Construction of 3D marigold-like Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Ag<Subscript>2</Subscript>O/CQDs heterostructure with superior visible-light active photocatalytic activity toward tetracycline degradation and selective oxidation

A novel visible-light-driven photocatalyst Bi₂WO₆/Ag₂O/CQDs (BWO/Ag₂O/CQDs), which possesses hierarchical superstructure with marigold-like appearance, was fabricated via a hydrothermal method, followed by a simple precipitation process. Ag₂O nanoparticles sized around 25 nm and CQDs with diameters of about 10 nm were evenly deposited on Bi₂WO₆ to form a unique heterostructure. The obtained BWO/Ag₂O/CQDs heterostructure showed excellent adsorption and remarkably enhanced photocatalytic performance in the photodegradation of antibiotic tetracycline (TC) under visible-light irradiation compared to pristine Bi₂WO₆. The degradation rate of TC over BWO/Ag₂O/CQDs photocatalyst is 16.2 times higher than that of pristine Bi₂WO₆ and a possible mechanism for the enhanced photocatalytic performance was discussed. In addition, BWO/Ag₂O/CQDs was applied in the selective oxidation of benzyl alcohol to benzaldehyde under visible-light illumination. The result demonstrated that the conversion rate and product selectivity are greatly improved over BWO/Ag₂O/CQDs compared to pristine Bi₂WO₆ in the same reaction conditions, making it a promising photocatalyst in the application of green chemical transformation. The co-coupling of CQDs and Ag₂O with matched band potentials gives a substantial promotion for the light harvesting ability and effective separation of photogenerated charge carriers, synergistically accounting for the improvement of photocatalytic efficiency.     

Fabrication of Bi2WO6/In2O3 photocatalysts with efficient photocatalytic performance for the degradation of organic pollutants: Insight into the role of oxygen vacancy and heterojunction

Photocatalysis is an attractive and green strategy for organic pollutant removal. The development of alternative and effective photocatalysts has attracted great attention. Herein, we rationally engineer an alternative rich-oxygen vacancies (OVs) Bi₂WO₆/In₂O₃ composite photocatalyst via integrating the calcination and hydrothermal method for removing organic dyes (rhodamine B). Thanks to the synergistic effect of OVs and heterojunction structure, the 80 wt% Bi₂WO₆/In₂O₃ (BiIn80) displays enhanced photocatalytic degradation effect. The degradation rate of BiIn80 is up to 97.3% under light irradiation within 120 min and the reaction rate constant k value (0.03221 min⁻¹) is about 15-fold and 4.17-fold as high as those of In₂O₃ (0.00203 min⁻¹) and Bi₂WO₆ (0.00772 min⁻¹), respectively. The heterostructure of Bi₂WO₆/In₂O₃ can extend the lifespan of the photogenerated charge carriers. Moreover, the density functional theory (DFT) calculations reveal that the OVs in Bi₂WO₆/In₂O₃ can boost visible light absorbability by decreasing band gap value and serve as the extra electron transfer channels to enhance the separation efficiency of photogenerated electron-hole pairs. This study not only provides an alternative route for fabricating highly efficient heterojunction photocatalysts, but also obtains better understanding of the synergistic effect of OVs and heterojunction on enhancing the photocatalytic performance.     

In-situ synthesis and characterizations of Bi2(O,S)3/Zn(O,S) composites for visible light hexavalent chromium reduction

Heterojunction construction with low band gap materials is an effective way of utilizing UV light active materials under visible light irradiation. Here, we report the synthesis of Bi₂(O,S)₃/Zn(O,S) heterostructure using simple solvothermal method without surfactant. The catalysts were investigated with different characterization techniques. All the composite catalysts showed high light absorption capacity in the whole visible light spectrum. The catalytic activity of the catalysts was evaluated by Cr(VI) reduction. While pure Zn(O,S) catalyst showed no significant Cr(VI) reduction, higher photocatalytic activity than individual components were exhibited after heterojunction construction with Bi₂(O,S)₃. 20-BiZnOS catalyst with Bi/Zn molar percentage of 20% showed the best photocatalytic activity among the composites with 99.5% Cr(VI) reduction within 12 min under visible light irradiation. Heterojunction formation between Bi₂(O,S)₃ and Zn(O,S) nanoparticle, and selective adsorption of Cr(VI) and desorption of Cr(III) on the surface of 20-BiZnOS composite catalyst were ascribed to the enhanced photocatalytic activity of the composite catalyst.     

Synergetic piezo-photocatalytic effect in ultrathin Bi2WO6 nanosheets for decomposing organic dye

In this work, ultrathin Bi₂WO₆ nanosheets (BWO NS) was synthesized by two-step hydrothermal process, which exhibited a lamellar structure with a thickness of about 10 nm and a transverse length of 100–400 nm. The piezoelectric properties and photocatalytic properties of BWO NS were coupled successfully, and the piezo-photocatalytic activity was studied through the decomposition of 10 mg L^??1 Rhodamine B (Rh B). The results showed that the degradation ratio of BWO NS for Rh B was about 98.39% within 70 min, which was higher than that of sole piezocatalysis (48.98%) and photocatalysis (61.84%). There was no significant degradation of the catalytic performance observed after being recycled four times. Moreover, piezo-photocatalysis of BWO NS efficiently produced active radicals that the major reactive oxidative species (ROS) such as superoxide radicals (·O₂^?) and hydroxyl radicals (·OH) were confirmed by radical capture experiment. The excellent piezo-photocatalysis of BWO NS endows it the potential application for decomposing organic dye via making full advantage of the vibration and solar energy present in natural environments.

     

Bi2WO6/NH2-MIL-88B(Fe) heterostructure: An efficient sunlight driven photocatalyst for the degradation of antibiotic tetracycline in aqueous medium

The development of highly efficient sunlight assisted photocatalysts has been acknowledged as a promising strategy for the enhanced degradation of antibiotics. In this work, effectual fabrication of a novel Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure was carried through solvothermal route. The structural, morphological and compositional analysis was done by employing number of analytical techniques, namely XRD, FTIR, HRTEM, FESEM, XPS, PL and BET surface area. The prepared Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure was utilized as an efficient photocatalyst towards decomposition of a typical antibiotic tetracycline (TC) in aqueous medium. It was found that Bi₂WO₆/NH₂-MIL-88B(Fe) heterostructure exhibited improved degradation efficiency of about 89.4% within 130 min of solar illumination than pristine NH₂-MIL-88B(Fe) under optimized parameters i.e. initial drug solution of 10 mg/L concentration at pH 4 with 0.35 g/L dose of catalyst. Moreover, adsorption studies, kinetics and isotherms of adsorption on TC were also investigated. Results revealed that adsorption kinetics followed pseudo 2nd order model and isotherm data fitted well with Freundlich model (R² = 0.99803) as compared to Temkin and Langmuir. The ameliorating photocatalytic capability could be primarily accredited to the heterojunction created among Bi₂WO₆ and NH₂-MIL-88B(Fe) which facilitated the charge transfer and thus determines high catalytic efficiency. The enhanced photocatalyic effect was further verified by electrochemical impedance and photocurrent studies. The prepared composite also exhibited longer carrier lifetime (140.72 ns) compared to pure MOF (132.05 ns) and Bi₂WO₆ (136.39 ns). Further, based on the radical trapping investigations, role of superoxide radicals was dominant and detailed mechanism was proposed for the photocatalytic degradation process. The major intermediates formed during the course of reaction were also examined using LCMS analysis. The photodegradation was also carried over simulated hospital wastewater by the prepared heterostructure and 60.5% TOC was obtained under solar light in 390 min. Moreover, the synthesized heterostructure showed good recyclability up to three cycles depicting good stability.     

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.     

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.     

Assembly of WO<Subscript>3</Subscript> nanosheets/Bi<Subscript>24</Subscript>O<Subscript>31</Subscript>Br<Subscript>10</Subscript> nanosheets composites with superior photocatalytic activity for degradation of tetracycline hydrochloride

In this work, a high-performance composite photocatalyst composed of WO₃ nanosheets and Bi₂₄O₃₁Br₁₀ nanosheets was successfully synthesized. The photocatalytic activity of the obtained samples was studied by the degradation of tetracycline hydrochloride under visible light irradiation. The results showed that Bi₂₄O₃₁Br₁₀ modified with the appropriate amount of WO₃ nanosheet exhibits higher catalytic activity and stability during the photocatalytic processes, and the holes (h⁺) is involved in the photolysis reaction as the main active species. The crystallization, morphology, optical and electrochemical properties of the as-prepared composite photocatalyst were characterized, and the mechanism of high photocatalytic activity was also explored. The optimal sample (10%-WO₃/Bi₂₄O₃₁Br₁₀) exhibited the best performance for tetracycline hydrochloride (TC) degradation, and more than 80% of the TC was degraded after 60 min under light irradiation. The degradation rate constant k was about 3.34-fold and 1.54-fold higher than pure WO₃ and Bi₂₄O₃₁Br₁₀, respectively. Its high photocatalytic performance can be attributed to the following reasons: the appropriate conduction band and valence band positions between WO₃ and Bi₂₄O₃₁Br₁₀, the close contact between the two visible light-driven photocatalysts, and the effective separation of the spatial charge. Our work may help to further expand the potential application of oxygen-rich bismuth oxyhalides photocatalyst in wastewater treatment, and provide a new strategy for the modification of nanostructured photocatalysts.     

One-pot solvothermal synthesis of heterogeneous Bi/Bi2WO6/BiOBr composite with high adsorption and photocatalytic performance

Adsorption and photocatalysis are two effective strategies to govern the worsening water pollution problem. Exploitation of multifunctional adsorbents and/or photocatalysts is one of the most attractive frontiers of current research. Bismuth-based compounds have stood out from enormous candidates in virtue of their abundance, low toxicity and high efficiency. In this study, heterogeneous Bi/Bi₂WO₆/BiOBr composite is synthesized via a facile one-pot solvothermal method. Benefiting from the large specific surface area, enhanced light absorption and high separation efficiency of the photogenerated electrons and holes, the tri-phase Bi/Bi₂WO₆/BiOBr composite exhibits outstanding adsorption performance for the cationic dye Rhodamine B and superior photocatalytic performance for Methyl Orange. The Bi/Bi₂WO₆/BiOBr composite degrades?~?97.8% of MO within 60 min, whose reaction rate is 13 times of Bi₂WO₆, 5 times of Bi/Bi₂WO₆, 1.9 times of Bi/BiOBr and 4.8 times of BiOBr. Simultaneously, the Bi/Bi₂WO₆/BiOBr photocatalyst shows excellent recycling efficiency. The multifunctional heterostructural composite holds promise for applications in the field of environmental treatment.

     

Synthesis and characterization of Bi2MoO6/MIL-101(Fe) as a novel composite with enhanced photocatalytic performance: Effect of water matrix and reaction mechanism

The integration of Bi₂MoO₆ with MIL-101(Fe) as a novel structure enhanced photocatalytic activity for RhB degradation. Bi₂MoO₆/MIL-101(Fe) composites were synthesized via the solvothermal procedure and characterized by XRD, EDX, FE-SEM, TEM, FT-IR, BET, TGA, UV–vis DRS, and PL. The optimal molar ratio Bi₂MoO₆:MIL-101(Fe) equal to 1:1 showed better photocatalytic activity than Bi₂MoO₆ and MIL-101(Fe) and other heterostructure composites. The effect of pH (5–9), reaction time (60–120 min), catalyst concentration (0.1–0.5 g/L), and dye concentration (10–20 ppm) were investigated on the removal performance of RhB by using central composite face-centered (CCF). In the optimal process factors where the [Catalyst]:0.4 g/L, [RhB]:20 ppm, pH: 6.5, irradiation time: 120 min, the RhB and TOC removal efficiency were 85% and 84.2%, respectively. The holes and superoxide radicals played a major role in the degradation of RhB. The addition of salt (NaCl, Na₂SO₄, and NaHCO₃) at different concentrations (100, 200, 400, and 800 ppm) revealed that the salts have an inhibitory role in the photocatalytic performance. At low concentrations of 100 ppm, the salts had a negative effect on removal efficiency (k_{Pure water} = 0.0155 min^?1, k_NaCl = 0.0075 min^?1, k_Na2SO4 = 0.0132 min^?1, k_NaHCO3 = 0.006 min^?1). Increasing the salt concentration to 800 ppm caused improved efficiency for NaCl (k_NaCl = 0.0141 min^?1), while for Na₂SO₄ this trend was decreasing (k_Na2SO4 = 0.011 min^?1), and for NaHCO₃ sharply diminished (k_NaHCO3 = 0.0026 min^?1).     

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.     

Synthesis of Z-scheme g-C3N4/Gd-doped Bi2WO6 heterojunction with enhanced visible-light photodegradation of organic dyes

Herein, we prepared the g-C₃N₄/Gd-doped Bi₂WO₆ Z-scheme heterojunction (BCN) composites by a simple hydrothermal method. The composites were investigated by SEM (EDX), TEM, XRD, XPS, UV–Vis DRS and PL analysis. The photocatalytic performance of composites was envaulted by degrading methylene blue (MB) under the irradiation of a 300 W mercury lamp. The results demonstrated that coupling g-C₃N₄ and doping Gd ³⁺ effectively enhanced the photocatalytic efficiency of pure Bi₂WO₆. The 92% of MB was degraded within 120 min by optimal 0.15–100 BCN sample, being 1.61 times as that of Bi₂WO₆. The greatly enhanced performance of 0.15–100 BCN was due to the synergistic effect of Gd ³⁺ doping and g-C₃N₄ coupling, which maintained high redox capacity. According to the experiment of capture active species, Z-scheme charge transfer mechanism was also deduced. This study may provide an efficient and green method for the treatment of dyestuff industrial wastewater.

     

Hierarchical BiOI and hollow Bi2WO6 microspheres: Topochemical conversion and photocatalytic activities

We present here a facile one-pot surfactant-free solvothermal route to synthesize hierarchical BiOI microspheres assembled from nanosheets at 120 °C for 16 h. The as-synthesized BiOI microspheres could be topochemically converted into hollow hierarchical Bi₂WO₆ ones built by nanoplates for the first time under hydrothermal condition because of the analogies of crystal structures. The transformation process of hierarchical BiOI microspheres to hollow Bi₂WO₆ ones was surveyed through XRD analyses and FE-SEM observations of the intermediates at different reaction stages. Rhodamine B (RhB) was selected as pollutant model and visible-light-driven photocatalytic activities of hierarchical BiOI and Bi₂WO₆ microspheres under the same measurement conditions were comparatively studied. As a result, the photocatalytic activities of BiOI obviously outshone Bi₂WO₆. The present study not only develops a new method for fabricating hierarchical architectures but also provides some useful information on relative visible-light-responding photocatalytic activity of hierarchical BiOI and Bi₂WO₆ microspheres.     

含钛高炉渣催化剂的光催化活性

以攀钢含钛高炉废渣为原料,在不同温度下煅烧合成了钙钛矿型硫酸掺杂的含钛高炉渣催化剂(sulfuric acid-modified titanium-bearing blast furnace slag,STBBFS),研究了混晶结构和硫掺杂对含钛高炉渣光催化活性的影响,结果表明,含钛高炉渣催化剂具有钙钛矿/锐钛矿混晶结构,粉体的颗粒形状不规则,煅烧后粒径变大;在紫外区域具有很强的光吸收能力,STBBFS催化剂的光催化活性由Cr(Ⅵ)的还原率评价.煅烧温度为400℃时,STBBFS催化剂的表面存在含量较高的SO2-4和较高的CaTiO3/TiO2晶相比,具有较高的光催化活性,用500 W中压汞灯照射10 h,可将浓度为20 mg·L-1的六价铬废水完全降解.     

Novel CuO/Bi2WO6 heterojunction with enhanced visible light photoactivity

Novel CuO/Bi₂WO₆ composites with different CuO to Bi₂WO₆ weight ratios were synthesized via a facile two-step approach. The as-prepared CuO/Bi₂WO₆ composite photocatalyst was characterized by XRD, SEM, TEM, XPS, BET, UV–vis diffused reflectance, fluorescence spectrum and photocurrent measurements to investigate their physical, optical and photochemical properties. The photocatalytic activity of CuO/Bi₂WO₆ composites was evaluated by the photocatalytic degradation of RhB under simulated sunlight. The optimum photocatalytic activity of the CuO/Bi₂WO₆ composites for the degradation of RhB is almost 2 times higher than those of bare Bi₂WO₆ and CuO. The enhanced photocatalytic performance could be mainly attributed to the improved light response and effective separation of the photogenerated electrons and holes at the heterojunction interface of p-CuO and n-Bi₂WO₆.     

Remarkable Improvement in Photocatalytic Performance for Tannery Wastewater Processing via SnS2 Modified with N‐Doped Carbon Quantum Dots: Synthesis,Characterization, and 4‐Nitrophenol‐Aided Cr(VI) Photoreduction

Photocatalytic pathways are proved crucial for the sustainable production of chemicals and fuels required for a pollution‐free planet. Electron–hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, the efficacy of the 0D N doped carbon quantum dots (N‐CQDs) is demonstrated in accelerating the charge separation and transfer and thereby boosting the activity of a narrow‐bandgap SnS₂ photocatalytic system. N‐CQDs are in situ loaded onto SnS₂ nanosheets in forming N‐CQDs/SnS₂ composite via an electrostatic interaction under hydrothermal conditions. Cr(VI) photoreduction rate of N‐CQDs/SnS₂ is highly enhanced by engineering the loading contents of N‐CQDs, in which the optimal N‐CQDs/SnS₂ with 40 mol% N‐CQDs exhibits a remarkable Cr(VI) photoreduction rate of 0.148 min^?1, about 5‐time and 148‐time higher than that of SnS₂ and N‐CQDs, respectively. Examining the photoexcited charges via zeta potential, X‐ray photoelectron spectroscopy (XPS), surface photovoltage, and electrochemical impedance spectra indicate that the improved Cr(VI) photodegradation rate is linked to the strong electrostatic attraction between N‐CQDs and SnS₂ nanosheets in composite, which favors efficient carrier utilization. To further boost the carrier utilization, 4‐nitrophenol is introduced in this photocatalytic system and the efficiency of Cr(VI) photoreduction is further promoted.     

Polypyrrole/Bi2WO6 composite with high charge separation efficiency and enhanced photocatalytic activity

The recombination of photogenerated electrons and holes is a crucial factor that limits the efficiency of photocatalysis and dye-sensitized solar cells. Conducting polymers are known to have high charge carrier mobility. Herein, a polypyrrole (PPy)/Bi₂WO₆ composite with promoted charge separation efficiency was designed by a “photocatalytic oxidative polymerization” method. The photo-degradation of a typical model pollutant, phenol, demonstrated that the PPy/Bi₂WO₆ composite possessed significantly enhanced photo-activity than pure Bi₂WO₆ under simulated sunlight irradiation. The higher photo-activity was attributed to the synergetic effect between PPy and Bi₂WO₆. The photogenerated holes on the valence band of Bi₂WO₆ could transfer to the highest occupied molecular orbital of PPy, leading to rapid photoinduced charge separation and enhancing the photocatalytic activity. This work provided a new concept for rational design and development of highly efficient polymer-semiconductor photocatalysts for environmental purification under simulated sunlight.     

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.     

Preparation and properties of Bi<Subscript>6</Subscript>Ti<Subscript>5</Subscript>WO<Subscript>22</Subscript>: a new phase in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> system

In a recent report, the evaluation of the phase relations in the Bi₂O₃–TiO₂–WO₃ ternary system has shown the existence of a new phase with nominal composition close to Bi₆Ti₅WO₂₂. In the present contribution we attempt to prepare this single phase by using a solid state route. Although XRD analyses also show traces of two minority Aurivillius-type phases in the synthesized materials, the crystal structure of the Bi₆Ti₅WO₂₂ phase has been determined by Rietveld analyses revealing a complex structure similar to that of Bi₃(AlSb₂)O₁₁ and PbHoAl₃O₈ related compounds. The electrical response of this new phase was characterized as well. Three peaks are observed in its dielectric response: two of them positioned around 0 °C and can be assigned to this Bi₆Ti₅WO₂₂ structure. The third one rises up to 665 °C and confirms the presence of the Aurivillius-type phases.     

Photoreduction of Cr(VI) in water using Bi2O3–ZrO2 nanocomposite under visible light irradiation

Chromium(VI) is a common heavy metal pollutant and extensively used in variety of industrial processes. In the present study, bismuth oxide–zirconium oxide nanocomposite (Bi₂O₃–ZrO₂) was synthesized to improve photoreduction of Cr(VI) under visible light irradiation. The synthesized photocatalyst was characterized by UV-visible-diffuse reflectance spectroscopy (UV-vis-DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (B.E.T) surface area analysis and photoluminescence spectroscopy (PL). Bi₂O₃–ZrO₂ was found to be more photoactive than Bi₂O₃, ZrO₂, TiO₂ and ZnO for the reduction of Cr (VI). The influences of various reaction parameters like the effect of catalyst concentration, initial Cr(VI) concentration and addition of inorganic salts on the photocatalytic activity have been investigated in detail. Meanwhile, the stability of Bi₂O₃–ZrO₂ was investigated by repeatedly performing Cr(VI) photoreducing experiments.