Aqueous synthesis and enhanced photocatalytic activity of ZnO/Fe2O3 heterostructures

We report a facile synthesis of ZnO/Fe₂O₃ heterostructures based on the hydrolysis of FeCl₃ in the presence of ZnO nanoparticles. The material structure, composition, and its optical properties have been examined by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance UV–visible spectroscopy. Results obtained show that 2.9 nm-sized Fe₂O₃ nanoparticles produced assemble with ZnO to form ZnO/Fe₂O₃ heterostructures. We have evaluated the photodegradation performances of ZnO/Fe₂O₃ materials using salicylic acid under UV-light. ZnO/Fe₂O₃ heterostructures exhibited enhanced photocatalytic capabilities than commercial ZnO due to the effective electron/hole separation at the interfaces of ZnO/Fe₂O₃ allowing the enhanced hydroxyl and superoxide radicals production from the heterostructure.     

Photocatalytic photodegradation of xanthate over C, N, S-tridoped TiO2 nanotubes under visible light irradiation

C, N, S-tridoped TiO₂ nanotubes were synthesized via hydrothermal synthesis and post-treatment, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), the Brunauer-Emmett-Teller method (BET), and UV-vis diffuse reflectance spectroscopy (DRS). The UV-diffuse reflectance spectra of all the C, N, S-tridoped TiO₂ nanotubes greatly extended the absorption edge to the visible light region, and the absorbance in the visible region increased with increasing molar ratio of thiourea to Ti (R), which could be attributed to C, N, S-tridoping in the form of cation C-doping, interstitial N-doping, cation S-doping, and adsorbed ions’ states. The photocatalytic activity of C, N, S-tridoped TiO₂ nanotubes was evaluated by photocatalytic photodegradation of potassium ethyl xanthate (KEX) under visible light irradiation. It was found that the photocatalytic activity of the prepared samples increased with increasing molar ratio of thiourea to Ti (R). At R=6, the photocatalytic activity of the tridoped sample TNTS-6 reached a maximum value. With further increase in R, photocatalytic activity of the sample decreased, which could be attributed to the high visible light activity resulting from the balance between visible light absorption and recombination of electron/hole pairs.     

Rapid microwave-assisted hydrothermal synthesis of Bi12TiO20 hierarchical architecture with enhanced visible-light photocatalytic activities

Flower-like Bi₁₂TiO₂₀ hierarchical nanostructures composed of numerous nanobelts were synthesized at 180 °C within 1 h by a microwave-assisted hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) for the first time. The as-prepared products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) absorption spectroscopy. Furthermore, the hierarchical Bi₁₂TiO₂₀ nanostructures exhibited higher photocatalytic activities in the degradation of Rhodamine B under visible-light irradiation than that of the samples prepared without CTAB. In addition, the role of CTAB cationic surfactant has been investigated thoroughly and a possible mechanism is proposed.     

Optical and photocatalytic properties of nanocrystalline TiO2 synthesised by solid-state chemical reaction

Nanoparticulate TiO₂ is of interest for a variety of technological applications, including optically transparent UV-filters and photocatalysts for the destruction of chemical waste. The successful use of nanoparticulate TiO₂ in such applications requires an understanding of how the synthesis conditions effect the optical and photocatalytic properties. In this study, we have investigated the effect of heat treatment temperature on the properties of nanoparticulate TiO₂ powders that were synthesised by solid-state chemical reaction of anhydrous TiOSO₄ with Na₂CO₃. It was found that the photocatalytic activity increased with the heat treatment temperature up to a maximum at 600 °C and thereafter declined. In contrast, the optical transparency decreased monotonically with the heat treatment temperature. These results indicate that solid-state chemical reaction can be used to prepare powders of nanoparticulate TiO₂ with properties that are optimised for use as either optically transparent UV-filters or photocatalysts.     

Improving the visible light photocatalytic activity of mesoporous TiO2 via the synergetic effects of B doping and Ag loading

B-doped together with Ag-loaded mesoporous TiO₂ (Ag/B–TiO₂) was prepared by a two-step hydrothermal method in the presence of boric acid, triblock copolymer surfactant, and silver nitrate, followed by heat treatment. The obtained samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption. It was revealed that all samples consist of highly crystalline anatase with mesoporous structure. For Ag/B–TiO₂, B was doped into TiO₂ matrix in the form of both interstitial B and substitutional B while Ag was deposited on the surface of B–TiO₂ in the form of metallic silver. Compared with the single B-doped or Ag-loaded TiO₂ one, mesoporous Ag/B–TiO₂ exhibits much higher visible light photocatalytic activity for the degradation of Rhodamine 6G, which can be ascribed to the synergistic effects of B doping and Ag loading by narrowing the band gap of the photocatalyst and preventing the fast recombination of the photogenerated charge carriers, respectively.     

Photophysical and enhanced daylight photocatalytic properties of N-doped TiO2/g-C3N4 composites

N-doped TiO₂/C₃N₄ composite samples were synthesized by heating the mixture of the hydrolysis product of TiCl₄ and C₃N₄ at different weight ratios. The samples were characterized by X-ray diffraction (XRD), Raman spectrum, UV–vis absorption spectrum, photoluminescence spectrum, X-ray photon electron spectrum (XPS) and surface photovoltage spectrum (SPS). The XRD and Raman results indicate that the introduction of C₃N₄ could inhibit the formation of rutile TiO₂. The composite samples show slight visible light absorption due to the introduction of C₃N₄. The XPS result reveals that some amount of nitrogen is doped into TiO₂, and C₃N₄ exists in the composite sample. The intensities of the SPS signal in the composite samples decrease with the rise in the amount of C₃N₄ in the samples. The photocatalytic activity was evaluated from the Rhodamine B (RhB) degradation under fluorescence light irradiation. The composite samples show significantly enhanced photocatalytic activities and the RhB self-sensitized photodegradation in this system was observed by measuring the photocurrent in the dye sensitized solar cell using the composite as the working electrode.     

TiO2 nanoparticles with high ability for selective adsorption and photodegradation of textile dyes under visible light by feasible preparation

Particular TiO₂ nanoparticles with high selective photocatalytic oxidation of anionic dyes are prepared by a feasible hydrothermal method. Moreover, its photocatalytic selectivity can be easily switched to cationic dyes by a simple post-treatment in ammonia solution, which makes the prepared TiO₂ have bi-directional selectivity in dye photodegradation. Based on the photocatalytic performances and the structure and surface characteristics of the catalyst, the bi-directional selectivity of the catalysts is found to be closely related to the adsorption selectivity. The adsorption selectivity originates from surface charge groups, which are introduced during the preparation and post-treatment progresses. This study provides a facile and economical approach towards selective degradation of dyes with high efficiency by the special TiO₂ nanoparticles synthesized through a simple hydrothermal method, which may be used practically in the future.     

Tailoring optical properties of TiO2 nanowires coated with Ag nanoparticles by plasmon coupling of Ag nanoparticles

TiO₂ nanowires were grown on titanium foil by an alkali hydrothermal growth method. The as-synthesized nanowires are structurally uniform with diameters of 50-100 nm and lengths of up to a few micrometers. The as-prepared TiO₂ nanowires were coated with Ag nanoparticles by reducing AgNO₃ in solution. The experimental results indicate that the Ag nanoparticles can aggregate together on the surfaces of TiO₂ nanowires by interconnection between nanoparticles. The degree of aggregation of Ag nanostructures can be controlled by changing the concentrations of Ag nanoparticles. The as-prepared nanostructures exhibit a wide optical absorption from 387 to 580 nm that can be easily tuned by controlling the degree of aggregation of Ag nanostructures. The results reveal that optical properties of the Ag-coated TiO₂ nanowires can be enhanced by plasmon coupling of Ag nanoparticles. The as-prepared nanostructures may find potential applications in the field of solar cells.     

Polyol-assisted synthesis of TiO2 nanoparticles in a semi-aqueous solvent

TiO₂ (anatase and rutile) nanoparticles with an average crystallite size of 20-40 nm have been prepared at room temperature by polyol-mediated synthesis technique in a semi-aqueous solvent medium using titanium iso-propoxide as the titanium source, acetone as the oil phase and ethylene glycol as the stabilizer. Phase and microstructure of the resultant materials have been characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Photocatalytic degradation of acetaldehyde using TiO₂ nanoparticles was investigated by gas-chromatography technique.     

Low-temperature hydrothermal synthesis of highly photoactive mesoporous spherical TiO2 nanocrystalline

TiO₂ microspheres with mesoporous textural microstructures and high photocatalytic activity were prepared by hydrothermal treatment of mixed solution of titanium sulfate and urea with designed time. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption measurements. The photocatalytic activity was evaluated via the photocatalytic oxidation of acetone in air at room temperature. The results show that the hydrothermal time significantly influences on the morphology, microstructure and photocatalytic activity of the as-prepared samples. With increasing hydrothermal time, specific surface areas and pore volumes decrease, contrarily, the crystallite size and relative anatase crystallinity increase. The photocatalytic efficiency of the as-prepared samples is obviously higher than that of commercial Degussa P25 (P25) powders. Especially, the as-prepared TiO₂ powders by hydrothermal treatment for 7 h shows the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2 times.     

Facile synthesis of monodispersed CeO2 nanostructures

CeO₂ nanostructures were successfully prepared by a facile and environmentally friendly mixed-solvothermal method under mild conditions. The X-ray diffraction (XRD) and transmission electron microscope (TEM) results indicated that the as-synthesized products were cubic CeO₂ polycrystalline structures with uniform diameters in the range of 10–20 nm and lengths up to 80 nm. X-ray photoelectron spectroscopy (XPS) spectra and EDX data demonstrated that stoichiometric CeO₂ was formed. A possible growth mechanism of the CeO₂ nanostructures was proposed. Moreover, ultraviolet absorption measurement revealed the band gap of the CeO₂ nanorods was estimated to be 3.85 eV, which is larger than the reported value for the bulk CeO₂ (E_g=3.2 eV). Enhancement of the band gap of the CeO₂ nanorods is attributed to the well-known quantum size effect.     

Bifunctional photocatalysis of TiO2/Cu2O composite under visible light: Ti in organic pollutant degradation and water splitting

Photocatalytic experiment results under visible light demonstrate that both TiO₂ and Cu₂O have low activity for brilliant red X-3B degradation and neither can produce H₂ from water splitting. In comparison, TiO₂/Cu₂O composite can do the both efficiently. Further investigation shows that the formation of Ti³⁺ under visible light has great contribution. The mechanism of photocatalytic reaction is proposed based on energy band theory and experimental results. The photogenerated electrons from Cu₂O were captured by Ti⁴⁺ ions in TiO₂ and Ti⁴⁺ ions were further reduced to Ti³⁺ ions. Thus, the photogenerated electrons were stored in Ti³⁺ ions as the form of energy. These electrons trapped in Ti³⁺ can be released if a suitable electron acceptor is present. So, the electrons can be transferred to the interface between the composite and solution to participate in photocatalytic reaction. XPS spectra of TiO₂/Cu₂O composite before and after visible light irradiation were carried out and provided evidence for the presence of Ti³⁺. The image of high-resolution transmission electron microscopy demonstrates that TiO₂ combines with Cu₂O tightly. So, the photogenerated electrons can be transferred from Cu₂O to TiO₂.     

Preparation, characterization and photocatalytic activity of metal-loaded NaNbO3

Fe-, Ni-, Co- and Ag- loaded NaNbO₃ catalysts were prepared and their activities have been investigated in the reaction of photocatalytic hydrogen generation. Me/NaNbO₃ were synthesized by impregnation of NaNbO₃ in an aqueous solution of metal nitrates and then by calcination at the temperature of 400 °C. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-Ray spectrometer (EDX) as its mode. The detailed analysis has revealed that all the investigated catalysts exhibit high crystallinity and the presence of Fe₂O₃, NiO, Co₃O₄ and Ag₂O oxides on Me/NaNbO₃ was confirmed. Finally, the influence of different metal loadings (Fe, Ni, Co and Ag) on the photocatalytic activity of NaNbO₃ for photocatalytic hydrogen generation has been investigated. Here we report that among all the Me/NaNbO₃ photocatalysts Ag-loaded NaNbO₃ exhibited higher photocatalytic efficiency for photocatalytic hydrogen generation than NaNbO₃.     

Synthesis,photophysical properties,and photocatalytic applications of Bi doped NaTaO3 and Bi doped Na2Ta2O6 nanoparticles

Phase formation and photophysical properties of bismuth doped sodium tantalum oxide (perovskite, defect pyrochlore) nanoparticles prepared by a hydrothermal method were studied in detail. It was revealed that the synthesis conditions like NaOH concentration and bismuth precursor (NaBiO₃·2H₂O) markedly affect the crystal structure of sodium tantalum oxide. At low NaOH concentration and high bismuth precursor (NaBiO₃·2H₂O) content, Bi doped Na₂Ta₂O₆ (defect pyrochlore) phase was predominantly formed, while at higher NaOH concentration, Bi doped NaTaO₃ (perovskite) phase was formed. It was observed that the defect pyrochlore (Bi doped Na₂Ta₂O₆) phase was formed and stabilized by the presence of dopant precursor (NaBiO₃·2H₂O). The chemical analysis of the samples confirmed the doping of Bi³⁺ cations in both phases. Doping of bismuth enabled visible light absorption up to 500 nm in perovskite and defect pyrochlore type sodium tantalum oxide. Bi doped NaTaO₃ samples showed better performance for the photocatalytic degradation of rhodamine B than that of Bi doped Na₂Ta₂O₆, under visible light irritation (λ>420 nm). The present results shed light on phase formation of sodium tantalate and these results are useful in understanding properties of NaTaO₃ based compounds, synthesized by the hydrothermal method.     

Elaboration and characterization of TiO2 nanoparticles incorporated in SiO2 host matrix

Nanometer-scale TiO₂ particles have been synthesized by sol-gel method. It was incorporated in a glass-based silica aerogel. The composite was characterized by various techniques such as particle size analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). The bulk glass presents a strong luminescence at wavelengths ranging from 750 to 950 nm. This PL was attributed to various non-bridging oxygen hole centers (NBOHCs) defects resulting from thermal treatment and crystallization of TiO₂ at the interface between titania nanoparticles and silica host matrix.     

Structure and photocatalytic properties of copper-doped rutile TiO2 prepared by a low-temperature process

Copper-doped titania with variable Cu/Ti ratios have been prepared via a simple aqueous-phase method at 85 °C. The obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectra analysis. The photocatalytic properties of the products were tested by photocatalytic degradation of aqueous brilliant red X-3B solution. The results showed that the sample with 2% copper doping has the best photocatalytic activity, which is 3 times that of undoped rutile titania. The effect of the doped copper on the structure and property of TiO₂ has also been discussed.     

g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity

Novel g-C₃N₄ modified Bi₂O₃ (g-C₃N₄/Bi₂O₃) composites were synthesized by a mixing-calcination method. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent-time measurement (PT). The photocatalytic activity of the composites was evaluated by degradation of Rhodamine B (RHB) and 4-chlorophenol (4-CP) under visible light irradiation (>400 nm). The results indicated that the g-C₃N₄/Bi₂O₃ composites showed higher photocatalytic activity than that of Bi₂O₃ and g-C₃N₄. The enhanced photocatalytic activity of the g-C₃N₄/Bi₂O₃ composites could be attributed to the suitable band positions between g-C₃N₄ and Bi₂O₃. This leads to a low recombination between the photogenerated electron–hole pairs. The proposed mechanism for the enhanced visible-light photocatalytic activity of g-C₃N₄/Bi₂O₃ composites was proven by PL and PT analysis.     

Size-controlled hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2 nanorods

Large amount of uniform orthorhombic LiMnO₂ (o-LiMnO₂) nanorods was fabricated by a hydrothermal route in 180 °C using γ-MnOOH nanorods as precursors through an isomorphous ion exchange process. The size of as-obtained o-LiMnO₂ nanorods was determined by that of γ-MnOOH precursors, which could be deliberately controlled. The electrochemical performance of o-LiMnO₂ nanorods was characterized via galvanostatic tests, which suggested that the size of as-obtained products played an important role in their electrochemical performances.     

Preparation and photocatalytic activity of nitrogen-doped TiO2 hollow nanospheres

TiO₂ hollow nanospheres were prepared using silicon oxide as a template. N-doped titanium oxide hollow spheres, TiO_2−xN_x were synthesized by reacting TiO₂ hollow spheres with thiourea at 500 °C. XRD and XPS data showed that oxygen was successfully substituted by nitrogen through the nitrogen-doping reaction, and finally N-doped TiO₂ hollow spheres were formed. The N-doped TiO₂ hollow spheres showed new absorption shoulder in visible light region so that they were expected to exhibit photocatalytic activity in the visible light. The photocatalytic activity of N-doped TiO₂ hollow spheres under visible light was similar to that of normal spherical TiO_2−xN_x in spite of the structural difference.     

Hydrothermal synthesis of BaYF5:Yb/Er upconversion luminescence submicrospheres by a surfactant-free aqueous solution route

BaYF₅:Yb³⁺/Er³⁺ upconversion (UC) luminescence submicrospheres have been synthesized by the hydrothermal synthesis method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), scanning probe microscope (SPM), transmission electron microscope (TEM), laser diffraction particle analyzer (LDPA) and UC emission spectra. The as-prepared highly crystalline BaYF₅:Yb³⁺/Er³⁺ submicrospheres are of uniform size depending on different reaction temperatures and reaction times. It is found that the usage of fluoride source NaBF₄ plays the crucial key in the formation of submicrosphere. Under the 980 nm excitation, the UC emission transitions for ⁴F_9/2→⁴I_15/2 (red), ²H_11/2, ⁴S_3/2→⁴I_15/2 (green) in the BaYF₅:Yb³⁺/Er³⁺ submicrospheres came from two-, two-, and two-photon UC processes, respectively. Further, the effects of Yb³⁺ ion concentration, size and surface of as-prepared submicrospheres, and pumping power on the UC luminescence properties of BaYF₅:Yb³⁺/Er³⁺ have also been discussed.