TiO2 Bi2WO6 Research Articles

Preparation of nano-Ag-Bi2WO6–TiO2/starch bionanocomposite membranes and mechanism of enhancing visible light degradation of ethylene

Ag–Bi2WO6–TiO2 (ABT) ternary composite photocatalyst was prepared using solvothermal and surface deposition method. Then, the nano photocatalyst was doped into the starch film liquid through internal loading method, and finally, ABT/starch composite film was constructed using tape casting method for visible light catalytic degradation of ethylene. Characterize and analyze the structure and physical properties of nano ABT/starch composite membranes prepared with different ABT loading amounts, and optimize the reaction conditions (ABT addition amount, light intensity, initial concentration of ethylene) on the visible light catalytic degradation performance for ethylene of the composite membrane. The results show that the nano ABT particles and starch molecules have good biocompatibility, and they can be well fused to form a film, without changing the crystal structure of ABT and generating other chemical bond. The results of photocatalytic degradation of ethylene showed that when the loading amount of ABT was 5 wt%, the light intensity was 60.5 mw/cm2, and the initial concentration of ethylene was 0.15 mg/L, the ABT/starch film had the best ethylene degradation performance, with a K′ value of 5.6111 × 10−4 min−1, which is 17.9 times that of the blank starch film. Under the optimal preparation conditions, the thickness, tensile strength, elongation at break of the starch composite film is 168.33 μm, 5.01 Mpa, 32.4%, respectively, and the maximum thermal decomposition temperature is 320.5 °C, which meets the requirements for food packaging materials. After 4 cycles, the catalytic degradation of ethylene by starch composite membrane only decreased by 13.98%, indicating good reusability.

Effect of nano-Ag proportion on the structure of Ag– TiO2–Bi2WO6 photocatalyst and its antibacterial property on Escherichia coli

In this study, TiO2–Bi2WO6 (TB) heterojunctions were synthesized by solvothermal method, nano-Ag was reduced by γ-ray irradiation, and a series of Ag–TiO2–Bi2WO6 (ATB) composite photocatalysts with different nano-Ag usage were constructed by chemical deposition and freeze-dried. The microstructure, crystalline phase composition, chemical composition, and light absorption properties of ATB were characterized, and its photocatalytic bacterial inhibition performance was analyzed against Escherichia coli. The results showed that the proportion of nano-Ag significantly improved the photocatalytic inhibition performance of ATB against E. coli, and the highest inhibition rate of ATB against E. coli (52.5%) was achieved when the Ag proportion was 15%, which was 2.5 times higher than that of TB. The improved photocatalytic inhibition performance of ATB was attributed to the combination of the interlaced heterostructure, SPR effect, and Schottky barriers, which narrowed the forbidden bandwidth, promoted the separation of electron-hole pairs, and generated a large number of reactive radicals such as h+, •O2-, and •OH under visible light. Influenced by this, the microbial cell structure was broken and inducted into the E. coli apoptosis. The results provided a novel photocatalyst in photocatalytic antibacterial research.

Degradation mechanism and pathway of tetracycline in milk by heterojunction N-TiO2-Bi2WO6 film under visible light

N-doped TiO2–Bi2WO6 (NTB) three-component photocatalyst was prepared using a glycol solvothermal method. The photocatalysts and films were characterized, and applied to the degradation of tetracycline (TC) in milk and its effect on the quality of milk. The results show that the NTB photocatalyst exhibits good photocatalytic activity under visible light, and its TC degradation rate is increased by 1.76, 1.49, 1.42, 1.16, and 1.13 times higher than that of TiO2, Bi2WO6, N–TiO2, N–Bi2WO6 and TiO2–Bi2WO6, respectively. Due to the N doping, the photogenerated electron-hole pair recombination rate of photocatalyst is greatly reduced, which improving its photocatalytic performance. Additionally, the absorption wavelength threshold is enlarged by 459 nm, the gap width is reduced to 2.69 eV, and the degradation rate of TC is still 83.24 % after 5 repetitions. HPLC–MS revealed the active species, intermediates and photodegradation pathways in the photocatalytic process.

Two dimensional S-scheme Bi2WO6–TiO2–Ti3C2 nanocomposites for efficient degradation of organic pollutants under natural sunlight

Two-dimensional (2D) materials have fascinated the researchers to exploit their properties including large surface area, ability to act as a support and to form face-to-face interfacial contact with other 2D materials for fabricating efficient photocatalytic materials. In this work, Bi2WO6, TiO2 and Ti3C2 nanosheets have been used synthesizing different series of binary Bi2WO6–TiO2 and ternary Bi2WO6–TiO2–Ti3C2 2D nanocomposites by an electrostatic self-assembly synthesis route. The as-prepared pristine materials and binary and ternary nanocomposites were characterized by different structural, morphological and compositional characterization techniques to confirm their successful synthesis and 2D morphology. It was found that the optimized Bi2WO6–TiO2 (20 wt%) and Bi2WO6–TiO2 (20 wt%)-Ti3C2 (5 wt%) nanocomposites showed 97.0% and 98.5% degradation of methyl green in 80 min and 40 min, respectively, which was higher than their pristine counterparts. The enhanced activity was credited to the large surface area offered by 2D nanocomposites, pollutant adsorption and enhanced photogenerated charge separation and transfer facilitated by S-scheme mechanism and face-to-face interfacial contact of different components of these nanocomposites. This work delivers an example of highly efficient 2D nanocomposites and discusses the role of Ti3C2 as an electron acceptor in S-scheme photocatalytic system.

The visible light photocatalytic degradation of ethylene using a polyvinyl alcohol film loaded with Ag2O-TiO2-Bi2WO6 heterojunction microspheres

In this study, Ag2O-TiO2-Bi2WO6(ATB) heterojunction microsphere photocatalyst was synthesized by hydrothermal and surface deposition method. ATB was loaded onto the surface and interior of polyvinyl alcohol (PVA) films to construct a novel ATB/PVA composite film with photocatalytic degradation performance of ethylene by internal doping and surface loading method. The ATB microspheres and ATB/PVA composite films were characterized, and the photodegradation effect and mechanism of ethylene by ATB/PVA composite films was investigated. The results showed that ATB had the best ethylene degradation effect, and the reaction rate constant K' value was 6.0722 × 10-4 min−1, which was 11.79, 2.71 and 1.48 times than that of TiO2, Bi2WO6 and TiO2/Bi2WO6(TB), respectively. The improvement of photocatalytic activity was mainly attributed to the addition of Ag2O, which enhanced the visible light absorption performance and reduced the band gap of ATB. The formation of ternary heterostructures promoted the separation and transfer efficiency of photogenerated carriers. When the internal doping amount of ATB was 3 wt% and the surface loading amount was 1.5 wt%, the ATB microspheres were well dispersed inside and on the surface of PVA film, and the ATB/PVA composite film had the best ethylene degradation performance with K 'value of 6.8107 × 10-4 min−1, which was increased by 12.16% compared with the pure internal doping film.

Three-dimensional porous spherical TiO2–Bi2WO6 decorated graphene oxide nanosheets photocatalyst with excellent visible light catalytic degradation of ethylene

Porous spherical graphene oxide/TiO2–Bi2WO6 (GTB) composite photocatalysts with different graphene oxide (GO) additions (0, 0.5, 1, 1.5, 2 wt%) are synthesized using hydrothermal and surface-deposition methods. The crystal phase composition, morphology, chemical composition, specific surface area and photoluminescence ability of the catalyst were characterized, and their photodegradation performance was evaluated. The results showed that the catalytic effect of TiO2–Bi2WO6 was significantly improved by appropriate GO addition. The 1.5% GTB provided the best synergistic effect of ethylene photocatalytic degradation, and the reaction rate constant, K′, values was 1.25 × 10−3 min−1 which is 15 times that of TiO2, two times that of Bi2WO6, and 1.25 times that of TB microspheres. This was mainly due to the formation of a ternary heterojunction between GO, TiO2 and Bi2WO6 through the interfacial interaction, which increased the specific surface area, reduced the bandgap, enhanced the utilization of visible light and inhibited the recombination of photogenerated electron–hole pairs, thus showing higher visible photocatalytic activity. GTB photocatalyst also had good stability and reusability.

A spherical TiO2-Bi2WO6 composite photocatalyst for visible-light photocatalytic degradation of ethylene

In this paper, Bi2WO6 porous microspheres were prepared via a hydrothermal method and nano-TiO2 uniformly dotted on the surface of the Bi2WO6 microspheres using deposition technology to self-assemble a porous layer spherical TiO2-Bi2WO6 (TB) composite photocatalyst. The photocatalytic activity of the composite photocatalyst was evaluated using ethylene as the target degradation product. The results show that the photocatalytic degradation of ethylene by the TB composite photocatalyst was significantly improved, especially 10 % TB. Samples containing 10 % titanium dioxide had the highest photocatalytic activity for ethylene degradation. In addition, the degradation rate of ethylene was as high as 20.90 %, which was 1.53 times higher than that of Bi2WO6 microspheres. The spherical structure of the porous layer gives the composite photocatalyst a high specific surface area, which can effectively promote the rapid migration of photogenerated carriers between TiO2 and Bi2WO6, and prevent the recombination of photogenerated electrons and photogenerated holes, thereby effectively improving the photocatalytic performance.

Construction of Bi2WO6–TiO2/starch nanocomposite films for visible-light catalytic degradation of ethylene

Bi2WO6–TiO2 (BT)/starch nanocomposite films were prepared by incorporating BT nano-particles through the casting method. The BT nano-particles used were synthesized by solvothermal method. The effects of BT loadings (0, 1, 2, 3, 4, and 5 wt% dry basis) on the optical, mechanical, microstructural, spectral, and thermal properties of the nanocomposite films were investigated, and their photocatalytic activities were evaluated from the degradation of ethylene under visible light. With the increase in BT loading, the tensile strength of the film specimens increased while elongation at break and transparency decreased; the nano-particle agglomerates increased when excess BT nano-particles were added into the films. When the loading was 4%, the film exhibited the highest photocatalytic activity, and the rate of ethylene degradation reached 12.47%. In conclusion, the BT/starch films can effectively degrade ethylene in gaseous phase, and they have the potential to be used as fruit and vegetable packaging materials.

Synthesis, characterization and application of TiO2–Bi2WO6 nanocomposite photocatalyst for pretreatment of starch biomass and generation of biofuel precursors

This study explores a novel photocatalytic approach for the conversion of complex biomass into smaller molecular units for their utility in generation of biofuel precursors. Following hydrothermal method, TiO2/Bi2WO6 nanocomposite photocatalyst for different ratio of TiO2 viz. 15% and 25% by weight have been synthesized. The efficiency of photodegradation of organic molecule is determined. Composite loaded with 25% TiO2 found to represent maximum photocatalytic efficiency of 99.9%. The structural and optical properties of the synthesized photocatalyst nanomaterial were characterized. A band gap of 2.7 eV was observed for 25% TiO2 composition which displayed an excellent visible light photoactivity, examined by removal of Rhodamine B. We further observe a four-fold higher photocatalytic activity in this composite compared to pristine Bi2WO6. Using this composite, solar energy is harvested to perform photocatalytic fragmentation of a biopolymer, namely starch, to derive smaller molecule precursors. Colorimetric analysis of reducing sugars from the degraded biomass quantifies the monomarization of starch. The linear chain molecular fragments thus formed were further analyzed by Raman, FTIR and ESI-MS. The results demonstrate photocatalytic pretreatment of starch by nanocomposite of TiO2/Bi2WO6 resulted in the formation of organic precursors that are common feedstock for the microbiota of anaerobic methanation and ethanol fermentation. We therefore conclude that photocatalytic pretreatment of biomass can be utilized for hydrolysis and partial acedogenesis of biomass in biofuel conversion processes. Such an approach represent environmentally benign way to convert biomass waste to biofuel.

Synthesis of anatase/brookite TiO2–Bi2WO6 multiheterojunction and its photocatalytic properties under visible-light irradiation

Anatase/brookite TiO2–Bi2WO6 multiheterojunction photocatalyst (TabB) has been synthesized via solvothermal method and its physiochemical properties compared with anatase TiO2–Bi2WO6 (TaB) and brookite TiO2–Bi2WO6 (TbB) with single-heterojunction structure. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) analyses, a heterojunction was formed between TiO2 and Bi2WO6 crystals. All of the TaB, TbB, and TabB samples consisted of free plate-like Bi2WO6 particles covered by many TiO2 nanoparticles. Compared with pure TiO2 (anatase and brookite), the absorption band edge of TabB was red-shifted and the bandgap decreased. The photocatalytic activity of the as-prepared samples under visible-light irradiation was investigated using rhodamine B (RhB), revealing photocatalytic activity in the order TabB > TaB > TbB. The heterojunction structure played a vital role in enhancing charge carrier separation and thus enhancing the photocatalytic activity. The related mechanism of the heterojunction photocatalyst is systematically discussed.

Solvothermal Synthesis of TiO2/Bi2WO6 Heterojunction Photocatalyst with Optimized Interface Structure and Enabled Photocatalytic Performance

TiO2/Bi2WO6 (TB) heterojunction photocatalyst was successfully synthesized and characterized by XRD, SEM, TEM, UV–vis and photoluminescence measurement. The heterojunction interface structure of TB heterojunction photocatalyst was optimized via adjusting the ethylene glycol/water (EG/W) ratio. Based on XRD, SEM and TEM, the crystal size of Bi2WO6 reduced from 14.6 nm to 8.8 nm, and the interface structure between Bi2WO6 nanosheets and TiO2 particle significantly changed with increasing EG concentration. Furthermore, the photocatalytic activity and the related mechanism of TB heterojunction photocatalyst were systematically discussed. Among them, TBEG/W sample shows the highest normalized apparent rate constant, which is attributed to its highest electron–hole pairs separation ability driven by optimized heterojunction interface between two semiconductors.

Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials.

The photocatalytic reduction of CO2 with H2O to produce CH4 in the gas phase was carried out in the presence of two Bi2WO6-based materials. For this purpose, single Bi2WO6 and a coupled Bi2WO6-TiO2 system were synthesised and metallised with Pt, through a Pt photodeposition method. Then, the samples were characterised and the photocatalytic activity was evaluated in a continuous fluidised-bed reactor irradiated with UV light. Single Bi2WO6 presents an interesting behaviour under H2O rich conditions. In particular, the metallisation improves the material's performance for CH4 formation, while the TiO2 addition to Bi2WO6 increases the CH4 yield only at low H2O/CO2 ratio. The Bi2WO6-TiO2 system metallised with a Pt photocatalyst displayed the highest CH4 yield among all the prepared photocatalysts. The stability of the system can be enhanced through the addition of a blue phosphor to the reactant mixture, especially under H2O rich conditions.

Photocatalytic propylene epoxidation on Bi2WO6-based photocatalysts

The photocatalytic epoxidation of propylene (PR) with molecular oxygen was carried out in a fluidized-bed reactor with several Bi2WO6-based materials under UV-A illumination. Three different photocatalysts were tested: one of single Bi2WO6 and two of coupled Bi2WO6–TiO2 heterostructures, thus showing that a mixed system of Bi2WO6 with commercial TiO2 Degussa-P25 leads to the best combination of conversion and PO selectivity. Then, direct support on glass spheres and silica gel was made, being a good alternative for improving the Bi2WO6 performance. Additionally, several reaction conditions of temperature and PR to O2 feed ratio were studied.

Facile hydrothermal synthesis of TiO2–Bi2WO6hollow superstructures with excellent photocatalysis and recycle properties

One-dimensional mesoporous TiO2-Bi2WO6 hollow superstructures are prepared using a hydrothermal method and their photocatalysis and recycle properties are investigated. Experimental results indicate that anatase TiO2 nanoparticles are coupled with hierarchical Bi2WO6 hollow tubes on their surfaces. The TiO2-Bi2WO6 structure has a mesoporous wall and the pores in the wall are on average 21 nm. The hierarchical TiO2-Bi2WO6 heterostructures exhibit the highest photocatalytic activity in comparison with P25, pure Bi2WO6 hollow tube and mechanical mixture of Bi2WO6 tube and TiO2 nanoparticle in the degradation of rhodamine B (RhB) under simulated sunlight irradiation. The as-prepared TiO2-Bi2WO6 heterostructures can be easily recycled through sedimentation and they retains their high photocatalytic activity during the cycling use in the simulated sunlight-driving photodegradation process of RhB. The prepared mesoporous TiO2-Bi2WO6 with hollow superstructure is therefore a promising candidate material for water decontamination use.

Erbium doped TiO2–Bi2WO6 heterostructure with improved photocatalytic activity under sun-like irradiation

Erbium doped TiO2–Bi2WO6 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Rhodamine B. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a progressive russelite cell contraction due to its incorporation in the Bi2WO6 lattice in substitutional sites. The best photocatalytic performance was attained for the samples with 1at% of Er. From the study of the photocatalytic activity under different irradiation conditions it can be inferred that Er3+ presence induces a significant improvement of the photoactivity in the UV range. The evolution of band-gap values seems to be similarly related with the reaction rate progression. Thus, the higher band-gap values in lower Er doped systems would be the cause of a better electron hole separation under UV irradiation.

Degradation of Rhodamine B/Phenol Mixtures in Water by Sun‐Like Excitation of a Bi2WO6–TiO2 Photocatalyst

Bi2 WO6 and Bi2 WO6-TiO2 (5% molar Ti) nano-heterostructures were synthesized by a hydrothermal method. The properties of the synthesized catalysts were characterized, having high photoactivity for Rhodamine B degradation under sun-like illumination, explained by a synergetic mechanism previously proposed through UV and visible induced processes, in which the photosensitization effect of Rhodamine B is considered. We now report that using Phenol, a molecule which does not lead the photosensitization process, the photoactivity decreased considerably, thus emphasizing how important is the model molecule selected as degradation substrate for evaluating the photoactivity. The photocatalytic properties of the synthesized catalysts have been evaluated by exposing a mixture of Rhodamine B and Phenol in water, to different illumination conditions. It can be confirmed that the photoinduced mechanism via the photosensitization of Rhodamine B is a key factor responsible for the increase on the photocatalytic activity showed by the Bi2 WO6-TiO2 compound and that the degradation mechanism of Rhodamine B is not changed by the simultaneous presence of other transparent substrate as Phenol.

Photocatalytic activity of single and mixed nanosheet-like Bi2WO6 and TiO2 for Rhodamine B degradation under sunlike and visible illumination

The photocatalytic activity, under sunlike illumination, for Rhodamine B (RhB) degradation using Bi2WO6–TiO2 samples, is reported. Two different kinds of Bi2WO6–TiO2 samples were studied, obtained by distinct methods: first, a mechanical mixing, by adding to synthesized nanosheet-like Bi2WO6 powder the corresponding amount of TiO2 nanoparticles (P25) in order to obtain physical mixtures of both catalysts with different percentages of TiO2 (5, 10 and 50wt%); second, a single Bi2WO6–TiO2 heterostructure was prepared by adding commercial TiO2-P25 to the Bi2WO6 precursors (50wt%) prior to the hydrothermal treatment, thus obtaining a sample with “in situ” TiO2 incorporation. Comparisons between the photocatalytic behaviour of these samples and those exhibited by the single materials Bi2WO6 and TiO2 (P25) were carried out, in order to establish the effect not only of the TiO2 addition but also of the way in which TiO2 (P25) is incorporated. The role of each single photocatalyst in the mixtures in the RhB degradation and mineralization under sunlike and just visible illumination was also studied.

Engineering Nanostructured Bi2WO6–TiO2 Toward Effective Utilization of Natural Light in Photocatalysis

Being expected as one of the most promising solutions in water and air purification as photocatalyst, TiO2 is attracting intensive and extensive research interests globally despite its wide band gap (~3.2 eV for anatase structure) which limits it only to be activated under UV irradiation. In pursuit of extending the active region of TiO2 toward visible light, considerable attention was devoted to develop TiO2‐based photocatalyst. We report herein, for the first time, novel “bud‐on‐branch” Bi2WO6–TiO2 nanofibers fabricated via a facile and large‐scale electrospinning technique from a biphased precursor. Formed by surface‐decorating continuous TiO2 nanofibers (mixed anatase–rutile system with an average diameter of about 100 nm) with ~13 nm well‐crystallized Bi2WO6 nanoparticles, the as‐synthesized Bi2WO6–TiO2 nanofibers achieved an evidently increased specific surface area. Furthermore, corresponding photocatalytic experiments revealed that the optimal photodegradation rate from our designed heterostructure was as high as three times to that of pure TiO2 nanofibers; this increase in optimal photodegradation rate is attributed to the relatively well‐matched energy band between TiO2 and Bi2WO6 and hence an excellent separation efficiency of photogenerated electron–hole pairs in both ultraviolet and visible light regions, suggesting that the designed heterostructures can give better rise to practise photocatalysis under natural light.

ChemInform Abstract: Sunlight Highly Photoactive Bi2WO6—TiO2 Heterostructures for Rhodamine B Degradation.

AbstractHighly efficient Bi2WO6—TiO2 heterostructures are synthesized by hydrothermal reaction of Na2WO4, Bi(NO3)3, and TiO2 in the presence of NEt3 (H2O, 140 °C, autoclave, 20 h) and subsequent calcination (300 °C, 4 h).

Solid‐State Compatibility in the System Bi2O3–TiO2–Bi2WO6

We have studied solid‐state compatibility in the Bi2O3–TiO2–Bi2WO6 ternary system. Based on previously reported data, we prepared different compositions and calcined them in air at 850°C. The crystalline phases and the microstructures were analyzed using X‐ray diffraction and scanning electron microscopy. The results allowed us to determine seven new compatibility triangles: Bi2O3–Bi12TiO20–Bi14W2O27, Bi12TiO20–Bi4Ti3O12–Bi14W2O27, Bi4Ti3O12–Bi6Ti3WO18–Bi14W2O27, Bi6Ti3WO18–Bi10Ti3W3O30–Bi14W2O27, Bi10Ti3W3O30–Bi2WO6–Bi14W2O27, Bi6Ti3WO18–Bi10Ti3W3O30–Bi6Ti5WO22, and Bi2WO6–Bi10Ti3W3O30–Bi6Ti5WO22. The existence of the Bi4WO9 phase, as reported in the Bi2O3–WO3 binary system, could not be confirmed. The Bi4Ti3WxO12+3x (x≤0.05) solid solution was detected and, therefore, the Bi4Ti3O12–Bi2Ti4O11–Bi6Ti3WO18 compatibility triangle was corrected to include two‐phase fields.