Enhancent Of Hydrogen Production Performance Of Ta₃N₅ Under Visible Light Irradiation By Surface Polarization-Induced Carrier Separation

Resource depletion and environmental pollution have always been the concerned problems of human development.Using photocatalytic hydrolysis to produce hydrogen is a green and sustainable strategy to solve this problem.Ta₃N₅-based materials have attracted much attention as promising catalyst substrates due to their high chemical stability,high corrosion resistance and low resistance.Due to its narrow band gap of 2.1eV,visible light absorption up to 600 nm,suitable conductive（valence）band position spans the redox potential of water,theoretically,solar energy to hydrogen conversion efficiency（STH）up to 15.9%,it is an ideal semiconductor photocatalytic material.However,due to its shortcomings such as easy recombination of photo-generated carriers and poor stability,its large-scale application in industry is limited.Ta₂O₅@Ta₃N₅nanoflowers were synthesized by a combination of hydrothermal and high-temperature nitridation methed.Based on themorphology evaluated by field emission scanning electron microscopy（SEM）,the preparation process of Ta₂O₅nanoflowers were optimized by regulating process condit ions including solvent type,amount of isopropanol,amount of hydrochloric acid,and hydrothermal time.Isopropanol solvent is beneficial to promote the formation of rod-like structure.When the amount of isopropanol is 14 mL and the amount of concentrated hydrochloric acid is800μL,Ta₂O₅ nanoflowers are prepared by hydrothermal treatment at 160℃for 4 h and roasted at 750℃for 2 h.The rod-like structure of nanoflowers is about 50 nm in diameter and about 200 nm in length.Then,Ta₂O₅@Ta₃N₅ nanoflowers were prepared by topological transformation of Ta₂O₅ nanoflowers,using high-temperature nitriding technology,under 50 mL·min^-1 NH₃ gas flow,after nitriding at 850℃for 3 h.The Ta₂O₅@Ta₃N₅ was surface-polarized by H₃PO₄ and H₃BO₃,and the modification process of H₃PO₄ and H₃BO₃ was optimized to construct surface polarization of mixed acids Ta₂O₅@Ta₃N₅ nano photocatalytic materials.Using modern techniques such as SEM,TEM,XRD,XPS,BET,DRS,electrochemical testing,and Zeta potential testing to characterize the samples and conduct hydrogen production performance tests.Discussion on surface polarization of mixed acids Ta₂O₅@Ta₃N₅hydrogen production activity mechanism of photocatalytic materials.The results show that the surface polarization of mixed acids does not change the crystal structure and energy band structure.Photocurrent testing has proven that mixed acid surface polarization effectively inhibits photogenerated carrier recombination,and mixed acid surface polarization Ta₂O₅@Ta₃N₅ the photocurrent density of the film is increased to0.23μA·cm^-2,which is the foundation Ta₂O₅@Ta₃N₅(0.13μA·cm^-2)1.77 times.When pH=7,the Zeta potential of mixed acid surface polarization Ta₂O₅@Ta₃N₅ is-20.2 mV,which is lower than that of Ta₂O₅@Ta₃N₅（-16.8 mV）.It shows that the surface of mixed acid surface polarization Ta₂O₅@Ta₃N₅ in aqueous solution has more negative charges,forming a surface negative electrostatic field.Under the action of the negative electrostatic field,photogenerated electrons and holes migrate in the opposite direction,inhibiting the photogenerated carrier recombination,thus improving the photocatalytic hydrogen evolution activity,with its photocatalytic hydrogen production rate reaching0.921 mmol·g^-1·h^-1.This paper provides a feasible new idea for the development of high efficiency and low cost tantalum nitride based photocatalytic materials.