Synthesis And Photocatalytic Activity Of Hierarchical ZnO Composites

With the rapid development of industry,environmental water pollution has become a major threat to human health.Recently,heterogeneous semiconductor photocatalysts have achieved significant progresses in the degradation of water pollutant.As a n-type typical photocatalysts,ZnO has attracted great interest due to its low cost,nontoxicity and high quantum efficiency for photocatalytic application.However,low light-harvesting efficiency and quick recombination of charge carries still hinder improving photocatalytic activity of those ZnO materials.Hierarchical ZnO nanocomposites reported in this thesis,display strong light-havesting ability and superior photocatalytic performance.The specific research results are as follows:(1)The HC ZnO prepared via hydrothermal method,consist of one dimensional nanorods.ThenHZ&CuO composite materials can be obtained via in-situ growth ofCuO nanoparticles on the surface ofHC ZnO substrate.The pn heterojunction formed between ZnO and CuO in this composites is beneficial to the separation of electrons and holes.Meanwhile,the light response range of the composites has broadened from ultraviolet band to visible-light band,and also visible-light absorption intensity has significantly enhanced.After illumination 75 min,the photocatalytic efficiency of HZ&G composite towards RhB reaches 100%.Nevertheless,only 50% of RhB is degenerated for HC ZnO catalyst.These results indicate that the photocatalytic activity of this composite is drastically superior to pure HC ZnO.(2)A facile method is carried out to obtain the composites in which graphene modified HC ZnO.Also,it is futher studied that different GO additions greatly influence the structure and photocatalytic performance of those composites.The HC ZnO are composed of secondary nanoparticles with diameter of 10 nm.In addition,the HC ZnO is well coated with gauze-like graphene in HZ&GO 15 composites.Afeter the modification of graphene,the visible-light absorption intensity of all the composites is markedly enhanced and thus the light conversion efficiency is remarkablyincreased.The transient photocurrent of HZ&GO 15 composites is twotimes higher than that of HC ZnO.Meanwhile,the Rctr value of HZ&G composite is~ 5500?,while that of HC ZnO is as high as 9600?.After illumination 35 min,the photocatalytic efficiency of HZ&GO 15 over methyl orange achieves 100%,which is the highest among the composites in this work and also far better than pure HC ZnO.(3)ZnO&CuO core-shell nanocomposites are prepared via a two-step solution method.As the results in XPS,the pn heterojunction is formed between ZnO and CuO in this composites.That can accelerate the separation of interfacial charge carriers and thus fluorescence intensity of the core-shell nanocomposites is much lower than pure ZnO.The transient photocurrent of ZnO&CuO composites is 2.5times higher than that of ZnO.Meanwhile,the Rctrvalue of HZ&G composite is ~1800?,while that of ZnO is as high as 3200?.After illumination 35 min,the photocatalytic efficiency of nanocomposites over methylene blue achieves 100%?Nevertheless,only 60% of methylene blue is degenerated for HC ZnO catalyst.