Sustainable magnesium doped nanofibrillated cellulose/bentonite composite for enhanced phosphate removal: process...

Excessive accumulation of phosphate anions in aquatic systems accelerates ecological degradation and threatens both environmental quality and public health. In this study, we developed magnesium-doped nanofibrillated cellulose/bentonite (Mg@NFC/BN) composite through a facile in situ modification, yielding a cellulose-clay hybrid with enhanced anion affinity. The optimized composite exhibited maximum phosphate adsorption capacity of 19.2 mg g^-1 and removal efficiency of 88.6%. The adsorption process attained equilibrium within 90 min, following pseudo-second-order kinetics and conforming to Langmuir isotherm behaviour, while thermodynamic analysis indicated a spontaneous and exothermic mechanism. The synthesized adsorbent remained effective across a wide pH range, with strong selectivity even in the presence of competing anions. Structural and surface analyses through point of zero charge (pH_PZC), XRD, FTIR, FESEM, EDX and XPS confirmed the successful synthesis of composite and incorporation of Mg, which strengthened electrostatic interactions and promoted inner-sphere ligand exchange with phosphate ions. Alkaline-assisted desorption enabled up to 90% phosphate release, and the adsorbent retained over 75% of its initial capacity even after seven cycles, demonstrating excellent stability and recyclability for nutrient recovery. Beyond water treatment, the phosphate-laden composites improved soil water retention, highlighting their potential for sustainable agricultural applications. Overall, this work expands the functional versatility of cellulose-clay composites, offering an environmentally benign strategy for integrated wastewater remediation and resource recovery.