Synthesis of Sodium Acrylate and Acrylamide Copolymer/GO Hydrogels and Their Effective Adsorption for Pb2+ and Cd2+

A serial of cross-linked sodium acrylate and acrylamide copolymer/graphene oxide (P(AANa-co-AM)/GO) hydrogels with different mass ratios of acrylic acid (AA) to acrylamide (AM) and different contents of N,N-methylenebis(acrylamide) (MBA) were prepared via dispersive polymerization. The prepared hydrogels were characterized by XRD, FT-IR, TGA, SEM, and BET in detail. The removal efficiency of Pb2+ and Cd2+ on the P(AANa-co-AM)/GO hydrogel have been improved significantly due to the addition of 1.0 wt % of GO. The P(AANa-co-AM)/GO hydrogel with AA/AM = 1 and 0.8 wt % of MBA has the highest removal efficiency for Pb2+ and Cd2+ and a suitable swelling ratio, which was selected as the adsorbent for systematic adsorption of Pb2+ and Cd2+ from aqueous solutions. The adsorption capacity and removal efficiency of Pb2+ and Cd2+ on the P(AANa-co-AM)/GO hydrogel were dependent on pH, initial heavy metal ion concentration, and adsorbent dosage. The presence of 0.01-0.05 M Mg2+ or Ca2+ has an obvious effect on the adsorption of Cd2+. The adsorption kinetics and adsorption isotherms of Pb2+ and Cd2+ on the P(AANa-co-AM)/GO hydrogel followed a pseudo-first order model and the Langmuir isotherm model, respectively. The maximum adsorption capacity of Pb2+ and Cd2+ on the P(AANa-co-AM)/GO hydrogel were calculated to be 452.3 and 196.4 mg/g at 298 K, respectively. The XPS analysis revealed that the adsorption mechanism of Pb2+ and Cd2+ on the P(AANa-co-AM)/GO hydrogel was ascribed to the chelation of -COO- with Pb2+ and the ion-exchange of -COO-Na+ with Cd2+, respectively. The P(AANa-co-AM)/GO hydrogel possesses good reusability and excellent fixed-bed column operation performance, which suggests that the P(AANa-co-AM)/GO hydrogel can be considered as a promising adsorbent for removing heavy metal ions from practical wastewater.