Nanoassembly of photoactive materials towards designing visible light heterostructured photocatalysts
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Currently, the low efficiency of photocatalytic water splitting is mainly attributed to limited light harnessing and high charge recombination phenomena of photocatalysts. Several strategies have been developed on designing photocatalysts for water splitting to address these issues. However, there is still a lot of scope in designing photocatalysts to prevent charge recombination problem using unique nanoassembled strategies. The aim of this work is to develop nanoassembled fabrication strategies for photoactive materials to enhance the photoexcited charge separation as well as improve light harnessing capabilities of photocatalysts in photocatalysis. Assembled nanostructures influence the catalytic activity of a photocatalyst; however, controlling the surface morphology and crystal structure of the photocatalysts during the formation of nanoasembly is challenging. In this work, nanoassembled SrTiO3 nanofibers are synthesized using a polymeric nanofiber template with controlled surface morphology and crystallite size. In addition, the crystal growth mechanism is explained in the nanoconfined system (composite nanofiber) during the formation of ordered nanoassembled structures which support our experimental data. Nanoassembled structures provide an ideal platform on which multifunctional materials can be deposited to fabricate nanoasembled heterostructures. It is found that nanoassembled SrTiO3-based heterostructures demonstrate enhanced photocatalytic H2 evolution rate when compared to their respective unassembled heterostructures. The advantageous SrTiO3 interparticle nanoassembly facilitates faster electron transport and high photoexcited charge separation, resulting in enhanced photocatalytic H2 evolution. Further to demonstrate the heterostructure concept in improving charge separation issue, a novel Co metal incorporated ternary heterostructured photocatalyst, CdS/CoOx/Co-metal, is developed which increases photocatalytic H2 evolution 30.5 folds compared to pure CdS under visible light. This work demonstrates for the first time the effect of the Co metal on photocatalytic H2 evolution using CdS-based ternary heterostructure. The synergistic charge separation improvement achieved by the combined cocatalytic effect of CoOx and the Co metal is found to be the reason for enhanced photocatalytic H2 evolution.