Efficient adsorption and photocatalytic degradation of Methylene Blue Dye Using ZnO modified activated carbon derived from pistachio shells: Optimization, Isotherms and Kinetics

Abstract The present study introduces a Zinc oxide modified activated carbon derived from pistachio shells (ZnO/ACPS), a nanocomposite for the efficient elimination of methylene blue (MB) dye from aqueous media through adsorption and photocatalytic degradation. Comprehensive characterization by Fourier Transform Infrared Spectroscopy, X-ray diffraction, Scanning Electron Microscopy, Energy-Dispersive X-Ray Spectroscopy, Brunauer-Emmett-Teller, and Thermogravimetric analysis confirmed the functional groups, crystalline structure, morphology, elemental composition, surface area, and thermal stability of the composite. Parameters, including “catalyst dosage, initial dye concentration, stirring speed, contact time, and pH, were systematically evaluated” to improve adsorption and photocatalytic degradation performance. At optimized conditions, the material exhibited nearly 90% efficiency in adsorption and 96% efficiency in photocatalytic degradation. Kinetic investigations revealed that adsorption occurred in a pseudo-second-order mechanism, highlighting chemisorption, whereas photocatalytic degradation indicates a single rate-limiting step driven by reactive species which obeyed a pseudo-first-order model. The adsorption isotherm confirmed Langmuir-type adsorption, suggesting a monolayer interaction, with q max of 58.82 mg/g. Thermodynamic parameters reveal that the adsorption of MB dye on ZnO/ACPS materials was spontaneous and endothermic. The hydrogen bonding, π-π interaction, and electrostatic interaction take place between ZnO/ACPS materials and Methylene Blue dye. The degradation of MB dye was studied under Ultraviolet light irradiation with a wavelength of 245 and 365 nm. Furthermore, reusability experiments demonstrated that the composite retained about 78% of its adsorption ability and 82% of its photocatalytic activity even after five consecutive cycles.