Thermodynamic study of the adsorption of Cd²⁺ and Ni²⁺ onto chitosan – Silica hybrid aerogel from aqueous solution

Adsorption studies have been conducted on aqueous solution to investigate the effect of temperature on the sorption of Cd²⁺ and Ni²⁺ by Chitosan-silica hybrid aerogel [(CS)_hA], which was developed using a blend of components from crab exoskeleton and bamboo biomass and synthesized using sol–gel method. The application of this derived aerogel for clean-up of water bodies polluted with heavy metals at varying temperatures was undertaken with a view to establish its effectiveness. The studied temperatures were 301 K, 308 K, 318 K, 328 K and 338 K at pH 3 and contact time of 180 mins and 60 mins for Cd²⁺ and Ni²⁺, respectively. Data obtained were subjected to Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models which were used to evaluate the adsorption process. Langmuir Isotherm model proved to be the best fit in interpreting the adsorption process with the maximum Cd²⁺ sorption values within 57.14 to 57.80 mg g⁻¹ while Ni²⁺ sorption values lie between 52.08 and 58.82 mg g⁻¹. The effect of enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) on the sorption of Cd²⁺ and Ni²⁺ by the derived aerogel were also deduced. The process is spontaneous, exothermic with the studied ions well aligned on the derived aerogel surface.