Engineered Supraparticles and Their Photocatalytic Applications

Abstract

Nature has developed highly specific and efficient catalysts to synthesize complex organic compounds, such as sugars in the process of photosynthesis. Due to the efficiency of these reactions, considerable effort has been placed to develop reaction schemes that can replicate the complexity of catalysts and products found in nature. The success of producing these biomimetic systems often leads to an improved understanding of biological systems, which can loop back and translate into better engineering of catalysts, aiming for instance, for enhanced stability and reduced cost. The use of inorganic nanoparticles (NPs) for developing biomimetic catalytic systems presents a favorable choice due to their ability to combine the robustness of inorganic catalysts with selectivity similar to that of enzymes. Other structural and functional characteristics similar to those of proteins can also be attained. Advancement in the understanding of NP self-assembly mechanisms allowed us to engineer terminal superstructures, known as supraparticles (SPs). The formation of SPs is not limited to the self-organization of inorganic NPs. Hybrid assemblies, containing NPs and multiple proteins at the same time have been developed. All these superstructures can potentially display catalytic functionalities replicating those of enzymatic assemblies, improving catalytic properties compared with singular NPs constituents due to collective interactions. The primary focus of this dissertation is to fabricate biomimetic suprastructures and explore their potential as photocatalysts. By taking advantage of the fundamental electrostatic interactions within the system, NP properties were tuned to conveniently fabricate hierarchical structures that mimic the structural complexity and functionality of materials found in nature. Thereby, a variety of semiconductor synthesis and assembly methods were established, offering immense tunability in the overall shape and size of SPs. Due to the general nature of supraparticles, which can be defined as complexes composed of two or more subunits or constituents, the composition of NPs within the SP was controllable, offering an additional level of design flexibility. Several key components were considered necessary when engineering SPs for catalytic application, including, facile and cost-effective synthesis method, absorption range, dispersion stability, and structural tunability. Overall, SPs offer a convenient platform for engineering catalysts using different building blocks as functional modules, leading to the development of more specific and sophisticated assemblies capable of replicating multiple functions of biological nanoassemblies.