A novel NH2-rich polymer/graphene oxide/organo-vermiculite adsorbent for the efficient removal of azo dyes

Abstract

A multifunctional polyethyleneimine-graphene oxide/organo-vermiculite composite (PGO/OVt) was successfully fabricated by introducing OVt (modified by dodecyl dimethyl benzyl ammonium chloride, 1227) and polyethyleneimine (PEI) onto GO. For PGO/OVt, the proportion of GO was 25%, while OVt accounted for 75%, which can not only effectively reduce the cost of GO-doped adsorbents, but also ensure a high adsorption efficiency. Various analyses, including FT-IR, XPS, AFM, SEM, TEM, TG-DTG, and XRD were used to characterize the structures and surfaces of PGO/OVt. The surface properties of graphene oxide (GO), the hydrophobicity of OVt, and abundant amino functional groups in polyethyleneimine made PGO/OVt an excellent, versatile adsorbent of Congo Red (CR) and Acid Red 1 (AR-1) in single and binary-dyes system. In single-dye systems, due to the existence of hydrogen bonding, π-π, hydrophobic, and electrostatic interactions between adsorbent and dyes, PGO/OVt exhibited excellent adsorption capacities of 570 mg/g and 365 mg/g for CR and AR-1, respectively. The adsorption processes were well described by pseudo-second-order kinetics (R2 > 0.99) and the Langmuir isotherm model (R2 > 0.98). The thermodynamic parameters demonstrated that the adsorption processes were nonspontaneous and endothermic. In the binary-dyes system, the maximum adsorption amount of CR was 491 mg/g, and that of AR-1 was 384 mg/g. The influence intensity factor (φ) revealed that the effect between the two components changed from competition to synergy with the variation of initial concentration. The synergistic effect indicated the possible presence of a π-π stacking effect between the molecules of adsorbed and dissociative dyes. Based on the obtained results, the resulting PGO/OVt was an efficient, and a lower cost adsorbent containing GO (GO-doped adsorbent). This work provided a reference for the development of GO composite adsorbents.