Photocatalytic Degradation Of Mesitylene On BiOBr

As the degree of industrialization continues to increase,the pollution of VOCs has been further expanded.The environmental protection department has strictly controlled the emission of VOCs.In this paper,the main research object is mesitylene which is widely used in chemical production.We adopt photocatalytic method to purify gas pollutants.BiOBr overcomes the defects of low utilization efficiency of the first-generation photocatalyst represented by TiO2.Therefore,BiOBr has been widely used.If preparation methods of BiOBr are different,the structure and properties will also be different.In this experiment,Bi(NO3)3 · 5H2O was used as bismuth source,CTAB was used as bromine source and water was used as a solvent.BiOBr catalyst was prepared by hydrothermal method.BiOBr catalyst with different properties was prepared by adjusting the pH of the initial solution of 1,2,3,4.Add dilute NaOH solution to precursor solution to get BiOBr catalyst with different properties.According to the XRD,TEM,SEM,BET and DRS characterization results of BiOBr,the prepared materials were made up of nanoscale slices and are single crystal structures.The XRD standard atlas corresponding to the BiOBr prepared by the precursor solution of 4 was different from the BiOBr prepared by the precursor solution of 1,2,3.When the pH value of the precursor solution increased,the width and thickness of the BiOBr sample were all smaller,the width of the forbidden band was smaller,the specific surface area was larger.The degradation of BiOBr samples in the precursor solution of pH 1,2,3 and 4 was studied in this paper.The photocatalytic activity and kinetic constant increased with the increase of the hydrothermal pH value of the precursor solution.The effects of reaction conditions,such as the initial concentration of mesitylene,the types of gas reactants,the amount of catalyst,the light intensity,relative humidity and the number of repeated use,were also discussed on the photocatalytic degradation efficiency and kinetic constants.In the subsequent photocatalytic experiment,the BiOBr sample prepared by the pH value of the precursor solution of 4 was further studied.The experimental results showed that:(1)With the increase of the initial concentration of mesitylene,the degradation rate of it was increased and then decreased.The reason was that the number of active points of the catalyst was certain,and the effect of photocatalytic degradation was worse when the concentration of mesitylene exceeded a certain degree.(2)The photocatalytic degradation of benzene,toluene,xylene and mesitylene were compared under the same reaction conditions.The effect of photocatalytic degradation and kinetic constant from large to small was mesitylene,o-xylene,m-xylene,p-xylene,toluene,benzene.After 98 min of illumination,mesitylene photocatalytic degradation was the best,and was nearly 20%higher than benzene degradation.(3)With the increase of photocatalyst dosage,the degradation rate of mesitylene firstly increased rapidly and then slowly increased.When the catalyst was overdosed,the BiOBr particles were reunited.The UV light was not easy to penetrate the catalyst and reduce the utilization of light.Therefore,the catalytic efficiency and the rate of reaction have not been greatly increased because of the increase of BiOBr dosage.(4)The increase of the power of ultraviolet light,mesitylene degradation rate and reaction rate were also increased.The greater the power of ultraviolet light,the more photons will be on the surface of the catalyst surface,and the degradation effect will be better.(5)As the relative humidity in the system increased,the photocatalytic degradation efficiency first becomed larger and then becomed smaller.This was because the water molecules can dissociate to generate free radicals such as ·OH.This helped the reaction to occur.However,when the relative humidity was too high,different molecules competed with each other.Water vapor will reduce the degradation rate of mesitylene.In this experiment,the photocatalytic degradation rate was the highest when the relative humidity was 40%,and the degradation rate was about 19%higher than when the relative humidity was 80%.(6)The degradation rate of the used BiOBr samples was not significantly changed after repeated four experiments.It is proved that BiOBr has strong stability,long term of effective use and high value.