Construction Of Carbon Nitride-based Heterojunction And Study Of Its Photocatalytic Carbon Dioxide Reduction Performanc

The continuous accumulation of carbon dioxide(CO2)in the atmosphere has destroyed the carbon balance of nature and aggravated global warming,which is one of the most urgent challenges facing mankind at present.Photocatalysis is an ecological friendly technology that can directly convert solar energy into other clean energy.Photocatalytic CO2 reduction is an effective strategy to achieve CO2 capture and conversion.It can not only reduce CO2 emissions,but also produce high-value-added chemicals.As a metal free polymer semiconductor,carbon nitride(C3N4)is considered as a promising photocatalyst due to its proper electronic band structure,good chemical stability and simple preparation method.However,C3N4 still faces the problem of low efficiency of photogenerated carrier separation.Constructing heterojunctions can adjust the direction of electron hole transfer through band position differences,promote charge separation,and extend the lifetime of photo generated carriers,thereby improving the photocatalytic ability of C3N4.The main research contents of this paper are as follows:ZnIn2S4/bulk C3N4 heterojunction material(ZIS/BCN)was synthesized by a simple hydrothermal method.ZnIn2S4 nanosheets were epitaxial grown on bulk C3N4,and there was a uniform and tight interfacial contact between the two components.At the same time,due to the difference in band positions,it was advantageous for the separation and transfer of photo generated electron hole pairs.In addition,the layered structure of ZnIn2S4 has a large specific surface area that can provide more catalytic active sites.Compared with pure C3N4,ZIS/BCN nanocomposites exhibit enhanced CO2 reduction ability without sacrificial agents.Among them,ZIS-20/BCN exhibits the best performance,with CO and CH4 generation rates of 24.30 and 4.16 μmol g-1 respectively after 4 hours of illumination.Fe2O3/tubular C3N4 heterojunction photocatalyst(Fe2O3/TCN)was prepared using a hydrothermal method.The introduction of Fe2O3 can effectively enhance the absorption of the photocatalyst in the visible light region,and the formed Z-scheme heterojunction structure can promote the transfer and separation of photo generated electron holes.Compared with TCN,Fe2O3/TCN exhibits higher CO and CH4 yields,with Fe2O3-10/TCN exhibiting a CO generation rate of 27.50 μmol g-1 and a CH4 generation rate of 6.37 μmol g-1 after illumination for 4 hours.The overall photocatalytic efficiency of Fe2O3-10/TCN is four times that of TCN and it exhibits excellent stability.The CeO2/C3N4 heterojunction material was successfully prepared by in-situ exfoliation and conversion strategy.C3N4 is a porous lamellar structure,and CeO2 nanoparticles are uniformly distributed on the nanosheet.As the specific surface area of the catalyst increases,the active sites and adsorption sites of the reaction increase.The intimate interface and Z-scheme charge transfer between CeO2 and C3N4 greatly promote the separation of photogenerated carriers.Under light irradiation for 4 hours,the CO and CH4 generation rates of the obtained CeO2/C3N4 heterojunction are 35.96 and 2.40 μmol g-1,which is 5 times higher than that of bulk C3N4.