Microwave-assisted Synthesis And Properties Of Ag/ZnO/g-C₃N₄ Micro/Nano Multilevel Composite Photocatalyst

One-dimensional of ZnO nano semiconductor material has been widely used in the field of photocatalysis due to its large exciton binding energy,high quantum yield,large specific surface area and low cost.However,it is necessary to modify ZnO because of its wide band gap,low utilization rate of visible light and easy recombination of photogenerated electron-hole.In this paper,noble metal Ag with surface plasmon resonance and a new type of green semiconductor g-C₃N₄ with narrow band gap have been combined to modify ZnO,Ag/ZnO/g-C₃N₄ micro/nano multilevel composites were prepared by microwave-assisted method with the advantages of fast and high efficient,energy saving and environmental protection,and in this way,the photocatalytic activity of ZnO was improved by increasing the separation efficiency of photogenerated electrons-holes,expanding the absorption spectrum range and increasing the specific surface area of the material.Firstly,ZnO micro/nano arrays and ZnO micro/nano rods were prepared by microwave assisted method using zinc acetate,six methyl four amine as raw materials.The phase,morphology,formation mechanism of samples and its photocatalytic activity in degradation of methylene blue?MB?solution under UV visible light have been discussed.The results show that when FTO with a ZnO seed layer is used as the substrate,the reactant concentration is 0.5 M,microwave power is 240 W,reaction time is 30 min,the obtained ZnO micro/nano arrays perpendicular to a high degree of orientation,uniform distribution,the length of rods are about 1.1 ?m,and its photocatalytic activity is relatively good;When there is no substrate,the reactant content is 5 mmol,microwave power is 240 W,reaction time is 15 min,the obtained ZnO micro/nano rods have good dispersion and uniform particle size,surface active sites and photocatalytic efficiency is higher than other samples.Secondly,Ag/ZnO micro/nano array composites photocatalyst were prepared also by microwave assisted method,the influence of Ag content on the microstructure,optional property,photoelectric characteristics and photocatalytic property of Ag/ZnOmicro/nano arrays have been discussed.The results show that when the content of Ag is 4 wt%,the Ag nano particles can uniformly deposited on ZnO micro/nano arrays,and the absorption capacity of the visible light of Ag/ZnO micro/nano arrays can be improved obviously,the photocurrent intensity and photocatalytic rate is 8 times and2.9 times of that of single ZnO micro/nano arrays,respectively.Then,Ag/ZnO micro/nano rods composites photocatalyst were synthesized by one-step microwave assisted method,the phase,morphology,optical property and photocatalytic property of Ag/ZnO have been characterized,the formation mechanism of Ag and ZnO has been discussed.The results show that when the content of Ag is 3mol%,the morphology and light absorption ability of Ag/ZnO are better,the MB solution can be completely degraded by Ag/ZnO within 60 min under UV visible light and its catalytic rate is about 4.1 times of that of single ZnO mcro/nano rods.Lastly,g-C₃N₄ powder were prepared by a simple condensation method,then the flake g-C₃N₄ were obtained by ultrasonic exfoliation;ZnO/g-C₃N₄ composites photocatalyst with different g-C₃N₄ contents were synthesized by microwave-assisted method,SEM and photocatalytic performance show that when the g-C₃N₄ content is0.1 g,ZnO micro/nano rods are wrapped by layered g-C₃N₄ which leading to form closely connected interface and effectively improve the rate of degradation of methylene blue under visible light?? ? 400 nm?.0.1 g of g-C₃N₄ was used as composite phase,and Ag/ZnO/g-C₃N₄ ternary composites photocatalyst with different contents of Ag were obtained via microwave-assisted method,and the phase,microstructure,optical properties and photocatalytic properties of samples have been investigated.The results show that 5 mol%-Ag/ZnO/g-C₃N₄ has good visible light absorption ability and remarkable catalytic effect,and its photocatalytic rates is 7.5,2.9 and 2.4 times of single ZnO,5 mol%-Ag/ZnO and ZnO/g-C₃N₄,respectively.The enhancement in photocatalytic performance can be attributed to the effective use of visible light and the efficient separation of photogenerated electron-hole pairs during the photocatalytic process in the ternary system consisting of Ag,ZnO,g-C₃N₄.