Papers by Keyword: Noble Metals

Abstract: The production of a high-sensitivity surface Plasmon resonance (SPR) sensor depends on a few main factors, such as metal thin film types and thicknesses, light coupling techniques and acceptable EM wave polarization modes. This work is carried out to investigate the impact on the SPR characteristics of noble metal thicknesses, namely gold and silver, for optical sensor applications. To excite surface Plasmon polaritons (SPP), a Kretschmann prism coupling was used. The thicknesses of noble metal thin films were varied between t=30nm and 60nm. The characteristics of SPR peaks such as Q-factor and FWHM were studied in SPR signal analyses. In comparison with silver, Q-factor results showed an outstanding optical property of gold at t= 40 nm due to its high Q-factor values, which confirms its ability to produce excellent SPP quantities. In conclusion, gold noble metal at t= 40nm is capable of producing optimum SPR. In the development of the highly sensitive SPR sensor, this excellent criterion put gold as a spectacular candidate for optical sensor applications.

Abstract: This study aims to describe the influence of adding graphene oxide to TiO₂-noble metal (Me=Ag, Au or Pd) composite nanoparticles on their bioactivity (formation of RGO/TiO₂-Me nanocomposite system). The obtained nanocomposite flakes and reference TiO₂-Me nanoparticles were characterized using SEM, HRTEM and XPS spectroscopy, N₂ sorption analysis and helium pycnometer. The analysis of the antibacterial properties of synthesized nanocomposites revealed a growth inhibiting effect of TiO₂-Ag particles on gram positive bacteria such as: Staphylococcus aureus, Sarcina lutea and Bacillus subtilis. In the case of nanocomposite flakes containing RGO the visible changes in bacteriostatic properties were observed, including unexpected reversal of the antimicrobial activity of silver-containing nanoparticles into the stimulation of growth of applied bacterial strains. The stimulation of growth was not observed for TiO₂-Au and Pd nanoparticles deposited on the surface of RGO.

Abstract: In this review different aspects of material and structural engineering of metal oxides aimed for application in conductometric gas sensors (chemiresistors) were analyzed. Results, mainly obtained for SnO₂ and In₂O₃–based sensors during surface functionalizing by noble metals have been used for showing an opportunity of material and structural engineering of metal oxides to optimize gas sensing characteristics.

Abstract: Gold and silver nanostructures (such as Au nanorods and Ag nanoplates) exhibit strong and tunable surface plasmon resonance in the near-infrared region (NIR). Under a certain NIR laser irradiation, noble metal nanostructrues achieve a high photo-thermal effect, which would be useful in the therapy. In this work, Au nanorods with longitude surface plasmon resonance (SPR_L) shifting in the region of 650 ~1100 nm were synthesized by a seed method. Ag nanoplates and nanocubes with SPR located in the region of 650~850 nm were produced by a hydrothermal method. Through adjusting laser power and irradiating time, the photo-thermal conversions of these nanostructures were studied under NIR laser irradiation. Under low power laser (808 nm, <1W) irradiation, the shape of the Au nanorods are stable and the temperature of colloid increase from room temperature to ~57°C. However, Au nanorods undergo deformation from rod to spherical particle under irradiation of high power (808 nm laser; 6W; 1064nm laser, 7W), resulting in the disappearance of SPR_L. Morphology evolutions and photo-thermal conversion of Ag nanostructures were also studied. Ag nanostructures have a lower photo-thermal conversion compared with that of Au nanorods colloid. Snipping and dendrite can be observed for Ag nanoplates after irradiating, while Ag nanocubes have no obvious shape change.

Abstract: Luminescence of trivalent lanthanide ions (Ln³⁺) doped glasses is influenced by many factors. The emission enhancement of Ln³⁺ can be achieved either through an external approach or an internal adjustment. The external approaches mainly include application of metal nanoparticles, which changes the local structure, local filed and interaction with active ions. In this work, efforts to obtain luminescence enhancement in Ln³⁺ through introducing noble metals are reviewed. The merits of different processes are concluded.

Abstract: We attempted the photo-chemical recovery of noble metals from solutions using inorganic-organic hybrid photocatalysts based on polyoxometallates (POMs) such as PMo₁₂O₄₀^3-, SiW₁₂O₄₀^4-, and γ-SiW₁₀O₃₆^8- coupled with a cationic surfactant, dimethyldioctadecylammonium (DODA). We also used γ-SiW₁₀O₃₆-O(SiC₁₈H₃₇)₂ as a photocatalyst. The four different photocatalysts dissolved in chloroform successfully photoreduced gold ions dissolved in water in a two-phase (chloroform/water) system under UV irradiation (λ< 475 nm). The γ-SiW₁₀O₃₆/DODA photocatalyst exhibited the best activity and was able to recover gold from solution. It was suggested that one-electron reduced γ-SiW₁₀O₃₆^9- , which was formed by UV irradiation, reduced gold ions to produce large two-dimensional particles. The formation of sheet-like particles indicates that the reduction of gold ions occurred at the interface between chloroform and water.

Abstract: A series of perovskite-type oxides catalyst LaAl_1-xNi_xO₃ (0≤x≤1) and modified by substitute noble metal La_0.4Al_0.2Ni_0.8M_0.6O₃ (M=Pt, Pd, Ru, Rh, Ir) prepared by the sol-gel method shows high activity, stability, good resistance to carbon deposition and sintering of the catalyst for the reforming of methane reaction. The reaction was studied under continuous flow using a mixture of CH₄:CO₂=1:1. Catalysts were characterized by using BET, XRD, SEM, EDS, and HR-TEM. The specific surface area of catalysts varied greatly from 3.07 to 10.18 m²/g with the different substitution (x) following calcination at 850°C. XRD analysis of the solids shows LaNiO₃ and/or LaAlO₃ as the main phases present on the solids depending on the degree of substitution and more intense peaks and cell parameters showed formation of Ni-Al solid solutions. SEM coupled to an energy dispersive X-ray spectrometer (EDS) shows the possibility to obtain a solid solution of LaAl_1-xNi_xO₃ (0≤x≤1) with propionic acid as solvent. The obtained results revealed that the Rh and Ru catalysts showed the highest activity and also showed a high catalytic stability without any decrease in methane conversion up to 3000min of reaction.