Simultaneous photocatalytic treatment of Cr(VI), Ni(II) and SDBS in aqueous solutions: Evaluation of removal efficiency and energy consumption

• Simultaneous treatment of nickel, chromium and SDBS species with only 40 mg/L photocatalyst is promising.
• A significant efficiency enhancement is relevant in mixture, compared with individual species.
• The important step is the substrate adsorption and mutual interactions that is influenced by the solution pH.
• Pseudo-first-order reactions with the Arrhenius temperature dependency are relevant for the species in the mixture.
• Economic analysis indicates that increasing temperature can significantly reduce the total energy cost.

Simultaneous photocatalytic reduction of poisonous Cr(VI) and Ni(II) ions, coupled with photocatalytic oxidation of sodium dodecyl benzene sulfonate (SDBS) were studied with a trace amount of commercial titania nanoparticles and by means of a direct-photo-irradiation reactor. The co-presence of metal ions and SDBS causes metal ions reduction as well as SDBS oxidation to enhance and energy efficiency to improve. XRD, XPS and FTIR analysis were used to characterize TiO2 particles before and after usage with the aim of evaluating the mechanism of reactions. The effect of major operating parameters, pH and temperature, was investigated. Under conditions of [Cr(VI)]0 = [Ni(II)]0 = 5 mg/L, [SDBS]0 = 10 mg/L, [TiO2] = 40 mg/L, pH 6 and T = 35 °C; the removal efficiencies of 55.4%, 71.2% and 57.2% were obtained, respectively, for Cr(VI) and Ni(II) reduction, as well as for SDBS oxidation, after 110 min operation. The relevant kinetic model jointed with the Arrhenius equation was introduced. Pseudo-first-order reactions are relevant. Energy consumption (electrical and thermal) evaluations revealed that operations at higher temperatures provide significant cost reduction. Meantime, a criterion was proposed for a consistent assessment of this kind of processes.

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