Synthesis And Characterization Of Novel Semiconductor Photocatalysts

With the rapid development of economy,the problem of environmental pollution has become increasingly prominent,especially the water pollution problem has endangered the survival of human beings.Semiconductor photocatalyst technology uses green and environmentally friendly approach to solve the problems of water pollution.As a common semiconductor oxide,Zn O has a wide band gap and is widely used in the field of photocatalysis.However,the photogenerated electrons and holes generated from Zn O photocatalyst after absorbing light energy are easy to recombine,which greatly affects the photocatalytic efficiency of the materials.At the same time,the recovery of most of Zn O photocatalysts is difficult,which is not conducive to protecting the environment and is likely to cause secondary pollution to the environment.Based on the above problems,different Zn O-based photocatalysts were prepared by the aqueous solution method to enhance the photocatalytic performance.The results were as follows:?1?Preparation of Zn O films with different morphologies:Zn O thin films with different morphologies were prepared by the aqueous solution method,which used zinc nitrate as a zinc source and regulated different experimental parameters?temperature,additives,reaction time,etc.?The photocatalytic performance of the Zn O photocatalysts with different dimensions and morphologies for the degradation of methylene blue?MB?was studied.The results showed that different forms of Zn O films had an effect on the use efficiency of ultraviolet light,among which the grassy Zn O had unique morphologies and structures,grew regularly and evenly on the glass substrates,and exhibited good photocatalytic performance.Correspondingly,the grassy Zn O had the best photocurrent response.The photocatalytic activity remains high after 8 cycles of the experiments.The grassy Zn O prepared at different p H values had different photocatalytic properties.The appropriate p H concentration can improve the performance of the sample.The intensity of the crystal plane diffraction peak was different.The corresponding photocatalytic performance of the photocatalyst was also changed.As the intensity of the crystal plane diffraction peak increased,the photocatalytic performance of the sample was increased.When the light irradiated on the photocatalyst,the light were reflected many times in the grassy Zn O tips,which greatly improved utilization efficiency of the light.Therefore,the crystal structure,morphologies,p H,and light use efficiency of Zn O were closely related to the photocatalytic performance.?2?Preparation of zinc oxide/reduced GO?Zn O/r GO?composite photocatalysts:Zn O/r GO composite photocatalysts with different morphologies were prepared at low temperature by the aqueous solution method and the chemical deposition method,using zinc nitrate as the zinc source.The photocatalytic performance of the Zn O/r GO composite photocatalysts with different morphologies were studied by degradation of MB.The results showed that the contact angle increased and the ultraviolet-visible absorption band gap was changed after addition of GO,which improved the photocatalytic performance of the samples.Under ultraviolet light,Zn O/r GO composite photocatalysts showed good photocatalytic performance,which was attributed to the presence of oxygen-containing groups in the GO.As an efficient electronic storage/transfer center,it can effectively reduce the photoelectron-hole recombination rate and improve the photocatalytic performance.After 120 min photocatalytic experiments,the Zn O arrays/r GO composite photocatalyst showed excellent photocatalytic performance compared with that of the Zn O seeds/r GO and the Zn O flowers/r GO.As the intensity of the crystal plane diffraction peak and the GO concentration increased,the Zn O arrays/r GO composite photocatalyst exhibited excellent photocatalytic performance.Therefore,the photocatalytic performance of the Zn O/r GO was closely related to the crystal structure,morphology and GO concentration of the samples.?3?Preparation of zinc oxide/silver?Zn O/Ag?composite materials:Zinc nitrate was used as the precursor to grow nano-Zn O arrays and grassy nano-Zn O on the glass substrates by aqueous solution method.Then,Ag was deposited on the Zn O surface by dipping reduction method to prepare Zn O/Ag composite photocatalytic materials.The effects of the concentration of the Ag ions,soaking time and reducing agent?Sn Cl₂?on the photocatalytic degradation of rhodamine B?Rh B?solution by Zn O/Ag photocatalyst were investigated.The results showed that the Zn O/Ag composites all exhibited the hexagonal wurtzite structure and were evenly dispersed on the substrate.The band gap of Zn O/Ag composites was reduced compared to that of Zn O due to the surface plasmon resonance?SPR?effect of Ag.The SPR effect of Ag enhanced the light absorption,greatly improved the photocurrent response of the Ag-modified Zn O/Ag composites,and thus improved the separation efficiency of electron-hole pairs in the near-surface region of Zn O.The Zn O/Ag composites showed excellent photocatalytic degradation rate of Rh B under light radiation.By reducing the concentration of Sn Cl₂,increasing the concentration of trifluoroacetic acid,reducing the concentration of Ag ions,and reducing the soaking time of the sample,the photocatalytic performance of the sample was also improved.When the intensity of the crystal plane diffraction peak of the sample was weakened,the photocatalytic performance of the samples showed excellent degradation performance.Therefore,the photocatalytic properties of the grassy Zn O/Ag composites were related to the strength of the crystal plane diffraction peak,the concentration of Ag⁺ions,the soaking time and the concentration of reducing agent.