A Bimetal Fe/Mg Immobilized on N‑Doped Biochar for Efficient Adsorption of Paracetamol: Performance Assessment,...

In this study, a series of bimetallic Fe/Mg-incorporated, N-doped biochars (Fe-Mg@N-BC) was prepared via pyrolysis of coconut shells for paracetamol (PCM) adsorption. In comparison to single-metal and N-doped biochars, Fe-Mg@N-BC exhibited significantly greater adsorption capacity, illustrating the synergistic effect of bimetallic codoping. The Fe-Mg@N-BC with an Fe content of 13.8 wt % (denoted as Fe-Mg@N-BC-3) exhibited the highest adsorption capacity, reaching 157.9 mg/g at 25 °C at 0.3 g/L adsorbent loading. The characteristics of Fe-Mg@N-BC-3 were evaluated using FTIR, XRD, XPS, SEM, and EDX, which indicated that metal atoms were uniformly distributed within the carbon layer, resulting in the formation of abundant active sites for PCM adsorption. The excellent performance of Fe-Mg@N-BC-3 was mainly attributed to the formation of favorable active sites and a larger specific surface area of 604.5 m²/g. The adsorption kinetics and isotherms were best described by the pseudo-second-order model (R² = 0.9987) and Langmuir model (R²=0.9998), respectively. The effects of Fe content, pH, adsorbent dosages, and water matrix on PCM adsorption were also investigated. Further characterization studies revealed that PCM adsorption on Fe-Mg@N-BC-3 is attributed to a combination of metal complexation, cation-π interactions, hydrogen bonding, and π-π stacking. Density functional theory calculations demonstrated that Fe-Mg@N-BC exhibited increased adsorption energy, thereby strengthening electronic interactions between the adsorbent's surface and PCM. Overall, the high removal efficiency and structural stability of Fe-Mg@N-BC-3 highlight its potential as an effective and environmentally sustainable adsorbent for antibiotic removal from water.