Photocatalytic Cr (VI) Removal with Nanomaterial Coated on Natural Stone

Abstract

Chromium is one of the most common elements in the earth which found in the inner layers of the ground and in the body of living organisms. Certain industrial processes cause serious environmental problems and produce waste streams containing contaminants such as heavy metals. The removal of heavy metal ions, which exhibit a significant toxic effect in wastewater is particularly important in the field of water pollution. Chromium plating, leather tanning, wood shielding and stainless-steel manufacturing industries wastewater mainly contain chromium with valance of 6+ and 3+ . Especially discharging of Cr(VI) to the environment is very dangerous and causes health problems. Therefore, different methods are applied for the treatment of wastewater containing Cr(VI). The most commonly applied methods are reduction of Cr(VI) to Cr(III). Although there are several widely used methods such as chemical precipitation, reduction, dialysis, ion exchange, evaporation, solvent extraction, reverse osmosis and ultrafiltration for Cr(VI) removal in wastewaters, photocatalytic oxidation method has gained great importance in recent periods. In photocatalytic removal, Cr(VI) reduced to Cr(III) with the help of photocatalyst and UV light. In this study, photocatalytic Cr (VI) removal was aimed and Ag and Ni doped TiO2 nanoparticles were coated on natural volcanic stones as a photocatalyst. Volcanic stones containing Ag and Ni doped TiO2 (0.5%, 1.0%, 2.5% and 5%) in four different compounds percentages were prepared by sol-gel method. In order to form a solid layer on the natural stone, the coated stones were kept in an oven of 600 oC for 1 hour to produce photocatalyst material and the nanomaterial percentages on the stones were determined by SEM-EDX analysis. Synthetic Cr (VI) containing water was used for removal experiments by using batch reactor. Cr (VI) removal was much higher in the experiment using nanomaterial produced with 0.5% doping. As a result of this study, in water it was determined that the increase in the percentage of Ag and Ni doping has showed a negative effect on the removal of Cr (VI).