Design And Performance Of Plasmonic Catalysts For Light-Driven Chemical Transformations

With the development of human society,fossil fuels such as coal,oil and natural gas are consumed in large quantities.Meanwhile,the combustion of large amounts of carbon-containing fuels has led to continuous increase of carbon dioxide concentration in the atmosphere.The resulting greenhouse effect has caused some environmental and climate problems such as rising sea levels,frequent typhoons and forest fires.Therefore,identifying a clean energy source to replace traditional fossil energy has received widespread attention from researchers in recent years.As one of the most widely used and clean energy sources on the planet,solar energy reaching the Earth every second is equivalent to burning 5 million tons of coal.Hence the effective use of solar energy is crucial to the future sustainable development of human beings.Plasmonic metal nanoparticles can strongly interact with incident light throughout the wavelength range of the solar spectrum(from ultraviolet to infrared range)depending on their composition,shape or size,exciting the localized surface plasmon resonance on the metal surface.This allows plasmonic metal nanoparticles to concentrate light energy in a space much larger than their geometric cross-section into a small region,causing strong light-molecule interaction through energy transfer,which makes it have great potential for realizing the efficient conversion between solar energy and chemical energy.In this dissertation,the surface catalytic sites of plasmonic metal nanoparticles are designed and modified through simple wet chemical synthesis method,which can improve the light absorption of the catalysts and the efficiency and selectivity of solar to chemical energy conversion.In combination with theoretical calculations and a series of in-situ characterization methods,the effects of design and modification of the catalytic sites on the activation of the reactant molecules and the energy transfer process can be understood.The research results of this dissertation can be used for further understanding on the plasmon-induced catalytic process and designing efficient catalysts for solar-to-chemical energy conversion.The main results are summarized as follows:1.We synthesize gold-ruthenium core-antenna nanostructures in a one-step process by reducing gold and ruthenium precursors in diethylene glycol.The gold cores provide surface plasmon under illumination,and the ruthenium antennas offer the ability of N2 adsorption and activation.Taken together,effective activation and dissociation of nitrogen molecules can be realized under mild conditions(normal temperature,low pressure,pure water and under illumination).The experiments prove the key role of ruthenium,in which the strong adsorption of nitrogen molecules on the catalyst surface facilitates the transfer of energy from metal surface to nitrogen molecules.In-situ DRIFTS and in-situ NAP-XPS confirm that nitrogen molecules are activated through dissociation path on the catalyst surface,which usually requires high temperature and high pressure conditions such as the Haber-Bosch process.In addition,the theoretical study shows that the enhanced electromagnetic near-field located in the catalyst-nitrogen interface,together with the generated energetic hot electrons induced by LSPR,promotes the adsorption,activation and hydrogenation of nitrogen molecules.This study provides a new choice for nitrogen fixation under mild conditions and provides new ideas for catalyst design based on surface plasmon.2.We obtain Au rod@CuPd core-shell nanostructure for plasmon-induced catalytic reduction of carbon dioxide by coating copper-palladium alloy on the surface of gold nanorods.The catalyst realizes the use of a full spectrum of sunlight,particularly the visible light and low-energy infrared light,to reduce carbon dioxide to hydrocarbons selectively.By monitoring the valence state of the catalyst surface atoms during the illumination process via in-situ NAP-XPS,we propose that the Cu0 and CuⅠ emerging under illumination play an important role in the selective generation of hydrocarbon products and C-C coupling.This study provides information for designing efficient and highly selective catalysts to utilize visible and infrared light,which accounts for the vast majority of solar energy.Moreover,it provides a new idea for the synthesis of artificial carbon-balanced fuels using clean solar energy.3.Through a simple wet chemical synthesis,gold atoms are deposited on the palladium concave nanocube to modified its lattice via surface alloying.By controlling the concentration of surface gold atoms,we can regulate the ability of palladium to activate oxygen molecules and improve the absorption of the catalyst in the visible range.The experimental results show that the activity and selectivity of the catalyst are well balanced in the oxidation of styrene with molecular oxygen.It is found that the electron density of palladium atoms is reduced by deposited gold atoms.Thus during the activation process,less electrons are injected into the anti-bond orbitals of the oxygen molecules,leading to weaker activation of oxygen molecules and avoiding the excessive oxidation of products.This study provides a reference how to balance catalytic activity and selectivity in the design of light-driven catalysts.4.We introduce lead atoms with a larger atomic radius to form lead-palladium alloy in the sub-surface layer of palladium nanocube through a series of synthetic methods in aqueous solution.As a result,we successfully introduce tensile stain into the catalyst surface lattice.Through systematic characterizations,we confirm the three-layer sandwich structure of the nanocubes.By coating a layer of palladium on the outer layer of the alloy,the tensile stain is well retained,while the effects of catalytic property of lead atoms and the charge transfer due to the difference in electronegativity between lead and palladium atoms on the overall catalytic performance of the catalyst can be excluded.In addition,without the use of oleic acid and oleylamine-the end-capping agents which can be hardly removed after synthesis,the application range of the catalyst is expanded.The tensile stain can shift up the d-band center of surface atoms and affect the adsorption mode of reactant molecules.Compared with bare palladium nanocubes of the same size,some unique properties are found in the light-driven activation of oxygen molecules,semi-hydrogenation of phenylacetylene and electrocatalytic carbon dioxide reduction.This study provides a method for introducing lattice strain,which can study the stain effect on the catalytic performance without other interferences.