Synthesis,Characterization and Photocatalytic Activity of TiO_2 Film/Bi_2O_3 Microgrid Heterojunction

TiO2 film modified by Bi2O3 microgrid array was successfully fabricated by using a microsphere lithography method.The structure and morphology of TiO2 film,Bi2O3 film and TiO2 film/Bi2O3 microgrid heterojunction were characterized through X-ray diffraction,atomic force microscopy and scanning electron microscopy.The optical transmittance spectra and the photocatalytic degradation capacity of these samples to rhodamine B were determined via ultraviolet-visible spectroscopy.The results indicated that the coupled system showed higher photocatalytic activity than pure TiO2 and Bi2O3 films under xenon lamp irradiation.The enhancement of the photocatalytic activity was ascribed to the special structure,which could improve the separation of photo-generated electrons and holes,enlarge the surface area and extend the response range of TiO2 film from ultraviolet to visible region.     

Increasing visible-light absorption for photocatalysis with black 2D Bi4Ti3O12 nanosheets

In this work, a simple method to prepare defect two-dimension (2D) Bi₄Ti₃O₁₂ nanosheets material by NaBH₄ reduction with Argon atmosphere was reported. The results of EPR and XPS demonstrated that the presence of oxygen vacancy in Bi₄Ti₃O₁₂, which resulted in color changed and extend photon-absorbance. By comparing to pristine Bi₄Ti₃O₁₂, the black Bi₄Ti₃O₁₂ exhibited higher photocatalytic activity to pollutants. The mechanism was also proposed for exploring the defect in the photocatalytic process.     

A simple method for fabricating p–n junction photocatalyst CuFe2O4/Bi4Ti3O12 and its photocatalytic activity

The synthesis of Bi₄Ti₃O₁₂ and CuFe₂O₄ powders was achieved using a conventional solid-state reaction and the Sol–Gel method, respectively. A novel p–n heterojunction photocatalyst CuFe₂O₄/Bi₄Ti₃O₁₂ was subsequently prepared through ball milling. The structures, morphologies, and optical properties of the photocatalysts were comprehensively characterized. The transmission electron microscopy (TEM) images showed a clear interface between CuFe₂O₄ and Bi₄Ti₃O₁₂, indicating that a heterojunction between CuFe₂O₄ and Bi₄Ti₃O₁₂ was formed during ball milling. In addition, the photocatalytic activity was evaluated based on the photocatalytic degradation of methyl orange (MO). The results indicated that the photocatalytic activity of the p–n heterojunction photocatalyst CuFe₂O₄/Bi₄Ti₃O₁₂ was higher than that of Bi₄Ti₃O₁₂ alone. The enhanced photocatalytic activity could be attributed to the formation of a heterojunction between CuFe₂O₄ and Bi₄Ti₃O₁₂, which suppressed the recombination of photogenerated electron–hole pairs. We also investigated the effects of procedure time and dispersant (H₂O) during ball milling on the photocatalytic activity. The mechanisms underlying the observed photocatalytic activity were also described based on the semiconductor energy band theory and p–n junction principle. Moreover, the analysis of the radical scavengers confirmed that •O₂⁻ and h⁺ were the primary reactive species to cause the degradation of the MO.     

Preparation and photocatalytic activity of alkali titanate nano materials A2TinO2n+1 (A = Li, Na and K)

Photocatalysts nano A₂Ti_nO_2n+1 (A = Li, Na, K) were prepared successfully by novel hydrothermal synthesis process. Powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) absorption spectra and field-emission scanning electron microscope (FE-SEM) measurements. These results showed that the compositions of lithium, sodium and potassium titanates were Li₂TiO₃, Na₂Ti₃O₇ and K₂Ti₈O₁₇, respectively. The nano crystals of Li₂TiO₃ were self-assembled as snowflakes while that of Na₂Ti₃O₇ and K₂Ti₈O₁₇ were nanorods. Photocatalytic properties of alkali titanates were also investigated. The results indicated that alkali titanates as prepared have higher photocatalytic activities compared with P25 TiO₂ in the degradation of chloroform under UV light irradiation. A combination of K₂Ti₈O₁₇ and NiO produces a photocatalyst effective for the degradation of chloroform in aqueous solution. The framework of the tunnel structure was suitable for accommodating cocatalysts such as NiO to induce a strong interaction between the active species and cocatalysts. Na₂Ti₃O₇ has high photocatalytic activity under visible-light irradiation due to its strong absorption in the visible light region. The photocatalytic properties of Li₂TiO₃ are inferior to that of Na₂Ti₃O₇ and K₂Ti₈O₁₇ due to its mono-perovskite structure.     

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.     

Photocatalytic property of La2Ti2O7 synthesized by the mineralization polymerizable complex method

High photocatalytic activity La₂Ti₂O₇ was synthesized by a novel mineralization polymerizable complex (MPC) method. Compared with La₂Ti₂O₇ prepared by polymerizable complex (PC) method, MPC-La₂Ti₂O₇ showed larger surface areas, higher crystallization and more uniform morphology. These factors resulted in a dramatic improvement of its photocatalytic activity for hydrogen evolution. The photocatalytic activity of MPC-La₂Ti₂O₇ was about three times higher than that of PC-La₂Ti₂O₇.     

In-situ synthesis of TiO2 nanostructures on Ti foil for enhanced and stable photocatalytic performance

TiO_2 nanostructures with strong interfacial adhesion and diverse morphologies have been in-situ grown on Ti foil substrate through a multiple-step method based on conventional plasma electrolytic oxidation(PEO) technology, hydrothermal reaction and ion exchange process. The PEO process is critical to the formation of TiO_2 seeding layer for the nucleation of Na_2Ti_3O_7 and H_2Ti_3O_7 mediates that are strongly attached to the Ti foil. An ion exchange reaction can finally lead to the formation of H_2Ti_3O_7 nanostructures with diverse morphologies and the calcination process can turn the H_2Ti_3O_7 nanostructures into TiO_2 nanostructures with enhanced crystallinity. The morphology of the TiO_2 nanostructures including nanoparticles(NP), nanowhiskers(NWK), nanowires(NW) and nanosheets(NS) can be easily tailored by controlling the NaOH concentration and reaction time during hydrothermal process. The morphology, composition and optical properties of TiO_2 photocatalysts were analyzed using scanning electron microscope(SEM), X-ray diffraction(XRD), photoluminescence(PL) spectroscopy and UV–vis absorption spectrum. Photocatalytic tests indicate that the TiO_2 nanosheets calcined at 500?C show good crystallization and the best capability of decomposing organic pollutants. The decoration of Ag cocatalyst can further improve the photocatalytic performance of the TiO_2 nanosheets as a result of the enhanced charger separation efficiency. Cyclic photocatalytic test using TiO_2 nanostructures grown on Ti foil substrate demonstrates the superior stability in the photodegradation of organic pollutant, suggesting the promising potential of in-situ growth technology for industrial application.     

Synthesis of TiO2/Bi2S3 heterojunction with a nuclear-shell structure and its high photocatalytic activity

TiO₂/Bi₂S₃ heterojunctions with a nuclear-shell structure were prepared by the coprecipitation method. The products were characterized by X-ray diffraction analysis, Raman spectra, transmission electron microscope images and energy dispersion X-ray spectra. Results showed that as-prepared Bi₂S₃ was urchin-like, made from many nanorods, and TiO₂/Bi₂S₃ heterojunctions have a similar nuclear-shell structure, with Bi₂S₃ as the shell and TiO₂ as the nuclear. The photocatalytic experiments performed under UV irradiation using methyl orange as the pollutant revealed that the photocatalytic activity of TiO₂ could be improved by introduction of an appropriate amount of Bi₂S₃. However, excessive amount of Bi₂S₃ would result in the decrease of photocatalytic activity of TiO₂. The relative mechanism was proposed.     

Preparation of Z-scheme Au-Ag2S/Bi2O3 composite by selective deposition method and its improved photocatalytic degradation and reduction activity

In this work, Z-scheme Ag₂S/Bi₂O₃ composites were fabricated through the precipitation of Ag₂S nanoplates on the surface of Bi₂O₃ microrods. Consequently, Au nanoparticles were selectively deposited on the Ag₂S nanoplates surface to obtain.Au-Ag₂S/Bi₂O₃ composites using near-infrared light photodeposition method. The characterization results indicate that the Ag₂S nanoplates were uniformly anchored on Bi₂O₃ surface, and Au nanoparticles were highly dispersed on the surface of Ag₂S nanoplate instead of Bi₂O₃. Acid orange 7 (AO7), Rhodamine B (RhB) and Cr(VI) were chosen as model reactant for the evaluation of photocatalytic degradation and reduction activity of the products under simulated sunlight irradiation. After the decoration of Ag₂S nanoplates, the photocatalytic activity of Ag₂S/Bi₂O₃ is much higher than that of bare Bi₂O₃, and the optimal catalytic efficiency is achieved by 12 %Ag₂S/Bi₂O₃ sample. More importantly, the photocatalytic activity of 12 %Ag₂S/Bi₂O₃ sample can be further enhanced by the selective decoration Au nanoparticles on the Ag₂S nanoplates. Among the ternary composites, 2Au-12 %Ag₂S/Bi₂O₃ sample with the Au content of 2% exhibits highest catalytic efficiency for 60 min (AO7: 96%; RhB: 56%; Cr(VI): 65%). The possible mechanism for the improvement of the photocatalytic activity of Bi₂O₃ by Ag₂S and Au decoration was proposed.     

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.     

Sonochemical assisted impregnation of Bi2WO6 on TiO2 nanorod to form Z-scheme heterojunction for enhanced photocatalytic H2 production

In this work, Bi₂WO₆/TiO₂ nanorod heterojunction was prepared by sonochemical assisted impregnation method. After loading 2 wt% Bi₂WO₆ on TiO₂ nanorods, the photocatalytic hydrogen production rate of 2026 µmol/h/g was achieved. Compared to commercial P25 and TiO₂ nanorods, ∼13 and ∼3 folds enhanced activity was observed. The excellent photocatalytic performance of Bi₂WO₆/TiO₂ nanorod photocatalyst was mainly attributed to i) reduction of bandgap due to heterojunction formation, ii) quick transport of photogenerated charge carriers, and iii) efficient charge carrier separation supported by UV-DRS, photocurrent measurement, Impedance study, and photoluminescence spectra analysis. The Z-scheme band alignment for Bi₂WO₆/TiO₂ nanorod heterojunction was proposed based on the Mott-Schottky measurement. This result demonstrated the effective utilization of Z-scheme heterojunction of Bi₂WO₆/TiO₂ for photocatalytic reduction application.     

Undoped visible-light-sensitive titania photocatalyst

Colorful rutile TiO₂ was prepared by heating Ti₂O₃ at 550–900 °C to develop novel visible-light-sensitive and eco-friendly photocatalysts for environmental remediation under visible-light irradiation. The colors of the prepared samples, which ranged from grayish green to yellowish off-white via yellow differed from the reported colors of reduced TiO₂, such as blue and black. The TiO₂ prepared in this study was characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and UV–Visible spectroscopy. These measurements showed that the TiO₂ contained Ti³⁺-interstitial sites. The TiO₂ was sensitive to visible light, and calculation of the band diagram demonstrated that this visible-light absorption is caused mainly by formation of Ti³⁺-interstitial sites in rutile TiO₂. Among the prepared samples, the TiO₂ prepared by heating Ti₂O₃ at 700 °C shows the highest photocatalytic activity under visible-light irradiation. In addition, the sample was further and mildly ground using a bead-milling machine. The ground sample possessed higher surface area and better photocatalytic activity.     

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.      

Effects of TiO2 addition on the superconducting properties of Bi-Sr-Ca-Cu-O system

The effects of TiO₂ addition in Bi₂Sr₂CaCu₂O₈Ti_y (Bi-2212) with y = 0, 0.05, 0.10 and 0.15 and (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀Ti_y (Bi-2223) with y = 0, 0.10,0.20 and 0.40 are studied and compared. The samples have been investigated by powder X-ray diffraction (XRD), dc electrical resistance, critical current density (J_c) and scanning electron microscopy (SEM). The XRD patterns of the Bi₂Sr₂CaCu₂O₈Ti_y materials showed the Bi-2212 as the dominant phase. In the TiO₂ added samples (with x = 0.05 and 0.1), the c lattice parameter decreased slightly from the non-added sample showing the possibility of Ti incorporating into the crystal structure of the Bi-2212 phase. In the undoped (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀ material, the XRD pattern showed the existence of mixed phases of Bi-2223 and Bi-2212. The TiO₂ added Bi-2223 samples do not show any systematic variation in the c lattice parameter, indicating that Ti may not be incorporated into the Bi-2223 crystal structure. The T_c values in both systems decreased with the addition of TiO₂. The critical current densities, J_c at 40 K in the Bi₂Sr₂CaCu₂O₈ system and at 77 K in the (Bi_1.6Pb_0.4)Sr_1.6Ca₂Cu_2.8O₁₀ system also decreased with the addition of TiO₂. SEM micrographs of both systems showed a slight decrease in average grain size when TiO₂ was added.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Photoreduction synthesis of silver on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites and their catalytic activity for the degradation of methyl orange

This paper demonstrates the preparation of pure TiO₂, 40% of Bi₂O₃ in TiO₂ and Ag loaded Bi₂O₃/TiO₂ nanocomposites by the hydrothermal method followed by the photoreduction process. The crystal structure, morphology and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy respectively. The dispersion of Ag nanoparticles on the surface of Bi₂O₃/TiO₂ nanocomposites are found to bring the conduction band near to the valence band, resulting in the narrow band gap compared to pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The XRD analysis demonstrated that silver nanoparticles were dispersed finely on the surface of Bi₂O₃/TiO₂ nanocomposites. All the characterization results revealed that the Ag/Bi₂O₃/TiO₂ nanocomposites were smaller crystallite size, stronger absorbance in the visible region and greater surface area than pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The photoluminescence intensity decreases with an increase in the UV-illumination time of Ag loaded Bi₂O₃/TiO₂ revealing a decrease in the recombination rate of electron–hole pairs. In order to test them as a photocatalyst, methyl orange was used as a standard. The photocatalytic degradation of methyl orange shows that the ABT5 sample exhibits the maximum degradation efficiency of 99% within 180 min of irradiation.     

Synthesis and characterization of TiO2/WO3 composite nanotubes for photocatalytic applications

TiO₂/WO₃ composite nanotubes were synthesized in an anodic aluminum oxide (AAO) template by a sol–gel method. The prepared nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, and Brunauer–Emmett–Teller surface area. Using the nanotubes embedded in the AAO templates as catalysts, photocatalytic degradation of methyl orange aqueous solution was carried out under UV light irradiation. The results showed that the TiO₂/WO₃ composite nanotubes with the thickness about 50 nm could be successfully synthesized by this method. TiO₂ showed anatase phase and WO₃ displayed monoclinic phase. The composite nanotubes (TiO₂/WO₃) exhibited higher photocatalytic activity than the pure nanotubes (WO₃ or TiO₂). The possible reason for improving the photocatalytic activity was also discussed.     

Enhanced visible-light-induced photocatalytic disinfection of Escherichia coli by ternary Bi2WO6/TiO2/reduced graphene oxide composite materials: Insight into the underlying mechanism

Composites coupling different semiconductors have attracted increasing attention for photocatalytic application owing to low visible-light absorption capability and weak photocatalytic activity of the single-component system. In this study, Bi₂WO₆/TiO₂/rGO ternary composites, successfully synthesized by a facile hydrothermal method, were manifested as an outstanding visible-light-response photocatalyst for the disinfection towards E. coli. X-ray diffraction, Fourier-transform infrared, and X-ray photoelectron spectroscopy demonstrated that GO coupled in the composites was efficiently reduced to rGO during the hydrothermal process, which was greatly beneficial for enhancing light harvest, promoting charge separation, and improving photocatalytic disinfection activity. UV–vis diffuse reflectance spectra, photoluminescence and time-resolved photoluminescence, photocurrent measurements, and ultraviolet photoelectron spectroscopy clearly showed that Bi₂WO₆/TiO₂/rGO composites had narrower band gap energy and much better suppression capability of photoinduced electron-hole recombination in comparison to the pure Bi₂WO₆ and TiO₂, and Bi₂WO₆/TiO₂. The radical trapping results revealed that the photogenerated holes (h⁺) were the leading active species responsible for the effective inactivation of E. coli under visible-light irradiation. Hence, the underlying mechanism for the enhanced photocatalytic disinfection performance of Bi₂WO₆/TiO₂/rGO composites was proposed. This study provides new insight into the design and development of composite materials with enhanced photocatalytic activity, which can be an inspiring alternative for environmental application.     

Low-temperature sintering and microwave dielectric properties of TiO<Subscript>2</Subscript>-based LTCC materials

Temperature stable high-K LTCC material was prepared. The influence of fabrication process on the crystalline phases, microstructures and microwave dielectric properties of TiO₂-Bi₂O₃-CuO ceramics were investigated. The crystalline phases and microstructures of TiO₂-Bi₂O₃-CuO ceramics were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that rutile TiO₂ phase and Bi₂Ti₄O₁₁ phase co-existed in the TiO₂-Bi₂O₃-CuO ceramics. Separate TiO₂ grains and Bi₂Ti₄O₁₁ grains distributed uniformly in the ceramic matrix. The composition 0.92TiO₂-0.08Bi₂Ti₄O₁₁ with 2 wt% CuO addition that was sintered at 900 °C for 2 h showed high dielectric constant (ε_r ~ 81), high quality factor (Q × f ~ 3,500 GHz) and near zero temperature coefficient of resonant frequency (τ_f ~ −5.1 ppm/°C), meanwhile the compatibility test showed that it could co-fire with silver electrode. The processing-microstructure-property interrelationship was also studied.     

Ternary novel TiO2/MgBi2O6/Bi2O3 nanocomposites with n-n-p heterojunctions: Impressive visible-light-triggered photocatalytic degradation of tetracycline

A series of novel ternary TiO₂/MgBi₂O₆/Bi₂O₃ nanocomposites were synthesized by a facile hydrothermal method. The ternary nanocomposites were characterized by XRD, FESEM, HRTEM, EDX, PL, EIS, Photocurrent, UV–vis DRS, BET, XPS, Raman, and FT-IR analyses. The photocatalytic performance of TiO₂ for the degradation of tetracycline antibiotic after combining with MgBi₂O₆/Bi₂O₃ was significantly improved, which is 46.1 and 18.5 times higher than pristine TiO₂ and MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. Furthermore, the ternary photocatalyst efficiently degraded MO, RhB, and MB dye pollutants, which is 22.5, 30.4, and 30.0 as high as TiO₂ and 11.2, 14.4, and 17.8 folds larger than MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. The photoluminescence and electrochemical analyses confirmed promoted separation and facile transfer of the charges thanks to construction of n-n-p heterojunctions among n-TiO₂, n-MgBi₂O₆, and p-Bi₂O₃ components and more production of charge carriers due to integration of small band gap MgBi₂O₆ and Bi₂O₃ components with wide band gap TiO₂.