CN111974374A - Preparation method of biochar modified nano ZnO composite powder - Google Patents

Abstract

The invention relates to a preparation method of biochar modified nano ZnO composite powder, belonging to the technical field of photocatalysts. According to the invention, a mixed solution of biochar and a zinc salt is subjected to a hydrothermal reaction at a temperature of 100-160 ℃ under an alkaline condition to obtain the biochar modified nano ZnO composite photocatalyst. The biochar modified nano ZnO composite photocatalyst has the advantages of large specific surface area and strong adsorption capacity, responds to visible light, and has the efficiency of degrading Methylene Blue (MB) pollutants under ultraviolet-visible light for 100min reaching 98.71 percent; the method utilizes renewable natural resource biochar to modify ZnO, has high catalytic activity, can be repeatedly utilized, and has no secondary pollution; meanwhile, the preparation method is simple, the production cost is low, and the method can be applied to industrial production.

Description

A kind of preparation method of biochar modified nano-ZnO composite powder

technical field

The invention relates to a preparation method of biochar modified nano-ZnO composite powder, and belongs to the technical field of photocatalysts.

Background technique

In recent years, ZnO has been widely used and developed as a photocatalyst because of its low price, non-toxicity, and high stability. Due to the wide energy gap (3.37ev) of ZnO, it only responds to ultraviolet light, and only less than 5% of ultraviolet light in sunlight, so the utilization rate of visible light is low; and the photogenerated electron-holes generated in the photocatalytic process It is easy to recombine, which affects the photocatalytic efficiency, and is accompanied by photochemical corrosion, which greatly limits the practical application of ZnO.

In order to improve the photocatalytic efficiency of ZnO, increase its utilization rate, and reduce the recombination of electrons and holes, ZnO is generally modified by calcination method, chemical precipitation method, sol-gel method and hydrothermal method, including noble metal doping. , the introduction of carbon-based materials and the compounding of semiconducting oxides. Among them, the synthesized Ag/ZnO, Au/ZnO, Pt-ZnO and other composite photocatalysts can improve the stability of the catalyst to a certain extent and broaden the absorption of visible light, but the cost is too high and there is a danger of secondary pollution; the introduced graphene , carbon nanotube carbon and other carbon-based materials also have the disadvantages of high cost and inability to achieve the best catalytic effect; binary catalysts ZnO/TiO ₂ , ZnO/Fe ₂ O ₃ , ZnO/Cu ₂ O synthesized by semiconductor oxides , the general process is complex, the response range to visible light is narrow, the catalytic performance cannot reach the best, and the environment is not friendly.

SUMMARY OF THE INVENTION

Aiming at the problems of high cost and poor catalytic effect of existing ZnO photocatalysts, the present invention provides a preparation method of biochar modified nano-ZnO composite powder. The present invention utilizes renewable natural resources biochar to modify ZnO, and has high catalytic activity, It can be reused without secondary pollution; meanwhile, the preparation method is simple, the production cost is low, and it can be applied to industrial production.

Biochar is formed by thermal decomposition of organic raw materials in an anoxic environment at a specific low temperature (<700°C). Its high carbon content, high specific surface area and electrical conductivity contribute to the mineralization of organic pollutants. Biochar modified ZnO catalyst The biochar can significantly inhibit the rapid recombination of photogenerated electron pairs in the photocatalytic process to achieve efficient degradation.

A preparation method of biochar modified nano-ZnO composite powder, the specific steps are as follows:

(1) Disperse biochar in ethanol to obtain mixed solution A, dissolve zinc salt into mixed solution A and stir for pretreatment for 1-2 hours to obtain mixed solution B;

(2) adding the alkaline solution dropwise to the mixed solution B and reacting until the system no longer precipitates, and then ultrasonically treating it for 30 to 60 min to obtain the precursor;

(3) The precursor is reacted at a temperature of 100-160 °C for 8-12 hours, the solid-liquid is separated, the solid is washed until the washing solution is neutral, and dried to obtain a biochar-modified nano-ZnO composite photocatalyst;

The biochar is preferably cannabis stem activated carbon, and the preparation method is as follows: the cannabis stem is pulverized to an average particle size of about 10 μm to obtain a cannabis stem fine material, and the hemp stem fine material is washed with deionized water to remove impurities, and dried at a temperature of 60° C. for 10 hours. Remove moisture; under the protection of Ar ₂ atmosphere, the hemp fines were carbonized in a tube furnace at a ventilation rate of 0.1 L/min and a temperature of 650 ° C for 3 h; and then cooled to room temperature in the same atmosphere, ground and passed through Biochar is obtained by sieving with a 300-mesh sieve;

In the step (1), the molar ratio of Zn ²⁺ in the biochar to the zinc salt is 1:0.5-3;

The step (1) zinc salt is Zn(CH ₃ COO) ₂ or Zn(NO ₃ ) ₂ .6(H ₂ O);

Described step (2) alkali solution is potassium hydroxide, sodium hydroxide or tetramethyl ammonium bicarbonate solution;

Preferably, the concentration of the alkaline solution is 0.1-0.5 mol/L;

Preferably, the stirring speed of the step (1) is 200-500rpm;

Preferably, in the step (3), the drying temperature is 40-60° C., and the drying time is 8-12 h.

The biochar modified nano-ZnO composite photocatalyst of the invention, under the irradiation of visible light, the electrons generated in the valence band (VB) of ZnO are excited and migrate to the conduction band (CB), leaving holes (h ⁺ ) in the valence band. The generated electron-hole pairs react with H ₂ O, O ₂ , etc. to generate active species with strong redox properties such as hydroxyl radicals (OH·) and superoxide radicals (·O ₂ ). The active species can convert organic The pollutants are mineralized and decomposed into H ₂ O, CO ₂ and other inorganic small molecular substances. During the catalytic process, biochar with high specific surface area and developed pore size rapidly adsorbs pollutants and transfers them to the surface of ZnO, resulting in a concentration difference to improve the light Catalytic efficiency; in addition, the attachment of ZnO on the surface of biochar increases the overall specific surface area of the catalyst and increases the active sites. At the same time, the biochar has good electron shuttling ability, and the synergistic effect with ZnO reduces the recombination of photogenerated electrons and holes. Improve catalyst efficiency.

The beneficial effects of the present invention are:

(1) The biochar modified nano-ZnO catalyst of the present invention has large specific surface area, many catalytic active sites, strong adsorption capacity, stable chemical properties, and the introduction of biochar realizes waste utilization, low cost and sustainable use;

(2) The biochar modified nano-ZnO catalyst of the present invention has high catalytic efficiency, strong activity, strong absorption of ultraviolet light in the spectral range from <400 nm, greatly improves the absorption in the visible light range, realizes the response to visible light, and has good stability ;

(3) The biochar-modified nano-ZnO catalyst prepared by the one-step hydrothermal method of the present invention is easy to operate, and the hydrothermal method is synthesized without the introduction of pollutants, and the catalyst is used without secondary pollution; Carbon quickly adsorbs pollutants and transfers them to the surface of ZnO, resulting in a concentration difference to improve the photocatalytic efficiency; in addition, the attachment of ZnO on the surface of biochar increases the specific surface area of the catalyst as a whole and increases the active sites. The electron shuttling ability, synergistic effect with ZnO reduces the recombination of photogenerated electron-holes and improves the efficiency of the catalyst.

Description of drawings

Fig. 1 is the XRD pattern of embodiment 1 and 2 biochar modified nano-ZnO composite powder;

Fig. 2 is the SEM image of embodiment 1 and 2 biochar modified nano-ZnO composite powder;

Fig. 3 is the ultraviolet-visible diffuse reflectance spectrum (UV-vis) of biochar modified nano-ZnO composite powder of Example 1;

Figure 4 is a graph showing the degradation efficiency of the biochar modified nano-ZnO composite powder in Example 1.

Detailed ways

The present invention will be further described in detail below with reference to the specific embodiments, but the protection scope of the present invention is not limited to the content.

Embodiment 1: a preparation method of biochar modified nano-ZnO composite powder, the specific steps are as follows:

(1) Disperse biochar (Hemp activated carbon) in ethanol to obtain mixed solution A, dissolve zinc salt (zinc nitrate) in mixed solution A and stir for pretreatment for 1h to obtain mixed solution B; wherein Hemp biochar (C The molar ratio of ) and zinc nitrate (Zn(NO ₂ )·6H ₂ O) is 1:0.5, and the stirring speed is 200rmp;

(2) alkaline solution (potassium hydroxide solution) is added dropwise to mixed solution B to react to system no longer to separate out precipitation, then ultrasonic treatment 60min obtains precursor; Wherein potassium hydroxide solution concentration is 0.1mol/L;

(3) The precursor was reacted at a temperature of 100 °C for 12 h, the solid-liquid was centrifuged, the solid was washed with deionized water until the washing liquid was neutral, and dried at a temperature of 40 °C for 12 h to obtain the biochar modified nano-ZnO composite catalyst of light;

The XRD pattern of the biochar-modified nano-ZnO composite photocatalyst in this embodiment is shown in Figure 1. It can be seen from Figure 1 that the product is zinc oxide with a hexagonal lead-zinc ore structure. As shown by PDF#99-0111, the peak positions of ZnO are at 31.76°, 34.41°, 36.25°, 47.53°, 56.59°, 62.85°, 66.37°, 67.94° and 69.08° for (100), (002), ( 101), (102), (110), (103), (200), (112) and (201) planes. Amorphous biochar has no obvious steamed bread peaks in XRD. The average grain size of the composite catalyst is calculated by the Scherrer formula: D _c =Kλ/(Bcosθ)(λ); where K is the Scherrer constant taking 0.89, D is the average thickness of the grains perpendicular to the crystal plane, and B is the diffraction peak of the sample The width at half maximum, θ is the diffraction angle, and γ is the X-ray wavelength (0.154056nm). The calculation results show that the average size of the composite catalyst is 31nm;

The SEM morphology characterization of the biochar-modified nano-ZnO composite photocatalyst in this example, as shown in Figure 2a, the composite photocatalyst has a 3D structure formed by nano-ZnO particles uniformly deposited on the surface of the hemp biochar, and shows a direction The crystallographic characteristics of the preferred orientation in the (002) direction; through the analysis of the ultraviolet-visible diffuse reflectance spectrum of the composite photocatalyst, it can be known that there is strong absorption in the ultraviolet-visible light region (see Figure 3);

The photocatalytic activity of the composite catalyst was evaluated by degrading the cationic pollutant methylene blue (MB) under ultraviolet-visible light. The details are as follows: 50 mg of the biochar-modified nano-ZnO composite photocatalyst prepared in this example was put into 200 mL of 30 mg/L In the methylene blue (MB) solution, take 4 mL of the suspension solution every 10 minutes, test the absorption concentration of the MB liquid after solid-liquid separation, and calculate the degradation rate; under the irradiation of a 300W xenon lamp for 100 minutes, the catalytic efficiency can reach 100 minutes. 98.71.8%, and the degradation rate was 96.23% after repeated degradation for 3 times (see Figure 4).

Embodiment 2: a preparation method of biochar modified nano-ZnO composite powder, the specific steps are as follows:

(1) Disperse biochar (Hemp activated carbon) in ethanol to obtain mixed solution A, dissolve zinc salt (zinc acetate) into mixed solution A and stir for pretreatment for 2h to obtain mixed solution B; wherein Hemp biochar (C ) and the mol ratio of zinc acetate Zn(CH ₃ COO) ₂ is 1:3, and the stirring speed is 500 rmp;

(2) alkaline solution (tetramethyl ammonium bicarbonate) is added dropwise to mixed solution B to react to system no longer to separate out precipitation, then ultrasonic treatment 120min obtains precursor; Wherein potassium hydroxide solution concentration is 0.5mol/L;

(3) The precursor was reacted at a temperature of 160 °C for 8 hours, the solid-liquid was centrifuged, the solid was washed with deionized water until the washing liquid was neutral, and dried at a temperature of 80 °C for 10 hours to obtain the biochar modified nano-ZnO composite catalyst of light;

The XRD pattern of the biochar-modified nano-ZnO composite photocatalyst in this example is shown in Figure 1. It can be seen from Figure 1 that the product is zinc oxide (ZnO) with a stable structure of hexagonal lead-zinc ore; after adjusting the ratio, the XRD results show the peak position of ZnO No change has occurred, but the peak intensity has increased;

The SEM morphology characterization of the biochar-modified nano-ZnO composite photocatalyst in this example, as shown in Figure 2b, the nano-ZnO particles form a 3D structure and are deposited on the surface of the hemp biochar, and the ZnO nano-grains are preferentially distributed on the biochar. surface;

The photocatalytic activity of the composite catalyst was evaluated by degrading the cationic pollutant methylene blue (MB) under ultraviolet-visible light. The details are as follows: Take 30 mg of the biochar-modified nano-ZnO composite photocatalyst prepared in this example and put it in 200 mL of 30 mg/L In the methylene blue (MB) solution, 4 mL of the suspension solution was taken every 10 minutes, and the absorption concentration of MB was tested after solid-liquid separation, and the degradation rate was calculated; irradiated under a 300W xenon lamp for 100 minutes, the catalytic efficiency can reach 95.8 after 100 minutes. %, and the degradation rate of repeated degradation was 94.35%.

Embodiment 3: a preparation method of biochar modified nano-ZnO composite powder, the specific steps are as follows:

(1) Disperse biochar (Hemp activated carbon) in ethanol to obtain mixed solution A, dissolve zinc salt (zinc nitrate) into mixed solution A and stir for pretreatment for 2h to obtain mixed solution B; wherein Hemp biochar (C ) and zinc nitrate (Zn(NO ₂ )·6H ₂ O), the molar ratio is 1:1, and the stirring speed is 350rmp;

(2) the alkaline solution (tetramethyl ammonium bicarbonate) is added dropwise to the mixed solution B to react to the system no longer to separate out precipitation, then ultrasonic treatment 80min obtains the precursor; Wherein the potassium hydroxide solution concentration is 0.2mol/L;

(3) The precursor was reacted at a temperature of 130 °C for 10 h, the solid-liquid was centrifuged, the solid was washed with deionized water until the washing solution was neutral, and dried at a temperature of 70 °C for 8 h to obtain the biochar modified nano-ZnO composite catalyst of light;

In this example, the activated carbon supports ZnO/CuxO photocatalytic composite powder, and the product is a stable structure zinc oxide (ZnO) of hexagonal lead-zinc ore. After adjusting the ratio, the XRD results show that the ZnO peak position has not changed, but the peak intensity has weakened;

The morphology of the biochar-modified nano-ZnO composite photocatalyst in this embodiment is that the nano-ZnO particles form a 3D structure and are deposited on the surface of the hemp biochar, which is uniformly dispersed and distributed in a preferred orientation along the (002) direction;

The photocatalytic activity of the composite catalyst was evaluated by degrading the cationic pollutant methylene blue (MB) under ultraviolet-visible light. The details are as follows: Take 10 mg of the biochar-modified nano-ZnO composite photocatalyst prepared in this example and put it in 200 mL of 10 mg/L In methylene blue (MB) solution, irradiated under 300W xenon lamp for 100min, take 4mL of suspension solution every 10min, test the absorption concentration of MB after solid-liquid separation, and calculate the degradation rate; after 100min, the catalytic efficiency can reach 97.6 %, and the degradation rate was 94% after repeated degradation for 3 times.

The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various Variety.

Claims (5)

1. A preparation method of biochar modified nano ZnO composite powder is characterized by comprising the following specific steps:

(1) dispersing biochar in ethanol to obtain a mixed solution A, dissolving zinc salt in the mixed solution A, and stirring for pretreatment for 1-2 hours to obtain a mixed solution B;

(2) dropwise adding the aqueous alkali into the mixed solution B to react until a system does not precipitate, and performing ultrasonic treatment for 30-60 min to obtain a precursor;

(3) and (3) reacting the precursor for 8-12 h at the temperature of 100-160 ℃, carrying out solid-liquid separation, washing the solid until the washing liquid is neutral, and drying to obtain the biochar modified nano ZnO composite photocatalyst.

2. The method for preparing the biochar modified nano ZnO composite powder according to claim 1, which is characterized by comprising the following steps: step (1) adding Zn into the biochar and the zinc salt²⁺The molar ratio of (A) to (B) is 1: 0.5-3.

3. The method for preparing the biochar modified nano ZnO composite powder according to claim 1, which is characterized by comprising the following steps: the zinc salt in the step (1) is Zn (CH)₃COO)₂Or Zn (NO)₃)₂.6(H₂O)。

4. The method for preparing the biochar modified nano ZnO composite powder according to claim 1, which is characterized by comprising the following steps: the alkali solution in the step (2) is potassium hydroxide, sodium hydroxide or tetramethyl ammonium bicarbonate solution.

5. The method for preparing the biochar modified nano ZnO composite powder according to claim 4, which is characterized by comprising the following steps: the concentration of the alkali solution is 0.1-0.5 mol/L.

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