Selective Growth Of Cuprous Oxide On Gold Nanocrystals For Near-Infrared Photocatalysis

The efficient utilization of clean and renewable solar energy to drive chemical reactions has been attracting widespread attention.Due to the unique energy band property and excellent photocatalytic capability,semiconductor nanomaterials are widely used as the photocatalysts for this conversion from solar energy to the chemical energy.Under solar illumination,the electrons in the valence band of semiconductor gain sufficient energy to cross the forbidden band and enter the conduction band,leaving the holes in the valence band.The electrons in conduction band and holes in valence band can take part in the reduction and oxidation reactions at different active sites,respectively.However,the photo-response ability of semiconductor materials is highly dependent on their band gap widths.Commonly used oxide semiconductor materials such as Ti O₂ and Zn O possess wide band gaps,which makes them can only response to the ultraviolet light.In contrast to those traditional wide-bandgap semiconductors,Cu₂O featuring with a narrower bandgap（～2.2 e V）is preferable candidate for the visible-light photocatalysis.In addition,to alleviate the low electron mobility and the high recombination rate of single semiconductor photocatalyst,the integration of semiconductor with plasmonic metals,especially Au nanocrystals,is a promising way.Once Cu₂O contacts with Au nanocrystals,a Schottky barrier is formed at the metal/semiconductor interface.Hot electrons generated by Local Surface Plasmon Resonance（LSPR）of Au nanocrystals have chance to cross the Schottky barrier and inject into the conduction band of the semiconductor to participate in the reduction reaction,known as the hot electron injection mechanism.This process can not only broaden the photo-response range but also promote the charge carrier separation,greatly improving the photocatalytic performance of the semiconductor.In this thesis,we described a general method for the selective growth of Cu₂O shell on the surface of Au nanocrystals to obtain three types of Au/Cu₂O heterostructures.Prior to the growth of Cu₂O,three types of Au nanocrystals with different architectures,including Au nanobipyramids（Au NBPs）,Au nanorods（AuNRs）,and triangular Au nanoplates（Au NPLs）were firstly pre-grown using the seed-mediated growth method.By precise control the reaction kinetics,Cu₂O shells were selectivity grown on the surface of Au nanocrystals,leading to the formation of different types of Au/Cu₂O heterostructures.Control experiment results suggested that the concentration of hexadecyltrimethylammonium bromide（CTAB）,the concentration of poly（vinylpyrrolidone）（PVP）,and the type of precursor were all crucial to the selective growth behavior.Owing to the sharp tip and large local electric field enhancement effect of Au NBPs,dumbbell-like Au NBP/Cu₂O heterostructures were selected as the photocatalyst for the study of the near-infrared nitrogen photofixation.Compared with the 68.15μmol/h/g NH₄⁺formation rate of the Au NBP@Cu₂O cored@shell structures,the dumbbell-like Au NBP/Cu₂O heterostructures can produce 131.4μmol/h/g NH₄⁺in the visible and near infrared.In the near infrared region,the dumbbell-like Au NBP/Cu₂O heterostructures still has the formation rate of69.20μmol/h/g NH₄⁺.In comparison with the photocatalytic performances of Au NBPs,Cu₂O spheres,and Au NBP@Cu₂O core@shell structures,the dumbbell-like Au NBP/Cu₂O heterostructures sample exhibited a better phtocatalytic activity toward the photoreduction of nitrogen.In summary,a general strategy for the selective growth of Cu₂O shell on Au nanocrystals was developed and the photocatalytic nitrogen fixation on the basis of dumbbell-like Au NBP/Cu₂O heterostructures was investigated in this thesis.The research work present in this thesis will be helpful for the design of plasmonic metal/semiconductor heterostructures and the understanding of plasmon-enhanced photocatalysis.