Layered double hydroxide (LDH) nanomaterials with engineering aspects for photocatalytic CO2 conversion to energy efficient fuels: Fundamentals, recent advances, and challenges

Carbon dioxide concentrations are constantly rising, resulting in global warming. Therefore, the photocatalytic conversion of CO2 to valuable products is receiving most attention. In this process, clean and sustainable energy like sunlight is used to reduce CO2 through photocatalysis. The scientific community continues to develop photocatalysts with enhanced properties to increase the efficiency of CO2 conversion. Several photocatalysts have been developed that have remarkable ability to reduce CO2, but have limitations such as insufficient bandgap energy, inappropriate valence and high recombination rate, and limited light absorption. Recently, layered double hydroxides (LDHs) have been studied extensively due to their tunable CO2 adsorption properties, morphologies, unique 2D layered structure, and easily alterable range for anions and cations. Moreover, LDH shows excellent physicochemical and electrical properties such as surface area and stability. This study aims to discuss LDH fundamentals, advances, and significance in different photocatalytic processes. The initial focus has been given to the fundamentals of LDH semiconductors including the basics of the LDH materials such as structure, properties, and types of classification. Then, the recent development of bimetallic and trimetallic LDH are systematically discussed. The efficiency enhancement of LDH semiconductors, including the morphology alternations, Schottky junctions, sensitizations, heterojunction, and Z-scheme heterojunction formations, are also disclosed. Moreover, the mechanism of CO2 reduction by photocatalysis, the limitations and pros of using LDH for CO2 conversion, and, recent studies for enhancing LDH efficiency are included. Finally, opportunities for utilizing LDH-based materials are discussed with future recommendations for different applications.