Abstract
The simultaneous photocatalytic reduction of Cr(VI) and oxidation of benzoic acid (BA) in aqueous suspensions using N-F-codoped TiO2and simulated solar irradiation were investigated in the present study. Chemometric optimization tools such as response surface methodology (RSM) and experimental design were used to model and optimize selected operational parameters of the simultaneous photocatalytic reduction of Cr(VI) and oxidation of BA. RSM was developed by considering a central composite design with three input variables, that are, N-F-codoped TiO2mass, ratio of Cr/BA, and pH. The removal of Cr(VI) and BA in binary systems, containing both Cr(VI) and BA, showed a synergistic photocatalytic decontamination as BA significantly facilitated Cr(VI) reduction, whereas Cr(VI) accelerated also BA degradation. Due to the anionic-type adsorption onto TiO2and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while the degradation of BA followed also the same trend. Under the optimum conditions (N-F-TiO2) = 600 mg L−1, ratio of Cr(VI)/BA = 5, pH = 4, the removal for both Cr and BA followed a pseudo first-order kinetic model. It was found that the selected variables have significant effect both on Cr(VI) removal and BA degradation efficiency. The results revealed the feasibility and the effectiveness of using N-F-codoped TiO2as photocatalyst for simultaneous decontamination of Cr(VI) and organic pollutants such as BA due to the appropriate oxidation and reduction ability of the photogenerated h+VB-e−CBpairs.
Highlights
The increasing level of global industrialization and urbanization has led to the transport and introduction of various contaminants in aquatic environment
Photocatalysis is a well-known and promising method based on the activation of a semiconductor and utilizes the photogenerated positive holes and various oxygen radical species for the oxidation of organic compounds as well as the photogenerated electrons for the reduction of heavy metal ions [11]
Photoreduction of a metal ion is promoted significantly if it is accompanied by simultaneous oxidation of an organic compound able to act as ligand or as “sacrificial electron donor” [12], because of the enhanced charge separation of photo-induced hole/electron pairs by the simultaneous reduction/oxidation reactions [11]
Summary
The increasing level of global industrialization and urbanization has led to the transport and introduction of various contaminants in aquatic environment. Water pollution had resulted in the development of the socalled advanced oxidation processes (AOPs) as alternative to the conventional water and wastewater treatment methods. These enhanced processes aim to degrade the non biodegradable contaminants of water into harmless species [6]. Photocatalysis is a well-known and promising method based on the activation of a semiconductor and utilizes the photogenerated positive holes and various oxygen radical species for the oxidation of organic compounds as well as the photogenerated electrons for the reduction of heavy metal ions [11]. Photoreduction of a metal ion is promoted significantly if it is accompanied by simultaneous oxidation of an organic compound able to act as ligand or as “sacrificial electron donor” [12], because of the enhanced charge separation of photo-induced hole/electron pairs by the simultaneous reduction/oxidation reactions [11]
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