Study On Reduction Mechanism Of Mono-chloronitrobenzene And Mono-chlorophenol Based On Inert And Catalytic Electrodes

Chloronitrobenzene and chlorophenol are common chloro aromatic pollutants in wastewater and are important chemical raw materials and intermediates,which are widely used in medicine,pesticide,petroleum,chemical industry,printing and other industries.These pollutants are toxic,stable and difficult to degrade,which have a great impact on the ecological environment.How to effectively remove chloro aromatic compounds has become a hot spot.Therefore,the study of reductive dechlorination mechanism of chloronitrobenzene and chlorophenol by electrochemical reduction method provides an important theoretical basis and technical support for environmental treatment.The main contents and conclusions of this study are as follows:In this study,a three-electrode system was used with N,N-dimethylformamide?DMF?as organic solvent and 0.1m tetrabutyltetrafluoroborate?TBABF ₄?as supporting electrolyte.The electrochemical reduction behavior and mechanism of monochloronitrobenzene and monochlorophenol on inert?GC?and catalytic electrodes?Ag and Pd?were investigated.The results showed that p-chloronitrobenzene showed two reduction peaks on GC and Ag electrodes,and the first peak potential was-1.075 V and-1.085 V,respectively.The first reduction peak is that p-chloronitrobenzene receives four electrons and proton transfer reduction to form p-chloro-hydroxylamine benzene,while the second reduction peak is the further electron reduction of p-chloro-hydroxyamine benzene to p-chloroaniline.Among them,the first reduction peak is reversible reaction,and there is a clear redox reversible peak in the cyclic volt-ampere curve,which is the reversible electric pair of p-chloro-hydroxyamine benzene-p-chloronitrobenzene.The cyclic Voltammetric behavior of m-chloronitrobenzene is the same as that of p-chloronitrobenzene and follows the same reduction path.On the other hand,o-chloronitrobenzene showed three reduction peaks on Ag electrode,which suggested that o-chloronitrobenzene intermediate was formed in the process of reaction.Due to the existence of reversible pairs,Ag electrode did not show catalytic reduction activity for three kinds of monochloronitrobenzene.Three kinds of monochloronitrobenzene did not break C-Cl bond on GC and Ag electrodes,but mainly carried out nitro reduc tion reaction.The molecular structure has an effect on the reduction activity of chloronitrobenzene.The reduction activities of three kinds of monochloronitrobenzene are as follows:M-chloronitrobenzene is greater than p-chloronitrobenzene than o-chloronitrobenzene.Because of the proton sparing characteristics of DMF,weak proton?water?and strong proton?acetic acid?donors were added to the system in order to control the electron transfer and proton transfer process of chloronitrobenzene reduction rea ction at the same time.The results showed that the addition of proton donor could significantly improve the reduction activity of chloronitrobenzene on inert?GC?and catalytic?Ag?electrodes,and promote the significant positive shift of reduction poten tial.Taking p-chloronitrobenzene as an example,the first reduction peaks of p-chloronitrobenzene on GC and Ag electrodes in DMF+H2O system were-0.856 V and-0.897 V,respectively,and the first reduction peaks on GC and Ag electrodes in DMF+HAc system were-1.11 V and-1.035 V,respectively.The existence of proton donor can change the electrochemical behavior of chloronitrobenzene on the electrode and affect its reduction path and product distribution.Therefore,the molecular structure,solvent conditions and electrode characteristics have effects on the electroreduction process of chloronitrobenzene.Based on the study of electroreduction of chloronitrobenzene,the electrochemical reduction behavior of monochlorophenols on inert?GC?and catalytic?Ag,Pd?electrodes was further investigated.The results show that monochlorophenol shows an irreversible reduction peak on the three electrodes,which is the reduction peak of C-Cl bond breaking,and the Ag and Pd electrodes show very strong electrocatalytic activity,which can significantly promote the positive shift of dechlorination reduction peak.Compared with the inert electrode,the catalytic activity of GC,p-chlorophenol at Ag and Pd electrodes was 0.47V and 1.05V,respectively,and the catalytic activity of Pd electrode was significantly stronger than that of Ag electrode.Similarly,the molecular structure determines the electroreductive dechlorination activity of monochlorophenol,which is p-chlorophenol and m-chlorophenol>o-chlorophenol.The study of electron transfer mechanism shows that monochlorophenol follows the sequential electron transfer mechanism on the GC electrode,while the electron transfer on the catalytic electrode follows the synchronous dissociative electron transfer mechanism due to t he adsorption of molecular structure and electrode surface.The addition of proton donor can also significantly promote the electroreduction dechlorination peak of chlorophenol,mainly because the addition of proton donor can promote the continuous regener ation of electrode surface active sites and the solvent effect on the leaving group?Cl^-?.This study provides a theoretical basis for the removal of chloronitrobenzene and chlorophenol by electroreduction,and is expected to achieve the effective removal of these two kinds of substances and obtain useful products.