A biomass-based catalyst based on an acid-base impregnation-high temperature combined process, a preparation method and applications thereof

Abstract

The application belongs to the technical field of environmental and energy material synthesis, and particularly relates to a biomass-based catalyst based on an acid-alkali impregnation-high-temperature combined process, a preparation method and application thereof. The preparation method is as follows: firstly, waste biomass is prepared by acid impregnation treatment, and then further impregnated by alkali solution after calcination, so as to form a biomass-based catalyst with furan structure as the main framework and no inorganic impurities loaded on the surface. The removal of inorganic impurities exposes the active sites on the surface of the catalyst, which is beneficial to the adsorption and activation of reactants. At the same time, multifunctional functional groups can be formed on the surface of the catalyst during the impregnation process. In addition, the step-by-step calcination process under a carbon dioxide atmosphere can slow down the structural evolution rate of the catalyst during calcination, so that the inorganic impurities are removed more completely without affecting the structure of the biochar, and the concentration of the functional groups on the surface of the catalyst is higher. Finally, the waste biomass is converted into a low-cost and high-activity photocatalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photocatalyst preparation, and particularly relates to a biomass-based catalyst based on an acid-alkali impregnation-high-temperature combined process, a preparation method and application thereof BACKGROUND

[0002] Photocatalysis is a green energy conversion technology, which can convert solar energy, which is environmentally friendly and easy to obtain, into chemicals with high energy. So far, researchers have made great progress in the field of semiconductor photocatalysis through in-depth exploration of photocatalytic mechanism. However, the traditional photocatalysts, such as titanium dioxide (TiO2) and zinc oxide (ZnO), have the problems of high electron-hole recombination and low activity. New high-performance photocatalysts, such as heterojunction photocatalysts and covalent organic frameworks (COF), often need to be loaded with noble metal sites, thus having the problems of high cost and complex synthesis process. Therefore, developing a photocatalyst with low cost, simple synthesis process and high activity is conducive to the industrialization development of photocatalysis.

[0003] The waste biomass generated in daily life, such as sugarcane residue and corn cob, can be converted into catalysts for recycling through simple synthesis processes such as calcination and hydrothermal treatment. The principle is that these biomasses can form polymerized biomass-based carbon after calcination, which has been proved to have great significance in simplifying the synthesis process and resource recycling. However, so far, these biomass modified carbon materials have low catalytic activity, because most of the inorganic impurities cannot be removed by simple heating in the biomass synthesis process. These inorganic impurities are coated on the surface of the carbon, covering the active sites on the surface of the catalyst, thus hindering the adsorption of reactants on the surface of the catalyst and the migration of photo-generated electrons and holes to the target. SUMMARY

[0004] In order to solve the problem that the active sites of the waste biomass modified carbon material are covered by inorganic impurities, causing low catalytic activity, the application provides a biomass-based catalyst based on an acid-alkali impregnation-high-temperature combined process, a preparation method and application thereof.

[0005] The application discloses a preparation method of a biomass-based catalyst based on an acid-alkali impregnation-high-temperature combined process, which comprises the following steps: step one, grinding dry waste biomass into powder, impregnating the ground biomass powder in a hydrofluoric acid solution with a certain concentration, collecting the biomass residue after impregnation for a period of time, continuously calcining in a CO2 atmosphere in steps, collecting the sample after calcination, washing with deionized water for several times, and drying after washing to obtain an acid-impregnated intermediate; step two, putting a certain amount of H-BS into a sodium hydroxide solution with a certain concentration, impregnating at room temperature for a period of time, further impregnating by heating, then centrifuging to collect the product, washing with deionized water for several times, and drying after washing to obtain the product, which is a biomass-based catalyst.

[0006] Further, the waste biomass is one or more of sugarcane residue and corn cob.

[0007] Further, in the step one, the ratio of the biomass powder to the hydrofluoric acid is 1 g: (10-40) mL; and the concentration of the hydrofluoric acid solution is 2-4 mol / L.

[0008] Further, in the step one, the time for the biomass powder to be immersed in the fluorine acid solution is 1-2 h; the continuous step-by-step calcination is divided into two steps, the first step is to calcine at 200 DEG C for 6 h, and the second step is to calcine at 300 DEG C for 6 h; and the washing times are 3-5 times.

[0009] Further, in the step two, the ratio of the acid-impregnated intermediate to the sodium hydroxide solution is 1 g: (10-40) mL; and the concentration of the sodium hydroxide solution is 1-4 mol / L.

[0010] Further, in the step two, the time for the normal-temperature immersion is 1-2 h; the time for the temperature-increasing immersion is 12 h, and the temperature after the temperature increasing is 60 DEG C.

[0011] Further, in the step two, the washing times are 3-5 times, the drying time is 12 h, and the drying temperature is 80 DEG C.

[0012] The biomass-based catalyst prepared by the preparation method can be excited by light. After the waste gas biomass is subjected to the steps of acid and alkali immersion and high-temperature calcination, the organic matter is converted into a carbon-containing semiconductor polymer structure and can be excited by light. The biomass-based catalyst can be applied to photocatalytic production of H2O2 as a photocatalyst.

[0013] (1) In the biomass-based catalyst preparation method, the hydrogen fluoride immersion treatment can remove part of the inorganic impurities on the surface of the biomass and load halogen groups (-F) on the surface of the catalyst, thereby providing proton binding force for the oxygen reduction reaction. (2) In the biomass-based catalyst preparation method, the sodium hydroxide immersion treatment loads hydroxyl functional groups (-OH) on the surface of the material, which reduces the *OOH energy barrier in the oxygen reduction reaction process, thereby proving the optimization effect of the acid and alkali immersion on the rate-limiting step. (3) In the biomass-based catalyst preparation method, the step-by-step calcination process converts the waste gas biomass into biochar in the first stage, and the second stage improves the calcination temperature to remove inorganic impurities, and the CO2 atmosphere slows down the structure evolution rate of the catalyst in the calcination process, so that the biochar conversion is better and the inorganic impurities removal is more thorough. (4) The inorganic impurities on the surface of the waste biomass-based catalyst prepared in the application are deeply removed, so that the inorganic impurities do not cover the sites, the active sites are exposed, the adsorption of oxygen molecules is facilitated, and the ordered electron hole transfer and enrichment are further improved.

[0014] (5) The waste biomass-based catalyst (H-OH-BS) prepared in this invention, as a new photocatalytic material, has multifunctional functional groups on its surface, which effectively improves the separation efficiency of photogenerated electron-hole pairs and is also beneficial to ·O 2- The formation of [a specific catalyst] effectively improves the yield of H2O2. The H2O2 yield of the waste biomass-based catalyst H-OH-BS prepared in this invention can reach 943.29 μmol / g, which is 6.3 times higher than that of unmodified BS (149.42 μmol / g). Attached Figure Description

[0015] Figure 1 The images show the Fourier transform infrared spectra of different samples; the samples are H-BS and H-OH-BS, respectively.

[0016] Figure 2 These are transmission maps of different samples; the samples are H-BS and H-OH-BS, respectively.

[0017] Figure 3 The images show the X-ray photoelectron spectra of different samples; the samples are H-BS and H-OH-BS, respectively.

[0018] Figure 4 The graph shows the photocatalytic H2O2 production yield of different samples; the samples are BS, H-BS and H-OH-BS, respectively.

[0019] Figure 5 This is the in-situ infrared image of the H-OH-BS sample. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] Example 1: (1) Preparation of BS: 2 g of dried bagasse was ground into powder and put into a tube furnace for calcination under CO2 atmosphere, the calcination temperature was 200 °C, keeping for 6 h, then the temperature was raised to 300 °C, keeping for 6 h. After calcination, the sample was collected, washed with deionized water, and dried to obtain BS.

[0024] (2) Preparation of H-BS: 2 g of dried bagasse was ground into powder, and the ground bagasse powder was put into a 30 mL hydrofluoric acid solution with a concentration of 3 mol / L for immersion. After 2 h of immersion, the bagasse was collected and put into a tube furnace for stepwise calcination under CO2 atmosphere. The first-stage calcination temperature was 200 °C, keeping for 6 h, then the temperature was raised to 300 °C for the second-stage calcination, keeping for 6 h. After calcination, the sample was collected, washed with deionized water, and dried to obtain the acid-impregnated intermediate H-BS.

[0025] (3) Preparation of H-OH-BS: H-BS was put into a 30 mL sodium hydroxide solution with a concentration of 2 mol / L, and immersed at room temperature for 2 h, then the temperature was raised to 60 °C and kept for 12 h. The product was then collected by centrifugation, washed with deionized water, and dried to obtain the modified biochar material, which was denoted as H-OH-BS.

[0026] Figure 1 The Fourier transform infrared (FT-IR) spectra of different samples are shown in the figure. As shown in the figure, in the FT-IR spectra of all materials, H-OH-BS does not have obvious Si-O-Si characteristic vibration peaks, further confirming the removal effect of acid and alkali immersion on Si in the inorganic component. At the same time, it is observed that the peaks at 1026 cm -1 and 1216 cm -1 belong to C-O-C stretching vibration, the peaks at 1612 cm -1 and 1505 cm -1 are divided into C=C stretching vibration, the peak at 1705 cm -1 is due to the stretching vibration of C=O, and C-H stretching at 2924 cm -1 and -OH stretching at 3423 cm -1 are also observed. It is particularly worth noting that H-OH-BS has a significantly enhanced -OH stretching vibration peak, confirming the successful modification of the hydroxyl functional group on the surface of the material. The above results show that the H-OH-BS material can achieve deep removal of inorganic impurities through the combined process of acid and alkali immersion and high temperature.

[0027] Figure 2TEM images of different samples. As shown in the figure, it was found by SEM observation that both materials exhibited microsphere structure with particle size of 1-3 μm, and the H-OH-BS treated by mixed solution showed significantly reduced surface roughness while maintaining the complete spherical morphology, indicating that the treatment process realized the deep removal of surface inorganic impurities on the basis of retaining the main structure of the material.

[0028] Figure 3 X-ray photoelectron spectrograms (XPS) of different samples. The characteristic peaks of C 1s of H-OH-BS in the figure correspond to the characteristic peaks of C-C, C-O and C=O bonds, respectively. The C-N characteristic peak of N 1s spectrum may be derived from the amino structure grafted on the edge of the carbon skeleton. The characteristic peaks of O 1s spectrum correspond to C=O and C-O bonds, respectively. In addition, the weak characteristic peak appearing at 536.57 eV is attributed to C-O-Si, and the newly appearing C-OH characteristic peak at 530.84 eV again proves the successful modification of hydroxyl groups. Figure 3 .3 e Si 2p spectrogram shows that the characteristic peak intensity of C-O-Si bond after alkali treatment is significantly weakened and disappears compared with H-BS. The above results can prove that the hydroxyl group is successfully modified in the material. Combined with the results of C 1s, O 1s spectrogram characteristics and infrared spectroscopy analysis, it further proves the successful preparation of H-OH-BS.

[0029] Evaluation method of photocatalytic hydrogen peroxide production activity: 20 mg of material was uniformly dispersed in a photochemical reaction container containing 100 mL of deionized water, and magnetic stirring was started under air condition. Under the irradiation of xenon lamp (power 300 W), 1 mL of reaction solution was taken every 15 min. After each sampling, a microporous filter membrane with a pore size of 0.22 μm was used for filtration treatment. The whole photocatalytic process lasted for 60 min, and the reaction system temperature was maintained at 20°C by external condensate water during the process. Figure 4 Photocatalytic H2O2 production rate graph of different samples. It is worth noting that the H-OH-BS material treated by acid-alkali impregnation-high temperature combined process showed significantly enhanced H2O2 generation performance compared with the untreated sample, reaching 943.29 μmol / g, which is 6.31 times that of the base material BS, which strongly confirms that the acid-alkali impregnation-high temperature combined process treatment can effectively promote the photocatalytic synthesis of H2O2.

[0030] Figure 5To further reveal the mechanism of H-OH-BS catalyst promoting the generation of H2O2, in-situ Fourier transform infrared spectroscopy was used to detect the experiment in aqueous solution. First, a small amount of catalyst was coated on the detection substrate of the instrument with a cotton swab. Oxygen was continuously supplied to the detection container during the detection, and the sample was continuously illuminated with a 365 nm light source. The detection time was 20 min. The lower line represents the dynamic change of the infrared spectrum from 0 min to 20 min. As shown in the figure, the peak of evaporated water (EW) appears at 1630 cm -1 , and the characteristic peaks of the sample at 1262 cm -1 and 1454 cm -1 are attributed to the characteristic vibration modes of the OOH intermediate adsorbed on the surface of the catalyst. At the same time, the intensity of the OHOOH vibration characteristic peak detected at 1395 cm -1 position shows a significant enhancement trend with the extension of illumination time. This dynamic change process provides direct evidence for the two-electron oxygen reduction reaction (2e - ORR) dominated H2O2 generation mechanism, accompanied by the enhancement of the free hydrogen peroxide molecule (O-H) signal peak at 3647 cm -1 , which means continuous and efficient production of H2O2 on the surface of the catalyst.

[0031] The present application first prepares waste biomass by acid impregnation treatment, and then further impregnates with alkali solution after calcination, forming a biomass-based catalyst with furan structure as the main framework and no inorganic impurities loaded on the surface. The inorganic impurities on the surface of the biomass-based catalyst are removed, so that the active sites on the surface of the catalyst are exposed, which is beneficial to the adsorption and activation of the reactants. At the same time, during the impregnation process, multifunctional functional groups (-F, -OH) can be formed on the surface of the catalyst. These functional groups can provide a hydrophilic surface to provide protons for the catalytic conversion of O2 to H2O2 during the oxygen reduction reaction, and can also provide an alkaline reaction microenvironment to reduce the decomposition efficiency of the product H2O2. In addition, the step-by-step calcination process in a carbon dioxide atmosphere can slow down the structural evolution rate of the catalyst during calcination, so that the inorganic impurities are removed more thoroughly without affecting the structure of the biochar, and the functional group concentration on the surface of the catalyst is higher. Ultimately, waste biomass can be converted into a low-cost, high-activity photocatalyst.

[0032] As described above, although the present application has been shown and described with reference to specific preferred embodiments, it is to be understood that the present application is not to be limited to the details of the foregoing illustrated embodiments. Various changes in form and details can be made without departing from the spirit and scope of the present application.

Claims

1. A method for preparing a biomass-based catalyst based on an acid-base impregnation-high temperature combined process, characterized in that, Includes the following steps: Step 1: Grind the dried waste biomass into powder, put the ground biomass powder into a hydrofluoric acid solution of a certain concentration for impregnation, collect the biomass residue after impregnation for a period of time, continuously calcine it in a stepwise manner in a CO2 atmosphere, collect the sample after calcination, wash it several times with deionized water, and dry it after washing to obtain the acid impregnation intermediate H-BS. The continuous stepwise calcination is divided into two steps: the first step calcination temperature is 200℃, and the second step calcination temperature is 300℃. Step 2: Place a certain amount of H-BS into a sodium hydroxide solution of a certain concentration, soak it at room temperature for a period of time, then further heat it for soaking, then centrifuge to collect the product, wash it several times with deionized water, and dry it to obtain the product, which is the biomass-based catalyst.

2. The preparation method according to claim 1, characterized in that, The waste biomass is one or more of sugarcane bagasse and corn cobs.

3. The preparation method according to claim 1, characterized in that, In step one: The ratio of biomass powder to hydrofluoric acid is 1 g : (10-40) mL; the concentration of hydrofluoric acid solution is 2-4 mol / L.

4. The preparation method according to claim 1, characterized in that, In step one: The biomass powder was soaked in the hydrofluoric acid solution for 1-2 hours. The continuous stepwise calcination is divided into two steps: the first step calcination time is 6 hours, and the second step calcination time is 6 hours. Wash 3-5 times.

5. The preparation method according to claim 1, characterized in that, In step two: The ratio of acid-impregnated intermediate H-BS to sodium hydroxide solution is 1 g : (10-40) mL; The concentration of sodium hydroxide solution is 1-4 mol / L.

6. The preparation method according to claim 1, characterized in that, In step two: The soaking time at room temperature is 1-2 hours; The immersion time was 12 hours, and the temperature after immersion was 60 °C.

7. The preparation method according to claim 1, characterized in that, In step two: The washing cycle is 3-5 times, the drying time is 12 hours, and the drying temperature is 80℃.

8. A biomass-based catalyst prepared by the preparation method according to any one of claims 1-6.

9. The application of the biomass-based catalyst according to claim 8 in photocatalytic H2O2 production.

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