The Effect Of Microwave On Photocatalytic Reaction Process And Its Mechanism

Current research status shows that photocatalysis has achieved remarkable results in the treatment of environmental pollution,because photocatalysis is a kind of green pollution treatment technology.But photocatalysis has one of the biggest shortcomings,that is,photogenerated electron-hole compound efficiency is too high,that can't achieve the desired treatment effect.Microwave(MW)radiation is used in organic synthesis,environmental treatment and other fields because of its special heating method.It can be seen from the research results of microwave assisted photocatalytic reaction in recent years that the hot spot effect produced by microwave can accelerate the chemical reaction very well.Microwave enhanced heterogeneous photocatalytic process also shows superior oxidation performance and significant pollutant degradation,but the relevant mechanism is not clear.This situation urges us to focus on the field of microwave photocatalysis,especially how to understand the effect of microwave in special photocatalytic reactions and its mechanism,as well as the application effect of microwave technology in new photocatalytic reactions.Therefore,we desire to further understand the influence of microwave on the photocatalytic reaction process and make new breakthroughs in its reaction mechanism.From comparing the effect of microwave on photocatalysis in the degradation of dye pollutants,to trying to apply microwave in the process of photocatalytic dissolution of precious metals,the main contents of this work can be summarized as the following two parts:1.Application and study of microwave assisted photocatalysis in the degradation of dye pollutants.Ti O₂ has good photocatalytic performance but the photocatalytic reaction rate is not ideal,while microwave can greatly improve the photocatalytic reaction rate.For this reason,we introduce the microwave field into the photocatalytic reaction system,and plan to synthesize a composite photocatalyst which can not only respond to light but also absorb microwave.We hope to enhance the catalyst's promoting effect on the reaction through microwave,improve the photocatalytic treatment effect and further discuss the influence mechanism of microwave on the photocatalytic reaction.In this study,Ti O₂/x CNT composite photocatalytic material of Ti O₂ nanoparticles and carbon nanotubes(CNT)was prepared by a simple alcohol-thermal method.Taking the degradation of methyl orange(MO)dye as the probe,the experimental results show that microwave can significantly improve the efficiency of photocatalytic degradation of pollutants,and h⁺/e^-,OH·and O₂^·-are the main substances that play an important role in photocatalytic degradation of pollutants.In the reaction process,the addition of microwave radiation improved the charge separation process of Ti O₂ particles,and the presence of carbon nanotubes also enhanced the absorption of microwave on the catalyst,promoting the adsorption of dye pollutants on the surface of Ti O₂ and the transfer of electrons on the surface.2.Study on the mechanism of microwave assisted photocatalytic dissolution of precious metalsAccording to the previous work of our group,photocatalysis technology can be applied to the dissolution of precious metals.Considering the remarkable advantages of microwave-assisted photocatalysis in the previous part of the work,we extend the study of microwave-assisted photocatalysis to the new reaction of photocatalytic recovery of precious metals.Through the commercial Ti O₂ catalyst,the solubility test of simulated precious metal catalyst and commercial precious metal catalyst was carried out,and the differences of precious metal dissolution under different irradiation conditions were compared,hoping to verify the effect of microwave and ultraviolet light on the promotion of precious metal dissolution reaction.The results of product analysis showed that Au was nearly 100%dissolved within 2 hours,which indicated that microwave could promote the photocatalytic dissolution of precious metals,while further analysis proved that the valence of precious metals increased,that is,the existing form changed.Finally,we take Au as an example to discuss and speculate the possible dissolution path of precious metals in microwave photocatalytic system,so as to explore a new breakthrough for the practical application of microwave-promoted photocatalytic reaction.