Use of nickel-electroplating wastewater to synthesize Ni-doped TiO2 and NiTiO3 coatings by plasma electrolytic oxidation to treat hexavalent chromium in real electroplating wastewater

Abstract

The use of residual water from nickel plating for the synthesis of Ni/TiO2 coatings using the PEO technique was carried out in this work. Evaluation by response surface methodology (RSM) for the studied coatings in the reduction of Cr(VI) present in chrome-plating wastewater is presented. Duty cycle variations between 2 % and 50 % on Ti substrates of 20 × 20 × 1 mm was employed to obtain the studied coatings. The coatings were characterized by XRD, AFM, SEM/EDS, XPS, and DRS, and computational analysis using DFT was performed. A strong dependence of the duty cycle on the anatase/rutile relation, surface roughness, and Ni incorporation in the coatings is showed. The sample obtained at 50 % of the duty cycle, in addition to the anatase and rutile phase, showed the formation of NiTiO3. Additionally, the incorporation of Ni in Ti sites in TiO2 as a consequence of the d orbitals of Ni, which generated a shift of the absorption band towards the visible and a decrease in the bandgap, is observed. The response surfaces obtained for the reduction of Cr(VI) in the samples of 2 % and 50 % of duty cycle, indicating that the voltage and the concentration of Cr(VI) are the variables with the greatest influence in the process, being the 2 % sample the one that presented the best performance in the photoelectrocatalysis process. In this sense, the optimal conditions for the 2 % sample were determined. Furthermore, the kinetic study to a pseudo-first order kinetic model was adjusted, and the efficiency of the material after 16 cycles of reuse is greater than ∼ 99.4 % in 10 min. Taking advantage of industrial wastewater as a resource using the PEO technique has potential applications in contributing to environmental sustainability.