Using a unique oblique angle co-deposition technique, well-aligned arrays of Ag nanoparticle embedded TiO2 composite nanorods have been fabricated with different concentrations of Ag. The structural, optical, and photocatalytic properties of the composite nanostructures are investigated using a variety of experimental techniques and compared with those of pure TiO2 nanorods fabricated similarly. Ag nanoparticles are formed in the composite nanorods, which increase the visible light absorbance due to localized surface plasmon resonance. The Ag concentrations and the annealing conditions are found to affect the size and the density of Ag nanoparticles and their optical properties. The Ag nanoparticle embedded TiO2 nanostructures exhibit enhanced photocatalytic activity compared to pure TiO2 under visible- or UV-light illumination. Ag plays different roles in assisting the photocatalysis with different light sources. Ag can be excited and can inject electrons to TiO2, working as an electron donor under visible light. While under UV illumination, Ag acts as an electron acceptor to trap the photogenerated electrons in TiO2. Due to the opposite electron transfer direction under UV and visible light, the presence of Ag may not result in a greater enhancement in the photocatalytic performance.

We investigate Au-decorated Fe2O3 nanoparticle catalysts, Fe2O3–Au, where the supporting Fe2O3 nanoparticles are of different shapes: spheres, rings, and tubes. The decoration procedure for the Fe2O3–Au nanoparticles is identical for each shape, and is analogous to the synthesis of pure Au nanoparticles (AuNPs). These similarities allows for direct comparison between the different shapes and the pure AuNPs. The morphological, optical, and magnetic characterizations reveal that the Fe2O3–Au nanoparticles are hybrid structures exhibiting both plasmonic and magnetic properties. The different shape Fe2O3–Au nanoparticles and the AuNPs are evaluated for their ability to catalytically reduce 4-nitrophenol. Remarkably, it is found that Fe2O3–Au nanoparticles are more efficient catalysts than AuNPs because they can achieve the same, or better, catalytic reaction rates using significantly smaller quantities of Au, which is the catalytically active material. Taking into account the Au-loadings, the Fe2O3 rings and tubes are superior to the Fe2O3 spheres as catalytic supports due to their γ-Fe2O3 crystal phase. It is also shown that the Fe2O3–Au nanoparticles have the additional benefit for catalysis in that they can be recovered and reused via magnetic collection. Furthermore, the Fe2O3–Au nanoparticles and AuNPs are found to efficiently transduce heat from light through plasmonic absorbance, and this phenomenon is exploited to demonstrate the photothermal catalytic reduction of 4-nitrophenol.

Only a few remaining technical hurdles currently prevent the implementation of SERS as a mainstream detection technology. Although oblique-angle deposited silver nanorod arrays provide superior analytical figures of merit for SERS sensing, stability issues of silver surfaces can impede their use for real-world sensing applications within certain environments. To circumvent this issue, silver nanorod arrays are modified with a straight-forward, inexpensive Au-coating via a galvanic replacement reaction. The morphological, structural, compositional, and optical properties of the Au-modified Ag nanorod arrays are studied by multiple ex situ morphological characterization techniques and in situ optical absorbance spectroscopy. Depending on the reaction time, the Au coating experiences five different stages of the morphological and compositional changes. The porosity of the Au layer and the content of Ag decrease with reaction time. The optical measurements show that the representative localized plasmon resonance peak of the nanorod red-shifts as the reaction proceeds. The surface enhanced Raman scattering (SERS) intensity, tested using 4-mercaptophenol, decreases exponentially with reaction time, due to the compositional evolution of the nanostructure from pure Ag to a Au-Ag alloy with increasing Au content. We show that the Au-modified Ag nanorod is very stable in NaCl solution compared to the as-deposited Ag nanorod, and the 20 or 30 minute Au-modified Ag nanorod substrate shows an improved SERS sensitivity for air contamination detection. Such an improved SERS substrate can be used in more hostile environments where a pure Ag nanorod substrate cannot be used, and is good for practical sensing applications.

In this work, hydrogen isotopes in the form of protium and deuterium were rapidly desorbed from magnetic-hydride iron oxide-palladium (Fe2O3-Pd) hybrid nanomaterials using an alternating magnetic field (AMF). Palladium, a hydride material with a well-known hydrogen isotope effect, was deposited on Fe2O3 magnetic nanoparticle support by solution chemistries and used as a hydrogen isotope storage component. The morphological, structural, optical, and magnetic studies reveal that the Fe2O3-Pd nanoparticles (NPs) are hybrid structures exhibiting both hydrogen isotope storage (Pd) and magnetic (Fe2O3) properties. The hydrogen isotope sorption/desorption behavior of metal hydride-magnetic nanomaterials was assessed by isothermal pressure-composition response curves (isotherms). The amount and rate of hydrogen isotope gas release was tuned by simply adjusting the strength of the magnetic field strength applied. Protium and deuterium displayed a similar loading capacity, namely H/M 0.55 and H/M=0.45, but different plateau pressures. Significant differences in the kinetics of release for protium and deuterium during magnetic heating were observed. A series of magnetically induced charge-discharge cycling experiments were conducted showing that this is a highly reproducible and robust process.