Nano

Personnel working in a confined environment can be exposed to hazardous gases. Certain gases can be extremely dangerous even in concentrations as low as a few parts per billion. The use of small and sensitive nanosensors can allow the placement of multiple devices over a large area, thus allowing for a precise and timely determination of a gas leak. ASRC Aerospace and its research partners are developing nanosensors for the detection of various gases, including but not limited to: H₂, NH₃, N₂O₄, hydrazine, and others. Initial laboratory testing has demonstrated the capability to detect the gases in concentrations as low as a few parts per billion and laboratory evaluation is ongoing to determine the sensitivity at levels in the order of parts per trillion. Different coatings and electrodes are currently being evaluated to determine the optimum configuration for the detection and identification of a variety of gases.

Pyrene is a high molecular weight polycyclic aromatic hydrocarbon (PAH) that is found in water systems worldwide. It is harmful to living organisms, even when taken in very small amounts. The photocatalytic degradation of pyrene in porous Pt/TiO₂–SiO₂ photocatalyst (PPtPC) suspension under UV irradiation was investigated in this study. PPtPC was prepared by a simple heat treatment of the compacted powder mixtures of anatase TiO₂ and amorphous SiO₂ with camphor as a pore directing template, followed by coating platinum by the dip-coating method. X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive analysis of the X-ray (EDX) system, and Brunauer–Emmett–Teller (BET) were used to characterize PPtPC. The degradation kinetics of pyrene in different experimental conditions, such as initial concentration of pyrene, oxygen concentrations, pH, and temperature, were investigated. The durability of PPtPC was also tested. The results indicate that the structure of TiO₂ in PPtPC is anatase. The aggregated size of PPtPC is in the range of 10–100 μm, the mean pore diameter is 3 nm, and the BET surface area is 109 m² g^-1. The photocatalytic degradation process of pyrene follows pseudo-first-order kinetics. The rate constants increase as the initial concentration of pyrene and pH decrease. Higher temperature slightly enhances the rate constant. The dissolved oxygen in the photocatalytic degradation process is not as important as in the photolysis process. The recovered PPtPC still shows high photoactivity. This work suggests that PPtPC offers a promising method for high molecular weight PAH removal.

Silicon-nitride-based composites with 3 wt% of multi-wall and single-wall carbon nanotubes and graphene have been prepared. A manufacturing process has been worked out to avoid the damage of nanotubes and graphene during sintering. This method provides their preservation even in severe circumstances at temperature 1700°C and gas pressure 2 MPa. In this work, the conductivity according to the type and concentration of the carbon additives was observed by applying four-point DC resistance measurements. Insulator and conductor composites can be produced depending on the type of additives.

The effect of ultraviolet, visible and near-infrared irradiation on the yield and morphology of single crystalline C₆₀ fullerene nanowhiskers (FNWs) and nanotubes (FNTs) was investigated in an effort to produce large-scale quantities of FNWs and FNTs. These fullerene nanomaterials were synthesized by the liquid–liquid interfacial precipitation method using pyridine and isopropyl alcohol (IPA) as solvents. The C₆₀–pyridine solution was illuminated using different wavelengths for 24 h at ambient pressure and temperature before addition of IPA. High yields (30–38 mg/L) were obtained upon irradiation using wavelengths in the ultraviolet region in accordance with the increased photoabsorption signal of solid C₆₀ and C₆₀ dissolved in pyridine acquired by a UV-VIS-NIR spectrophotometer. However, elevated yields (21–27 mg/L) were also obtained in the 600–800 nm regions, where C₆₀ absorption is particularly weak. Such an enhanced yield of FNTs and FNWs is probably related to the reported rise in transient absorption of the triplet excited state of C₆₀ in the 740 nm region formed by the decay of the photoexcited singlet C₆₀ through intersystem crossing. The formation of photopolymerized fullerene nanofibers was also observed by Raman spectroscopy, it is attributed to ultraviolet and visible light irradiation. SEM and TEM observations suggest that preparation of FNWs and FNTs by irradiation using different wavelengths of light does not produce apparent morphological transformations on the surface of these fullerene materials.

Tubular, needle-like crystals of C₆₀ with diameters ranging from micro to nano sizes have been synthesized by the liquid–liquid interfacial precipitation (LLIP) method. The C₆₀ nano- and microtubes can absorb various solutions of alcohol and water, showing that they can be promising containers for materials storage and recovery. Further, C₆₀ microtubes vertically aligned on porous alumina membranes have been successfully prepared for the first time by a modified LLIP method. The vertically aligned C₆₀ microtubes will find a variety of application for bio and environmental uses.

Dithionite can be used to reduce Fe(II) and produce nanoscale zero-valent iron (nZVI) under conditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfite hydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does not appear to affect their degradation performance under air or N₂ gas conditions. The efficiency of trichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured using dithionite (nZVI_S2O4), is similar to if not slightly better than that of the more conventional borohydride procedure (nZVI_BH4). The other advantages of the dithionite method are that (i) it uses a less expensive and widely available reducing agent, and (ii) there is no production of potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVI_S2O4 particles results in different byproducts than those produced when nZVI_BH4 particles are used. The low oxidant yield based on hydroxybenzoic acid generation is offset by the production of higher concentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH^• addition is not the primary oxidation pathway when one is using the nZVI_S2O4 particles. It is proposed that sulfate radicals () are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVI_S2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions.

Two types of ferrocene(Fc)-doped C₆₀ nanowhiskers [C₆₀/Fc NWs and C₆₀/ferrocene pyrrolidine-C₆₀(C₆₀-Fc) NWs] were prepared by the liquid–liquid interfacial precipitation method using toluene solution of C₆₀ and Fc or C₆₀-Fc and isopropyl alcohol (IPA). The morphology of C₆₀ precipitates was remarkably changed by the addition of Fc or C₆₀-Fc to the C₆₀ toluene solution. The scanning TEM mapping analysis of C₆₀/Fc NWs showed that the intensity of ferrocene is high at the edge, indicating that ferrocene covers the outside surface of the NWs. In the case of C₆₀/C₆₀-Fc NWs, however, the scanning TEM mapping analysis showed that C₆₀-Fc disperses well in the NWs.

The growth rate of C₆₀ fullerene nanowhiskers (C₆₀NWs) prepared by the liquid–liquid interfacial precipitation method is measured and the growth mechanism is discussed. The growth of C₆₀NWs is investigated from the data obtained at the growth temperatures of 5, 10, 15 and 20°C. It is found that the convection of the solution scarcely influences the growth rate, suggesting that a surface reaction of C₆₀ molecules dominates the growth process. The activation energy of C₆₀NWs' growth is estimated at about 52.8 kJ/mol from their initial stage of growth. This activation energy is much greater than that of C₆₀ diffusion in solutions found in the literature. This result suggests that the desolvation process of C₆₀ on the whisker surface governs the growth of C₆₀NWs.

In this paper we report on the preparation of nanobrushes of ZnO on quartz substrate by a direct atmosphere evaporation method using Zn metal flakes. Activated charcoal was used as a catalyst that facilitated the formation of nanobrushes in which the brush stem was about 15–20 μm in length and the bristles (100–200 nm thick) were made up of nanofibrous ZnO whose tips were 10–15 nm in width and were angled in some cases. These aligned nanobrushes can find potential applications as nanopower generators and high aspect ratio AFM probes by virtue of the piezoelectric property of ZnO. This technique is simple for realizing aligned ZnO nanobrushes with metallic Zn as the source material.

Here we report, for the first time, the synthesis of highly crystalline novel mesoporous carbon/nitrogen (C/N)-codoped TiO₂ (MCNT) using ethylene diamine and carbon tetrachloride as the source for nitrogen and carbon, KIT-6 as the template, and titanium tetraisopropoxide as the TiO₂ source. The obtained material has been unambiguously characterized by various sophisticated techniques. XRD and TEM analysis revealed that the MCNT material possesses highly crystalline 3D structure with a continuous network of mesoporous channels as well as structure corresponding to TiO₂. UV-DRS analysis indicated that light absorption shifted to lower energy and stronger absorption in the visible light region. XPS revealed that C and N were doped effectively and C or N dopants might be present in the chemical environment of Ti–O–N or Ti–O–C. It has been found that the material is highly crystalline and possesses high surface area, pore volume and uniform pore size distribution. Owing to its textural characteristics, it could be useful for various applications, such as photocatalysis, fuel cells, bulky biomolecule adsorption and nanotechnology.

TiO₂ aerogel–10 mol% TiO₂ nanowire composite was prepared by a sol–gel technique with the addition of TiO₂ nanowires to TiO₂ sol, followed by supercritical drying in CO₂. TiO₂ nanowires (anatase with minor rutile phases) as dispersoid were prepared by a hydrothermal process followed by calcination in air at 600°C. The TiO₂ nanowires were dispersed in a 2-propanol/H₂O/HNO₃ solution, and the mixture was added drop by drop to a tetrabutyl orthotitanate [i.e. Ti (IV) n-butoxide] solution in 2-propanol. After gelation, the TiO₂ alcogel–TiO₂ nanowire composite was dried in supercritical CO₂ to obtain the final, TiO₂ aerogel–TiO₂ nanowire composite. TEM analysis revealed that a unique "nanowire network" structure was formed within the mesoporous aerogel matrix. The aerogel–TiO₂ nanowire composite had a relatively large surface area 427 m²/g, with mesopores ~ 16 nm in diameter and a pore of volume of 1.63 cm³/g.

The objective of this investigation is to evaluate a series of polymer electrolyte membrane materials based on sulfonated ladder pyridine polymers and SiO₂ nanoparticles that enhance water retention and favor high temperature (> 120°C) applications. Nanoparticles are used to improve water uptake at levels of 20–38% to increase the level of sulfonation. A study of relevant characteristics of these polymers will provide an alternative to existing polymers, thus offering simple processing steps, as well as nonexotic polymers and higher performances.

Theoretical investigation of the interaction between positive hydrogen ions and electrons located in wurtzite InN containing oxygen impurity atoms is presented in this paper. The interaction is investigated on the basis of the energy pockets for both the electrons and the holes having places in the structure of InN containing oxygen atoms. These energy pockets are found on the basis of the electron band structure of wurtzite InN containing oxygen impurity atoms. A model of the system located electron–positive hydrogen ion is created. It is called the "inversed" hydrogen model, because the electron is fixed in the pocket, and the positive hydrogen ion can change its position (this ion can either be on the surface of InN or belong to a neighboring quasi-elementary cell). The Schrödinger equation for the "inversed" hydrogen model of the electron–hydrogen ion system is determined. The binding energy and the hydrogen-like energy levels of the electron–positive system hydrogen ion system are found.

Noise plays a major role in the behavior of various physical and biological systems, its effects being increasingly pronounced with decrease in system size. While it is jeopardizing the future development of several nanotechnologies, such as magnetic data storage, noise can also play a constructive role in many nonlinear systems, activating a resonance response. In this paper, it is proven that various hysteretic systems can exhibit such coherent behavior — a phenomenon that is generally known as coherence resonance when is solely induced by noise, and stochastic resonance when an external oscillatory signal is present. The quantity used to characterize the regularity of the stochastic output is the power spectrum, which displays a maximum at the resonance frequency. The calculation of the spectral densities for the outputs of hysteretic systems is performed in the framework of stochastic processes defined on graphs. The case of hysteretic systems described by rectangular loops is discussed and analytical expressions for the output power spectra are derived. These theoretical results suggest that hysteretic systems can be used by nanotechnology for concentrating the energy of a flat, noisy input into a short bandwidth frequency region.

The photocatalytic activity of zinc oxide (ZnO) nanoparticles, films and nanowires as a potential visible light photocatalyst is presented in this work. ZnO nanoparticles were synthesized in different alcoholic solvents. Crystal defects were introduced either by doping the crystallites with manganese or by fast crystallization (using microwave irradiation during synthesis). ZnO, with a band gap of 3.37 eV, normally absorbs electromagnetic waves in the ultraviolet region, but introducing defects into its crystal lattice can shift the absorption more toward the visible light band from 400 nm to 700 nm by creating intermediate states which inhibit electron–hole recombination. The undoped ZnO nanoparticles synthesized using microwaves showed comparable photocatalytic activities to the doped samples using the conventional heating method. To increase the effective surface area of the photocatalyst, ZnO nanowires were grown by a solution-based technique. Methylene blue degradation was observed to be enhanced in the presence of the ZnO nanowires compared to the ZnO nanoparticles. Intentional defect creation in photocatalysts could be an attractive possibility to apply in the visible light photocatalytic degradation studies.

Fe-decorated fullerene nanowhiskers were prepared by using the liquid–liquid interfacial precipitation method. The prepared nanowhiskers were characterized using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD) and Raman spectroscopy. Formation of both tubular and nontubular nanowhiskers was observed with fine dispersion of Fe ions. The XRD and Raman-spectroscopic studies showed the fcc crystalline nature and polymerization of the nanowhiskers, respectively. The results were compared with Ce- and Ni-incorporated fullerene nanowhiskers.