Graphene Oxide (GO) Coated Metal-TiO2 Nanocomposites for Photocatalytic Applications

Abstract

Abstracts Chapter-1 This chapter provides a brief introduction to semiconductor-based photocatalysis, how TiO2 acts as a photocatalyst, and its advantages and applications, such as photocatalyst for the degradation of hazardous water pollutants and photocatalytic hydrogen production, are discussed in this chapter. To overcome its drawbacks, the modification of TiO2 with metal deposition and carbon-rich graphene oxide (GO) has been outlined. The related literature has been systematically reviewed, and a brief description of characterization techniques for assessing the properties of synthesized GO-modified metal- TiO2 nanocomposites has been provided. In this regard, the realized research gaps were mentioned with the objective of the current research work.

Chapter-2 Graphene oxide (GO), an atomic sheet structure made of sp2-bonded carbon atoms with superior optoelectronic, and catalytic properties, has attracted much interest. Incorporating a carbon-rich material, onto metal-loaded TiO2 is reported to increase the photocatalytic properties of resultant composites. This research aimed at the deposition of different amounts (1-5 wt%) of GO using the ultrasonication method on bare TiO2 and Ag (3wt%)-TiO2 (AT3) and studied their influence on piroxicam-20 degradation under visible light and methanol dehydrogenation under UV light. The prepared composites' structural, optical, and morphological properties were characterized using XRD, DRS, HR-TEM, FE-SEM, and XPS. HRTEM analysis confirmed the existence of GO layers and spherical-shaped Ag nanoparticles deposited over the TiO2 surface. GO(5wt%)@Ag(3wt%)-TiO2 (G5@AT3) displayed better photodegradation efficiency (78%) (k = 0.0082 min-1) under 120 min, and GO(1wt%)@Ag(3wt%)-TiO2 (G1@AT3) composite produced higher amount (427 mmol) of H2 from photocatalytic dehydrogenation of CH3OH under 5h relative to TiO2 (2 mmol), AT3 (166 mmol) and GO(5wt%)@TiO2 composite (GT5) (11 mmol). HRMS analysis was performed to identify the piroxicam-20 degradation intermediates. Thus, this research provides a proactive strategy highlighting the cooperative effect of Ag and GO loading to improve the photocatalytic efficiency of TiO2 photocatalyst using both UV-visible light irradiation. Chapter-3 The high efficiency of the production of hydrogen from alcohols is vital to the advancement of energy technology. This study thoroughly investigates the process of alcohol dehydrogenation utilising GO-modified Cu-TiO2 photocatalyst under UV light and sunlight exposure. GO-modified Cu-TiO2 photocatalyst was synthesised using the hydrothermal method. Various experimental techniques, including FESEM, HRTEM, XPS, and DRS, confirmed the formation of the ternary composite. The influence of different alcohols (methanol, ethanol, propanol) and their concentrations (same vol% and molarity) on the amount of hydrogen (H2) production was examined in this study. The study thoroughly investigated the impact of various parameters, such as the influence of GO and Cu loading on TiO2 and their combined effect, time course, nature of alcohol and the reaction conditions on the photocatalytic hydrogen production. The GO(0.5wt%)/Cu(3wt%)-TiO2 (G0.5C3T) composite demonstrated the highest quantity of hydrogen production during methanol dehydrogenation when subjected to both UV and sunlight irradiation. The composite exhibited remarkably about three-fold higher hydrogen evolution in sunlight(881 mmol) than in UV light(294 mmol). The exceptional performance of this composite can be attributed to the efficient transfer of charge carriers and the delayed recombination of electron-holes, which is a result of the cooperative effect of GO and Cu deposited over the TiO2 system. This approach offers a proactive strategy, signifying the synergetic effect of loading GO and Cu over TiO2 to enhance the photocatalytic hydrogen production, which is regarded as a green fuel solution, and turns these materials into useful energy sources by using inexpensively synthesised photocatalysts.

Chapter-4 Graphene oxide (GO) has now emerged as one of the most promising materials in different areas such as photocatalysis, adsorption, and energy storage due to its high surface area, unique layered structure, etc. Among various types of precursors, anthracite coal has attracted a lot of attention nowadays as it affords GO a high concentration of sp2 carbons, resulting in high conductivity and superior absorbance in the visible region. In this report, we have prepared GO-TiO2 nanocomposites as it is supposed to possess high photocatalytic activity owing to facile electron transmission from the conduction band of TiO2 to the GO surface, resulting in a much lower degree of electron-hole pair recombination. To boost the photocatalytic activity further, TiO2 was coated with Ag nanoparticles also. These hybrid structures were characterized by different analytical techniques, for example, XRD, HR-TEM, SEM, Raman spectroscopy, etc. The XRD pattern of these composites consists of characteristic peaks corresponding to GO, TiO2 and Ag. The HR-TEM studies confirm the presence of GO layers, cube-shaped TiO2 and spherical Ag nanoparticles. Phenol and 4-nitrophenol have been used as model pollutants to evaluate the photooxidation efficiencies under both UV and visible light irradiation. Under UV irradiation, the GO/Ag-TiO2 ternary nanocomposite shows better photooxidation efficiency (62%) compared to Ag-TiO2 (38%), GO-TiO2 (9%), GO (17%), TiO2 (8%) towards phenol degradation. The GO/Ag-TiO2 also has the highest photocatalytic activity towards the removal of phenol under visible light irradiation (34%). The ternary heterostructure (85%) also possesses superior photooxidation activity compared to, Ag-TiO2 (44%) and GO-TiO2 (71%) towards the degradation of p-nitrophenol under UV light radiation for 60 minutes. The above observation reveals that the cooperative effect of Ag, TiO2, and GO plays a crucial role in resulting in the high photooxidation activity of the GO/Ag-TiO2 hetero-nanocomposites.