Nonaqueous sol-gel synthesis and growth mechanism of single crystalline TiO2 nanorods with high photocatalytic activity

In this paper, we report on a nonaqueous synthesis of single crystalline anatase TiO₂ nanorods by reaction between TiCl₄ and benzyl alcohol at a low temperature of 80 °C. The resulting samples were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectrometry and UV-vis diffuse reflectance spectroscopy. We proposed that the TiO₂ nanorods were formed through an oriented attachment mechanism. More importantly, these single crystalline anatase TiO₂ nanorods exhibited significantly higher photocatalytic activities than commercial photocatalyst P25. This study provides an environmentally friendly and economic approach to produce highly active TiO₂ photocatalyst.     

2D spinodal phase-separated TiO2 films prepared by sol-gel process and photocatalytic activity

For the purpose of obtaining oxide thin films with high photocatalytic activity, we have successfully prepared the TiO₂ anatase polycrystalline films with a two-dimensional spinodal phase-separated structure (2D-SPSS) in micron size by the sol-gel dip-coating method from a titanium tetraisopropoxide solution containing polyoxyethylene(20) nonylphenyl ether. It has been also found that TiO₂ films with a variety of morphologies in addition to the 2D-SPSS can be formed by controlling the molar ratio of water to titanium tetraisopropoxide. The methylene blue photodegradation activity of the 2D-SPSS TiO₂ film was higher than that of dense TiO₂ film prepared from a TiO₂ sol without co-existing polymer. This fact can be interpreted in terms of possessing a high specific surface area available for the photocatalytic reaction.     

Photoinduced charge property of nanosized perovskite-type LaFeO3 and its relationships with photocatalytic activity under visible irradiation

In this paper, ABO₃-type perovskite LaFeO₃ nanosized photocatalysts were synthesized by a sol-gel method, using citric acid (HOOCCH₂C(OH)(COOH)CH₂COOH) as complexing reagent and La(NO₃)₃·6H₂O and Fe (NO₃)₃·9H₂O as raw materials. The as-prepared samples also were characterized by several testing techniques, such as thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), infrared spectrum (IR), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity of different LaFeO₃ nanoparticles for degrading Rhodamine B solution under visible irradiation (λ > 400 nm) was evaluated. The effects of thermal treatment temperature on photoinduced charge property and photocatalytic activity were mainly investigated, together with their relationships. The results show that the LaFeO₃ sample calcined at 500 °C exhibits higher activity, and the activity decreases with increasing calcination temperature, which is in good agreement with the characterization results. The weaker is the PL and SPS signal, the higher is the photocatalytic activity. Moreover, the activity of all as-prepared LaFeO₃ samples is higher than that of international P-25 TiO₂ under visible irradiation.     

Synthesis and photocatalytic activity of titania microspheres with hierarchical structures

A combined sol-gel and solvothermal process was introduced to fabricate the titania microspheres with hierarchical structures by using lauryl alcohol as the structure-directing agent. Scanning electron microscope, high-resolution transmission electron microscope, Fourier transform infrared spectrograph and powder X-ray powder diffraction indicated that the molar ratio of lauryl alcohol, water and tetra-n-butyl titanate was the key factor for the formation of the mono-dispersed titania with anatase phase and the optimal ratio was 1.2:4:1. The diameter of the end-product was 523 ± 74 nm and it was composed of smaller nanoparticles with about 6.8 nm size in diameter. Photocatalytic activity of the end-product was investigated by employing Rhodamine B and Methylene blue as the model compounds. The target microspheres exhibited the higher photocatalytic efficiency compared with commercial Degussa P25 titania and this result might be due to the hierarchical structures of microspheres according to the analysis of Brunauer-Emmett-Teller specific surface areas.     

Preparation and characterization of nanostructured MWCNT-TiO2 composite materials for photocatalytic water treatment applications

Nanoscale composite materials containing multi-walled carbon nanotubes (MWCNT) and titania were prepared by using a modified sol-gel method. The composites were comprehensively characterized by thermogravimetric analysis, nitrogen adsorption-desorption isotherm, powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy. The analysis revealed the presence of titania crystallites of about 7.5 nm aggregated together with MWCNT in particles of 15-20 nm of diameter. The photoactivity of the prepared materials, under UV or visible irradiation, was tested using the conversion of phenol from model aqueous solutions as probe reaction. A synergy effect on the photocatalytic activities observed for the composite catalysts was discussed in terms of a strong interphase interaction between carbon and TiO₂ phases by comparing the different roles of MWCNT in the composite materials.     

Macroporous TiO2/carbon composites prepared via a simple soaking process

A new-type composite photocatalyst of three-dimensional ordered macroporous (3DOM) TiO₂/C was prepared and tested in this paper. 3DOM carbon materials were first prepared by colloidal crystal templating process, and then the sols of TiO₂ from tetrabutyl titanate were infiltrated in the macroporous structures via capillary force. After calcinations at nitrogen flow, TiO₂/C composite materials were prepared. The obtained samples were analyzed by SEM, TEM, XRD and BET. The results indicated that macroporous TiO₂/C can remain the three-dimensional ordered structure and TiO₂ nanoparticles distributed in the interior of macropores uniformly. Eventually, 3DOM TiO₂/C materials were used as a new-type photocatalysts to decompose the methyl orange solution under ultraviolet light, which displayed excellent catalytic activity and regenerative ability.     

Synthesis and characterization of mesoporous-TiO2 with enhanced photocatalytic activity for the degradation of chloro-phenol

Mesoporous-titania (TiO₂) photocatalysts have been synthesized using polyethylene glycol (PEG) as a template in dilute acetic acid aqueous solution by hydrothermal process. The effect of PEG molecular weights and thermal treatment on the resultant structure and photocatalytic activity are investigated. Structural and phase compositional properties of the resultant photocatalysts are characterized by transmission electron microscopy, X-ray diffraction and nitrogen sorption analysis. When the molecular weights of PEG vary from 600 to 20,000, the particle sizes of mesoporous structure decrease from 15.1 to 13.3 nm and mean pore sizes increase from 6.9 to 10.6 nm. The chemical reactions of the formation of mesoporous-TiO₂ during its synthesis have been proposed and discussed. The activities of mesoporous-TiO₂ photocatalysts are evaluated and compared with Degussa P-25 using chloro-phenol as a testing compound. The reaction mechanism of photodegradation is also described on the basis of high performance liquid chromatography.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Quasi-cube ZnFe2O4 nanocrystals: Hydrothermal synthesis and photocatalytic activity with TiO2 (Degussa P25) as nanocomposite

The fabrication and photocatalytic application of zinc ferrite nanocrystals were reported. Quasi-cube ZnFe₂O₄ nanocrystals with typical small sizes of 5-15 nm were successfully synthesized by a facile hydrothermal approach. ZnFe₂O₄/P25 nanocomposite was prepared by physically grinding the ZnFe₂O₄ nanocrystals with TiO₂ (commercial Degussa P25) at ambient temperature, and it exhibited excellent photocatalytic activity for the mineralization of Rhodamine B. UV-vis measurement and photocatalytic test results showed that ZnFe₂O₄ nanocrystals exhibited effective band-gap coupling to P25 nanopowders by simply physical grinding without any surface modification or high-energy balling, which is usually adopted in conventional mixture process. This phenomenon can be attributed to the high surface activities of the as-obtained tiny ZnFe₂O₄ nanocrystals and commercial P25 nanoparticles. It may imply that the mixing process of composite materials would be simplified by further lowering the grain sizes of their component particles.     

Characterization and photocatalytic activity of Bi3TiNbO9 nanocrystallines synthesized by sol-gel process

Nanocrystalline Bi₃TiNbO₉ powders were synthesized by a sol-gel process, based on a colloid solution of bismuth acetate, titanium butoxide and niobium ethoxide. X-ray diffraction analysis revealed that pure Aurivillius phase of Bi₃TiNbO₉ could be prepared at a calcination temperature of 500 °C. By using scanning electron microscopy and gas adsorption method, the morphology and the specific surface area of the powders were examined. The photophysical properties of Bi₃TiNbO₉ were investigated by means of the UV-visible diffuse reflectance spectrum, from which a band gap ∼3.2 eV was empirically calculated. The as-prepared Bi₃TiNbO₉ powders were applied in the photodegradation of organic contaminant for the first time, and they showed effective photocatalytic activity for the complete decomposition of methyl orange under UV light irradiation.     

One step synthesis of Bi@Bi2O3@carboxylate-rich carbon spheres with enhanced photocatalytic performance

Bi@Bi₂O₃@carboxylate-rich carbon core-shell nanosturctures (Bi@Bi₂O₃@CRCSs) have been synthesized via a one-step method. The core–shell nanosturctures of the as-prepared samples were confirmed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Raman spectroscopy. The formation of Bi@Bi₂O₃@CRCSs core–shell nanosturctures should attribute to the synergetic roles of different functional groups of sodium gluconate. Bi@Bi₂O₃@CRCSs exhibits significant enhanced photocatalytic activity under visible light irradiation (λ > 420 nm) and shows an O₂-dependent feature. According to trapping experiments of radicals and holes, hydroxyl radicals were not the main active oxidative species in the photocatalytic degradation of MB, but O₂⁻ are the main active oxidative species.     

Synthesis and enhanced photocatalytic activity of tin oxide nanoparticles coated on multi-walled carbon nanotube

A nanocomposite of SnO₂ nanoparticles coated on multi-walled carbon nanotube (MWNT@SnO₂) was synthesized and characterized by thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, nitrogen physisorption measurements, photoluminescence. The results show that the SnO₂ nanoparticles with a narrow size of 4 nm are uniformly deposited on MWNT. The photocatalytic activity of the nanocomposite was studied using methyl orange as a model organic pollutant. MWNT@SnO₂ exhibits much higher photocatalytic activity than that of commercial TiO₂ (P-25). The promotion is mainly contributed from electron transfer between SnO₂ and MWNT.     

Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

Gd2O3:Eu@mesoporous SiO2 bifunctional core-shell composites: Fluorescence label and drug release

A novel kind of core-shell nanocomposite Gd₂O₃:Eu³⁺@mesoporous SiO₂ was successfully fabricated, which consisted of a solvothermal synthesized Gd₂O₃:Eu³⁺ nanospheres core, a thin nonporous silica midterm layer and an ordered mesoporous silica shell. The XRD, SEM, TEM, FTIR, N₂ adsorption/desorption and PL spectra were employed to characterize the composites. The cytotoxicity of Gd₂O₃:Eu³⁺@mesoporous SiO₂ and Gd₂O₃:Eu³⁺ was assessed by the standard MTT assay. The composites had spherically monodisperse morphology and a narrow size distribution around 180 nm in diameter. Furthermore, they also demonstrated the strong photoluminescence of ⁵D₀-⁷F_J emissions. In addition, the composites exhibited good property of sustained drug release by using ibuprofen (IBU) as model drug in the drug delivery process. Therefore, the drug release process could be easily tracked and identified through photoluminescence. Overall, the present composites have potential significant biomedical application as ideal bifunctional materials.     

Structure and dielectric performance of K-doped (Pb0.5Ba0.5)ZrO3 thin films

In the present investigation (Pb_0.5Ba_0.5)ZrO₃ (PBZ) thin films doped by K (KPBZ) from 0 to 5 mol% were successfully deposited on Pt-buffered silicon substrates by a sol-gel method. The K content dependence of microstructure and electrical properties of KPBZ thin films were studied in detail. It was found that, although all the films displayed a pure perovskite structure without obvious difference, the surface roughness of KPBZ films was decreased with increasing K content. Dielectric measurements showed that the figure of merit (FOM) values of KPBZ thin films were greatly increased by K-doping, and at the same time that the temperature-dependent stability was also improved. Thus, K doping is a promising way to optimize the overall electrical properties of PBZ thin films for potential application in tunable devices.     

Dielectric and ferroelectric properties of Ba(Sn0.15Ti0.85)O3 thin films grown by a sol-gel process

Ferroelectric Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were deposited on LaNiO₃-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 × 10⁻⁷ A/cm² and 5 × 10⁻⁵ A/cm² and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.     

Electrical properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films on TiO2 buffer layer

Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ antiferroelectric thin films with thickness of 500 nm were successfully deposited on TiO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates via sol-gel process. Microstructure of Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was studied by X-ray diffraction analyses. The antiferroelectric nature of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was confirmed by the double hysteresis behaviors of polarization and double buffer fly response of dielectric constant versus applied voltage at room temperature. The capacitance-voltage behaviors of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films with and without TiO₂ buffer layer were studied, as a function of temperature. The temperature dependence of dielectric constant displayed a similar behavior and the Curie temperature (T_c) was 193 °C for films on both substrates. The current caused by the polarization and depolarization of polar in the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films was detected by current density-electric field measurement.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.     

Insulating properties of rapid thermally processed Bi2Ti2O7 thin films by a chemical solution decomposition technique

Crack-free Bi₂Ti₂O₇ thin films on silicon substrates were prepared using chemical solution decomposition technique, and then treated by rapid thermal annealing. The microstructure of the films was studied by scanning electron microscopy. The effects of different fabricating procedures and various annealing temperatures and times on the leakage current density were investigated. The results show that the leakage current density decreases with increasing annealing temperature, while increases with increasing annealing time. Annealing temperature has a much stronger effect on the insulating properties of Bi₂Ti₂O₇ thin films than that of annealing time.