Cadmium removal from water by green synthesized nanobioadsorbent [SiO2@DOPP]: Mechanism, isotherms, kinetics and regeneration studies

Abstract

In this study, dried orange peel powder [DOPP] is chemically modified with nanosilica (SiO2) employing sonication technique to produce nanobioadsorbent [SiO2@DOPP]. [SiO2@DOPP] This nanoadsorbent was evaluated for Cd2+ removal from aqueous systems. Successful functionalization of [DOPP] into nanosilica was confirmed by various analytical techniques like XRD, FTIR, SEM, EDX, TEM, DLS, pHzpc and TGA. XRD, FTIR and EDX confirmed the emergence of new peaks after modification of [DOPP] by nanosilica and adsorption of Cd2+ onto [SiO2@DOPP]. Further, TGA spectrum suggested that [SiO2@DOPP] nanoadsorbent is thermally more stable than [DOPP]. pH plays a major role to Cd2+ adsorption onto [SiO2@DOPP]. The optimum conditions for Cd2+ removal include pH = 6.5 and 0.03g adsorbent dose with 100 min contact time. Different adsorption isotherms models [best fitted-(Langmuir adsorption model)], adsorption kinetics [best fitted�(Pseudo second order and Intraparticle diffusion)] were examined for the removal of Cd2+. The maximum monolayer adsorption capacity [qmax] was 142 mg/g. Thermodynamic evaluation indicates the endothermic and spontaneous nature of Cd2+ adsorption onto [SiO2@DOPP]. Furthermore complexation mechanism of Cd2+ onto [SiO2@DOPP] is discussed in detail. The results indicate involvement of functional group interactions, ?�metal interactions, proton exchange, chelate complexes and electrostatic interactions during adsorption of Cd2+ onto [SiO2@DOPP]. Based on the results it has been inferred that [SiO2@DOPP] is a promising nanobioadsorbent to manage environment burden of Cd2+ from aqueous systems. � 2020 Elsevier B.V.