Liquid-Phase Plasma-Assisted in Situ Synthesis of Amino-Rich Nanocarbon for Transition Metal Ion Adsorption

Amino-modified nanocarbon (NH2-C) has been widely used as an adsorbent for transition metal ion adsorption due to its high specific surface area, high electrical charge, and the ability to form a coordinate linkage to a transition metal ion. In this work, NH2-C was successfully synthesized from a mixture of phenol and (3-aminopropyl)triethoxysilane (APTES) through solution plasma processing, which performs both carbonization and amination simultaneously. This synthesis method eliminates the need to functionalize carbon with amino groups, as is required in the conventional process. Our NH2-C shows a better dispersion and a higher number of amino groups on both the external surface and inner pores, which enhances the adsorption capacity. The maximum capacities for Cu2+, Zn2+, and Cd2+ adsorption were 144.9, 115.4, and 102.0 mg g–1, respectively. These values were higher than those of five typical NH2-Cs synthesized by a conventional process. Based on the adsorption mechanism derived from adsorption kinetic, isotherm, and thermodynamic studies, the transition metal ions were chemisorbed to the surface in a monolayer endothermically and spontaneously. Moreover, it was found that NH2-C was suitable for use in ten consecutive adsorption–desorption cycles without significant loss of adsorption capacity.