Valorizing Glycerol into Valuable Chemicals Through Photocatalytic Processes Utilizing Innovative Nano-Photocatalysts

Significant research efforts focused on the utilization of renewable resources have been increased as a result of the development of environmentally friendly and efficient methods of chemical synthesis. Glycerol, a by-product of biodiesel production, has been identified as a promising renewable feedstock due to its abundant availability. Photocatalysis represents an innovative and sustainable pathway for the conversion of glycerol into a variety of valuable chemicals, including hydrogen, alcohols, aldehydes, ketones, acids, and other high-value compounds. Through the cleavage of either a single C–H or O–H bond, glycerol can be transformed into four distinct intermediates, each leading to different products. This chapter offers an in-depth examination of the photocatalytic valorization of glycerol, emphasizing the role of various nano-photocatalysts in this process. It highlights the critical function of nano-photocatalysts in augmenting the efficiency of glycerol conversion reactions, achieved through increased surface area, optimized charge separation, and enhanced light absorption properties. The complexity of the photocatalytic process is influenced by several catalyst characteristics, such as crystalline structure, surface morphology, hydroxyl group presence, substrate and ion adsorption, all of which directly impact the activity and selectivity of the reaction. Furthermore, the kinetics of the photocatalytic process are intricately affected by substrate concentration, reflecting a complex dynamic interplay between substrate oxidation and carrier recombination (back-reactions), mediated by the substrate itself. This comprehensive analysis provides valuable insights into the multifaceted nature of photocatalytic glycerol valorization and the potential of nano-photocatalysts to revolutionize this field. Numerous semiconductor catalyst materials are available for the valorization of glycerol, including TiO2, MOF, WO3, Bi2WO6, g-C3N4, and ZnO, each of which is discussed in detail. Approaches such as elemental doping, co-catalyst hybridization, heterojunction formation, and morphological control can be employed to enhance the photocatalytic activity of these materials. Additionally, synthesis methods such as sol–gel, hydrothermal, and co-precipitation techniques exert influence on the structural, morphological, and optical properties of the photocatalysts. Titanium dioxide (TiO2) is recognized as an efficient photocatalyst under UV light, but its wide energy bandgap (~3.2 eV), high rate of electron–hole recombination, and limited surface area restrict its photocatalytic performance. Zeolitic imidazolate frameworks, novel photocatalytic materials, are characterized by high specific surface area and abundant structural variability but suffer from poor charge carrier separation efficiency. Tungsten trioxide (WO3) is notable for its high efficiency, low cost, high catalytic activity, low toxicity, abundant availability, and environmental friendliness. Its narrow bandgap, high electron mobility, and good chemical stability make WO3 suitable for a wide range of applications, including environmental remediation and solar energy conversion. Bismuth tungsten oxide Bi2WO6 (BWO) possesses a relatively low band gap energy (2.70–3.0 eV) and its morphology can be easily controlled, owing to its unique layered crystal structure. Graphitic carbon nitride (g-C3N4) features a compatible bandgap (2.7 eV) and can be synthesized from abundant precursors, enhancing its availability and cost efficiency. Its high stability, non-toxicity, and structural versatility make g-C3N4 suitable for various applications. Zinc oxide (ZnO) is a widely studied material with a direct bandgap of 3.30–3.37 eV at room temperature. It offers advantages over TiO2 due to its higher electron mobility, leading to increased electronic transfer efficiency and reduced recombination losses. Additionally, Zinc oxide (ZnO) is attractive due to its cost-effectiveness, non-toxic nature, and the ability to retain high stability and crystallinity. However, its application is limited to ultraviolet (UV) excitation, which constitutes only a minor portion of the solar spectrum. Therefore, this chapter summarizes the current state of knowledge and highlights the potential for nanomaterials to facilitate the sustainable conversion of glycerol into valuable compounds. This chapter also emphasizes recent progress and existing challenges in the field, particularly the creation of innovative nano-photocatalysts with customized characteristics. Serving as a comprehensive guide for researchers and scientists working in the areas of catalysis, renewable energy, and sustainable chemistry, this chapter aims to inspire continued exploration and innovation in the specialized area of glycerol valorization.