Design And Preparation Of Composited Photocatalytic Materials For Photocatalytic Hydrogen Evolution

With the advance of society,people are urgently looking for a green energy because of emerging environmental issues.Therefore,hydrogen energy,as a clean energy,has drawn great attention from human beings.However,traditional hydrogen-production technologies heavily rely on fossil fuels.Because total amount of solar energy is huge and it is easy to use,people hope to utilize solar energy and recyclable raw materials to produce hydrogen.Thus,people extensively focused on techniques of photocatalytic hydrogen generation.Nevertheless,many single-component photocatalysts have disadvantages such as low charge carrier separation efficiencies,insufficient solar spectrum utilization,poor light stability and high preparation costs This paper elaborates the works to improve photocatalytic H2-evolution performance of cadmium sulfide(CdS)and graphite phase carbon nitride(g-C3N4)via various modification.The main contents are as follows:(1)AuNPs/CdS composite was synthesized by a facile microwave-assisted method for photocatalytic hydrogen generation from water splitting,Photocatalytic activity of optimized AuNPs/CdS composite prepared by microwave-assisted method was 26 times higher than that of pure CdS,2.1 times higher than that of 5 wt%AuNPs/CdS synthesized by traditional hydrothermal method and almost 5 times higher than that of classic Pt/CdS.This study showed that the improvement in photocatalytic performance can be attributed to localized surface plasmon resonance effect(LSPR)of AuNPs and the strong interaction of AuNPs and CdS,leading to better generation rate and separation efficiency of charge carriers.This two aspects were greatly beneficial to photocatalytic activity and photostability.(2)Noble-metal-free ternary heterostructured NiS-CUS-C3N4 composite was prepared by a simple hydrothermal method for photocatalytic hydrogen generation from water splitting.Photocatalytic activity of optimal NiS-CUS-C3N4 was 114 times,9 times,8 times and 3 times higher than that of pure C3N4,NiS-C3N4,CuS-C3N4 and Pt/C3N4,respectively.The photocatalyst above was discussed in detail by a series of characterization methods.Finally,a reasonable reaction mechanism was proposed.The reasons for the improvement of photocatalytic performance were shown as follows:(i)Higher surface area;(ii)Greatly extended light absorption range from visible light to the near-infrared region;(iii)The band structure formed between C3N4 and CuS;(iv)The role of NiS with beneficial H adsorption energy for HER and the effect of trapping electrons.These factors collectively led to enhanced photocatalytic activity of NiS-CuS-C3N4.Therefore,this work laid the foundation for designing high-performance noble-metal-free ternary C3N4-based heterostructured photocatalysts.(3)A Ni-diaminoethylenedioxime-g-C3N4 complex for photocatalytic hydrogen generation from ethanol splitting was designed and fabricated based on the ligand-to-metal charge transfer(LMCT)mechanism.The reaction of ethanol splitting could proceed under room temperature.And ethanol could be directly converted to acetaldehyde and hydrogen without forming COx.Compare pristine C3N4,optimal Ni-Diaminoglyoxime-g-C3N4 complex photocatalyst showed 21-fold enhancement of photocatalytic activity and excellent photo-stability.This enhancement of photocatalytic performance can be attributed to the transfer of electrons from the conduction band can be easily transferred to Ni(?),and then generate H2 and acetaldehyde through the LMCT mechanism,leading to greatly improved efficiency of charge carrier separation.Therefore,this research was of great significance for the design of efficient g-C3N4-based complex photocatalysts for future green energy conversion.