l-cysteine doped polypyrrole (PPy@L-Cyst): A super adsorbent for the rapid removal of Hg+2 and efficient catalytic activity of the spent adsorbent for reuse

Abstract

A growing worldwide concern about the detection and removal of the most toxic element Hg2+ being released excessively into the water environment from various sources. The aim of this study is to develop a new material for rapid and efficient removal of Hg2+ ions from aqueous media. In the present study, a new adsorbent has been developed through the surface modification of polypyrrole with l-cysteine (PPy@L-Cyst) via radical polymerization method for effectively elimination of Hg2+ from aqueous solutions. The detailed characterization of PPy@L-Cyst composite before adsorption and together with its adsorbed Hg2+ ions after adsorption were extensively investigated using various instrumental techniques including FTIR, FE-SEM, HR-TEM, XRD, TGA, XPS. The capability of Hg2+ exclusion from aqueous medium was evaluated by performing a series of batch studies under different parameters using ICP-OES technique. The obtained experimental outcomes were investigated with the help of different adsorption kinetic and isotherm models. PPy@L-Cyst exhibited rapid adsorption of Hg2+ ions through pseudo-second-order kinetics whereas the Langmuir was the best fitted isotherm model among other models with maximum uptake capacity of 2042.7 mg/g at 25 °C. A plausible mechanism for the interaction of adsorbent and adsorbate was proposed to explain the reason behind the adsorption behavior of PPy@L-Cyst. In addition, current study also highlighted the reusability of toxic metal ions loaded spent adsorbent for the catalytic organic transformation. The mercury-laden catalysts played an important role for the organic transformation reaction of phenylacetylene to desired product, acetophenone, with 52% yield. Obviously, this is a new approach for the reuse of Hg2+ adsorbed material for catalytic application, which has a great environment impact for the minimization of waste derived from conventional adsorption techniques.