Design and Development of Nanostructured Covalent Organic Framework Hybrid Composites as Platform for Sunlight-driven CO2 Reduction PDF Download

Author: Vishnu Nair Gopalakrishnan
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Languages : en
Pages : 0

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Book Description
The ensuing thesis examines the conversion of carbon dioxide (CO2) to value-added chemical and fuels under solar light irradiation by employing some of the emerging photocatalytic materials known as covalent organic frameworks (COFs). This approach of photocatalytic process is considered to be one of the most viable remedies to global warming and energy crisis dilemmas. Importantly, this thesis delivers three novel nanostructured hybrid composites based on COFs for photocatalytic CO2 reduction to value-added chemicals and fuels. Light-harvesting, charge separation, and surface reactions are critical aspects that have an enormous impact on CO2 photoreduction. Covalent organic frameworks can be suitable candidates for these processes as they offer outstanding structural features and properties. Diverse nanostructured photocatalysts are actively being developed for CO2 photoreduction. Multidimensional nanostructures and nanocomposite heterostructures are widely studied because of their excellent attributes such as efficient separation and long lifetime of the excited charge carriers. Promisingly, nanostructures and nanocomposites of the covalent organic frameworks with graphene and its derivatives, metal dichalcogenides and plasmonic materials exhibit excellent photocatalytic performance, according to the literature reports. In this investigation, a keto-enamine TpPa-1 covalent organic framework and reduced graphene oxide nanosheet nanocomposite are developed by an in-situ assembling technique. The covalent interactions between TpPa-1 and rGO facilitated the formation of band edges with required potential and thereby to achieve an improved charge separation along with rapid migration of charge carriers to the surface toward the selective reduction of CO2. By the support of the electron mediator [Co(bpy)3]2+ in the hybrid served as the active sites for the coordination, activation, and reduction of CO2 molecules to CO. A hollow nano spherical TpPa-1 covalent organic framework (COF) integrated with single atom Co-1T-MoS2 (TpPa-1/Co-1T-MoS2) is further designed and developed through a dual-ligand strategy to tune the band edge potential and enhance the charge separation to improve CO2 photoreduction efficiency of the system. The interactions between TpPa-1 and Co-1T-MoS2 aided and enhanced the charge separation as well as charge carrier migration to the surface resulted in selective conversion CO2 to CO. Au plasmonic nanoparticles adorned three-dimensional hollow porphyrin-based covalent organic framework with Co single atom (COF-366-Co[subscript (H)]/Au) is developed via dual-ligand strategy and post-synthetic metallization method and found that this system significantly boosted up the CO2 photoreduction efficiency. It utilizes the plasmon-induced energetic electron transfer, enhanced light harvesting, and surface reactions to drive the photocatalytic redox reactions. The developed COF-366-Co[subscript (H)]/Au exhibited fine activity toward photocatalytic CO2 reduction under visible light irradiation, which yielded the CO at a rate up to ~1200 μmolg−1h−1 with a selectivity of 98% over H2.