In-situ synthesised hydroxyapatite-loaded films based on cellulose nanofibrils for phenol removal from wastewater

Abstract

Phenol removal from aqueous medium was studied by the batch method using novel and fully biobased solvent-cast films prepared from cellulose nanofibrils (CNFs) and in situ synthesised hydroxyapatite (HAp) by the wet-chemical precipitation method and different concentrations of HAp precursors and weight mass of CNFs. The chemical and morphological structures of as-prepared films were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy, while their physical properties were determined by water contact angle and swelling kinetic measurements. The HAp precursor leads to a surface modification of CNFs, which increases its activity by forming differently structured, sized and distributed HAp particles, influencing the phenol adsorption kinetic and capacity. The phenol adsorption was faster and higher (~64 mg g−1) in an acidic solution (pH 2) compared to the original phenol solution pH (pH 7.4, ~30 mg g−1) using films with unevenly-distributed and positively-charged calcium-richer HAp particles synthesised on the CNFs’ surface, being reflected also in its higher water swelling properties, compared to their hybrid counterparts. The phenol adsorption is identified to follow pseudo-second order kinetic and intra-particle diffusion models. A highly-efficient reusing ability of the selected film with 86% adsorption capacity of the initial value at the third sequential regeneration cycle, is also confirmed. A super-hydrophilic nature of the films with high water-diffusing and transport properties, as well as low swelling, indicates their potential in the development of highly-effective adsorbents and, potentially, filter membranes for water purification.