Synthesis of polyquaternium-functionalized hydrochar for adsorptive removal of methyl orange and diclofenac sodium

Polyquaternium modified hydrochar was prepared via free radical grafting. • PQHC exhibits high adsorption capacities for MO/DS (660.89/615.32 mg·g −1 ). • PQHC maintains high performance in real water matrices (tap and river water). • Adsorption mechanism was dominated by electrostatic attraction and anion exchange. The widespread use of anionic pharmaceuticals and dyes has led to serious water pollution. As a biosorbent for water treatment, hydrochar shows poor affinity for anionic contaminants due to its negative surface charge, limiting its practical applicability. In this study, a novel cationic polyquaternium-functionalized hydrochar (PQHC) was synthesized via radical graft polymerization of (3-methacrylamidopropyl)trimethylammonium chloride (MAPTAC) onto hydrochar for removal of these anions. PQHC maintained a stable positive charge over a broad pH range (2−12), and achieved exceptional adsorption capacity for representative anionic pollutants such as diclofenac sodium (DS) and methyl orange (MO). The adsorption capacities for DS and MO maximized to 615.32 and 660.89 mg·g −1 , respectively. Kinetic studies demonstrated exceptionally rapid adsorption, with the uptakes of MO and DS (at 400 and 200 mg·L −1 , respectively) attaining 97.8% and 95.8% of their equilibrium values within the first 5 min. Characterizations revealed a multifaceted adsorption mechanism centered on electrostatic attraction and Cl − /pollutant anion exchange, synergistically enhanced by hydrogen bonding and n/π-π interactions. In addition, PQHC removed both pollutants at high rates in tap water and river water. Thus, this work develops a rapid and efficient biosorbent for capturing anionic pollutants from complex wastewater, and proposes a facile and efficient modification method for preparing cationic-functionalized hydrochars with great potential for practical water treatment applications. Download: Download high-res image (213KB) Download: Download full-size image