Graphene oxide interpenetrated polymeric composite hydrogels as highly effective adsorbents for water treatment

Abstract

Recent studies showed that polymeric hydrogels presented promising applications in adsorption to various water contaminants. However, the usages of these synthetic hydrogels are hindered by several inherent shortages, e.g. limited inner porosity, low adsorption capacity and long equilibrium time. In this study, synthetic GO interpenetrated poly(acrylic acid) (PAA) hydrogels as 3D highly-efficient adsorbents were prepared and systematically studied for the first time. The mediating ability of GO on the inner structure and adsorption capacities is examined using two types of PAA hydrogels (PAA1 and PAA2 with different inner structures, prepared by in situ cross-linked polymerization of monomer AA). The results indicated that the prepared PAA2/GO hydrogels exhibited a well-defined and interconnected 3D porous network, which allowed the adsorbate molecules to diffuse easily into the absorbent. The adsorption experiments indicated that the obtained interconnected polymeric composite hydrogels could efficiently remove cationic dyes and heavy metal ions from wastewater; the highest adsorption capacity of the prepared PAA2/GO composite hydrogels could reach as high as 1600 mg g⁻¹, which is highly promising in the treatment of environmental toxins. Moreover, the initial concentration, pH value, desorption ratio, dynamic kinetics and isotherms of the methylene blue (MB) adsorption processes of the prepared PAA2/GO composite hydrogels were also studied in detail. The experimental data of MB adsorption fitted the pseudo-second-order kinetic model and the Langmuir isotherm very well, and the adsorption process was controlled by the intraparticle diffusion. Moreover, due to its facile preparation and low-cost, the GO interpenetrated PAA composite hydrogels may function as promising adsorbents for wastewater treatment, and this method might also be extended to improve the adsorption capacity of other polymeric hydrogels.