Photocatalytic CO2 reutilisation to value-added products on metal-organic framework supported copper clusters

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Atmospheric carbon dioxide (CO2) is one of the biggest contributors to climate change and as CO2 concentration in the atmosphere is constantly increasing, solutions to prevent CO2 emissions are urgently needed. Shifting to renewable, carbon neutral or negative technologies could prevent further growth of CO2 levels. However, these technologies are able to reduce only further CO2 emissions. Meanwhile, CO2 storage and conversion to value added- products are promising strategies to tackle the problem in the current situation. Nonetheless, conversion of CO2 to other chemicals instead of storing it would be needed to solve the issue. Promising approaches for CO2 reutilisation to value-added products is the reduction to methanol or the addition reaction to another molecule to produce useful chemicals, such as amino or carboxylic acids. CO2 can be converted to value-added products by photoactivation. Photoactivation saves energy and resources as it can be performed in the presence of catalysts and by using light instead of thermal energy and therefore, it would be more plausible option in terms of sustainability. Homogenous photocatalytic CO2 reutilisation has been performed in synthesis of numerous products using metal cluster complexes; however, performing it in a heterogenous manner would have advantages in terms of catalyst separation, durability, and reusability. Copper is frequently used for CO2 reutilisation due to its' ability to activate CO2 molecules. Single atom catalysts (SACs) or clusters of few atoms could increase the reactivity of the metal centre anchored in heterogeneous supports, while improving the atom-economy of the processes. To the best of our knowledge, CO2 reutilisation for the synthesis of amino acids or carboxylic acids using heterogeneous photocatalysts based on SACs has not been extensively explored. Proposed solution and methodology This project aims to design of heterogenous photocatalysis for CO2 reutilisation. The focus is on the use of metal-organic frameworks (MOFs) as photoactive supports for Cu as catalytic centres. MOFs are highly uniform and crystalline porous materials with an enormous surface area forming a framework structure between organic linkers and metal nodes. Consequently, MOFs offer a great platform for catalyst deposition and designing of tailored catalysts for various applications. Porphyrin and pyrene-based organic molecules have excellent light absorption properties in the visible light region and therefore they are applicable photosensitizers. These photosensitizers can be incorporated to MOF structures as the linkers allowing the photocatalytic processes to undergo in the heterogenous phase, facilitating catalysts recovery and extending their lifetime. Moreover, the photocatalytic properties of the MOFs could be further tuned by deposition of Cu on them by post-synthetic deposition techniques. Cu is proven to activate CO2 molecules as well as it can be incorporated with photosensitizers allowing tuning of photocatalytic properties. By applying Cu SACs or clusters on the MOFs, it could be possible to enhance efficiency of the MOF-based photocatalysts. The rigid and stable structure and wide mesopores of MOFs allow multiple strategies for post-synthetic catalyst deposition, such as atomic layer deposition (ALD), wet impregnation and magnetron sputtering as a solvent-free technique. To obtain deeper understanding of structure-activity relationship in the catalysts, catalytic reactions will be explored in situ by X-ray photoelectron spectroscopy and ex situ by spectroscopic and microscopic techniques. Finally, computational studies will be carried out for understanding of the experimental results comparing with theoretical models.