Adsorption and photocatalytic removal of murexide using ZnO/rGO and ZnO/g-C₃N₄ composites

The combination of semiconductor nanoparticles with a substrate to form nanocomposites is known to improve the properties of the resulting material. The new composite forms a synergy of the precursor materials and chemistry plays an important role in the design and synthesis process of these compounds. In this study, the removal efficiency of two composites of graphene oxide and protonated graphitic carbon nitride functionalized with ZnO was explored in the removal of murexide (Mx) from water. The uniqueness of this study is premised on the synthesis process as well as the application in the removal of murexide. The ZnO nanoparticles were prepared via the thermal decomposition of a precursor compound (N-butyl-N-phenyl dithiocarbamate), and a wurtzite crystal phase with a rod-like structure was confirmed. The formation of the nanocomposites of the ZnO with the two carbonaceous materials (graphene oxide and protonated graphitic carbon nitride) was achieved ex-situ to afford ZnO/GO, and ZnO/ gCN respectively. The physicochemical, structural, and optical properties of the prepared nanocomposites were studied using techniques including Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The morphology of both nanocomposites revealed a similar structure showing a conglomerate of sheets, from the carbonaceous materials, and short rods (from the ZnO), which were intertwined on the surface. The photocatalytic and adsorption removal capacities of the composites were assessed using methyl orange and were found to be 82.5 and 96.5% photo removal efficiency for ZnO/GO and ZnO/P-gGN respectively. In the adsorption study, to be influenced by the nature of the support material. In the adsorption study, Mx sorption followed the Langmuir isotherm with a maximum adsorption capacity of 48.30 mg/g obtained for ZnO/P-gGN. Pseudo-second order kinetic model gave the best fit to the experimental data, and possible mechanisms of action of each composite were proposed. Overall, both the composites showed enhanced activity compared to pristine ZnO and the improvement in the removal capacity was influenced by the nature of the support material.