Synthesis and Applications of Zinc Oxide Nanorods, Copper-Doped Zinc Oxide Nanorods, Nickel Hydroxide/Zinc Oxide Nanorods, Iron (III) Oxide/Zinc Oxide Nanorods and Zinc Oxide/Graphene Oxide Nanorods for Batch Adsorption, Fixed-Bed Column Study, and Degradation of Cationic Dye (Blue Tur-XGB B-3) from Wastewater

Abstract

Industrial dyes from commercial sector are one of the major contributors to the environmental contamination. This research work mainly focuses on the elimination of synthetic cationic dye (Blue Tur-XGB B-3) through column and batch studies followed adsorption phenomenon. Various methods were employed to prepare the Zinc Oxide nanorods (ZnO) and different metal doped Zinc Oxide nanorods (Cu/ZnO, Ni(OH)₂/ZnO, α-Fe₂O₃/ZnO, GO/ZnO) as adsorbents. The synthesize nanorods were characterized by using FTIR analysis and SEM to confirmed the morphology and functional group of the prepared nano adsorbents. Followed the adsorption procedure the optimum pH for the cationic dye (Blue Tur-XGB B-3) was detected in the basic range which was 9 for ZnO (29.54 mg g⁻¹), 10 for Cu/ZnO (37.96 mg g⁻¹), 10 for Ni(OH)₂/ZnO (35.76 mg g⁻¹), 9 for α-Fe₂O₃/ZnO (31.88 mg g⁻¹), 9 for GO/ZnO (33.05 mg g⁻¹). The optimum dosage for all the prepared adsorbents were detected 0.05 g/50 mL and showed best adsorption capacity at temperature of 30 °C and 60 min of contact time. The initial concentration of dye was observed at the range of 125–150 mg L⁻¹ and best adsorption capacity was achieved at 100 mg L⁻¹ by all adsorbents. Photocatalysis experiment for determination of effect indicated the highest degradation efficiency of 90.49% for Cu doped ZnO NRs, 87.90% for Ni(OH)₂/ZnO NRs, 79.16% for α-Fe₂O₃/ZnO, 70% for ZnO/GONRs and 60.53% for ZnO NRs at 308 K for catalytic degradation of cationic dye (Blue Tur-XGB B-3). Adsorption followed both Langmuir and Freundlich isotherms for all adsorbents. Kinetic adsorption data supported Pseudo 1st and pseudo 2nd order kinetics while thermodynamics analysis indicated spontaneous and exothermic nature. Effect of surfactants, electrolytes, heavy metals and desorption were also evaluated. For column study, optimum bed height (3 cm), optimum flow rate (1.8 mL min⁻¹) and optimum inlet dye concentration (70 mg L⁻¹) were also observed for maximum adsorption of cationic dye (Blue Tur-XGB B-3). With the help of ZnO, the degradation of Blue Tur-XGB B-3 dye was also investigated. These methods are very cost effective, ecofriendly and easy to manufacture. The recycling results show that the ZnO nanostructures displayed good stability and long-term durability.

Graphical Abstract