Hydrothermal synthesis of fluorescent schiff base functionalized carbon dot composite for the removal of Cd(II) ions from aqueous solution: Optical, equilibrium and kinetic studies

Abstract

The search for nanoparticle metal chelator biomarker has been on the rise in recent years. In this study, bis(salicylidene)ethylenediamine (SALEN) functionalized carbon dot derived from waste banana peels was synthesized using facile hydrothermal technique and the optical biomarker and adsorption properties of the highly fluorescent red nanomaterial was studied. The carbon dot and its functionalized counterpart were characterized using FTIR, SEM/EDX, and UV-Visible spectrophotometry. Evaluation of the optical properties of the yellowish brown carbon dot and reddish highly luminescent functionalized carbon dot indicated band gap energy values of 1.85 and 2.04 eV, respectively. Extraneous variables such as effect of initial metal ion concentration, pH, and contact time were studied in the batch extraction process for the sorption of Cd(II) ions from aqueous solution. The sorption of Cd(II) ion was observed to be highest at pH 5 with 99.3 % removal efficiency. The adsorption isotherm and kinetic models indicated interplay of physisorption and chemisorption processes. The mechanism for the chelation of Cd(II) ions onto the surface of the functionalized carbon dot was mainly governed by inner sphere chelation and ion exchange. Reusability of the material was evaluated using adsorption-desorption experiments. Results of the study indicated the potential of the functionalized carbon dot as (i) semiconductor materials with strong photoluminescence at the visible region which could be used as environmental biomarker and as sensor, and (ii) effective, efficient and low cost adsorbent for remediating Cd(II) ions contaminated environment.