Fine Construction And Photocatalytic Properties Of Mineral Composites Derived From MOFs

In order to achieve the strategic goals of“carbon peaking”and“carbon neutrality”,direct conversion of solar energy into solar fuels through photocatalytic technology（including photocatalytic water splitting for hydrogen production and photocatalytic CO₂ reduction）has been recognized as one of the promising strategies for tackling the energy and environmental problems,which greatly relies on the exploration of advanced photocatalysts.Lately,metal organic frameworks（MOFs）derived inorganic semiconductors have received increasing attention.It is widely believed that the derivatives can not only inherit the original MOFs morphology,but also obtain porous materials with high specific surface area through the decomposition and volatilization of organic components,thereby significantly promoting photocatalytic activity.In this dissertation,the synthesis and application of a series of advanced inorganic mineral composites based on MOFs-derived strategy for photocatalytic water splitting for hydrogen production and photocatalytic CO₂ reduction were investigated,respectively.As discussed,the main research results are summarized as follows:（1）Controllable preparation and visible-light driven photoreduction of CO₂ to CO of Ni/Co-MOFs-derived Ni-Co-O porous microrods.A series of novel Ni/Co-MOFs microrods with different mole ratios of Ni and Co content was first prepared via the hydrothermal method,and then the Ni-Co-O solid solution hierarchical mesoporous microrods were obtained as CO₂ photoreduction photocatalyst through the calcination of Ni-Co bimetallic MOFs precursors.The photocatalytic CO₂ reduction performance and mechanism were investigated with the introduction of photosensitizer in liquid-solid model.As a result,they exhibit overall enhanced photocatalytic performance with both high activity and remarkable selectivity for reducing CO₂ into CO under visible-light irradiation,which is superior to most related photocatalysts reported.Accordingly,the MR-N_0.2C_0.8O photocatalyst delivers high efficiency for photocatalytic CO₂reduction into CO at a rate up≈277μmol?g^-1?h^-1,which is≈35 times that of its Ni O counterpart.Furthermore,they display a high selectivity of 85.12%,which is not only better than that of synthesized Co₃O₄（61.25%）but also superior to that of reported Co₃O₄-based photocatalysts.It is confirmed that the Co and Ni species are responsible for CO₂-CO conversion activity and selectivity,respectively.In addition,it is verified,by adjusting the Ni contents,that the band structure of Ni-Co-O microrods can be tailored with favorable reduction band potentials,which thus enhance the selectivity towards CO₂ photoreduction.（2）Engineering the S-scheme heterojunction between Ni-MOFs derived Ni O and Mg Al-LDH mineral for photocatalytic CO₂ reduction.As a typical mineral,Mg Al-LDH,which has a high basicity of Mg²⁺cations,exhibits the advantages of low cost,high availability,and high CO₂ adsorption capacity,and it has the potential to be a large-scale photocatalyst in the CO₂ photoreduction region.Nevertheless,significant electron-hole recombination hinders the applications of Mg Al-LDH as photocatalyst.According to the band structure characteristics of the synthesized Ni-Co-O,the novel p-Ni O/n-Mg Al-LDH S-scheme heterojunction photocatalyst has been engineered via in-situ anchoring Mg Al-LDH nanoplates on the selected MOF-derived Ni O microrod host due to its high reducibility,excellent CO₂ adsorption and high CO₂ reduction selectivity through the hydrothermal process for further boosted CO₂ photoreduction.In order to further improve the selectivity of CO₂ reduction,the photocatalytic CO₂reduction performance and mechanism were investigated by gas-solid mode.As a result,the spontaneous built-in internal electric field directs the photogenerated electron transferred from the conduction band of Mg Al-LDH to the valance band of Ni O,which is evidenced by the experiments and theoretical results.Moreover,the in-situ grown Mg Al-LDH nanoplates could enhance the specific surface area and CO₂ adsorption capacity of Ni O.Consequently,such a rationally designed catalyst achieves a high selectivity of 91.2%for CH₄ production,with a yield of 8.98μmol?g^-1?h^-1 by using pure water as the proton source,which is 4.23 and 2.07 times those of pristine and revitalized Ni O,respectively.Therefore,Mg Al-LDH mineral material with abundant sources and low cost represents practical application potential on photocatalytic CO₂ reduction.（3）MIL-68 derived iron manganese ore type In₂O₃/g-C₃N₄ heterojunction for photocatalytic hydrogen production.The In₂O₃/g-C₃N₄heterojunction photocatalyst is composed of MIL-68-derived iron manganese ore type In₂O₃ nanorods and g-C₃N₄nanosheets for photocatalytic hydrogen production.As a result,the In₂O₃/g-C₃N₄composites possessing nanosheet-microrod composite structures exhibited remarkably improved photocatalytic performance in comparison to pure g-C₃N₄ and In₂O₃photocatalysts for the evolution of hydrogen via the water-splitting process.（4）NH₂-MIL-68 derived fusiform iron manganese ore type In₂O₃/Cd Zn S heterojunction for visble-light photocatalytic hydrogen production.The development of efficient visible-light-driven photocatalysts is one of the critically important issues for solar hydrogen production.Herein,high-efficiency visible-light-driven In₂O₃/Cd Zn S hybrid photocatalysts are employed by a facile oil-bath method,in which ultrafine Cd Zn S nanoparticles are anchored on NH₂-MIL-68-derived fusiform In₂O₃mesoporous nanorods.It is disclosed that the as-prepared In₂O₃/Cd Zn S hybrid photocatalysts exhibit enhanced visible-light harvesting,improves charges transfer and separation as well as abundant active sites.Correspondingly,their visible-light-driven H₂ production rate is significantly enhanced by more than 185 times that of pristine In₂O₃ nanorods,and superior to most the In₂O₃-based photocatalysts ever reported,representing their promising applications in advanced photocatalysts.This dissertation has 71 figures,16 tables and 341 references.