Research On Adsorption Of Hexavalent Chromium And Rhodamine B Onto(Reduced) Graphene Oxide/Montmorillonite Functional Materials

Graphene oxide(GO) and graphene can be used as excellent adsorbents in water pollution control due to their high specific areas and abundant oxygen-containing function groups. Montmorillonite(Mt), a traditional adsorbent, is also known for its excellent cation exchange capacity. However, GO is difficult to be separated from water due to its hydrophilicity, which hinder its application, and graphene nanosheets tend to aggregate during the preparation, resulting in significant loss in specific area. Thus, in order to make effective use of these two materials, improving the separability of GO and protecting graphene from aggregation are the key problems needed to be solved.In this study, graphene oxide/montmorillonite(GOCM) and graphene/montmorillonite(GCM) functional materials has been synthesized via a simple solvent method with GO and Mt as precursors. The properties of the obtained materials were also explored through a series of characterization methods. The adsorption of hexvalent chromium(Cr(VI)) and Rhodamine B onto GOCM/GCM functional materials were studied with various solution pH, contact time, adsorbents dosage, temperature and initial concentration. Besides, adsorption kinetics, thermodynamics and isotherms were also studied, and used to explain the adsorption process, as well as adsorption mechanism. Regeneration studies of the adsorbent were also done to evaluate its regenerability.The results showed that GO/graphene and montmorillonite successfully combined together to form stable functional materials, and CTAB played a key role in the synthesis. The combination of GO/graphene and montmorillonite made GO easily to be separated from solution, and effectively protecting graphene from aggregation, which helped GO and graphene to give full play to their adsorption performance. Results showed that adsorption of Cr(VI) onto GCM functional materials were favored in acidic media, and the rate of the adsorption followed pseudo-second-order kinetics and intraparticle diffusion model. The experimental data fit better to the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 12.86 mg/g, which was decline with increasing temperature. The mechanism of Cr(VI) adsorption onto GCM functional materials could be attributed to the electrostatic attraction and complexation. Furthermore, the Cr-loaded adsorbent could be reutilized efficiently with only a small decrease in adsorptive capacity. By contrast, the adsorptions of Rhodamine B onto GOCM/GCM functional materials were pH-independent. The adsorption rate also followed pseudo-second-order kinetics. Both Langmuir and Freundlich isotherm model could describe the adsorption process, which were found to be spontaneous and endothermic physical adsorption. Besides, the main mechanism in these processes was hydrogen bonding interaction. The maximum monolayer adsorption capacities of Rhodamine B by GOCM20 and GCM20 were 77.94 mg/g and 74.02 mg/g, respectively.