Engineering the MxZn1−xO (M = Al3+, Fe3+, Cr3+) nanoparticles for visible light-assisted catalytic mineralization of methylene blue dye using Taguchi design

Here, we developed a sustainable solution to address the water pollution especially due to organic dye industries. Visible light-activated catalytic degradation of aqueous solution of methylene blue (MB) dye was studied by using trivalent metal ion-doped ZnO nanoparticles as a photocatalyst. The nano-photocatalysts were synthesized by microwave-irradiated solution combustion method using d-glucose as a fuel. Various experimental parameters were optimized using Taguchi design of experiment, analysis of variance (ANOVA) and Grey relational analysis in order to obtain potential ZnO photocatalyst. Using ANOVA and Grey relation analysis, the optimum conditions were estimated that 5.5 mol% Cr3+-doped ZnO with 4 min MW heating and calcined at 450 °C, which shows very impressing photo-catalytic property. The ANOVA confirms that the calcination temperature and dopants significantly influence crystallite size with contribution factor of 42.28% and 40.02%, respectively. The band gap energy of the photocatalyst was largely influenced by a type of dopant with contribution 85.77%. Grey relational grading indicates that the 5.5% Al3+ doping, 4 min MW heat treatment, 450 °C calcination temperature to get lesser band gap (3.05 eV) and smaller crystallite size (46.96 nm). As compared with other L9 orthogonal array, the degradation efficiency is found to be higher (89.31%) on the Grey theory predication result for MB dye. Herewith, we strongly confirm that the Taguchi design was an promising tool in engineering the ZnO photocatalyst with a very less experimental trials and cost saving approach.