Superior stability and high biosorbent efficiency of carboxymethylchitosan covalently linked to silica-coated core-shell magnetic nanoparticles for application in copper removal

Abstract

Given the daily increase of polluted biomass (e.g. sludge) with heavy metals (such as copper), the removal of the latter is essential in order to recovery biomass resources into more beneficial products. By virtue of its higher efficiency and lower costs, environmental nanotechnology in combination with naturally-derived biopolymers must result into novel nanobiosorbents with high efficiency for metal ions cleaning process technology. This contribution presents the synthesis of novel environment friendly magnetic nanocomposites, based on 13 nm-sized magnetic maghemite core, coated with approximately 7 nm thick silica layer. For the first time, abundant silanol groups on silica coating were directly chemically coupled with amino-biopolymer carboxy-methyl chitosan (CMC) using carbodiimide chemistry, which resulted in strong and stable ester bond formation. Nanobiosorbent crystal structure was determined using X-ray powder diffraction (XRD), whereas morphology, size and silica-layer thickness (core-shell structure) were analysed with transmission electron microscopy (TEM). CMC chemical coupling of silica-coated magnetic nanoparticles was carefully executed experimentally and was examined via infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), electrokinetic measurement supported with dynamic light scattering (DLS) and termogravimetric analysis (TGA). Magnetic properties of novel nanoparticles were measured with vibration sample magnetometer (VSM). The stability of bounded CMC, as important however often neglected parameter for practical application, was tested at alkaline pH value using XPS analysis and biopolymer desorption was negligible. The resulted nanoadsorbent revealed superior tendencies for copper adsorption (∼350 mg g−1 maximum adsorption capacity) among other state-of-the-art reported magnetic-chitosan-based adsorbent, proving the promising potential of studied nanocomposite for heavy metal removal applications.