Removal of Ni2+ and Cd2+ from aqueous solutions by bionanosorbents: Isotherm, thermodynamic and mechanistic studies

Abstract

The present work presents the efficiency and the limit in using bionanosorbents (cellulose, chitin and modified chitin nanocrystals) for the sorption of metal ions M²⁺ (M = Ni and Cd) in batch systems. Bionanosorbents were extracted from plants and shrimp shells, two available and low-cost materials. If cellulose and chitin nanocrystals did not efficiently remove metals in the experimental conditions of this work, the surface-modified chitin exhibited enhancement for the Ni²⁺ and Cd²⁺ adsorption capacity than original chitin nanocrystals. The Langmuir and Freundlich models fitted well to the experimental data from which the maximum adsorption capacity was 139.2 mg Ni g⁻¹ and 38.4 mg Cd g⁻¹. Regarding the Gibbs free energy and the Hall parameter, the sorption of Ni²⁺ and Cd²⁺ were spontaneous and favourable for pH around the neutrality. This corroborates the examination of IR spectra of oxidized chitin nanocrystals before and after the sorption process from which the metal removal mechanism was mainly attributed to the formation of complexes and ion exchanges of the bionanosorbent and metal ions. Element mappings of the bionanosorbents after sorption revealed a homogeneous distribution of Cd(II).