Metal oxide based nanocomposite materials for the chemicals synthesis and energy applications

Abstract

Title: Metal oxide based nanocomposite materials for the chemicals synthesis and energy applications The increasing research interest has been focused on developing alternative strategies to utilize sustainable renewable energy worldwide efficiently. The imminent shortage of fossil fuels and growing environmental concerns are pushing scientists and engineers to exploit sustainable, clean, and highly efficient technologies to supply and store energy. Moreover, our earth atmosphere provides a universal feedstock of N2, CO2, and H2O, which can be potentially converted to various fine chemicals and fuels. Another issue the industrial sector faces for fine chemical production is the operational risk with carbon emission. Concerning this fact, light-induced chemical synthesis is an eco-friendly and greener approach. In this regard, various photo-electrochemical energy storage/conversion systems, such as water splitting, electrochemical capacitors (ECs), CO2 reduction/activation, and fuel cells (FCs), are becoming more appealing than ever. Unfortunately, the widespread commercialization of these innovative electrochemical energy technologies is still greatly hampered by their high cost, insufficient long-standing durability, and operability problems, which are ultimately related to severe materials challenges. Therefore, elaborate exploration and rational design of new materials that can lower the cost, increase efficiency, and improve the durability will have a significant impact on making these promising energy technologies commercially viable. In this prospect, nanostructures metal-oxides have attracted much attention because metal oxides are the fascinating functional materials due to their low cost and ease of synthesis. Further, to diminish the detrimental environmental impact associated with chemical industries like high-temperature operation and complicated reaction setup, a plethora has been developed to utilize the naturally occurring sunlight for the semiconductor mediated chemical synthesis as a greener approach. In this context, metal oxide-based nanocomposites materials have been developed and applied for energy conversion purposes by electrocatalysis, chemical, fuel, and chemical production by traditional thermal catalysis and photocatalysis, respectively. The base materials investigated here are mixed transition metal oxide, spinel, and perovskite-type metal oxide. However, metal oxide alone is not sufficient to exhibit the orthodox properties in traditional catalysis, electrocatalysis, and photocatalysis. Hence, a suitable support material needs to be integrated with a metal oxide to make it worthy in the afore-mentioned targeted applications. In the electrocatalytic fuel cell, nanoporous zeolite was considered to make nanocomposite because it has a high surface area, mesoporous nature, and surface hydroxyl groups, and the metal oxide can evenly be dispersed, thus, providing easy accessibility which can activate the reactant molecule efficiently. However, zeolite is non-semiconducting in nature, thus, a semiconductor material graphitic carbon nitride and carbon dot have been considered to fabricate heterojunction materials in solar fuel production and chemical synthesis. For further improvement, noble metal nanoparticles Au and Pd have been decorated over metal oxide/graphitic carbon nitride heterojunction nanocomposite photocatalysts. The applications of these materials in fuel and chemical synthesis are demonstrated with the combinatorial contribution from three individual catalytic processes comprising of traditional catalysis, electrocatalysis, and photocatalysis. Anode materials for methanol oxidation reaction for methanol fuel cells have been developed, which exhibit better catalytic activity than the state-of-art electrocatalysts. The traditional catalysis and photocatalysis are employed for aromatic and benzylic C-H bond activation, aerobic oxidation of alcohol, amines, oxidative condensation reaction, co-catalyst/additive-free CO2 activation reaction, esterification and transesterification reaction, and synthesis of important drug intermediate 2,4-quinazoline-di-one. The solar fuel applications are carried out via water splitting and CO2 reduction via suspension photocatalysis and photoelectrochemical processes. Throughout this thesis, the emphasis is devoted to establishing that visible light is our future energy source and an alternative platform that can replace the traditional thermal energy-based catalytic processes for bulk chemicals and fuel production.