Morphology-Controllable Synthesis Of Dumbbell-Shaped Plasmonic Photocatalysts And Their Applications In Photocatalysis

With the growth of the world population and the rapid development of various industries,people’s demand for energy has increased dramatically,and fossil fuels have been rapidly consumed.Artificial photosynthesis of fuels and feedstocks using solar energy is an innovative way to meet the rapidly growing energy demands.Among various solar-to-chemical conversion strategies,the reduction of green-house gas CO₂ to value-added hydrocarbons and the reduction of naturally abundant N₂ to NH₃ have triggered extraordinary interests recently.However,the weak light-harvesting capability and the rapid charge carrier recombination of the classical semiconductor or metal catalysts heavily limit their practical applications in photocatalysis.Therefore,the design and construction of efficient photocatalysts is a significant challenge but is highly desired.Plasmonic metal nanocrystals（e.g.,Au,Ag,and Cu）have drawn increasing attention in recent years because of their interesting surface plasmon resonance properties.The integration of plasmonic metal with those catalytically active semiconductor or metal catalysts to construct?antenna-reactor?photocatalysts holds great promise in photocatalysis.However,the spatial architecture of the antenna-reactor photocatalyst plays a vital role in their photocatalytic performance.For example,the traditional core@shell nanostructures bury the active sites of the plasmonic metal inside completely,which blocks the transfer of the reactant molecules and decreases the photocatalytic activity.The ideal photocatalysts should possess spatially separated architecture that can efficiently expose the active sites of constituent components to reactant molecules.In this thesis,two types of"dumbbell-shaped"plasmonic photocatalysts are successfully developed through the site-selective growth strategy and their photocatalytic performances in driving CO₂ reduction and N₂ photofixation are systematically examined.The main results are as follows:（1）Construction of spatially separated gold nanocrystal/cuprous oxide architecture for plasmon-driven CO₂ reduction.Plasmonic hot electrons have shown great potential in photocatalysis,but little is known about the hot hole-driven chemical reactions due to the lack of desired plasmonic metal/p-type semiconductor architectures.Herein,we describe a general and robust strategy for the site-selective growth of a p-type semiconductor,Cu₂O on Au nanocrystals（NCs）,to produce diverse spatially separated Au/Cu₂O heterostructures.The preferential growth of Cu₂O on the tips/ends/edges of Au NCs is directed by the sparse coverage of the surfactant molecules at the high-curvature sites of Au NCs.The obtained dumbbell-shaped nanostructures serve as the ideal platforms for probing the hot-hole-mediated CO₂ reduction reaction.Benefiting from the hot-hole injection,a new reaction pathway is unlocked,and the C₂ product activity and selectivity are significantly improved.This study demonstrates the genuine superiority of the dumbbell-shaped nanostructures in photocatalysis,offering a new unique avenue to explore the underlying mechanism of hot-hole-mediated chemical reactions.（2）Steric hindrance-induced selective growth of rhodium on gold nanobipyramids for plasmon-enhanced nitrogen fixation.The construction of an antenna-reactor plasmonic photocatalyst that is composed of a plasmonic and a catalytically active metals holds great promise in driving N₂ photofixation,but their photocatalytic performance is highly dependent on the spatial distribution of the two components.Up to now,the fabrication of dumbbell-shaped nanostructures featuring with spatially separated architecture remains challenging.Herein,we develop a facile synthetic strategy for the site-selective growth of Rh nanocrystal“reactor”on two tips of Au nanobipyramid（NBP）“antenna”through the precise manipulation of the steric hindrance toward Rh overgrowth.The obtained Au NBP/tip-Rh nanodumbbells（Au NBP/tip-Rh NDs）can function as an excellent antenna-reactor plasmonic photocatalyst for N₂ photofixation.In this scenario,Au nanoantenna harvests light and generates hot electrons under plasmon resonance,meanwhile the hot electrons are transferred to the active sites on Rh nanocrystals for N₂ reduction.In comparison with that of classical core@shell nanostructures,the spatially separated architecture of the Au NBP/tip-Rh NDs facilitates the charge separation,greatly improving the photocatalytic activity.This study sheds new light on the structure-function relationship for N₂ photofixation and benefits the design and construction of spatially separated plasmonic photocatalyst.