Current Developments and Future Trends in Photocatalytic Glycerol Valorization: Photocatalyst Development

Abstract

Glycerol is a significant byproduct of biomass conversion into biodiesel, and numerous studies have been focused on its valorization technologies in recent years. Photocatalytic glycerol valorization is a promising technology to convert solar energy into chemical energy by producing hydrogen and value-added liquid products. This technology is desirable from the point of view of both green chemistry and sustainable development since it can operate at ambient temperature and atmospheric pressure by using renewable solar energy. The key element for a successful photocatalytic glycerol valorization process is the development of highly active and stable photocatalysts. In this context, the present review deals with novel techniques to improve photocatalysts’ activity. It reviews the main characteristics, preparation methods, advantages, and drawbacks as well as the performance of different TiO2-based and non-TiO2-based photocatalysts for glycerol conversion. Also, an analysis is presented on the most effective approaches for increasing the photocatalytic activity, including cocatalyst deposition, doping with metallic and nonmetallic ions, development of carbonaceous composites, and formation of heterojunctions. The review also offers the readers ongoing challenges and opportunities for research on photocatalyst development to selectively convert glycerol into hydrogen and value-added liquid products.

Research Progress on the Photo-Driven Catalytic Production of Biodiesel

“…In addition, the photocatalytic materials can be prepared with different morphologies, such as multilayer nanosheets, multilayer hollow, and nano-helical column structures, which can promote the multiple reflection absorption of sunlight ( de Medeiros et al, 2020 ; Ghani et al, 2021 ). The most direct way is to directly add dyes, quantum dots, and other sensitizers to photocatalytic materials, which can also enhance light absorption ( Karimi Estahbanati et al, 2020 ).…”

“…The heterojunction is the interface region formed by the contact of two different semiconductors, which produces electron and hole concentration differences at the interface, thus forming a heterojunction electric field that can promote the separation of carriers. The morphology of photocatalytic materials affects their photocatalytic performance, and the exposure of different crystal faces may affect the interface reaction process ( Karimi Estahbanati et al, 2020 ). By adjusting the morphology of catalysts, including nanotubes, wires and rods, the excellent charge transferability is attributed to their high crystallization and oriented structure.…”

“…It has long been regarded not only as a sustainable green fuel, but also as a raw material or intermediate for the synthesis of fine chemicals (e.g., industrial solvents, surfactants, and lubricants) ( Zhang et al, 2019a ; Zhang et al, 2019b ). The carbon dioxide produced in the combustion process can be recycled through photosynthesis to slow down the greenhouse effect, which has good environmental protection performance ( Karimi Estahbanati et al, 2020 ). Biodiesel has the advantages of good combustion performance, good low temperature starting performance, excellent lubrication performance, and high safety performance, which can effectively reduce the wear rate of engine parts and prolong the service life of the engine ( Zhao et al, 2019 ; Guo et al, 2021 ).…”

“…Biodiesel production has been continuously increasing over the past years and is anticipated to increase further in the future ( Ahmed et al, 2016 ). In 2008, approximately 36.8 million liters of biodiesel were produced worldwide, and its total production is estimated to reach approximately 44 million liters in 2027 ( Zhang et al, 2019b ; Karimi Estahbanati et al, 2020 ). Overall, biodiesel is one of the most promising candidates for replacing fossil fuels to power the world.…”

Introduction of the year 2020

“…76 This topic was the subject of several reviews in 2020; among them, we would like to cite the report of Wang and coworkers, focused on the photocatalytic cleavage of C-O and C-C bonds in polysaccharides and lignin, 77 the minireview authored by Faungnawakij and coworkers, that reviewed recent efforts on photocatalytic biomass depolymerization and functionalization (including partial oxidation hydrogenolysis, and hydrogenation) 78 and the review focused on the heterogeneous photocatalysts employed in the glycerol reforming. 79 As concerning original works, cellulose derived Carbon Dots (CDs) have been tested as homogeneous photocatalysts for the solar metal-free reforming of different ligneocellulosic materials, including carbohydrates and glycerol. Notably, the process occurs efficiently also in untreated seawater.…”