| Due to the fast degradation rate, effective removal of nonbiodegradable pollutants, high efficiency and environmental compatibility of electrochemical removal of pollutants, two types of Ti-based electrodes, Ti/TiO2-NTs/Ce-PbO2 (anode) and Ti/CNTs/Cu-Pd (cathode), were fabricated for the degradation of RhB and the reduction of nitrate, respectively. Preparation processes of the electrodes were optimized based on the analysis of the microstructure, compostion and the removal efficiency towards targeted pollutants.Firstly, a layer of TiO2 nanotubes (TiO2-NTs) was obtained by anodic oxidation of Ti plate. PbO2 or Ce-PbO2 was deposited into the treated TiO2-NTs via constant current deposition. The obtained electrode was named Ti/TiO2-NTs/PbO2 or Ti/TiO2-NTs/Ce-PbO2. To achieve the highest electrocatalytic activity of Ti/TiO2-NTs/Ce-PbO2, the electrode’s preparation parameters were optimized to be 3 mM Ce(NO3)3 in the electrolyte at a deposition time of 60 min based on the analysis of the RhB degradation efficiency. Cerium doped into PbO2 crystal lattice in the form of Ce(Ⅳ), which resulted in the conversion of β(101) to β(200) of PbO2 crystal face. Compared to Ti/TiO2-NTs/PbO2, the surface of Ti/TiO2-NTs/Ce-PbO2 was denser and smoother. The prepared Ti/TiO2-NTs/Ce-PbO2 has a 2.3 times longer accelerated lifetime than Ti/TiO2-NTs/PbO2. Besides, the doping of cerium into Ti/TiO2-NTs/PbO2 increased the oxygen evolution overpotential from 1.72 V to 1.81 V. No direct electron transfer occurred between the electrode and RhB during the electrochemical process and the degradation of RhB was achieved via electrochemical oxidation mediated by radicals originating from electrolysis. The removal of RhB by Ti/TiO2-NTs/Ce-PbO2 anode was investigated under different conditions. The higher the current density, the better the degradation efficiency with a lower current efficiency. Effective removal of RhB could be achieved over a wide pH range from acidic (pH 2.0) to quasi-neutral (pH 5.2) solution. Although degradation effect was sensitive to dye concentration, Ti/TiO2-NTs/Ce-PbO2 presented outstanding RhB decolorizing ability. The chroma of solution with 150 mg/L RhB was undetectable in 40 min. In addition, the presence of chloride ions could promote the removal efficiency of RhB. The higher the chloride concentration, the more obvious the promotion effect.Secondly, a layer of carbon nanotubes was deposited on Ti plate by electrophoretic method. The prepared Ti/CNTs showed good uniformity, high electrochemical activity and stability. Deposition potential and deposition time were optimized for Cu-Pd codeposition on Ti/CNTs to get the highest electrocatalytic activity, which is -700 mV deposited for 5 min (named Ti/CNTs/Cu-Pd). The bimetal deposited on CNTs uniformly and formed the Cu-Pd alloy. Due to the higher deposition rate of Pd than Cu, the Pd/Cu atomic ratio in the film was higher than that in the deposition bath. Among the electrodes with different Cu/Pd ratios, Ti/CNTs/Cu5-Pd5 possessed outstanding stability as well as the highest electrocatalytic activity with the best nitrate conversion yield and proper N2 selectivity, indicating a synergistic effect of Cu and Pd. Thus Ti/CNTs/Cu5-Pd5 was considered as a promising electrode for electrocatalytic reduction of nitrate. SEM and XPS results indicated that numerous functional groups on CNTs provided sufficient active sites for metal deposition, favoring the uniform and highly dispersed formation of Cu-Pd alloy. The introduction of CNTs into Ti/Cu5-Pd5 optimized the electrode’s microstructure, enhancing its electrocatalytic activity, product selectivity and stability significantly.In conclusion, the fabricated Ti/TiO2-NTs/Ce-PbO2 and Ti/CNTs/Cu-Pd possessed high electrocatalytic activity, high removal ability, good product selectivity and stable performance, indicating their high research value and good application prospect. |
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