Synthesis and photocurrent of amorphous boron nanowires.

Although theoretically feasible, synthesis of boron nanostructures is challenging due to the highly reactive nature, high melting and boiling points of boron. We have developed a thermal vapor transfer approach to synthesizing amorphous boron nanowire using a solid boron source. The amorphous nature and chemical composition of boron nanowires were characterized by high resolution transmission electron microscopy, selected area electron diffraction, and electron energy loss spectroscopy. Optical properties and photoconduction of boron nanowires have not yet been reported. In our investigation, the amorphous boron nanowire showed much better optical and electrical properties than previously reported photo-response of crystalline boron nanobelts. When excited by a blue LED, the photo/dark current ratio (I/I0) is 1.5 and time constants in the order of tens of seconds. I/I0 is 1.17 using a green light.

Silica decorated TiO2 for virus inactivation in drinking water--simple synthesis method and mechanisms of enhanced inactivation kinetics.

A new method of modifying TiO2 photocatalysts with SiO2 is developed in which SiO2 nanoparticles are simply mixed with TiO2 in water under ambient conditions. This method does not require the use of toxic solvents or significant energy input. Although the SiO2 modification slightly reduces hydroxyl free radical production, the composite SiO2-TiO2 nanomaterials have markedly higher photocatalytic inactivation rates for a common surrogate virus, bacteriophage MS2 (up to 270% compared to the unmodified TiO2), due to the greatly improved adsorptive density and dark inactivation of MS2. The Langmuir isotherm describes the adsorption data well and shows that the TiO2 modified with 5% SiO2 has a maximum adsorption density qmax 37 times that of the unmodified TiO2. The Langmuir-Hinshelwood model fits the photocatalytic inactivation kinetic data well. The SiO2-TiO2 material produces a greater maximum initial inactivation rate yet a lower intrinsic surface reaction rate constant, consistent with the reduced hydroxyl radical production and enhanced adsorption. These results suggest that modifying photocatalyst surface to increase contaminant adsorption is an important strategy to improve photocatalytic reaction efficiency. Simple and cheap synthesis methods such as that used in this study bring photocatalysis closer to being a viable water treatment option.

3D nanoporous nanowire current collectors for thin film microbatteries.

Conventional thin film batteries are fabricated based on planar current collector designs where the high contact resistance between the current collector and electrodes impedes overall battery performance. Hence, current collectors based on 3D architectures and nanoscale roughness has been proposed to dramatically increase the electrode-current collector surface contact areas and hence significantly reduce interfacial resistance. The nanorod-based current collector configuration is one of several 3D designs which has shown high potential for the development of high energy and high power microbatteries in this regard. Herein we fabricate a nanoporous nanorod based current collector, which provides increased surface area for electrode deposition arising from the porosity of each nanorods, yet keeping an ordered spacing between nanorods for the deposition of subsequent electrolyte and electrode layers. The new nanostructured 3D current collector is demonstrated with a polyaniline (PANI)-based electrode system and is shown to deliver improved rate capability characteristics compared to planar configurations. We have been able to achieve stable capacities of ~32 µAh/cm(2) up to 75 cycles of charge/discharge even at a current rate of ~0.04 mA/cm(2) and have observed good rate capability even at high current rates of ~0.8 mA/cm(2).

Simple route to enhanced photocatalytic activity of p25 titanium dioxide nanoparticles by silica addition.

Silica doped TiO2(P25) nanoparticles are tested for its photocatalytic activity in the degradation of bacteriophage MS2. During our studies it was found that treatment of TiO2(P25) in the glass flasks sealed with silicone grease resulted in a significant improvement in the catalytic activity of the titania. Further improvement can be made by the purposeful reaction of TiO2(P25) with 2.5 wt % silica. This non in situ method of incorporating silica to TiO2(P25) nanoparticles is tested for their role in killing of viruses, and it is found that the rate constant is three times higher to kill viruses with the addition of silica. BET measurements show no significant change/increase in the surface area of silica doped TiO2(P25)-SiO2, compared to the undoped TiO2(P25). Further studies show that the addition of silica increases the adsorption of viruses onto the catalyst. There is a significant difference in the activity of the TiO2(P25)-SiO2 samples in the presence of methanol, supporting the notion that hydroxide radical (HO·) is responsible for the antiviral action. The TiO2(P25)-SiO2 either produces more HO· than non silica-doped material, or the enhanced adsorption of MS2 to the catalyst results in greater exposure to the HO·, or both mechanisms may work in concert. XPS studies suggest the formation of silica species on the surface of the TiO2(P25), while UV-visible spectroscopy suggests that the presence of the silica results in a small increase in the measured band gap. We suggest that the enhanced catalytic activity is a result of increased adsorption and/or band bending which can occur at the interface within TiO2(P25)-SiO2. One result of this would be a reduction of the electron-hole recombination, the formation of a greater concentration of OH·, and hence an improved catalytic performance.