Adsorption-catalysis bifunctional composite catalyst as well as preparation method and application thereof

Abstract

The preparation method comprises the following specific steps: adding a porous aluminum borate framework material (PKU-1) and a polymer carbon nitride (PCN) into an organic solvent, carrying out uniform ultrasonic dispersion, continuously stirring under the irradiation of a xenon lamp until the organic solvent is completely volatilized, collecting a solid, washing, and drying to obtain the adsorption-catalysis dual-function composite catalyst. The adsorption-catalysis bifunctional composite catalyst (PKU / PCN) is obtained. Through interface coupling of porous aluminum borate (PKU-1) and polymer carbon nitride (PCN), the composite material PKU / PCN with the functions of efficient CO trapping and photocatalytic conversion is constructed, the generation rate of CO and CH of the composite material is obviously higher than that of pure PCN, and the composite material is excellent in stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and in particular relates to an adsorption-catalysis dual-function composite catalyst and a preparation method and application thereof. Background Art

[0002] Against the backdrop of surging energy demand driven by rapid global economic growth, a consumption structure dominated by fossil fuels has led to a continuous increase in CO2 emissions. This contradiction between excessive CO2 accumulation and lagging progress in clean energy substitution not only exacerbates environmental crises such as the greenhouse effect and ocean acidification, but also poses dual challenges to industrial transformation and sustainable human development. Against this backdrop, developing a CO2 resource utilization technology system has become a key breakthrough in resolving the energy-environment-development triangle. Among these, photocatalytic CO2 conversion, driven by solar energy, has become a research hotspot in the clean energy conversion field due to its green, sustainable nature and low energy consumption. It converts CO2 into carbon-based fuels and fine chemicals through solar-driven, targeted conversion. However, the practical application of this technology still faces two major bottlenecks: insufficient CO2 capture capacity of photocatalysts and low efficiency in separating photogenerated charge carriers. The former leads to insufficient reactant concentration on the catalyst surface, while the latter limits the conversion of light energy to chemical energy. The development of materials that combine efficient CO2 capture and photocatalytic conversion could address both of these challenges.

[0003] Currently, adsorbents with excellent CO₂ capture capabilities include activated carbon, zeolites, molecular sieves, activated alumina, silica gel, and lithium compounds. The recently emerging metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have attracted widespread attention in the academic community due to their flexible structural properties, which allow them to easily achieve ultra-high surface areas and increase their CO₂ adsorption capacity. After years of research, MOFs and COFs have become resistant to high temperatures and certain acid and alkali corrosion. However, significant research remains to be done on preparation costs, product yields, and the detoxification of these materials.

[0004] Porous aluminum borate is an emerging class of inorganic porous materials with low cost and environmental friendliness. Professor Lin Jianhua's research group at Peking University has developed a series of porous aluminum borate framework materials (designated the PKU series) doped with various elements. Unlike traditional aluminosilicate molecular sieves, the PKU-1 framework is composed of AlO₂ octahedra and BO clusters, forming a three-dimensional open-pore structure with a rich structure and tunable pore size, avoiding the diffusion limitation of traditional molecular sieves. More importantly, the surface of the three-dimensional open-pore structure is rich in terminal hydroxyl groups, which selectively adsorb CO₂ molecules through weak hydrogen bonding, achieving efficient enrichment even at low concentrations. Furthermore, this material exhibits moderate photocatalytic CO₂ conversion activity, particularly by significantly enhancing its photocatalytic activity by incorporating photocatalytically active components such as Ga and Fe into its framework structure. However, overall, the photocatalytic CO₂ conversion activity of this material is relatively low. Therefore, if PKU-1 is used as a CO₂ capture support and combined with a catalyst with high CO₂ photocatalytic conversion activity, it is expected to achieve efficient CO₂ enrichment and conversion.

[0005] Polymeric carbon nitride (PCN), a non-metallic polymer semiconductor material with a two-dimensional layered structure similar to graphite, has been widely studied in photocatalytic CO2 reduction and water splitting due to its wide visible light response, excellent chemical and thermal stability, environmental friendliness, and low cost. However, pure carbon nitride also has significant disadvantages: its layered structure results in a limited specific surface area and weak physical adsorption capacity for CO2; at the same time, the rapid recombination of photogenerated electron-hole pairs severely restricts catalytic activity. Optimizing the band structure of photocatalytic materials (such as element doping) or constructing heterojunctions (such as semiconductor composites) can promote charge separation and help improve their photocatalytic conversion efficiency, but these strategies often overlook the improvement of CO2 adsorption capacity. To address this problem, researchers have attempted to combine PCN with porous materials, such as MOFs, to enhance CO2 adsorption. However, the poor stability of MOFs and the poor energy level matching between the active sites and PCN have limited the improvement in catalytic performance.

[0006] References:

[0007] 1. Ju, J.; Lin, J.; Li, G.; Yang, T.; Li, H.; Liao, F.; Loong, CK; You, L., Angew. Summary of the Invention

[0008] In order to address the shortcomings of the existing technology, the purpose of the present invention is to provide an adsorption-catalysis bifunctional composite catalyst, its preparation method and application, and construct a composite material PKU / PCN with both efficient CO2 capture and photocatalytic conversion functions through the interface coupling of porous aluminum borate (PKU-1) and polymer carbon nitride (PCN). The composite material has significantly higher CO and CH4 generation rates than pure PCN and excellent stability.

[0009] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0010] A method for preparing an adsorption-catalysis dual-function composite catalyst comprises the following specific steps:

[0011] The porous aluminum borate framework material (PKU-1) and polymer carbon nitride (PCN) were added to an organic solvent and ultrasonically dispersed evenly. The mixture was continuously stirred under xenon lamp irradiation until the organic solvent was completely evaporated. The solid was collected, washed, and dried to obtain an adsorption-catalysis bifunctional composite catalyst (PKU / PCN).

[0012] Preferably, the preparation method of the aforementioned porous aluminum borate framework material is: mixing aluminum nitrate nonahydrate and boric acid, grinding them evenly, performing solid phase reaction, washing, and drying to obtain the porous aluminum borate framework material.

[0013] Preferably, the molar ratio of the aluminum nitrate nonahydrate to boric acid is 1:18-22, the reaction temperature is 200-250°C, the reaction time is 100-150h, and the drying temperature is 50-70°C.

[0014] Preferably, the preparation method of the aforementioned polymer carbon nitride is: mixing urea and ammonium formate, calcining at high temperature, and cooling to obtain polymer carbon nitride.

[0015] Preferably, the mass ratio of the aforementioned urea to ammonium formate is 100:2-4, the calcination temperature is 500-600° C., the heating rate is 2-4° C. / min, and the holding time is 1.5-2.5 h.

[0016] Preferably, the addition amount of the aforementioned porous aluminum borate framework material is 10 to 20 wt % of the total mass of the porous aluminum borate framework material and the polymer carbon nitride.

[0017] Preferably, the aforementioned organic solvent is one of ethanol, ethylene glycol or methanol, and the ratio of the total mass of the porous aluminum borate framework material and polymer carbon nitride to the volume of the organic solvent is (40-60) mg: (8-12) mL.

[0018] Preferably, the drying temperature is 50-70° C., and the drying time is 12-36 hours.

[0019] An adsorption-catalysis dual-function composite catalyst is prepared by the above method.

[0020] Application of adsorption-catalysis bifunctional composite catalysts in photocatalytic CO2 reduction.

[0021] The present invention is beneficial in that:

[0022] The present invention synthesizes PKU-1 through solid-phase reaction and interfaces with PCN with an ultra-thin two-dimensional layered structure to construct a dual-functional composite material with selective adsorption and efficient catalysis. The introduction of PKU-1 significantly increases the local concentration of CO2 on the PCN surface. At the same time, its surface hydroxyl groups stabilize key intermediates and accelerate the breakage of C=O bonds. The composite material achieves CO and CH4 generation rates that are 2 times and 1.5 times that of pure PCN, respectively, and has excellent stability, providing new ideas for the design of CO2 reduction materials with both efficient adsorption and catalytic functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 :Preparation flow chart of PKU / PCN catalyst;

[0024] Figure 2 :(a) SEM image of PKU; (b) SEM image of PCN; (c) SEM image of PKU / PCN; (d, e) TEM images of PKU / PCN; (f, g) corresponding mapping images of SEM and PKU / PCN;

[0025] Figure 3 :(a) XRD patterns of PKU / PCN catalysts in Examples 1 to 3; (b) FT-IR patterns of PKU, PCN, and PKU / PCN catalysts in Example 1; (c) N2 adsorption / desorption isotherms and pore size distribution curves of PKU, PCN, and PKU / PCN catalysts in Example 1; (d) XPS patterns of PKU, PCN, and PKU / PCN catalysts in Example 1;

[0026] Figure 4 :(a) C1s high-resolution XPS spectra of PCN and PKU / PCN catalysts in Example 1;(b) N1s high-resolution XPS spectra of PCN and PKU / PCN catalysts in Example 1;(c) B1s high-resolution XPS spectra of PKU and PKU / PCN catalysts in Example 1;(d) Al 2p high-resolution XPS spectra of PKU and PKU / PCN catalysts in Example 1;

[0027] Figure 5:(a) Photocatalytic products of PKU, PCN, and the PKU / PCN catalysts in Examples 1 to 3; (b) Comparison of the molar concentration of photogenerated electrons in CO2 photoreduction; (c) Photocatalytic CO2 reduction activity of the PKU / PCN catalyst in Example 1 under different reaction conditions; (d) Stability test of the photocatalytic CO2 reduction of PKU / PCN in Example 1;

[0028] Figure 6 :(a) Photoluminescence spectra of PKU, PCN and PKU / PCN catalysts in Example 1; (b) TRPL spectra of PKU, PCN and PKU / PCN catalysts in Example 1; (c) EIS measurement of PKU, PCN and PKU / PCN catalysts in Example 1; (d) Time-varying photocurrent of PKU, PCN and PKU / PCN catalysts in Example 1;

[0029] Figure 7 :(a) UV-Vis diffuse reflectance spectra of different photocatalysts; (b) CO2 adsorption-desorption isotherms, (c) in situ FTIR spectra of PKU / PCN. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The preparation process of PKU / PCN catalyst is as follows: Figure 1 As shown: First, orange polymer carbon nitride (PCN) is synthesized by thermal polymerization. Ammonium formate is added during the urea polymerization process to introduce oxygen atoms, which promotes the rearrangement of the electron density of carbon nitride and significantly improves its catalytic activity. At the same time, the white PKU material is prepared by solid-phase reaction, in which boric acid has the dual functions of reactant and medium. The synthesis can be completed without additional solvent, which simplifies the steps and reduces the risk of impurities. Subsequently, PKU and PCN are dispersed in ethanol solution and fully compounded by light-assisted evaporation strategy under continuous stirring. This light-assisted method can accelerate the medium transfer and interface bonding efficiency to form a structurally stable composite catalyst. The prepared composite catalyst can make full use of the adsorption capacity of PKU and the catalytic ability of PCN to achieve a significant improvement in CO2 conversion capacity.

[0032] Example 1

[0033] A method for preparing an adsorption-catalysis dual-function composite catalyst comprises the following specific steps:

[0034] (1) Preparation of PKU-1

[0035] Al(NO₃)₃·9(H₂O) and H₃BO₃ were mixed in a molar ratio of 1:20, ground uniformly in an agate mortar, and placed in a reactor. The mixture was reacted at 220°C for 120 hours. After the reaction, the temperature was naturally cooled, and the mixture was thoroughly washed with deionized water to remove unreacted boric acid. The final product was then dried at 60°C. For ease of discussion of subsequent experimental results, PKU-1 will be abbreviated as PKU.

[0036] (2) Preparation of PCN

[0037] 10g of urea and 0.3g of ammonium formate were ground and mixed in a mortar until uniform. The mixture was then placed in a covered alumina crucible. The crucible was then placed in a muffle furnace and kept at 550°C for 2 hours (heating rate of 3°C / minute). After cooling to room temperature, the orange solid was ground into a powder, represented by PCN.

[0038] (3) Preparation of PKU / PCN catalyst

[0039] A total mass of 50 mg of PCN powder and PKU powder was added to 10 mL of ethanol and ultrasonically dispersed evenly, wherein the mass proportion of PKU in the PKU / PCN photocatalyst was 10 wt%. Then, stirring was continued under irradiation of a 300 W xenon lamp until the ethanol was completely evaporated. Finally, the solid was collected, washed, and dried in air at 60°C for 24 hours. The obtained catalyst was named 10 wt%-PKU / PCN.

[0040] Example 2

[0041] The preparation steps of this embodiment are the same as those of Example 1, with the specific difference being that the mass proportion of PKU in the PKU / PCN photocatalyst is 15 wt %. The obtained catalyst is named 15 wt %-PKU / PCN.

[0042] Example 3

[0043] The preparation steps of this embodiment are the same as those of embodiment 1, with the specific difference being that the mass proportion of PKU in the PKU / PCN photocatalyst is 20 wt %. The obtained catalyst is named 20 wt %-PKU / PCN.

[0044] Performance test

[0045] (1) Photocatalytic performance test method

[0046] A 300W xenon lamp was used as the light source for the photocatalytic reaction. First, 5 mg of PKU / PCN photocatalyst was weighed and placed in a photocatalytic reactor, 12 mL of ultrapure water and 4 mL of triethanolamine were added, and ultrasonic dispersion was performed. The reactor was then evacuated and high-purity CO2 was introduced to maintain the pressure at around 85 kPa. The operation was repeated three times before a photocatalytic CO2 reduction test was performed. After 5 hours of illumination, the content of the generated gas products was detected using a gas chromatograph equipped with TCD and FID. The catalyst cycle stability test steps were similar to the above steps. After the 5-hour reaction was completed, the reactor was evacuated and high-purity CO2 was introduced again without replacing the catalyst, and then the next round of photocatalytic CO2 reduction reaction test was performed, for a total of 5 rounds of testing.

[0047] (2) The micromorphology of the catalyst prepared in Example 1 was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 2 .

[0048] from Figure 2 It can be clearly seen in (a) that PKU presents a unique rod-like stacking morphology, which may form larger stacking pores. The orange carbon nitride PCN shows a flake-like morphology ( Figure 2 (b)), the thin sheet structure often has a larger specific surface area, providing more active sites for subsequent catalytic reactions. After light-assisted composite treatment, PKU / PCN showed the remarkable characteristics of uniform dispersion of nanosheets and nanorods ( Figure 2 (c)). This uniformly dispersed state creates favorable conditions for the catalytic reaction, allowing the different components to fully contact and synergize. In order to further explore the microstructure of PKU / PCN, TEM was used to further observe it ( Figure 2 (d), (e)). The results show that the composite material exhibits a unique structure of nanorods embedded in nanosheets. This unique structure facilitates the effective coupling of adsorption and catalytic sites, providing a more efficient reaction environment for the photocatalytic CO2 reduction reaction, thereby significantly improving the photocatalytic CO2 reduction performance.

[0049] In addition, the elemental composition of the composite catalyst was characterized by elemental scanning EM mapping technology ( Figure 2 (f), (g). The results show that the elements C, N, O, Al, and B are uniformly distributed in the composite catalyst. This uniform distribution of elements is strong evidence of the successful composite of PKU and PCN, indicating that the two materials are well integrated during the composite process, laying a solid foundation for the catalyst's performance improvement.

[0050] (3) The PKU / PCN catalyst was analyzed by XRD, Fourier transform infrared (FT-IR), nitrogen adsorption-desorption isotherm and X-ray photoelectron spectroscopy (XPS). The specific results are shown in Figure 3 and Figure 4 .

[0051] In order to further explore the phase composition and crystal structure of the samples, XRD analysis was carried out on the catalysts prepared in Examples 1 to 3. Figure 3 As shown in (a), the typical diffraction peaks of PCN at 13.3° and 27.25° correspond to the (100) and (002) crystal planes of carbon nitride, respectively. These two crystal planes represent the ordered structure stacking in the plane and the interlayer structure stacking, respectively. For PKU, the strong diffraction peak at 8.06° corresponds to the (110) crystal plane of PKU-1, and all peak positions are highly consistent with the simulated XRD peak positions, which fully demonstrates that PKU-1 has been successfully prepared. When PCN and PKU form a complex, the diffraction peaks attributable to PKU and PCN are still clearly distinguishable. This phenomenon strongly indicates that the crystal structure of PCN and PKU has not changed during the light-assisted recombination process.

[0052] In order to obtain further information about the microstructure of PCN and PKU in Example 1, FT-IR spectra were measured. Figure 3 As shown in (b), at 810 cm -1 1100~1800cm -1 and 3000~3300cm -1 The characteristic peaks at 3187 cm correspond to the bending vibration of the heptazine ring, the stretching vibration of the carbon-nitrogen heterocycle, and the stretching vibration of the nitrogen-hydrogen group in PCN. -1 and 1660cm -1 The absorption peaks at 1361 cm-1 correspond to the stretching vibration and bending vibration of hydroxyl groups, respectively, which indicates the presence of hydroxyl groups in PKU. -1 and 702cm -1 The peak at is the asymmetric stretching vibration of the BO group in the triangular planar [BO3] group. After the composite structure is formed, the peaks of both PCN and PKU do not change significantly, indicating that the composite process does not alter the structural properties of the monomer components, which is consistent with the XRD conclusions.

[0053] The specific surface area and pore size distribution of the catalyst in Example 1 were further investigated by nitrogen adsorption-desorption isotherm analysis. Figure 3 As shown in (c), after calculation, the BET specific surface areas of PKU, PCN and PKU / PCN catalysts are 26.9 m 2 / g,30.6m 2 / g and 25.2m 2 / g. The average pore sizes are and After PKU and PCN are compounded, BET does not change significantly, but the average pore size increases significantly. This may be caused by the formation of new stacking pores during the compounding process. The larger pore size is conducive to the storage and transmission of carbon dioxide and accelerates the catalytic conversion process.

[0054] In order to verify the close interfacial contact between PKU and PCN, XPS analysis was performed on the catalyst prepared in Example 1. The results are shown in Figure 2. Figure 3 (d) and Figure 4 The full XPS spectrum shows that there are five elements, namely C, N, O, O, and Al, in the composite catalyst. The high-resolution C1s spectrum shows peaks at 284.8eV and 288.4eV, corresponding to CC and NCN species, respectively ( Figure 4 (a)). In the N1s spectrum, the peaks at binding energies of 400.5eV, 399.2eV, and 398.5eV correspond to CN-(H)2, N-(C)3, and C=NC in PCN, respectively. Figure 4 (b)). The peaks at 194.0eV and 75.3eV correspond to B1s and Al 2p, respectively. Figure 4 (c) and (d)). There is no obvious change in the chemical environment of the elements before and after recombination, indicating that the recombination process is mainly physical recombination.

[0055] (4) The photocatalytic performance test was carried out under a 300W xenon lamp light source, using triethanolamine (TEOA) as a hole sacrificial agent, and the catalyst performance was evaluated by online gas chromatography analysis of the products of the CO2 reduction reaction.

[0056] like Figure 5 As shown in (a), pure PKU has the lowest CO2 reduction efficiency, with CO and CH4 yields of 6.28 and 1.76 μmol·g, respectively. -1 ·h -1 The CO2 reduction efficiency of pure PCN is significantly higher than that of PKU, with the CO and CH4 yields of 19.50 and 16.3 μmol·g, respectively. -1 ·h -1 The results show that the main catalytic active center in the composite catalyst PKU / PCN is PCN. When PCN is modified with PKU, PKU / PCN shows significantly improved CO2 reduction performance, especially for the selective generation of CO. When the amount of PKU added is 15wt%, PKU / PCN reaches the highest CO yield (40.43μmol·g -1 ·h -1 ) and CH4 yield (25.02 μmol·g -1 ·h -1), which are 2 times and 1.5 times higher than those of PCN, respectively; excessive addition (such as 20wt% PKU) leads to a decrease in catalytic performance, but it is still higher than that of pure PCN. Most of the photogenerated electrons in PKU / PCN are used to photocatalytically reduce CO2 to CO, which explains why CO is the main product ( Figure 5 (b)). Figure 5 (c) shows that there is no product in the absence of catalyst and in a dark environment, indicating that both catalyst and light are necessary for the photocatalytic CO2 reduction reaction. When argon is used instead of CO2 as the reducing gas, no carbon product is produced. It can be inferred that the carbon source of the photocatalytic CO2 reduction products all comes from CO2. It is satisfying that after 5 rounds of cycle performance testing, PKU / PCN still shows relatively stable CO2 reduction performance ( Figure 5 (d)).

[0057] (5) In order to further analyze the kinetic characteristics of photogenerated electrons in the catalyst, a variety of technical means such as photoluminescence (PL) spectroscopy, time-resolved photoluminescence (TRPL) spectroscopy and photoelectrochemical testing were used to systematically analyze the excitation and transmission process of photogenerated electrons. The specific results are shown in Figure 6 .

[0058] like Figure 6 As shown in (a), the fluorescence intensity of the PKU / PCN composite material is significantly reduced compared with the original PCN, indicating that the construction of the composite material effectively inhibits the recombination of photogenerated electrons and holes. In addition, the fluorescence decay curve (fluorescence intensity-time curve) was obtained by TRPL test, and the electron-hole pair dissociation kinetics ( Figure 6 (b)). Compared with the original PCN (3.25ns) and PKU (4.32ns), the exciton lifetime of the PKU / PCN composite (3.23ns) is shorter, indicating that the exciton dissociates faster and participates in the CO2 reduction reaction at a faster rate. Electrochemical impedance spectroscopy (EIS) was used to evaluate the carrier transfer resistance of the photocatalyst-electrolyte interface ( Figure 6 (c)). Compared with pristine PCN and PKU, the Nyquist radius of the PKU / PCN composite is reduced, reflecting the reduction in carrier migration resistance. Consistent with this, PKU / PCN also shows a significantly increased photocurrent density in the photocurrent periodicity measurement ( Figure 6 (d) further demonstrates an improvement in the migration efficiency of photogenerated charge carriers. The fluorescence and photoelectrochemical results above confirm that the addition of PKU effectively promotes the conversion of photogenerated electrons, improving the separation, transport, and migration efficiency of photogenerated charge carriers, ultimately significantly enhancing the photocatalytic CO2 reduction activity.

[0059] (6) In order to evaluate the light absorption characteristics of the material, the catalyst in Example 1 was subjected to ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) testing. The specific results are shown in Figure 7 .

[0060] from Figure 7 (a) shows clearly that PCN absorbs light between 200-500nm, with the strongest absorption at approximately 300nm. In sharp contrast, PKU has a very narrow absorption range and only has absorption ability in the ultraviolet region below 300nm. Comparing the PKU / PCN composite material with PCN, the former shows a significant red shift phenomenon, indicating that PKU / PCN has better visible light absorption ability. The CO2 adsorption test further confirms the effect of the optimized microenvironment on the adsorption and desorption of reactants. The CO2 adsorption isotherm shows that the maximum adsorption values of PCN, PKU and PKU / PCN at room temperature are 8.6cm 3 ·g -1 、27.4cm 3 ·g -1 and 9.4cm 3 ·g -1 ( Figure 7 (b)), indicating that the introduction of PKU significantly enhances the CO2 capture capacity of the prepared composite material. This increased local concentration of CO2 on the PCN surface can promote the activation of more CO2 molecules, thereby increasing their availability in the reduction reaction and enhancing the photocatalytic CO2 reduction performance. In situ Fourier transform infrared spectroscopy was used to study the absorption and activation process of CO2, providing key experimental evidence for further analysis of the photocatalytic CO2 reduction mechanism of PKU / PCN composite materials ( Figure 7 (c)). Under continuous illumination, characteristic adsorbed species can be clearly traced on the catalyst surface: bidentate carbonate (b-CO3 2- , wave number 1356cm -1 ), monodentate carbonate (m-CO3 2- , wave number 1300cm -1 ), bicarbonate (HCO3 - , wave number 1454cm -1 and 1390cm -1 ), carboxylates (CO2 - , wave number 1213cm -1 ). It is worth noting that the peak intensity of the above-mentioned adsorbed species is positively correlated with the illumination time, which clearly reveals the continuous interaction between the adsorbed state *CO2 and the photogenerated electrons of the catalyst. In addition, at 1656cm -1 and 1097cm -1At the wavelength of 1.5 Å, absorption peaks of two important intermediates in the carbon dioxide reduction process appeared, corresponding to *COOH and *CHO, respectively. These peaks increased in intensity with increasing illumination time. *COOH is produced by the interaction between adsorbed *CO2 and surface protons and can be further converted to CO. CHO is a key intermediate in the reduction of carbon dioxide to CH4. The presence of this species indicates a significant tendency for the system to undergo deep reduction to generate CH4.

[0061] Based on the detection of intermediate products in the photocatalytic CO2 reduction reaction, a possible pathway for CO2 photoreduction was proposed. In the adsorption and activation stage, CO2 molecules form hydrogen bonds through the terminal hydroxyl groups of the PKU molecular sieve to form a large amount of adsorbed *CO2 on the catalyst surface. Subsequently, the adsorbed *CO2 combines with surface protons to form a key intermediate *COOH. This process involves a single electron transfer reaction, and *COOH generates CO through a step-by-step proton-electron coupling mechanism. In the deep reduction stage, some *CO intermediates undergo continuous protonation to generate transition states such as *CHO, and are eventually converted into CH4 and desorbed from the catalyst surface. In addition, TEOA, as a hole sacrificial agent, continuously consumes photogenerated holes, accelerates the photogenerated charge transfer kinetics, and thus allows more photogenerated electrons to participate in the CO2 reduction reaction. Based on reaction path analysis and intermediate product tracking, the photocatalytic reduction process of CO2 can be summarized as follows:

[0062] *+CO2→CO2*

[0063] H2O→H + +e - + OH

[0064] *CO2+e - +H + →*COOH

[0065] *COOH+e - +H + →*CO+H2O

[0066] *CO→CO↑+*

[0067] *CO+e - +H + →*CHO

[0068] *CHO+5e - +5H + →CH4↑+H2O+*.

[0069] By interfacially coupling porous aluminum borate (PKU-1) with polymeric carbon nitride (PCN), a composite material with both efficient CO2 capture and photocatalytic conversion capabilities was successfully constructed. Experiments showed that the three-dimensional open pore structure of PKU-1 significantly increased the local concentration of CO2. In situ FT-IR revealed the dynamic generation and enrichment of *COOH and *CHO intermediates during illumination, indicating that the terminal hydroxyl groups of PKU-1 may stabilize key intermediates through hydrogen bonding, synergistically promoting the CO2 reduction process. The composite 15wt%-PKU / PCN material exhibited excellent performance, with a CO yield twice that of pure PCN and remaining stable after five cycles, confirming the effectiveness of the adsorption-catalysis synergistic strategy. This achievement not only provides new material design ideas for CO2 resource recovery technology, but also lays a theoretical foundation for the study of interface engineering between porous materials and semiconductor photocatalysts.

[0070] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the scope of protection of the present invention.

Claims

1. An adsorption-catalysis bifunctional composite catalyst, characterized in that: The porous aluminum borate frame material is composited with polymer carbon nitride, and the mass of the porous aluminum borate frame material is 10-20 wt% of the total mass of the porous aluminum borate frame material and the polymer carbon nitride.

2. The method for preparing the adsorption-catalysis bifunctional composite catalyst according to claim 1, characterized in that: The specific steps include: The porous aluminum borate framework material and polymer carbon nitride are added to an organic solvent and ultrasonically dispersed uniformly. The mixture is continuously stirred under xenon lamp irradiation until the organic solvent is completely volatilized. The solid is collected, washed, and dried to obtain an adsorption-catalysis dual-functional composite catalyst.

3. The method for preparing an adsorption-catalysis bifunctional composite catalyst according to claim 2, characterized in that: The preparation method of the porous aluminum borate framework material comprises the following steps: mixing aluminum nitrate nonahydrate and boric acid, grinding the mixture evenly, performing solid phase reaction, washing, and drying the mixture to obtain the porous aluminum borate framework material.

4. The method for preparing an adsorption-catalysis bifunctional composite catalyst according to claim 3, characterized in that: The molar ratio of aluminum nitrate nonahydrate to boric acid is 1:18-22, the reaction temperature is 200-250°C, the reaction time is 100-150 h, and the drying temperature is 50-70°C.

5. The method for preparing an adsorption-catalysis bifunctional composite catalyst according to claim 2, characterized in that: The preparation method of the polymer carbon nitride comprises the following steps: mixing urea and ammonium formate, calcining at high temperature, and cooling to obtain the polymer carbon nitride.

6. The method for preparing an adsorption-catalysis dual-function composite catalyst according to claim 5, characterized in that: The mass ratio of urea to ammonium formate is 100:2-4, the calcination temperature is 500-600°C, the heating rate is 2-4°C / min, and the holding time is 1.5-2.5 h.

7. The method for preparing an adsorption-catalysis dual-function composite catalyst according to claim 2, characterized in that: The organic solvent is one of ethanol, ethylene glycol or methanol, and the ratio of the total mass of the porous aluminum borate framework material and the polymer carbon nitride to the volume of the organic solvent is (40-60) mg: (8-12) mL.

8. The method for preparing an adsorption-catalysis dual-function composite catalyst according to claim 2, characterized in that: The drying temperature is 50-70°C, and the drying time is 12-36 hours.

9. Use of the adsorption-catalysis bifunctional composite catalyst according to claim 1 in photocatalytic CO2 reduction.

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