Adsorptive decontamination of Cu2+-contaminated water and soil by carboxylated graphene oxide/chitosan/cellulose composite beads

Abstract

Graphene adsorbents have been applied to remove diverse pollutants from aqueous systems. However, the mechanical strength of most graphene adsorbents is low and the fragile graphene sheets are released into the environment. In this study, we prepared carboxylated graphene oxide/chitosan/cellulose (GCCSC) composite beads with good mechanical strength for the immobilization of Cu2+ from both water and soil. The proportional limit of GCCSC beads was 3.2 N, a much larger value than graphene oxide beads (0.2 N). The largest pressure for GCCSC beads recorded before brittle failure was 26 N. The Cu2+ adsorption capacity of GCCSC beads was 22.4 mg/g in aqueous systems at initial Cu2+ concentration of 40 μg/mL, which is competitive with many efficient adsorbents. The partition coefficient (PC) for the Cu2+ adsorption onto GCCSC beads was 1.12 mg/g/μM at Ce of 0.83 mg/L and qe of 14.3 mg/g. The PC decreased to 0.055 mg/g/μM at Ce of 26.0 mg/L and qe of 22.4 mg/g. The adsorption kinetics of Cu2+ on GCCSC beads were moderately fast and required approximately 3 h to reach equilibrium with a k2 of 0.0021 g/(mg·min). A lower temperature and higher pH slightly increased the adsorption capacity of GCCSC beads. The ionic strength did not influence the adsorption. The porous structure of GCCSC beads blocked the direct contact between soil and the graphene surface; thus, a high Cu2+ immobilization efficiency was achieved by GCCSC beads applied to soil. The implications for the design of high-performance graphene adsorbents for water and soil remediation are discussed.