Synthesis and characterization of TiO2/Fe2O3/Spent coffee ground-derived activated carbon composite for methylene blue removal: Mechanistic and thermodynamic studies

Methylene Blue (MB), a cationic dye is highly stable and non-degradable under natural conditions, posing significant threats to both ecosystems and human health. Exposure to MB may result in negative effects, including dermal irritation, stomach discomfort, and possible long-term ecological consequences. This study explores the adsorption of MB from aqueous solution using a novel TiO2/Fe2O3/SCGDAC composite adsorbent prepared via one-step hydrothermal method. The adsorbent was characterized through X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), and scanning electron microscopy (SEM). The composite performance as adsorbent for MB removal was assessed under varying pH, initial dye concentration, adsorbent dosage, and contact time. The results revealed that the optimal conditions for achieving 99.46% MB removal at pH 8, MB concentration of 15 mg L-1, adsorbent dosage of 0.26 g, and contact time of 90 min. The kinetic and isotherm equilibrium data were well fitted by pseudo-second-order and Langmuir models with adsorption capacity of 98.72 mg g-1, indicating monolayer adsorption on homogeneous surface. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic. The mechanism analysis revealed electrostatic interactions, Van der Waals force, hydrogen bonding, π-π stacking, ion-exchange, precipitation, and surface complexation may control the adsorption process. Notably, the composite maintained substantial adsorption efficiency, demonstrating excellent reusability. In general, the proposed composite offers a promising, recoverable, and eco-friendly approach for industrial wastewater contaminated with cationic dyes such as MB dye.