Investigations Of Light Absorption Modulation And Photocatalytic Property On Plasmonic Nanostructures/TiO₂ Composite Nanofibers

For the traditional TiO₂ semiconductor photocatalyst,a few of drawbacks still hinder its practical photocatalytic activity,including the narrow light absorption range and low quantum efficiency.To solve these problems,researchers have been trying to combine TiO₂ with different types of photosensitizers.Among the plenty of new-type photosensitizers,plasmonic nanostructures have attracted extensive attention because of their unique optical properties.In this paper,we use plasmonic Au and W₁₈O₄₉ nanostructures,which have the localized surface plasmon resonance(LSPR)behavior,as the photosensitizers to contruct several kinds of plasmonic nanostructures/TiO₂ composite nanofibers(CNFs)photocatalysts.The activity of composite nanostructures for photocatalytic hydrolysis of NH₃BH₃ for H₂ generation and CO₂reduction were also investigated.The main research contents are as follows:(1)Au/TiO₂ CNFs were fabricated via electrospinning technique.And the Au content in the Au/TiO₂ CNFs was controlled by changing the molar ratio of Au to Ti.The images of scanning electron microscopy(SEM)and transmission electron microscopy(TEM)of the as-fabricated samples revealed that Au nanoparticles(NPs)were randomly distributed in the interior of Au/TiO₂ CNFs.The UV-vis absorption spectra of the as-fabricated samples showed that,compared to the pure TiO₂ NFs,the Au/TiO₂ CNFs exhibit obvious LSPR absorption in the visible region.Due to the LSPR effect of embedded Au NPs,the visible-light-driven photocatalytic activity of the Au/TiO₂ CNFs for H₂ generation/CO₂ reduction was much higher than that of the pure TiO₂ NFs.In addition,the results of finite-difference-time-domain(FDTD)simulations showed that LSPR enhanced electric fields are mainly distributed near the Au/TiO₂hetero-interface with the maximum enhancement factor of 25(|E|²/|E₀|²),indicating that the LSPR-excited hot electrons of Au NPs mainly populate near the hetero-interface.Through the temperature-controlled and wavelength-controlled experiments,we concluded that LSPR-excited hot electrons of Au NPs in the Au/TiO₂ CNFs can transfer to the adherent TiO₂ to participate in the reduction reaction,leading to the enhanced photocatalytic performance of Au/TiO₂ CNFs.(2)W₁₈O₄₉/TiO₂ CNFs were fabricated through two-step method:(i)electrospinning fabrication of TiO₂ NFs;(ii)hydrothermal growth of W₁₈O₄₉ nanowires(NWs)on the TiO₂NFs surfaces.The UV-vis absorption spectra of the as-fabricated samples showed that,compared to the pure TiO₂ NFs,the W₁₈O₄₉/TiO₂ CNFs exhibit an obvious LSPR absorption in the visible-IR region.Through ultrafast transient absorption(TA)spectroscopy and FDTD simulations,we demonstrated that the LSPR-excited hot electrons of W₁₈O₄₉ in the W₁₈O₄₉/TiO₂ CNFs can transfer to the TiO₂ with a large rate constants(3.78×10¹²s^-1).Upon the IR light excitation,the photocatalytic activities of H₂ generation and CO₂ reduction could be enhanced by².4 and².5 times as compared to the pure W₁₈O₄₉ NWs.(3)Au/W₁₈O₄₉/TiO₂ CNFs were fabricated through hydrothermal growth of W₁₈O₄₉ NWs on the TiO₂ NFs surfaces.TEM images of as-fabricated samples showed that there was a"sandwich"structure of Au-TiO₂-W₁₈O₄₉ in the system with the distance between Au NPs and W₁₈O₄₉ NWs of 1?5 nm.And UV-vis absorption spectra of the as-frabricaed samples showed that there was an overlap between LSPR absorption peak of Au NPs and LSPR absorption band of W₁₈O₄₉ NWs.These features obtain an opptunity for LSPR-coupling effect between Au NPs and W₁₈O₄₉ NWs.Due to the LSPR-coupling effect between Au NPs and W₁₈O₄₉NWs,Au/W₁₈O₄₉/TiO₂ CNFs showed the stronger absorption of visible light than Au/TiO₂CNFs and W₁₈O₄₉/TiO₂ CNFs.As a result,upon the visble-IR light irradiation,as compared to Au/TiO₂ CNFs and W₁₈O₄₉/TiO₂ CNFs,the photocatalytic activities of H₂ generation were enhanced by⁴.1 and² times,respectively;the photocatalytic activities of CO₂ reduction were enhanced by³.88 and².08 times,respectively.