Photoelectrocatalytic Oxidation Of Cyanidecontaining Wastwater By TiO₂-based Nanoarray Film Electrode

Exploring green and cost-effective methods to remove cyanide from cyanide-containing wastewater effectively and to recover heavy metals from metal cyanide complexes is one of the problems to be solved urgently.In this paper,Ag-cyanide complex?Ag?CN?₂^-?and free cyanides?CN^-?were selected as the treatment objects,respectively,which represent cyanide complexs and simple cyanide in water.The photoelectrocatalytic system with the highly ordered TiO₂-basaed nanorods array served as the photoanode was developed.The main contents and results are as follows:The highly ordered titanium dioxide nanorods array electrodes have been constructed through hydrothermal growth,and a photoelectrocatalytic system for oxidation of Ag-cyanide complexes with simultaneous silver recovery was developed.TiO₂ NRs electrode was served as a photoanode for photoelectrocatalytic oxidation of cyanide;and titanium plate was used as the cathode for silver cathodic deposition the light is proved by a 300 W xenon lamp.The results show that in comparison with photocatalysis and electrochemistry,the photoelectrocatalytic process exhibited the highest removal efficiency for cyanide and recovery ratio for silver.The oxidation products of cyanide was analyzed and the surface variations of the TiO₂ NRs anode and titanium cathode were characterized by SEM,EDS,XRD,and XPS techniques.It was observed that the cyanide is oxidized to CNO^-and that metallic Ag was mainly recovered at the cathode,and partially silver was deposited onto the TiO₂ NRs photoanode in the form of Ag₂O nanoparticles.Ag₂O in situ formation on the TiO₂NRs enhance the PEC performance of TiO₂ NRs.Combined with the results of the active species trapping experiments,the photogenerated holes and superoxide radicals were identified as the main reactive oxygen species of Ag?CN?₂^-,and a possible mechanism of the Ag-cyanide complexes'oxidation was proposed.The TiO₂ NRs/g-C₃N₄ electrodes were synthesized by a liquid-based reaction in which the g-C₃N₄ were fabricated on the TiO₂ NRs electrodes.The preparation conditions were optimized,and the TiO₂ NRs/g-C₃N₄ electrodes were used as photoanodes in photoelectrocatalysis system for oxidation of cyanide.Compared with the titanium,the carbon aerogel?CA?electrode used as the cathode can improve the CN^-the removal efficiency efficiently.The TiO₂ modified by g-C₃N₄ can greatly improve the H₂O₂ production on the cathode so as to promote the CN^-removal efficiency.Dissolved oxygen and bias potentials have a great influence on the formation of H₂O₂,which affects the removal of CN^-.At the same time,the removal efficiency of CN^-is gradually decreased by the increase of CN^-initial concentration.The stability experiments showed that the TiO₂ NRs/g-C₃N₄electrodes have a good stability.Finally,a systematically mechanism of using photo-induced electrons in situ production H₂O₂ through the carbon aerogel cathode which enhanced the CN^-removal ability of TiO₂ NRs/g-C₃N₄ photoanode was proposed with innovation.In this paper,the photoelectrocatalytic oxidation of cyanide-containing wastewater by TiO₂-based nanorods array thin film electrode not only can make the use of the oxidation of potoanode,but also the reduction of the cathode in the photoelectrocatalytic system.It has a certain reference value for the treatment of cyanide-containing wastewater and the application of photoelectrocatalytic technology in water treatment.