Entrapment of TiO2 and ZnO powders in alginate beads: Photocatalytic and reuse efficiencies for dye solutions and toxicity effect for DNA damage

Semiconductor photocatalysts; zinc oxide (ZnO) and titanium dioxide (TiO2) were used to entrap in calcium alginate (Ca-Alg) beads for photocatalytic oxidation of azo dye solutions. The decolorization of two textile dyes, Basic Red 18 (BR18) and Reactive Red 180 (RR180), was investigated in this study. The effect of catalyst loading and initial dye concentration were systematically evaluated. Complete decolorization (100%) of RR180 was obtained by ZnO/Ca-Alg beads at 10 g/L loading and 25 mg/L initial dye concentration for 180 min. However, at the same conditions, decolorization of 45.6% of RR180 was determined by TiO2/Ca-Alg beads. The results also showed that the highest BR18 decolorization levels were 98.4% at 10 g/L loading and 25 mg/L initial dye concentration for 180 min when ZnO/Ca-Alg beads were used as an entrapping matrix. However, a maximum decolorization of 87.1% of BR18 was obtained by TiO2/Ca-Alg beads at similar conditions for 180 min. Catalyst reusability was also tested during ten cycles and ZnO/Ca-Alg beads showed good stability compared to TiO2/Ca-Alg beads. Photocatalytic decolorization efficiency of ZnO/Ca-Alg beads was better than TiO2/Ca-Alg beads for both dyes. Using the comet assay for the genotoxic effect induced on Saccharomyces cerevisiae was also evaluated by entrapped ZnO and TiO2 powders in Ca-Alg beads. Genotoxicity study showed that the proportion of damaged cells and the genetic damage index (GDI) increased after exposed to entrapped beads in the light phase. (C) 2019 Elsevier B.V. All rights reserved.