Fabrication And Photocatalytic Performance Under Visible Light Of Nano-composite Photocatalysts Based On G-C₃N₄ And WO₃

Photocatalysis is considered as a promising technology in the field of environment,because it could degrade or even mineralize persistent organic pollutants under mild condition.However,it is restricted by the problems of narrow response range to light and high recombination rate of photoinduced charges.Heterojunction Photocatalysis composed of different semiconductor materials could broaden the light absorption range,promote the separation of photogenerated charge and reduce the recombination rate.Therefore,construction of heterojunction is an effective method to enhance the photocatalytic efficiency.However,the construction of heterojunction is influenced by many factors,such as the contact area and the bonding method between different semiconductors,the energy band structure,the light absorption range,the energy band barriers at the interface,the migration of photogenerated carriers and so on.Therefore,it is challenging to design a heterojunction photocatalyst with high efficiency.In this thesis,several works have been carried out as follows:?1?The Graphite nitride carbon?g-C₃N₄?nanosheets were coated on the tungsten trioxide?WO₃?nanoparticles by the self-assembly method to form a WO₃@g-C₃N₄ composite photocatalyst with a shell-core nanostructure.The morphology was observed by scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.The results show that the size of WO₃ nanoparticles is between 100 nm and 200 nm,and the g-C₃N₄ nanosheets are tightly coated on the surface of WO₃ particles.This nanoscale shell-core hetero-structure significantly enhances the interface area between the two semiconductors.The photocurrent,photoluminescence spectra and electrochemical impedance measurements,the photo-generated charge WO₃@g-C₃N₄ photocatalytic charge separation efficiency and charge migration ability have been significantly improved.The photocatalytic activity of the composite photocatalyst was investigated by degrading Rh B.The degradation rate by WO₃@g-C₃N₄ was 7.7 times and3.5 times than the rate of degradation by WO₃ and g-C₃N₄,respectively.It was found that the shell thickness of g-C₃N₄ has an effect on the photocatalytic properties.It is not conducive to the formation of heterojunctions and the adsorption of pollutants when the proportion of g-C₃N₄below 1 wt.%.It is not conducive to migration of photogenerated charge to the surface in the degradation reaction when the proportion of g-C₃N₄ is higher than 1 wt.%.The photocatalytic efficiency is the highest when the proportion of g-C₃N₄ is 1wt.%.The free radical trapping experiments revealed that the holes?h⁺?in the valence band of g-C₃N₄ play a major role in the degradation of Rh B.?2?A composite photocatalyst was constructed by attaching g-C₃N₄ and WO₃nanoparticles on RGO nanosheets.The morphology of the photocatalyst was observed by SEM and TEM.The results show that both g-C₃N₄ and WO₃ particles are 50-100 nm and 100-200nm,respectively,which significantly reduces the photocharge-induced charge transfer distance compared to bulk semiconductor materials and facilitates the rapid migration of photogenerated charge to the interface,thus it reduces the probability of recombination.The analysis of photoluminescence spectra and electrochemical impedance demonstrates that the separation and migration of photogenerated charge of g-C₃N₄/RGO/WO₃ composites are better than those of g-C₃N₄/WO₃ composite photocatalysts and pure g-C₃N₄ and WO₃ photocatalysts.The photocatalytic activity of the composite photocatalyst g-C₃N₄/RGO/WO₃ was investigated using ciprofloxacin?CIP?as the target.Within 180 min,the photocatalytic degradation rate of CIP by g-C₃N₄/RGO/WO₃ reached 80%.The degradation rates of CIP by g-C₃N₄ NS and WO₃NP were 65%and 10%,respectively.The CIP degradation rate by g-C₃N₄/WO₃ was about 50%.Radicals capture experiments showed that h⁺,hydroxyl radicals?·OH?and superoxide radicals?·O₂^-?play an important role in the photocatalytic degradation of in CIP by g-C₃N₄/RGO/WO₃,while only h+plays a role in photocatalytic degradation of CIP by g-C₃N₄/WO₃.It shows that the charge transfer mechanism of the Z-scheme photocatalytic system of g-C₃N₄/RGO/WO₃maintains the original redox ability of g-C₃N₄ and WO₃.Electron paramagnetic resonance?EPR?also measured the generation of·OH and·O₂^-in the g-C₃N₄/RGO/WO₃ system.