Adsorption of Cd(II) in water by graphene oxide/calcium alginate hydrogel composite membrane

The crosslinked graphene oxide (GO)/calcium alginate (CA) hydrogel composite membranes, prepared by blending GO, porogenas as well as Na alginate hydrogel (SA), cross-linking with CaCl₂, were used as adsorbent for wastewater containing heavy metal ions. SEM and TEM were used to characterize the composite membranes. The influences of GO on the mechanical properties, average pore diameter, water flux and surface functional groups of the composite membrane were analyzed. To explore the adsorption performance of GO/CA hydrogel composite membrane, the influencing factors of Cd(II) adsorption including pH (6-7), initial ion concentration, contact time and temperature (all positively correlated) were investigated. The composite membranes before and after adsorption of Cd(II) were characterized by FTIR and XPS; The adsorption kinetics and adsorption isotherm model were introduced to analyze the adsorption mechanism. The results show that the introduction of GO improves the mechanical properties, average pore diameter and water flux of the composite membrane. The adsorption process follows the Langmuir isotherm, belonging to the monolayer adsorption. The maximum adsorption capacity is 173.61 mg/g. The pseudo-first and pseudo-second adsorption kinetics could describe the adsorption process at low and high concentration, respectively. The adsorption mechanism is mainly physical force adsorption and ion exchange. The recyclability of the GO/CA hydrogel composite membranes was demonstrated by five successive adsorption-desorption cycles.