out water bath reaction for 7 hours at 95 ℃, washing the obtained solid by adopting deionized water, centrifuging, and drying at 60 ℃;

(5) Preparation of Ag/ZnO/CdS: 0.3g ZnO/CdS was dispersed in 150mL triethanolamine aqueous solution (water to triethanolamine volume ratio of 4:1), then 6mL silver nitrate aqueous solution (concentration of 8.88 mol/L) was added, stirred for 1 hour under 220W xenon lamp irradiation, followed by washing with ethanol, centrifugation, and drying at 60℃to obtain the final product.

Example 2:

the specific steps are the same as those of the embodiment 1, except that the cadmium salt selected in the step (1) is cadmium chloride, and the rest conditions are unchanged.

Example 3:

the specific steps are the same as those of the embodiment 1, except that the cadmium salt selected in the step (1) is cadmium sulfate, and the rest conditions are unchanged.

Example 4:

the specific procedure is identical to example 1, except that the sulfide selected in step (1) is thioacetamide, the remaining conditions being unchanged.

Example 5:

the specific procedure is identical to example 1, except that in step (1) the molar ratio of cadmium salt to sulfide is 1:1, specifically 0.005mol of cadmium nitrate and 0.005mol of thiourea, the remaining conditions being unchanged.

Example 6:

the specific procedure is identical to example 1, except that in step (1) the molar ratio of cadmium salt to sulfide is 1:6, specifically 0.005mol of cadmium nitrate and 0.030mol of thiourea, the remaining conditions being unchanged.

Example 7:

the specific procedure is identical to example 1, except that in step (3) the molar ratio of zinc nitrate to hexamethylenetetramine is 2:1, in particular 0.01mol of zinc nitrate and 0.005mol of hexamethylenetetramine, the remaining conditions being unchanged.

Example 8:

the specific procedure is identical to example 1, except that in step (3) the molar ratio of zinc nitrate to hexamethylenetetramine is 1:5, in particular 0.01mol of zinc nitrate and 0.05mol of hexamethylenetetramine, the remaining conditions being unchanged.

Example 9:

the specific procedure was the same as in example 1, except that in step (4), the mass of CdS was 0.1g, and the remaining conditions were unchanged.

Example 10:

the specific procedure was identical to example 1, except that in step (4) the mass of CdS weighed was 1.0g, with the remaining conditions unchanged.

Example 11:

the specific procedure was identical to example 1, except that the water bath time in step (4) was 9 hours, with the remaining conditions unchanged.

Example 12:

the specific procedure was identical to example 1, except that the water bath time in step (4) was 12 hours, with the remaining conditions unchanged.

Example 13:

the specific procedure was identical to example 1, except that 9mL of silver nitrate solution was added in step (5), with the remaining conditions unchanged.

Example 14:

the specific procedure was identical to example 1, except that 3mL of silver nitrate solution was added in step (5), with the remaining conditions unchanged.

Comparative example 1:

CdS was prepared and used as a photocatalyst by the method of example 1, step (1).

Comparative example 2:

the ZnO nanorods were prepared and used as a photocatalyst by the method of steps (2), (3) and (4) in example 1, except that CdS solid was not added in step (4), and the remaining conditions were unchanged.

Comparative example 3:

ZnO/CdS was prepared and used as a photocatalyst in the steps (1) (2) (3) (4) in example 1.

Comparative example 4:

preparing CdS coated ZnO nano-rods as a photocatalyst, namely preparing CdS/ZnO, specifically:

(1) ZnO nanorods were prepared by the method of comparative example 2;

(2) Preparation of CdS/ZnO: dissolving 0.005mol of cadmium nitrate and 0.015mol of thiourea in 50mL of deionized water, stirring for 1 hour, adding 0.2g of polyvinylpyrrolidone powder, continuously stirring for 30 minutes until the solution is clear, then adding 0.9g of ZnO nanorods prepared in the step (1), uniformly stirring, transferring the solution into a 100mL reaction kettle, reacting for 5 hours at the constant temperature of 200 ℃, washing with deionized water, centrifuging, and drying at the temperature of 60 ℃ to obtain CdS/ZnO.

Comparative example 5:

preparing Ag/CdS coated ZnO nano-rods as a photocatalyst, namely preparing Ag/CdS/ZnO, wherein the preparation method specifically comprises the following steps: 0.3g of the CdS/ZnO powder prepared in step (2) of comparative example 4 was taken and Ag/CdS/ZnO was prepared in the same manner as in step (5) of example 1.

Comparative example 6:

preparing ZnO nanorod coated Ag/CdS as a photocatalyst, namely preparing ZnO/Ag/CdS, specifically:

(1) CdS crystals were prepared by the same method as in step (1) of example 1;

(2) An Ag/CdS composite catalyst was prepared by the method in step (5) of example 1, except that 0.3g ZnO/CdS in step (5) was changed to 0.3g CdS;

(3) A ZnO/Ag/CdS composite photocatalyst was prepared by the method in steps (2), (3) and (4) in example 1, except that 0.3g of CdS in step (4) was changed to 0.3g of Ag/CdS.

Experimental example 1]

Methylene blue is a dark green bronze-containing glossy powder having the formula: c (C) ₁₄ H ₁₈ N ₃ ClS A phenothiazine salt, which is generally soluble in ethanol and water, insoluble in ether species, exhibits alkalinity. Methylene blue is generally used widely in chemical reagents, dyes, printing and dyeing industries and in pharmaceuticals. In the invention, 150mL of methylene blue solution with the concentration of 20mg/mL is firstly prepared, then 80mg of catalyst is added, the mixture is irradiated for 30 minutes under the condition of a 220W simulated sunlight source (AM 1.5 light sheet), samples are taken every 5 minutes, and the supernatant is measured by an ultraviolet-visible spectrophotometer to obtain the absorbance (the maximum absorption peak position lambda of methylene blue) at 664nm wavelength _max =664 nm). By measuring the change in absorbance a of methylene blue over time, and by the formula: d (D) _r ＝(A ₀ -A)/A ₀ 100%, calculate the photocatalytic degradation efficiency (D _r ) Wherein A is ₀ The initial absorbance of methylene blue is the absorbance of the methylene blue solution measured at time t, and t is the reaction time. The photocatalysts prepared in examples 1 to 14 and comparative examples 1 to 6 were subjected to photocatalytic degradation efficiency tests by the above-described methods, respectively, and the test results are shown in table 1:

TABLE 1

Experimental example 2]

Bacteria are widely distributed in daily environment, and the bacteria exceeding the standard easily cause human infection and pathogenicity, thereby endangering human health. In the invention, gram-negative bacteria (escherichia coli) and gram-positive bacteria (staphylococcus aureus) are selected as representative strains for photocatalysis sterilization experiments. The staphylococcus aureus (or escherichia coli) on the slant culture medium is hooked by an inoculating loop to 100mL of liquid culture medium for culturing for 12 hours to obtain a standby bacterial solution (the bacterial concentration is about 10 ⁶ ～10 ⁷ CFU/mL). Preparing Ag/ZnO/CdS dispersion liquid with the concentration of 0.25mg/mL, respectively adding 100 mu L of standby bacterial liquid into 30mL of Ag/ZnO/CdS dispersion liquid with different concentrations, respectively setting an illumination group (220W xenon lamp irradiates, a light source is 20cm away from the dispersion liquid) and a dark group (dark box is dark), comparing, standing for 30 minutes, respectively adding 100 mu L of reaction liquid into 9.9mL of sterile water, uniformly coating 100 mu L of diluent into a solid culture medium, culturing for 24 hours in a constant temperature incubator at 37 ℃, observing the number of colonies, adopting a colony counting method and adopting the following formula: η= (N) ₀ -N)/N ₀ X 100% calculated sterilization rate, where N ₀ The number of blank colonies was counted, and N was the number of immediate colonies. The blank group was subjected to experiments with 100. Mu.L of the bacterial liquid added to 30mL of deionized water under a dark condition. The photocatalytic antibacterial experiments were performed using the photocatalysts prepared in examples 1 to 14 and comparative examples 1 to 6, respectively, by the above-described methods, and the test results are shown in table 2:

TABLE 2

As can be seen from tables 1, 2 and figures 1-3, the ZnO nanorods are obviously positioned on the shell layer, and the composite photocatalyst prepared in the embodiment 1-4 only needs 30 minutes under the sunlight condition, the removal rate of methylene blue can reach more than 99%, and the sterilization rate of staphylococcus aureus and escherichia coli can reach more than 94%, so that the composite photocatalyst prepared in the embodiment 1-4 has high photocatalytic degradation efficiency, strong sterilization capability, excellent organic matter degradation removal and sterilization capability on wastewater, and good practical effect and application prospect.

Examples 5 to 6, compared with example 1, changed the ratio of cadmium salt to sulfur source in step (1) of example 1, wherein the molar ratio of cadmium salt to sulfur source in example 5 was 1:1, and the particle size of the synthesized CdS was reduced (as shown in fig. 4) due to the reduced amount of sulfur source, which is unfavorable for the adsorption of ZnO seed crystals, so that the compounding effect of CdS and ZnO nanorods was poor, thereby reducing the photocatalytic effect, but the sterilizing rate was improved compared with example 1 due to the small particle size of CdS particles, which is easily dispersed in solution. In the embodiment 6, the molar ratio of the cadmium salt to the sulfur source is 1:6, so that the dosage of the sulfur source is increased, the cadmium salt fully reacts, and meanwhile, the overall size of the CdS crystal is increased (as shown in fig. 5), so that the ZnO nano rod is unfavorable for coating the CdS crystal, and the exposure of the CdS crystal is increased, and therefore, compared with the embodiment 1, the photocatalysis effect is slightly reduced, but the sterilization rate is improved compared with the embodiment 1.

Examples 7 to 8, in which the molar ratio of zinc nitrate to hexamethylenetetramine in step (3) of example 1 was changed as compared with example 1, wherein example 7 reduced the amount of hexamethylenetetramine, znO nanorods were reduced in size (as shown in fig. 6), the degree of crystallization was reduced, example 8 increased the amount of hexamethylenetetramine, znO nanorods were increased in diameter (as shown in fig. 7), the electron transport resistance was increased, and electron transfer with CdS and separation of electrons and holes were adversely affected, and thus, the photocatalytic degradation efficiency of examples 7 to 8 was slightly reduced as compared with example 1, and the sterilization performance was also reduced.

Examples 9 to 10, compared with example 1, changed the mass of CdS dispersed in the ZnO sol in step (4) of example 1, wherein the addition amount of CdS in example 9 was reduced to 0.1g, and the coated ZnO nanorods on the surface were too dense and have poor morphology (as shown in FIG. 8) due to the smaller amount of CdS, the light absorption characteristics of the core layer CdS could not be utilized, and the problem of agglomeration of ZnO nanorods could not be solved, so that the photocatalytic degradation rate and the sterilization rate were slightly reduced compared with example 1; in example 10, the addition amount of CdS was increased to 1.5g, the ZnO nanorods could not completely encapsulate CdS, a large amount of free ZnO nanorods were generated, and both could not form a uniform composite structure (as shown in fig. 9), resulting in increased leakage of CdS, significantly reduced photocatalytic degradation efficiency compared with example 1, but slightly improved sterilization performance.

The water bath reaction time of the step (4) of the embodiment 1 is prolonged in the embodiments 11-12 compared with the embodiment 1, the morphology of the obtained composite photocatalyst is not changed remarkably (as shown in fig. 10), the photocatalytic degradation rate and the sterilization rate are not changed remarkably, and the water bath time is 7 hours, so that the reaction is complete.

Compared with the embodiment 1, the embodiment 13-14 changes the addition amount of the silver nitrate solution in the step (5) of the embodiment 1, wherein the addition amount of the silver nitrate in the embodiment 13 is 9mL, the Ag particle loading rate on the surface of the ZnO nano rod is higher (as shown in fig. 11), and compared with the embodiment 1, the photocatalytic degradation rate is not changed significantly, and meanwhile, the sterilization rate is improved compared with the embodiment 1 because the Ag has sterilization performance; in example 14, the amount of silver nitrate added was 3mL, and since the amount of silver particles supported on the ZnO surface was small, the light absorption and electron conduction properties (SPR effect) of nano Ag could not be fully exhibited, and the photocatalytic degradation rate was slightly lower than in example 1.

In comparative examples 1-2, pure CdS (as shown in fig. 12) and pure ZnO (as shown in fig. 13) synthesized under the same conditions are used as photocatalysts, and the CdS valence band potential is low, so that hydroxyl radicals cannot be generated, the ZnO forbidden band width is high, electrons are difficult to transition and transfer, the photocatalytic degradation rate of both is significantly lower than that of example 1, but the sterilizing rate is slightly higher than that of example 1 due to biotoxicity generated by CdS exposure.

In comparative example 3, znO-coated CdS composite photocatalyst ZnO/CdS (as shown in fig. 14), compared with example 1, the ZnO surface lacks the load of nano Ag, and thus the light absorption and electron conduction properties (SPR effect) of nano Ag cannot be fully exerted, and the photocatalytic degradation rate and sterilization rate are reduced compared with example 1.

Comparative example 4 is a composite photocatalyst in which CdS coats ZnO nanorods, that is, cdS/ZnO (as shown in fig. 15), comparative example 4 has the same composition as that of the photocatalyst described in comparative example 3, but has the opposite loading relationship, and the photocatalytic degradation rate is significantly lower than that of example 1 and comparative example 3, which indicates that when CdS is located in the outer layer, the problem of too low potential of the valence band of CdS cannot be overcome, and furthermore, cdS/ZnO maintains a relatively high sterilizing effect due to the exposure of CdS.

Comparative example 5 the Ag/CdS/ZnO composite photocatalyst was formed on the basis of comparative example 4, i.e., the Ag/ZnO/CdS composite photocatalyst prepared by the scheme described in example 1 was completely identical in composition, but ZnO was inversely supported with CdS, and the photocatalytic degradation rate of comparative example 5 was significantly lower than that of example 1, indicating that the catalytic activity of the photocatalyst was not enhanced when CdS was in the outer layer of ZnO, but the sterilization rate of comparative example 5 was substantially equal to that of example 1 because CdS crystals of comparative example 5 were relatively in the outer layer.

In the comparative example 6, the ZnO nanorod coated Ag/CdS and the ZnO/Ag/CdS is used as a composite photocatalyst (as shown in FIG. 17), compared with the comparative example 1, the photocatalytic degradation rate is remarkably reduced, because the nano Ag is coated in the ZnO, the light absorption and electron transfer properties of the Ag are difficult to exert, and the overall photocatalytic degradation activity is reduced; further, since both Ag and CdS were coated with ZnO, the sterilization performance was not enhanced, and the sterilization performance was lowered as compared with comparative example 1.

The above examples and comparative examples show that even though the components of the photocatalyst are completely the same, the photocatalytic degradation effect and the sterilization effect will be significantly different due to the loading relationship and the different structures of the inner and outer layers of the material, and the photocatalytic degradation effect and the sterilization effect can be effectively improved by placing ZnO on the CdS outer layer and loading nano Ag on the ZnO surface.

Furthermore, the (1) XRD patterns (as shown in FIG. 18) of the photocatalysts prepared by the schemes described in example 1 and comparative examples 1 to 3 confirm the presence of Ag simple substance, znO and CdS crystals, i.e., the preparation of the composite photocatalyst Ag/ZnO/CdS was successful; (2) the impedance diagram and the photoelectric diagram (shown in figure 19) prove that the photocurrent intensity of the composite photocatalyst Ag/ZnO/CdS is the largest and the electron transmission resistance is the smallest; (3) the fluorescence spectrum (shown in figure 20) shows that the composite photocatalyst Ag/ZnO/CdS has the lowest electron and hole recombination probability, namely the highest utilization rate of photoelectrons and holes; (4) the active species trapping graph (shown in figure 21) proves that the composite photocatalyst Ag/ZnO/CdS can simultaneously generate holes (the trapping agent is triethanolamine), hydroxyl free radicals (the trapping agent is isopropanol) and superoxide anion free radicals (the trapping agent is vitamin C) under the illumination condition.

The embodiments of the present invention are all preferred embodiments of the present application, and are not intended to limit the scope of the present application in this way, therefore: all equivalent changes in structure, shape and principle of this application should be covered in the protection scope of this application.

Claims

1. The preparation method of the composite photocatalyst Ag/ZnO/CdS is characterized by comprising the following steps:

(5) And dispersing ZnO/CdS powder in an aqueous solution of triethanolamine, then adding a silver nitrate solution, and stirring under the irradiation of a xenon lamp light source to obtain the composite photocatalyst Ag/ZnO/CdS.

2. The method for preparing the composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (1)

The cadmium salt is at least one of cadmium nitrate, cadmium chloride or cadmium sulfate;

the sulfide is at least one selected from thiourea or thioacetamide.

3. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (1),

the molar ratio of the cadmium salt to the sulfide is 6:1 to 1:6, and the concentration of the cadmium salt is 50-200 mmol/L;

the mass concentration of the added polyvinylpyrrolidone is 4-8 g/L.

4. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (1),

the reaction temperature is 100-300 ℃;

the reaction time is 1-10 hours.

5. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (2),

the concentration ratio of the sodium hydroxide to the zinc acetate is 4:1 to 1:1, and the volume ratio is 1:5 to 3:5.

6. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (3),

the molar ratio of zinc nitrate to hexamethylenetetramine in the ZnO solution is 3:1 to 1:6.

7. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (4),

the dispersion concentration of CdS crystal in ZnO sol is 0.005-0.3 g/mL;

the water bath reaction temperature is 90-100 ℃ and the reaction time is 6-12 hours.

8. The method for preparing a composite photocatalyst Ag/ZnO/CdS according to claim 1, wherein in the step (5),

the volume ratio of water to triethanolamine in the aqueous solution of triethanolamine is 5:1 to 1:1;

the ZnO/CdS powder is dispersed in an aqueous solution of triethanolamine, and the mass concentration of the ZnO/CdS is 1g/L to 3g/L;

the mass ratio of the silver nitrate to the ZnO/CdS is 1:100 to 1:20;

the silver nitrate solution is a silver nitrate aqueous solution with the concentration of 7-9 mol/L;

the irradiation time of the xenon lamp is 45-60 minutes.

9. An Ag/ZnO/CdS composite photocatalyst prepared by the preparation method of any one of claims 1 to 8.