Design Of Metal Nanostructures For Solar-to-Chemical Energy Conversion

The rapid growth of human society raised higher demands for energy and environmental issues.It is becoming highly urgent to develop clean and sustainable energy sources to solve the potential environmental problems.Solar energy with its worldwide accessable,clean and sustainable features has drawn worldwide attention.Coupling solar energy into catalytic reaction will be of great value in academic research and future industry applications.The development of new materials and processes for solar energy conversion is an important topic in this research field.Plasmonic nanocatalysts with broad-band light absorption and high solar conversion efficiency have recently been applied to photocatalytic chemical reactions.By integrating efficient plasmonic materials with catalytic sites,we can develop photocatalytic nanomaterials for future energy applications.Leveraging surface and interface control,we can develop a new way to couple solar energy into catalytic reactions.In this dissertation,based on the controllable synthesis of nanomaterials,we rationally designed the light-absorption centers and catalytic sites for solar energy conversion.The relationship between surface/interface structures and performance in solar-to-chemical energy conversion has been investigated.By precisely manipulating the structure of plasmonic nanocatalysts,we revealed the involved mechanisms of plasmon decay in the solar energy conversion.In addition,by utilizing the pore effect and thermal insulation function of metal-organic frameworks,we accomplished the light-driven alkyne semihydrogenation by the designed plasmonic nanocatalysts.We also utilized the alloy effect of metallic nanocrystals and pore structure of metal-organic frameworks to improve the catalytic activity and functional group hydrogenation selectivity.Based on the electronic state control of surface catalytic sites,the performance for formic acid decomposition was enhanced under UV light illumunation.The main results can be summarized as follows:1.The Au nanorods-Pd core-shell(Au NRs@Pd)nanocatalysts were synthesized by controlling Pd shell thickness at atomic level precision.The photothermal effect and hot-electron effect associated with plasmon resonance were investigated for organic reaction.Au NRs@Pd nanostructures with 4 different shell thicknesses were prepared throught solution-phase synthesis method for light-driven organic hydrogenation.We found that Au NRs@Pd with 14 atomic Pd layers exhibited the highest conversion in catalytic reaction.The solar-driven styrene hydrogenation yield is comparable to that by thermal-driven reactions at 80?.Combined with ultrafast absorption spectroscopy characterization,we investigated the catalytic performance under light illumination with various wavelengths.Then we revealed the intrinsic relationship between photothermal effect and electron-phonon scattering,as well as that between hot-electron effect and charge recombination during plasmon decay.This work provides us a new direction for the rational design and controllable synthesis of plasmonic nanocatalysts towards solar-to-chemical energy conversion.2.Based on the previous study,we further coated porous metal-organic frameworks(MOFs)on the surface of catalytically active Au NRs@Pd.This triple-component nanocatalysts showed advantages in hydrogen enrichment,heat preservation and molecular sieving.In that case,the Au NRs@Pd@ZIF8 showed high reactivity and selectivity in solar-driven alkyne semihydrogenation.It is worth mentioning that the catalytic performance of Au NRs@Pd@ZIF8 in alkyne semihydrogenation was enhanced by light illumination at a safe hydrogen concentration.This work expands the fundamental research in plasmon-driven catalytic reactions and further promotes future industrial applications.3.As noble metals are expensive and rare,our goal is to reduce the cost of metal nanocatalysts while ensuring the high catalytic activity.Based on previous works,alloying is an efficient approach to reduce the catalyst costs.We grew catalytically active Pt-Au alloys on the surface of Au NRs to form Au NRs@PtAu nanostructures.The obtained plasmonic nanocatalysts could be used for selective hydrogenation of cinnamaldrhyde molecules.The increasing catalytic performance benefited from the elevated d-band center of Pt atoms.In addition,the porosity of MOFs could manipulate the adsorption configuration of cinnamaldehyde molecules on the catalyst surface.By integrating the catalyst with UIO66,we could further promote the selective hydrogenation of functional groups in catalytic reactions.This work extends the application of plasmonic nanomaterials to organic synthesis with functional group selectivity.4.Pd nanocrystals with different surface structures(including atomic structure and electronic structure)have shown various catalytic performance in the related reactions.The increased electric density of Pd nanocatalysts showed enhanced activity in formic acid decomposition.Based on Pd {111} facet,we proposed the surface modification on Pd nanotetrahedron-TiO2 structure to enhance the decomposition performance of formic acid.The electron density of Pd sites could be increased by the Mott-Schottky junction and the polarization between Pd and modified atoms for light-driven formic acid decomposition.We revealed that the conversion of catalytic formic acid decomposition was increased from 14.6%to 98.7%by Pd@Ag nanotetrahedron-TiO2.This strategy provides us a new route to the rational design of surface and interface structure for catalytic reactions.