Novel hybrid multifunctional composite of chitosan and altered basalt for barium adsorption: Experimental and theoretical studies

Abstract

Herein, the starting low‒cost and eco‒friendly weathered basalt (WB) was found to be rich in zeolite and clay minerals, which have wide applications in water purification. WB was chemically activated by hydrogen peroxide (H2O2) followed by the interaction with chitosan (Ch) to fabricate a new hybrid composite (WB/Ch) with multifunctional groups. The resulted WB/Ch composite was characterized by XRD, FTIR, SEM, and applied for Ba (II) adsorption at pH 5.0 and different temperatures (i.e., 25, 35 and 45 °C). The adsorption data were fitted to kinetics, classical (Langmuir, Freundlich and Dubinin–Radushkevich) as well as advanced statistical (multilayer) models. The adsorption data of Ba(II) onto WB/Ch were described well by the pseudo-second-order and the applied traditional equilibrium models. The monolayer adsorption capacity (qmax = 45.78 mg g−1) reflected the high removal efficiency of WB/Ch for Ba(II) uptake as compared to varied natural and synthetic adsorbents. Steric and energetic parameters of the multilayer model were interpreted to understand the interaction mechanism between the Ba(II) ions and WB/Ch active sites. Theoretical number of receptor sites (n) was less than unity at all temperatures revealing multi–docking adsorption mechanisms. Interaction between Ba(II) and WB/Ch of the first layer played the principle role in increasing the adsorption capacities (Qsat) from 115.06–128.86 mg g‒1 within the temperature range of 25–45 °C. The total adsorbed Ba(II) layers (the Nt parameter) decreased from 2.79 to 2.02 with temperature thus reflecting its insignificant role to determine the Qsat values. The calculated adsorption energies varied from 22.35 to 28.56 kJ mol‒1 indicated that the Ba(II) adsorption onto the WB/Ch composite was endothermic and related to physical forces. Thermodynamic parameters including Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) reflected the endothermic and spontaneous nature of Ba(II) adsorption process.