Environment Friendly Synthesis of Reduced Graphene Oxide from Spent Lithium-Ion Battery Graphite and Its Nanocomposite with MoO3 Nanorods for Photocatalytic Hydrogen Evolution

Photocatalytic water splitting from solar H2 generation systems is of great interest as a sustainable fuel and an environmentally benign approach. A photocatalyst should be cost-efficient and highly productive to obtain a green H2 fuel. Thus, photocatalytic water splitting is significant for real-world applications. In the present work, we have successfully synthesized MoO3@rGO nanocomposite material with heterojunction as a stable and high-performance photocatalyst for the H2 evolution reaction in deionized (DI) water and natural seawater. First, MoO3 was prepared through a low-temperature hydrothermal method and composites with graphene oxide (GO) and reduced graphene oxide (rGO) precursors, followed by ultrasonication. rGO was obtained from GO, which is obtained from the spent graphite (anode material) by the modified Hummer's method. The rGO powder was reduced by an ascorbic acid-reducing agent under microwave irradiation using GO. The nanocomposite materials were characterized using XRD, Raman spectra, XPS, photoluminescence, FE-SEM, HR-TEM, and BET. The photocatalytic water splitting ability of MoO3@rGO was measured under visible light (λ ≥ 420 nm) irradiation with the TEOA sacrificial reagent. The H2 generation rate in DI water and natural seawater was found to be 2183.41 and 2294.26 μmol g–1 h–1, with an apparent quantum efficiency (AQE) of 5.72 and 5.98%, respectively. Such a high rate of H2 generated is ascribed to the novel surface contact between MoO3 and the rGO sheet as evident from HR-TEM images, wherein the rGO sheet is seen wrapped around MoO3. Consequently, the synergistic effect between MoO3 and rGO sheets is expected without the use of any other cocatalysts. Thus, electron–hole recombination is significantly minimized during the water reduction reaction. We believe that the MoO3@rGO nanocomposite is a potential photocatalyst for energy production.