| Nowadays,the production of electroplating wastewater is very large.Electroplating wastewater contains a large number of complex agents,the composition is usually complicated.So it is difficult to remove the harmful substances by conventional chemical precipitation method.With the deterioration of environment,higher and stricter discharge standard for electroplating wastewater has been put forward.Ni-EDTA is widely used and the typical complex in nickel electroplating technology.With stable structure and poor biodegradability,Ni-EDTA is the key problem for the standardized discharge.Thus,there is an urgent need to explore a low cost and stable method to removal Ni-EDTA.In this study,a novel Pd modified Ti/SnO2-Sb electrode was fabricated by thermal decomposition method and used as an anode in the electrolytic cell to degrade Ni-EDTA.First,it was intensive studied about the surface morphology,crystal structure,element valence,electrochemical performance and service life of different Pd doped Ti/SnO2-Sb electrodes.The electrode performance change was revealed after doping and the doping level was optimized.Then,the shape and stability of the prepared electrodes under different calcination temperatures was discussed.And the optiminal calcination temperature was choosed.Finally,degradation condition to Ni-EDTA was explored,including the current density,initial pHs,variety and concentration of electrolyte.The influence fators were discussed.These work provided a theoretic guidance to the engineering application.With Pd doping,the crystallization of the Ti/SnO2-Sb electrode surface was smoother and smaller.When Pd: Sn was 2.5%,the cell was thinnest.The average size of SnO2 was 6.7 nm,and the volume was 0.070931 nm3.The addition of Pd element promoted the smaller Sb5+ to entrance SnO2 and the value change of Sb5+to Sb3+.After Pd doping,the oxygen hole decreased,the adsorbed oxygen could reach 19.71%,and the molar ratio of lattice oxygen to metal could reach 2.45,indicating a high catalytic efficiency.At the same time,Pd doping maintained high oxygen evolution potential and high exchange current density,improving the electrochemical active area.In addition,after Pd doping,the service life of the electrode increased more than 40 times.The prepared electrodes under different calcination temperatures showed a huge difference.When the temperature was low,the surface oxide layer was not fully formed.When the temperature was 500 ℃,metal oxide was thoroughly formed.With smaller crystallization and larger specific surface area,the catalytic efficiency was highest and the life also increased.When the temperature was more than 500 ℃,the average cell size and volume increased dramatically.The largely generated TiO2 was not conducive to transfer electron and weaked the stability of the electrode.The current density,initial pH value and electrolyte kinds showed a great influence for Ni-EDTA removal.When the current density was 10 mA cm-2,the initial pH value was 2.3,the electrolyte concentration of Na2SO4 was 0.08 M,the highest removal efficiency was gotten.After 2 h electrolysis,93.1% Ni-EDTA was removaled,the reaction rate was 2.26×10-2 min-1,the recovery ratio of nickel was 23.6%,and the removal ratio of TOC was 30.3%.In the degradation system,direct and indirect oxidation coexisted at the same time.The bonding force between the physically adsorbed hydroxyl and anodic metal oxide was stronger enough to generate the metal oxide of high value,which could oxidize Ni-EDTA to the organic matters of small molecule. |
