Synthesis of hierarchical MoO2/MoS2 nanofibers for electrocatalytic hydrogen evolution.

Perpendicularly attached MoS2 nanosheets on MoO2 conductive nanofibers were synthesized by combining electrospinning, calcination, and sulfurization processes. Compared to randomly stacked MoS2 nanosheets on MoO2 nanofiber, they show greater hydrogen evolution reaction (HER) performance (i.e., onset potential of -180 mV versus normal hydrogen electrode with the Tafel slope of 59 mV dec-1). HER performance decreases with increasing MoS2 nanocrystal size.

Synthesis of gold structures by gold-binding peptide governed by concentration of gold ion and peptide.

Although biological synthesis methods for the production of gold structures by microorganisms, plant extracts, proteins, and peptide have recently been introduced, there have been few reports pertaining to controlling their size and morphology. The gold ion and peptide concentrations affected on the size and uniformity of gold plates by a gold-binding peptide Midas-11. The higher concentration of gold ions produced a larger size of gold structures reached 125.5 µm, but an increased amount of Midas-11 produced a smaller size of gold platelets and increased the yield percentage of polygonal gold particles rather than platelets. The mechanisms governing factors controlling the production of gold structures were primarily related to nucleation and growth. These results indicate that the synthesis of gold architectures can be controlled by newly isolated and substituted peptides under different reaction conditions.

Electrochemical synthesis of CdTe/SWNT hybrid nanostructures and their tunable electrical and optoelectrical properties.

A facile electrodeposition technique was utilized to deposit single-walled carbon nanotubes (SWNTs) with cadmium telluride (CdTe) with well-controlled size, density, surface morphology, and composition. By controlling the applied charge, the morphology of these hybrid nanostructures was altered from CdTe nanoparticles on SWNTs to SWNT/CdTe core/shell nanostructures and the composition of the CdTe nanoparticles was altered from Te-rich (29 at% Cd) to Cd-rich (79 at% Cd) CdTe by adjusting the deposition potential. The electrical and optoelectrical properties of these hybrid nanostructures showed that photo-induced current can be tuned by tailoring the conductivity type (n-type or p-type), morphology, and size of the CdTe nanostructures, with a maximum photosensitivity (ΔI/I(0)) of about 30% for SWNT/Cd-rich CdTe (n-type) core/shell nanostructures. This work demonstrates a novel approach for synthesizing metal chalcogenide/SWNT hybrid nanostructures for various electrical and optoelectrical applications.

Growth mechanism of amorphous selenium nanoparticles synthesized by Shewanella sp. HN-41.

Shewanella sp. HN-41 was exploited for selenium nanoparticles synthesis from aqueous selenite compounds under anaerobic conditions. Various reaction conditions, including reaction time, initial biomass, and initial selenite concentration, were systematically investigated to determine their effects on particle size distribution and formation rate. The biomass concentration of Shewanella sp. HN-41 had no significant effect on average particle size but strongly influenced reduction rate and size distribution. Initial selenite concentration (0.01-1.0 mM) also had no significant effect on the average particle size, but affected the early growth stage mechanism of selenium particle production, which was modeled using a Michaelis Menten model. The HR-TEM and SAED patterns indicated that the synthesized selenium nanoparticles were amorphous.

Peptide-mediated shape- and size-tunable synthesis of gold nanostructures.

While several biological processes have been shown to be useful for the production of well-designed, inorganic nanostructures, the mechanism(s) controlling the size and shape of nano and micron size particles remains elusive. Here we report on the controlled size- and shape-specific production of gold nanostructures under ambient reaction conditions using a dodecapeptide, Midas-2, originally selected from a phage-displayed combinatorial peptide library. Single amino acid changes in Midas-2 greatly influence the size (a few nanometers to approximately 100 microm) and shape (nanoparticles, nanoribbons, nanowires and nanoplatelets) of the gold nanostructures produced, and these are controllable by adjusting the solution pH and gold ion concentration. The ability to control the shape and size of the gold nanostructures by changing the peptide structure and reaction conditions will lead to many potential applications, including nanoelectronics, sensors and optoelectronics, because of their unique size- and shape-dependent optical and electrical properties.

Sensitive detection of H2S using gold nanoparticle decorated single-walled carbon nanotubes.

Herein, we demonstrate that highly sensitive conductometric gas nanosensors for H(2)S can be synthesized by electrodepositing gold nanoparticles on single-walled carbon nanotube (SWNT) networks. Adjusting the electrodeposition conditions allowed for tuning of the size and number of gold nanoparticles deposited. The best H(2)S sensing performance was obtained with discrete gold nanodeposits rather than continuous nanowires. The gas nanosensors could sense H(2)S in air at room temperature with a 3 ppb limit of detection. The sensors were reversible, and increasing the bias voltage reduced the sensor recovery time, probably by local Joule heating. The sensing mechanism is believed to be based on the modulation of the conduction path across the nanotubes emanating from the modulation of electron exchange between the gold and carbon nanotube defect sites when exposed to H(2)S.

Size-controlled electrochemical synthesis and properties of SnO2 nanotubes.

SnO(2) nanotubes with controlled diameter and length were synthesized using an electrochemical method at room temperature. The length and wall thickness of the nanotubes increased monotonically with the deposition time and the diameter of the nanotubes was altered by varying the pore size of the scaffolds. Post-annealing at 400 degrees C in dry air significantly improved the crystallinity while maintaining the nanotube structure. The temperature-dependent photoluminescence spectra indicated an activation energy of 58 meV for emission centered at 410 nm. The temperature-dependent electrical resistance revealed that the dominant electrical conduction mechanism alters from the ionization of the main donor centers to impurity scattering as the temperature decreases. The electrical conductance of 200 nm diameter nanotubes increased to 33 times the original value upon UV illumination at 254 nm.

Magnetically assembled 30 nm diameter nickel nanowire with ferromagnetic electrodes.

Facile, cost-effective, and manufacturable techniques to create single-nanowire based devices with good electrical interconnects is demonstrated by combining template directed electrodeposition, magnetic assembly, and a post-annealing in a reducing environment. Nickel nanowires with a diameter of approximately 30 nm were electrodeposited from low-stress nickel sulfamate baths at room temperature using in-house made anodized alumina as a nanotemplate. After electrodeposition, nanowires were released from the template, efficiently positioned, trapped, and assembled on ferromagnetic electrodes using the magnetic interaction between the nanowires and the electrodes. By annealing the interconnect in a reducing environment of 5%H(2)+95%N(2) at 300 °C for 30 min, the interconnect's resistance was dramatically reduced from >10 M Ω to 835 Ω. Magnetotransport studies at 300 K on a single nickel interconnect with diameters ranging from 30 to 200 nm show a strong diameter dependent magnetoresistance, which might be attributed to different domain structure within the interconnect.