Decolorization of Azo Dyes by Chemically and Biosynthesized ZnO Nanoparticles.

Dye contaminants in industrial effluents contribute significantly to environmental pollution. Conventional wastewater treatment methods are expensive and energy-consuming. These limitations could be overcome by the use of nanobioremediation processes. The present work was an effort to study decolorization of azo dyes by ZnO nanoparticles (NPs). Rubine GDB (R-GDB) and Congo Red (CR) were the azo dyes selected for the study. The ZnO NPs were successfully synthesized by chemical and biological methods. Chemical synthesis of ZnO NPs was carried out by co-precipitation method; biosynthesis was done using bacteria Bacillus subtilis. The synthesized nanoparticles were characterized by UV-Vis Spectroscopy, SEM, and XRD. The UV spectrophotometer showed peaks in the range of 300-400 nm. SEM pictures indicated the presence of NPs in the size of 100-200 nm. XRD results were analyzed based on the peaks that were seen. EDX analysis showed the presence of Zn particles and oxygen particles majorly. Decolorization efficiency was evaluated by calculating % decolorization by Meyer's method. Chemically synthesized NPs showed maximum % decolorization of the R-GDB (89.55 ± 0.44%) and CR (88.52 ± 0.90%). The biosynthesized NPs showed the least decolorization (R-GDB, 18.46 ± 0.45% and CR, 21.41 ± 1.02%). However, moderate percentages of decolorization of both the azo dyes were observed when a combination of the NPs was used (R-GDB, 36.25 ± 0.22% and CR, 39.47 ± 0.94%). Nanoparticles showed good potential for the decolorization of the azo dyes. With further optimization of the parameters, the present findings show that dye decolorization by chemically synthesized ZnO NPs could be used as a probable nanobioremediation approach to treat wastewaters.