| Much VOCs?volatile organic compounds?have been released into atmosphere with the development of industry and the combustion of fuels,and the existence of VOCs is harmful to environment and people's health.Among so many methods of eliminating VOCs,photocatalysis has attracted much attention due to its thorough mineralization,direct usage of sunlight and environmental-friendly property.Therefore,the existence of VOCs in atmosphere has provoked the research and development of highly-efficient photocatalysts.Among so many photocatalysts,TiO2 has been recognized as an ideal photocatalyst to eliminate VOCs due to its low price,non-toxicity,abundance and good stability.Although TiO2 has so many advantages,some challenges still exist when it was applied into gaseous photocatalysis.On the one hand,TiO2 has poor performance towards the photodegradation of VOCs,which results from its narrow light-absorption range,quick recombination of e--h+pairs and inferior adsoptive capacity.On the other hand,the process and mechanism of TiO2 photodegrading VOCs are not clear,such as the roles of active radicals,the effect of photothermal conversion and gaseous molecule adsorption on the photocatalysis.Therefore,it is necessary to synthesize efficient TiO2-based photocatalyst and explore its process and mechanism of photodegrading VOCs.In addition,acetaldehyde and o-xylene as two typical volatile organic compounds extensively exist in our living environment.Based on above consideration,we designed and synthesized efficient TiO2-based photocatalyst,and the process and mechanism of acetaldehyde and o-xylene photodegradation were also investigated.The detailed research content and results are as follows:1.Enhanced Photocatalytic Performance of Ag@TiO2 for the Gaseous Acetaldehyde PhotodegradationHere,Ag@TiO2 photocatalyst with high photocatalytic activity was synthesized through a simple solvothermal process.The existence of Ag@TiO2 core-shell morphology was beneficial to the enhanced light absorption induced by surface plasmon resonance,and it was also benficial to the separation of e--h+pairs.0.5wt%Ag sample had the best photocatalysis of 72%?Irradiation:260W lamp,Contact time:4.8min?,which was much higher than that of TiO2?37%?.The photocatalyst also showed ultrastable activity in the 15 weeks usage,which ensured their practical applications in the air purification field.With the help of electron spin resonance and radicals quenching tests,·O2-was proved to be the main active radicals in the degradation of acetaldehyde.The outstanding performance of the composite materials and the thoroughly understanding of the reaction mechanism would cast light on the purposively design and optimization of TiO2-based catalysts.2.The Synthesis of Ta S2/TiO2 and Its Study on the Photodegradation of Gaseous AcetaldehydeHere,Ta S2/P25?P25:commercial TiO2?was synthesized for the first time to explore the effect of the addition of Ta S2 on the photocatalytic degradation of gaseous acetaldehyde.On the one hand,the adsorptive capacity of Ta S2/P25 for gaseous acetaldehyde boosted greatly?234.4 m L?,which was three times of that of P25?76.4m L?.On the other hand,the separation efficiency of e--h+pairs of Ta S2/P25 also increased extremely?15.5mA/cm2?,which was almost four times of that of P25?4.2mA/cm2?.Ta S2/P25 had the highest removal ratio of 98%,which was twice of that of P25?48%?.Ta S2/P25 still had good activity after 6 cyclic tests.With the help of electron spin resonance and radicals quenching tests,·O2-was proved to be the main active radicals while·OH was the secondary one in the degradation of acetaldehyde.Briefly,this work not only created the pioneer of the application of Ta S2 in the photocatalytic field but also verified Ta S2 an efficient co-catalyst in gaseous photocatalysis.3.The Photothermal Conversion of RGO/P25 and Its Study on the Photodegradation of Gaseous AcetaldehydeHere,RGOP?reduced graphene oxide/P25?was synthesized to explore roles of the enhanced light adsorption and photothermal conversion in the photocatalytic process.Compared with P25,RGOP had enhanced absorbance,but it was with lower available light utilization.In the effect of available light utilization,transfer resistance and hydrophilicity,RGOP generated less·O2-but more·OH.With the help of radicals quenching tests,·O2-was proved to be the main active radicals while·OH was the secondary one.The change of radicals of RGOP was harmful to its photocatalysis compared with P25.However,it still had better activity than P25 owing to its good adsorptive capacity.The improved photocatalytic activity of RGOP was ascribed to its superior adsorptive ability aside from active radicals?·O2-,·OH?.4.The Effect of O-xylene and Acetaldehyde Adsorption on the Band Structure and Radicals Generation of TiO2Here,we first disclosed how the adsorption of two typical VOCs influenced the band bending of P type rutile TiO2,and consequently change the amount of reactive radicals.This will provide a new way to deeply understand the experimental phenomenon in heterogeneous reaction.Theoretical computation of adsorptive model and zeta potential tests both verified that o-xylene was acceptor molecule when it adsorbed on TiO2 surface,and it tended to attract electrons from TiO2.On the contrary,acetaldehyde was donor molecule.Distinct electron transfer direction between TiO2 and adsorptive molecule?o-xylene and acetaldehyde?induced different band bending degree.O-xylene adsorption alleviated the downward band bending of TiO2 itself,while acetaldehyde adsorption strengthened the downward band bending.The probability of electrons and holes reaching on TiO2 surface would be influenced by this change,which had a great influence on the generation of active radicals.Consequently,o-xylene adsorption led to more hydroxyl radicals generation,while acetaldehyde adsorption resulted in less hydroxyl radicals generation.As a result,hydroxyl radicals played the predominant role in the degradation of o-xylene,while the photocatalysis of acetaldehyde was dominant by superoxide radicals. |
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