Phenol removal from pharmaceutical effluent using silver doped magnetite biochar: adsorption efficiency and kinetic studies

This study explores the removal of phenol from pharmaceutical wastewater using silver-doped magnetic biochar (Ag–Fe₃O₄/BC) as an advanced adsorbent. The biochar was derived from microalgae biomass <i>via</i> carbonization at 500 °C for 2 h and subsequently modified with silver and magnetite nanoparticles to enhance its surface properties and adsorption performance. Structural and chemical characterizations of both unmodified biochar (BC) and modified biochar (MD-BC) were conducted using high-resolution scanning electron microscopy (HRSEM), energy-dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) surface area analysis. The modification process significantly increased the surface area from 96.63 m²/g for BC to 590.21 m²/g for MD-BC. Batch adsorption experiments were performed by varying contact time (30–300 min), adsorbent dosage (0.1–0.4 g/20 mL), and temperature (30–50 °C). Maximum phenol removal efficiencies of 78.6% and 92.9% were achieved using BC and MD-BC, respectively, at a contact time of 300 min, 30 °C, and an adsorbent dosage of 0.33 g/20 mL. Adsorption data were best fitted to the Langmuir isotherm and pseudo-second-order kinetic models, indicating monolayer chemisorption as the dominant mechanism, corroborated by Dubinin–Radushkevich-derived energy values. The thermodynamic analysis confirmed the process to be spontaneous and endothermic, with enthalpy (ΔH°) and entropy (ΔS°) changes of 15.81 kJ/mol and 59.54 J/mol·K for BC, and 8.52 kJ/mol and 37.72 J/mol·K for MD-BC. The findings demonstrate the potential of silver-doped magnetic biochar as a highly efficient and sustainable adsorbent for phenol removal from pharmaceutical wastewater.