Sonochemical fabrication of morpho-genetic TiO<Subscript>2</Subscript> with hierarchical structures for photocatalyst

Titanium oxides (TiO₂) with hierarchical structures have been successfully replicated from biotemplate using a sonochemical method. The bio-templates, cedarwoods, were irradiated under ultrasonic waves in TiCl₄ solutions and then calcined at temperatures between 450 and 600 °C. The fine replications of the biotemplates in TiO₂ down to nanometer’s level were verified using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The photocatalytic activities were assessed by measuring the percentage degradation of methylene blue using UV–vis spectroscopy. The calcination temperature has a strong effect on the structural replication and photocatalytic activity of the replicas. It appears that the calcination temperature of 450 °C results in the best structural replication with the highest surface area of 54.8 m² g⁻¹, and thus has the best photocatalytic properties. This method provides a simple, efficient, and versatile technique for fabricating TiO₂ with hierarchical structures, and it has the potential to be applied to other systems for producing functional hierarchical materials for chemical sensor and nanodevices.     

Microwave-assisted synthesis of nanoparticulate perovskite LaFeO3 as a high active visible-light photocatalyst

Single phase perovskite LaFeO₃ nanoparticles are directly synthesized by a one-step microwave-assisted route without additional high temperature calcination process. The prepared sample is characterized by X-ray diffraction (XRD), field emission scanning microscope (FE-SEM), Brunauer–Emmett–Teller (BET) specific surface area measurement, diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). XRD and SEM show that the prepared LaFeO₃ is single phase perovskite and sphere-like shape. The DRS result shows that the prepared LaFeO₃ has strong visible-light absorption and an optical absorption onset of 525 nm, corresponding to an optical band gap of 2.36 eV. The photocatalytic experiment demonstrates that LaFeO₃ is highly visible-light photocatalytic active for the degradation of methylene blue. It is suggested that the narrow band gap and the strong visible-light absorption are responsible for the high visible-light photocatalytic activity of the prepared LaFeO₃.     

Synthesis and formaldehyde sensing performance of LaFeO3 hollow nanospheres

Metal oxide semiconductors with hollow structure and morphology have attracted considerable attentions because of their promising application on gas sensors. In this paper, LaFeO₃ hollow nanospheres have been prepared by using carbon spheres as templates in combination with calcination. Based on the observation of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM), the structure and morphology of the products were characterized. It has been revealed that as-prepared LaFeO₃ samples have a uniform diameter of around 300 nm and hollow structures with thin shells of about 30 nm consisting of numerous nanocrystals and nanopores. Owing to the hollow and porous structure, large surface area and more surface active sites, the sensor based on LaFeO₃ hollow nanospheres exhibited high response, good selectivity and stability to formaldehyde gas (HCHO). It suggests that the as-prepared LaFeO₃ hollow nanospheres are promising candidates for good performance formaldehyde sensor.     

Tuning X/(TiO2)x–(SiO2)100 – x (0 < x < 40) xerogel photocatalysts

Microporous (TiO₂) _x –(SiO₂)_{100 − x} (0 < x < 40) xerogels have been produced by sol–gel methods either by partial pre-hydrolysis or reflux of tetraethoxysilane and titanium isopropoxide. These have been characterised by ²⁹Si nuclear magnetic resonance, X-ray diffraction, EXAFS at the Ti–K edge, X-ray photoelectron spectroscopy, temperature-programmed reduction, FT infrared, N₂ adsorption at 78 K (BET), transmission electron microscopy and dynamic light scattering (DLS). These were dip coated onto fused silica and characterised by atomic force microscopy and UV–visible absorption. Their photoactivity in removal of alkylphenol ethoxylate TX100 from water was less than for less porous titania. The advantages of including thermally removable PEG or PPG templates in terms of increasing surface, meso-porosity and photon absorbance at visible wavelengths to give nanoengineered photocatalytic films are described.     

Study on the photocatalytic activity of TiN/TiO2 nanoparticle formed by ball milling

TiN/TiO₂ nanoparticle photocatalyst was prepared by ball milling of TiO₂ in H₂O solution doped with TiN. The photocatalyst was characterized by UV–Vis diffuse reflection spectroscopy, X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Based on the results of the characterization, the mechanism of the increase in photocatalytic activity was investigated. The results show that when the amount of doped TiN is 0.15 wt%, the photocatalytic activity of the TiN/TiO₂ is at its peak. Compared with TiO₂, the photoabsorption wavelength range of the TiN/TiO₂ photocatalyst red-shifts about 30 nm, and the photoabsorption intensity increases as well. The photocatalytic activities of the photocatalyst are higher than that of TiO₂ under UV and visible light irradiation. The increase of surface Ti³⁺ reactive center and the extension of the photoabsorption wavelength are the main factors for the increase in the photocatalytic activity of the TiN/TiO₂. Doped TiN neither changes the TiO₂ crystal phase nor creates new crystal phase by ball milling.     

Characterization and applications of as-grown β-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles prepared by hydrothermal method

The production of low-dimensional nanoparticles (NPs) with appropriate surface modification has attracted increasing attention in biological, biochemical, and environmental applications including chemical sensing, photocatalytic degradation, separation, and purification of toxic molecules from the matrices. In this study, iron oxide NPs have been prepared by hydrothermal method using ferric chloride and urea in aqueous medium under alkaline condition (pH 9 ~ 10). As-grown low-dimensional NPs have been characterized by UV–vis spectroscopy, FT-IR, X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy, High-resolution Transmission electron microscopy, and Electron Diffraction System. The uniformity of the NPs size was measured by the scanning electron microscopy, while the single phase of the nanocrystalline β-Fe₂O₃ was characterized using powder X-ray diffraction technique. As-grown NPs were extensively applied for the photocatalytic degradation of acridine orange (AO) and electrochemical sensing of ammonia in liquid phase. Almost 50% photo-catalytic degradation with AO was observed in the presence of UV sources (250 W) with NPs. β-Fe₂O₃ NP-coated gold electrodes (GE, surface area 0.0216 cm²) have enhanced ammonia-sensing performances in their electrical response (I–V characterization) for detecting ammonia in liquid phase. The performances of chemical sensor were investigated, and the results exhibited that the sensitivity, stability, and reproducibility of the sensor improved significantly using β-Fe₂O₃ NPs on GE surface. The sensitivity was approximately 0.5305 ± 0.02 μAcm⁻²mM⁻¹, with a detection limit of 21.8 ± 0.1 μM, based on a signal/noise ratio of 3 with short response time.     

Surface photovoltage properties and photocatalytic activities of nanocrystalline CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> particles with porous superstructure fabricated by a modified chemical coprecipitation method

In this study, nanocrystalline CoFe₂O₄ particles with porous timber-like superstructure were synthesized by a modified chemical co-precipitation route with calcination temperatures of 573, 673, 773, 873, and 973 K, respectively. The structural properties of the samples were systematically investigated by X-ray powder diffraction, scanning electronic microscopy, energy-dispersive X-ray spectra, UV–Vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the CoFe₂O₄ samples were comparatively studied by the degradation of 4-chlorophenol under Xe lamp irradiation. The results indicated that the sample calcined at 673 K exhibited the highest photocatalytic efficiency among the five samples.     

Photocatalytic disinfection of water with Ag–TiO2 nanocrystalline composite

A method of solution impregnation and calcination has been demonstrated for synthesizing nanoparticles of Ag–TiO₂ composite photocatalysts for use in the disinfection of water. Only a small proportion of the TiO₂ surface is covered by nano-islands of Ag corresponding to a loading of 4 wt.% of Ag; thus, most of the TiO₂ surface is available for photocatalytic function. Although the primary particles of both Ag and TiO₂ are in the 10- to 20-nm range, microscopic studies indicate that the primary particles of Ag are deposited on nano-agglomerates of 30- to 70-nm-sized TiO₂. It is seen that the relatively small loading of Ag has not caused any UV–vis spectral shift but has enhanced the rate of photocatalytic antibacterial action of TiO₂, presumably by electron trapping.     

An efficient composite growing N-doped TiO<Subscript>2</Subscript> on multi-walled carbon nanotubes through sol–gel process

High-activity, visible-light-driven photocatalysts were prepared by forming N-doped TiO₂ on multi-walled carbon nanotubes (MWCNTs). The use of MWCNTs as the support in a N-doped TiO₂ system favored electron trapping, because the recombination process could be retarded, thus promoting photocatalytic activity. The prepared photocatalysts were systematically characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunaure–Emmett–Teller (BET) spectroscopy, and UV–Vis diffuse reflectance spectroscopy (UV–Vis/DRS). The results indicated that the N-doped TiO₂ coated on MWCNTs improved the surface area and slightly modified the optical properties of the composite. The activities of the photocatalysts were probed by photodegradation of methanol in the presence of visible light irradiation. The experimental results revealed that the strong interphase linkage between the MWCNTs and the N-doped TiO₂ played a significant role in improving photocatalytic activity. However, the mechanical process for MWCNT–TiO_2-x N _x mixtures showed lower activity than just pure N-doped TiO₂. In this study, N-doped TiO₂ precursors coated with pretreated MWCNTs during a sol–gel process could effectively form a MWCNT–TiO_2-x N _x composite. The composite showed excellent activity and effectively enhanced the efficiency of N-doped TiO₂ under the visible light region.     

Influence of pH on the preparation of dispersed Ag–TiO<Subscript>2</Subscript> nanocomposite

In this paper, data concerning the effect of pH on the morphology of Ag–TiO₂ nanocomposite during photodeposition of Ag on TiO₂ nanoparticles is reported. TiO₂ nanoparticles prepared by sol–gel method were coated with Ag by photodeposition from an aqueous solution of AgNO₃ at various pH levels ranging from 1 to 10 in a titania sol, under UV light. The as-prepared nanocomposite particles were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and N₂ adsorption/desorption method at liquid nitrogen temperature (−196 °C) from Brunauer–Emmett–Teller (BET) measurements. It is shown that at a Ag loading of 1.25 wt.% on TiO₂, a high-surface area nanocomposite morphology corresponding to an average of one Ag nanoparticle per titania nanoparticle was achieved. The diameter of the titania crystallites/particles were in the range of 10–20 nm while the size of Ag particles attached to the larger titania particles were 3 ± 1 nm as deduced from crystallite size by XRD and particle size by TEM. Ag recovery by photo harvesting from the solution was nearly 100%. TEM micrographs revealed that Ag-coated TiO₂ nanoparticles showed a sharp increase in the degree of agglomeration for nanocomposites prepared at basic pH values, with a corresponding sharp decrease in BET surface area especially at pH > 9. The BET surface area of the Ag–TiO₂ nanoparticles was nearly constant at around a value of 140 m² g⁻¹ at all pH from 1–8 with an anomalous maximum of 164 m² g⁻¹ when prepared from a sol at pH of 4, and a sharp decrease to 78 m² g⁻¹ at pH of 10.     

Thermostable photocatalytically active TiO<Subscript>2</Subscript> anatase nanoparticles

Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO₂ and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO₂/SiO₂ particles were synthesized by a flame aerosol process with TiCl₄ and SiCl₄ as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO₂/SiO₂ samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO₂ P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was found that SiO₂ stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO₂ layer/bridge as spacer between TiO₂ particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination at 1,000 °C. Due to the stabilizing effect of SiO₂ the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either due to intensified cracking of the SiO₂ layer or due to enhanced transport of SiO₂ into the necks thus releasing additional titania surface.     

Morphologically different WO3 nanocrystals in photoelectrochemical water oxidation

Different morphologies of WO₃ nanocrystals such as nanorods and nanoplates have been obtained under hydrothermal conditions using ammonium metatungstate as the precursor in presence of different organic acids such as citric, oxalic, and tartaric acid in the reaction medium. Detailed characterization of the crystal structure, particle morphology, and optical band gap of the synthesized powders have been done by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and solid-state UV–visible spectroscopy study. The as-synthesized materials are WO₃ hydrates with orthorhombic phase which transform to the hexagonal WO₃ through dehydration upon heating at 350 °C. The resultant products are crystalline with nanoscale dimensions. Finally, the photoactivity of the synthesized materials annealed at 500 °C has been compared employing in photoelectrochemical water oxidation under the illumination of AM 1.5G simulated solar light (100 mWcm⁻²). The photocurrent measurements upon irradiation of light exhibit obvious photocatalytic activity with a photocurrent of about 0.77, 0.61, and 0.65 mAcm⁻² for the WO₃ film derived with the oxalic acid, tartaric, and citric acid assisting agents, respectively, at 1.8 V versus Ag/AgCl electrode.     

Investigation on F–B–S tri-doped nano-TiO<Subscript>2</Subscript> films for the photocatalytic degradation of organic dyes

F–B–S tri-doped titanium dioxide thin films on common glass were prepared by a modified sol–gel method, in which tetrabutyl titanate (Ti(OC₄H₉)₄) was chosen as the precursor and boric acid (H₃BO₃), sodium fluoride (NaF), and thiourea (N₂H₄CS) were employed as boron, fluorine, and sulfur sources, respectively. The microstructure and optical property were characterized by X-ray diffraction, high-resolution field emission scanning electron microscopy, N₂ adsorption–desorption isotherms, photoluminescence spectrum, and UV–Vis diffraction reflectance spectroscopy. The photocatalytic performances were evaluated by decomposition of organic dyes in solution. The experimental results revealed that the F–B–S tri-doped TiO₂ thin film was composed of uniform round-like nano-particles with the size range of 5–8 nm. F–B–S tri-doping not only significantly promoted the UV-induced photodecomposition activities of TiO₂ films but also extended the optical response of TiO₂ red shift to visible light region, herein improving the visible light-induced degradation of organic dyes. The improvement mechanism by F–B–S tri-doping was also discussed.     

Methoxycarbonyl-terminated hyperbranched poly(amine-ester) as templates for synthesis of silver nanoparticles

Highly stable and spherical silver nanoparticles, stabilized by methoxycarbonyl-terminated hyperbranched poly(amine-ester) (HPAE-COOCH₃), were synthesized in water with reducing AgNO₃/HPAE-COOCH₃ using two methods, viz. NaBH₄ and ultraviolet irradiation. HPAE-COOCH₃ was found to play a key role in the formation of nanoparticles. UV–visible absorption, Transmission electron microscopic (TEM), and Fourier transform infrared spectroscopy (FT-IR) had been used to study the structure and characterization of the silver nanoparticles. The absorption peaks of the silver nanoparticles appear at ~420 nm in UV–visible absorption spectra; average particle size reduced by NaBH₄ is ~30 nm, which is ~10 and ~15 nm, respectively, when ultraviolet irradiation time is 12 and 24 h. FT-IR spectra confirm that there is strong interaction between silver nanoparticles and HPAE-COOCH₃. And silver nanoparticles/HPAE-COOCH₃ aqueous solution can keep stable for more than 3 months.     

Preparation and characterization of p–n heterojunction photocatalyst p-CuBi2O4/n-TiO2 with high photocatalytic activity under visible and UV light irradiation

In this article, the p-type CuBi₂O₄ powder was prepared by the solid-state reaction method. The p–n heterojunction photocatalyst p-CuBi₂O₄/n-TiO₂ was prepared by ball milling. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy (SEM), and photoluminescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr₂O₇ ²⁻ and photocatalytic oxidation of methyl orange (MO). The results showed that the photocatalytic activity of the p–n heterojunction photocatalyst p-CuBi₂O₄/n-TiO₂ was much higher than that of TiO₂ and the mixture of p-CuBi₂O₄–n-TiO₂ without ball milling under visible and UV light irradiation. The optimal percentage of doped p-CuBi₂O₄ is 20 wt%. Compared with pure TiO₂, the photoabsorption wavelength range of the photocatalyst is extended greatly toward visible light and improves the utilization of the total spectrum. The effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The optimum ball milling time is 6 h. The mechanisms of influence of p-CuBi₂O₄ on the photocatalytic activity of p-CuBi₂O₄/n-TiO₂ were also discussed by the p–n junction principle and the valance band theory.     

Synthesis of Cr2O3/TNTs nanocomposite and its photocatalytic hydrogen generation under visible light irradiation

A novel Cr₂O₃/TNTs nanocomposite was prepared by loaded suitable amount of amorphous Cr₂O₃ on titanate nanotubes (TNTs) via hydrothermal reaction and impregnation process. XRD, SEM and TEM results demonstrated that the amorphous Cr₂O₃ nanoparticles were homogeneously dispersed on the surface of TNTs. The diffuse reflectance UV–visible absorption spectra exhibited that the spectral response of TNTs was extended to visible light region by coupled with Cr₂O₃. The 2.5Cr₂O₃/TNTs nanocomposite showed the highest activity of hydrogen generation by photocatalytic water-splitting under visible light irradiation (λ > 400 nm). The high activity of H₂ evolution for Cr₂O₃/TNTs nanocomposites was associated with the donor level in the forbidden band of TNTs semiconductor provided by dopant Cr³⁺ and a probably photocatalytic mechanism was proposed.     

Effect of the Si/Ce molar ratio on the textural properties of rare earth element cerium incorporated mesoporous molecular sieves obtained room temperature

Rare earth Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized via a direct and nonhydrothermal method at room temperature from sodium silicate and ammonium cerium (IV) nitrate as raw materials. Cetyltrimethyl ammonium bromide (CTAB) was used as a template. The resultant samples were characterized by means of powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis) and N₂ physical adsorption, respectively. The effect of the Si/Ce molar ratio on the crystalline structure and textural properties of CeMCM-41 was also investigated. The experimental results show that ordered CeMCM-41 mesoporous molecular sieves were successfully synthesized at room temperature and the resultant mesoporous materials have specific surface areas in the range of 594–1369 m²/g and average pore sizes in the range of ca. 2.5–2.8 nm. It has been found that the structural properties are strongly related to the amounts of cerium incorporation. When the cerium content increased in the samples, the intensity of the peak (1 0 0) was gradually reduced, and the surface area and structural regularity were diminished.     

镧掺杂介孔TiO2光催化剂的制备、表征及其光催化性能

以钛酸四正丁酯和硝酸镧为原料, 以P123为模板剂,采用模板法合成了La掺杂型介孔TiO₂光催化剂, 借助TGA-DSC、BET、XRD及UV-Vis等测试手段对样品进行了表征,并以苯酚为模型污染物考察了镧掺杂量对样品光催化活性的影响．结果表明: La掺杂介孔TiO₂光催化剂孔径分布较均匀(～10 nm),比表面积可达165 m²/g．与纯介孔TiO₂相比,经掺杂改性后的样品在紫外光区及可见光区的吸收显著增强,对光具有更高的利用率,La掺杂可显著提高介孔TiO₂的光催化活性.     

Electrochemical performances of FePO<Subscript>4</Subscript>-positive active mass prepared through a new sol–gel method

This investigation is a contribution to the research on alternative cathode materials with much more promising performances for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO₄, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor at temperatures (T _c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with the decrease in T _c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S _BET, as high as 28 m² g⁻¹ for the sample annealed at 400°C. The electrochemical properties of FePO₄-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum reversible capacity of 132 mAh g⁻¹, which fell with the increase in T _c. A direct correlation was established between the activity of the material and its active surface area.     

Iron–cobalt nanocrystalline alloy supported on a cubic mesostructured silica matrix: FeCo/SBA-16 porous nanocomposites

A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal stability. Low-angle X-ray diffraction, N₂ physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction in H₂ flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix and they seem in a large extent to be allocated inside the pores.