A method for preparing a floating honeycomb-like biochar composite material for capturing and converting CO2 and its application.

Abstract

The application belongs to the field of environmental protection, and particularly relates to a preparation method of a floating type honeycomb-like biochar composite material for capturing and converting CO2 and application thereof. Farming and forestry wastes are washed, cut into sections and dried, then immersed in a metal nitrate solution, and after complete adsorption, the whole type honeycomb-like metal element / biochar composite material is obtained through calcination under nitrogen protection. The floating type honeycomb-like composite material as a catalyst provides a gas-water interface for the photocatalytic reduction of CO2, avoids the close contact of the light-thermal catalyst with the main water phase, and causes heat loss and a decrease in light energy utilization, at the same time, the biomass can reduce metal ions into metal element nanoparticles with plasmonic resonance effect in the heat treatment process and grow in situ on the biochar, and is applied to the capture of CO2 at normal temperature and pressure and the conversion of CO2 into methanol under photocatalysis. A new way is opened up to alleviate the environmental pollution caused by solid waste and CO2 emission.

Description

Technical fields:

[0001] This invention belongs to the field of environmental protection, specifically relating to metallic elemental / honeycomb-like biochar composite materials, their preparation methods, and applications. Background technology:

[0002] Excessive carbon dioxide emissions have a profound impact on the Earth's climate and life cycle. In recent years, "carbon neutrality" has received increasing attention. While reducing carbon emissions can address the problem at its source, carbon capture, utilization, and storage (CCUS) technology is essential for CO2 emissions. Currently, various solid adsorbents for CO2 capture have been developed, including porous carbon, zeolites, metal oxides, porous polymers, and metal-organic frameworks (MOFs). Among these, biochar has become a promising adsorbent due to its low cost, abundant raw materials, and high porosity. Biochar, as a natural, green, and renewable carbon source, is mainly obtained through the thermochemical treatment of biomass or carbon-containing solid waste. With the development of thermochemical conversion of biomass solid waste, biochar production has reached a significant level and continues to increase. However, biochar itself has a relatively low CO2 adsorption capacity, and most of it is in powder form, which is not conducive to cleaning and recycling.

[0003] Compared to capture and reuse methods, photocatalytic reduction of carbon dioxide has proven to be a favorable alternative, utilizing abundant solar energy to convert CO2 and H2O into CH3OH and O2. However, the selectivity of methanol is limited by the complex kinetics of photocatalytic CO2 reduction, as different products (i.e., CO, CH4, and CH3OH) have similar thermodynamic potentials. Furthermore, CO2 molecules are thermodynamically stable and chemically inert. Although introducing thermal energy into the photocatalytic reaction as an additional driving force can significantly enhance the CO2 catalytic conversion process, increasing the temperature of non-concentrating semiconductor catalysts by adding external resistance presents the following problems: 1) Direct heating raises the temperature of the entire reaction system to the same level, increasing energy consumption; 2) Specific devices need to be designed to achieve the reaction; 3) The synergistic effect between the heating temperature field and the light field is not ideal.

[0004] Based on the fundamental principle of photocatalytic CO2 reduction, the preferential formation of CH3OH requires... * CO intermediates exhibit suitable adsorption strength at active sites. Due to their specific d-electron configuration, transition metals such as Cu, Co, and Ni demonstrate good plasmon resonance effects and methanol production selectivity. Reports indicate that Cu-doped BiOBr promotes the photocatalytic conversion of CO2 to methanol in a pure H2O environment. The presence of Cu on the photocatalyst can promote the intermediate... * CO is converted to * CHO, thereby promoting the formation of methanol liquid product from CO2.

[0005] This invention prepares a metal element / honeycomb-like monolithic biochar composite material for CO2 capture and conversion under ambient temperature and pressure using a simple impregnation and thermal synthesis method. After heat treatment, the bulk biomass forms a hierarchical, porous, rigid structure that floats on water, providing a gas-liquid-solid interface for the CO2 reduction reaction. This allows for localized, concentrated heating, which is beneficial for promoting the synergistic effect between CO2 capture and in-situ conversion. Simultaneously, the honeycomb-like biochar, as a monolithic adsorbent, is easier to recover. Summary of the Invention

[0006] To address this issue, the present invention provides a method for preparing a metal element / floating honeycomb-like biochar composite material and its application. The metal element / floating honeycomb-like biochar composite material is prepared by impregnation and thermal synthesis methods, and is used as an adsorbent for capturing and converting CO2.

[0007] The monolithic biochar prepared by this invention can float on water due to its buoyancy, allowing for localized and concentrated heating under light without requiring overall environmental heating. Secondly, the capillary action of the biochar and solar interface evaporation technology deliver liquid water to the catalyst, providing a gas-water interface for the CO2 reduction reaction while avoiding heat loss and reduced light energy utilization caused by close contact between the photothermal catalyst and the bulk aqueous phase. This ensures localized photothermal action of the catalyst while constructing a gas-liquid-solid three-phase interface catalytic system. Furthermore, due to exposure to a CO2 atmosphere, the H2 generation rate is lower than in the liquid-solid mode, thus reducing the hydrogen evolution competition reaction and resulting in higher selectivity.

[0008] To achieve the above objectives, the technical solution adopted by the present invention includes the following steps:

[0009] (1) Take waste biomass, wash it, cut it into sections and dry it to obtain cylindrical block biomass material with a diameter of 2-5cm and a height of 3-6cm.

[0010] (2) Dissolve different masses of metal nitrates in deionized water to prepare solutions;

[0011] (3) Immerse the waste biomass from step (1) in the solution prepared in step (2);

[0012] (4) The biomass impregnated in step (3) is calcined under N2 atmosphere to obtain metal element / floating honeycomb biochar.

[0013] Furthermore, the agricultural and forestry wastes in step (1), such as straw, corn cobs, and enoki mushrooms, have a honeycomb-like morphology, are widely available, and are inexpensive.

[0014] Furthermore, in step (2), the metal nitrate, such as copper nitrate, cobalt nitrate, or nickel nitrate, has a mass of 1%-7% of the biomass mass.

[0015] Furthermore, the impregnation process in step (3) involves multiple impregnations and drying until the solution is completely adsorbed.

[0016] Furthermore, in step (4), the calcination temperature is 400-800℃ and the calcination time is 2-3h. At this calcination temperature, the structure will not collapse and will be stable.

[0017] The prepared floating honeycomb-like biochar composite material was used as a catalyst for capturing and converting CO2 to methanol. Specifically, the prepared floating honeycomb-like biochar composite material was floated on water and then added to a photocatalytic reactor. CO2 was introduced into the reactor, and the reactor was irradiated with sunlight to perform photocatalytic reduction of CO2 to methanol.

[0018] Compared with existing technologies, the advantages of this invention are as follows:

[0019] 1. This invention utilizes monolithic, hierarchical, porous biochar obtained from the calcination of agricultural and forestry waste as a carrier. Its layered porous structure helps increase the surface area, providing more attachment sites for active components. Furthermore, the honeycomb-like biochar, as a monolithic catalyst, can float on water, improving the catalyst's light absorption efficiency. Under sunlight, the biochar rapidly heats up, allowing for localized heating of the catalyst to above 100°C. This avoids heat loss and reduced light energy utilization caused by close contact between the photo-thermal catalyst and the main aqueous phase, thereby enhancing photo-thermal catalytic efficiency and reducing energy consumption. Simultaneously, this biochar catalyst also facilitates water evaporation into a gaseous state, thus constructing a gas-solid interface and enhancing CO2 conversion efficiency.

[0020] 2. The hierarchical porous structure and capillary action of monolithic biochar transport liquid water to the catalyst surface, providing a gas-water interface for the CO2 reduction reaction, reducing the hydrogen evolution competition reaction, resulting in higher product selectivity and easier recovery.

[0021] 3. During thermal treatment, biomass can reduce metal ions into metallic elemental nanoparticles with a plasmonic resonance effect, which are then grown in situ on biochar. This nanoparticles can be used for CO2 capture at ambient temperature and pressure and converted into methanol under photocatalysis. The susceptibility of metallic elemental materials to oxidation hinders their practical application, while biochar can protect them from oxidation. Attached Figure Description

[0022] Figure 1 The images show XRD patterns of copper nitrate / biochar with different mass ratios in Examples 1-4, and different metal nitrates / biochar in Examples 5-6.

[0023] Figure 2 These are scanning electron microscope images of the Cu / biochar surface at different scale ranges obtained in Example 1.

[0024] Figure 3 This is a transmission electron microscope (TEM) image of the Cu / biochar surface in the 200 nm range obtained in Example 1.

[0025] Figure 4 The UV-Vis-NIR spectra of Cu / biochar and biochar obtained in Example 1 are shown.

[0026] Figure 5 This is a thermal imaging image of Cu / biochar obtained in Example 1. Detailed Implementation

[0027] Example 1

[0028] Waste biomass was washed, dried, and used to obtain biomass material. Copper nitrate at 5% of the mass of the waste biomass was dissolved in deionized water to prepare a solution. Cylindrical blocks of waste biomass, 2 cm in diameter and 6 cm in height, were repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, the blocks were placed in a tube furnace under a N2 atmosphere and kept at 600℃ for 2 hours to obtain the finished Cu / biochar product.

[0029] Without affecting the overall structure of the biochar, powder was scraped off the biochar and X-ray powder diffraction was performed on the sample. Simultaneously, the morphology and structure of the Cu / biochar were observed under a scanning electron microscope. The XRD pattern of the Cu / biochar nanostructured composite material prepared according to the process parameters of Example 1 is shown below. Figure 1 As shown, by comparing with the PDF card for Cu, it can be seen that Cu-specific diffraction characteristic peaks appear at angles of 40.3°, 50.4°, and 74.1°. Furthermore, because the carbon in the composite material is in an amorphous state, its corresponding characteristic diffraction peaks cannot be displayed in the XRD pattern. This is further confirmed by combining scanning electron microscopy... Figure 2 and transmission electron microscopy Figure 3 This proves that biomass will convert Cu 2+ Cu nanoparticles with a particle size of about 20 nm were uniformly grown on biochar.

[0030] UV-Vis-NIR spectra and thermal images of Cu / biochar composites are as follows: Figure 4 and Figure 5 As shown, the Cu / biochar composite material exhibits a plasmonic resonance effect, and the surface temperature of the catalyst rises to 127.8℃ when it floats on the water surface under 300W xenon lamp irradiation.

[0031] This invention also provides a method for using Cu / biochar composite materials for CO2 capture and conversion at room temperature and pressure.

[0032] The method is as follows: The Cu / biochar composite material obtained in Example 1 is placed in the quartz tube of the evaluation device. The simulated gas is a mixture of CO2 and N2. The initial concentration of CO2 is 15 vol%, and the gas flow rate is about 90 mL / min. Adsorption is performed at room temperature and pressure. The concentration of CO2 in the gas before and after the adsorption reaction is analyzed by a CO2 concentration detector. When the CO2 concentration in the outlet gas reaches 15 vol%, the adsorption is at equilibrium.

[0033] The photocatalytic carbon dioxide reduction application method is as follows: 0.5g of the prepared Cu / biochar composite material is floated on 50mL of deionized water and then added to the photocatalytic reaction device. CO2 is introduced into the reaction device at a flow rate of 30mL / min. After 60min of CO2 introduction, a 300W xenon lamp is used as a simulated light source for irradiation. 5mL of sample is collected every 60min. After centrifugation, the sample is quantitatively analyzed by gas chromatography with external standard method.

[0034] The adsorption performance of the Cu / biochar composite material for CO2 was tested using the above method and found to be 3.25 mmol / g. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 to methanol in pure water was 4.1 μmol·g. -1 ·h -1 .

[0035] Example 2

[0036] Waste biomass was washed, dried, and the resulting biomass material was obtained. 1% (by weight) of copper nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, the solution was placed in a tube furnace and held at 400°C for 2 hours under a nitrogen atmosphere to obtain the finished Cu / biochar product.

[0037] The CO2 adsorption performance of the Cu / biochar composite material was tested using the above method and found to be 2.89 mmol / g.

[0038] The application method is the same as in Example 1; after 4 hours of simulated sunlight, the yield of methanol produced by photocatalytic reduction of CO2 in pure water was 4.2 μmol·g. -1 ·h -1 .

[0039] Example 3

[0040] Waste biomass was washed, dried, and the resulting biomass material was obtained. Copper nitrate at 3% of the mass of the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, the solution was placed in a tube furnace and kept at 500℃ for 3 hours under a N2 atmosphere to obtain the finished Cu / biochar product.

[0041] The adsorption performance of the Cu / biochar composite material for CO2 was tested using the above method and found to be 3.05 mmol / g. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 to methanol in pure water was 3.9 μmol·g. -1 ·h -1 .

[0042] Example 4

[0043] Waste biomass was washed, dried, and used to obtain biomass material. 7% (by weight) of copper nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and kept at 700℃ for 3 hours to obtain the finished Cu / biochar product.

[0044] The adsorption performance of the Cu / biochar composite material for CO2 was tested using the above method and found to be 3.10 mmol / g. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 to methanol in pure water was 4.3 μmol·g. -1 ·h -1 .

[0045] Example 5

[0046] Waste biomass was washed, dried, and used to obtain biomass material. Cobalt nitrate at 5% of the mass of the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and kept at 550℃ for 2.5 hours to obtain the finished Co / biochar product.

[0047] The CO2 adsorption performance of the Co / biochar composite material was tested using the above method and found to be 2.84 mmol / g. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 to methanol in pure water was 4.2 μmol·g. -1 ·h -1 .

[0048] Example 6

[0049] Waste biomass was washed, dried, and used to obtain biomass material. 5% (by weight) of nickel nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and held at 450℃ for 2.5 hours to obtain the finished Ni / biochar product.

[0050] The adsorption performance of the Ni / biochar composite material for CO2 was tested using the above method and found to be 2.71 mmol / g. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 to methanol in pure water was 4.0 μmol·g. -1·h -1 .

[0051] Comparative Example 1

[0052] Waste biomass was washed, dried, and used to obtain biomass material. 5% (by weight) of copper nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and held at 300℃ for 2 hours to obtain the finished Cu / biochar product.

[0053] In this comparative example, the calcination temperature of the composite material prepared was too low, resulting in Cu... 2+ The CO2 was not completely reduced to elemental Cu. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 in pure water was only 1.5 μmol·g. -1 ·h -1 .

[0054] Carbothermic reduction is difficult to perform under low temperature conditions, which makes it impossible to fully reduce metal ions. At the same time, the ash in biochar will block its pores, which is not conducive to the formation of a hierarchical porous structure.

[0055] Comparative Example 2

[0056] Waste biomass was washed, dried, and used to obtain biomass material. 5% (by weight) of copper nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging, it was dried and placed in a muffle furnace at 600℃ for 2 hours to obtain the finished Cu / biochar product.

[0057] The composite material prepared in this comparative example, due to the lack of nitrogen-protected calcination, resulted in Cu... 2+ The CO2 was not completely reduced to elemental Cu. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 in pure water was only 1.6 μmol·g. -1 ·h -1 .

[0058] Comparative Example 3

[0059] Waste biomass was washed, dried, and used to obtain biomass material. Copper nitrate at 5% of the mass of the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace and kept at 900℃ for 2 hours under a N2 atmosphere to obtain the finished Cu / biochar product.

[0060] The composite material prepared in this comparative example suffered from excessive carbon loss due to excessively high calcination temperature, resulting in metal agglomeration on the biochar and the loss of the plasmon resonance effect in the Cu / biochar. Simultaneously, the honeycomb structure collapsed, failing to maintain its hierarchical porous overall structure. Under simulated sunlight for 4 hours, the yield of methanol produced by photocatalytic reduction of CO2 in pure water was 1.3 μmol·g. -1 ·h -1 .

[0061] Comparative Example 4

[0062] Waste biomass was washed, dried, and used to obtain biomass material. 8% (by weight) of copper nitrate from the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and held at 600℃ for 1.5 hours to obtain the finished Cu / biochar product.

[0063] The Cu particles in the composite material prepared in this comparative example exhibited severe aggregation on biochar. After 4 hours of simulated sunlight irradiation, the yield of methanol produced by photocatalytic reduction of CO2 in pure water was 1.7 μmol·g. -1 ·h -1 .

[0064] Comparative Example 5

[0065] Waste biomass was washed, dried, and pulverized, then passed through a 30-mesh sieve to obtain biomass powder. Copper nitrate at 5% of the mass of the waste biomass was dissolved in deionized water to prepare a solution. The waste biomass was repeatedly immersed in the solution to ensure complete adsorption. After purging and drying, it was placed in a tube furnace under a N2 atmosphere and kept at 600℃ for 2 hours to obtain the finished Cu / biochar product.

[0066] The composite material prepared in this comparative example is dispersed in solution, and the catalyst surface temperature is low under light irradiation. After 4 hours of simulated sunlight irradiation, the yield of methanol produced by photocatalytic reduction of CO2 in pure water is 0.9 μmol·g. -1 ·h -1 .

[0067] Because powder cannot adequately provide microchannels for water to evaporate into gaseous flow, the liquid-solid reaction is transformed into a more complete gas-solid reaction.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a floating honeycomb-like biochar composite material for capturing and converting CO2, characterized in that: (1) Take waste biomass, wash it, cut it into sections and dry it to obtain block biomass material; the waste biomass is straw or corn cob; (2) Dissolve copper nitrate in deionized water to prepare a solution; the mass of the copper nitrate is 1% to 7% of the biomass mass; (3) Immerse the block biomass material from step (1) in the solution prepared in step (2), dry it, and repeat the immersion process until the solution is completely adsorbed; (4) The biomass impregnated in step (3) is calcined in a N2 atmosphere at a temperature of 400-800 ℃ for 2-3 h to obtain elemental copper / floating honeycomb biochar.

2. The method for preparing floating honeycomb-like biochar composite material for capturing and converting CO2 according to claim 1, characterized in that: The size of the block biomass material is a cylinder with a diameter of 2-5cm and a height of 3-6cm.

3. The application of the floating honeycomb-like biochar composite material prepared according to claim 1, characterized in that: Floating honeycomb-like biochar composite materials are used as catalysts to capture and convert CO2 into methanol.

4. The application according to claim 3, characterized in that: The prepared floating honeycomb-like biochar composite material was floated on water and then added to a photocatalytic reaction device. CO2 was introduced into the reaction device, and then the device was irradiated with sunlight to carry out photocatalytic reduction of CO2 to methanol.

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