ABSTRACT
Catalytic CO2 hydrogenation is an effective approach to producing clean fuels, but this process is expensive, in addition to the low efficiency of catalysts. Thus, photothermal CO2 hydrogenation can effectively utilize solar energy for CH4 production. Metal-organic framework (MOF) derived materials with a controlled structure and morphology are promising to give a high number of active sites and photostability in thermal catalytic reactions. For the first time, a novel heterostructure catalyst was synthesized using a facile approach to in situ grow MOF-derived 0D Co3O4 over 1D TiO2 nanowires (NWs). The original 3D dodecahedral structure of the MOF is engineered into novel 0D Co3O4 nanospheres, which were uniformly embedded over Ni-dispersed 1D TiO2 NWs. In situ prepared 10Ni-7Co3O4@TiO2 NWs-I achieved an excellent photothermal CH4 evolution rate of 8.28 mmol/h at 250 °C under low-intensity visible light, whereas UV light treatment further increased activity by 1.2-fold. UV irradiations promoted high CH4 production while improving the susceptibility of the catalyst to visible light irradiation. The photothermal effect is prominent at lower temperatures, due to the harmonization of both solar and thermal energy. By paralleling with mechanically assembled 10Ni-7Co3O4/TiO2 NWs-M, the catalytic performance of the in situ approach is far superior, attributing to the morphological transformation of 0D Co3O4, which induced intimate interfacial interactions, formation of oxygen vacancies and boosted photo-to-thermal effects. The co-existence of metallic/metal oxide Ni-Co provided beneficial synergies, enhanced photo-to-thermal effects, and improved charge transfer kinetics of the composite. This work uncovers a facile approach to engineering the morphology of MOF derivatives for efficient photothermal CO2 methanation.
ABSTRACT
Introducing new materials with low cost and superior solar harvesting efficiency requires urgent attention to solve energy and environmental challenges. Titanium carbide (Ti3C2T x ) MXene, a 2D layered material, is a promising solution to solve the issues of existing materials due to their promising conductivity with low cost to function as a cocatalyst/support. On the other hand, metal-organic frameworks (MOFs) are emerging materials due to their high surface area and semiconducting characteristics. Therefore, coupling them would be promising to form composites with higher solar harvesting efficiency. Thus, the main objective of this work to disclose recent development in Ti3C2T x -based MOF nanocomposites for energy conversion applications to produce renewable fuels. MOFs can generate photoinduced electron/hole pairs, followed by transfer of electrons to MXenes through Schottky junctions for photoredox reactions. Currently, the principles, fundamentals, and mechanism of photocatalytic systems with construction of Schottky junctions are critically discussed. Then the basics of MOFs are discussed thoroughly in terms of their physical properties, morphologies, optical properties, and derivatives. The synthesis of Ti3C2T x MXenes and their composites with the formation of surface functionals is systematically illustrated. Next, critical discussions are conducted on design considerations and strategies to engineer the morphology of Ti3C2T x MXenes and MOFs. The interfacial/heterojunction modification strategies of Ti3C2T x MXenes and MOFs are then deeply discussed to understand the roles of both materials. Following that, the applications of MXene-mediated MOF nanotextures in view of CO2 reduction and water splitting for solar fuel production are critically analyzed. Finally, the challenges and a perspective toward the future research of MXene-based MOF composites are disclosed.
ABSTRACT
In efforts to achieve a sustainable development goal, the utilization of CO2 to generate renewable fuels is promising, as it is a sustainable technology that provides affordable and clean energy. To realize the production of renewable green fuels, a proficient and low-cost technology is required. Using photo/thermal catalytic process, the goal of sustainable CO2 hydrogenation can be achieved. There have been several types of catalysts under exploration, however, they are expensive with limited availability. In the current development, green materials such as mineral clays are emerging as cocatalyst/supports for CO2 hydrogenation. Clays are bestowed with various beneficial properties such as a large surface area, high porosity, abundant basic sites, excellent thermal stability and chemical corrosion resistance. Clays are promising materials that can drastically reduce the cost in catalyst preparation, partially fulfil the energy demand and reduce greenhouse gas emission. This review aims to focus on the various types of clays and their applications in the field of photo/thermal CO2 hydrogenation to renewable fuels. Firstly, the classifications of clays are provided, whereby they can be differentiated based on their silicate layers, namely 1:1 and 2:1 type clay and their properties are thoroughly discussed to provide advantages and applications. The applications of various clays such as kaolinite, halloysite, montmorillonite, attapulgite, saponite and volkonskoite for CO2 hydrogenation reactions are systematically discoursed. In addition, various approaches to improve the capability of raw clays as catalyst support are critically discussed, which include thermal treatment, exfoliation, acid-leaching and pillaring approaches. A critical discussion regarding the engineering aspects to further enhance clay-based catalyst for CO2 hydrogenation are further disclosed. In short, clays are freely available materials that can be found in abundance. However, there are many more different types of natural green clays that have not been studied and explored in various energy applications.