HAp@Cell bio-films engineered from local resources involving molecular mechanisms of dye adsorption and antibacterial activity

Abstract

This work describes the eco-friendly synthesis and multifunctional performance of hydroxyapatite/cellulose (HAp@Cell) bio-films prepared from Moroccan natural phosphate and cotton-derived cellulose through a solvent-free, low-temperature (< 100 °C) route. Structural (XRD) and morphological (SEM) analyses confirmed nanocrystalline HAp homogeneously dispersed in a semi-crystalline cellulose matrix, creating a rough and porous network favorable for molecular interactions. The optimized film (PC5) exhibited outstanding adsorption toward methylene blue (qₑ,max ≈ 85 mg g⁻¹) and natural indigo (~ 95% removal). Kinetic data fitted the pseudo-second-order model, while the Freundlich isotherm best described multilayer adsorption, indicating a heterogeneous surface with high affinity for cationic dyes. At the molecular scale, non-covalent interactions such as hydrogen bonding, electrostatic attraction, and π–π coupling between dye molecules and surface hydroxyl/phosphate groups dominate the adsorption process. The same surface chemistry governs the antibacterial mechanism, where the controlled release of Ca²⁺ and PO₄³⁻ ions combined with electrostatic contact destabilizes bacterial membranes, producing inhibition zones of 25 mm for S. aureus and 20 mm for E. coli. The films maintain over 85% adsorption efficiency after five reuse cycles, demonstrating high stability and regeneration potential. These results position the HAp@Cell composite as a sustainable, dual-function material for wastewater decolorization and antimicrobial protection within Morocco’s eco-circular strategy.