Preparation Of Indium-based Hollow Heterojunctions And Their Photocatalytic Performance

With the rapid development of global economy,the continuous consumption of fossil fuels has aggravated the world energy crisis.The excessive carbon dioxide（CO₂）produced by the burning of fossil fuels has caused serious environmental problems such as the greenhouse effect,which has limited the sustainable development of society and human survival.Solar driven CO₂conversion into chemical fuels is a promissing method to alleviating the energy crisis and solving environmental problems.Because the CO₂ molecule is too stable to be activated,the development of high-efficiency photocatalysts is the key to realize the practical application of photocatalytic CO₂ reduction technology.However,most semiconductor photocatalytic materials have poor visible light utilization efficiency and serious recombination of photogenerated electrons and holes,which greatly limit their photocatalytic activity.Constructing a heterojunction is an effective way to improve photocatalytic performance.Hollow-structured materials exhibit excellent photocatalytic performance due to their good light absorption ability,short diffusion length of photogenerated carriers and abundant exposed active sites.However,the fabrication of hollow heterojunction materials is still a challenge.Therefore,the development of a simple and effective method to prepare hollow heterojunction is of great significance to the high-efficiency photocatalytic CO₂conversion.A hollow In₂S₃/polymeric carbon nitride（IS/CN）heterojunction was prepared via electrostatic self-assembly and in-situ sulfidation using In-MIL-68 as the precursor.A intimately contacted interface between IS and CN is formed,which improves the charge separation and transfer efficiency,demonstrating by XPS and TEM.The heterojunction displays a significantly improved activity of photocatalytic CO₂ reduction than the pure semiconductor due to the hollow structure and the high CO₂ adsorption capacity.Under visible light irradiation,the optimized IS/CN-5 sample exhibits good stability and high CO evolution rate of 483.4μmol g^-1 h^-1,which is 99 and 6 times as high as that of IS and CN,respectively.Finally,a possible photocatalytic mechanism of CO₂ reduction by the IS/CN heterojunction was proposed on the basis of the band structures.A In₂O₃-C/CdIn₂S₄（IOC/CIS）ternary tubular hollow heterojunction was synthesized though one-step pyrolysis of In-MIL-68 precursor and solvothermal reaction.The construction of heterojunction improves the charge seperation and transfer efficiency.The CO₂ adsorption capacity of the photocatalyst is enhanced by the introduction of carbon material.Meanwhile,carbon material with excellent conductivity acts as a“bridge”to accelerate the transfer of photogenerated charges at the interface between IO and CIS.Under visible light irradiation,the 5IOC/CIS sample shows good cycle stability and remarkable CO₂photoreduction activity with a CO evolution rate of 2432μmol g^-1 h^-1,which is much better than most reported photocatalysts.Moreover,the type-II charge transfer mechanism of the heterojunction was confirmed by the electron paramagnetic resonance characterization.