Improved photodegradation activity of TiO2 via decoration with SnS2 nanoparticles

The particles of TiO₂ modified with various amounts of SnS₂ nanoparticles (TiO₂/SnS₂) were synthesized via the hydrothermal method by reacting SnCl₄·5H₂O with thioacetamide in 5% (vol.) acetic acid aqueous solution in the presence of TiO₂. The obtained products were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflection spectra, scanning and transmission electron microscopy. The photodegradation activities of TiO₂/SnS₂ composites have been investigated by using methyl orange as target in water under the light irradiation of 250–400, 360–600 and 400–600 nm. It was found that the photodegradation activity of TiO₂/SnS₂ composites depended on the mass ratio of SnS₂ and the wavelength of the irradiating light. The composites containing 33% SnS₂ exhibited the maximum activity under the light irradiation of 250–400 and 360–600 nm. However, the more SnS₂ in the composites, the higher activity appeared under the irradiation of 400–600 nm light. All the results reveal that the composites possess much better activity than the pristine TiO_2.     

Photochemical synthesis and characterization of Bi2S3 nanofibers

Bismuth sulfide (Bi₂S₃) nanofibers have been successfully prepared by a photochemical method from an aqueous solution of bismuth nitrate (Bi(NO₃)₃) and thioacetamide (TAA) in the presence of complexing agents of nitrilotriacetic acid (NTA) at room temperature. It was found that the irradiation time, the pH of the solution, and the species of complexing agents play important roles in the morphology control of the bismuth sulfate (Bi₂S₃) nanomaterials. The nanofibers were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectra (XPS), and UV-Visible absorption spectra (UV-Vis). Probable mechanisms for the photochemical formation of Bi₂S₃ nanofibers in aqueous solutions are proposed. The photochemical method is a convenient approach for controlling the shape for other metal sulfide semiconductor nanocrystals.     

Investigation on solar photocatalytic activity of TiO2 loaded composite: TiO2/Eggshell, TiO2/Clamshell and TiO2/CaCO3

The TiO₂/Eggshell, TiO₂/Clamshell and TiO₂/CaCO₃ loaded composites were prepared by sol-gel method and characterized by XRD and SEM. Their photocatalytic activities were measured through the degradation of Acid Red B under solar light irradiation. The influences of TiO₂ loaded content, heat-treated temperature and time on the photocatalytic activities were reviewed. The effects of irradiation time and dye initial concentration on the photocatalytic degradation were also investigated. The results showed that the photocatalytic activity can be greatly enhanced by appropriate TiO₂ loaded content.     

The role of Ag particles deposited on TiO2 or Al2O3 self-organized nanoporous layers in their behavior as SERS-active and biomedical substrates

In this paper, we present recent results of investigations of hybrid materials consisting of nanoporous oxides layers loaded with Ag nanoparticles: Ag/TiO₂-n/Ti and Ag/Al₂O₃-n/Al (where “n-“stands for nanotubes), which could be used as active SERS substrates or as bioactive materials in medicine (implants). Simple electrochemical, chemical and physical methods appear suitable for fabricating such hybrid materials having different functional properties.     

Electrospun polymeric nanofibrous composites containing TiO2 short nanofibers

In this study, polymeric nanofibrous composites containing anatase TiO₂ short nanofibers (TiO₂-SNF) were successfully produced via electrospinning. The fabrication of the nanofibrous composite structure includes two steps. First, anatase TiO₂ nanofibers were obtained by calcination of electrospun PVP/TiO₂ nanofibers and then crushed into short nanofibers ranging from few microns in length. Second, these TiO₂-SNF were dispersed into polymer solutions and then electrospun into nanofibrous composites. We obtained nanofibers containing TiO₂-SNF from different polymer types including PMMA, PAN, PET and PC. The SEM and TEM imaging indicated that some of the TiO₂-SNF were fully covered by the polymeric matrix whereas some TiO₂-SNF were partially covered and/or stick on the surface of the fibers. The photocatalytic activity of nanofibrous composites containing TiO₂-SNF was evaluated by monitoring the photocatalytic decomposition of a model dye (rhodamine-6G) under UV irradiation.     

Faceted MoS2 nanotubes and nanoflowers

A simple synthesis of novel faceted MoS₂ nanotubes (NTs) and nanoflowers (NFs) starting from molybdenum oxide and thiourea as the sulphur source is reported. The MoS₂ nanotubes with the faceted morphology have not been observed before. Further the as-synthesized MoS₂ nanotubes have high internal surface area. The nanostructures have been characterized by a variety of electron microscopy techniques. It is expected that these MoS₂ nanostrutures will find important applications in energy storage, catalysis and field emission.     

The effect of Pt nanoparticles loading on H2 sensing properties of flame-spray-made SnO2 sensing films

SnO₂ nanoparticles loaded with 0.2–2 wt% Pt have successfully been synthesized in a single step by flame spray pyrolysis (FSP) and investigated for gas sensing towards hydrogen (H₂). According to characterization results by X-ray diffraction, nitrogen adsorption, scanning/high resolution-transmission electron microscopy and analyses based on Hume-Rothery rules using atomic radii, crystal structure, electronegativities, and valency/oxidation states of Pt and Sn, it is conclusive that Pt is not solute in SnO₂ crystal but forms nanoparticles loaded on SnO₂ surface. H₂ gas sensing was studied at 200–10,000 ppm and 150–350 °C in dry air. It was found that H₂ response was enhanced by more than one order of magnitude with a small Pt loading concentration of 0.2 wt% but further increase of Pt loading amount resulted in deteriorated H₂-sensing performance. The optimal SnO₂ sensing film (0.2 wt% Pt-loaded SnO₂, 20 μm in thickness) showed an optimum H₂ response of ∼150.2 at 10,000 ppm and very short response time in a few seconds at a low optimal operating temperature of 200 °C. In addition, the response tended to increase linearly and the response times decreased drastically with increasing H₂ concentration. Moreover, the selectivity against carbon monoxide (CO) and acetylene (C₂H₂) gases was also found to be considerably improved with the small amount of Pt loading. The H₂ response dependence on Pt concentration can be explained based on the spillover mechanism, which is highly effective only when Pt catalyst is well-dispersed at the low Pt loading concentration of 0.2 wt%.     

Ultrasonic spray pyrolysis of surface modified TiO2 nanoparticles with dopamine

Spherical, submicronic TiO₂ powder particles were prepared in the low temperature process of ultrasonic spray pyrolysis (150 °C) by using as a precursor aqueous colloidal solutions consisting of surface modified 45 Å TiO₂ nanoparticles with dopamine. Detailed structural and morphological characterization of colored submicronic TiO₂ spheres was performed by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser particle size analysis and FTIR techniques. Also, optical characterization of both dopamine-modified TiO₂ precursor nanoparticles and submicronic TiO₂ powder particles was performed using absorption and diffuse reflectance spectroscopy, respectively. A significant decrease of the effective band gap (1.9 eV) in dopamine-modified TiO₂ nanoparticles compared to the band gap of bulk material (3.2 eV) was preserved after formation of submicronic TiO₂ powder particles in the process of ultrasonic spray pyrolysis under mild experimental conditions. Due to the nanostructured nature, surface-modified assemblage of TiO₂ nanoparticles preserved unique ability to absorb light through charge transfer complex by photoexcitation of the ligand-to-TiO₂ band, conventionally associated with extremely small TiO₂ nanoparticles (d < 20 nm) whose surface Ti atoms, owing to the large curvature, have penta-coordinate geometry.     

Facile synthesis of luminescent TiO2 nanorods using an anionic surfactant: Their photosensitization and photocatalytic efficiency

Mixed phase (rutile/anatase) TiO₂ nanorods have been synthesized using an anionic surfactant template. Nanorod synthesis has been achieved using mild reaction conditions and without using any rod-shaped template. The shape and crystallinity of the TiO₂ nanomaterials can be modulated by careful control of the surfactant concentration. The novelty of the present work is that the anatase/rutile mixed phase nanorods were formed without using the well-known layer by layer assembly method or the hydrothermal method. These mixed phase TiO₂ nanorods are highly luminescent, can be easily sensitized by fluorescent dyes, show significant dye adsorption ability and function as efficient photocatalysts.     

Nanostructured leaf like hydroxyapatite/TiO2 composite coatings by simple sol-gel method

We demonstrate an approach for the coating of nanostructured leaf like hydroxyapatite (HAp)/TiO₂ composite on glass substrate by sol-gel dip coating process. HAp/TiO₂ nanocomposite thin film was obtained by controlling the dipping rate and the dipping cycle. It was observed from Scanning Electron Microscope that leaf like nanostructured film was deposited on the glass substrate. However, the structure of the film was changed with the dipping cycle and dipping rate. Transmission Electron Microscopic analysis further confirms the morphology of the nanostructured coatings. The presence of Ti, O, Ca and P was detected by Energy Dispersive X-ray Analysis. We further confirmed the composite by X-ray diffraction analysis. Atomic Force Microscope analysis indicates that the films are composed of nanoparticles ranging from 100 to 200 nm and the films were observed to present well-defined grain boundaries. It has been shown that nanocomposite coatings are dependent on the sol concentration, dipping parameters, and the composition of HAp and TiO₂.     

Preparation,phase structure and microwave dielectric properties of a new low cost MgLi2/3Ti4/3O4 compound

A novel Li-based spinel compound with the composition of MgLi_2/3Ti_4/3O₄ was synthesized by the conventional solid-state reaction method. The phase structure was studied by X-ray diffraction (XRD) technique. When the calcination temperature was over 1050 °C, a single phase compound which has a cubic structure [Fd-3m (227)] with cell parameters of a = 8.4057 Å, V = 593.91 Å³, ρ = 3.51 g cm⁻³ and Z = 8 was obtained. MgLi_2/3Ti_4/3O₄ ceramic could be well densified after sintering above 1125 °C. The microwave dielectric properties were measured using a microwave vector network analyzer in the frequency range of 7–9 GHz MgLi_2/3Ti_4/3O₄ ceramic sintered at 1125 °C for 2 h showed microwave dielectric properties of ?_r = 20.2, Q × f = 62,300 GHz, and τ_f = −27.1 ppm °C⁻¹. Furthermore, 0.95MgLi_2/3Ti_4/3O₄–0.05CaTiO₃ ceramic sintered at 1200 °C for 2 h exhibited good properties of ?_r = 22.6, Q × f = 48,000 GHz, and τ_f = −2.3 ppm °C⁻¹.     

Fabrication and characterization of electrospun Ag doped TiO2 nanofibers for photocatalytic reaction

Titanium dioxide is one of the best semiconductor photocatalysts available for photocatalytic reaction of dye pollutants. To prevent the recombination caused by the relatively low photocatalytic efficiency, Ag doped TiO₂ nanofiber was prepared by electrospinning method. The photocatalysts (pure TiO₂ nanofiber and Ag doped TiO₂ nanofiber) were characterized by FE-SEM, XRD, XPS, and PL analysis. These photocatalysts were evaluated by the photodecomposition of methylene blue under UV light. Ag doped TiO₂ nanofiber was found to be more efficient than pure TiO₂ fiber for photocatalytic degradation of methylene blue. The photocatalytic degradation rate was applied to pseudo-first-order equation. The degradation of Ag doped TiO₂ nanofiber was significantly higher than the degradation rate of pure TiO₂ nanofiber. Activation energy was calculated by applying Arrhenius equation from the rate constant of photocatalytic reaction. The activation energies for the pure TiO₂ nanofibers calcined at 400 and 500 °C were 16.981 and 12.187 kJ/mol and those of Ag doped TiO₂ nanofibers were 18.317 and 7.977 kJ/mol, respectively.     

Hydrophilic and photocatalytic properties of the SiO2/TiO2 double layers

The hydrophilic and photocatalytic properties of the SiO₂/TiO₂ double layers composed of a 20-nm-thick porous SiO₂ layer on the 200-nm-thick columnar anatase TiO₂ layer were studied. The hydrophilicity of the double layers was strictly determined by the relative coverage of organic contaminants. The intrinsic hydrophilicity of 0° of SiO₂ in terms of the water contact angle was restored by the photocatalytic decomposition of organic contaminants under the UV light irradiation.Electron spin resonance measurements revealed the generation of OH radicals under the UV light irradiation onto the SiO₂/TiO₂ double layers. Photoconductivity measurements showed that the current decay in O₂ gas atmosphere was remarkably fast in comparison with that in H₂O vapor. These observations support our view that the generation of OH radicals effective for decomposing organic contaminants on the surface begins with the reaction between O₂ molecules and the photoexcited electrons. We propose together with other experimental facts herein that OH radicals would be generated via O₂⁻ and H₂O₂ in the double layer system.     

Structure and microstructure of In4Te3 nanopowders prepared by solid state reaction

In this paper, we investigated the structure and microstructure of In₄Te₃ nanopowders obtained by mechanically alloying an In₇₅Te₂₅ powder mixture. Structural, chemical, thermal and vibrational studies of the In₇₅Te₂₅ powder mixture were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The orthorhombic In₄Te₃ phase (In₃Se₄-type) was nucleated in 2 h of synthesis, although non-reacted tetragonal indium (In) was still present at that time. Small amounts of cubic In₂O₃ phase were observed after 31 h of synthesis. Rietveld analyses allowed the measurement of mean crystallites sizes and phase fraction variations when milling times were increased. These analyses showed that, after 31 h of synthesis, about 65 wt% of In₄Te₃ phase contained mean crystallite sizes smaller than 27 nm and microstrains greater than 1.5%. The crystallite and interfacial components sizes were determined by high resolution transmission electron microscopy. Differential scanning calorimetry measurements showed the influence of nanometric crystallite sizes on the melting of the In₄Te₃ and non-reacted In phases. Raman measurements showed that the trigonal Te and α-TeO₂ modes, observed for the precursor Te powder, are absent for the sample milled for 31 h. The structural stability of the nanocrystalline phases of the In₇₅Te₂₅ sample milled for 31 h was attested by X-ray diffraction measurements performed twelve months after its production.     

Mechanochemical synthesis and characterization of TiB2 and VB2 nanopowders

A novel method for the synthesis of transition-metal boride nanopowder has been developed using a mechanochemical reaction between LiBH₄, LiH and transition-metal chloride (TiCl₃ and VCl₃) by high energy ball milling. This method successfully produces TiB₂ and VB₂ particles dispersed within a soluble LiCl matrix. Subsequent washing with distilled water, ethanol and acetone to remove the LiCl matrix phase yields TiB₂ and VB₂ nanopowders of 15-60 nm particle size. From the X-ray diffraction patterns and high resolution transmission electron microscopy image, it is found that each particle is polycrystalline consisting of 3-5 nm crystallites. Neither particle nor crystallite size are increased significantly after heating at 680 °C.     

Preparation and characterization of TiO2 nanosponge

A procedure was developed to coat functionalized polystyrene spheres with well-defined layer of amorphous titanium dioxide. The core–shell particles can be turned into TiO₂ nanosponge by calcining the dried particles in a furnace. The phase transformation temperature of TiO₂ hybrid microspheres from anatase to rutile was increased by about 200 °C due to the blocking function of the calcined polymer remainder.     

Surface characterization of poly(methylmethacrylate) based nanocomposite thin films containing Al2O3 and TiO2 nanoparticles

Poly(methylmethacrylate) (PMMA) based nanocomposite electron beam resists have been demonstrated by spin coating techniques. When TiO₂ and Al₂O₃ nanoparticles were directly dispersed into the PMMA polymer matrix, the resulting nanocomposites produced poor quality films with surface roughnesses of 322 and 402 nm respectively. To improve the surface of the resists, the oxide nanoparticles were encapsulated in toluene and methanol. Using the zeta potential parameter, it was found that the stabilities of the toluene/oxide nanoparticle suspensions were 7.7 mV and 19.4 mV respectively, meaning that the suspension was not stable. However, when the TiO₂ and Al₂O₃ nanoparticles were encapsulated in methanol the zeta potential parameter was 31.9 mV and 39.2 mV respectively. Therefore, the nanoparticle suspension was stable. This method improved the surface roughness of PMMA based nanocomposite thin films by a factor of 6.6 and 6.4, when TiO₂ and Al₂O₃ were suspended in methanol before being dispersed into the PMMA polymer.     

Hydrothermal synthesis, characterization and properties of TiO2 nanorods on boron-doped diamond film

The rutile TiO₂ nanorods have been hydrothermally synthesized on boron-doped diamond (BDD) film with a ZnO buffer layer. It is demonstrated that the ZnO buffer layer plays a key role in increasing the density and improving the morphology of synthesized TiO₂ nanorods. The heterojunction of n-TiO₂ nanorods/p-BDD shows an evident rectifying behavior with a ratio of ∼ 180 at 6 V. Experimentally, the TiO₂ nanorod-covered BDD exhibits an improved electron field-emission property over that without using a ZnO buffer layer.     

喷雾热解法制备高产率石墨/炭纳米纤维及其特征研究

基于石墨/炭纳米纤维(GNFs)的克量级(>1 g)制备及其特征表征,通过苯的喷雾热解制备了GNFs,并采用XRD,TEM及SEM对GNFs进行了表征.结果表明:高产率GNFs的最佳生长条件是:喷管内径～0.52mm,苯液流量～5 mL/min,反应温度～750℃,载气H2流量～1 500 mL/min.所制GNFs的典型长度和直径分别为～60um和～250 nm,大部分GNFs样品呈现螺圈/螺旋纤维状.喷雾热解生长模式中GNFs的产率为克量级(1.45 g)/产程.     

Fabrication of vertically aligned CuInSe2 nanorod arrays by template-assisted mechanical approach

A facile, low cost, and vacuum free method for fabricating vertically aligned copper indium diselenide (CuInSe₂) nanorod (NR) arrays from pre-synthesized CuInSe₂ nanoparticles (NPs) by mechanical approach using porous anodic aluminum oxide (AAO) as a template was demonstrated. This approach utilizes a rubbing technique to fill CuInSe₂ NPs suspension into AAO template. X-ray diffraction and Raman spectroscopy study is employed to confirm the phase of CuInSe₂ NPs before and after the formation of NRs. The polycrystallinity and composition of NRs are confirmed by using transmission electron microscopy. Optical studies of CuInSe₂ NPs film reveal a reflectance of ∼9.8% while a significant reduction of the reflectance to ∼1.2% is observed after the formation of CuInSe₂ NR arrays. The observed low reflectance behavior is attributed to a concept of gradual refractive index with vertical array structures. From differential reflectance spectra of CuInSe₂ NRs, a band gap of ∼1.01 eV was observed, which is identical to its bulk value.