Functioned ZIF-8 Photocatalyt For CO₂ Reduction

Excessive use of fossil fuels and constant emission of CO₂ greenhouse gas lead to the depletion of fossil fuel and worsening of global environment,it is extremely urgent to explore new types of environmentally-friendly renewable energy sources.Since 1979 Inoue and coworkers reported the photocatalytic reduction of CO₂ into hydrocarbon fuels in aqueous using semiconductor powders,mumerous semiconductors including titanium dioxide,zinc oxide,cadmium sulfide,ZnGa₂O₄,g-C₃N₄ and Zn₂GeO₄ were studied for photocatalytic reduction of CO₂.Therefore,photocatalytic reduction of CO₂ to hydrocarbon fuels by semiconductor photocatalysis has been paid widespread attention.However,traditional zinc oxide photocatalysts can only absorb UV light which seriously affect its photocatalytic activity as a whole.In addition,the specific surface area of reported zinc-oxide is not high enough to effectively adsorb CO₂ molecules.Based on these considerations,a variety of strategies were explored to broaden the range of optical absorption,increase the specific surface area,inhibit the recombination of photogenerated electrons and holes,thus to enhance the performance of photocatalytic CO₂ reduction.This work mainly focuses on the following:1.Visible-light responsive porous ZnO photocatalysts with special bimodal carbon modification,that is,simultaneous carbon doping and surface carbon coating,were fabricated by calcining pre-synthesized ZIF-8?a kind of zeolitic imidazolate framework?polyhedra as solid precursor which was pre-prepared by a room temperature stirring methord using Zn?NO₃?₂·6H₂O,2-methylimidazole and methanol as precursors at suitable calcination temperature in air.The as-prepared samples were characterized by X-ray diffraction,electron microscopy,Fourier transform Raman spectroscopy,X-ray photoelectron spectroscopy,thermogravimetry and differential thermal analysis,nitrogen sorption,CO₂ absorption,UV–Vis diffuse reflectance spectra and photoelectrochemical measurement.Overall,the as-prepared mesoporous ZnO photocatalyst was efficient in both CO₂ capture and photocatalytic CO₂reduction towards CH₃OH as a typical solar fuel under full-spectrum Xe lamp irradiation.Especially,the 500^oC-calcined sample manifested the highest photocatalytic CO₂ reduction activity(0.83?mol/?h·g?,which was about six folds higher than that of hydrothermally synthesized ZnO nanorods as reference.The superior photocatalytic CO₂ reduction performance was associated with the bimodal carbon modification,high specific surface area and porous framework,which contributed to enhanced visible light harvesting,charge transport and CO₂ capture.2.Porous core@shell ZnO@ZIF-8 photocatalysts were successfully fabricated by one-step solvothermal method in a mixed solution of dimethyl formamide and deionized water using 2-methylimidazole and ZnO nanorod as presursors.The as-prepared samples were characterized by X-ray diffraction?XRD?,electron microscopy?FESEM and TEM?,nitrogen sorption,CO₂ absorption and UV-vis diffuse reflectance spectra.Overall,the as-prepared mesoporous ZnO@ZIF-8photocatalyst was efficient in both CO₂ capture and photocatalytic CO₂ reduction under full-spectrum Xe lamp irradiation.Especially,the optimized ZnO@ZIF-8photocatalyst exhibited a high photocatalytic CO₂ reduction activity at 6 h hydrothermal reaction.The superior photocatalytic CO₂ reduction performance was associated with high specific surface area and porous framework of ZIF-8,which contributed to the enhanced CO₂ capture.Furthermore,the absorbed light energy can activate the CO₂ molecules and accelerate the photocatalytic reduction reaction.This work may provide a facile hydrothermal method for preparing highy performance ZnO@ZIF-8 composite photocatalyst.