Post-treatment And In Situ Doping Improve The Stability Of PEDOT Electrode During Photoelectric Reaction In Water

Poly(3,4-ethylenedioxthiophene)(PEDOT)had a unique carrier migration channel,which was widely used in the modification of photocatalytic electrodes to increase the density and mobility of carriers,so as to improve the efficiency of photocatalytic removal of pollutants.As a photocatalytic material,the stability of PEDOT would limit its photoelectric performance.In this study,post-treatment and in-situ doping methods were used to improve the stability of PEDOT under photoelectric reaction conditions,and the mechanism affecting its stability was explored.Specific researches are as follows:(1)PEDOT was polymerized on the graphite substrate electrode by electropolymerization.The PEDOT electrode was processed by eight post-treatment methods,including deionized water,anhydrous ethanol,immersion in p H=2 sulfuric acid solution and their combination.The stability of different post-treated PEDOT electrodes in photoelectric reaction system was studied.The dissolution of PEDOT in the photoelectric reaction was detected by ultraviolet visible spectroscopy,and the amount of dissolved substance was evaluated by the peak absorbance at 280 nm.The Comparing with control sample of PEDOT washed with deionized water(DW),five post-treatment methods can reduce the amount of PEDOT dissolution during the photoelectric reaction.Among them,the post-treatment method of anhydrous ethanol and deionized water washing(ET+DW)was the most significant in controlling the dissolution of PEDOT.Compared with the control sample,the dissolution amount was reduced by 35%,and the photocurrent response was increased by 11%,indicating that this post-treatment method could not only enhance the stability of PEDOT electrode,but also improve the photoelectric performance of PEDOT.Fourier infrared(FT-IR)results showed that the structure of PEDOT was not affected by post-treatment(ET+DW).Scanning electron microscopy(SEM)showed that the surface morphology and structure changed slightly,with the addition of small holes between 30 nm and 90 nm.The post-treatment increased the average contact angle of PEDOT from 23° to 30°,indicating that the post-treatment(ET+DW)reduced the surface hydrophilicity of PEDOT,which was conducive to improving the stability of PEDOT electrode in aqueous solution.(2)In the process of PEDOT electropolymerization,anthraquinone-2-sulfonate(AQS),dimethyl sulfoxide(DMSO),sodium p-styrene sulfonate(PSS),p-toluene sulfonic acid(Ts OH),polyvinylpyrrolidone(PVP)were selected as dopants for in-situ doping of PEDOT.Then the above optimal post-treatment method was adopted for doping PEDOT.The influence of doping on PEDOT dissolution in the photoelectric reaction system was evaluated.The stability of Ts OH and K30 PVP doped PEDOT was significantly improved,with dissolution amount decreased by 58% and 52%,respectively,compared with the control sample(DW).Meanwhile,the photocurrent response was improved by 59% and 31%,respectively.After doping Ts OH and K30 PVP,the contact angles of the samples were increased from 23° to 38° and 29°,and the grain sizes were changed from 40 nm to 35 nm and 33 nm,respectively.This indicated that the decrease of grain size and hydrophilicity was conducive to the improvement of the stability of PEDOT.(3)For in-situ doping PEDOT,there was a certain degree of negative correlation between the dissolution amount and the contact angle through correlation analysis.The correlation coefficient was-0.43,and the P value was 0.34.The dissolution amount was decreased when the contact angle was increased and the hydrophilicity was decreased.There was a significant positive correlation between the dissolution amount and the grain size for in-situ doping PEDOT samples.The correlation coefficient was 0.75,and the P value was 0.09.As the grain size decreased,the dissolution amount decreased accordingly.The absolute values of correlation coefficients between the dissolution amount and the photocurrent response were both about 0.8 for K30 PVP and Ts OH doped PEDOT,indicating that there was a significant correlation between the dissolution amount and the photocurrent response.This negative correlation suggested that less dissolution was beneficial for maintaining a higher photocurrent response.(4)The dissolution amount of PEDOT electrode in water environment under light,electrical and photoelectric conditions was investigated for post-treatment and in-situ doping PEDOT.Based on the sum of peak absorbance at 280 nm,the dissolution under photocatalysis,electrocatalysis and photocatalysis was accounted for 4%,45% and 51% of the total dissolved amount for post-treatment sample,respectively.For in-situ doping PEDOT,photocatalysis,electrocatalysis and photocatalysis contributed 6%,44% and 50% of the dissolution,respectively.The results showed that electrocatalysis was the main reason for the dissolution of PEDOT in water under photoelectric condition.(5)According to the results of LC-MS,post-treatment and doping can not only reduce the dissolution amount of PEDOT in water environment under photoelectric condition,but also reduce the types of dissolved products.The toxicity prediction analysis indicated the potential biohazard of some dissolved products.It is necessary to control the dissolution of PEDOT in water environment under photoelectric condition.