Synthesis of heterostructured Bi2O3–CeO2–ZnO photocatalyst with enhanced sunlight photocatalytic activity

The development of heterostructured semiconductor photocatalysts makes a noteworthy advancement in environmental purification technology. In this work, a novel heterostructured Bi₂O₃−CeO₂−ZnO, fabricated by a combination of microwave-assisted hydrothermal and thermal decomposition methods, showed an enhanced photocatalytic activity for Rhodamine B (RhB) degradation under sunlight, as compared to pristine ZnO, Bi₂O₃, CeO₂, and commercial Degussa TiO₂-P25. The obtained products were thoroughly characterized by various techniques including X- ray powder diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), elemental color mapping, energy-dispersive X-ray spectroscopy (EDAX), Raman spectrometry, Fourier transform infrared (FT-IR) spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence (PL) spectroscopy. PXRD analysis reveals that the heterostructure has the monoclinic lattice phase of α-Bi₂O₃, the cubic phase of CeO₂ and the hexagonal wurtzite phase of ZnO. FE-SEM images show that Bi₂O₃−CeO₂−ZnO has an ordered mixture of nanorod and nanochain structures. EDAX, elemental color mapping, Raman and FT-IR analyses confirm the successful formation of the heterostructured Bi₂O₃−CeO₂−ZnO. The UV–Vis DRS results demonstrate that Bi₂O₃−CeO₂−ZnO exhibits wide visible-light photoabsorption in 400–780 nm range. Moreover, the reduction in PL intensity of the heterostructured Bi₂O₃−CeO₂−ZnO, when compared to the pristine Bi₂O₃, CeO₂, and ZnO, indicates enhanced charge separation. The study on the mechanism displayed that the improved photocatalytic activity of Bi₂O₃−CeO₂−ZnO could be attributed to (1) the efficient separation of photoinduced electrons and holes of the photocatalysts, caused by the vectorial transfer of electrons and holes among ZnO, CeO₂ and Bi₂O₃, and (2) the wide visible-light photoabsorption range. This study introduces a new class of promising sunlight-driven photocatalysts.     

Mesoporous BiVO4/2D-g-C3N4 heterostructures for superior visible light-driven photocatalytic reduction of Hg(II) ions

In this contribution, a Z-scheme mesoporous BiVO₄/g-C₃N₄ nanocomposite heterojunction with a considerable surface area and high crystallinity was synthesized by a simple soft and hard template-assisted approach. This material demonstrates superior visible light-driven photocatalysis for the photoreduction of Hg(II) ions. TEM and XRD results show that the mesoporous BiVO₄ NPs, with a monoclinic phase and an ellipsoid-like shape, are highly dispersed onto the porous 2D surfaces of g-C₃N₄ nanosheets with a particle size of 5–10 nm. The obtained BiVO₄/g-C₃N₄ nanocomposites with a p-n heterojunction show significantly enhanced Hg(II) photoreduction efficiency compared to the mesoporous BiVO₄ NPs and pristine g-C₃N₄. Among all synthesized photocatalysts, the 1.2% BiVO₄/g-C₃N₄ nanocomposite indicated the highest photoreduction of Hg(II) performance, reaching ~ 100% within 60 min; this result is 3.9 and 4.5 –fold larger than that of the BiVO₄ NPs and pristine g-C₃N₄. The Hg(II) photoreduction rates highly increase to 208.90, 314.95, 411.23 and 418.68 μmol g⁻¹min⁻¹ for the mesoporous 0.4, 0.8, 1.2 and 1.6% BiVO₄/g-C₃N₄ nanocomposites, respectively. The reduction rate of the mesoporous 1.2% BiVO₄/g-C₃N₄ nanocomposite demonstrated a 5.2 and 3.8 times larger increase than that of the pristine g-C₃N₄ nanosheets and pure BiVO₄ NPs. The superior Hg(II) photoreduction efficiency was ascribed to decreased carrier recombination and the improved utilization of visible light by constructing BiVO₄/g-C₃N₄ nanocomposites with a p-n junction. Transient photocurrent measurement and photoluminescence spectra were employed to confirm the possible Hg(II) photoreduction mechanism over these BiVO₄/g-C₃N₄ photocatalysts. This research provides an accessible route for the nanoengineered design of mesoporous BiVO₄/g-C₃N₄ heterostructures that demonstrated unique photocatalytic performance.     

Bi4Ti3O12/TiO2 heterostructure: Synthesis,characterization and enhanced photocatalytic activity

A multicomponent oxide, Bi₄Ti₃O₁₂/TiO₂ heterostructure was successfully synthesized via a two-step synthesis route based on an anodic oxidation procedure and a subsequent hydrothermal technique. X-ray diffraction confirmed that the composition of the as-fabricated sample was a Bi₄Ti₃O₁₂/TiO₂ composite. Scanning and transmission electron microscopy observation reveals that the as-synthesized sample consisted of TiO₂ nanotubes decorated with Bi₄Ti₃O₁₂ nanocubes. The photocatalytic property of Bi₄Ti₃O₁₂/TiO₂ heterostructure was evaluated by decomposing methyl orange as a model organic compound. Compared with the unmodified TiO₂ nanotube arrays, Bi₄Ti₃O₁₂/TiO₂ heterostructure exhibits a higher photocatalytic activity in the decomposition of methyl orange under UV light. The prominent photocatalytic activity could be ascribed to the formation of the heterostructure between Bi₄Ti₃O₁₂ and TiO₂ as well as a good dispersity of Bi₄Ti₃O₁₂ nanocubes, which could effectively separate the photogenerated carriers and reduce the electron–hole recombination.     

Enhanced CO2 photocatalytic conversion into CH3OH over visible‐light‐driven Pt nanoparticle-decorated mesoporous ZnO–ZnS S-scheme heterostructures

In the present contribution, the design and fabrication of Pt nanoparticle-decorated mesoporous ZnO–ZnS heterostructures were described and used effectively for photocatalytic CO₂ conversion to yield CH₃OH. TEM images of the mesoporous Pt/ZnS–ZnO heterostructure demonstrated spherical ZnO NPs ~20 nm, and Pt NPs ~3 nm were well dispersed on the porous ZnS–ZnO heterostructure. The formation of CH₃OH over the Pt/ZnS–ZnO heterostructure was 78, 39 and 20 times larger than that bare ZnS, ZnO NPs and ZnS–ZnO, respectively. The optimal Pt/ZnO–ZnS heterostructure exhibited a high CH₃OH formation rate of 81.1 μmolg^-1h^-1, which is about 44, 22 and 20 times larger than that of bare ZnS (1.86 μmolg^-1h^-1), ZnO (3.72 μmolg^-1h^-1), and ZnO–ZnS (4.15 μmolg^-1h^-1), respectively. The significantly enhanced reduction of CO₂ was imputed to the synergistic effects of the ZnO–ZnS heterostructure and the incorporation of Pt NPs. The synthesized photocatalyst provides a new transfer route through which carriers can migrate to the outer surface as well as pore channels of the mesoporous ZnO–ZnS, therefore significantly minimizing the transfer distance for carriers, inhibiting photoinduced electron-hole recombination, and diminishing the mobility resistance, as determined using photoluminescence, photocurrent response, and electrochemical impedance spectra measurements.     

Soft Template-Assisted Controllable Synthesis of Nanocrystalline Orthorhombic YFeO3 Decorated Porous g-C3N4 with Enhanced Hg(II) reduction

Mesoporous single-crystalline perovskite YFeO₃ nanoparticles was synthesized through a soft template-assisted approach. Mesoporous YFeO₃ NPs were decorated porous g-C₃N₄ nanosheets with variation YFeO₃ NPs percentages, and the newly synthesized photocatalysts were assessed towards Hg(II) reduction and HCOOH oxidation in aqueous solution upon visible light exposure. XRD and HR-TEM revealed the formation of single-crystalline orthorhombic YFeO₃ with uniformly dispersed and the average particle size of 10?±?5 nm_, thereby constructing a mesoporous YFeO₃/g-C₃N₄ heterojunctions for the promotion of the photocatalytic performances compared to bare YFeO₃ NPs and g-C₃N₄. 3% YFeO₃/g-C₃N₄ heterostructure revealed the highest and optimum Hg(II) reduction (100%) within 60 min, which determined 3.7 and 5 times larger than of bare YFeO₃ NPs and g-C₃N₄ obeyed by pseudo-first-order kinetics. The YFeO₃/g-C₃N₄ photocatalyst could be recycled five continuous cycles and kept remarkable photostability for long time illumination. The superior Hg(II) reduction over mesoporous YFeO₃/g-C₃N₄ heterojunction is referred to as lower recombination of carriers, the unique electronic structure, higher visible light utilization and high surface area. This work focused on constructing the YFeO₃/g-C₃N₄ heterojunction, indicating outstanding photocatalytic performances in a facile route.

     

Development of mesoporous Bi2WO6/g-C3N4 heterojunctions via soft- and hard-template-assisted procedures for accelerated and reinforced photocatalytic reduction of mercuric cations under vis light irradiation

In this study, mesoporous Bi₂WO₆/g-C₃N₄ heterojunctions were developed using soft and hard templates [triblock copolymer surfactant (F127) and mesoporous silica (MCM-41), respectively]. The performance of the developed heterojunctions was assessed through the photocatalytic reduction of mercuric cations under Vis light illumination, with HCOOH being adopted to provide sacrificial holes agent. Surface measurements demonstrated that the fabricated specimens acquired large specific surface areas when compared with the neat ingredient. Furthermore, a transmission electron microscopy (TEM) analysis of the developed heterojunctions showed the homogeneous distribution of the spherical Bi₂WO₆ nanoparticles (NPs) on the surface of g-C₃N₄ nanosheets. Meanwhile, an accelerated rate (700 μ·mol·g^?1·h^?1) of photocatalytic mercuric cation reduction with improved efficiency (approximately 100%), compared with those of the pure ingredients [rate of 55 μ·mol·g^?1·h^?1 and efficiency of 13% for g-C₃N₄ nanosheets; rate of 95 μ·mol·g^?1·h^?1 and efficiency of 20% for mesoporous Bi₂WO₆ NPs], was accomplished via testing of the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ after 40 min of illumination. Evidently, the efficiency of the photocatalytic reduction of mercuric cations endorsing the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ NPs is 7.7 and 5 times more when compared with those of the neat g-C₃N₄ nanosheets and mesoporous Bi₂WO₆ NPs, respectively. The improved performance of the fabricated heterojunctions in the photocatalytic reduction of mercuric cations could be ascribed to i) fast diffusion of the mercuric cations through the mesoporous texture to the active ensembles, ii) greater specific surface area, iii) limited bandgap magnitude, iv) homogenous dispersion of the Bi₂WO₆ NPs on the surface of the nanosheets, and v) finite particle dimension of the mesoporous Bi₂WO₆ NPs. The durability and stability of the Bi₂WO₆/g-C₃N₄ heterojunctions were confirmed via their recyclability, which was maintained for up to five runs without pronounced activity loss.     

Enhanced visible light response of heterostructured Cr2O3 incorporated two-dimensional mesoporous TiO2 framework for H2 evolution

Mesoporous TiO₂ frameworks incorporated with diverse percentages of Cr₂O₃ nanoparticles (NPs) were achieved through the one-step sol-gel approach for photocatalytic H₂ evolution under visible-light exposure. The obtained isotherms could be classified as type IV, indicating mesopore 2D-hexagonal symmetry. The H₂ evolution rate over mesoporous Cr₂O₃/TiO₂ photocatalyst was observably promoted employing glycerol as a sacrificial agent, providing a comparatively high H₂ yield of 14300 μmolg^?1. The highest photocatalytic efficiency was achieved with an optimal 4% Cr₂O₃/TiO₂ photocatalyst, and the evolution rate was enhanced 1430-fold compared to pristine TiO₂. The eminent photocatalytic performance of mesoporous Cr₂O₃/TiO₂ was ascribable to different key factors such as the narrow bandgap, wide visible light photoresponse, Cr₂O₃ as photosensitizer, synergistic effect and high surface area. The recycle tests for five times over synthesized photocatalyst revealed excellent durability and stability without loss in H₂ evolution. The photocatalytic mechanisms for H₂ evolution over Cr₂O₃/TiO₂ photocatalyst were proposed according to the photocurrent transient and photoluminescence measurements and photocatalytic H₂ evolution results.     

Z-scheme g-C3N4 nanosheet photocatalyst decorated with mesoporous CdS for the photoreduction of carbon dioxide

Herein, novel mesoporous CdS nanoparticle (NP)-incorporated porous g-C₃N₄ nanosheets with large surface areas and varying CdS NP percentages were constructed for the first time. The synergistic effect of mesoporous CdS NPs and porous g-C₃N₄ nanosheets indicated effective charge carrier separation and promoted CO₂ photoreduction to form CH₃OH upon illumination. The highest yield of CH₃OH over 3% CdS-g-C₃N₄ heterostructures was determined to be approximately 1735 μmol g^?1, which was 3.8- and 5.50 times greater than those of mesoporous CdS NPs and pristine g-C₃N₄ nanosheets, respectively. In addition, the mesoporous 3%CdS-g-C₃N₄ heterostructure showed an outstandingly enhanced CO₂ photoreduction rate of 192.7 μmol g^?1 h^?1, which was estimated to be ~4.1 and 5.9- times better than CdS (47.1 μmol g^?1 h^?1) and pristine g-C₃N₄ (32.6 μmol g^?1 h^?1), respectively. The photoreduction performance was retained at approximately 94.7% after five cycles of illumination for 45 h. The remarkable synthesized mesoporous CdS-g-C₃N₄ heterostructure played an essential role, with its narrow bandgap and high surface area enabling improved photoinduced carrier separation and a widened range of light absorption. A plausible mechanism for CO₂ photoreduction by the mesoporous CdS-g-C₃N₄ heterostructure was proposed and verified by photoelectrochemical and photoluminescence measurements.     

Study on the effect of EDTA on the photocatalytic reduction of mercury onto nanocrystalline titania using quartz crystal microbalance and differential pulse voltammetry

In-situ technique quartz crystal microbalance (QCM), differential pulse voltammetry (DPV) and cyclic voltammetry (CV) were employed to investigate the effect of disodium ethylenediamine tetraacetate (EDTA) on photocatalytic reduction of mercury onto nanocrystalline titania (TiO₂). Effects of EDTA on adsorption of Hg(II) and its photocatalytic reduction process at the surface of TiO₂ in different pH solutions had been studied in detail. From the in-situ response to the adsorption of Hg(II) onto TiO₂, the reaction rate and saturation adsorption amount were estimated about 4.71 × 10⁻⁶ g mol⁻¹ min⁻¹ and 46.36 (mg Hg(II)/g TiO₂) via the model of pseudo-second-order kinetics respectively. The photocatalytic reduction of Hg at the surface of TiO₂ was influenced by pH and the mole ratio of Hg(II) to EDTA. When the ratio of Hg(II) to EDTA 1:1, it was most favorable for the photocatalytic reduction of mercury. In addition, the effects of HCOOH and EDTA on the reduction of Hg(II) was comparatively investigated and the mechanism on the photocatlytic reduction of mercury was illustrated. Therefore, it could be concluded that QCM, DPV and CV were effective methods for the investigation of photocatalytic reduction of complex heavy metal ions onto the surface of nanocrystalline TiO₂.     

Effect of bulk and nanoparticle Bi2O3 on attenuation capability of radiation shielding glass

The aim of this study is to examine the effect of Bi₂O₃ concentration and particle size on Bi₂O₃ glass. The tested glasses had the composition of SiO₂–Bi₂O₃–CaO–MgO–B₂O₃–K₂O–Na₂O–ZnO. Ordinary glass was compared with glasses with 10% Bulk Bi₂O₃, 10% Bi₂O₃ Nanoparticles (NPs), 20% Bulk Bi₂O₃, and 20% Bi₂O₃ nanoparticles. The mass attenuation coefficients (MACs) of all the investigated glasses were determined between 0.0595 MeV and 1.41 MeV. The results demonstrated that increasing the Bi₂O₃ content in the glass matrix improved their shielding capability, as well as showing that the NPs provided greater attenuation than the bulk Bi₂O₃ at the same concentration. The percent increase in the MAC between the bulk and nano Bi₂O₃ was also calculated and analyzed. From the MAC values, the LAC of the glass was determined and similar results were found compared to the MAC figure. The HVL and MFP of the glass were then analyzed and the results demonstrated that the glass with Bi₂O₃ NPs attenuated the same amount of photons at a smaller thickness, making the NP shield more effective. The heaviness of the samples illustrated that all the tested samples have a smaller weight than pure lead, making them more desirable. The attenuation factor of the glass (Att. Factor %) showed that increasing the Bi₂O₃ content in the samples and increasing the thickness of the shields both improve the shielding capability of the glass. Lastly, the d_lead of the glasses was determined, indicating that the greatest reduction in thickness occurs near the K-absorption edge of bismuth. Overall, the glass with 20% Bi₂O₃ NPs demonstrated to have the greatest potential for radiation shielding applications.     

Optical and structural properties of ZnO NPs and ZnO–Bi2O3 nanocomposites

Pure ZnO and ZnO–Bi₂O₃ nanocomposites with 5 wt% and 10 wt% of Bi₂O₃ content were synthesized using the co-precipitation method. Optical properties such as refractive index (n), extinction coefficient (k), bandgap (E_g), and Urbach energies, as well as the band structure, were determined by modeling the experimental transmittance and reflectance UV–Vis spectra. The deduced bandgap and Urbach energies for pure ZnO (3.758 eV) increase with the increase of the doping degree of Bi₂O₃ in ZnO–Bi₂O₃ nanocomposite films. X-ray diffraction and scanning electron microscopy (SEM) was used to study the structural and morphological properties of these nanocomposite films. Pure ZnO and nanocomposites with Bi₂O₃ exhibit crystalline domains with wurtzite hexagonal structures, and as the doping degree of Bi₂O₃ increases, the crystallite size decreases. Based on SEM micrographs, the ZnO nanoparticles (NPs) structure shows the presence of aggregation. Moreover, Bi₂O₃ NPs in the nanocomposite film led to the further aggregation in the form of large rods. The elemental and chemical properties of the nanocomposites were investigated using infrared and energy-dispersive X-ray spectroscopy. The charge transfer process in the studied system is between ZnO and Bi₂O₃ conduction bands. Density-functional theory (DFT) calculations were performed for ZnO, Bi₂O₃, and ZnO-Bi₂O₃ compounds to investigate structural, optical, and electronic properties, being in agreement with the experimental results.     

Bi@Bi4Ti3O12/TiO2 films on glass with photocatalytic and self-cleaning performance

A stable and translucent Bi@Bi₄Ti₃O₁₂/TiO₂ film was fabricated on conventional glass substrates for the first time. The film exhibited a good photocatalytic performance and efficient self-cleaning capability against organic dyes under full spectral irradiation and visible light irradiation. Bi₄Ti₃O₁₂/TiO₂ film was first prepared on a glass substrate with colloidal silica as a high temperature binder, followed by implantation of nanoscale Bi in it by an in-situ partially reduction of Bi₄Ti₃O₁₂ to generate Bi@Bi₄Ti₃O₁₂/TiO₂ films. The improved photocatalytic ability is probably attributed to the surface plasmon resonance of Bi atom as well as the enhanced electron transfer efficiency and synergistic effect of Bi₄Ti₃O₁₂ and TiO₂. According to trapping experiments, hydroxyl radicals (OH) were active species in the photocatalytic degradation of dyes under full spectral light irradiation and possible photocatalytic mechanism was proposed. The film prepared in this work may well have potential practical applications in many aspects, such as cleansing treatments for high building external decorative panels and also systematic characterization of the film suggests that the in-situ reduction is an effective and simple way to produce nanoscale Bi@Bi₄Ti₃O₁₂.     

Preparation of Dual Z-scheme Bi2MoO6/ZnSnO3/ZnO Heterostructure Photocatalyst for Efficient Visible Light Degradation of Organic Pollutants

In this study, a double Z-type Bi₂MoO₆/ZnSnO₃/ZnO heterostructure photocatalyst was prepared by hydrothermal method to realize effective charge separation and improve photocatalytic activity. The synthesized samples were carefully examined by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy, photoluminescence (PL), and other analytical techniques. Meanwhile, the photocatalytic performance was further evaluated by multi-mode photocatalytic degradation with crystal violet (CV). The results show that the composite material has a relatively homogeneous cubic structure in size and shape. In the cubic structure, a heterogeneous structure exists between Bi₂MoO₆, ZnSnO₃ and ZnO. Simultaneously, the dramatic changes in physical morphology, such as the specific surface area and particle size of the composites, led to a series of unique properties, such as a significant climb in light absorption properties and superior photocatalytic activity. In addition, compared to ZnO, Bi₂MoO₆ and ZnSnO₃/ZnO, the Bi₂MoO₆/ZnSnO₃/ZnO composite material shows lower PL intensity, smaller arc radius, and stronger photocurrent response. Meanwhile, Bi₂MoO₆/ZnSnO₃/ZnO shows higher photocatalytic efficiency for CV and tetracycline hydrochloride (TC), and maintains good stability after 3 cycles of photodegradation experiments. Based on experimental results, the existence of heterojunctions between ZnO, ZnSnO₃ and Bi₂MoO₆ and the possible photocatalytic mechanism for the degradation of CV by dual Z-scheme composites are proposed. In conclusion, this study provides a feasible strategy for the photocatalytic degradation of organic pollutants by introducing ZnSnO₃ and Bi₂MoO₆ to successfully construct composite catalysts with dual Z-scheme heterostructures.

     

Synthesis of Bi2O3/TiO2 nanostructured films for photocatalytic applications

Dendritic growth of bismuth oxide nanostructured films was accomplished by reactive magnetron sputtering. The deposition of the Bi₂O₃ template layers was adapted to abide a vapour-liquid-solid mechanism in order to develop a 3D growth morphology with high surface area templates for photocatalytic applications. TiO₂ photocatalytic thin films were deposited at a later stage onto Bi₂O₃ layers. The obtained heterostructured films were characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, the photocatalytic efficiency was assessed by conducting an assay using methylene blue dye as testing pollutant under a UV-A illumination. The photocatalytic tests revealed that the Bi₂O₃ layers functionalized with TiO₂ thin films are more efficient at degrading the pollutant, by a factor of 6, when compared with the individual layered films.     

Matrix phase induced boosting photoactive performance of ZnO nanowire turf-coated Bi2O3 plate composites

A new nanocomposite consisting of ZnO nanowire turf-coated Bi₂O₃ plates was synthesized using a method combining a chemical bath and hydrothermal crystal growth through sputtering ZnO seed layer-assisted growth. Structural analysis revealed that highly crystalline, high-density, one-dimensional (1D) ZnO crystals were uniformly coated on the organized two-dimensional (2D) Bi₂O₃ plates with a single β phase or dual α/β polymorphic phases. The Bi₂O₃–ZnO composites exhibited enhanced absorption properties in the ultraviolet and visible regions compared with pristine Bi₂O₃ and ZnO. Furthermore, the Bi₂O₃–ZnO composites exhibited higher photoactive performance than that of the pristine Bi₂O₃ and ZnO because of the low recombination rate of photoinduced electron−hole pairs caused by the vectorial transfer of electrons and holes between ZnO and Bi₂O₃ and the substantially increased surface area of the unique composite morphology. The ZnO nanowire turf-coated Bi₂O₃ plates with a α/β-Bi₂O₃ matrix exhibited photoelectrochemical and photocatalytic properties superior to those of the composite with a single β-Bi₂O₃ matrix. The coexistence of α/β homojunction in the Bi₂O₃ matrix and the abundant heterojunctions between the ZnO nanowires and Bi₂O₃ plates substantially enhanced photoexcited charge separation efficiency. Growing high-density 1D ZnO on 2D Bi₂O₃ via a combination methodology and crystallographic phase control provided a promising material design route for nanocomposite systems with high photoactivity for photoexcited device applications.     

Influence of Bi2O3/TiO2, Sb2O3 and Cr2O3 doping on low-voltage varistor ceramics

The influence of the amount of Bi₂O₃ and TiO₂ additions at a TiO₂/Bi₂O₃ ratio of 1, as well as Sb₂O₃ and/or Cr₂O₃ doping, on the microstructural development and electrical properties of varistor ceramics in the ZnO–Bi₂O₃–TiO₂–Co₃O₄–Mn₂O₃ system was investigated. In samples with a low level of Bi₂O₃ and TiO₂ (0·3 mol%) and therefore small amount of liquid phase, exaggerated growth of the ZnO grains results in high microstructural inhomogeneity. Co-doping with Sb₂O₃ significantly changes the phase composition of TiO₂ doped low-voltage varistor ceramics. The Bi₃Zn₂Sb₃O₁₁ type pyrochlore phase forms at the expense of the γ-Bi₂O₃ and Bi₄Ti₃O₁₂ phases and decreases the amount of liquid phase in the early stages of sintering. Already small amounts of Sb₂O₃ and/or Cr₂O₃ added to a TiO₂ doped low-voltage varistor ceramics limit ZnO grain growth and increase the threshold voltage V_T of the samples.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Titanium based composite-graphene nanofibers as high-performance photocatalyst for formaldehyde gas purification

Semiconductor driven photocatalysis has galvanized great attention as it holds tremendous promise to address the worldwide environmental and energy issues. Photocatalysis, in which photons are used for redox reactions, is at the central point to achieve this goal. The heterogeneous photocatalysts with integrated functional nano-composites can combine the advantages of different nano-composites to overcome the drawbacks of single nano-photocatalysts. Coupling of TiO₂ with narrow band gap semiconductor nanocomposites has been a strategy used by researchers to obtain visible light active photocatalysts. In this work, graphene has been used to improve the performance of photocatalysts based on its great charge conductivity as well as other exciting properties. The edge effect has been removed by introducing the 2D graphene into circular rolls inserted in the 65–140?nm TiO₂, TiO₂-CuO (TC), and TiO₂/ZnO/Bi₂O₃ (TZB) nanofibers (NFs) and free electrons can only travel in specific direction along the axis of the TiO₂, TiO₂-CuO (TC), and TiO₂/ZnO/Bi₂O₃ (TZB) (NFs). The resulting (NFs) has less band-gap energy that facilitates harvesting of the visible light spectrum. The graphene incorporation helps to harvest more energy from the entire UV–vis spectrum and almost doubled the surface area of the (NFs) when maximum amount of graphene is embedded into the (NFs). The T-Gr, TC-Gr and TZB-Gr photocatalyst, after optimized with as much as 32.18%, 16.87% and 26.5% respectively by mass of graphene in the (NFs), has superior photoactivity in degradation of formaldehyde under solar irradiation. The kinetics and fundamental mechanism of formaldehyde degradation are also addressed. The graphene insertion controls the work function of photocatalysts, which is critical for photocatalytic reactions.     

Bi2O3 nanoparticles incorporated porous TiO2 films as an effective p‐n junction with enhanced photocatalytic activity

Porous TiO₂ films decorated with Bi₂O₃ nanoparticles are fabricated via alkali‐hydrothermal of titanium (Ti) plate by varying the reaction time. The amorphous TiO₂ is transformed into anatase after annealing the films at 500°C in air. The p‐type Bi₂O₃ nanoparticles are successfully assembled on the surface of porous n‐type TiO₂ films through the ultrasonic‐assisted successive ionic layer adsorption and reaction (SILAR) technique to form Bi₂O₃/TiO₂ nanostructure by the two cycles. The obtained Bi₂O₃/TiO₂ films are consisted of a well‐ordered and uniform porous structure with an average pore diameter of about 100‐200 nm containing homogeneously dispersed Bi₂O₃ nanoparticles of ~5 nm diameter. Moreover, the resultant composites present excellent photocatalytic performance toward methyl blue (MB) degradation under UV and visible light irradiation, which could be mainly ascribed to the enhanced light adsorption capacity of unique composite structure and the formation of p‐n heterojunctions in the porous Bi₂O₃/TiO₂ films. This research is helpful to design and construct the highly efficient heterogeneous semiconductor photocatalysts.     

Inversion boundary induced grain growth in TiO2 or Sb2O3 doped ZnO-based varistor ceramics

In low-voltage varistor ceramics, the phase equilibrium and the temperature of liquid-phase formation are defined by the TiO₂/Bi₂O₃ ratio. The selection of a composition with an appropriate TiO₂/Bi₂O₃ ratio and the correct heating rate is important for the processing of low-voltage varistor ceramics. The total amount of added Bi₂O₃ is important as the grain growth is slowed down by a larger amount of Bi₂O₃-rich liquid phase at the grain boundaries. Exaggerated grain growth in low-voltage varistor ceramics is related to the occurrence of the liquid phase and the presence of TiO₂ which triggers the formation of inversion boundaries (IBs) in only a limited number of grains, and as a result the final microstructure is coarse grained. The Zn₂TiO₄ spinel phase only affects grain growth in compositions with a TiO₂/Bi₂O₃ ratio higher than 1.5. In high-voltage varistor ceramics, just a small amounts of Sb₂O₃ trigger the formation of IBs in practically every ZnO grain, and in compositions with a Sb₂O₃/Bi₂O₃ ratio lower than 1, grain growth that is controlled entirely by an IBs-induced grain growth mechanism results in a fine-grained microstructure. The spinel phase interferes with the grain growth only at higher Sb₂O₃/Bi₂O₃ ratios.