| Electrocatalytic dechlorination(ECH)technology is one of the most typical,and efficient technologies in the control of chlorinated organic compounds(COCs).However,the catalytic activity and stability of the palladium/nickel foam electrode,which was commonly used in ECH technology,need to be improved.Hence,this study proposes to prepare a Pd/carbon particle electrode with carbon-based particle carrier to optimize the dispersibility,and utilization of Pd in the electrode,resulting in improving the electrocatalytic dechlorination activity of catalyst electrode.At the same time,with the help of adsorption characteristics by carbon-based particle carrier,it promotes the adsorption,concentration and migration of the target pollutants in the liquid phase,and accelerates the electrocatalytic dechlorination of target pollutants.To investigate the construction method,and electrocatalytic dechlorination activity of Pd/carbon particle electrode,granular activated carbon(GAC)was used as carrier to prepare the Pd/GAC particle electrode,and 2,4-dichlorobenzoic acid(2,4-DCBA)was used as the target pollutant.Results of characterization,such as transmission electron microscope,showed that Pd formed nanoscale particles on the surface of GAC with good dispersion.Under the reaction conditions with 8 mg Pd usage,10 m A constant current,4 initial p H,and 10 m M electrolyte concentration,Pd/GAC particle electrode could degrade 98%of 2,4-DCBA in 180 min.At the same time,The activity test results showed that the pseudo-first-order kinetic apparent degradation rate constant of 2,4-DCBA(kobs,2,4-DCBA)using Pd/GAC particle electrode was 22.2×10-3min-1,which was 5,and 22 times than that of chemideposiition,and electrodepositon palladium/nickel foam electrode,respectively.These results proved that GAC as a carrier instead of Ni foam can effectively improve the dechlorination degradation efficiency of 2,4-DCBA.On the one hand,GAC can improve the dispersibility,and utilization of Pd to obtain more reactive sites.On the other hand,the adsorption characteristic of GAC can promote the adsorption,concentration,and migration of 2,4-DCBA in the liquid phase,resulting in accelerating the rate of electrocatalytic dechlorination reaction.After 15 electrocatalytic dechlorination reactions,Pd/GAC particle electrode could still degrade 94%of 2,4-DCBA in the 15th reaction,and the inductively coupled plasma massspectrometry test did not detect significant dissolution of Pd,which proved that Pd/GAC particle electrode had good stability.To reveal the key role of adsorption characteristic electrocatalytic dechlorination process of Pd/carbon particle electrode,carbon black(CB),multi-walled carbon nanotubes(MWCNTs),and GAC were selected to prepare Pd/CB,Pd/MWCNTs,and Pd/GAC particle electrodes.Results of characterization,such as diffraction of x-rays,showed that the difference in carbon-based particle carriers would not cause significant differences between the physical,and chemical properties of these Pd/carbon particle electrodes.The activity test results show that kobs,2,4-DCBA of Pd/CB particle electrode was 65.0×10-3 min-1,which was 1.7,and 3.3 times than that of Pd/MWCNTs,and Pd/GAC particle electrode,respectively.Langmuir adsorption isotherm model fitting results showed that the 2,4-DCBA adsorption capacity of Pd/CB particle electrode without electricity was 49.7 mg g-1,which was 1.6,and 5.2 times than that of Pd/MWCNTs and Pd/GAC particle electrode,respectively.These results showed that there was a positive correlation between the 2,4-DCBA electrocatalytic dechlorination activity of Pd/carbon particle electrode,and its adsorption performance.Through the pre-adsorption-electrocatalytic dechlorination process,it was verified that the adsorption characteristic of Pd/carbon particle electrode can promote its electrocatalytic dechlorination efficiency.It was concluded that the adsorption performance of Pd/carbon particle electrode plays an important role in its electrocatalytic dechlorination process.To further enhance the promoting effect of adsorption on electrocatalytic dechlorination of Pd/carbon particle electrode,hexadecyltrimethylammonium bromide(CTAB)was used to modify the adsorption behavior of Pd/GAC particle electrode,and prepared a modified CTAB-Pd/GAC particle electrode,thus improving the electrocatalytic dechlorination efficiency of 2,4-DCBA.The results of zeta potential,and contact angle tests showed that CTAB could improve the electrostatic adsorption between Pd/carbon particle electrode,and negative organic pollutants,as well as the hydrophobicity of Pd/carbon particle electrode surface,resulting in improving the adsorption performance of Pd/carbon particle electrode for 2,4-DCBA.When CTAB load was 40 mg g-1,the kobs 2,4-DCBAof CTAB-Pd/GAC was 39.2×10-3 min-1,which was11 times than that of Pd/GAC particle electrode.At the same time,the adsorption capacity of 2,4-DCBA increased from 1.5 mg g-1(Pd/GAC)to 2.1 mg g-1,while the adsorption capacity of BA decreased from 12.0 mg g-1(Pd/GAC)to 3.0 mg g-1.It is proved that CTAB can improve the electrocatalytic dechlorination activity of Pd/carbon particle electrode,and at the same time enhance its adsorption performance for 2,4-DCBA,and strengthen its desorption effect on BA.Thus,the adsorption-electrocatalytic dechlorination mechanism of Pd/carbon particle electrode was proposed.Firstly,CTAB-Pd/GAC particle electrode adsorbs 2,4-DCBA.Secondly,the electrocatalytic dechlorination of 2,4-DCBA is achieved.Finally,CTAB-Pd/GAC particle electrode desorbs the dechlorination product BA.Besides,the adsorption-electrocatalytic dechlorination-desorption is a cyclic process.Therefore,the CTAB modification can improve the adsorption behavior of the palladium/carbon particle electrode to 2,4-DCBA,and at the same time weaken the adsorption capacity of the palladium/carbon particle electrode to BA,thereby effectively promoting the CTAB-Pd/GAC particle electrode to 2,4-The electrocatalytic dechlorination effect of DCBA. |
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