Optimized CTAB-Modified Nanofibrillated Cellulose for Phosphate Recovery: Adsorption Mechanisms and Performance Insights

To address the environmental challenges posed by eutrophication, removal of excess phosphorus from aquatic ecosystems is imperative. This study presents a cationic adsorbent synthesized by modifying nanofibrillated cellulose (NFC), derived from agrowaste, using surfactant cetyltrimethylammonium bromide (CTAB). Comprehensive characterization techniques, including XRD, FTIR, HR-SEM, SEM-EDX, BET, and XPS, confirmed successful introduction of quaternary ammonium groups, significantly enhancing the surface chemistry of NFC. This modification imparted a positive ζ potential over a wide pH range, ensuring a strong affinity for negatively charged phosphate ions. Increased surface roughness and improved active site availability resulted in a nearly threefold improvement in phosphate removal efficiency compared to pristine NFC. The adsorption followed a pseudo-second-order kinetic model and Sips isotherm, achieving a maximum capacity of 21.78 mg P/g within 120 minutes. The adsorbent displayed pH-dependent behavior, retaining stability and optimal performance under weakly acidic to neutral conditions, with minimal desorption (12.61%) after three cycles. Mechanistic insights from XPS and FTIR revealed that electrostatic interactions and hydrogen bonding were the primary drivers of phosphate adsorption.