Lignin-based materials for light-driven redox biotransformation

Abstract

Chapter 1 elucidates lignin and their attractive properties (e.g., physical properties, redox activity, and metal ion chelation/reduction) as a functional material. Recent developments in lignin processing, integration, and applications in the areas of energy conversion, energy storage, and environmental remediation are outlined. This chapter paves the way to future potentials and opportunities of lignin as a renewable material for energy and environmental applications. Chapter 2 describes a sustainable photosynthetic platform through lignin-assisted stabilization of porous CaCO3 vaterite microspheres for integrated artificial photosynthesis through encapsulation of key active components such as photosensitizer (eosin y, EY) and redox enzyme (L-glutamate dehydrogenase, GDH). The lignin-vaterite/EY/GDH photobiocatalytic platform enabled regeneration of reduced nicotinamide cofactor under visible light and facilitated rapid conversion of α-ketoglutarate to L-glutamate. This chapter provides a simple approach for solar-to-chemical conversion using a sustainable, integrated light-harvesting system. Chapter 3 demonstrates the capability of lignin-induced vaterite as a versatile sacrificial-template for the synthesis of nanostructured metal oxide minerals [e.g., Zn(CO$_3$)$_x$(OH)$_y$⋅n H$_2$O, FeOOH, Cu$_2$Cl(OH)$_3$, and MnCO$_3$] through a simple and environmentally friend procedures. Urchin-like ZnO nanostructures were prepared followed by calcination the as-synthesized zinc hydroxide carbonate at different temperatures, and their photocatalytic performance in H$_2$O$_2$ production was examined under simulated sunlight irradiation, which was further coupled with H$_2$O$_2$-mediated peroxygenase catalytic reaction. This results suggests a plausible strategy for facile synthesis of nanostructured electrocatalysts through biomimetic CaCO$_3$ mineralization. Lastly, Chapter 4 presents the bias-free, solar reformation of lignin coupled with redox biotransformation in a tandem structure of a BiVO$_4$ photoanode and perovskite photovoltaic. BiVO$_4$-catalyzed photoelectrochemical oxidation of lignin facilitated the fragmentation of higher molecular weight lignin into smaller carboxylated aliphatic and aromatic acids. Lignin oxidation induced photocurrent generation at the photoanode, which enabled efficient electroenzymatic reactions at the cathode. This chapter shows the oxidative valorization of lignin as well as biocatalytic reductions in an unbiased biocatalytic PEC platform, which provides a new strategic approach for photo-biocatalysis using naturally abundant renewable resources.