Improving the electrical catalytic activity of Pt/TiO<Subscript>2</Subscript> nanocomposites by a combination of electrospinning and microwave irradiation

One of the greatest challenges in preparing TiO₂-based oxygen electrodes for PEM fuel cells is increasing the electrical catalytic activity of Pt nanoparticle/TiO₂ composites by improving the dispersion of Pt. This article describes a new way for improving the dispersion of Pt nanoparticles by depositing them on TiO₂ fibers and using microwave irradiation. The Pt nanoparticles used in this experiment is about 5 nm in diameter and the diameter of TiO₂ fibers could be controlled ranging from 30 to 60 nm and Pt nanoparticles still keep their size when the deposition amount is increased on the surface of TiO₂ fibers. The Pt nanoparticles were highly dispersed without agglomeration even at a weight percentage of composites as high as 40%. The position of Pt nanoparticles located in the fiber and the composition of Pt/TiO₂, which had great influence on the electric conductivity and electrical catalytic activity of the composite, could be easily controlled.     

Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.     

High-yield fabrication of W<Subscript>18</Subscript>O<Subscript>49</Subscript>@TiO<Subscript>2</Subscript> core–shell nanoparticles: microstructures and optical-thermal properties

In the present study, high-yield W₁₈O₄₉@TiO₂ core–shell nanoparticles were prepared by modified plasma arc gas condensation without any catalysts or substrates. All the as-prepared samples were characterized by FEG-SEM, XRD, FEG-STEM, and HAADF analytic techniques. The results of the structural analysis show that the as-prepared nanoparticles presenting a core–shell morphology with an average diameter of 43.5 ± 8.0 nm were composed of non-stoichiometric tungsten oxide (W₁₈O₄₉ phase) as the core (20–40 nm) and rutile-phase TiO₂ as the shell with non-uniform thickness (10–20 nm). For the optical properties of the as-prepared W₁₈O₄₉@TiO₂ core–shell nanoparticles, Raman spectroscopy and photoluminescence (PL) spectra were used. Compared with pure TiO₂ and W₁₈O₄₉ nanocrystals, the experimental results reveal that the defects in the lattice between the core and shell layers induced the board and shifted peaks in Raman spectra. Also, W₁₈O₄₉@TiO₂ core–shell nanoparticles exhibited green emission at 483 nm wavelength observed in PL spectrum. Thermal gravimetric analyzer (TGA) results indicate that the TiO₂ shell served a stable layer and prevented further oxidation from the atmosphere of the W₁₈O₄₉ core, thereby improving the thermal stability of W₁₈O₄₉ nanoparticles.     

Characterization and relative sonocatalytic efficiencies of a new MWCNT and CdS modified TiO2 catalysts and their application in the sonocatalytic degradation of rhodamine B

TiO₂ nanoparticles modified with MWCNTs and CdS were synthesized by the sol–gel method followed by solvothermal treatment at low temperature. The chemical composition and surface structure of the CdS/CNT–TiO₂ composites were investigated by X-ray diffraction, specific surface area measurements, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. Then a series of sonocatalytic degradation experiments were carried out under ultrasonic irradiation in the presence of CNT/TiO₂ and the CdS/CNT–TiO₂ composites. It was found that RhB was quickly and effectively degraded under different ultrasonic conditions. As expected, the nanosized CdS/CNT–TiO₂ photocatalyst showed enhanced activity compared with the non CdS treated CNT/TiO₂ material in the sonocatalytic degradation of RhB. The sonocatalyst CCTb with 34.68% contents of Ti heat treated at 500 °C for 1 h showed the highest sonocatalytic activity. The synergistic effect of the greater surface area and catalytic activities of the composite catalysts was examined in terms of their strong adsorption ability and interphase interaction by comparing the effects of different amounts of MWCNTs and CdS in the catalysts and their roles. The mechanism of sonocatalytic degradation over the CdS/CNT modified TiO₂ composites under different ultrasonic conditions was also discussed.     

Efficient visible light-induced photoelectrocatalytic degradation of rhodamine B by polyaniline-sensitized TiO<Subscript>2</Subscript> nanotube arrays

Self-organized anodic TiO₂ nanotube arrays were sensitized with polyaniline by a simple electrodeposite method. The morphological and structural properties studied by scanning electron microscopy and fourier transform infrared spectroscopy reveal the successful deposition of polyaniline on the nanotube arrays. The polyaniline-sensitized TiO₂ nanotube arrays exhibit a distinguishable red shift on the absorption spectrum. Electrochemical impedance investigation attested to a significant improvement of the interfacial electron-transfer kinetics for promoted electron–hole effective separation. The as-prepared samples showed a high efficiency for the photoelectrocatalytic degradation of rhodamine B under visible-light irradiation (λ > 400 nm). The enhanced photoelectrocatalytic activity could be attributed to the extended absorption in the visible-light region by the polyaniline and the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the polyaniline/TiO₂ nanotube arrays interface.     

Morphology modification of TiO<Subscript>2</Subscript> nanotubes by controlling the starting material crystallite size for chemical synthesis

TiO₂ nanotubes (NTs) were prepared by low-temperature chemical synthesis using anatase TiO₂ particles with different crystallite sizes in a NaOH solution followed by water washing and HCl neutralization. The synthesized TiO₂ NTs showed diverse morphologies depending on the starting materials. The crystallite size of TiO₂ raw materials increased with an increase in annealing temperature, and larger TiO₂ NTs, around 31 nm in diameter, were obtained from large raw powder with a crystallite size of 117 nm. X-ray diffraction and Raman spectroscopy revealed that the obtained TiO₂ NT exhibited lower crystallinity; however, Raman vibration seems to be more likely than a rutile structure.     

Influence of the oxygen concentration on the formation of crystalline phases of TiO<Subscript>2</Subscript> during the low-pressure arc-discharge plasma synthesis

The synthesis of titanium dioxide (TiO₂) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation–condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO₂ is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using X-ray phase analysis, it is established that the concentration of the TiO₂ anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO₂ anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.     

Fabrication and characterization of CdS-sensitized TiO<Subscript>2</Subscript> nanotube photoelectrode

CdS quantum dot (Qd)-sensitized TiO₂ nanotube array photoelectrode is synthesised via a two-step method on tin-doped In₂O₃-coated (ITO) glass substrate. TiO₂ nanotube arrays are prepared in the ethylene glycol electrolyte solution by anodizing titanium films which are deposited on ITO glass substrate by radio frequency sputtering. Then, the CdS Qds are deposited on the nanotubes by successive ionic layer adsorption and reaction technique. The resulting nanotube arrays are characterized by scanning electron microscopy, X-ray diffraction (XRD) and UV–visible absorption spectroscopy. The length of the obtained nanotubes reaches 1.60 μm and their inner diameter and wall thickness are around 90 and 20 nm, respectively. The XRD results show that the as-prepared TiO₂ nanotubes array is amorphous, which are converted to anatase TiO₂ after annealed at 450 °C for 2 h. The CdS Qds deposited on the TiO₂ nanotubes shift the absorption edge of TiO₂ from 388 to 494 nm. The results show that the CdS-sensitized TiO₂ nanotubes array film can be used as the photoelectrode for solar cells.     

TiO2 nanoparticle thin film deposition by matrix assisted pulsed laser evaporation for sensing applications

The MAPLE technique has been used for the deposition of nanostructured titania (TiO₂) nanoparticles thin films to be used for gas sensors applications. An aqueous solution of TiO₂ nanoparticles, synthesised by a novel chemical route, was frozen at liquid nitrogen temperature and irradiated with a pulsed ArF excimer laser in a vacuum chamber. A uniform distribution of TiO₂ nanoparticles with an average size of about 10 nm was deposited on Si and interdigitated Al₂O₃ substrates as demonstrated by high resolution scanning electron microscopy-field emission gun inspection (SEM-FEG). Energy dispersive X-ray (EDX) analysis revealed the presence of only the titanium and oxygen signals and FTIR (Fourier transform infra-red) revealed the TiO₂ characteristic composition and bond. A comparison with a spin coated thin film obtained from the same solution of TiO₂ nanoparticles is reported. The sensing properties of the films deposited on interdigitated substrates were investigated, too.     

Photoconductivity studies on amorphous and crystalline TiO<Subscript>2</Subscript> films doped with gold nanoparticles

In this work, amorphous and crystalline TiO₂ films were synthesized by the sol–gel process at room temperature. The TiO₂ films were doped with gold nanoparticles. The films were spin-coated on glass wafers. The crystalline samples were annealed at 100°C for 30 minutes and sintered at 520°C for 2 h. All films were characterized using X-ray diffraction, transmission electronic microscopy and UV-Vis absorption spectroscopy. Two crystalline phases, anatase and rutile, were formed in the matrix TiO₂ and TiO₂/Au. An absorption peak was located at 570 nm (amorphous) and 645 nm (anatase). Photoconductivity studies were performed on these films. The experimental data were fitted with straight lines at darkness and under illumination at 515 nm and 645 nm. This indicates an ohmic behavior. Crystalline TiO₂/Au films are more photoconductive than the amorphous ones.     

Synthesis and gas sensing properties of perovskite CdSnO<Subscript>3</Subscript> nanoparticles

The CdSnO₃ semiconducting oxide that can be used as a gas-sensitive material for detecting ethanol gas is reported in this paper. CdSnO₃ nanoparticles were prepared by a chemical co-precipitation synthesis method, in which the preparation conditions were carefully controlled. The n-type gas-sensing semiconductors were obtained from the as-synthesized powders calcined at 600°C for 1 h. The phase and microstructure of the obtained nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) method with a gas adsorption analyzer. CdSnO₃ has a small particle size range of 30–50 nm and a high surface area of 9.12 m²/g, and a uniformity global shape. The gas sensitivity and operating temperature, and selectivity of CdSnO₃-based sensors were measured in detail. The gas sensors fabricated by CdSnO₃ nanoparticles had good sensitivity and selectivity to vapor of C₂H₅OH when working temperature at 267°C, the value of gas sensitivity at 100 ppm of C₂H₅OH gas can reach 11.2 times. Furthermore, gas-sensing mechanism was studied by using chromatographic analysis.     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

Gas sensing properties of MoO<Subscript>3</Subscript> nanoparticles synthesized by solvothermal method

MoO₃ nanoparticles were prepared by thermally oxidizing the MoO₂ nano-crystallites synthesized by solvothermal reaction, and their gas sensing properties were investigated. Ethanol and water mixed solvents were used in the solvothermal synthesis, and it was observed that the phase, size, and morphology of the products were strongly dependent on the composition of solvents. Well-crystallized and spherical MoO₂ nano-crystallites (~20 nm) were obtained in the mixed solvent (water:ethanol = 40:10 in vol), and subsequent heat treatment at 450 °C produced the well-separated, slightly elongated MoO₃ nano-particles of ~100 nm. The nano-particle MoO₃ gas sensor responded to both oxidizing and reducing gases, but it exhibited the extremely high gas response toward H₂S with a short response time (<10 s). In particular, the magnitude of gas response of nano-particle MoO₃ gas sensor was about 10 times higher than that of micron-sized commercial MoO₃ powder sensor at 20 ppm H₂S.     

Experimental evaluation of individual protection devices against different types of nanoaerosols: graphite,TiO<Subscript>2,</Subscript> and Pt

In this study different conventional individual protection devices, well-qualified for submicron particles were tested for different types of polydispersed nanoaerosols of TiO₂, Pt, and graphite. The electrical mobility diameters of the generated particles are ranging from 9 to 19 nm for Pt, 9 to 90 nm for TiO₂, and 15 to 90 nm for graphite. Toward this purpose, two specific test benches were used: one for the filter-based devices which are tested under a controlled air flow, and the other one for protective clothing and gloves under diffusion and without air flow. Different types of nanoaerosols, such as TiO₂, Pt, and graphite, were generated. Electrostatic and HEPA (High Efficiency Particle Air) filters have shown the highest efficiency for graphite nanoparticles. The main hypothesis for explaining this effect is that electrostatic forces could enhance the graphite nanoparticles capture. Air-tight fabrics made of non-woven textile seem much more efficient in protecting workers against Pt, and TiO₂ nanoparticles than cotton and polypropylene. With regard to protective clothing, no obvious effect linked to the aerosol type was observed. Gloves are found very efficient for TiO₂ and Pt nanoaerosols. Therefore, no effect of aerosol on the protection efficiency of gloves was evidenced.     

A new green synthesis method of CuInS<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript> nanoparticles and their integration into thin films

A new preparation method for CuInS₂ and CuInSe₂ nanoparticles synthesis is described without using any organic solvent. Heating Cu, In, and S/Se precursors dissolved in water for 30 min in a microwave oven in the presence of mercapto-acetic acid leads to monodispersed chalcopyrite nanoparticles. No precipitation of these nanoparticles is observed after several months at room temperature. These new materials have been thoroughly characterized to confirm their compositions, sizes, and structure without any filtration. Transmission electron microscopy (TEM) confirmed particle sizes below 5 nm. Energy dispersive X-ray analysis (EDXA) confirmed the chemical composition of these samples. X-ray diffraction (XRD) showed a chalcopyrite-type structure with crystallite size of about 2 nm. No difference has been observed between batch and continuous synthesis processes. Cu _x InS₂ and Cu _x InSe₂ nanoparticles, with x < 1, have been also synthesized and identified. Simulation using a commercial software confirmed the difference between copper poor (Cu _x InS₂) and copper rich (CuInS₂) chalcopyrite structures. Conventional spray deposition techniques have been used to form relatively thin films on solid substrates.     

Structural properties of amorphous TiO<Subscript>2</Subscript> nanoparticles

Structural properties of amorphous TiO₂ spherical nanoparticles have been studied in models with different sizes of 2 nm, 3 nm, 4 nm and 5 nm under non-periodic boundary conditions. We use the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of an amorphous nanoparticle obtained at 350 K have been analyzed in detail through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Moreover, we show the radial density profile in a nanoparticle. Calculations show that size effects on structure of a model are significant and that if the size is larger than 3 nm, amorphous TiO₂ nanoparticles have a distorted octahedral network structure with the mean coordination number Z_Ti-O ≈6.0 and Z_O-Ti ≈3.0 like those observed in the bulk. Surface structure and surface energy of nanoparticles have been obtained and presented.     

One-step synthesis of colloidal Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> and γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles at room temperature

A facile room-temperature synthesis has been developed to prepare colloidal Mn₃O₄ and γ-Fe₂O₃ nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process has been proposed.     

Computational study on the structural and surface properties of amorphous hydroxylated TiO<Subscript>2</Subscript> spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO₂) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO₂ in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO₂ surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 ^o . The bulk system was developed using periodic boundary conditions. The TiO₂ nanoparticles were extracted by applying a spherical cut section in the bulk TiO₂ melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO₂ nanoparticles and bulk amorphous TiO₂, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO₂ nanoparticles are strongly size-dependent and different from those of the bulk TiO₂. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO₂ nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO₂ nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO₂ spherical nanoparticles is estimated to be around 8.1/nm ², which lies in the range of 8–16/nm ², found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.     

Structural and optical properties of novel surfactant-coated Yb@TiO<Subscript>2</Subscript> nanoparticles

In this paper a novel hybrid approach to synthesise composite nanoparticles is presented. It is based on the laser ablation of a bulk target (Yb) immersed in a reversed micellar solution which contains nanoparticles of a different host material (TiO₂ nanoparticles) previously synthesised by chemical method. This approach thus exploits the advantages of the chemical synthesis through reversed micellar solution (size control, nanoparticle stabilisation), and of the laser ablation (“clean” synthesis, no side reactions). Central role is played by the microscopic processes controlling the deposition of the ablated Yb atoms onto the surface of TiO₂ nanoparticles which actually behave as nucleation seeds. The structural features of the resulting Yb@TiO₂ composite nanoparticles have been studied by Transmission Electron Microscopy, whereas their peculiar optical properties have been explored by UV–Vis spectroscopy and steady-state fluorescence. Results consistently show the formation of Yb and TiO₂ glued nanodomains to form nearly spherical and non-interacting nanoparticles with enhanced photophysical properties.     

Nanoparticles dispersion in processing functionalised PP/TiO<Subscript>2</Subscript> nanocomposites: distribution and properties

Future innovations in textiles and fibrous materials are likely to demand fibres with enhanced multifunctionality. The fibres can be functionalized by dispersing nanoadditives into the polymer during melt compounding/spinning. TiO₂ nanoparticles have the potential to improve UV resistance, antistatic, as well as impart self-cleaning by photocatalysis and thereby de-odour and antimicrobial effects. In this study, a micro-lab twin-screw extruder was used to produce samples of polypropylene (PP) nanocomposite monofilaments, doped with nano titanium oxide (TiO₂)/manganese oxide (MnO) compound having size ranging from 60 to 200 nm. As a control sample, PP filaments without additives were also extruded. Three samples were produced containing different concentrations (wt%) of the TiO₂ compound, i.e. 0.95, 1.24 and 1.79%. Nano metal-oxide distribution in the as-spun and drawn nanocomposite filaments was analysed. Although, there are small clusters of the nanoparticles, the characterizing techniques showed good dispersion and distribution of the modified TiO₂ along and across the processed filaments. From UV spectroscopy and TGA, a significant enhancement of polypropylene UV protection and thermal stability were observed: PP with higher percentage of TiO₂ absorbed UV wavelength of 387 nm and thermally decomposed at 320.16 °C accompanied by 95% weight loss.