Enhanced adsorptive removal of methylene blue and Congo red from aqueous solution using zinc oxide-graphene nanocomposite

The persistent nature of water pollution is one of the greatest global threats to the environment and human health. One well-known amelioration method that effectively and efficiently removes contaminants from water is adsorption. In this study, Hummer’s method was used to produce zinc oxide-graphene nanocomposite (ZnO-GO), and its potential as an adsorbent material for wastewater remediation. Specifically, kinetics and isothermal analyses in batch configuration were employed to investigate the adsorption behavior of the produced nanocomposite using two dye pollutants: methylene blue (MB) and congo red (CR). X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, UV-Vis, Fourier Transform Infrared, and Zeta potential have been used to evaluate the produced nanocomposite along with demonstrating its effective synthesis. The synthesized composite has a high adsorption capacity and the ability to remove dye contamination, as studied by optimizing the effect of various parameter, such as initial dye concentration, dose, time, temperature, and pH of solution. The pseudo second order rate kinetics best explained the adsorption kinetics, suggesting that chemisorption dominated the process. Equilibrium adsorption results revealed that the Langmuir isotherm provided a better fit compared to Temkin, Freundlich, and D-R models, suggesting monolayer adsorption on a homogeneous surface. According to Langmuir fitting, ZnO-GO showed a higher MB affinity with maximum adsorption capacities of 320.12 mg g⁻¹ compared to 175.24 mg g⁻¹ for CR. Surface functional groups, electrostatic interactions, H-bonding, π-π interactions, and dye molecule penetration into the adsorbent’s pores were all suggested as components of the adsorption mechanism. After being washed with ethanol and 0.1 M HCl, adsorbent demonstrated good performance for up to five cycle.