School of Chemistry - Theses

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Author: Agnihotri, Shruti ×

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    Photocatalytic carbon dioxide reduction with water
    Agnihotri, Shruti ( 2021)
    Abstract New catalyst discovery to enhance photocatalytic reduction of CO2 with H2O is a materials space problem, where determining the ideal catalyst composition, catalyst processing conditions, and optimising the reaction conditions is a “wicked” problem. To examine more of the materials space, we need to develop new high throughput screening methods. A new continuous flow photocatalytic reactor with enhanced capabilities to discover robust photocatalyst for the photocatalytic reduction of CO2 is thus designed in this project. A key component in the new reactor is in-situ thermal monitoring of the activated catalyst. A more detailed analysis is made on selected catalysts that promote a greater temperature drop under constant illumination, that is more active catalysts will require more energy for this highly endothermic reaction. This reactor has the potential to accelerate the discovery/optimization process of required catalysts, when fully automated. Additionally, its continuous gas flow configuration, flexibility to test varied set of reaction parameters with precise control over input parameters makes it distinguished from conventionally used reactors. Validation of this custom-designed photocatalytic reactor setup, which is based on entirely new metric to identify reactivity of an active catalyst was commenced using benchmark catalyst material TiO2. Further, extended experiments using TiO2/C3N4 as photocatalysts confirmed the usefulness of in-situ temperature monitoring screening method, as detected enhanced CO2 reduction was linear to monitored drop in catalyst’s temperature. This newly built photocatalytic reactor set up was then used to explore photocatalytic CO2 reduction reactions over range of prepared catalysts. Catalyst designing was focussed to suppress recombination losses during photocatalytic reaction, which is reported as key responsible factor of low obtained product yields in the field. For this, nanoparticle – nanocomposites of C3N4 with various transition metal complexes were synthesized in this work and subsequently tested as photocatalysts. C3N4 based composite catalysts were found to be effective in enhancing photocatalytic CO2 reduction reaction, when compared to only single catalyst systems. Also, controlled syngas formation was made possible when modified C3N4 was combined with cobalt phosphate using layer by layer assembly method. Obtained results were also exemplifying that composite photocatalyst’s performance is also sensitive to used catalyst preparation method, which relates to provisioning more active sites over catalyst surface to enhance photocatalytic reaction rates. In addition to C3N4, another low-cost semiconductor option- FexOy has also been explored as photocatalyst for CO2 reduction reaction. Low conduction band edge energy of Fe2O3 was addressed by structural and surface modifications, where electrospinning method was used for fibrous catalyst preparation with additional doped metal cations. These strategies were helpful in enhancing selective CO formation as CO2 reduction product, significantly. Structural and morphological parameters of explored nano composites effecting catalytic performance were investigated using X-ray absorption spectroscopy and Electron microscopy.