Preparation method and application of a novel biomass-derived photocatalyst with si-o-c bond

Abstract

The application belongs to the field of photocatalysis, and discloses a preparation method of a novel biomass-derived photocatalyst with Si-O-C bonds and application thereof. The method uses urea and rice husk powder as raw materials, and prepares a rice husk-derived intermediate through physical grinding and high-temperature calcination, then mixes the intermediate with melamine, adds deionized water, stirs and calcines again to obtain a biomass-derived modified carbon nitride photocatalyst DK-BCN. The introduction of the rice husk-derived component does not change the overall structure of the bulk carbon nitride, and forms Si-O-C covalent bonds; mechanism analysis shows that the introduction of the bonds can cause electron rearrangement, promote the separation and migration of photo-generated carriers and reduce the recombination. The obtained catalyst can be used for photocatalytic decomposition of water to produce hydrogen under visible light irradiation, and the hydrogen production activity is about 2.6 times that of the bulk carbon nitride BCN. The preparation process is simple and easy to control, the rice husk agricultural waste is used as a biomass precursor, and the application has the characteristics of low cost, green environmental protection and sustainable utilization.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, specifically to a method for preparing a novel biomass-derived photocatalyst with Si-OC bonds and its application in photocatalytic water splitting for hydrogen production under visible light irradiation. Background Technology

[0002] With the rapid development of science and technology, the environmental pollution caused by the combustion of fossil fuels has become increasingly prominent. How to obtain clean energy in a green and efficient way has become an important research direction in the field of energy and environment. Photocatalytic water splitting has the characteristics of being green, efficient, safe and stable. The light absorption capacity of photocatalysts, the separation and migration efficiency of photogenerated carriers, and the number of surface active sites are important factors affecting the performance of photocatalytic hydrogen production.

[0003] Graphitic carbon nitride materials have attracted widespread attention in the field of photocatalytic water splitting due to their environmental friendliness, lack of pollution, and ability to generate photogenerated charge carriers with redox capabilities after photoexcitation. However, bulk g-C3N4 (bulkg-C3N4) prepared by the traditional thermal polycondensation method has shortcomings such as easy exciton recombination, low electrical conductivity, small specific surface area, and narrow light absorption range, which limit its photocatalytic hydrogen production performance. To overcome the above problems, existing studies usually use element doping, morphology control, and defect engineering to modify g-C3N4.

[0004] Agricultural wastes such as rice husks are widely available and inexpensive, and have resource utilization value as precursors for renewable biomass. This invention introduces rice husk-derived material DK into bulk carbon nitride (BCN) to obtain biomass-derived modified carbon nitride DK-BCN. The introduction of DK does not change the overall structure of BCN. O replaces N in the amino groups at the edge of BCN and forms new Si-OC covalent bonds. The introduction of Si-OC bonds leads to electron rearrangement, which can promote the separation and migration of photogenerated carriers and reduce recombination, thereby improving photocatalytic performance. Summary of the Invention

[0005] The purpose of this invention is to provide a novel method for preparing biomass-derived photocatalysts with Si-OC bonds, so as to improve the problems of low visible light utilization of bulk carbon nitride, easy recombination of photogenerated carriers and low photocatalytic efficiency, while realizing the resource utilization of rice husk agricultural waste.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A novel method for preparing biomass-derived photocatalysts with Si-OC bonds includes the following steps: S1. Add urea and rice husk powder to a mortar and grind evenly; S2. Place the ground mixed powder in a crucible, then place it in a muffle furnace for calcination. After cooling to room temperature, remove it and grind it to obtain an intermediate. S3. Mix and grind a certain proportion of intermediate with melamine, place in a crucible and add deionized water and stir, then heat in a muffle furnace to the set temperature at a set heating rate and keep warm; after cooling, grind the obtained solid evenly to obtain a novel biomass-derived photocatalyst with Si-OC bonds.

[0007] Preferably, in step S1, the mass of urea is 1.62g and the mass of rice husk powder is 0.63g.

[0008] Preferably, in step S2, the heating rate of the muffle furnace is 3℃ / min, the reaction temperature is 900℃, and the reaction time is 2h.

[0009] Preferably, in step S3, the ratio of intermediate to melamine is 0.05 to 0.2, and 3 mL of deionized water is added; the heating rate for the second calcination is 2 °C / min, the reaction temperature is 550 °C, and the reaction time is 4 h.

[0010] More preferably, in step S3, after adding deionized water, the mixture is stirred for 30 minutes; when the amount of intermediate is 0.1g and the amount of melamine is 1g, the resulting sample is named DK-BCN-10.

[0011] The present invention also provides the application of the novel biomass-derived photocatalyst with Si-OC bonds prepared by the above method in photocatalytic water splitting to produce hydrogen under visible light irradiation.

[0012] Compared with the prior art, the present invention has the following beneficial effects: In this invention, the composite of rice husk-derived components alters the morphological characteristics of bulk carbon nitride, resulting in a material with a larger specific surface area and more potential active sites. The introduction of Si-OC bonds induces electron rearrangement and optimizes the electronic structure, which is beneficial for the separation and migration of photogenerated carriers and reduces electron-hole pair recombination.

[0013] The DK-BCN-10 obtained by this invention exhibits enhanced absorption capacity in the visible light region, reduced fluorescence emission intensity, decreased electrochemical impedance, and photocurrent intensity approximately four times that of bulk carbon nitride, demonstrating superior charge separation and migration capabilities.

[0014] Under visible light irradiation, the photocatalytic water splitting and hydrogen production activity of DK-BCN-10 is approximately 2.6 times that of BCN.

[0015] The preparation method of this invention is simple, easy to control, and has good repeatability. Using rice husk agricultural waste as a renewable biomass precursor, it is low-cost, green and environmentally friendly, and conducive to further large-scale preparation. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope (SEM) image of the biomass-derived photocatalyst DK-BCN-10 prepared in Example 2 of the present invention; Figure 2 The N2 isotherm adsorption-desorption curves of bulk carbon nitride BCN and DK-BCN-10 are shown. Figure 3 The solid-state UV diffuse reflectance spectra of bulk carbon nitride BCN and DK-BCN-10 are shown. Figure 4 The solid-state fluorescence (PL) spectra of bulk carbon nitride BCN and DK-BCN-10 are shown. Figure 5 Electrochemical impedance spectroscopy (EIS) spectra of bulk carbon nitride BCN and DK-BCN-10; Figure 6 Photocurrent response diagrams of bulk carbon nitride BCN and DK-BCN-10; Figure 7 The graph shows the photocatalytic water splitting and hydrogen production curves of bulk carbon nitride (BCN) and DK-BCN-10 under visible light irradiation. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, without changing the overall technical solution of the present invention, the following content mainly focuses on the disclosed raw material composition, calcination sequence, process parameters, and characterization results, further elaborating on each operational step and their interrelationships to provide a clearer understanding of the preparation process and photocatalytic performance of the present invention. The temperatures, heating rates, holding times, raw material amounts, and sample names involved in the following embodiments are all based on the description in this scheme, and do not introduce new reaction systems or new performance data.

[0018] Example 1: Preparation of bulk carbon nitride (BCN) 2g of melamine was placed in a crucible and then placed in a muffle furnace for heat treatment. The muffle furnace was heated to 550℃ at a heating rate of 2℃ / min. After reaching the set temperature, it was held for 4 hours to allow the melamine to form bulk carbon nitride under these heat treatment conditions. After the holding time was completed, the heating was stopped, and the sample was cooled before the solid was taken out. The solid was then ground thoroughly into a relatively uniform powder to obtain the bulk carbon nitride sample, which was named BCN.

[0019] The BCN prepared in this embodiment serves as a comparative sample to the DK-BCN-10 obtained in Example 2. As can be seen from the preparation conditions, the BCN was prepared by direct calcination of melamine. The heating rate, final calcination temperature, and holding time used in the calcination stage were 2℃ / min, 550℃, and 4h, respectively. These are consistent with the main heat treatment conditions used in Example 2 when the intermediate and melamine were calcined together for the second time. Therefore, by comparing the morphology, specific surface area, light absorption, fluorescence, electrochemical response, and photocatalytic hydrogen production performance of BCN and DK-BCN-10, the changes in the material properties obtained after the introduction of the rice husk-derived intermediate can be demonstrated. It should be noted that the purpose of this embodiment is to obtain a bulk carbon nitride reference sample without the introduction of rice husk-derived components, without changing the composition and preparation route of BCN in this scheme.

[0020] Example 2: Preparation of DK-BCN-10 Step 1: Weigh 1.62g of urea and 0.63g of rice husk powder, and add both raw materials together to a mortar for physical grinding. During the grinding process, mix the urea and rice husk powder as evenly as possible so that the two solid raw materials form a relatively uniformly dispersed mixture before entering the first high-temperature calcination. This step uses a simple physical mixing method, which does not require the introduction of additional chemical reagents or complex pretreatment, and maintains the characteristics of the preparation method described in this scheme as simple and easy to control. The amount of urea and rice husk powder is kept at 1.62g and 0.63g respectively, without changing the original raw material ratio.

[0021] Step 2: Transfer the mixed powder obtained from the first grinding step to a crucible, place the crucible in a muffle furnace, heat it to 900°C at a heating rate of 3°C / min, and maintain it at 900°C for 2 hours. This process is the first calcination process for preparing the rice husk-derived intermediate in this invention. After the heat treatment, allow the crucible and the solid material inside to cool to room temperature, then remove the solid and grind it evenly to obtain the intermediate required for subsequent compounding with melamine.

[0022] In this step, urea and rice husk powder are first calcined together at high temperature, and then the resulting intermediate is used in the next stage to be calcined together with melamine. This is the process sequence adopted in this invention. The heating rate of the first calcination is 3℃ / min, the reaction temperature is 900℃, and the reaction time is 2h. All of the above conditions are kept consistent with the materials in this scheme. After cooling, the intermediate is ground again to keep the resulting intermediate in a relatively uniform powder state so that it can be physically blended with melamine in the future. This intermediate is the rice husk-derived component used to construct the DK-BCN composite system in the future.

[0023] Step 3: Weigh 0.1g of the above intermediate and 1g of melamine, grind and mix them, then place them in a crucible, add 3mL of deionized water and stir for 30min. The amounts of intermediate and melamine used in this embodiment correspond to the specific preparation conditions of the DK-BCN-10 sample in this scheme, and the ratio of intermediate to melamine is within the range of 0.05 to 0.2 described in this scheme. After adding deionized water and stirring, the intermediate and melamine are further contacted and mixed.

[0024] The mixture and crucible were placed in a muffle furnace and heated to 550°C at a heating rate of 2°C / min. The mixture was then held at 550°C for 4 hours to complete the second calcination. After the calcination was completed and the mixture was cooled, the resulting solid was removed and ground evenly to obtain a novel biomass-derived photocatalyst with Si-OC bonds, which was named DK-BCN-10.

[0025] From the overall preparation sequence, this embodiment first obtains an intermediate by grinding urea and rice husk powder and calcining at 900℃. Then, the intermediate is physically blended with melamine and co-calcined at 550℃. This method does not change the core route of "direct calcination after physical blending of rice husk derivatives and melamine" in this scheme. Through the above two-stage treatment, the rice husk derivative component is introduced into the carbon nitride system, and finally DK-modified carbon nitride material DK-BCN is obtained. The mechanism analysis in this scheme shows that the modification of DK does not change the overall structure of BCN. O replaces N in the edge amino group of BCN and forms a new Si-OC covalent bond. The introduction of Si-OC bond can lead to electron rearrangement and enhance charge carrier dynamics.

[0026] Further examining the relationship between process parameters, the two calcinations in Example 2 represent different stages of material construction. The first calcination uses the aforementioned mixture of urea and rice husk powder as the treatment target, heating to 900°C at 3°C / min and holding for 2 hours, with the product serving as a rice husk-derived intermediate. The second calcination uses a mixture of this intermediate and melamine as the treatment target, heating to 550°C at 2°C / min and holding for 4 hours, ultimately yielding DK-BCN. The two stages are connected through a "cooling-grinding-remixing" operation, ensuring that the product obtained from the first calcination... The intermediate can be further contacted with melamine in powder form. This scheme also provides a ratio of intermediate to melamine of 0.05 to 0.2. This embodiment uses a specific combination of 0.1g intermediate and 1g melamine, corresponding to the DK-BCN-10 sample. Since this scheme does not provide complete preparation data and performance test results for other specific samples within this ratio range, this specification does not make assumptions about the hydrogen production performance of samples with other ratios. The above treatment retains the relatively wide process range summarized in the claims and also ensures that the data source of the specific embodiment is consistent with this scheme.

[0027] Performance characterization and photocatalytic hydrogen production applications To evaluate the changes in material characteristics and photocatalytic performance of DK-BCN-10 obtained in Example 2 compared to BCN obtained in Example 1, comparisons were made using scanning electron microscopy, N2 isothermal adsorption-desorption, solid-state UV diffuse reflectance, solid-state fluorescence spectroscopy, electrochemical impedance spectroscopy, photocurrent response, and photocatalytic water splitting for hydrogen production under visible light irradiation. The following is a summary of these comparisons. Figures 1-7 To further explain the above results, all characterizations were carried out on two samples, BCN and DK-BCN-10, to illustrate the changes in the rice husk-derived modified materials from different aspects such as morphology, surface features, light absorption capacity, and photogenerated carrier behavior.

[0028] like Figure 1 As shown, the DK-BCN-10 obtained in Example 2 exhibits a thinner morphology with more wrinkles. Compared with bulk carbon nitride (BCN), it is thinner and has more wrinkles. This morphological change is consistent with the description in this scheme regarding the influence of biomass derivative composites on the morphological characteristics of bulk carbon nitride. The thinner morphology with more wrinkles is beneficial for exposing the material surface, providing a corresponding characterization basis for the subsequent increase in specific surface area and active sites from a morphological perspective. Here, the morphology judgment is based solely on the SEM results shown in this scheme, without any additional numerical limitations on the sheet thickness or particle size.

[0029] like Figure 2 As shown, the N2 isotherm adsorption-desorption curves of BCN and DK-BCN-10 differ. Analysis of the curves reveals that DK-BCN-10 has a higher specific surface area than BCN. This increased specific surface area means that, under the same material mass conditions, more accessible surface can be provided, thus increasing the number of surface active sites that may participate in the photocatalytic reaction. This result is consistent with... Figure 1 The corresponding changes in morphology, characterized by thinner thickness and more wrinkles, indicate that the introduction of rice husk-derived components not only forms new chemical bonding features but also affects the morphology and surface structure of carbon nitride materials.

[0030] like Figure 3 As shown, both BCN and DK-BCN-10 exhibit corresponding light absorption in the ultraviolet and visible light regions, while DK-BCN-10 has stronger absorption capacity in the visible light region than BCN. Photocatalytic reactions first require materials to respond effectively to incident light, so enhancing visible light absorption capacity is beneficial to improving the utilization of visible light. In conjunction with the application objectives of this invention, this light absorption change provides optical characterization support for DK-BCN-10 to obtain higher photocatalytic hydrogen production activity under visible light irradiation conditions. This scheme provides a new band gap value, therefore, this embodiment does not impose additional limitations on its band gap.

[0031] like Figure 4 As shown, the solid-state fluorescence (PL) emission intensity of DK-BCN-10 is significantly lower than that of BCN. For the two carbon nitride materials studied in this scheme, this change indicates that DK-BCN-10 can more effectively suppress the recombination of photogenerated carriers, thereby improving the separation efficiency of photogenerated electrons and holes. Combined with the Si-OC bond interaction mechanism proposed in this scheme, it can be considered that the electron rearrangement generated after the introduction of Si-OC bonds is related to the improvement of carrier dynamics, making the photoexcited carriers more conducive to participating in the subsequent migration process, rather than recombination.

[0032] like Figure 5 As shown, the radius of the EIS curve of DK-BCN-10 is significantly smaller than that of BCN. The smaller radius reflects the higher charge transfer efficiency of DK-BCN-10. This result further confirms the improved carrier migration behavior in the DK-modified material from the perspective of electrochemical response, and is consistent with... Figure 4 The trend reflected is consistent with the suppression of photogenerated carrier recombination. In other words, the introduction of rice husk-derived components not only affects the light absorption and surface morphology of the material, but also plays a positive role in the separation and transport of photogenerated charges.

[0033] like Figure 6 As shown in the figure, under the same test conditions, DK-BCN-10 exhibits a significantly higher photocurrent response than BCN, with its photocurrent intensity being approximately four times that of bulk carbon nitride BCN. The higher photocurrent response indicates that more photogenerated carriers can participate in migration after illumination, suggesting that DK-BCN-10 has better charge separation capability. This result is consistent with the trend obtained from PL spectroscopy and EIS testing, namely that recombination of photogenerated carriers in DK-BCN-10 is suppressed, while the carrier migration efficiency is improved. These changes together contribute to improving the charge utilization efficiency in the photocatalytic hydrogen production process.

[0034] like Figure 7 As shown, both BCN and DK-BCN-10 exhibited an increasing trend in hydrogen production as the visible light irradiation time increased. However, the hydrogen evolution curve corresponding to DK-BCN-10 showed a more significant increase. The photocatalytic hydrogen production activity of DK-BCN-10 through water splitting was approximately 2.6 times that of BCN. This indicates that after modifying BCN with rice husk-derived intermediates, the actual photocatalytic hydrogen production performance of the material was significantly improved. This improvement is consistent with the aforementioned characterization results, such as enhanced visible light absorption, increased specific surface area, reduced photogenerated carrier recombination, and improved charge transfer efficiency.

[0035] comprehensive Figures 1-7It can be seen that this invention does not simply improve photocatalytic performance by changing a single physical parameter, but rather by combining rice husk-derived components with the carbon nitride system to synergistically change the morphology, surface features, light absorption, and photogenerated carrier behavior of the material. The modification of DK does not change the overall structure of BCN. O replaces N in the edge amino group of BCN and forms Si-OC bonds. The new Si-OC covalent bonds cause electron rearrangement, thereby enhancing charge carrier dynamics, promoting the separation and migration of photogenerated electron-hole pairs and reducing recombination. As a result, more photogenerated carriers can participate in the interfacial reactions related to photocatalytic water splitting for hydrogen production, ultimately resulting in higher hydrogen production activity of DK-BCN-10 compared to BCN.

[0036] Therefore, the process route of "calcining urea and rice husk powder to form an intermediate, then co-calcining the intermediate with melamine" adopted in this embodiment has a clear correspondence with the final material properties. The first stage obtains a rice husk-derived intermediate, and the second stage introduces the intermediate into carbon nitride to form a DK-BCN system and form Si-OC bonds. At the same time, the specific surface area, visible light absorption, and carrier separation and migration characteristics of the material are all improved. The above results together demonstrate that the present invention can utilize rice husk, an agricultural waste, as a renewable precursor, and achieve effective improvement of the photocatalytic performance of bulk carbon nitride while maintaining simple preparation steps and easy-to-control conditions.

[0037] The DK-BCN-10 obtained by this invention can be used for photocatalytic water splitting to produce hydrogen under visible light irradiation. Compared with BCN in Example 1, its hydrogen production activity is increased by about 2.6 times. Since the core preparation process of this invention mainly includes solid raw material grinding, two-stage calcination, deionized water stirring and cooling followed by grinding, the required process flow is relatively straightforward. At the same time, rice husk is a renewable agricultural waste source, which meets the characteristics of low cost, green environmental protection and being conducive to large-scale production.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a novel biomass-derived photocatalyst with Si-OC bonds, characterized in that, Includes the following steps: S1. Add urea and rice husk powder to a mortar and grind them evenly to obtain a mixed powder. S2. Place the mixed powder in a crucible, calcine it for the first time in a muffle furnace, cool it to room temperature, take it out and grind it to obtain an intermediate; S3. The intermediate is mixed and ground with melamine and placed in a crucible. Deionized water is added and stirred. Then, it is calcined for the second time in a muffle furnace. After cooling, the resulting solid is ground evenly to obtain a novel biomass-derived photocatalyst with Si-OC bonds.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass of urea is 1.62g and the mass of rice husk powder is 0.63g.

3. The preparation method according to claim 1, characterized in that, The heating rate for the first calcination in step S2 is 3℃ / min, the calcination temperature is 900℃, and the holding time is 2h.

4. The preparation method according to claim 1, characterized in that, In step S3, the ratio of the intermediate to melamine is 0.05 to 0.2, and the volume of deionized water added is 3 mL.

5. The preparation method according to claim 1 or 4, characterized in that, After adding deionized water in step S3, stir for 30 minutes.

6. The preparation method according to claim 1, characterized in that, The heating rate for the second calcination in step S3 is 2℃ / min, the calcination temperature is 550℃, and the holding time is 4h.

7. The preparation method according to any one of claims 1, 4 to 6, characterized in that, In step S3, the amount of the intermediate used is 0.1g, and the amount of melamine used is 1g.

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