Preparation Of Modified MOFs Catalyst And Its Application In Photocatalytic Reduction Of Carbon Dioxide

With the society development,the current consumption mode,mainly relying on the limited fossil energy,has led to the sharply increasing CO₂ content in the atmosphere.Utilizing solar energy to convert CO₂ into energy materials is an effective way to solve these problems such as the energy crisis and the greenhouse effect,but it also faces enormous challenges.Conventional semiconductor materials,molecular sieve materials modified by transition metal and other photocatalysts were limited in application due to their low catalytic efficiency and poor structural tunability.Therefore,developing new and efficient photocatalytic materials is imminent.In order to solve these scientific problems,this thesis demonstrates some methods for the preparation of novel metal-organic framework?MOF?catalysts for CO₂ photoreduction including modification of MOF materials or incorporation of polyoxometalate in MOF structures.The work presented here exhibits new ideas and methods for modification of MOF catalysts,and provides guidance for photocatalytic CO₂ reduction.The main contents of this thesis including:?1?Two kinds of composite materials were obtained by loading the polyoxometalate into MIL-101-Cr and NH2-MIL-101-Cr,respectively.The composite SiMo12O40@NH2-MIL-101-Cr shows high CO₂ adsorption capacity due to the existence of amino groups.Meanwhile,the silicomolybdic acid molecules were introduced into NH₂-MIL-101-Cr.Due to the increased overall active sites,the obtained composite SiMo₁₂O₄₀@NH₂-MIL-101-Cr,showed good catalytic acitivity with the CO yield of 28.4?mol/?g·h?and the CO selectivity up to 94.6%.?2?The polyoxometalate was encapsulated in the sulfonic acid-modified MIL-101-Cr by diffusion.These methods not only maintained the structural integrity of MIL-101 but also increased the catalytic active site of the material.The CO yield of the composite material SiMo₁₂O₄₀@SO₃H-MIL-101-Cr in the CO₂ photoreduction was as high as 82.95?mol/?g·h?,and the selectivity of CO was 93.2%.The improvement of the catalytic performance of SiMo₁₂O₄₀@SO₃H-MIL-101-Cr could be attributed to the synergistic effect of the sulfonic acid group and the silicomolybdic acid molecule,which effectively promote the separation of photo-generated carriers and suppress the recombination of photo-generated electrons and hole pairs.?3?Immobilized different chain lengths alkylamines on sulfonic acid-modified SO₃H-MIL-101-Cr by utilizing Br?nsted acid-base reaction to obtain a series of alkylamine-modified composites,EN-SO₃H-MIL-101-Cr,DETA-SO₃H-MIL-101-Cr,and TETA-SO₃H-MIL-101-Cr.These modified materials retained its high CO₂ adsorption of the alkylamine,and also had good light response and low band gap.Among them,EN-SO3H-MIL-101-Cr showed the highest catalytic activity with the CO yield of 47.2?mol/?g·h?and the CO selectivity of 95.6%as well as good recyclability in the acetonitrile-free sacrificial system.These advantages can be attributed to the high affinity toward CO₂ and the less space occupancy of ethylenediamine chains in MOFs.