CN113213579A

CN113213579A - Application of photocatalytic biochar composite material in catalytic degradation of printing and dyeing wastewater

Info

Publication number: CN113213579A
Application number: CN202110573354.5A
Authority: CN
Inventors: 王盛; 徐国敏; 张兵兵; 杨照; 薛斌; 陈蔚洁; 安明泽; 丁小艳; 娄金分
Original assignee: Guizhou Material Industrial Technology Research Institute
Current assignee: Guizhou Material Industrial Technology Research Institute
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2021-08-06
Anticipated expiration: 2041-05-25
Also published as: CN113213579B

Abstract

The invention provides an application of a photocatalytic biochar composite material in catalytic degradation of printing and dyeing wastewater. The photocatalytic biochar composite material provided by the invention is applied to catalytic degradation of printing and dyeing wastewater, wherein the photocatalytic biochar composite material comprises biochar and a ZnO/ZnS mixture, the loading rate of the ZnO/ZnS mixture is 14-20%, and the ZnO/ZnS mixture is loaded in micropores and/or on the surface of the biochar.

Description

Application of photocatalytic biochar composite material in catalytic degradation of printing and dyeing wastewater

Technical Field

The invention relates to the field of environment functional materials, in particular to a photocatalytic biochar composite material and a preparation method and application thereof.

Background

Textile dyeing and finishing are traditional prop industries and important civil industries in China, but the discharge amount of printing and dyeing wastewater is large, accounts for 60-80% of total water consumption of a factory, the annual discharge amount exceeds 15 hundred million tons, has the characteristics of high chromaticity, high toxicity, high organic matter content, high salinity, complex components, large water quality change and the like, is recognized industrial wastewater which is difficult to treat at home and abroad, and needs to be treated for three times or deeply. After advanced treatment, the printing and dyeing wastewater can be secondarily used for production, so that the pollution is reduced, the water is saved, the enterprise cost is reduced, and the method has important practical significance for realizing the green manufacturing technology of the textile industry.

Common advanced treatment methods include advanced oxidation, membrane biological methods, physical adsorption methods, photocatalytic oxidation methods and the like. Advanced oxidation processes (e.g., application publication nos. CN202499737U and CN102180558A) have extremely short free radical existence time and no selectivity, have high requirements for water distribution, have complex process, and may introduce secondary pollutants. The membrane biological method (such as application publication numbers of CN111285448A and CN210656547U) has high dye removal rate and simple process, but has high membrane cost and high process energy consumption, and the industrial popularization is limited. The physical adsorption method has simple process, and common adsorbents are activated carbon, biomass carbon and the like (such as application publication numbers CN111003744A and CN103803754A), but the preparation and regeneration of the activated carbon need high temperature (more than or equal to 850 ℃) so that the cost of the adsorbents is increased; the biomass charcoal is prepared by pyrolyzing biomass such as agricultural and forestry waste at low temperature (<700 ℃) in a complete or partial anoxic state, is rich in raw materials, simple to manufacture and low in cost, but has a limited adsorption effect and is not easy to regenerate. The photocatalytic oxidation method (such as application publication numbers CN110723777A, CN110683608A, and CN105384308A) has the advantages that the photocatalytic material is generally expensive, easily runs off in use, is not easily recycled, and needs an additional ultraviolet light source to stimulate catalytic reaction, thereby increasing the complexity and cost of the process. The simple and efficient low-cost advanced treatment technology for the printing and dyeing wastewater becomes the focus of increasing attention of people and the technical problem to be solved urgently.

Disclosure of Invention

Aiming at the problems in the prior art, the development of the advanced treatment method for the printing and dyeing wastewater, which has the advantages of simple process, high efficiency, low cost and easy large-scale popularization and application, is urgent.

The invention aims to solve the technical problems and finds that waste straw powder is coated with ZnSO₄The modified biochar is prepared by low-temperature pyrolysis after being fully soaked in the solution, and methylene blue organic macromolecules in the wastewater can be quickly removed under the condition of natural light. The surface of the modified biochar composite material is firmly combined with a large number of photocatalytic active points, organic dye molecules in wastewater are quickly adsorbed, the adsorbed dye molecules are oxidized and degraded under the induction and excitation of natural light, and the used modified biochar can be recycled after simple regeneration treatment, so that the effect is stable. The photocatalytic biochar composite material is simple in production process, short in production period and low in cost, breaks through the upper limit of the absorption of biochar by utilizing the catalytic degradation of natural light, does not need to be supported by an ultraviolet light source, greatly simplifies the wastewater treatment process and cost, can be recycled, and really realizes the low-cost advanced treatment of printing and dyeing wastewater.

The invention provides an application of a photocatalytic biochar composite material in catalytic degradation of printing and dyeing wastewater, wherein the photocatalytic biochar composite material comprises biochar and a ZnO/ZnS mixture, the loading rate of the ZnO/ZnS mixture is 14-20%, and the ZnO/ZnS mixture is loaded in micropores and/or on the surface of the biochar.

The loading ratio of the ZnO/ZnS mixture in the present invention is defined by (W)_UBC-W_BC)/W_UBCX 100% calculated, wherein, W_UBCAnd W_BCRespectively the quality of the photocatalytic biochar composite material and the straw biochar at different pyrolysis temperatures.

Preferably, the mass percentage of the Zn element in the surface element of the photocatalytic biochar composite material is 25-40%.

The mass percentage of the Zn element in the surface element of the photocatalytic biochar composite material is detected by an energy spectrometer.

Preferably, the specific surface area of the photocatalytic biochar composite material is 300-500m²·g^-1Preferably 330-²·g^-1；

Or, preferably, the pore volume of the photocatalytic biochar composite material is 0.220-0.330 cm³Per g, preferably from 0.240 to 0.330cm³/g。

Preferably, the solution chroma is 0.0-22.9 after 4g/L of the photocatalytic biochar composite material is added into 10-100mg/L of methylene blue solution for 1-30 h;

or its use in COD_crAfter 4g/L of the photocatalytic biochar composite material is added into 75-170mg/L for 1-30h, the COD of the solution is_crThe value is 0-11 mg/L;

or 4g/L of the photocatalytic biochar composite material is added into 10-100mg/L of methylene blue solution for 1-30h, and the degradation rate is 97-100%.

Preferably, the preparation method of the photocatalytic biochar composite material comprises the following steps:

(1) soaking the straw powder in a zinc source aqueous solution, and then drying to prepare a composite material precursor;

(2) and (2) placing the composite material precursor obtained in the step (1) in an inert gas atmosphere, preserving heat at 100-150 ℃, and then heating for pyrolysis to obtain the photocatalytic biochar composite material.

Preferably, the straw in the step (1) is any one of tobacco stem, corn straw, coix seed straw and sorghum straw and a mixture thereof.

Preferably, the zinc source aqueous solution in the step (1) is ZnSO₄An aqueous solution of a carboxylic acid and a carboxylic acid,

preferably, the ZnSO₄The mass concentration of the aqueous solution is 1-5%, preferably, the ZnSO₄The mass concentration of the aqueous solution is 3 to 5 percent, and the ZnSO is further optimized₄The mass concentration of the solution is 3 percent;

preferably, the ZnSO₄The mass ratio of the aqueous solution to the straw powder is (2-4) to 1, and preferably, the ZnSO is₄The mass ratio of the water solution to the straw powder is (2-3) to 1.

Preferably, the ZnSO of step (1)₄The temperature of the aqueous solution is 60-100 ℃, and preferably 80 ℃;

preferably, the straw powder is coated with ZnSO₄Soaking in the solution for 5-12 h, and further preferably soaking the straw powder in ZnSO₄Dipping in the solution for 8-10 h;

alternatively, preferably, the stirring rate is 100-,

or, preferably, the stirring time is 3-5 h, preferably 5 h;

or, preferably, the drying temperature is 60-100 ℃, preferably the drying temperature is 70-90 ℃,

or, preferably, the drying time is 10-24h, and preferably, the drying time is 10-13 h.

Preferably, the heat preservation temperature of the inert gas atmosphere in the step (2) is 100-120 ℃, preferably, the heat preservation time is 1-5 h, preferably, the heat preservation time is 1.5-3 h;

or, preferably, the pyrolysis temperature in the step (2) is 400-700 ℃, and preferably, the pyrolysis temperature is 600 ℃;

or, preferably, the heating rate is 8-10 ℃/min;

or, preferably, the pyrolysis time is 1-4 h and 2-2.5 h;

alternatively, preferably, the inert gas is N₂Or Ar;

or, preferably, the flow rate of the inert gas is 40-100 ml/min;

alternatively, preferably, the pyrolysis reaction is carried out in a tube furnace.

Preferably, the CODcr value of the printing and dyeing wastewater organic dye is lower than 200mg/L,

preferably, the pH value of the printing and dyeing wastewater is 6-9.

Preferably, the catalytic degradation reaction is performed under natural light.

The invention also provides a printing and dyeing wastewater treatment method, which comprises the following steps:

adding the photocatalytic biochar composite material in the application into printing and dyeing wastewater to be treated, and oscillating under natural light conditions to perform catalytic degradation reaction;

the photocatalytic biochar composite material comprises biochar and a ZnO/ZnS mixture, wherein the loading rate of the ZnO/ZnS mixture is 15-20%, and the ZnO/ZnS mixture is loaded in micropores and/or on the surface of the biochar.

Preferably, the specific surface area of the photocatalytic biochar composite material is 300-550m²·g^-1Preferably 340-380m²·g^-1；

Or, preferably, the pore volume of the photocatalytic biochar composite material is 0.220-0.330 cm³Per g, preferably from 0.250 to 0.270cm³/g。

the straw powder is in ZnSO₄Soaking in the solution for 5-12 h, and further preferably soaking the straw powder in ZnSO₄Dipping in the solution for 8-10 h;

alternatively, preferably, the stirring rate is 100-,

or, preferably, the stirring time is 3-5 h, preferably 5 h;

or, preferably, the drying temperature is 60-100 ℃, the drying temperature is 70-90 ℃,

or, preferably, the drying time is 10-24h and 10-13 h.

or, preferably, the heating rate is 8-10 ℃/min;

or, preferably, the pyrolysis time is 1-4 h and 2-2.5 h;

alternatively, preferably, the inert gas is N₂Or Ar;

or, preferably, the flow rate of the inert gas is 40-100 ml/min;

alternatively, preferably, the carbonization reaction is carried out in a tube furnace.

Preferably, the oscillation is carried out at a temperature of 28-32 ℃;

preferably, the oscillation frequency is 250-300 times/min;

preferably, the oscillation time is 1-30 h.

The beneficial effects of the invention include:

1. the photocatalytic biochar composite material is prepared by low-temperature pyrolysis of waste straws by an infiltration method, the production cost is greatly reduced compared with that of a common photocatalyst, the preparation process is simple, the preparation condition is mild, no secondary pollution is caused, the environment is friendly, the photocatalytic adsorption performance is quick and efficient, raw water with the CODcr value lower than 100mg/L is treated by low-temperature pyrolysis biochar at the temperature of 600 ℃, the removal rate is higher than 94% in 0.5h, and the removal rate reaches 100% in 1 h.

2. The regeneration process of the photocatalytic biochar composite material provided by the invention is simple to operate, low in cost, strong in settleability and small in mass loss, solves the problems that a common nano photocatalyst is easy to lose and difficult to recover in use, has the removal capacity of more than 95% of that of the original nano photocatalyst after five times of cyclic utilization, reduces the post-treatment cost of an enterprise on an adsorbent, and reduces the environmental pressure.

3. The method for deeply treating the organic dye wastewater by natural light catalytic adsorption has the advantages of no need of ultraviolet light source, simple treatment process and good treatment effect, can obtain 100 percent of decolored wastewater after 1 hour of treatment under the conditions that the concentration of the organic dye is lower than 30mg/L, the pH value of the wastewater is 7-7.5 and the CODcr value is lower than 100mg/L, is higher than the recycling standard, and meets the technical requirement of low-cost advanced treatment of the printing and dyeing wastewater.

Drawings

FIG. 1 is a nitrogen adsorption desorption isothermal curve of photocatalytic biochar composite in examples 1-4;

FIG. 2 is a graph of removal rate of methylene blue versus time of the photocatalytic biochar composite UBC400-700 under natural light in example 5;

FIG. 3 is a comparison FTIR chart of the photocatalytic biochar composite UBC600 before and after photocatalytic adsorption of methylene blue under natural light in example 5, wherein,

FIG. 3(a) is a graph of organic functional groups on the surface of a photocatalytic biochar composite UBC600 before and after wastewater treatment;

FIG. 3(b) is a graph of 1000-^-1Organic functional group diagrams of the surfaces of the wave band photocatalytic biochar composite material UBC600 before and after wastewater treatment;

FIG. 4(a) shows the mechanism of methylene blue light catalytic degradation,

FIG. 4(b) shows Zn²⁺A schematic electron transfer diagram;

FIG. 5(a) is an SEM photograph of a photocatalytic biochar composite UBC600 before wastewater treatment,

FIG. 5(b) is an SEM photograph of a photocatalytic biochar composite UBC600 after wastewater treatment,

FIG. 5(c) is an EDX photograph of photocatalytic biochar composite UBC600 before wastewater treatment,

FIG. 5(d) is an EDX photograph of photocatalytic biochar composite UBC600 prior to treatment of wastewater;

FIG. 6 is a graph comparing the removal rate of methylene blue with time under natural light and dark conditions for photocatalytic biochar composite UBC400-700 in example 5 and comparative example 1, wherein,

FIG. 6(a) is a comparison graph of the removal rate of methylene blue-time curve of the photocatalytic biochar composite UBC400 under natural light and dark conditions,

FIG. 6(b) is a comparison graph of the removal rate of the photocatalytic biochar composite UBC500 under natural light and dark conditions versus the methylene blue removal rate-time curve,

FIG. 6(c) is a comparison graph of the removal rate of methylene blue-time curve of the photocatalytic biochar composite UBC600 under natural light and dark conditions,

FIG. 6(d) is a graph comparing the removal rate of methylene blue versus time of a photocatalytic biochar composite UBC700 under natural light and dark conditions;

fig. 7 is a kinetic model of photocatalytic biochar composite UBC600 in example 5 and comparative example 1 for removing methylene blue under natural light and dark conditions, wherein,

FIG. 7(a) is a quasi-first order kinetic model under natural light,

FIG. 7(b) is a quasi-first order kinetic model under dark conditions,

FIG. 7(c) is a quasi-secondary kinetic model under natural light,

FIG. 7(d) is a quasi-secondary kinetic model under dark conditions;

FIG. 8 is a graph showing the degradation rate of methylene blue of different initial concentrations of photocatalytic adsorption of a photocatalytic biochar composite UBC600 under natural light in examples 5 and 6;

FIG. 9 is an isothermal adsorption model of photocatalytic biochar composite UBC600 under natural light for removing methylene blue in examples 5 and 6;

FIG. 10 is a comparison of the removal rate of methylene blue after regeneration cycles of photocatalytic biochar composite UBC400-700 in example 7.

Detailed Description

The invention provides a photocatalytic biochar composite material, which comprises biochar and a ZnO/ZnS mixture, wherein the ZnO/ZnS mixture is loaded in micropores and/or on the surface of the biochar.

The present invention will be described in further detail with reference to specific examples in order to provide those skilled in the art with a better understanding of the invention. It should be understood by those skilled in the art that this should not be construed as limiting the scope of the claims of the present invention. It should be noted that the reagent or the apparatus of the present invention can be obtained by commercially available methods without specific mention.

In the embodiment of the invention, UBC400 ℃ represents the photocatalytic biochar composite material prepared at the carbonization temperature of 400 ℃.

The photocatalytic biochar composite material in the invention can be recycled and regenerated by a method comprising the following steps: collecting the photocatalytic biochar composite material, drying at 80-160 ℃ for 8-24 h, adding into the dye wastewater again for recycling, and circulating according to the cycle, wherein the degradation rate is not obviously reduced after multiple cycles. If the removal effect of the photocatalytic biochar composite material is obviously reduced, the photocatalytic biochar composite material can be recovered after being dried and aired for one week or more under natural light.

Specific sources of reagents used in the present invention are listed in table 1 below.

TABLE 1 raw materials and apparatus for examples and comparative examples

The invention is further described below with reference to the drawings and specific preferred embodiments in the description, without thereby limiting the scope of protection of the invention.

Example 1

(1) Crushing the corn straw waste, and screening the crushed corn straw waste through a 50-mesh screen; then 30g of sieved corn straw powder is added into 60g of ZnSO with the temperature of 80 ℃ and the mass concentration of 3%₄Stirring and soaking the powder in an aqueous solution at the speed of 200r/min for 8h, taking out the solution, washing the solution with deionized water until the aqueous solution is neutral, and then drying the washed powder in a vacuum drying oven at the temperature of 80 ℃ for more than 12h to obtain the composite material precursor.

Meanwhile, after the corn straw waste is crushed, the corn straw waste is sieved by a 50-mesh screen; then 30g of the sieved corn straw powder is used for preparing the biochar material.

(2) Respectively putting the composite material precursor and the corn straw powder into N₂Heating to 100 ℃ at the temperature rise rate of 8 ℃/min in a tubular furnace quartz dish at the flow rate of 60ml/min, preserving heat for 1h, heating to 400 ℃ at the temperature rise rate of 8 ℃/min, preserving heat for 2h, and naturally cooling to obtain the photocatalytic biochar composite material UBC 40013.7 g and biochar BC40011.5 g.

Example 2

30g of composite material precursor and 30g of sieved corn straw powder are prepared according to the step (1) in the embodiment 1, except that the temperature is raised to 500 ℃ in the step (2), the temperature is kept for 2 hours, and the mixture is naturally cooled to obtain the photocatalytic biochar composite material UBC 50013.1 g and the biochar BC50011.0 g.

Example 3

30g of composite material precursor and 30g of sieved corn straw powder are prepared according to the step (1) in the embodiment 1, except that the temperature is raised to 600 ℃ in the step (2), the temperature is kept for 2 hours, and the mixture is naturally cooled to obtain 12.6g of photocatalytic biochar composite material UBC600and 10.5g of biochar BC600.

Example 4

30g of composite material precursor and 30g of sieved corn straw powder are prepared according to the step (1) in the embodiment 1, except that the temperature is raised to 700 ℃ in the step (2), the temperature is kept for 2 hours, and the mixture is naturally cooled to obtain the photocatalytic biochar composite material UBC 70012.1g and the biochar BC70010.3g.

Example 5

S1, preparing 10mg/L methylene blue simulation wastewater, adjusting the pH value to 7.0 +/-0.2 and COD_crThe value is 77.2mg/L, and 25mL of the solution is respectively put into 4 100mL conical flasks;

s2, directly adding the photocatalytic biochar composite materials UBC400, UBC500, UBC600 and UBC700 prepared in the embodiments 1 to 4 into 4 parts of wastewater according to 4g/L respectively, placing the wastewater in a constant temperature oscillator with the temperature of 30 ℃ under the condition of natural light, wherein the oscillation frequency is about 275 times/min, and the adsorption time is 4 hours;

and S3, precipitating and filtering to obtain the wastewater after advanced treatment.

Example 6

S1, respectively preparing 4 different kinds of waste water:

(1) the methylene blue concentration is 30mg/L, COD_crSimulated wastewater with the value of 85.3mg/L and the pH value of 7.0 +/-0.2,

(2) the methylene blue concentration is 50mg/L, COD_crSimulated wastewater with the value of 89.7mg/L and the pH value of 7.0 +/-0.2,

(3) the methylene blue concentration is 70mg/L, COD_crSimulated wastewater with the value of 125.7mg/L and the pH value of 7.0 +/-0.2,

(4) the methylene blue concentration is 100mg/L, COD_crThe simulated wastewater with the value of 168.0mg/L and the pH value of 7.0 +/-0.2,

respectively taking 25mL of the 4 kinds of wastewater, and putting the wastewater into 4 conical bottles with 100 mL;

s2, directly adding the photocatalytic adsorbent UBC600 prepared in the embodiment 3 into 4 parts of wastewater according to the proportion of 4g/L, and placing the wastewater in a constant-temperature oscillator at the temperature of 30 ℃ under the condition of natural light, wherein the oscillation frequency is about 275 times/min, and the adsorption time is 24 hours;

Example 7

(1) The photocatalytic biochar composite materials UBC400, UBC500, UBC600 and UBC700 used in example 5 were collected after filtration, and were placed in an oven for drying at 110 ℃ for 12 hours to obtain regenerated photocatalytic biochar composite materials UBC400, UBC500, UBC600 and UBC 700.

(2) S1, preparing 25mL of 10mg/L methylene blue simulated wastewater, putting the 10mg/L methylene blue simulated wastewater into a100 mL conical flask, adjusting the pH value to 7.0 +/-0.2, and adjusting the CODcr value to 77.2 mg/L;

s2, directly adding regenerated photocatalytic biochar composite materials UBC400, UBC500, UBC600 and UBC700 into the wastewater according to the concentration of 4g/L, placing the wastewater in a constant-temperature oscillator under the condition of natural light, keeping the temperature at 30 ℃, enabling the oscillation frequency to be 275 times/min, and enabling the adsorption time to be 4 hours;

and S3, precipitating and filtering to obtain the advanced treatment wastewater.

(3) The above steps are cycled five times.

Comparative example 1

s2, directly adding the photocatalytic biochar composite materials UBC400, UBC500, UBC600 and UBC700 prepared in the examples 1-4 into 4 parts of wastewater according to the proportion of 4g/L, placing the wastewater in a constant temperature oscillator with the temperature of 30 ℃ under the condition of keeping out of the sun, wherein the oscillation frequency is about 275 times/min, and the adsorption time is 4 hours;

Photocatalytic performance characterization of examples and comparative examples

The photocatalytic biochar composite materials UBC400, UBC500, UBC600, UBC700 prepared in examples 1-4 were subjected to nitrogen adsorption-desorption isotherm curves at 77K using Brunauer-Emmett-Teller (BET, Quantachrome NOVA1000) test materials, and the obtained curves are shown in fig. 1.

By the Multi-BET method (P/P)₀0.005-0.02) and calculating the specific surface area of the material.

The average pore diameter of the material was calculated by BHJ analysis.

Pore volume is from P/P₀0.95 of N₂And calculating the adsorption value.

The specific surface area, average pore diameter and pore volume results of the photocatalytic biochar composites prepared in examples 1-4 are shown in table 2.

The removal rate of the wastewater is determined by the formula: removal rate ═ C₀-C_t)/C₀X 100% calculated. Calculating the concentration C of methylene blue in the wastewater under different treatment times by using an ultraviolet spectrophotometry_tInitial concentration of methylene blue is denoted C₀. The removal rate-time curve of the photocatalytic biochar composite material in example 5 for methylene blue is shown in fig. 2, wherein the removal rate at 4 hours is detailed in table 2.

CODcr is obtained by using potassium dichromate (K)₂Cr₂O₇) The chemical oxygen consumption, i.e. the dichromate index, was measured as the oxidant. In example 5, the chemical oxygen demand COD of the water was measured by dichromate method (HJ 828-2017 dichromate method for measuring chemical oxygen demand of Water quality)_crThe results are detailed in Table 2.

The water quality chromaticity is measured by a platinum-cobalt colorimetric method (ISO 7887-1985, inspection and determination of water quality color). The colorimetric values of the wastewater stock solution in example 5 were 116.1, and the colorimetric values of the wastewater after 4 hours of advanced treatment are shown in Table 2.

The actual loading ratio of the ZnO/ZnS mixture is given by the formula: load factor (W)_UBC-W_BC)/W_UBCx 100% is calculated, wherein, W_UBCAnd W_BCThe photocatalytic biochar composite and the straw biochar quality at different pyrolysis temperatures are given in examples 1-4, respectively.

TABLE 2 structural parameters of photocatalytic biochar composite and parameters of wastewater treated under natural light for 4h

As can be seen from FIG. 2 and Table 2, the removal rate of the photocatalytic biochar composite material UBC400-700 to methylene blue increases with time until the methylene blue is balanced, the removal rate in 4 hours is close to or reaches 100%, and the COD is_crThe value and the chroma are both higher than the industrial wastewater reuse standard (GB/T19923-. Wherein the removal rate of the wastewater treated by the photocatalytic biochar composite material UBC600 reaches 94.07% in 20min, the removal rate reaches 100% in 1h, and the COD of the wastewater treated for 4h_crThe value and the chroma are both 0.0, and the treatment effect is optimal. The degradation performance of the photocatalytic biochar composite material on methylene blue is arranged from high to low: UBC600 > UBC700 > UBC500 > UBC 400.

The results of analyzing the organic functional groups on the surface of the photocatalytic biochar composite UBC600 before and after wastewater treatment in example 5 are shown in FIG. 3, in which FIG. 3(a) is a graph of the organic functional groups on the surface of the photocatalytic biochar composite UBC600 before and after wastewater treatment, and FIG. 3(b) is a further enlarged graph of 1000-^-1The comparison curve of (1). From FIG. 3(b), it can be seen that the UBC600 of the photocatalytic biochar composite material before wastewater treatment is 444cm^-1The wide strong peak is the accumulation of C-C vibration absorption peaks of various aromatics on the carbon surface, methylene blue organic macromolecules are easy to generate large pi conjugated adsorption with aromatic derivatives, and further generate photocatalytic degradation; the UBC600 of the photocatalytic biochar composite material after wastewater treatment is 419cm^-1、450cm^-1Two small peaks appear, which are C-C vibration absorption peaks of meta-position and para-position binary substituted benzene, and are intermediate products after methylene blue light catalytic degradation, and are shown in detail in figure 4 (a). The external deformation vibration of N-H is the characteristic absorption of amines in a fingerprint area, and is wide and strong. 878-752cm of photocatalytic biochar composite UBC600 before and after wastewater treatment^-1Multiple small and wide peaks are-NH on the surface of the charcoal₂The peak of the primary amine structure but the part of the photocatalytic biochar composite material UBC600 after treatment is weakened or disappeared, which indicates that the surface N-containing group is an effective adsorption point of methylene blue. 1565cm^-1The micro peak is-NH-vibration, and the photocatalysis is carried out after the treatmentThe peak intensity of the biochar composite UBC600 is weakened, and partial adsorption exists. UBC600 at 1379cm before treatment^-1Having a minor peak of an aromatic tertiary amine

1702cm, C-N vibration of^-1The peak is-CHO vibration, and the two tiny peaks remain unchanged after treatment, which indicates that the tertiary amine and the aldehyde group are not adsorption sites of methylene blue. And a new 1327cm appears on the treated photocatalytic biochar composite material UBC600^-1And the frequency is reduced by a tiny peak, which shows that a new product containing a structure of the aliphatic and aromatic mixed primary-secondary amine appears, and further proves that the methylene blue is degraded by photocatalysis. Before and after treatment, the UBC600 of the photocatalytic biochar composite material is at 3400cm^-1The large and wide peaks at all belong to-OH associated in the biochar molecules, and the peak shape of the associated body is wide. The greater the degree of association, the broader the peak, and the lower the wavenumber. 2922. 2844, 2337cm^-1The small peak comes from the lattice vibration of ZnO on the surface of the carbon, and the peak basically disappears as the surface is covered by methylene blue and products thereof after adsorption. Zn²⁺The electron transfer upon excitation by a photon is shown in detail in FIG. 4 (b).

And after vacuum filtration, drying the used photocatalytic biochar composite material UBC 600. The shapes of micropores of the photocatalytic biochar composite material UBC600 before and after treatment with methylene blue under natural light were observed by a Scanning Electron Microscope (SEM), and the results are shown in fig. 5(a) and (b). As shown in fig. 5(a) and (b), the photocatalytic biochar is an adsorbent material with a rich microporous structure, and the microporous structure is not damaged after use, and still has good adsorption performance. The photocatalytic biochar composite material UBC600 was analyzed by an energy spectrometer (EDX) for the types and contents of surface elements of the material before and after use, and the results are shown in fig. 5(c), (d) and table 3. As can be seen from table 3, the front surface of the photocatalytic biochar composite material UBC600 is mainly C, O, S, Zn four elements, and Zn mainly exists in the states of ZnO and ZnS; after the photocatalytic biochar composite material UBC600 is regenerated, the mass percent of O on the surface of the material is increased, and a small amount of P and K elements are adsorbed from the wastewater, so that the mass percent of Zn and S is slightly reduced. In general, the photocatalytic active ingredients of the photocatalytic biochar composite material UBC600 are basically unchanged before and after use, and the surface contains increased O groups, probably because the catalytic degradation products of organic matters are adsorbed on the surface of the carbon material.

TABLE 3 analysis results of surface elements before and after use of photocatalytic biochar composite UBC600

UBC600	Cwt.％	Owt.％	Swt.％	Znwt.％	Pwt.％	Kwt.％
							Before use	46.19	16.30	7.33	30.19
After use	42.92	24.49	5.72	22.01	3.93	0.93

In comparative example 5 and comparative example 1, the removal rate-time curve of the photocatalytic biochar composite material UBC400-700 under natural light and dark conditions for methylene blue further proves the effect of natural light in a photocatalytic degradation methylene blue degradation system, as shown in FIG. 6. Wherein fig. 6(a) is a comparison graph of a removal rate-time curve of a photocatalytic biochar composite material UBC400 under natural light and dark conditions, fig. 6(b) is a comparison graph of a removal rate-time curve of a photocatalytic biochar composite material UBC500 under natural light and dark conditions, fig. 6(c) is a comparison graph of a removal rate-time curve of a photocatalytic biochar composite material UBC600 under natural light and dark conditions, and fig. 6(d) is a comparison graph of a removal rate-time curve of a photocatalytic biochar composite material UBC700 under natural light and dark conditions. On the whole, the photocatalytic biochar composite material UBC400-700 shows that the degradation effect of methylene blue under the natural light condition is better than that under the light-shielding condition, and the superiority of the natural light condition compared with the light-shielding condition is more obvious along with the rise of the pyrolysis temperature of the photocatalytic biochar.

Fig. 7 is a quasi-first order kinetic and quasi-second order kinetic model of photocatalytic biochar composite UBC600 in example 5 and comparative example 1 for removing methylene blue under natural light and dark conditions, wherein fig. 7(a) is the quasi-first order kinetic model under natural light, fig. 7(b) is the quasi-first order kinetic model under dark conditions, fig. 7(c) is the quasi-second order kinetic model under natural light, and fig. 7(d) is the quasi-second order kinetic model under dark conditions. The model equation is as follows:

a quasi-first order kinetic model:

a quasi-second order kinetic model:

in the formula, Q_eIs a fitting value of equilibrium adsorption capacity in mg/g;

Q_tthe adsorption capacity at the moment t is unit mg/g;

k₁is a quasi first-order adsorption rate constant in min^-1；

k₂Quasi-second order adsorption rate constant, unit g.mg^-1·min^-1；

k₂ ⁰＝k₂Q_e ²As initial adsorption rate constant, in mg g^-1·min^-1。

In general, the process of removing methylene blue from the photocatalytic biochar composite material UBC600 under natural light and dark conditions better conforms to a quasi-secondary kinetic model, and the kinetic parameter calculation results are shown in Table 4.

Table 4 quasi-first and second order kinetic parameters of photocatalytic biochar composite UBC600 for removing methylene blue under natural light and dark conditions

FIG. 8 is a graph of removal rate versus time for photocatalytic biochar composite UBC600 at initial concentrations of 10, 30, 50, 70, 100mg/L methylene blue treated under natural light in examples 5 and 6, respectively. As can be seen from fig. 8, as the initial concentration of methylene blue increases, the removal performance of the photocatalytic biochar composite material UBC600 gradually decreases, because the photocatalytic adsorption of the photocatalytic biochar reaches equilibrium within a certain time, but the removal rate of the methylene blue continuously increases even after the treatment time is prolonged to 24 hours or even days, which is consistent with the quasi-kinetic adsorption rate constant of the system in table 4. The Langmuir and Freundlich isothermal adsorption models were fitted to the above system, respectively, and the results are shown in FIG. 9.

The isothermal adsorption model equation is as follows:

langmuir isothermal adsorption model:

in the formula, C_eIs the equilibrium concentration of the solution, unit mg/L;

Q_maxthe maximum adsorption capacity (or called saturated adsorption capacity) is unit mg/g;

K_Lis the Langmuir constant, in L/g, related to the affinity and adsorption energy of the binding site.

The Langmuir molecular adsorption model can well represent an experimental result when the adsorption effect of the solid surface is quite uniform and the adsorption is limited to a monomolecular layer, and the goodness of fit of the Langmuir molecular adsorption model and the experimental system is poor.

Freundlich isothermal adsorption model

In the formula, Q_eThe unit is mg/g for the adsorption amount when the adsorption reaches the equilibrium;

C_ethe concentration of adsorbate in the solution is in mg/L during adsorption equilibrium;

K_Fconstants relating to adsorption capacity and adsorption strength under the Freundlich model;

the 1/n is a Freundlich constant, generally between 0 and 1, and the magnitude of the value indicates the strength of the influence of the concentration on the amount of adsorption.

The smaller the 1/n, the better the adsorption performance. 1/n is 0.1 to 0.5, which means that adsorption is easy, and adsorption is difficult when 1/n > 2.

Compared with a Langmuir isothermal adsorption model, the system is more consistent with a Freundlich isothermal adsorption model, and the corresponding parameter calculation results are shown in Table 5. The system 1/n is 0.13107, which shows that the photocatalytic biochar composite material UBC600 is a material which is easy to adsorb methylene blue, andgreater K_FAnd the n value is an indicator that the adsorbent has better adsorption performance.

Table 5 Freundlich isothermal adsorption model parameters for removing methylene blue under natural light conditions for photocatalytic biochar composite UBC600

K_F	n	R²
			2.18595	7.62951	0.91463

The photocatalytic biochar can repeatedly treat organic dye wastewater for many times through a simple regeneration process, obtains a stable removal effect, and has a vital significance for realizing the cost reduction of organic dye wastewater treatment.

Example 7 proves that the photocatalytic biochar can be recycled for recycling and reusing when used for treating printing and dyeing wastewater, and the photocatalytic biochar has cyclic regeneration property. Example 7 compares the 4h removal rate of methylene blue after five regeneration cycles of photocatalytic biochar composite UBC400-700, and the results are shown in fig. 10. As can be seen from fig. 10, after five times of recycling, the removal rate of methylene blue for 4 hours is still maintained above 95%, which proves that the photocatalytic biochar has good recycling performance.

The prior art of furniture and low-cost aspects of ZnOxyococcus nanocomposites for effect and stable photodegradation of methyl blue dye, Mingxin Chen et al,journal of Analytical and Applied Pyrolysis 139(2019) 319-332. The prior art is a biochar material only loaded with ZnO. The specific surface area of the material provided in the prior art is 4.71-62.2 m²·g^-1The photocatalytic biochar composite material has a larger specific surface area (300-550 m)²·g^-1). The removal rate of the ZnO-loaded biochar material in the prior art after being degraded for 60 minutes under the ultraviolet light condition is less than 100 percent, while the removal rate of the photocatalytic biochar composite material in the invention after being degraded for 60 minutes under natural light can reach 100 percent, and COD (chemical oxygen demand) is realized_crThe chroma was 0.0.

The above description is only a basic description of the present invention, and any equivalent changes made according to the technical solution of the present invention should fall within the protection scope of the present invention.

Claims

1. The application of the photocatalytic biochar composite material in catalytic degradation of printing and dyeing wastewater is characterized in that the photocatalytic biochar composite material comprises biochar and a ZnO/ZnS mixture, the loading rate of the ZnO/ZnS mixture is 14-20%, and the ZnO/ZnS mixture is loaded in micropores and/or on the surface of the biochar.

2. The use of claim 1, wherein the mass percentage of Zn element in the surface element of the photocatalytic biochar composite material is 25-40%.

3. The use as claimed in claim 1 or 2, wherein the photocatalytic biochar composite has a specific surface area of 300-500m²·g^-1Preferably 330-²·g^-1；

4. The use of any one of claims 1 to 3, wherein the solution color of the photocatalytic biochar composite material is 0.0 to 22.9 after 4g/L of the photocatalytic biochar composite material is added into a10 to 100mg/L methylene blue solution for 1 to 30 hours;

5. The use according to any one of claims 1 to 4, wherein the preparation method of the photocatalytic biochar composite material comprises the following steps:

6. The use of claim 5, wherein the straw in step (1) is any one of tobacco stem, corn straw, coix seed straw, sorghum straw and a mixture thereof.

7. The use according to claim 5 or 6, wherein the aqueous solution of zinc source of step (1) is ZnSO₄An aqueous solution of a carboxylic acid and a carboxylic acid,

8. Use according to any one of claims 5 to 7Characterized in that ZnSO is adopted in the step (1)₄The temperature of the aqueous solution is 60-100 ℃, and preferably 80 ℃;

alternatively, preferably, the stirring rate is 100-,

or, preferably, the stirring time is 3-5 h, preferably 5 h;

9. The use according to any one of claims 5 to 8, wherein the inert gas atmosphere in the step (2) is kept at 100 to 120 ℃, preferably for 1 to 5 hours, preferably for 1.5 to 3 hours;

or, preferably, the heating rate is 8-10 ℃/min;

or, preferably, the pyrolysis time is 1-4 h and 2-2.5 h;

alternatively, preferably, the inert gas is N₂Or Ar;

or, preferably, the flow rate of the inert gas is 40-100 ml/min;

10. The use according to any one of claims 1 to 9, wherein the dyeing wastewater organic dye has a CODcr value of less than 200mg/L,

preferably, the pH value of the printing and dyeing wastewater is 6-9.

11. Use according to any one of claims 1 to 10, wherein the catalytic degradation reaction is carried out under natural light.

12. The printing and dyeing wastewater treatment method is characterized by comprising the following steps:

adding the photocatalytic biochar composite material in the application of any one of claims 1 to 11 into printing and dyeing wastewater to be treated, and oscillating under natural light conditions to perform catalytic degradation reaction;

13. The process according to claim 12, characterized in that the oscillation is carried out at a temperature of 28-32 ℃;

preferably, the oscillation frequency is 250-300 times/min;

preferably, the oscillation time is 1-30 h.