Enhanced tetracycline elimination by template-synthesized mesoporous biochar: Adsorption performance and mechanistic...

The conversion of waste resources into functional materials via environmentally benign processes is essential for sustainable development. In this study, residues from Dendrobium nobile Lindl (DL), a traditional Chinese herbal medicine (CHM), were valorized to produce mesoporous biochar (DMB) through a "one-pot" carbonization strategy using magnesium citrate (MgCi) as a dual-function activating agent and sacrificial template. Notably, DMB-2 exhibited exceptional textural properties, featuring a specific surface area (S_BET) of 1287.07 m²/g and a total pore volume (V_Total) of 1.593 cm³/g among the samples. Systematic adsorption investigations for tetracycline (TC) revealed that the process adheres to pseudo-second-order (PSO) kinetics and the Langmuir isotherm model, achieving a maximum adsorption capacity of 1295.67 mg/g at 318 K, highlighting excellent adsorption performance. Thermodynamic analysis confirmed that the adsorption is spontaneous and endothermic. Furthermore, fixed-bed column studies demonstrated robust dynamic adsorption performance, yielding breakthrough and saturation times of 260 and 760 min, respectively (C₀ = 150 mg/L, Z = 2 cm, V = 1 mL/min). Mechanistic studies identified pore filling (60.4%) as the predominant adsorption driver, supplemented by π-π interactions (15.7%), hydrogen bonding (13.5%), and electrostatic interactions (10.4%). DMB-2 maintained over 70% removal efficiency across ten consecutive regeneration cycles and demonstrated economic feasibility with an estimated production cost of 1.09 $/kg, underscoring its potential for practical application. Overall, this research establishes a comprehensive theoretical and technological foundation for the valorization of herbal waste into high-performance biochars for advanced wastewater remediation.