Synthesis and Characterization of Graphene Based Nanocomposites for Adsorption, Catalysis and Antimicrobial Applications

Abstract

Facile in situ synthesis of Graphene oxide–gold (GO–Au), graphene oxide-silver (GOAg) and reduced graphene oxide-ZnS (rGO-ZnS) nanocomposite has been reported. These composites were studied for their applications as (i) an adsorbent materials for the removal of some toxic industrial dyes from aqueous medium, (ii) as a catalyst for the individual and simultaneous reduction of mixture of dyes and nitro compound and as (iii) an antibacterial agent for the destruction of some harmful microorganisms existent in wastewater. Graphene oxide, GO was prepared using a modified Hummers method. Gold (Au), silver (Ag) and zinc sulphide (ZnS) nanoparticles were integrated on GO sheets by reducing Au+ ions, Ag+ ions and Zn++ ions on the surfaces of GO sheets using sodium citrate, sodium borohydride (NaBH4) and sodium sulphide in DMF as a reducing agent respectively. Prepared nanocomposites were extensively characterized for their morphology and composition using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy and thermal gravimetric analysis (TGA) techniques. All prepared nanocomposites demonstrated remarkable adsorption capacities and desorption for malachite green (MG) and ethyl violet (EV) dyes. Various experimental parameters affecting adsorptive behavior of nanocomposites such as temperature, pH, time of contact between dyes and adsorbent, and adsorbent dose were evaluated thoroughly. Experimental data was simulated with different adsorption isotherms and kinetic models to evaluate adsorption behavior of both dyes. Results confirmed that adsorption of both the dyes followed Langmuir adsorption isotherm in case of GO-Ag and Freundlich isotherm in case of GO-Au nanocomposite. Also, pseudo 2nd order kinetic model was found to be favorable in case of all nanocomposites. Moreover, adsorbent could be well regenerated in a suitable media for both dyes without any loss in removal efficiency. The catalytic performance for the reduction of 2-nitroaniline (2-NA) has been investigated in detail using GO-Au and GO-Ag nanocatalysts. Most importantly, nanocomposites under study showed simultaneous adsorption of cationic and anionic dyes from water and simultaneous catalytic reduction of a mixture of dyes (MG, MO, and EV) and 2-NA. Additional advantages of prepared nanocomposite were their iii antibacterial activities due to the presence of different metal/metal sulphide nanoparticles. Two bacterial strains (Gram-negative bacterium, E. coli and the Grampositive bacterium, S. aureus) were used to test antibacterial activity of composite and the results confirmed the remarkable performance of the nanocomposites in destroying harmful pathogens. So, considering the facile synthesis process and the multiple functions of all the nanocomposites, this work opens up a tremendous opportunity to use GO based nanocomposites in wastewater treatment and nanomedicines. Also, this work opens up a tremendous opportunity to bring GO based nanocomposites from experimental research to practically applied materials for wastewater treatment