Croton macrostachyus leaf extract mediated synthesis of highly efficient ZnO NPs and ZnO/bentonite nanocomposites for photocatalytic degradation of organic dyes under solar irradiation

Abstract

In this study, ZnO NPs and ZnO/BT nanocomposites were synthesized using an aqueous leaf extract of Croton macrostachyus. The nanomaterials were characterized using XRD, FT-IR, SEM, and UV–visible spectroscopy. XRD results showed wurtzite hexagonal phases and a space group of P63mc for both ZnO NPs and ZnO/BT nanocomposites, with average crystallite sizes of 21.65 and 13.73 nm for ZnO NPs and ZnO/BT nanocomposites, respectively. FT-IR results showed the formation of Zn-O bonds. SEM analysis showed the formation of aggregates and a heterogeneous zigzag surface for ZnO NPs and ZnO/BT nanocomposites, respectively. UV–visible results showed the band gap energies of ZnO NPs and ZnO/BT nanocomposites are 3.59 eV and 3.4 eV, respectively. The photocatalytic degradation experiment result showed that 95.97 %, 97.49 %, and 97.86 % degradation efficiency were obtained at pH 12, 10, and 8 with catalyst doses of 0.3, 0.25, and 0.25 g, initial concentrations of 20, 20, and 160 mg/L, and exposure times of 90, 180, and 150 min, respectively, for MB, CV, and CR using ZnO NPs. Whereas, 99.54 %, 99.33 %, and 98.85 % degradation efficiencies were obtained at pH 7, 7, and 6, with catalyst doses of 0.2, 0.25, and 0.3, initial concentrations of 25, 25, and 160 mg/L, and exposure times of 30, 180, and 150 min, respectively, for MB, CV, and CR using ZnO/BT nanocomposites. The experimental data fit well the second, zero, and first order kinetics for CV, CR, and MB, respectively, using ZnO NPs, whereas the pseudo-zero order fit well for all dyes with ZnO/BT nanocomposites.