Controlled Synthesis Of Metal-Organic Layers And Study On Photocatalytic CO₂ Reduction And Water Splitting Hydrogen Production

Using photocatalytic energy conversion technology to convert solar energy into chemical energy is a very promising approach to mitigate the energy and environmental crisis.Development of efficient,robust and low-cost catalysts is necessary and desirable for their practical application.As a new class of crystalline catalysts,metal-organic frameworks(MOFs)have garnered tremendous attention on photocatalytic energy conversion,due to the versatile components and coordination modes.Compared with bulk MOFs,metal-organic layers(MOLs)inherits the advantages of two-dimensional materials with open double-sided planar structures and unique electronic properties,which will benefit the mass diffusion and permeability.In addition,MOLs have more exposed active sites,which strenthens the contact with CO₂ molecules and thus results in high reaction rates.In this thesis,a series of MOLs-based catalysts with high activity for photocatalytic CO₂reduction and water splitting were obtained.The structure-activity relationship was studied and the catalytic mechanism was revealed by theoretical calculation.The main research contents of this paper are shown as follows:1.For crystalline catalysts,it is well known that different crystal facets primarily determine their catalytic performances by providing various active sites that affect the reaction energetics.Using a crystal engineering approach,we have successfully prepared two ultrathin2D Ni-based MOLs with different exposed crystal facets,which exhibit different catalytic performances in photochemical CO₂-to-CO conversion.We demonstrate for the first time that a nickel metal–organic layer(MOL)exposing rich(100)crystal facets(Ni-MOL-100)shows a much higher photocatalytic CO₂-to-CO activity than the one exposing rich(010)crystal facets(Ni-MOL-010)and its bulky counterpart(bulky Ni-MOF),with a catalytic activity up to 2.5 and 4.6 times more active than Ni-MOL-010 and bulky Ni-MOF,respectively.The combined results of experiments and DFT calculations indicate that the enhanced activity of Ni-MOL-100 is attributed to the synergistic catalysis between two adjacent nickel sites with a close distance of 3.50?on the surface of(100)facet.2.We report the preparation of a novel CdS/Ni-MOLs 2D/2D photocatalyst via a facile solvothermal method for the first time.Impressively,the optimized composite catalyst exhibits superior hydrogen production performance,with the H₂ yield of 29810?mol×g^-1×h^-1,this value is 7 and 2981 times higher than that of 2D CdS and Ni-MOFs,respectively.The superior photocatalytic performance of CdS/Ni-MOLs heterostructure can be attributed to the abundant exposed active sites on the heterojunction surface and the stable 2D/2D intimate interface in the heterojunction facilitating for fast charge carriers separation and transfer.3.It is urgent yet challenging to develop photocatalysts for visible-light-driven CO₂ reduction with high efficiency and inexpensive.We report a facile template strategy to prepare a series of transition metal-organic layer on CN to act as a cocatalyst ensemble for efficient CO₂ photoreduction.Owing to unsaturated coordination sites and opposite charge for CN and MOLs,a stable 2D/2D configuration can be formed.The introduction of MOLs into the CN reaction system can not only generate efficient catalytic active sites but also promotes e^--h⁺separation.In addition,the CO₂ reduction performance tests exhibit a strong dependence on the nature of the transition metal,not only in the yield of CO,but also in terms of the CO/H₂molar ratio.The as-synthesized 2D/2D heterostructure Co-MOL/CN(400)exhibit excellent visible-light photocatalytic CO₂ reduction performance,with CO-production rate of 539?mol h^-1 g^-1,much higher than that of CN and Co-MOL nanosheets in same condition,respectively.This work demonstrates a facile way for constructing ultrathin metal–organic layers based2D/2D photocatalysts for artificial reduction of CO₂ to chemical fuels.