Polyamine-modified reduced graphene oxide: a new and cost-effective adsorbent for efficient removal of mercury in waters

Abstract

This paper describes the synthesis and characterization of polyamine modified reduced graphene oxide rich with mixed amino groups as a cost- and performance- efficient adsorbent for mercury removal from waters. The synthetic approach is based on a simple process to functionalize graphene oxide (GO) with low-cost commercial polyamine epoxy hardener followed by the reduction of created polyamine-GO hybrid by hydrothermal (HT) or chemical reduction (CM) process with hydrazine. Both polyamine modified reduced graphene oxide (rGO), referred as HT-rGO-N and CM-rGO-N, exhibited 8.28% and 5.47% N content, respectively. Mercury adsorption study showed that these rGO functionalized composites have high adsorption kinetics, reaching equilibrium within the first ten minutes. The adsorption kinetics and equilibrium of their adsorption process can be well described using pseudo-second order and Freundlich isotherm models with estimated sorption capacity of 63.8 mg/g and 59.9 mg/g for HT-rGO-N and CM-rGO-N respectively. The adsorption capacity for Hg is achieved in broad range of pH (pH 5–9) and can be described as high-performing compared with other amino based adsorbents reported in the literature. More importantly, these adsorbents showed very high selectivity towards Hg(II), outperformed the commercial activated carbon adsorbent with only ~16% mercury removal efficiency achieved in multimetallic solution consisting of Hg(II), Cd(II), Co(II), Cu(II) and Pb(II) ions in both solid and dispersed forms. Finally, these polyamine functionalized rGO adsorbents confirmed their notable performance in regeneration and removal of spiked mercury from natural waters mimicking real applications. These results demonstrated realistic water remediation capabilities of developed polyamine functionalized rGO adsorbents as promising candidates for environmental applications.