Extracellular biosynthesis of CuO-TiO2 nanocomposites using Alcaligenes aquatilis for the photodegradation of reactive and azo dyes under visible light irradiation

In this study, CuO/TiO2 nanocomposites were biologically synthesized using cell-free supernatant (CFS) of Alcaligenes aquatilis growth culture by two-step synthesis method, one-pot method with sequential addition of precursors, and one-pot method with simultaneous addition of precursors. The one-pot method with simultaneous addition of precursors was found to be the best method for the synthesis in terms of degradation of reactive blue-220 (RB-220) and acid yellow-17 (AY-17) dyes under visible light irradiation. CuO/TiO2 nanocomposite was found to have the crystallite size of 14.7nm and the bandgap energy of 2.5 eV. The effect of synthesis parameters such as synthesis time, pH of CFS, and the ratio of Cu to Ti in the synthesis mixture on the photocatalytic degradation efficacy of these nanocomposite structures under visible light irradiation was studied. The optimum conditions for the synthesis of CuO/TiO2 nanocomposite particles by one-pot method with simultaneous addition of precursors were found to be pH 12 of CFS, synthesis duration of 24 h, and molar ratio of Cu to Ti in the synthesis mixture as 1:22 for RB-220 dye and 1:25 for AY-17 degradation. CuO/TiO2 nanocomposite particles synthesized under the optimum conditions and without any calcination could degrade RB-220 and AY-17 dyes completely in 120 min and 150 min, respectively. The kinetics of degradation of RB-220 and AY-17 by CuO@TiO2 nanocomposite particles followed first-order kinetic model with rate constant of 0.028 min−1 and 0.018 min−1, respectively.