Novel method for doping nano TiO2 photocatalysts by chemical vapour deposition

Highly active photocatalytic Fe-doped nano TiO₂ was successfully synthesised by chemical vapour deposition (CVD) method using FeCl₃ as Fe source. CVD was carried out by evaporating FeCl₃ at 350°C in nitrogen flow during 30–90?min. The amount of Fe incorporated into TiO₂ framework is adjusted by the amount of FeCl₃ used and the evaporation time. The obtained sample was characterised by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), energy dispersive X-ray spectroscopy (EDS), UV-Vis, Fourier transform-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of the samples were tested in photocatalytic decomposition of 2-propanol in liquid phase using visible light instead of UV light irradiation. Non-doped TiO₂ and high Fe loading TiO₂ samples showed very low photocatalytic activity, whereas the low Fe loading TiO₂ sample exhibited high photocatalytic activity under visible light. The high photocatalytic activity of this sample was rationalised by the existence of defects (Ti–OH groups) as the active sites.     

Structural and electrochemical investigations of nanostructured NiTiO<Subscript>3</Subscript> in acidic environment

Electrochemically stable nanostructured nickel titanate (NiTiO₃) was prepared by sol-gel method and the structural and electrochemical properties were studied in the presence of H₂SO₄+CH₃OH electrolyte. XRD and Raman studies confirmed the single phase of NiTiO₃ with the rhombohedral structure. Thermal stability was studied by TGA. Microstructure analysis by SEM confirmed the uniformly distributed spherical shaped NiTiO₃ particles, and TEM studies showed the spherical shaped particles with an average size of 90 nm. The UV-Vis analysis shows the absorption spectrum of NiTiO₃, while the FTIR spectrum showed the vibrations related to Ni-O and Ti-O stretching. Electrochemical tests were carried out by cyclic voltammetry (CV) and polarization studies. The CV measurements were made at room temperature as well as at 60°C: at room temperature, the NiTiO₃ did not show any activity towards methanol oxidation whereas there observed an activity at the potential of 0.69 V at the operating temperature of 60°C. The ilmenite structured NiTiO₃ has oxygen vacancies, most probably on the surface, which could have also contributed to the methanol oxidation. Thus the nanostructured NiTiO₃ is proposed to be an active support material for metal electrocatalysts.     

Preparation of TiO2, Ag-doped TiO2 nanoparticle and TiO2–SBA-15 nanocomposites using simple aqueous solution-based chemical method and study of their photocatalytical activity

Nanocrystalline TiO₂, Ag-doped TiO₂ and TiO₂–SBA-15 nanocomposites have been synthesised using a simple aqueous solution-based chemical method. Nanocrystalline TiO₂ was synthesised by calcining the precursor prepared by using ethylenediamine tetraacetic acid and TiCl₃ in aqueous medium. Formation of crystalline phase (anatase, rutile or mixed phase) and crystallite size were found to be dependent on calcination temperature. To enhance the photocatalytic activity, Ag-doped TiO₂ was synthesised by doping of Ag during the synthesis step of TiO₂. TiO₂–SBA-15 nanocomposites were synthesised by impregnation method. Pure anatase TiO₂ nanoparticle was formed in the amorphous matrix of the silicate SBA-15, even though the loading of the TiO₂ in the silicate matrix was as low as 5?wt%. The synthesised materials were characterised using thermal analysis, powder X-ray diffraction method, surface area and porosimetry analysis, diffuse reflectance analysis and transmission electron microscopy. The photocatalytic property of the synthesised materials was investigated towards the degradation of methyl orange under sunlight exposure and monitored by UV–visible spectrophotometer. Ag-doped TiO₂ exhibited enhanced photocatalytic activity than undoped TiO₂. TiO₂–SBA-15 nanocomposites showed impressive photocatalytic activity even with 10?wt% TiO₂ loading.     

Nickel titanate microtubes constructed by nearly spherical nanoparticles: Preparation, characterization and properties

In this paper, we report the successful synthesis of NiTiO₃ microtubes constructed by nearly spherical nanoparticles via a simple solution-combusting method employing a mixture of ethanol and ethyleneglycol (V/V = 60/40) as the solvent, nickel acetate as the nickel source, tetra-n-butyl titanate as the titanium source and oxygen gas in the atmosphere as the oxygen source. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS). The UV-vis absorption spectrum of the product showed two absorption peaks centered at 258.6 and 350.1 nm, respectively. The Brunauer-Emmett-Teller (BET) surface area of the product was 14.06 m²/g and the pore size distribution mainly located from 20 to 30 nm. The photocatalytic degradation property of the product for organic dyes showed that the as-obtained porous NiTiO₃ microtubes could strongly promote the degradation of organic dyes including Pyronine B, Safranine T and Fluorescein.     

Preparation of nitrogen co-doped SiO2/TiO2 thin films on ceramic with enhanced photocatalytic activity under visible-light irradiation

In this study, we have successfully deposited N-doped SiO₂/TiO₂ thin films on ceramic tile substrates by sol–gel method for auto cleaning purpose. After dip coating and annealing process the film was transparent, smooth and had a strong adhesion on the ceramic tile surface. The synthesised catalysts were then characterised by using several analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM) and UV-vis absorption spectroscopy (UV-vis). The analytical results revealed that the optical response of the synthesised N-doped SiO₂/TiO₂ thin films was shifted from the ultraviolet to the visible light region. The nitrogen substituted some of the lattice oxygen atoms. The surface area of co-doped catalyst increased, and its photocatalytic efficiency was enhanced. The photocatalytic tests indicated that nitrogen co-doped SiO₂/TiO₂ thin films demonstrated higher than of the SiO₂/TiO₂ activity in decolouring of methylene blue under visible light. The enhanced photocatalytic activity was attributed to an increasing of the surface area and a forming of more hydroxyl groups in the doped catalyst.     

Optical and photocatalytic properties of the Fe-doped TiO2 nanoparticles loaded on the activated carbon

In this work, Fe-doped (1?wt%) TiO₂ loaded on the activated carbon nano-composite was prepared using a sol-gel method. A prepared nano-composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), BET surface area, Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) spectroscopy and UV–Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-composite was evaluated through degradation of synthetic textile wastewater, reactive red 198, under visible light irradiations. The XRD result indicated that the TiO₂ nano-composite contained only anatase phase. The surface area of the TiO₂ increased from 48?m²/g to 100?m²/g through the fabrication of the nano-composite. The FE-SEM results indicate that the TiO₂ particles with an average particle size of 35–70?nm can be deposited homogeneously on the activated carbon surface. DRS showed that the Fe doping in the TiO₂ -activated carbon nano-composite induced a significant red shift of the absorption edge and then the band gap energy decreased from 3.3 to 2.9?eV. Photocatalytic results indicated that the photocatalytic activity of the Fe doped TiO₂ increased under visible light irradiation in the presence of the activated carbon.     

Kinetic dissociation of nickel titanate and nickel tungstate in oxygen potential gradients

Nickel titanate (NiTiO₃) and nickel tungstate (NiWO₄) were exposed to oxygen potential gradients at 1400 and 1100° C, and they were found to dissociate into their constituent oxides, namely, NiO and TiO₂, and WO₃ and NiO, respectively. This is consistent with the non-equilibrium phenomenon of kinetic decomposition. In the case of nickel titanate, at the low-oxygen-potential side, TiO₂ was formed as sharp needle-like structures within the titanate matrix, while at the high-oxygen-potential side, NiO was formed. In contrast, NiO was formed at the lower-oxygen-potential side in the case of nickel tungstate, while WO₃ volatized off from the high-oxygen-potential side. This indicated that W diffuses faster than Ni in tungstates. In both cases, there were significant macroscopic shifts of the oxide with respect to the original position, established with Pt markers, towards the high-oxygen-potential side.     

Visible light photocatalytic activity of nitrogen-doped La<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> nanosheets originating from band gap narrowing

Approximately 15 nm thick nitrogen-doped lanthanum titanate (La₂Ti₂O₇) nanosheets with a single-crystalline perovskite structure have been prepared by hydrothermal processing and subsequent heat treatment in NH3 at 600 °C. Doping nitrogen into the La₂Ti₂O₇ nanosheets results in the narrowing of the band gap, extending the light absorption into the visible light region (∼495 nm). The nitrogen-doped La₂Ti₂O₇ nanosheets not only show significant visible light photocatalytic activity toward the decomposition of methyl orange but also exhibit enhanced the ultraviolet light photocatalytic activity. The enhancement of photocatalytic activity originates from the narrowing of the band gap of La₂Ti₂O₇ nanosheets. The results obtained show that the desirable route to extend the photocatalytic activity of a semiconductor from the ultraviolet to the visible light region is to narrow the band gap rather than to create localized mid-gap states.      

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Facile preparation of Sn/BiOCl composite oxides and their photocatalytic performance

Sn-doped BiOCl (Sn/BiOCl) photocatalysts were synthesized by a precipitation method using Bi(NO₃)₃?·?5H₂O as a bismuth source, SnCl₂ as an Sn source, imidazole hydrochloride as a chlorine source, a solvent, and a template agent. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, surface area analysis (Brunauer, Emmett and Teller [BET]), and diffuse reflectance spectroscopy. The XRD results showed a greater increase in the peak intensity of Sn/BiOCl because of its high degree of crystallinity. The UV–Vis results indicated a redshift from 368?nm (BiOCl) to 418?nm (Sn/BiOCl), leading to the reduced band gap of BiOCl because of Sn doping in BiOCl. The Sn/BiOCl not only retained ultraviolet photocatalytic activity of BiOCl but also showed visible photocatalytic activity. The BET results showed that the surface area of Sn/BiOCl (23.35?m²?) was bigger than that of BiOCl (13.54?m²?g). The bigger surface show higher photocatalytic activity due to more contact opportunity between reactants. Hence, the increased photocatalytic activity of Sn/BiOCl in the degradation of rhodamine B can be attributed to a higher degree of crystallinity, larger surface area, and broader range of optical absorption. The Sn/BiOCl needed only 20?min under visible light and 40?min under ultraviolet light to completely degrade rhodamine B. Moreover, the photocatalytic experiment did not require any other chemical reagent such as H₂O₂. The microstructures of BiOCl and Sn/BiOCl ensured that the catalyst still has high recovery rate when it is reused. The microstructures of catalyst have a little of loss.     

Photocatalytic degradation of an azo dye using Bi3.25M0.75Ti3O12 nanowires (M = La,Sm, Nd,and Eu)

Bi_3.25M_0.75Ti₃O₁₂ (BMT, M = La, Sm, Nd, and Eu) nanowires were synthesized through simple hydrothermal route and their structural and photocatalytic properties were investigated. XRD results indicated that these compounds are of layered perovskites structure. In addition, the band gaps of Bi_3.25La_0.75Ti₃O₁₂ (BLT), Bi_3.25Sm_0.75Ti₃O₁₂ (BST), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT), and Bi_3.25Eu_0.75Ti₃O₁₂ (BET) were estimated to be about 2.403, 2.594, 2.525, and 2.335 eV, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Bi_3.25M_0.75Ti₃O₁₂ (M = La, Sm, Nd, and Eu) showed markedly higher catalytic activity compared to traditional N doped TiO₂ (N-TiO₂) and pure bismuth titanate (Bi₄Ti₃O₁₂, BIT) for MO photocatalytic degradation under visible light irradiation. The high photocatalytic performance of Bi_3.25M_0.75Ti₃O₁₂ photocatalysts could be attributed to the strong visible light absorption and the recombination restraint of the e^?/h⁺ pairs resulting from doping of rare earth metal ions. Furthermore, BET nanowires exhibited the highest photocatalytic activity.     

Yolk-shell CdS@void@TiO2 composite particles with photocorrosion resistance for enhanced dye removal and hydrogen evolution

Yolk-shell CdS@void@TiO₂ (cadmium sulfide@void@titanium dioxide) composite particles (CPs), consisting of three parts: core (CdS) synthesized by solvent thermal reaction, void generated by polypyrrole (PPy) sacrificed layers and porous shell (TiO₂) by sol-gel method, were innovatively fabricated. The actual yolk-shell structure and chemical composition of the resultant CdS@void@TiO₂ were verified by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction analyses (XRD), and X-ray photoelectron spectroscopy (XPS). CdS@void@TiO₂ CPs possessed enhanced visible light response due to its narrower energy gap (2.9 eV) than TiO₂ (3.2 eV). With the support of photocatalytic performance test results, CdS@void@TiO₂ exhibits much higher hydrogen evolution rate up to 1893.5 μmol h⁻¹ g⁻¹ as well as dye removal efficiency both under visible and UV light irradiation than pristine TiO₂. The covering of TiO₂ shell remarkably promotes the photocorrosion resistance of CdS. The unique yolk-shell structure promotes striking photocatalytic performance in dye removal and hydrogen evolution. A possible photocatalytic mechanism about enhanced photocatalytic activity and robust photostability is also proposed.     

Improved visible-light responsive photocatalytic activity of N and Si co-doped titanias

Thermal reaction of titanium tetraisopropoxide and tetraethyl orthosilicate in 1,4-butanediol afforded nanocrystalline silica-modified titanias having large surface area and superior thermal stability. In this study, the thus-obtained silica-modified titanias were treated in an NH₃ flow at high temperatures, and their physical and photocatalytic properties were investigated. Compared with NH₃-treated TiO₂ without silica modification, the NH₃-treated silica-modified titanias showed a stronger absorption in the visible region (400–500 nm) and had a larger peak at 396 eV in the N 1s XPS spectrum. These results indicate that a larger amount of nitrogen was stably doped in the silica-modified titania. The obtained products exhibited a high photocatalytic activity for degradation of Rhodamine B and decomposition of acetaldehyde under visible light irradiation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural, photophysical and photocatalytic properties of Bi2MTaO7 (M = La and Y)

Bi₂MTaO₇ (M = Y and La) were synthesized by solid-state reaction method and their structural and photocatalytic properties were investigated. The results indicated that these compounds crystallize in the pyrochlore-type structure, cubic system with space group Fd-3 m. In addition, the band gaps of Bi₂LaTaO₇ and Bi₂YTaO₇ were estimated to be about 2.17(3) and 2.22(7) eV, respectively. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water respectively with Bi₂MTaO₇ (M = Y and La) as the photocatalysts under ultraviolet light irradiation. Photocatalytic degradation of aqueous methylene blue (MB) dye over these compounds was further investigated under visible light irradiation. Bi₂MTaO₇ (M = Y and La) showed markedly higher catalytic activity compared to P-25 for MB photocatalytic degradation under visible light irradiation. Complete removal of aqueous MB was observed after visible light irradiation for 190 min with Bi₂LaTaO₇ as the photocatalyst and for 200 min with Bi₂YTaO₇ as the photocatalyst. The decrease of the total organic carbon (TOC) and the formation of inorganic products, SO₄²⁻ and NO₃⁻, demonstrated the continuous mineralization of aqueous MB during the photocatalytic process.     

Experimental investigations on barium titanate nanocomposite thin films as an opto-electronic humidity sensor

This article reports the synthesis and characterisation of Barium titanate (BaTiO₃) nanocomposite and its application as opto-electronic humidity sensor. Titanium tetrachloride and barium hydroxide were mixed in molar ratio 1?:?1 in deionised water under continuous stirring at room temperature. Later, sodium hydroxide solution was added to above solution with continuous stirring. Finally, BaTiO₃ gel was obtained. The synthesised nano-composite material was characterised using a scanning electron microscope, X-ray diffraction (XRD) and UV-Visible spectrophotometer. SEM image of the composite film shows that the film is porous having uniform grains. From XRD the minimum crystallite size of BaTiO₃ was found to be 8?nm using Debye–Scherer formula. UV-Visible absorption spectroscopy was used for optical characterisation of the film. It was found that the optical band gap of the composite material was 3.50?eV. Barium titanate thin film was deposited on the base of an equilateral prism using sol–gel spin coating process at 4000?rpm. The humidity sensing properties of the film was investigated at different angles of incidence. It was observed that the intensity of reflected light increased with an increase in relative humidity (%RH) in the range 5–95% at a particular angle of incidence. Sensing element has maximum sensitivity ～6?µW/%RH, which is quite significant for sensor fabrication purposes.     

Synthesis and photochemical properties of Cu2+ doped layered hydrogen titanate

Cu²⁺ doped layered hydrogen titanate was prepared by the calcination of K₂CO₃, TiO₂ and CuO mixtures with the K₂CO₃:TiO₂:CuO molar ratio of 1:2.5(1−x):2.5x at 1200°C for 5 h followed by an ion-exchange reaction in 1 M HCl solution. The crystalline phase changed from monoclinic hydrogen tetratitanate to an orthorhombic lepidocrocite-type hydrogen titanate by increasing the amount of Cu²⁺ doped. Both compounds could be excited by visible light irradiation (λ>400 nm) and were capable of hydrogen gas evolution from an aqueous methanol solution, where the photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was slightly greater than that of Cu²⁺ doped lepidocrocite-type hydrogen titanate. The photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was enhanced by constructing Pt and TiO₂ pillars in the interlayer, and the incorporation of Pt in Cu²⁺ doped hydrogen tetratitanate enabled the cleavage of water into hydrogen and oxygen by irradiating visible light (λ>400 nm) without a sacrificial hole acceptor.     

Characterization of LiF-doped TiO2 and its photocatalytic activity for decomposition of trichloromethane

LiF-doped TiO₂ was prepared by hydrolysis of tetrabutyl titanate in a mixed LiF-H₂O-alcohol solution. The prepared LiF-doped TiO₂ powders were characterized by X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy and photoluminescence spectra (PL). The photocatalytic activity was evaluated by the decomposition of trichloromethane (CHCl₃). The results showed that LiF-doping increased the amount of O_OH and oxygen vacancy (OV) on the surface of TiO₂, which were beneficial to photocatalytic activity. LiF-doping inducted the new isolated energy band located above the valence band of TiO₂, which extended the absorption region of TiO₂ to visible light. The results of photocatalytic reaction showed that the photocatalytic activity of LiF-doped TiO₂ was 2.5 times higher than that of pure TiO₂.     

Hydrothermal synthesis,characterisation and photocatalytic properties of BiOIO3 nanoplatelets

In this work, BiOIO₃ nanoplatelets were successfully prepared by a simple hydrothermal method. The as-prepared samples were characterised by energy-dispersive spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction and ultraviolet visible diffuse reflectance spectroscopy. The photocatalytic activities of the as-prepared BiOIO₃ nanoplatelets were evaluated by photodegradation of rhodamine B (RhB) under simulated solar light. The results showed that the change of temperature within a certain range has almost no influence on the morphology and size of BiOIO₃ nanoplatelets. However, it had an obvious effect on the photocatalytic performance of BiOIO₃ nanoplatelets. The results showed that the BiOIO₃ sample synthesised at 130 °C exhibited the highest photocatalytic activities compared to others, with RhB completely decomposed in 80 min. The products with proper crystallinity formed at 130 °C have the optimal rate of RhB photodegradation. It indicated that the most favourable crystallinity made it beneficial to improve the photocatalytic activity. The possible mechanism of the photocatalytic reaction based on deep analysis and the experimental results was discussed in detail.     

Decomposition of water by a CaTiO3 photocatalyst under UV light irradiation

Platinized CaTiO₃ powder (band gap 3.5 eV) had a high photocatalytic activity of decomposing water into H₂ and O₂ under the irradiation of UV light, especially with photon energies above 3.8 eV. The existence of this photocatalytic activity is further supported on electrochemical grounds in that the photoinduced current spectrum measured between a CaTiO₃ single crystal and a Pt electrode without applied voltage in water showed a maximum near 4.1 eV. This result indicates that the direct measurement of the spectrum corresponding to the efficiency of water decomposition is an effective method to survey photocatalytic activities of materials.     

Recycling of glass in synthesis of MCM-48 mesoporous silica as catalyst support for Ni<Subscript>2</Subscript>O<Subscript>3</Subscript> photocatalyst for Congo red dye removal

Glass was successfully recycled in the synthesis of mesoporous silica MCM-48 which was used as catalyst support for nickel oxide photocatalyst. The resulted products were evaluated using X-ray diffraction, scanning electron microscope and UV–Vis spectrophotometer. The precipitated nickel oxide is of Ni₂O₃ form and loading of it onto MCM-48 resulted in a reduction in the band gap energy from about 3.66 eV to about 2.4 eV. The role of MCM-48 as catalyst support for Ni₂O₃ in enhancing the adsorption capacity and photocatalytic properties of nickel oxide was evaluated through series of equilibrium studies and photocatalytic degradation of Congo red dye under visible light. Using of glass-based MCM-48 as catalyst support for Ni₂O₃ showed enhancing the adsorption capacity by 31.3 and 14.8% higher than the adsorption capacity of Ni₂O₃ and MCM-48, respectively. Also, the photocatalytic degradation percentage increased by about 67.3% relative to the Ni₂O₃ degradation percentage. The nature of MCM-48/Ni₂O₃ adsorption mechanism is chemisorption and occurs in multilayer form throughout the heterogeneous surface of the composite. The using of MCM-48 as support for Ni₂O₃ photocatalyst enhanced the adsorption capacity through increasing the total surface area. The loading process resulted in fixing of the Ni₂O₃ particles throughout the porous structure which producing more exposed active photocatalyst sites and active adsorption sites for the incident photons as well as preventing the nickel oxide particles from agglomeration. Based on the obtained results, supporting of Ni₂O₃ particles onto MCM-48 is promising active centers for the degradation of Congo red dye molecules.