Turning waste into value: Iron-cobalt bimetallic hydrochar for efficient removal of persistent chlorinated pollutants – Mechanistic insights and adsorption models

In this study, a hydrothermal carbonization process was used to convert maple leaves into hydrochar, a sustainable bio-adsorbent, for the removal of pentachlorophenol (PCP) from wastewater. The hydrochar was further magnetized with iron and cobalt through hydrothermal treatment, enabling easy magnetic separation. Successful synthesis was confirmed by various physicochemical characterization techniques. Magnetic characteristics like saturation magnetization, remanence, and coercivity of synthesized hydrochar were studied to assess the functionalization. A removal efficiency of 94 % was achieved within 30 min at optimized conditions (0.06 g/L adsorbent dose, 10 mg/L initial PCP concentration, and pH 3). The adsorption process followed a pseudo-second-order kinetic model (R²= 0.995). Adsorption capacity decreased with an increasing pH from 3 to 11. At low pH values, the electrostatic interactions between PCP and adsorbent were favored by greater attractive forces. It was also observed that elevated temperature negatively impacted adsorption capacity. Reusability studies revealed a minimal reduction (16 %) in the removal efficiency over five cycles, highlighting the material’s durability. These findings demonstrated that the synthesized magnetic biosorbent effectively adsorbed PCP, and the adsorption capacity was influenced by factors like adsorbent dose, pH of reaction solution, and temperature.