Metal Oxide-Decorated Graphene Oxide Nanocomposites for Catalytic and Photocatalytic Applications

Abstract

Graphene and graphene-based materials, owing to their unique physical and chemical properties, have attracted considerable attention across the scientific communities worldwide. It has heralded a revolution in almost all the branches of materials science and chemistry. The attractive properties of graphene have led the extensive investigations to design and develop low-cost and high yield preparation protocols for chemically-derived graphene (graphene oxide). Graphene oxide (GO), a two-dimensional sheet of sp2 hybridized carbon, has received increasing attention as it possesses similar properties to that of graphene, as well as the availability of polar functional groups i.e. hydroxyl, carboxyl, etc. on its planar surface. Because of its high surface area, thermal stability, mechanical and electrical properties, it can be used as a potential supporting material and has already shown many promising applications.

Keeping this in mind, the overall objectives of this PhD thesis is broadly focused on two main objectives; (1) synthesis of GO based nanocomposite such as GO–SnO2 ,GO-CuFe2O4 and GO-MnO2 for catalytic application and (2) Synthesis of GO based GO-SnO2-TiO2 and GO-CuFe2O4-ZnO ternary nanocomposite for photocatalytic application. In the heterogeneous catalysis part, emphasis was given on using graphene oxide based binary nanocomposite for the synthesis of biologically active molecules. As there was no significant literature(s) available at the start of my PhD work demonstrating the use of graphene oxide-based heterogeneous catalyst for biologically active molecules syntheses, it gave us a possible scope to explore and investigate towards the objective. In the first major project, a graphene oxide–SnO2 nanocomposite was utilized as potential nanocatalyst for biologically active molecules synthesis. For the first time, we have demonstrated the use of a GO–based nanocomposite as an extremely efficient catalyst for the synthesis of β-enaminones and β–enaminoesters biologically active molecules (RSC Adv., 2015, 5, 39193). The GO–SnO2 nanocomposites exhibited synergistically more superior catalytic efficiency compared to pure graphene oxide and SnO2 nanoparticles. Highlighting the importance of recyclability, in the next project, graphene oxide based magnetic nanocomposite was explored as novel recyclable heterogeneous catalyst for xanthenes synthesis. Magnetic graphene oxide based nanocomposites are important in catalysis as they can minimize the amount of catalyst loss during recyclability study and make the catalyst separation easy. In the second objective, a facile, efficient and environmentally-friendly protocol for the synthesis of xanthenes by graphene oxide-based
GO-CuFe2O4 nanocomposite was developed by one-pot condensation route. (Sci. Rep.7, 2017: 42975). This approach offers several advantages such asshort reaction times, high yields, easy purification, a cleaner production and superior recovery and reusability of the catalyst by a magnetic field. Continuing this narrative, in the next objective, emphasis was given for the synthesis of a simple magnetic graphene oxide-MnO2 binary nanocomposite as an efficient nanocatalyst for other biologically active molecule synthesis. GO-MnO2 nanocomposite was used as an efficient catalyst for chalcones synthesis (Manuscript Submitted).The superior catalytic activity of this GO-based nanocomposite can be attributed to the synergistic interaction between GO and metal oxide nanoparticles, high surface area and presence of small sized metal oxide nanoparticles.

In the next two projects, the focus was given to design GO-based ternary nanocomposite photocatalyst to degrade the toxic organic dyes present in water via solar light driven photocatalysis. Towards this objective, a, GO-SnO2-TiO2 ternary nanocomposite was designed as an efficient photocatalyst to degrade toxic organic dyes (RSC Adv., 2015, 5, 39193). This ternary (GO-SnO2-TiO2) nanocomposite have shown enhanced photocatalytic performance due to the stepwise structure of conduction band-edge (CB) levels of the individual component, TiO2 (CB)> SnO2(CB)> GO. It was found that such energy levels are beneficial for photo-induced electrons to transfer from TiO2 CB via SnO2 CB to GO, which can efficiently separate the photo-induced electrons and hinder the charge recombination in electron-transfer process, thus, enhancing its photocatalytic performance. In the last objective, emphasis was given to design magnetic GO-CuFe2O4-ZnO ternary nanocomposite as an efficient photocatalyst for the degradation of a series of toxic phenol and organic dyes under sunlight (New J. Chem., 2017, 41, 10568–10583.). In this work, attempts were made for efficient separation and recyclability process and to increase the photocatalytic efficiency under sunlight. The ternary nanocomposite was found to be more active as compared to their binary composite. The improved photocatalytic activity of the ternary nanocomposite can be ascribed due to the superior light assimilation, proficient charge transfer process, synergistic effect, high surface area, as well as superior durability of the composite. Solution combustion route was used to synthesize the GO based ternary photocatalyst which holds great promise for the synthesis of other GO-based nanocomposites.