Visible light assisted mineralization of malachite green dye by green synthesized xanthan gum/agar@ZnO bionanocomposite

Abstract

The current research presents the ecofriendly and cost-effective green synthesis of zinc oxide nanoparticles (ZnO NPs) through bio-reduction process by a blend of xanthan gum (XG)– agar (AA) biopolymer. The bionanocomposite (BNC) material was explored as a potential photocatalyst and characterized by various instrumental techniques and thus found to have a distorted hexagonal geometry observed through X-ray diffraction (XRD) data. The optical studies suggested the successful nucleation of ZnO NPs in the biopolymer matrix with reduction in optical band gap energy from 3.54 eV to 2.55 eV. The synthesized BNC material showed a strong affinity towards the removal of malachite green (MG) through photocatalytic degradation under visible light irradiation. Response surface methodology-central composite design (RSM–CCD) module was utilized as computational modeling for the optimization of photocatalytic reaction variables and the computed results were found to be as irradiation time (46 min), pH (8.0), MG concentration (70 mg L–1) and catalyst dose (7.0 g L–1). The rate of MG degradation was explained in terms of the pseudo first order kinetics (R2 = 0.999) i.e., formation of adsorption-desorption equilibrium first and then in presence of reactive oxidant species (ROS) ·O2–radicals degradation occurs. The material shows high stability towards photocatalytic experiments and can be reused for five consecutive cycles with high degradation efficiency.