Mechanisms of dyes adsorption on titanium oxide– graphene oxide nanocomposites

Graphene oxides (GOs), synthesized with different oxidation degrees and associated with Titanium dioxide (TiO2) nanoparticles show efficient adsorption processes for dye molecules in solution. The structural, morphology, electronic and optical features of the nanocomposites were investigated by dedicated methods. Water remediation was investigated through the adsorption efficiency of methylene blue (MB) dye as a function of the nanocomposites concentration from 1 to 5 g/L in solutions. While pristine TiO2 showed a maximum removal of ∼44%, the incorporation of the GO ensures the fast and complete elimination of MB within 9 min. The ball milling process contributed to the increase in the number of defects and surface area in the nanocomposites, which was demonstrated by ID/IG ratios by Raman spectroscopy and surface areas by BET. Pseudo-second-order and mechanistic kinetic models were considered, and the performed analysis points out the relevance of the pseudo-second-order model to account for the adsorption kinetics. The Langmuir and Freundlich isotherm models were applied to the experimental data to find an adequate model to describe the adsorption equilibrium, as well as the intra-particle diffusion model during the different adsorption stages involved in the TiO2/GO nanocomposites. The role of the oxidation degree of GO was clarified through their respective efficiency in the removal of the dyes.