Narrow Results

Inorganic fullerene-like (IF) nanoparticles of MoS₂ were synthesized using gas-phase reaction starting from MoCl₅ and H₂S. The IF-MoS₂ nanoparticles are spherical and in some cases faceted with diameters in general ranging between 20 and 80 nm. The IF-MoS₂ nanoparticles have large hollow cores, filled in some cases with amorphous material. Various parameters have been investigated to understand the growth and formation of the IF-MoS₂ nanoparticles. The parameters that have been studied include flow rates of the various carrier gases, temperature at which the reaction was carried out, time of the reaction and heating of the precursor material. The best set of conditions wherein maximum yields of the IF-MoS₂ nanoparticles are obtained have been identified. Additionally, annealing the as-obtained samples or heating them in a mixture of H₂ along with H₂S improves the crystallinity and reduces the amorphous material filling in the core. Apart from the fullerene-like nanoparticles under certain experimental conditions nanotubes of MoS₂ have also been obtained nonetheless in small yields.

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.

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.

Ultra-thin (10–100 nm) conformal coatings of poly(ethyl 2-cyanoacrylate) and poly(p-xylylene) have been synthesized via vapor deposition in the confined nanochannels of anodized alumina membranes. Poly(ethyl 2-cyanoacrylate) nanotubes and coaxial poly(ethyl 2-cyanoacrylate)/poly(p-xylylene) nanotubes with precisely-controlled wall thickness were obtained after the removal of the inorganic anodized alumina membrane. Platinum nanoparticles have also been deposited in the coaxial nanotubes via supercritical carbon dioxide.

Time-dependent wet-processing of HiPCo nanotubes in ~ 0.5 M phosphoric acid and its effect on the structural, transport, infrared light absorption and photoconduction characteristics have been studied. Nanotubes were treated for nominal time intervals of 1, 2 and 3 h. The treatment is found to be a two-step process that initially results in the removal/partial replacement of most pre-existing C-O, O–H and CH_x groups with phosphorous oxy and carbonyl groups. According to T-dependent current–voltage measurements, the differential conductance, G of nanotube network varies with temperature as ~ T^a, with a exhibiting a slight increase as a result of the treatment, attributed to a slight increase in disorder and not doping effects. The nanotubes processed for three hours also show an order of magnitude improvement in photoconduction response time compared to that of untreated tubes, with growth/decay characteristic time constants approaching a sub-second range.

New types of core–shell nanoparticles are reported: Pb@GaS fullerene-like and nanotubular structures, achieved via the continuously high reactor temperatures and ultra-hot strong-gradient annealing environments created by highly concentrated sunlight. Structural and chemical characterizations suggest a formation mechanism where vaporized Pb condenses into nanoparticles that are stabilized as they become covered by molten GaS, the ensuing crystallization of which creates the outer layers. Hollow-core GaS fullerene-like nanoparticles and nanotubes were also observed among the products, demonstrating that a single solar procedure can generate a variety of core–shell and hollow nanostructures. The proposed formation mechanisms can account for their relative abundance and the characterization data.

Pure and Eu-doped (1.0, 3.0, 5.0wt.%) $\alpha$-Fe₂O₃ (PFO and EFO) nanotubes and nanowires have been successfully synthesized through the combination of electrospinning and calcination techniques. The structures, morphologies and chemical compositions of the as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry (TG-DSC) and energy dispersive spectrum (EDS), respectively. To demonstrate the superior gas sensing performance of the doped nanotubes, a contrastive gas sensing study between PFO (EFO) nanotubes and nanowires was performed. It turned out that Eu doping could magnify the impact of morphology on gas sensitivity. Specifically, at the optimum operating temperature of 240${}^{\circ }$C, the response value of PFO nanotubes to 100ppm acetone is slightly higher than that of nanowires (3.59/2.20). EFO (3.0wt.%) nanotubes have a response of 84.05, which is almost 2.7 times as high as that of nanowires (31.54). Moreover, they possess more rapid response/recovery time (11s and 36s, respectively) than nanowires (17s and 40s, respectively). The lowest detection limit for acetone is 0.1ppm and its response is 2.15. In addition, both of EFO nanotubes and nanowires sensors have a good linearity (0.1–500ppm) and favorable selectivity in acetone detection.