Bi2WO6 Nanoplates Research Articles

Why Does Bi2WO6 Visible-Light Photocatalyst Always Form as Nanoplatelets?

Bi2WO6 nanocrystals exhibit excellent photocatalytic properties in the visible range of the solar spectrum, and intense efforts are directed at designing effective synthesis processes with control of size, morphology, and hierarchical structure. All known hydrothermal syntheses produce either nanoplatelet morphology or hierarchical structures based on such primary entities. Here we investigate the nucleation and growth of Bi2WO6 nanocrystals under hydrothermal conditions using in situ X-ray total scattering (TS) and powder X-ray diffraction (PXRD) measurements. It is shown that the preferential growth of Bi2WO6 nanoplates is due to the presence of disordered layers of Bi2O22+ molecular complexes in the precursor solution with an approximate length of 13 Å. These layers interact with tetrahedral WO42- molecular units and eventually form the disordered cubic (Bi0.933W0.067)O1.6) crystalline phase. When enough tungsten units are intertwined between Bi2O22+ layers formation of Bi2WO6 pristine nanoplates takes place by necessary sideways addition of units in the ac plane. The experimentally observed formation mechanism suggests that the Bi/W atomic ratio must play a central role in the nucleation (assembly of initial crystal layers). Indeed, it is observed in separate continuous flow supercritical synthesis that for a stoichiometric (Bi/W = 2:1) precursor, a (Bi0.933W0.067)O1.6) impurity phase is always observed together with the main Bi2WO6 product. Excess tungsten is required in the precursor to form phase-pure Bi2WO6 material. Thus, the present study also reports a fast, scalable, and green method for production of this highly attractive photocatalyst.

Topotactic Transformation of Bismuth Oxybromide into Bismuth Tungstate: Bandgap Modulation of Single-Crystalline {001}-Faceted Nanosheets for Enhanced Photocatalytic CO2 Reduction.

The photocatalytic conversion of CO2 to energy-rich CH4 solar fuel is an ideal strategy for future energy generation as it can resolve global warming and the imminent energy crisis concurrently. However, the efficiency of this technology is unavoidably hampered by the ineffective generation and utilization of photoinduced charge carriers. In this contribution, we report a facile in situ topotactic transformation approach where {001}-faceted BiOBr nanosheets (BOB-NS) were employed as the starting material for the formation of single-crystalline ultrathin Bi2WO6 nanosheets (BWO-NS). The as-obtained BWO-NS not only preserved the advantageous properties of the 2D nanostructure and predominantly exposed {001} facets but also possessed enlarged specific surface areas as a result of sample thickness reduction. As opposed to the commonly observed bandgap broadening when the particle sizes decrease to an ultrathin nanoscale owing to the quantum size effect, the developed BWO-NS exhibited a fascinating bandgap narrowing compared to those of pristine Bi2WO6 nanoplates (BWO-P) synthesized from a conventional one-step hydrothermal approach. Moreover, the electronic band positions of BWO-NS were modulated as a result of ion exchange for the reconstruction of the energy bands, where BWO-NS demonstrated significant upshifting of CB and VB levels; these are beneficial for photocatalytic reduction applications. This propitious design of BWO-NS through integrating the merits of BOB-NS caused BWO-NS to exhibit substantial 2.6 and 9.3-fold enhancements of CH4 production over BOB-NS and BWO-P, respectively.

Facet-engineered surface and interface design of WO3/Bi2WO6 photocatalyst with direct Z-scheme heterojunction for efficient salicylic acid removal

WO3 (0 0 1) and WO3 (0 0 1)&(1 1 0) were initially grown on the surface of Bi2WO6 (0 1 0) nanoplates via simple hydrothermal route, respectively. Compared to WO3 (0 0 1)/Bi2WO6, the developed WO3 (0 0 1)&(1 1 0)/Bi2WO6 was endowed with the stronger interfacial interaction property. Moreover, the developed composite could present a broad visible light response at an absorption edge of 440 nm. Not only that, the optimized interfacial carriers were newly achieved, leading to the enhanced separation and transfer of photogenerated electron-hole pairs. The resulting WO3 (0 0 1)&(1 1 0)/Bi2WO6 was implemented to salicylic acid removal (up to 74.5%) under visible light irradiation, demonstrating a kinetics of about 2.4 times faster than that of WO3 (0 0 1)/Bi2WO6. The significantly improved photocatalysis of developed composite was attributed to the conversion from traditional heterojunction to Z-scheme heterojunction, thus, promoting the oxidation ability of photogenerated holes so as to engender abundant ·OH. Ultimately, based on the analysis of energy band structures, the migration pathways of photogenerated carriers in composites was explained. Noticeably, it may open a new door towards the Z-scheme strategy of compound photocatalyst without any electronic mediators via controllable facet exposure engineering for highly photocatalysis.

Hydrothermal synthesized Bi2WO6 nanoplates: growth mechanism and photocatalytic activities

Bi2WO6 nanoplates were successfully synthesized at 200 °C with bismuth citrate (C6H13BiN2O7·H2O) and sodium tungstate dihydrate (Na2WO4·2H2O) as raw materials in hydrothermal environment. The phase composition and morphology were characterized by x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution TEM. The average sizes of the Bi2WO6 nanoplates were ca. 300 ∼ 400 nm in lateral size and ca. 30 nm in thickness, respectively, and the nanoplates were parallel to (010) planes. To completely understand the growth mechanism of the Bi2WO6 nanoplates, a series of time-dependent tests were applied, and a possible mechanism was proposed. Additionally, Rhodamine (RhB) degradation testing was carried out to investigate the photocatalytic activity.

Ti3C2 MXene-modified Bi2WO6 nanoplates for efficient photodegradation of volatile organic compounds

Air pollution of volatile organic compounds (VOCs) threatens human health. Developing advanced photocatalysts for VOCs elimination thus attracts much interest. Bi2WO6 shows the merits of stability, nontoxicity and visible light absorbance but suffers from its rapid electron/hole recombination. Herein Ti3C2 MXene nanoparticles were electrostatically adsorbed on Bi2WO6 nanoplates for efficient electron/hole separation. Upon hybridization, electrons in Bi2WO6 flow to Ti3C2 Mxene as evidenced by XPS analysis, implying that Ti3C2 Mxene has impressive capability of trapping photoinduced electrons. As-prepared BT4 reveals increased photocurrent and weak photoluminescence under light irradiation owing to the electron-trapping effect of Ti3C2 Mxene. DFT simulations reveal that Ti3C2 Mxene has strong chemical adsorption for HCHO and CH3COCH3 for while Bi2WO6 shows weak physical adsorption. Such strong adsorption of Ti3C2 Mxene is attributed to the charge transfer between Ti3C2 Mxene and VOC molecules as disclosed by differential charge density and Bader charge analyses. The superoxide radical (O2−) and hydroxide radical (∙OH) participated in the photo-oxidation process. As-obtained BT4 revealed 2 times and 6.6 times higher photocatalytic activity towards the degradation of HCHO and CH3COCH3 in comparison with Bi2WO6. Such superior performance of BT4 can be ascribed to favourable adsorption of VOCs and efficient electron/hole separation of Ti3C2 MXene.

Synthesis and Characterization Ag Nanoparticles Supported on Bi2WO6 Nanoplates for Enhanced Visible-Light-Driven Photocatalytic Degradation of Rhodamine B

Heterostructure Ag/Bi2WO6 nanocomposites with different weight contents of Ag nanoparticles for photodegradation of rhodamine B (RhB) were successfully synthesized by solution precipitate-deposition method using sodium borohydride (NaBH4) as a reducing agent. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) certify the successful synthesis of cubic Ag nanoparticles supported on the surface of orthorhombic Bi2WO6 nanoplates. X-ray photoelectron spectroscopy (XPS) revealed the presence of metallic Ag species supported on Bi2WO6 nanoplates. The photocatalytic performance of heterostructure Ag/Bi2WO6 nanocomposites were investigated through the degradation of RhB under visible light irradiation. In this research, Ag/Bi2WO6 nanocomposites exhibited excellent chemical stability and recyclability under visible light irradiation. The 5 wt% Ag/Bi2WO6 showed the highest photodegradation of RhB due to the Ag nanoparticles acting as an electron trapper, to restrain the recombination of photo-induced electrons and holes, to improve the charge separation, and to enhance the photocatalytic performance of Bi2WO6.

Precipitation-Deposition of Visible-Light-Driven AgCl/Bi2WO6 Nanocomposites used for the Removal of Rhodamine B

In this research, the effect of weight percent of AgCl nanospheres loaded on Bi2WO6 nanoplates for photocatalytic degradation of rhodamine B (RhB) was studied. The Bi2WO6 nanoplates were synthesized by the hydrothermal method and followed by the precipitation-deposition of AgCl nanospheres on Bi2WO6 nanoplates at room temperature. The as-synthesized samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy, including the intermediates of rhodamine B (RhB) that were investigated by m/z mass spectroscopy. The analytical results revealed very good dispersed cubic AgCl nanospheres supported on orthorhombic Bi2WO6 nanoplates. The photocatalytic performance of Bi2WO6 and AgCl/Bi2WO6 samples was monitored through photodegradation of RhB under visible light irradiation. AgCl/Bi2WO6 nanocomposites have photocatalytic activity higher than pure Bi2WO6. A photodegradation mechanism of AgCl/Bi2WO6 nanocomposites was also discussed according to the experimental results.

Bi2WO6 Semiconductor Nanoplates for Tumor Radiosensitization through High- Z Effects and Radiocatalysis.

The radioresistance of tumor cells is considered to be an Achilles' heel of cancer radiotherapy. Thus, an effective and biosafe radiosensitizer is highly desired but hitherto remains a big challenge. With the rapid progress of nanomedicine, multifunctional inorganic nanoradiosensitizers offer a new route to overcome the radioresistance and enhance the efficacy of radiotherapy. Herein, poly(vinylpyrrolidone) (PVP)-modified Bi2WO6 nanoplates with good biocompatibility were synthesized through a simple hydrothermal process and applied as a radiosensitizer for the enhancement of radiotherapy for the first time. On the one hand, the high- Z elements Bi ( Z = 83) and W ( Z = 74) endow PVP-Bi2WO6 with better X-ray energy deposition performance and thus enhance radiation-induced DNA damages. On the other hand, Bi2WO6 semiconductors exhibit significant photocurrent and photocatalytic-like radiocatalytic activity under X-ray irradiation, giving rise to the effective separation of electron/hole (e-/h+) pairs and subsequently promoting the generation of cytotoxic reactive oxygen species, especially hydroxyl radicals (•OH). The γ-H2AX and clonogenic assays demonstrated that PVP-Bi2WO6 could efficiently increase cellular DNA damages and colony formations under X-ray irradiation. These versatile features endowed PVP-Bi2WO6 nanoplates with enhanced radiotherapy efficacy in animal models. In addition, Bi2WO6 nanoplates can also serve as good X-ray computed tomography imaging contrast agents. Our findings provide an alternative nanotechnology strategy for tumor radiosensitization through simultaneous radiation energy deposition and radiocatalysis.

Visible-light-driven photocatalytic degradation of rhodamine B by Ag2CO3/Bi2WO6 nanocomposites

0–10 wt% Ag2CO3/Bi2WO6 nanosamples were prepared by hydrothermal method combined with solution precipitation–deposition method. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV–visible spectroscopy. They certified that spherical Ag2CO3 nanoparticles supported on orthorhombic Bi2WO6 nanoplates. Their photocatalytic activities were investigated through photodegradation of rhodamine B (RhB) under visible-light irradiation. In this research, 10 wt% Ag2CO3/Bi2WO6 nanocomposites show the highest performance for photodegradation of RhB induced by visible radiation.

Zn2SnO4 QDs decorated Bi2WO6 nanoplates for improved visible-light-driven photocatalytic removal of gaseous contaminants

Abstract Zn2SnO4 quantum dots (QDs) decorated Bi2WO6 nanocomposites were prepared via a two-step hydrothermal reaction progress. The Zn2SnO4 QDs were highly dispersed onto the surface of plate-shaped n-type Bi2WO6, which allows more photons to be harvested and effectively improve the separation and utilization efficiencies of photoinduced electrons and holes due to the formation of heterojunction. Among them, 3% Zn2SnO4 QDs/Bi2WO6 nanocomposite showed the highest photocatalytic performance (95.5% of acetone degradation), compared with other different amounts of Zn2SnO4 QDs, which are 5.86 and 1.99 times higher than those of pure Bi2WO6, respectively. Meanwhile, the hybridized sample was investigated by four successive photocatalytic degradation of acetone under visible light, displaying great photo-stability. Furthermore, through in-situ FTIR, acetaldehyde, acetic acid and formaldehyde were certified as intermedias during the photocatalytic degradation of acetone. Based on these results, the relationship between photocatalytic activity and the formation of Zn2SnO4 QDs/Bi2WO6 heterojunction is further discussed and the possible reaction mechanism is proposed. Such novel photocatalyst as visible light responsive catalyst provides a new choice for the efficient degradation of contaminants.

Built-in electric field-assisted charge separation over carbon dots-modified Bi2WO6 nanoplates for photodegradation

Bi2WO6 photocatalyst has attracted much interest but suffers from easy recombination of electron-hole pairs. Herein carbon dots (CDs) as a cocatalyst were hydrothermally hybridized with Bi2WO6 nanoplates with aim of efficient separation of charge carriers. Electron transfer from CDs to Bi2WO6 across their interfaces upon contact was revealed by XPS results and further supported by differential charge density analyses. Such electron transfer led to a built-in electric field pointing from CDs to Bi2WO6, which drove photoinduced electrons flowing to CDs under light irradiation. DFT simulation showed the introduced electron was mainly distributed on CDs instead of Bi2WO6, which implied that CDs had impressive capability of taking photoinduced electrons under irradiation. Such efficient charge separation was experimentally supported by photoelectrochemical analyses. The superoxide radicals and holes were found to participate in the photodegradation of RhB under visible light irradiation. The enhanced photocatalytic activity of CDs/Bi2WO6 could be ascribed to the efficient charge separation and large specific area of Bi2WO6 nanoplates.

Photocatalytic application of Bi2WO6 nanoplates structure for effective degradation of methylene blue

A visible-light driven photocatalysts of Bi2WO6 nanoplates were fabricated through a hydrothermal route. Bi2WO6 nanoplates prepared by different reaction times were used to examine the photodegradation efficiency of MB. Structure and morphology analysis of samples were carried out by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). XRD pattern confirms the well-defined orthorhombic structure of Bi2WO6. Optical band gap values (∼2.7, 2.79 and 2.80 eV) range shows wide band gap for samples have been determined by diffuse reflectance spectroscopy (UV-DRS) and it was calculated by Kubelka-Munk function. Raman spectra confirm the crystal structure and vibration modes of the prepared samples. Bi2WO6 nanoplates prepared by 24 h reaction time shows better photocatalytic activity of 84% degradation of Methylene blue under visible light for 120 min due to its hierarchical structure, crystallite size and lower band gap value.

Precipitation–deposition synthesis, characterization, and visible light-driven photocatalytic properties of heterostructure AgI/Bi2WO6 nanocomposites

AgI nanoparticle-modified Bi2WO6 nanoplates were prepared by a precipitation–deposition method. X-ray diffraction and transmission electron microscopy certified the formation of hexagonal AgI nanoparticles with the size of 5–8 nm as minor phase well supported on orthorhombic Bi2WO6 nanoplates as major phase. The photocatalytic properties of heterostructure AgI/Bi2WO6 nanocomposites were investigated through photodegradation of rhodamine B (RhB) induced by xenon visible light. The 10 wt% AgI/Bi2WO6 nanocomposites exhibited the highest photocatalytic activity because of the recombination rate reduction of photoexcited electrons and photogenerated holes during photocatalysis. A possible photodegradation mechanism of RhB by AgI/Bi2WO6 nanocomposites was proposed and discussed in this research.

Three-dimension hierarchical heterostructure of CdWO4 microrods decorated with Bi2WO6 nanoplates for high-selectivity photocatalytic benzene hydroxylation to phenol

For the first time Bi2WO6/CdWO4 (BCW) hierarchical heterostructure of CdWO4 microrods decorated with uniform Bi2WO6 nanoplates was prepared. Using BCW as photocatalyst and O2 as oxidant, we achieved satisfactory catalytic activity (benzene conversion 7.3% and selectivity of phenol > 99%) in the hydroxylation of benzene to phenol at room temperature. It was found that the unique hierarchical heterostructure is beneficial for the absorption of visible light and the separation of photoinduced charge carriers. Moreover, we confirm the pivotal role of hydroxyl radicals and propose a plausible mechanism for the hydroxylation reaction.

Synthesis and Photocatalytic Properties of the Bi<sub>2</sub>MoO<sub>6</sub> and Bi<sub>2</sub>WO<sub>6</sub> Photocatalysts

Two different Bi-based semiconductor photocatalysts Bi2MoO6 and Bi2WO6 were synthesized by a simple one-pot hydrothermal reaction at 453 K for 10 h. The properties of the photocatalysts, including structures, morphology, light-absorption band and photoluminescence, etc were characterized by X-ray diffraction, scanning electron microscopy, UV-Vis diffuse reflectance spectrum and fluorescence spectrum. Further, their photocatalytic properties were compared by the degradation of two different organic dyes: Rhodamine B and methylene blue. It is important to note that the Bi2WO6 nanoplate structure exhibited better photocatalytic activity than the Bi2MoO6 nanowires aggregates due to its high surface area, higher light absorption and lower recombination of electron-hole pairs.

Decolorization of rhodamine B photocatalyzed by Ag3PO4/Bi2WO6 nanocomposites under visible radiation

Heterostructure Ag3PO4/Bi2WO6 nanocomposites were synthesized by precipitation-deposition method. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and UV-visible spectrophotometry revealed that cubic Ag3PO4 nanospheres with <20 nm diameter were supported on orthorhombic Bi2WO6 nanoplates and that Ag3PO4/Bi2WO6 nanocomposites exhibited more enhanced photodegradation of rhodamine B than pure Bi2WO6.

Synthesis, characterization and photocatalysis of heterostructure AgBr/Bi2WO6 nanocomposites

0–15 wt% AgBr/Bi2WO6 nanocomposites used as visible-light-driven photocatalysts were successfully synthesized by a deposition-precipitation method. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) revealed the presence of cubic AgBr nanospheres supported on orthorhombic Bi2WO6 nanoplates. Their photocatalytic performance was investigated through the degradation of rhodamine B (RhB) under visible-light irradiation within 40 min. In this research, 10 wt% AgBr/Bi2WO6 nanocomposites has the highest photocatalytic performance of 99.83% and are the promising material used for removal of contaminants in wastewater.

Hydrothermal preparation of visible-light-driven Br-doped Bi2WO6 photocatalyst

Bi2WO6 loaded with 0–3wt% Br was hydrothermally prepared and further characterized by XRD, Raman spectroscopy, TEM, SAED and XPS. In this research, both doped and un-doped samples were uniform orthorhombic Bi2WO6 nanoplates. Their photocatalysis was evaluated through photodegradation of rhodamine B under visible radiation. Bi2WO6 loaded with 3wt% Br has the highest activity and can be used asa visible-light-driven photocatalyst.

Construction of an all-solid-state artificial Z-scheme system consisting of Bi2WO6/Au/CdS nanostructure for photocatalytic CO2 reduction into renewable hydrocarbon fuel

An all-solid-state Bi2WO6/Au/CdS Z-scheme system was constructed for the photocatalytic reduction of CO2 into methane in the presence of water vapor. This Z-scheme consists of ultrathin Bi2WO6 nanoplates and CdS nanoparticles as photocatalysts, and a Au nanoparticle as a solid electron mediator offering a high speed charge transfer channel and leading to more efficient spatial separation of electron–hole pairs. The photo-generated electrons from the conduction band (CB) of Bi2WO6 transfer to the Au, and then release to the valence band (VB) of CdS to recombine with the holes of CdS. It allows the electrons remaining in the CB of CdS and holes in the VB of Bi2WO6 to possess strong reduction and oxidation powers, respectively, leading the Bi2WO6/Au/CdS to exhibit high photocatalytic reduction of CO2, relative to bare Bi2WO6, Bi2WO6/Au, and Bi2WO6/CdS. The depressed hole density on CdS also enhances the stability of the CdS against photocorrosion.

CTAB-Assisted Fabrication of Bi₂WO₆ Thin Nanoplates with High Adsorption and Enhanced Visible Light-Driven Photocatalytic Performance.

Two-dimensional thin Bi2WO6 nanoplates have been fabricated using a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. We investigated the proposed formation mechanism based on the crystalline structures of the thin Bi2WO6 nanoplates. The high adsorption ability and excellent visible-light driven photocatalytic activities of the Bi2WO6 nanoplates were illustrated, in view of exposed (001) facets of nanoplates possessing faster separation of photo-generated charge carriers and increased catalytically active sites. Such a cost-effective way to obtain Bi2WO6 nanoplates offers new possibilities for the design of adsorptive semiconductor photocatalysts with strengthened photocatalytic activities.