Synthesis and characterization of calcium alginate and cellulose nanocrystal films for lead removal

Abstract

The contamination of water with lead (Pb) is a society concern since this metal as a toxic cation. Cellulose nanocrystals (CNC) are rod-like structures with variable size, which are prepared by acid hydrolysis of cellulose natural sources, so it is a renewable, biodegradable material, with good mechanical performance. Sodium alginate (SA) is a biopolymer, biodegradable and renewable. This biopolymer can chelate bivalent cations forming gel networks. This work focuses on the combination of these two natural biopolymers to create a film of calcium alginate with CNC with the aim to remove non-essential elements on contaminated water. SA and CNC were mixed forming a dispersion, then they were left to dry and reticulated with sodium chlorate (CaCl2) solution. To determine the adsorption kinetics, the films were put in contact with Pb solution, the mixture was maintained under agitation, at constant speed and temperature, the Pb and calcium (Ca) concentrations in supernatant aliquots were determined using the Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES) and Flame Atomic Absorption Spectroscopy (FAAS), respectively. The results were applied on three kinetic models of adsorption: pseudo-first order; pseudo-second order and Weber-Morris. Characterizations of films were carried by Fourier Transform Infrared (FTIR); Atomic Force Microscopy (AFM); Scanning Electron Microscopy (SEM). AFM and SEM topography study showed a very flat and smooth surface for the films. The adsorption of Pb onto film increased with time contact. Maximum adsorption of Pb was 3.5 mg per gram of film. The prepared films were characterized by AFM and SEM. FTIR confirmed the structure of both polysaccharides. The Pb adsorption experimental data showed an adjusting for pseudo-second model, agreeing with published papers. Further analysis should be done to evaluate isotherms of adsorption and methods for removing the non-essential elements of the film, with the aim of a possible reuse of it.