Synthesis and ethanol sensing properties of Fe-doped SnO2 nanofibers

Fe-doped SnO₂ nanofibers are synthesized through an electrospinning method and characterized by scanning electron microscopy and transmission electron microscopy. The sensor fabricated from these nanofibers exhibits high sensitivity and rapid response/recovery to ethanol at 300 °C. The sensitivity is up to 15.3 when the sensor is exposed to 100 ppm ethanol, and the response and recovery time is about 1 and 3 s, respectively. The linear dependence of the sensitivity on the ethanol concentration is observed in the range of 10-300 ppm. These results demonstrate that Fe-doped SnO₂ nanofibers can be used as the sensing material for fabricating high performance ethanol sensors.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.     

Photocatalytic treatment of acidic waste water by electrospun composite nanofibers of pH-sensitive hydrogel and TiO2

The composite nanofibers of poly(vinyl alcohol)/poly(N,N-dimethylaminopropyl acrylamide) hydrogel and TiO₂ were prepared by electrospinning for a novel treatment of acidic waste water. The anatase TiO₂ was used as a photocatalyst due to its high photodegradation efficiency. TiO₂ was immobilized in the electrospun fibers for an easy recovery of TiO₂ after the waste treatment. The hydrogel nanofibers swelled rapidly in the acidic condition due to the repulsion among the protonated amine groups in the polymer chains. High efficiency of photocatalytic decomposition of dye was obtained by the fast swelling of hydrogel in the acidic condition and the uniform dispersion of TiO₂ by sonication.     

Influence of silver doping on the phase transformation and crystallite growth of electrospun TiO2 nanofibers

Ag doped TiO₂ nanofibers were fabricated by electrospinning technique using polyvinyl pyrrolidone (PVP) and titanium isopropoxide (TiP) as precursor. The effects of silver and calcination temperature on the preparation of electrospun TiO₂ nanofibers were investigated. The calcination temperature determines the TiO₂ phases as ether anatase or rutile. When the calcination temperature increased, crystallite size of TiO₂ nanofiber increased. The crystallite size of Ag doped TiO₂ nanofiber is smaller than that of the pure TiO₂ nanofiber because silver is retrained in this phase transformation. Silver controlled the phase transformation as well as had an inhibition effect on the growth of anatase crystallite.     

Improved ethanol sensing properties of Cu-doped SnO2 nanofibers

Pure and Cu-doped SnO₂ nanofibers are synthesized via a simple electrospinning method, and characterized by transmission electron microscopy and X-ray diffraction. The sensor fabricated from Cu-doped SnO₂ nanofibers exhibits improved sensing properties to ethanol at 300 °C. The sensitivity is up to 3 when this sensor is exposed to 5 ppm ethanol. The response and recovery times are about 1 and 10 s, respectively. The linear dependence of the sensitivity on the ethanol concentration is observed in the range of 5-500 ppm. Good selectivity is also observed in our studies. The results make Cu-doped SnO₂ nanofibers good candidates for fabricating high performance ethanol sensors.     

HCHO sensing properties of Ag-doped In2O3 nanofibers synthesized by electrospinning

Ag-doped In₂O₃ nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In₂O₃ nanofibers could be used to fabricate high performance HCHO sensors in practice.     

Facile synthesis of rice-like anatase TiO2 nanocrystals

Rice-like anatase TiO₂ nanocrystals have been synthesized by hydrothermal treating Ti(OH)₃ precursor in deionized water, which is easy to form in-situ a stable TiO₂ aqueous dispersion and no post-synthetic purification process is required. The influences of synthetic parameters, such as reaction time and pH value, on the morphologies of the resulting nanocrystals have been investigated. It is found that the crystallinity and sizes of TiO₂ nanocrystals increase with the reaction time increased. The pH value is important for controlling the sizes and shapes of TiO₂ nanocrystals. As pH value increases from 2 to 11, spherical, rice-like, and rod-like TiO₂ nanocrystals are obtained, respectively. The formation mechanism of rice-like anatase TiO₂ nanocrystals is supposed to be a hydrothermal crystallization and Ostwald ripening process.     

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.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.     

Facile preparation of TiO2 nanostructures by direct annealing of the Ti foil

TiO₂ nanostructures have been fabricated by direct annealing of the Ti foil with Pd catalyst. The Pd catalysts play an important role in reducing sintering temperature for the synthesis of TiO₂ nanostructures. The morphologies can be varied between the nanowires (NWs) and nanobelts (NBs) by adjusting the amount of Pd and annealing temperature. It shows that the vapor liquid solid and vapor solid may be the most suitable mechanism for the TiO₂ nanostructure growth. Experimental results suggest that this method is an effective, simple and inexpensive route for the preparation of TiO₂ nanostructures with high quality and high yield.     

Preparation and humidity sensing properties of Ba0.8Sr0.2TiO3 nanofibers via electrospinning

Ba_0.8Sr_0.2TiO₃/Poly (vinylpyrrolidone) (BST/PVP) composite fibers were successfully synthesized via electrospinning. The ceramic nanofibers were obtained after calcining the composite at 800 °C for 2 h. The morphology and structure of the BST fibers were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that the as-synthesized BST nanofibers show a diameter of 50-150 nm with the length over 0.1 mm, and a well-defined perovskite crystal structure. The electrical properties of the as-synthesized BST nanofibers were investigated through an impedance-type humidity sensor. The nanofibers exhibited excellent humidity sensing properties at room temperature. The possible sensing mechanism was proposed.     

Nanocrystalline anatase TiO2 prepared via a facile low temperature route

Nanocrystalline anatase TiO₂ was prepared by a facile sol-gel route at a temperature of 65 °C under mild conditions. Tetrabutyl titanate was used as a titanium precursor, glacial acetic acid was used as an inhibitor, and anhydrous ethanol was used as a solvent. XRD, TEM, FT-IR and XPS spectra were applied to characterize the crystal phase, microstructure, and other physicochemical properties of the nanoanatase TiO₂. The results showed that as prepared ellipse-shaped anatase TiO₂ with an average diameter of 7 nm, which is rich in surface hydroxyl groups, was found to exhibit high dispersibility.     

Visible-light photocatalysis in nitrogen-carbon-doped TiO2 films obtained by heating TiO2 gel-film in an ionized N2 gas

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO₂ films were obtained by heating a TiO₂ gel in an ionized N₂ gas. The as-synthesized TiO_2−x−yN_xC_y films have shown an improvement over titanium dioxide in optical absorption and photocatalytic activity such as photodegradation of methyl orange under visible light. The process of the oxygen atom substituted by nitrogen and carbon was discussed. Oxygen vacancy induced by the formation of Ti³⁺ species and nitrogen and carbon doped into substitution sites of TiO₂ have been proven to be indispensable for the enhance of photocatalytic activity, as assessed by UV-Vis Spectroscopy and X-ray photoemission spectroscopy.     

SiO2/TiO2 multilayer films grown on cotton fibers surface at low temperature by a novel two-step process

A novel two-step process was developed to synthesize and deposit SiO₂/TiO₂ multilayer films onto the cotton fibers. In the first step, SiO₂ particles on cotton fiber surface were synthesized via tetraethoxysilane hydrolysis in the presence of cotton fibers, in order to protect the fibers against photo-catalytic decomposition by TiO₂ nanoparticles. In the second step, the growth of TiO₂ nanoparticles into the modified cotton fiber surface was carried out via a sol-gel method at the temperature as low as 100 °C. The as-obtained SiO₂/TiO₂ multilayer films coated on cotton fibers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and X-ray diffraction, respectively.     

Structural investigations on TiO2 and Fe-doped TiO2 nanoparticles synthesized by laser pyrolysis

Undoped and Fe-doped TiO₂ nanopowders with Fe/Ti (atomic ratio) precursor concentration ranging from 7% up to 25% have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl₄ and Fe (CO)₅ was used as titanium and iron precursor, respectively. Reference undoped titania samples with a major concentration of anatase phase (about 90%) were obtained by the same technique by using very high flows of the oxidizing agent (air). The effects of the iron-dopant concentration on the essential structural properties of the resultant powders such as the phase formation, the crystallinity, the average particle size and distributions were systematically investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The decrease of the TiO₂-anatase crystalline phase, the simultaneous increase of the amorphous phase and the decrease in size of particle mean diameter appear as main effects induced by the Fe-dopant concentration.     

Templated synthesis of Ag loaded TiO2 nanostructures using amphiphilic polyelectrolyte

A graft-type amphiphilic polyelectrolyte, i.e. poly(vinylidene fluoride-co-chlorotrifluoroethylene)-g-poly(styrene sulfonic acid) (P(VDF-co-CTFE)-g-PSSA) with 47 wt.% of PSSA was synthesized via atom transfer radical polymerization (ATRP) and used as a template film for the in-situ formation of Ag nanoparticles. This nanocomposite material was further combined with titanium(IV) isopropoxide (TTIP) to form Ag loaded TiO₂ nanostructural hybrid materials. UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed successful synthesis of Ag-TiO₂ nanostructures templated in the P(VDF-co-CTFE)-g-PSSA graft copolymer film. It was also found that the d-spacing of the graft copolymer in XRD patterns was increased from 4.1 to 4.4 Å, presumably due to the chain expansion resulting from the incorporation of nanoparticles in highly entangled polymeric chains.     

Fabrication of patterned CdS/TiO2 heterojunction by wettability template-assisted electrodeposition

A wettability template-assisted process was applied to selectively deposit cadmium sulfide (CdS) nanospheres on TiO₂ nanotube layers to form uniformly coupled CdS/TiO₂ semiconductor heterojunction micropatterns. The effect of deposition time on the size and morphology of the as-prepared CdS/TiO₂ array patterns was investigated. It is shown that the CdS nanocrystals with a highly ordered, hierarchically porous structure in nano-micro dual scales could be selectively grown within the superhydrophilic regions. The patterned CdS/TiO₂ heterojunctions have demonstrated enhanced photo-response under both UV and visible light irradiation. This novel template patterning technique, which is based on wettability contrast, can be applied to a broad range of technological areas, such as sensor arrays and optoelectronic devices.     

Preparation, characterization, and gas-sensing properties of Pd-doped In2O3 nanofibers

Pure and Pd-doped In₂O₃ nanofibers are synthesized via a simple electrospinning method and characterized by scanning electron microscopy and X-ray diffraction. Comparing with pure In₂O₃ nanofibers, Pd-doped In₂O₃ nanofibers exhibit much higher sensitivity to ethanol at 200 °C. The sensor fabricated from Pd-doped In₂O₃ nanofibers can detect ethanol down to 1 ppm (the corresponding sensitivity is 4) with good selectivity, and the response and recovery times are 1 and 10 s, respectively. The sensing mechanism and the effect of Pd doping are discussed. The results indicate that the Pd-doped In₂O₃ nanofibers can be used to fabricate high performance ethanol sensors.     

Fabrication of photocatalytic heat-mirror with TiO2/TiN/TiO2 stacked layers

The photocatalytic heat-mirror based on TiO₂/TiN/TiO₂ stacked layers is prepared by reactive magnetron sputtering on quartz substrates under substrate-heating condition. We find that the addition of a thin Ti interlayer between the TiN and the outer TiO₂ layers drastically improves the heat-insulating performance. This type of stacked layer also exhibits higher photocatalytic activity for decomposition of acetaldehyde gas, compared with a TiO₂ single layer. The optical property of the TiN in TiO₂/TiN/TiO₂ stacked layers is the key not only revealing excellent heat-insulating effect but also improving the photocatalytic performance of the outer TiO₂ layers in the stacked layers.     

Pt纳米颗粒负载SrTiO3/TiO2异质结结构制备及制氢性能

本文以固定n(Sr)/n(Ti)摩尔比0.4的SrTiO_3/TiO_2(金红石相)异质结纳米颗粒,通过"光催化还原沉积方法"制备不同质量分数的纳米铂颗粒(0、1%、2%、5%),探究其催化活性的变化,采用XRD、SEM、UV-vis、XPS方法对其进行表征,并做了相关光催化分解水产氢性能测试.结果表明:负载贵金属Pt纳米颗粒量越大,对应的Pt晶粒平均尺寸为40.8 nm,1%Pt纳米颗粒SrTiO_3/TiO_2异质结构的BET比表面积在23.195 m~2/g处最高,并且介孔材料的特征是平均Barrett-Joyner-Halenda(BJH)孔径为13.60 nm,总孔体积为0.079 cm~3/g;高BET表面积和大的总孔体积强烈地支持SrTiO_3/TiO_2具有介孔结构的事实;相应的催化剂催化活性越高,其中负载5%Pt纳米颗粒的SrTiO_3/TiO_2纳米颗粒光催化8 h产氢量为3.574 mmol,平均产氢效率为0.447 mmol/(gcat·h),但从性价比的角度来考虑,其催化效率远不及负载1%Pt纳米颗粒的SrTiO_3/TiO_2纳米颗粒催化效率的5倍,因此负载5%Pt的SrTiO_3/TiO_2纳米颗粒光催化效率最高.