Synthesis and Thermoelectric Characterization of Lead Telluride Hollow Nanofibers.

Lead telluride (PbTe) nanofibers were fabricated by galvanic displacement of electrospun cobalt nanofibers where their composition and morphology were altered by adjusting the electrolyte composition and diameter of sacrificial cobalt nanofibers. By employing Co instead of Ni as the sacrificial material, residue-free PbTe nanofibers were synthesized. The Pb content of the PbTe nanofibers was slightly affected by the Pb2+ concentration in the electrolyte, while the average outer diameter increased with Pb2+ concentration. The surface morphology of PbTe nanofibers was strongly dependent on the diameter of sacrificial nanofibers where it altered from smooth to rough surface as the Pb2+ concentration increased. Some of thermoelectric properties [i.e., thermopower (S) and electrical conductivity(σ)] were systematically measured as a function of temperature. Energy barrier height (Eb) was found to be one of the key factors affecting the thermoelectric properties-that is, higher energy barrier heights increased the Seebeck coefficient, but lowered the electrical conductivity.

Viral-templated gold/polypyrrole nanopeapods for an ammonia gas sensor.

One-dimensional gold/polypyrrole (Au/PPy) nanopeapods were fabricated using a viral template: M13 bacteriophage. The genetically modified filamentous virus displayed gold-binding peptides along its length, allowing selective attachment of gold nanoparticles (Au NPs) under ambient conditions. A PPy shell was electropolymerized on the viral-templated Au NP chains forming nanopeapod structures. The PPy shell morphology and thickness were controlled through electrodeposition potential and time, resulting in an ultra-thin conductive polymer shell of 17.4 ± 3.3 nm. A post-electrodeposition acid treatment was used to modify the electrical properties of these hybrid materials. The electrical resistance of the nanopeapods was monitored at each assembly step. Chemiresistive ammonia (NH3) gas sensors were developed from networks of the hybrid Au/PPy nanostructures. Room temperature sensing performance was evaluated from 5 to 50 ppmv and a mixture of reversible and irreversible chemiresistive behavior was observed. A sensitivity of 0.30%/ppmv was found for NH3 concentrations of 10 ppmv or less, and a lowest detection limit (LDL) of 0.007 ppmv was calculated. Furthermore, acid-treated devices exhibited an enhanced sensitivity of 1.26%/ppmv within the same concentration range and a calculated LDL of 0.005 ppmv.

Synthesis and optimization of Fe2O3 nanofibers for chromate adsorption from contaminated water sources.

In this work, α-Fe2O3 nanofibers were synthesized via electrospinning and characterized to observe optimal morphological and dimensional properties towards chromate removal. The Fe2O3 nanofiber samples were tested in aqueous solutions containing chromate (CrO4(2-)) to analyze their adsorption capabilities and compare them with commercially-available Fe2O3 nanoparticles. Synthesized Fe2O3 nanofibers were observed with a variety of different average diameters, ranging from 23 to 63 nm, while having a constant average grain size at 34 nm, point zero charge at pH 7.1, and band gap at 2.2 eV. BET analysis showed an increase in specific surface area with decreasing average diameter, from 7.2 to 59.2 m(2)/g, due to the increased surface area-to-volume ratio with decreasing nanofiber size. Based on CrO4(2-) adsorption isotherms at pH 6, adsorption capacity of the Fe2O3 nanofibers increased with decreasing diameter, with the 23 nm sized nanofibers having an adsorption capacity of 90.9 mg/g, outperforming the commercially-available Fe2O3 nanoparticles by nearly 2-fold. Additionally, adsorption kinetics was also analyzed, increasing with decreasing nanofiber diameter. The enhanced performance of the nanofiber is suggested to be caused solely due to the increased surface area, in part by its size and morphology. Electrospun Fe2O3 nanofibers provide a promising solution for effective heavy metal removal through nanotechnology-integrated treatment systems.

Synthesis and optimization of Ag-TiO2 composite nanofibers for photocatalytic treatment of impaired water sources.

In this work, Ag-TiO2 composite nanofibers were fabricated by electrospinning, where the composition and crystallinity were tuned by controlling the precursor composition and annealing conditions. Characterization revealed that bulk-embedded Ag nanoparticles inhibited anatase-to-rutile phase transformation and a decrease in band gap from 3.2 down to 2.8 eV with increase in the Ag content. The photocatalytic activity of 0.5 at.% Ag-TiO2 nanofibers toward phenol degradation was the greatest, outperforming both unmodified TiO2 nanofibers and commercially available TiO2 Aeroxide(®) P25 by a factor of ∼3. The high reactivity of the low content Ag-TiO2 nanofibers can be attributed to the addition of electron traps, which provide efficient carrier separation and, therefore, decreased recombination. However, further increase in Ag content led to lower photoreactivity, most likely due to the growth of the Ag nanoparticles, which suggests an optimal size of 2 to 3 nm for the Ag nanoparticles at 0.5 at.% provided the greatest photoreactivity. Ag-TiO2 nanofibers show great promise as innovative and highly performing nanomaterials for future nanotechnology-based treatment systems, particularly when the photoreactivity demonstrate herein is used in synergy with the established antimicrobial activity of nano-Ag.

Tailored synthesis of photoactive TiO 2 nanofibers and Au/TiO 2 nanofiber composites: structure and reactivity optimization for water treatment applications.

Titanium dioxide (TiO2) nanofibers with tailored structure and composition were synthesized by electrospinning to optimize photocatalytic treatment efficiency. Nanofibers of controlled diameter (30-210 nm), crystal structure (anatase, rutile, mixed phases), and grain size (20-50 nm) were developed along with composite nanofibers with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts. Their reactivity was then examined in batch suspensions toward model (phenol) and emerging (pharmaceuticals, personal care products) pollutants across various water qualities. Optimized TiO2 nanofibers meet or exceed the performance of traditional nanoparticulate photocatalysts (e.g., Aeroxide P25) with the greatest reactivity enhancements arising from (i) decreasing diameter (i.e., increasing surface area), (ii) mixed phase composition [74/26 (±0.5) % anatase/rutile], and (iii) small amounts (1.5 wt %) of surface-deposited, more so than bulk-integrated, Au nanoparticles. Surface Au deposition consistently enhanced photoactivity by 5- to 10-fold across our micropollutant suite independent of their solution concentration, behavior that we attribute to higher photocatalytic efficiency from improved charge separation. However, the practical value of Au/TiO2 nanofibers was limited by their greater degree of inhibition by solution-phase radical scavengers and higher rate of reactivity loss from surface fouling in nonidealized matrixes (e.g., partially treated surface water). Ultimately, unmodified TiO2 nanofibers appear most promising for use as reactive filtration materials because their performance was less influenced by water quality, although future efforts must increase the strength of TiO2 nanofiber mats to realize such applications.

One-dimensional nanostructures based bio-detection.

This paper presents a review on recent developments of one-dimensional (1-D) nanostructures based label-free chemiresistive/chemFET biosensors and the various sensing mechanisms used for biomolecular detection. The sensor performance including sensitivity, selectivity, and reliability is compared in terms of material synthesis of the sensor's element, relating surface functionalization schemes to their properties with respect to selected bioreceptors, its method of fabrication, and its intended operation. As a final point, we outline the prospects of chemiresistive/chemFET biosensors and recommend specific advancements in this field.

Highly sensitive hydrogen sulfide (H2S) gas sensors from viral-templated nanocrystalline gold nanowires.

A facile, site-specific viral-templated assembly method was used to fabricate sensitive hydrogen sulfide (H2S) gas sensors at room temperature. A gold-binding M13 bacteriophage served to organize gold nanoparticles into linear arrays which were used as seeds for subsequent nanowire formation through electroless deposition. Nanowire widths and densities within the sensors were modified by electroless deposition time and phage concentration, respectively, to tune device resistance. Chemiresistive H2S gas sensors with superior room temperature sensing performance were produced with sensitivity of 654%/ppm(v), theoretical lowest detection limit of 2 ppb(v), and 70% recovery within 9 min for 0.025 ppm(v). The role of the viral template and associated gold-binding peptide was elucidated by removing organics using a short O2 plasma treatment followed by an ethanol dip. The template and gold-binding peptide were crucial to electrical and sensor performance. Without surface organics, the resistance fell by several orders of magnitude, the sensitivity dropped by more than a factor of 100 to 6%/ppm(v), the lower limit of detection increased, and no recovery was detected with dry air flow. Viral templates provide a novel, alternative fabrication route for highly sensitive, nanostructured H2S gas sensors.

Palladium/single-walled carbon nanotube back-to-back Schottky contact-based hydrogen sensors and their sensing mechanism.

A Schottky contact-based hydrogen (H2) gas sensor operable at room temperature was constructed by assembling single-walled carbon nanotubes (SWNTs) on a Si/SiO2 substrate bridged by Pd microelectrodes in a chemiresistive/chemical field effect transistor (chemFET) configuration. The Schottky barrier (SB) is formed by exposing the Pd-SWNT interfacial contacts to H2 gas, the analyte it was designed to detect. Because a Schottky barrier height (SBH) acts as an exponential bottleneck to current flow, the electrical response of the sensor can be particularly sensitive to small changes in SBH, yielding an enhanced response to H2 gas. The sensing mechanism was analyzed by I-V and FET properties before and during H2 exposure. I-Vsd characteristics clearly displayed an equivalent back-to-back Schottky diode configuration and demonstrated the formation of a SB during H2 exposure. The I-Vg characteristics revealed a decrease in the carrier mobility without a change in carrier concentration; thus, it corroborates that modulation of a SB via H2 adsorption at the Pd-SWNT interface is the main sensing mechanism.

Metal nanoparticles and DNA co-functionalized single-walled carbon nanotube gas sensors.

Metal/DNA/SWNT hybrid nanostructure-based gas sensor arrays were fabricated by means of ink jet printing of metal ion chelated DNA/SWNTs on microfabricated electrodes, followed by electroless deposition to reduce metal ions to metal. DNA served as a dispersing agent to effectively solubilize pristine SWNTs in water and as metal ion chelating centers for the formation of nanoparticles. Noble metals including palladium, platinum, and gold were used because the high binding affinity toward specific analytes enhances the selectivity and sensitivity. The sensitivity and selectivity of the gas sensors toward various gases such as H2, H2S, NH3, and NO2 were determined at room temperature. Sensing results indicated the enhancement of the sensitivity and selectivity toward certain analytes by functionalizing with different metal nanoparticles (e.g., Pd/DNA/SWNTs for H2 and H2S). The combined responses give a unique pattern or signature for each analyte by which the system can identify and quantify an individual gas.

Branched tellurium hollow nanofibers by galvanic displacement reaction and their sensing performance toward nitrogen dioxide.

Electrospinning and galvanic displacement reaction were combined to synthesize ultra-long hollow tellurium (Te) nanofibers with controlled dimensions, morphology and crystallinity by simply tailoring the electrolyte concentration applied. Within different morphologies of nanofibers, the branched Te nanostructure shows the greatest sensing performance towards NO2 at room temperature.

Synthesis of ultra-long hollow chalcogenide nanofibers.

Electrospinning and galvanic displacement reaction are combined to fabricate ultra-long hollow chalcogen and chalcogenide nanofibers in a cost-effective and high throughput manner. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions and morphology, thereby imparting control over the composition and shape of the nanostructures evolved during galvanic displacement reaction. It is believed to be a general route to form various ultra-long hollow semiconducting nanofibers.