Reduction Of Silver Nanoparticles By Plasma And Its Photoelectricity Applications Of Low-dimension TiO₂ Based On Surface Plasmon Enhancement Effect

Metal nanoparticles have attracted much attention over the past decades owing to their relatively unique physical and chemical properties.Metal nanoparticles can be used in various applications by controlling the size and distribution precisely.Due to the local surface plasmon resonance?LSPR?based on the nano-dimension,the photocatalytic performance can be enhanced by improving the light absorption and restraining the recombination of photogenerated electron-hole pairs.Meanwhile,ultrasensitive detecting of the organic macromolecule can also be realized by surface enhanced Raman scattering?SERS?.The key to achieve the goals above is to terminate the particle growth reaction.However,the harsh condition and complicated processing of the presented methods limit the practical application of metal nanoparticles.To solve the problem above,supported Ag nanoparticles are synthesized byheterogeneous precipitation and cold plasma reduction and deposited on the diverse low dimensional TiO₂ substrates to synthesize surface plasmon photocatalyst which can be excited by visible light.Moreover,the hybrid nanocomposites show ultrasensitive SERS signals of the organic macromolecules.The main research contents and results in present dissertation are as follows:?1?Ag NPs of small size have been embedded on TiO₂ surface by a novel two-step method employing a precipitation reaction and cold plasma without the use of any environmentally and biologically hazardous reducing chemicals.TEM results reveal that Ag NPs deposited homogeneously on the P25 surface.The Ag NPs have narrow size distribution between 2 and 5 nm.The average particle size of the AgNPs is 3.7 nm X-ray photoelectron spectroscopy shows that the supported silver ions are completely reduced to the metallic state.UV-visible absorption spectra indicate that the Ag/TiO₂ nanocomposites could absorb the visible light resulting from the LSPR effect.PL results show that the Ag NPs could restrain the recombination of photogenerated electron-hole pairs.The Ag NPs-modified samples show remarkable improvement for methylene blue?MB?photodegradation under visible light compared to pure TiO₂.?2?TiO₂ nanotubes with co-modification by nitrogen doping and decorating with silver nanoparticles are synthesized by ion-exchange method and the two-step method.X-ray photoelectron spectroscopy and UV-Visible absorption spectra analyses indicate that nitrogen enter into the TiO₂ lattice and the supported silver ions are completely reduced to the metallic state enabling the LSPR effect,which significantly improve the optical properties.The morphology and dispersion of the Ag NPs characterized by TEM show that the Ag NPs are homogeneously distributed on the TiO₂ nanotubes with an average particle size of 5 nm,thereby facilitating the LSPR effect.The Ag/N co-modified samples show remarkable improvement for methylene blue?MB?photodegradation under visible light compared to the pure TiO₂.?3?Ag NPs are deposited on the TiO₂ nanorod arrays on FTO glass synthesized by hydrothermal method.X-ray photoelectron spectroscopy and UV-visible absorption spectra show that the supported metal ions are completely reduced to the metallic state within a short time.XRD and Raman results indicate that the as-prepared TiO₂ nanorods are rutile phase.The morphology and dispersion of the Ag NPs were characterized by scanning electron and transmission electron microscopy.The results show that the Ag NPs are homogeneously distributed with an average particle size of 5.8 nm,which brings the effect LSPR.The Ag NPs-modified samples show remarkable improvement for reducing CO₂ to CO and CH4 with yields of 72 ?mol g-1 and 6.8 ?mol g-1 under visible light compared to pristine TiO₂.The formation mechanism of the method for the reduction and stabilization of Ag NPs is also discussed.?4?SERS detection is employed based on the TiO₂ nanorod arrays film decorated by Ag NPs.The results of XPS,SEM and TEM indicate that the Ag NPs are distributed homogeneously on the TiO₂ nanorods surface.The 3D hybrid substrate presents sensitive SERS signals of rhodamine 6G?R6G?and the relative standard deviation?RSD?for the main Raman vibration modes?611,776,1164 and 1651 cm-1?is 4.49%,3.71%,2.90%and 6.65%,respectively.The interactions of the significant amount of Ag NPs which play the role of“hot spots”contribute to the excellent enhanced performance and spatial uniformity.Moreover,the substrate also exhibits enhanced SERS ability in detecting the adenine molecule?10-2 M?.The results above indicate that the green synthesis can be promising for preparing the 3D hybrid nanostructure substrate.Based on the results above,compare with the conventional methods,the approach presented in this dissertation have following virtues:?1?environmentally friendly as it does not require utilization of any reducing chemicals or employ environmentally and biologically hazardous reducing agents,?2?operates at room temperature,?3?inclusion-free,?4?homogeneous distribution and small diameter size of the metal nanoparticles,?5?cost-effective,and?6?ease of immobilization and stabilization between metal nanoparticles and support material surfaces.It would improve the application of Ag NPs,and also inspire the researcher to preparing other metal nanoparticles.