Simultaneous photocatalytic reduction/degradation of divalent nickel/naphthalene pollutants in aqueous solutions.

Toxic heavy metals and organic pollutants simultaneously exist in the wastewater of some industries. This study explores reduction of toxic divalent nickel ions, from either nitrate or sulfate salts, coupled with naphthalene (NA) degradation using titania photocatalyst in an efficient photo-sono reactor. A synergism appears when reduction and degradation treatments occur simultaneously in the media. With initial concentrations of [Ni(II)] = 5 mg/L and [NA] = 10 mg/L, under dominant mild conditions, removal efficiencies of 54.5% and 56.6% were obtained for Ni(II) and NA, respectively, when nickel nitrate was used. These efficiencies were enhanced to 59.2% and 57.5%, respectively, with nickel sulfate, all after 90 min operation. For evaluating the mechanism of reactions, reactive oxygen species analysis on solutions as well as Fourier transform infrared, scanning electron microscopy and Brunauer-Emmett-Teller analyses on the titania nanoparticles, before and after usage, was performed. The reaction kinetics was also followed for individual species in the mixed solution and, accordingly, the energy consumption was evaluated for one order of magnitude decrease in pollutant concentration. The high performance of the used method was revealed in comparison to the similar reported reduction/degradation processes.