Research On The Mechanism Of Microwave Field On Photocatalytic Reaction

In the 21st century,a major goal of chemical research is to develop a high-performance technology to replace energy-consuming processes that are harmful to the environment.The emergence and application of photocatalytic selective redox systems have greatly met the energy and environmental requirements.In photocatalytic selective redox systems,the conditions required for the reaction to occur are not only milder than the traditional catalytic conditions,but also avoid the use of some strong oxidizing agents and hazardous reducing materials.In addition,microwave chemistry is an emerging frontier interdisciplinary subject that has shown unprecedented vitality in a wide range of practical applications.Microwave fields can act directly on chemical systems to promote or change various chemical reactions in a unique way.Herein,we first proposed the use of microwave field-assisted photocatalytic reaction processes.Microwave-assisted photodegradation of organic pollutants was used as a probe reaction to explore the effect of microwave on photocatalytic degradation process.In addition,the microwave field and photocatalysis are introduced into the organic synthesis reaction system,so that the quantum efficiency of the photocatalytic process is significantly improved under the synergistic reaction of microwave fields and ultraviolet light,and then the reaction speed and selectivity is also greatly increased.The main content and innovation of this thesis are divided into the following three parts:1.Microwave field-assisted photocatalysis in degradationThe behavior of microwave in photocatalytic oxidation reaction is tentatively investigated.Photocatalytic degradation of p-chlorophenol and methyl orange as probes under microwave irradiation was used to study the behavior of microwave in photocatalytic degradation.The catalyst is modified by simple,inexpensive,and readily available TiO₂ on its surface with nanoparticle Ag.In this study,we successfully prepared small Ag nanoparticles,which have good stability.The study of photocatalytic degradation of different organic pollutants found that microwave can enhance the photocatalytic degradation rate.We found that not only microwave thermal but also significant non-thermal effects during the process of Microwave-assisted degradation of organic pollutants.Further studies have shown that photo-generated holes are the main active species involved in photocatalytic degradation.Under microwave irradiation,silver nanoparticles not only promote the charge separation process,but also enhance the adsorption of organic pollutants on the surface of TiO₂.In addition,we have also studied the degradation mechanism.2.Microwave field-assisted Pd/TiO₂ photocatalytic the Suzuki carbon-carbon coupling reactionThis part uses microwave fields and photocatalytic combination system to provide a simple and environmentally friendly reaction environment.The rapid heating function of microwave can shorten the reaction time and ensure the activity of the catalyst.The biphenyl compound obtained by the coupling reaction is a classical reaction,which is an extremely important organic synthesis intermediate.The carrier of the catalyst is a common photocatalyst TiO₂ with the metal particles Pd supported on the surface thereof.The effect of microwave fields on photocatalytic organic synthesis was investigated by studying the activity change of the Suzuki coupling reaction under different reaction systems.The experimental results show that the addition of microwave fields is beneficial to the photocatalytic organic synthesis.The reaction activity is 1.7 times more than UV+CH conditions and 26 times more than the action of MW alone.The role of microwave in the reaction system is not only the thermal effect of increasing the temperature of the reaction system,but also the non-thermal effect of promoting the formation of more intermediates in the reaction process.It is the combination of microwave fields and photocatalysis that not only expands the application range of Suzuki coupling reaction under mild conditions but also activating nanomaterials and reaction substrates,which can be used in a wide range of chemical reactions.3.Microwave field-assisted photocatalysis of Pd/PbTiO₃ applied to the Suzuki carbon-carbon coupling reactionThe pyroelectric effect of PbTiO₃ crystal promotes organic reaction and enhances reactivity under the action of microwave fields and ultraviolet light.Taking the bromobenzene-directed Suzuki coupling reaction as an example,the effect of microwave on the catalyst was studied.At the same time,how the Pd/PbTiO₃ promoted the thermal reaction under the action of microwave and ultraviolet light was also investigated.The experiment prepared a single crystal PbTiO₃ nanosheet by a simple hydrothermal reaction.The results show that current can be generated at both ends of the materials by changing the temperature.Generally,thermoelectric materials are capable of converting thermal energy into electrical energy,which can generate positive and negative charges?q⁺and q^-?.The positive and negative charges generated at the high temperature will be transferred from the surface of the hot catalyst to the reactant molecules to participate in the reaction.