Cu monatomic anchoring g-C3N4 / Bi2O3 photocatalyst based on biomass conversion as well as preparation method and application of g-C3N4 / Bi2O3 photocatalyst

Abstract

The invention provides a g-C3N4 / Bi2O3 photocatalyst based on biomass conversion Cu monatomic anchoring as well as a preparation method and application of the g-C3N4 / Bi2O3 photocatalyst, and belongs to the technical field of liquid biomass catalytic conversion. The preparation method of the photocatalyst comprises the following steps: taking g-C3N4 and a bismuth source as raw materials, and performing solvothermal reaction to obtain a precursor; calcining the precursor to obtain a g-C3N4 / Bi2O3 composite carrier; the g-C3N4 / Bi2O3 composite carrier is soaked in an alcoholic solution of copper salt, a solid product is collected after soaking is completed, then the solid product is calcined, and the Cu single atom anchored g-C3N4 / Bi2O3 photocatalyst is obtained. The photocatalyst is rich in oxygen vacancies, so that the band gap of the catalyst is effectively reduced, and the light response range is widened to a near-infrared region. In addition, the special structure of the catalyst significantly improves the carrier separation capability, and improves the utilization capability of high-energy photons.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid biomass catalytic conversion, and particularly relates to a g-C3N4 / Bi2O3 photocatalyst based on biomass conversion Cu monatomic anchoring and a preparation method and application thereof. BACKGROUND

[0002] The large consumption of traditional fossil energy and the increasing difficulty of exploitation lead to the global energy supply becoming increasingly tight. Under this background, accelerating the development of renewable energy, promoting the transformation of energy structure, and reducing the dependence on fossil energy have become the key path to realize sustainable development. Biomass energy, as the only renewable resource based on carbon in nature, has the advantages of wide distribution, diverse types and low cost, and is recognized as the fourth largest energy source after coal, oil and natural gas. Efficiently converting renewable biomass resources into fuels and high-value fine chemicals helps to alleviate the energy crisis. Among them, liquid biomass catalytic refining of biodiesel is concerned due to its technical feasibility and environmental friendliness. Biodiesel is widely sourced and renewable, and has the potential to replace traditional fossil fuels. The pollutant emissions during its combustion process are significantly lower than those of fossil fuels, and it has excellent lubricating properties, which helps to reduce engine wear and improve the biocompatibility of the fuel system. Therefore, it is urgent to develop green and efficient liquid biomass value-added conversion and environmental remediation technologies to co-respond to the dual challenges of energy shortage and environmental pollution.

[0003] As a green chemical technology, photocatalysis can directly convert light energy into chemical energy to drive organic conversion reactions. However, traditional ultraviolet and visible light catalysis usually relies on high-energy photons, which easily triggers side reactions or causes irreversible degradation of photosensitive substrates, limiting its applicability in complex reaction systems. In contrast, near-infrared light has longer wavelength and lower photon energy, which not only significantly reduces the risk of photodamage to reactants, but also exhibits excellent medium penetration ability, thereby providing the possibility for realizing mild and highly selective catalytic processes. Nevertheless, the research on the preparation of biodiesel using near-infrared photocatalytic technology is still limited. At the same time, due to the lower photon energy, how to design an efficient light harvesting system to achieve full absorption and effective utilization of near-infrared light energy has become a key scientific challenge in this field. SUMMARY

[0004] Therefore, the present application aims to provide a g-C3N4 / Bi2O3 photocatalyst based on biomass conversion Cu monatomic anchoring and a preparation method and application thereof.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: One of the technical solutions of the present application is a preparation method of a Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst based on biomass conversion, comprising the following steps: A precursor is obtained by a solvothermal reaction using g-C3N4 and a bismuth source as raw materials. The precursor is calcined to obtain a g-C3N4 / Bi2O3 composite carrier. The g-C3N4 / Bi2O3 composite carrier is immersed in an alcohol solution of copper salt, and after the immersion is completed, a solid product is collected, and then the solid product is calcined to obtain the Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst.

[0006] The second technical solution of the present application is a Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst prepared by the above preparation method.

[0007] The third technical solution of the present application is an application of the above Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst in photocatalytic liquid biomass oil synthesis of biodiesel.

[0008] The fourth technical solution of the present application is a method for preparing biodiesel, which comprises mixing liquid biomass oil, methanol and the above Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst, and then performing a reaction under room temperature and light conditions.

[0009] The present application discloses the following technical effects: The Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst provided by the present application has rich oxygen vacancies, effectively narrows the band gap of the catalyst, and widens the light response range to the near-infrared region. In addition, the special structure of the catalyst significantly improves the carrier separation ability and enhances the utilization ability of high-energy photons.

[0010] The Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst provided by the present application can efficiently utilize light energy to realize efficient conversion of liquid biomass into biodiesel, and the biodiesel yield does not decrease significantly during repeated use for 5 times, which has good application prospect and economic benefit.

[0011] The method for preparing biodiesel provided by the present application can be carried out at room temperature, and the reaction conditions are mild, avoiding high temperature, high pressure and high pH reaction conditions, and can realize controllable generation of reaction products, and the operation process is simple, which has great application potential. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed in the embodiments will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0013] Figure 1 X-ray diffraction spectra of different samples in embodiments 1-3 of the present application; Figure 2 Infrared spectra of different samples in embodiments 1-3 of the present application; Figure 3 Nitrogen adsorption-desorption spectra of different samples in embodiments 1-3 of the present application; Figure 4 K-edge near-edge spectra and extended edge spectra of Cu element in the Cu2 / g-C3N4 / Bi2O3 photocatalyst in embodiment 2 of the present application; wherein a is the Cu K-edge X-ray absorption near-edge structure spectrum of the Cu2 / g-C3N4 / Bi2O3 photocatalyst in embodiment 2 of the present application, b is the Fourier transform extended X-ray absorption fine structure spectrum of the Cu2 / g-C3N4 / Bi2O3 photocatalyst in embodiment 2 of the present application, c is the wavelet transform extended X-ray absorption fine structure of the Cu2 / g-C3N4 / Bi2O3 photocatalyst in embodiment 2 of the present application, and d is the wavelet transform extended X-ray absorption fine structure of a copper foil; Figure 5 Electron spin resonance spectra of different samples in embodiments 1-3 of the present application; Figure 6 UV-visible diffuse reflectance spectra of different samples in embodiments 1-3 of the present application; Figure 7 Experimental results of the preparation of biodiesel by the Cux / g-C3N4 / Bi2O3 photocatalyst in the present application; wherein a is the yield of biodiesel of different catalysts under different light source conditions; b, c, and d are the effects of the interaction between the molar ratio of alcohol to oil and reaction time, the molar ratio of alcohol to oil and catalyst dosage, and the catalyst dosage and reaction time on the yield, respectively; e is the biodiesel yield of the catalyst for various oil substrates; and f is the recycling result of the catalyst. DETAILED DESCRIPTION

[0014] The various exemplary embodiments of the present application will now be described in detail, which should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present application.

[0015] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of, for example, concentration, intensity, and time, and the like, every intermediate value of the range is specifically included in the scope of the application. Where the context permits, any reference to a number of steps, compositions, and the like, can refer to one or more steps or compositions. The use of "adapted to" and other future tense

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference in this specification is not an admission that it is prior art.

[0017] Many modifications and variations of this application of the present application can be made without departing from its spirit or scope, which will be apparent to those skilled in the art. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only. It is to be understood that the application is not limited in scope by the specific embodiments described herein. Rather, the intent is to embrace all changes and modifications that can come within the spirit and scope of the application.

[0018] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional, unrecited elements or method steps.

[0019] In the present application, room temperature means 25°C to 30°C.

[0020] Bismuth-based semiconductors are unique 6δ 2Lone pair electron effects, visible light response, and environmental friendliness have attracted significant attention in the field of photocatalysis. β-Bi₂O₃, with a band gap of approximately 2.4 eV, effectively absorbs visible light and is rich in oxygen vacancies, which is beneficial for reactant adsorption and activation. g-C₃N₄ and Bi₂O₃ are complementary in terms of band structure and light absorption range: g-C₃N₄ absorbs blue-violet light, while Bi₂O₃ absorbs yellow-green light; their coupling can broaden the light response range and form a direct Z-shaped heterojunction. This structure promotes recombination of conduction band electrons in g-C₃N₄ and valence band holes in Bi₂O₃ through an interfacial built-in electric field, retaining highly oxidizing holes and highly reducing electrons, achieving efficient charge separation. Furthermore, single atoms, with their high atomic utilization, tunable electronic structure, and well-defined coordination environment, can not only serve as highly efficient active centers to lower reaction energy barriers but also extend light absorption to the near-infrared region through localized surface plasmon resonance effects. This invention loads copper single atoms onto the surface of g-C3N4 / Bi2O3, utilizing the synergistic effect of single-atom catalytic centers and oxygen vacancies to effectively broaden the photoresponse range to the near-infrared region and significantly improve the photogenerated charge separation efficiency, thereby achieving efficient esterification / transesterification of liquid biomass to produce biodiesel under near-infrared light-driven conditions.

[0021] The first aspect of this invention provides a method for preparing a g-C3N4 / Bi2O3 photocatalyst based on Cu single-atom anchoring from biomass conversion, comprising the following steps: The precursor was obtained by solvothermal reaction using g-C3N4 and bismuth source as raw materials; The precursor was calcined to obtain the g-C3N4 / Bi2O3 composite support; The g-C3N4 / Bi2O3 composite support was impregnated in an alcoholic solution of copper salt. After impregnation, the solid product was collected and then calcined to obtain the Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst.

[0022] In a preferred embodiment of the present invention, the preparation method of g-C3N4 is as follows: melamine is calcined at high temperature and then ground; the calcination parameters are set as follows: after calcining at 500~600 ℃ for 2~6 h, the temperature is programmed to rise to 520~700 ℃ at a heating rate of 2 ℃ / min, and calcination is continued for 0~4 h.

[0023] In the preparation of the g-C3N4 support, this invention employs a two-stage programmed temperature-increasing calcination strategy (holding at 500–600℃ for 2–6 h, then increasing the temperature at 2℃ / min to 520–700℃ and continuing calcination for 0–4 h). This not only ensures that melamine fully condenses to form highly crystalline g-C3N4, but also introduces appropriate amounts of nitrogen vacancies and surface defects by precisely controlling the heat treatment conditions, providing active sites for the subsequent anchoring of metal ions. If the temperature is too low, the condensation will be incomplete, and if it is too high, the g-C3N4 structure will collapse, both of which are detrimental to the performance of the composite catalyst.

[0024] In a preferred embodiment of the present invention, the precursor is obtained by a solvothermal reaction using g-C3N4 and a bismuth source as raw materials, specifically: Bismuth source and g-C3N4 were added to glacial acetic acid. After the bismuth source dissolved, ethanol was added and mixed evenly. Then, a solvothermal reaction was carried out.

[0025] In a preferred embodiment of the present invention, the bismuth source is bismuth nitrate; the molar ratio of bismuth in the g-C3N4 and the bismuth source is (1~4):1; the temperature of the solvothermal reaction is 160~200 ℃ and the time is 16~20 h.

[0026] More preferably, the molar ratio of bismuth in the g-C3N4 and the bismuth source is 2.7:1; the temperature of the solvothermal reaction is 180 °C, and the time is 16~20 h.

[0027] In this invention, when constructing the g-C3N4 / Bi2O3 heterojunction, the molar ratio of g-C3N4 to bismuth source (preferably bismuth nitrate) is strictly limited to (1–4):1, and further optimized to 2.7:1. Combined with solvothermal reaction conditions of 180℃ and 16–20h, high dispersion and tight interfacial coupling of Bi2O3 on the g-C3N4 surface can be achieved. Deviating from this ratio easily leads to insufficient Bi2O3 loading or agglomeration, weakening the heterojunction's ability to promote charge separation. Crucially, the solvent system uses glacial acetic acid to dissolve the bismuth source before adding ethanol for dilution. This mixed solvent design effectively suppresses Bi2O3... 3+ Rapid hydrolysis avoids the formation of impurity phases, thus ensuring the in-situ uniform nucleation of Bi2O3 nanocrystals.

[0028] In a preferred embodiment of the present invention, after the solvothermal reaction is completed, the reaction system is further cooled to room temperature, and then the solid product is collected, washed and dried.

[0029] In a preferred embodiment of the present invention, the precursor is calcined at a temperature of 300-400 °C for a time of 3-6 h.

[0030] In a preferred embodiment of the present invention, the mass-to-volume ratio of copper salt to alcohol in the alcohol solution of the copper salt is 50-80 mg:75 mL; the mass ratio of the g-C3N4 / Bi2O3 composite support to copper salt in the alcohol solution of the copper salt is 300:50-70.

[0031] More preferably, the mass-to-volume ratio of copper salt to alcohol in the alcohol solution of the copper salt is 60 mg:75 mL; the mass-to-volume ratio of the g-C3N4 / Bi2O3 composite support to the alcohol solution of the copper salt is 300:50, 300:60, or 300:70.

[0032] In this invention, the process of immersing the g-C3N4 / Bi2O3 in an alcoholic solution of copper salt further includes stirring or sonication to ensure that the g-C3N4 / Bi2O3 is fully bonded to copper ions. This invention does not impose specific limitations on the stirring or sonication parameters; conventional techniques skilled in the art can be used, such as stirring at 60 °C for 1-6 h.

[0033] In a preferred embodiment of the present invention, after the impregnation is completed, the solid product is collected, and the process further includes washing, drying and grinding the collected solid product.

[0034] In the introduction of Cu single atoms, this invention employs a seemingly high-concentration but actually precisely controlled copper salt alcohol solution impregnation strategy (copper salt dosage 50–80 mg / 75 mL alcohol, g-C3N4 / Bi2O3 support to copper salt mass ratio 300:50–70), and promotes Cu introduction through stirring or ultrasound. 2+ Sufficient bonding with N / O coordination sites on the support surface; despite a high apparent loading, subsequent rigorous washing and low-temperature calcination selectively retain single-atom Cu anchored at defect sites while removing unbonded copper species. If the copper salt concentration is too low, the single-atom density is insufficient, resulting in a lack of catalytically active sites; if it is too high, migration and aggregation easily occur during calcination, forming copper oxide or metallic Cu nanoparticles, which destroy the single-atom structure and introduce carrier recombination centers.

[0035] In a preferred embodiment of the present invention, when calcining the solid product, the calcination temperature is 300~400 ℃ and the time is 2~4 h.

[0036] In this invention, both calcinations are strictly controlled within the range of 300–400℃ (precursor calcination 3–6h, Cu impregnation product calcination 2–4h). This temperature window can effectively remove organic residues, complete the Bi2O3 crystal phase transformation and stabilize the Cu species, and avoid adverse side reactions such as g-C3N4 thermal decomposition, Bi2O3 grain coarsening or Cu single-atom sintering. If the temperature is below 300℃, the precursor transformation will be incomplete, and if it is above 400℃, it will lead to structural deterioration and single-atom deactivation.

[0037] The second aspect of the present invention provides a Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst prepared by the above preparation method.

[0038] The third aspect of this invention provides the application of the above-mentioned Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst in the photocatalytic preparation of synthetic diesel from liquid biomass oil.

[0039] In a preferred embodiment of the present invention, the liquid biomass oil is selected from at least one of oleic acid, palmitic acid, stearic acid, jatropha oil and castor oil.

[0040] The fourth aspect of the present invention provides a method for preparing biodiesel, which involves mixing liquid biomass oil, methanol and the above-mentioned Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst, and then reacting them under room temperature and light conditions.

[0041] In a preferred embodiment of the present invention, the amount of Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst is 0.5-5% of the mass of liquid biomass oil; the molar ratio of methanol to liquid biomass oil is (5~15):1; the reaction time is 1~5 h; and the spectral range of the light conditions is 320~2500 nm. The liquid biomass oil is selected from at least one of oleic acid, palmitic acid, stearic acid, jatropha oil, and castor oil.

[0042] More preferably, the amount of Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst is 0.5%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, or 1.6% of the mass of liquid biomass oil; the molar ratio of methanol to liquid biomass oil is 6:1, 7:1, 9:1, 10:1, 10.2:1, or 12:1; the reaction time is 1 h, 1.2 h, 1.5 h, 1.5 h, or 2 h; and the spectral range of the illumination conditions is 320~780 nm or 780~2500 nm.

[0043] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0044] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0045] Example 1 This embodiment provides a Cu-C3N4 / Bi2O3 photocatalyst (denoted as Cu1 / g-C3N4 / Bi2O3) based on Cu single-atom anchoring in biomass conversion. The preparation steps are as follows: (1) Place 10 g of melamine in a covered crucible and calcine it at 500 °C for 2 h. Then, raise the temperature to 520 °C at a rate of 2 °C / min and continue calcining for 2 h. After naturally cooling to room temperature, the resulting yellow blocky product is ground to obtain g-C3N4 powder.

[0046] (2) 3.8 g Bi(NO3)3·5H2O and 2 g g-C3N4 were added to 10 mL of glacial acetic acid. After complete dissolution, 70 mL of ethanol was added and stirred for 30 min. Then, the mixture was reacted at 180 °C for 20 h. After cooling, centrifugation, washing, and drying at 60 °C, a gray precursor was obtained. The gray precursor was thoroughly ground and then calcined at 350 °C for 4 h to obtain g-C3N4 / Bi2O3.

[0047] (3) 50 mg CuCl2 and 300 mg g-C3N4 / Bi2O3 powder were added to 75 mL of ethanol and stirred at 60 °C for 4 h. After centrifugation and washing, the mixture was dried at 70 °C, ground thoroughly, and then calcined at 350 °C for 2 h to finally obtain Cu1 / g-C3N4 / Bi2O3 catalyst.

[0048] Example 2 This embodiment provides a g-C3N4 / Bi2O3 photocatalyst based on Cu single-atom anchoring in biomass conversion. The preparation method differs from Example 1 only in that the amount of CuCl2 added is adjusted to 60 mg; all other steps and parameters are the same as in Example 1. The resulting catalyst is denoted as Cu2 / g-C3N4 / Bi2O3.

[0049] Example 3 This embodiment provides a g-C3N4 / Bi2O3 photocatalyst based on Cu single-atom anchoring from biomass conversion. The preparation method differs from Example 1 only in that the amount of CuCl2 added is adjusted to 70 mg; all other steps and parameters are the same as in Example 1. The resulting catalyst is denoted as Cu3 / g-C3N4 / Bi2O3.

[0050] Example 4 This embodiment provides a method for the photocatalytic esterification of oleic acid to methyl oleate, which is carried out according to the following steps: 1 g of oleic acid, methanol (molar ratio of methanol to oleic acid 9:1), and Cu1 / g-C3N4 / Bi2O3 catalyst (0.8 wt% of oleic acid) were added to a quartz photoreactor. A 300 W xenon lamp (spectral range 320–2500 nm) was used as the light source, and the mixture was stirred at room temperature for 1 h. After the reaction was complete, the supernatant was extracted with petroleum ether, and residual methanol and petroleum ether were removed by rotary evaporation to obtain purified biodiesel. Finally, [the process was] utilized... 1 The corresponding biodiesel yield was determined by H NMR and calculated to be 60.9%.

[0051] Example 5 This embodiment provides a method for the photocatalytic esterification of oleic acid to methyl oleate, which is the same as that in Example 4, except that the photocatalyst Cu1 / g-C3N4 / Bi2O3 in Example 1 is replaced with the photocatalyst Cu2 / g-C3N4 / Bi2O3 in Example 2. 1 The corresponding biodiesel yield was determined by H NMR and calculated to be 87.1%.

[0052] Example 6 This embodiment provides a method for the photocatalytic esterification of oleic acid to methyl oleate, which is the same as that in Example 4, except that the photocatalyst Cu1 / g-C3N4 / Bi2O3 in Example 1 is replaced with the photocatalyst Cu3 / g-C3N4 / Bi2O3 in Example 3. 1 The corresponding biodiesel yield was determined by H NMR and calculated to be 71.7%.

[0053] Example 7 To investigate the effect of different spectral ranges on the yield of biodiesel produced by photocatalysis of oils, this invention, based on the catalytic activity test in Example 4, conducted control experiments by placing the reaction system under darkness, ultraviolet-visible light, and near-infrared light conditions, respectively, and calculated the biodiesel yield accordingly. (1) The catalytic activity test was the same as in Example 4, except that the reaction was placed in the dark and the biodiesel yield was calculated to be 2.7%.

[0054] (2) The catalytic activity test was the same as in Example 4, except that the spectral range of the xenon lamp was adjusted to 320-780 nm, and the biodiesel yield was calculated to be 72.4%.

[0055] (3) The catalytic activity test was the same as in Example 4, except that the spectral range of the xenon lamp was adjusted to 780-2500 nm, and the biodiesel yield was calculated to be 90.8%.

[0056] Example 8 To investigate the optimal reaction conditions for the catalyst in the photocatalytic preparation of biodiesel from oils, this invention, based on the catalytic activity test in Example 4, adjusted the reaction time under near-infrared light irradiation, the molar ratio of methanol to oleic acid, and the mass percentage of catalyst in oleic acid, and calculated the biodiesel yield, specifically as follows: (1) The catalytic activity test was the same as in Example 4, except that the stirring time of the mixture at room temperature was adjusted from 1.0 h to 1.5 h and 2 h, respectively. When the reaction time was 1.5 h, the biodiesel yield was calculated to be 95.7%, and when the reaction time was 5 h, the biodiesel yield was calculated to be 94.8%.

[0057] (2) The catalytic activity test was the same as in Example 4, except that the molar ratio of methanol to oleic acid was adjusted from 9:1 to 6:1 and 12:1. When the methanol-oleic acid molar ratio was 6:1, the biodiesel yield was calculated to be 85.8%, and when the methanol-oleic acid molar ratio was 12:1, the biodiesel yield was calculated to be 92.7%.

[0058] (3) The catalytic activity test was the same as in Example 4, except that the catalyst dosage was adjusted from 0.8 wt% to 1.2 wt% and 1.6 wt%. The calculated biodiesel yields were 84.9% and 93.7%.

[0059] (4) The reaction conditions obtained by response surface optimization were 1.4 h, 1.3 wt%, and 10.2:1, that is, the highest biodiesel yield can be obtained when the mixture is stirred at room temperature for 1.3 h, the mass ratio of catalyst to oleic acid is 1.3%, and the molar ratio of methanol to oleic acid is 10.2:1. The biodiesel yield is 98.6%.

[0060] Characterization results: Cu obtained in Examples 1-3 x The / g-C3N4 / Bi2O3 photocatalyst was characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Figure 1 and 2 It can be seen that the present invention successfully prepared Cu single-atom anchored g-C3N4 / Bi2O3 photocatalyst, and each step of the reaction in the preparation process was successful.

[0061] Cu obtained in Examples 1-3 x The nitrogen adsorption-desorption and pore size distribution of the / g-C3N4 / Bi2O3 photocatalyst were characterized by... Figure 3It can be seen that the nitrogen adsorption isotherm of the Cu2 / g-C3N4 / Bi2O3 photocatalyst prepared in this invention is a typical type IV, with obvious hysteresis loop, and it has mesoporous characteristics and a high BET specific surface area.

[0062] The Cu2 / g-C3N4 / Bi2O3 photocatalyst obtained in Example 2 was characterized by near-edge and extended-edge spectra of the Cu element at the K-side. Figure 4 It can be seen that Cu exists in the form of single atoms in the Cu2 / g-C3N4 / Bi2O3 photocatalyst prepared by this invention, which further proves that the preparation steps are successful.

[0063] Cu obtained in Examples 1-3 x Electron spin resonance characterization of the / g-C3N4 / Bi2O3 photocatalyst was performed. Figure 5 It can be seen that the Cu prepared by this invention x / g-C3N4 / Bi2O3 photocatalyst is rich in oxygen vacancies.

[0064] Cu obtained in Examples 1-3 x The / g-C3N4 / Bi2O3 photocatalyst was characterized by UV-Vis diffuse reflectance analysis. Figure 6 It can be seen that Cu single-atom anchoring increases the light absorption range of g-C3N4 / Bi2O3 photocatalyst to the near-infrared region.

[0065] Cu obtained in Examples 1-3 x The photocatalytic performance of the / g-C3N4 / Bi2O3 photocatalyst was tested. Figure 7 It was found that the Cu2 / g-C3N4 / Bi2O3 photocatalyst exhibited excellent catalytic activity under different light source irradiation conditions, with the highest biodiesel yield under near-infrared light irradiation, indicating that the catalyst has good near-infrared response capability. The reaction conditions were systematically optimized using response surface methodology, and the optimal process parameters were determined to be: a methanol to oleic acid molar ratio of 10.2:1, a catalyst dosage of 1.3 wt%, and a reaction time of 1.4 h. Under these optimized conditions, the biodiesel yield reached 98.6%. Furthermore, the catalyst maintained high catalytic activity after five consecutive cycles, demonstrating good stability and reusability. Further application of this catalyst to various liquid biomass feedstocks yielded biodiesel yields exceeding 90%, fully verifying its versatility and high efficiency in different feedstock systems.

[0066] In summary, the catalytic material prepared in this invention effectively modulates its band structure by constructing a synergistic structure of single atoms and oxygen vacancies, broadens the light absorption range, and significantly promotes the rapid separation of photogenerated carriers at the interface, thereby greatly enhancing photocatalytic activity. When this catalyst was applied to the photocatalytic production of biodiesel from oleic acid, under optimized conditions of a methanol / oleic acid molar ratio of 10.2:1, a catalyst dosage of 1.3 wt%, and a reaction time of 1.4 h, the biodiesel yield reached 98.6%. After five cycles, the yield remained above 90%, demonstrating excellent stability and reusability. Furthermore, this catalyst exhibited good substrate versatility when catalyzing the production of biodiesel from various substrates, showing broad application prospects.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass transformation-based Cu monatomic-anchored g-C3N4 / Bi2O3 photocatalyst, characterized in that, The method comprises the following steps: a precursor is obtained by a solvothermal reaction using g-C3N4 and a bismuth source as raw materials; the precursor is calcined to obtain a g-C3N4 / Bi2O3 composite carrier; the g-C3N4 / Bi2O3 composite carrier is immersed in an alcohol solution of a copper salt, and then the solid product is collected after the immersion is completed, and the solid product is calcined to obtain the Cu single-atom-anchored g-C3N4 / Bi2O3 photocatalyst.

2. The production method according to claim 1, characterized by, The g-C3N4 is prepared by grinding melamine after high-temperature calcination; the parameters of the calcination are set as follows: the melamine is calcined at 500-600 ℃ for 2-6 h, then the temperature is programmed to rise to 520-700 ℃ at a rate of 2 ℃ / min, and the calcination is continued for 0-4 h.

3. The production method according to claim 1, characterized by, The bismuth source is bismuth nitrate; the molar ratio of bismuth in the g-C3N4 and the bismuth source is (1-4):1; the temperature of the solvothermal reaction is 160-200 ℃, and the time is 16-20 h.

4. The method of claim 1, wherein, When the precursor is calcined, the temperature of the calcination is 300-400 ℃, and the time is 3-6 h.

5. The preparation method according to claim 1, characterized in that, The mass-volume ratio of the copper salt to alcohol in the alcohol solution of the copper salt is 50-80 mg:75 mL; the mass ratio of the g-C3N4 / Bi2O3 composite carrier to the copper salt in the alcohol solution of the copper salt is 300:50-70.

6. The method of claim 1, wherein, When the solid product is calcined, the temperature of the calcination is 300-400 ℃, and the time is 2-4 h.

7. A Cu single-atom-anchored g-C3N4 / Bi2O3 photocatalyst prepared by the preparation method of any one of claims 1-6.

8. Application of the Cu single-atom-anchored g-C3N4 / Bi2O3 photocatalyst of claim 7 in the preparation of synthetic diesel from photocatalytic liquid biomass oil.

9. A method of producing biodiesel, characterized by, The liquid biomass oil, methanol and the Cu single-atom-anchored g-C3N4 / Bi2O3 photocatalyst of claim 7 are mixed, and then the reaction is carried out at room temperature and under light conditions.

10. The method of claim 9, wherein, The amount of the Cu single-atom-anchored g-C3N4 / Bi2O3 photocatalyst is 0.5-5% of the mass of the liquid biomass oil; the molar ratio of the methanol to the liquid biomass oil is (5-15):1; the reaction time is 1-5 h; and the spectral range of the light conditions is 320-2500 nm.

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