Bamboo-derived nitrogen-doping magnetic porous hydrochar coactivated by K2FeO4 and CaCO3 for phenol removal: Governing factors and mechanisms

In this study, a novel nitrogen-doped magnetic Fe–Ca codoped biochar for phenol removal was successfully fabricated via a hydrothermal and coactivation pyrolysis method. A series of adsorption process parameters (K2FeO4 to CaCO3 ratio, initial phenol concentration, pH value, adsorption time, adsorbent dosage and ion strength) and adsorption models (kinetic models, isotherms and thermodynamic models) were determined using batch experiments and various analysis techniques (XRD, BET, SEM-EDX, Raman spectroscopy, VSM, FTIR and XPS) to investigate the adsorption mechanism and metal-nitrogen-carbon interaction. The biochar with a ratio of Biochar: K2FeO4: CaCO3 = 3:1:1 exhibited superior properties for adsorption of phenol and had a maximum adsorption capacity of 211.73 mg/g at 298 K, C0 = 200 mg/L, pH = 6.0 and t = 480 min. These excellent adsorption properties were due to superior physicomechanical properties (a large specific surface area (610.53 m2/g) and pore volume (0.3950 cm3/g), a well-developed pore structure (hierarchical), a high graphitization degree (ID/IG = 2.02), the presence of O/N-rich functional groups and Fe-Ox,Ca-Ox, N-doping, as well as synergistic activation by K2FeO4 and CaCO3). The Freundlich and pseudo-second-order models effectively fit the adsorption data, indicating multilayer physicochemical adsorption. Pore filling and π-π interactions were the predominant mechanisms for phenol removal, and H-bonding interactions, Lewis-acid-base interactions, and metal complexation played an important role in enhancing phenol removal. A simple, feasible approach with application potential to organic contaminant/pollutant removal was developed in this study.