Preparation Of Ta₃N₅-based Nanocomposites Co-modified By Fe-Ni-Co And Its Photocatalytic Performance For Hydrogen Evolution From Water-splitting

The burning of traditional fossil fuels has caused serious environmental pollution,resource shortage and climate change.At the two sessions,the Party pointed out the need to make solid efforts to reach a carbon peak and achieve carbon neutrality,strengthen pollution prevention and control and ecological improvement,and develop green energy as a national development strategy.Hydrogen combustion product is water,can store easy transportation,become the clean fuel that attracts the most attention in the 21st century.Use of semiconductor material visible light push to split water hydrogen evolution has application prospect,is expected to achieve commercial hydrogen technology development.Ta₃N₅photocatalyst can absorb and expand to 600nm visible light,and has a band position suitable for the whole water decomposition with a band gap of about 2.1 e V.Theoretically,the efficiency of water hydrogen evolution induced by light can reach 15.9%,which makes it an ideal visible light catalytic hydrogen production material.However,its shortcomings,such as poor carrier transport,easy recombination of carriers,low separation efficiency and poor photocorrosion stability,limit its practical application in the field of photocatalysis.The hexahedral morphology of Ta₂O₅@Ta₃N₅was controlled by the mixed molten salt assisted technology.The type of flux,relative proportion of mixed molten salt,dosage of Na OH,roasting time,roasting temperature,relative proportion of Ta₂O₅to mixed molten salt,nitriding temperature,nitriding time and other technological conditions were adjusted and controlled.The results showed that the hexahedron Ta₂O₅@Ta₃N₅photocatalyst of 60 nm with clear edges and good dispersion was successfully prepared by Ta₂O₅precursor with adding 0.5 m L Na OH aqueous solution,grinding and mixing with 1:3 Na Cl+Na₂CO₃（molar ratio 1:1）molten salt,calcining at750℃for 2 h,and nitriding at 800℃for 3 h.The measured photocurrent density is 0.28μA·cm^-2.Furthermore,the process of high temperature nitriding and synchronous preparation of mixed molten salt was compared.After nitriding at 800℃for 4 h,the Ta₂O₅@Ta₃N₅product was obtained.The photocurrent density of the sample is 0.57μA·cm^-2,which is 2.03 times of the former and is 3.8 times of the sample without nitriding(0.15μA·cm^-2).The hexahedral morphology and the construction of Ta₃N₅/Ta₂O₅heterojunction promote the photogenerated electron hole separation,which provides a prerequisite for the further realization of spatially selective surface modification of the co-catalyst.The precursor of Ta₂O₅@Ta₃N₅was modified by impregnation.Ni OOH/Ta₂O₅/Ta₃N₅and Ni₄N/Ta₃N₅/Ta₂O₅nanocomposite photocatalysts with double heterostructures were successfully constructed by impregnating and adsorbing 2%Ni²⁺at room temperature,nitriding reduction at 480℃for 1 h,and then heat treatment at180℃for 0.5 h in air atmosphere.The activity of water splitting and hydrogen evolution was improved to 1294μmol·g^-1·h^-1under visible light irradiation.Compared with the basic Ta₂O₅@Ta₃N₅sample,the visible light absorption ability is obviously enhanced;the photocurrent density(1.3μA·cm^-2)is doubled compared with the basic Ta₂O₅@Ta₃N₅sample(0.57μA·cm^-2),it promotes the photogenerated electron hole separation;the carrier migration resistance is further reduced,Ni OOH reduces OER overpotential and provides an active site for oxygen production;Ni₄N reduces HER overpotential and provides an active site for hydrogen production,thus promoting the redox reaction of water decomposition.The advanced photocatalytic activity is attributed to enhanced visible light absorption,improved carrier separation efficiency,migration rate,and accelerated surface reactions.The above research provides a new strategy for the further modification of Ta₃N₅based nano-photocatalyst.The preliminary experimental results show that the co-modification of Fe and Co has a synergistic effect on Rh-Ta₂O₅@Ta₃N₅modification and improves the photocatalytic hydrogen production performance.On this basis,in order to achieve Fe-Ni-Co multiple synergistic modification,further improve the performance of Ta₂O₅@Ta₃N₅nanocomposite photocatalytic material,explore the relative proportion of modifier,post-treatment temperature and other technological conditions,the current results do not meet the expectations,related research experiments are in progress.