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The present study is targeted on the feasibility of photocatalytic treatment of industrial wastewater containing metal ions. Photoreductive deposition of metal ions using solar energy irradiated TiO2, has been investigated in presence of citric acid as a hole scavenger. Treatment studies have also been performed at pH values 2, 4, 7, 8, and 10 to determine optimum reaction conditions. Results showed that at the pH value of 2, 100% reduction was achieved for Cr(VI) in a minimum time period. A maximum removal of 95.5% was achieved for Ni(II) at the pH value of 10.

This article describes the photocatalytic reduction and deposition of four metal ions Cr(VI), Ni(II), Zn(II), and Cu(II) present in the wastewater from a chrome plating industry using solar energy irradiated TiO2. A parabolic trough reactor was used to carry out the reaction. Experiments were carried out to find an optimum dose of hole scavenger used (citric acid). The adsorption and reduction of the metal ions at different pH values was also investigated. It was observed that the solar photocatalytic process was effective in removing most of the metal ions in specific reaction conditions. Alkaline pH was found to be more suitable for removal of nickel and zinc. However, Cr(VI) reduced completely even at catalyst concentrations as low as 0.5 mg/L at pH 2. Maximum reaction was completed in the first 4 h of solar exposure. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

The present study is targeted on solar photocatalytic removal of metal ions from wastewater. Photoreductive deposition and dark adsorption of metal ions Cu(II), Ni(II), Pb(II) and Zn(II), using solar energy irradiated TiO 2 , has been investigated. Citric acid has been used as a hole scavenger. Modeling of metal species has been performed and speciation is used as a tool for discussing the photodeposition trends. Ninety-seven percent reductive deposition was obtained for copper. The deposition values of other metals were significantly low [nickel (36.4%), zinc (22.2%) and lead (41.4%)], indicating that the photocatalytic treatment process, using solar energy, was more suitable for wastewater containing Cu(II) ions. In absence of citric acid, the decreasing order deposition was Cu(II) > Ni(II) > Pb(II) > Zn(II), which proves the theoretical thermodynamic predictions about the metals.

A laboratory scale parabolic trough collector has been tested for photocatalytic reaction application to wastewater treatment under different reaction conditions. The photocatalytic reduction of Cr(VI) to Cr(III), using TiO2 suspensions under solar irradiation, has been investigated. The influence of reaction conditions has been illustrated using an organic additive (citric acid) in varying doses and also by performing the reaction at different pH values and doses of TiO2. An attempt has also been made to investigate the reuse performance of the photocatalyst. The rate of reduction was found to increase steadily with increasing concentration of organic additive, TiO2 dose and decreasing pH. Complete reduction of Cr(VI) to Cr(III) was achieved in 2 h and very low catalyst concentration at pH 2. The reuse studies showed that the catalyst can be used 2–3 times for lower Cr(VI) concentrations.

The present study is targeted on the effect of pH on solar photocatalytic removal of metal ions from wastewater. Photoreductive deposition and dark adsorption of metal ions Cu(II), Ni(II), Pb(II) and Zn(II), using solar energy irradiated TiO 2 , has been investigated at pH values 2, 4, 7, 8 and 10. Modeling of metal species at the studied pH values has been performed and speciation is used as a tool for discussing the photodeposition. The decreasing order of metal deposition at pH 2 and 4 was found to be Pb(II) > Cu(II) > Ni(II) ≅ Zn(II). In the neutral and alkaline pH conditions (pH 7, 8 and 10) the order was Cu(II) > Zn(II) > Ni(II) > Pb(II).

Photocatalysis has been a widely studied technology since the 1970s. Many investigations have been carried out with the aim of understanding the fundamental processes and enhancing photocatalytic efficiencies especially for water, air, and soil pollution control. In this comprehensive paper, studies focused on the treatment of hazardous wastewater (bearing heavy metals and organic compounds) by photocatalysis and the effects of various parameters such as pH, light intensity, dissolved oxygen, etc., are reviewed. In addition, the design features and efficiencies of various photoreactors used for this process are discussed. Some studies on the economic analysis of photocatalytic systems are also included. It can be concluded that the photocatalysis process is suitable for the treatment of drinking water and industrial wastewater. Also, harvesting the energy of the sun for photoreactions would make it a cleaner and more cost-effective treatment method.