Construction Of Metal Porphyrin-functionalized Bismuth Oxyhalide-based Materials And Corresponding Photocatalytic CO₂ Reduction Performance Studies

The massive consumption of fossil fuels has caused an energy crisis,the release of carbon dioxide（CO₂）has also posed serious environmental and ecological problems,making the energy crisis and environmental pollution one of the major challenges facing the world today.The artificial photosynthesis process can realize the direct catalytic conversion of CO₂ into carbon-based chemicals,which not only meets the specific requirements of the national“double carbon”target,but also opens up a new way to prepare important chemical raw materials by non-fossil routes,the key of which is the design of high-performance catalysts and the construction of catalytic systems.The current photocatalytic CO₂ reduction catalysts still have bottlenecks,such as unsatisfactory charge separation,lack of active sites and difficult regulation of proton-coupled electron processes.In response to the key scientific problems of the above catalysts,bismuth-rich haloxy bismuth was used as a catalyst research platform,and a variety of organic-inorganic composite catalysts based on bismuth haloxy bismuth metalloporphyrin molecules were constructed based on the structural properties of organic metalloporphyrin molecules.Effective combination of bismuth-rich bismuth halide oxide materials with metalloporphyrin molecules was realized through defect induction and polarization engineering strategies,as well as the metal porphyrin molecule center metal/substituent modulation and topological assembly.These approaches achieved the effective enhancement of catalyst photogenerated carrier separation and transport,CO₂ adsorption and activation,and intermediate adsorption-diffusion-coupling process regulation,finally realizing the photocatalytic CO₂ reduction to generate C₂ products with significantly improved product selectivity and conversion efficiency.At the same time,the effects of the assembly method of bismuth-rich bismuth halide oxide semiconductor and metalloporphyrin molecules on the catalyst performance were systematically investigated,the mechanism of the organic-inorganic composite structure on the enhancement of photogenerated carrier separation efficiency was elucidated,the adsorption-diffusion-mass transfer-coupling model of CO₂ on the catalyst surface was established,and the regulatory mechanism of the catalyst active site design on the intermediate morphology and product selectivity was revealed.The related research provides new research thoughts for efficient photocatalytic CO₂ conversion and resource utilization,as well as new approaches for the synthesis of fine chemicals by non-fossil routes.The research results achieved are as follows:1.In order to address the problems of unsatisfactory charge separation and insufficient reactive sites of monomeric Bi3O4Br catalysts in photocatalytic CO₂ reduction,5,10,15,20-tetra（4-carboxyphenyl）porphyrin cobalt（II）（Co-TCPP）was induced with Bi₃O₄Br（B341）by constructing oxygen-deficient structures on the surface of Bi₃O₄Br through Bi–O bridge bond,and a series of Co-TCPP/Bi₃O₄Br organic-inorganic composite catalysts were successfully prepared.The performance studies showed that the interfacial Bi–O bridge bond induced by surface oxygen defects formed as a fast transfer channel for photogenerated electrons,which effectively promoted the transfer of photogenerated electrons from B341 to the Co-TCPP structure.Meanwhile,the metal Co atoms in Co-TCPP act as active sites for CO₂ reduction,effectively enhancing the CO₂adsorption-activation ability of the material.The photocatalytic CO₂ reduction performance test for 5 h shows that the composite material has significantly improved photocatalytic CO₂ reduction performance compared with the monomeric B341 material,and the 0.5%Co-TCPP/B341 material has the best photocatalytic CO₂ to CO yield up to 356.5μmol g^-1,which is 2.53 times higher than that of the monomeric material.Theoretical calculations and in situ spectra revealed possible mechanisms for photocatalytic CO₂ reduction.2.In order to further investigate the effect of metalloporphyrin structure on the performance of composite catalysts,Cu porphyrins with different substituent structures of–COOH,–CN and–NO₂ were synthesized and effectively compounded with Bi₃O₄Br（B341）using Cu porphyrins as the basic structural model.Thus,the Cu porphyrin-bismuth halide oxide organo-inorganic composite catalysts with different substituents were prepared.Studies have shown that the modulation of different electron-absorbing characteristic substituents can significantly enhance the photogenerated electron transfer rate and the reduction ability of the Cu atom active site in porphyrins.The photocatalytic CO₂ reduction activity test for 5 h showed that the CO yields of B341-Cu（COOH）,B341-Cu（CN）and B341-Cu（NO₂）for the photocatalytic reduction of CO₂could reach 287.07,347.52 and 412.11μmol g^-1,which were 2.12,2.57 and 3.05 times higher of B341.The in situ spectra revealed the possible mechanism for the photocatalytic CO₂ reduction.3.In order to address the functional and structural design difficulties of the catalyst active site,Pt atoms were introduced into the porphyrin structure to synthesize Pt-TCPP metalloporphyrin to enhance the proton feeding ability of the porphyrin,and Pt-TCPP/Bi₃O₄Br catalysts with surface Pt unit sites and Pt atom-pair sites were prepared respectively based on the molecular aggregation effect and surface defect induction strategy,thus realizing the construction of Pt atom-pairing sites on the surface of Bi₃O₄Br（B341）.The study showed that the construction of Pt atomic para-site Pt-TCPP/Bi₃O₄Br catalysts enhanced the number of active sites and the ability to activate CO₂molecules compared to Pt single-site Pt-TCPP/Bi₃O₄Br catalysts,strengthening the intermediate C-C coupling process.The photocatalytic CO₂ reduction performance test for 5 h showed that the Pt-TCPP/Bi₃O₄Br catalyst could achieve direct photocatalytic CO₂ reduction to C₂H₄ products,and the yield of atomic para-site Pt-TCPP/Bi₃O₄Br catalyst for photocatalytic CO₂ reduction to C₂H₄(13.18μmol g^-1)was higher than that of single-site material(1.62μmol g^-1)by a factor of8.14.Series characterization and in situ spectroscopy revealed the possible mechanism for the photocatalytic CO₂ reduction.4.In order to address the difficulties of insufficient number of active sites and slow interfacial charge transfer in photocatalysts,a Cu porphyrin-based atomic layer structure（PML-Cu）was constructed using Cu-TCPP porphyrin as a substrate,which was further combined on the surface of Bi₁₂O₁₇Br₂（BOB）to prepare PML-Cu/Bi₁₂O₁₇Br₂（PBOB）catalysts through stress engineering strategy.The study shows that the construction of PML-Cu on the surface of PBOB confers a high density of active sites,and the surface interface polarization between BOB and PML-Cu enhances the rate of photogenerated electron transfer from BOB material to the active Cu atoms.The photocatalytic CO₂ reduction performance test for 5 h showed that the yield of photocatalytic reduction of CO₂ to CO by PBOB could reach 584.3μmol g^-1,which is 7.83 times higher than that of the BOB material.Series characterization and in situ spectroscopy revealed the possible mechanism for the photocatalytic CO₂ reduction.5.In order to address the challenge of C-C coupling regulation during photocatalytic CO₂reduction to C₂ products,Cu₄O₃/PML-Cu/Bi₁₂O₁₇Br₂（Cu@PBOB）structured catalysts were successfully prepared by using PML-Cu periodic structure to induce domain-limited growth of Cu₄O₃ on the surface based on the above PBOB catalyst design.The study showed that the presence of Cu₄O₃ on the catalyst surface not only provided a large number of Cu（I）and Cu（II）active sites,but also acted as a catalyst skeleton to strengthen the domain-limiting role of intermediates and facilitated the C-C coupling of C₁ intermediates.The photocatalytic CO₂ reduction performance test for 5 h showed that hat the photocatalytic CO₂ reduction performance of Cu@PBOB to C₂H₄can reach 50.01μmol g^-1.Series characterization and in situ spectroscopy revealed the possible mechanism for the photocatalytic CO₂ reduction.