Enhanced photosensitized activity of a BiOCl-Bi2WO6 heterojunction by effective interfacial charge transfer

Confining Bismuth-Halide Perovskite in Mesochannels of Silica Nanomembranes for Exceptional Photocatalytic Abatement of Air Pollutants

Spatially confined photocatalysis has emerged as a viable strategy for the intensification of various redox reactions, but the influence of confined structure on reaction behavior is always overlooked in gas-solid reactions. Herein, we report a nanomembrane with confining Cs3 Bi2 Br9 nanocrystals inside vertical channels of porous insulated silica thin sheets (CBB@SBA(⊥)) for photocatalytic nitric oxide (NO) abatement. The ordered one-dimensional (1D) pore channels with mere 70 nm channel length provide a highly accessible confined space for catalytic reactions. A record-breaking NO conversion efficiency of 98.2 % under a weight hourly space velocity (WHSV) of 3.0×106  mL g-1  h-1 , as well as exceptionally high stability over 14 h and durability over a wide humidity range (RH=15-90 %) was realized over SBA(⊥) confined Cs3 Bi2 Br9 , well beyond its nonconfined analogue and the Cs3 Bi2 Br9 confine in Santa Barbara Amorphous (SBA-15). Mechanism studies suggested that the insulated pore channels of SBA(⊥) in CBB@SBA(⊥) endow concentrated electron field and enhanced mass transfer that render high exposure of reactive species and lower reaction barrier needs for ⋅O2 - formation and NO oxidation, as well as prevents structural degradation of Cs3 Bi2 Br9 . This work expands an innovative strategy for designing efficient photocatalysts for air pollution remediation.

Activating two-dimensional semiconductors for photocatalysis: a cross-dimensional strategy

The emerging two-dimensional (2D) semiconductors substantially extend materials bases for versatile applications such as semiconductor photocatalysis demanding semiconductive matrices and large surface areas. The dimensionality, while endowing 2D semiconductors the unique properties to host photocatalytic functionality of pollutant removal and hydrogen evolution, hurdles the activation paths to form heterogenous photocatalysts where the photochemical processes are normally superior over these on the mono-compositional counterparts. In this perspective, we present a cross-dimensional strategy to employ thenD (n= 0-2) clusters or nanomaterials as activation partners to boost the photocatalytic activities of the 2D semiconductors. The formation principles of heterogenous photocatalysts are illustrated specifically for the 2D matrices, followed by selection criteria of them among the vast 2D database. The computer investigations are illustrated in the density functional theory route and machine learning benefitted from the vast samples in the 2D library. Synthetic realizations and characterizations of the 2D heterogenous systems are introduced with an emphasis on chemical methods and advanced techniques to understand materials and mechanistic studies. The perspective outlooks cross-dimensional activation strategies of the 2D materials for other applications such as CO2removal, and materials matrices in other dimensions which may inspire incoming research within these fields.

Outstanding photo-thermo synergy in aerobic oxidation of cyclohexane by bismuth tungstate-bismuth oxychloride high-low heterojunction

The difficulty of achieving both high conversion rate and high selectivity is a huge challenge in the catalytic aerobic oxidation of cyclohexane. In this paper, bismuth tungstate-bismuth oxychloride (Bi2WO6-BiOCl) nanoflower heterojunctions prepared via a one-step solvothermal process were applied in the photo-thermo synergetic catalytic oxidation of cyclohexane in the dried air. With the addition of little water at different reaction temperature, the ratio of bismuth to tungsten and the mass ratio of Bi2WO6 to BiOCl can be precisely tailored in the nanoflower sphere composites with thin nanosheets. Their microscopic morphology, elemental composition, crystal structure, and photoelectrochemical characteristics were explored by different characterization methods. The Bi2WO6-BiOCl composites possessed poor photocatalytic and thermal performances with the low conversion rates of 1.43% and 2.68%, respectively. However, through the photo-thermo catalytic oxidation process, an exceptional conversion rate of 13.32% was achieved with excellent selectivity of 99.22% for cyclohexanone and cyclohexanol (KA oil) using the same Bi2WO6-BiOCl composites. This superior performance outstrips Bi2WO6 flowers, BiOCl nanosheets and Bi2WO6-BiOCl composites with other compounding ratios. The creation of a high-low heterojunction in the Bi2WO6-BiOCl composite was confirmed by band energy analysis. The opto-electronic analysis, band energy analysis, sacrifice experiments, and active radical analysis were employed to elucidate the mechanism for the exceptional photo-thermo catalytic performance in detail. This work offers an exploratory solution to the challenges of high energy consumption and the difficulty in simultaneously achieving high selectivity and high conversion rates in cyclohexane oxidation, thus holding significant value.

Optimization of Intercalated 2D BiOCl Sheets into Bi2WO6 Flowers for Photocatalytic NH3 Production and Antibiotic Pollutant Degradation

Photocatalytic N2 fixation is a complex reaction, thereby prompting researchers to design and analyze highly efficient materials. Herein, one-pot hydrothermal Bi2WO6-BiOCl (BW-BiOCl) heterojunctions were synthesized by varying the molar ratio of tungsten: chlorine precursor. Major morphological transformations in BiOCl were observed wherein it turned from thick sheets ∼230 nm in pure BiOCl to ∼30 nm in BW-BiOCl. This was accompanied by extensive growth of {001} facets verified from X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) analyses. A p-n heterojunction was formed between Bi2WO6 and BiOCl evidenced via photoluminescence (PL), time-resolved photoluminescence (TRPL), photocurrent response, and electrochemical impedance spectroscopy (EIS) analyses. The formation of heterojunction between Bi2WO6 and BiOCl led to the reduction of the work function in the BW-BiOCl 0.25 hybrid confirmed via ultraviolet photoelectron spectroscopy (UPS) analysis. BW-BiOCl 0.25 could produce ammonia up to 345.1 μmol·L-1·h-1 owing to the formation of a robust heterojunction with an S-scheme carrier transport mechanism. Recycle tests resulted in no loss in N2 reduction activities with post-catalytic analysis, showcasing the high stability of the synthesized heterojunction. Novel performance was owed to its excellent chemisorption of N2 gas on the heterojunction surface verified by N2-temperature programmed desorption (TPD). BW-BiOCl 0.25 also displayed a superior rate constant of 3.03 × 10-2 min-1 for 90 min CIP degradation time, higher than pristine BiOCl and Bi2WO6. Post-photocatalytic Fourier transform infrared (FTIR) spectroscopy of BW-BiOCl 0.25 revealed the presence of C-H stretching peaks in the range of 2850-2960 cm-1 due to adsorbed CIP and methanol species in CIP degradation and N2 fixation, respectively. This also confirmed the enhanced adsorption of reacting species onto the heterojunction surface.

Photocatalytic synergistic biofilms enhance tetracycline degradation and conversion

Tetracyclines are refractory pollutants that cause persistent harm to the environment and human health. Therefore, it is urgently necessary to develop methods to promote the efficient degradation and conversion of tetracyclines in wastewater. This report proposes a photobiocatalytic synergistic system involving the coupling of GeO₂/Zn-doped phosphotungstic acid hydrate/TiO₂ (GeO₂/Zn-HPW/TiO₂)-loaded photocatalytic optical hollow fibers (POHFs) and an algal-bacterial biofilm. The GeO₂/Zn-HPW/TiO₂ photocatalyst exhibits a broad absorption edge extending to 1000 nm, as well as high-efficiency photoelectric conversion and electron transfer, which allow the GeO₂/Zn-HPW/TiO₂-coated POHFs to provide high light intensity to promote biofilm growth. The resulting high photocatalytic activity rapidly and stably reduces the toxicity and increases the biodegradability of tetracycline-containing wastewater. The biofilm enriched with Salinarimonas, Coelastrella sp., and Rhizobium, maintains its activity for the rapid photocatalytic degradation and biotransformation of intermediates to generate the O₂ required for photocatalysis. Overall, the synergistic photocatalytic biofilm system developed herein provides an effective and efficient approach for the rapid degradation and conversion of water containing high concentrations of tetracycline.

Effective BiOCl Electrons Collector for Enhancing Photocarrier Separation of Bi2WO6/BiOCl Composite

Enhancing photocarrier separation is a key step of photocatalysis, and in situ constructed composition interface is an advanced method to achieve this aim. Therefore, we report a face-to-face Bi2WO6/BiOCl (BWOC) which was synthesized via the continuous in situ ion-exchange method. As UV light is harmful to the human body, BWOC exhibits excellent photocatalytic activity only in visible light, and this is an important feature because visible light is a human-friendly operating condition. Under 50 W visible LED lamp illumination, unexcited BiOCl (BOC) only extracts electrons of excited Bi2WO6 (BWO), and holes remain on BWO, resulting in excellent photocarrier spatial separation efficiency through the face-to-face interface. This is why BWOC can be safe to use for the removal of hazardous substances. Compared with BWO and BOC, BWOC possesses 2.6 and 5.6 times higher photodegradation activity than RhB. This work provides a novel insight of efficient visible light photocatalytic system for environmental remediation.

Macroscopic Spontaneous Polarization and Surface Oxygen Vacancies Collaboratively Boosting CO2 Photoreduction on BiOIO3 Single Crystals

Prompt recombination of photogenerated electrons and holes in bulk and on the surface of photocatalysts harshly impedes the photocatalytic efficiency. However, the simultaneous manipulation of photocharges in the two locations is challenging. Herein, the synchronous promotion of bulk and surface separation of photoinduced charges for prominent CO₂ photoreduction by coupling macroscopic spontaneous polarization and surface oxygen vacancies (OVs) of BiOIO₃ single crystals is reported. The oriented growth of BiOIO₃ single-crystal nanostrips along the [001] direction, ensuing substantial well-aligned IO₃ polar units, renders a large enhancement for the macroscopic polarization electric field, which is capable of driving the rapid separation and migration of charges from bulk to surface. Meanwhile the introduction of surface OVs establishes a local electric field for charge migration to catalytic sites on the surface of BiOIO₃ nanostrips. Highly polarized BiOIO₃ nanostrips with ample OVs demonstrate outstanding CO₂ reduction activity for CO production with a rate of 17.33 µmol g^-1 h^-1 (approximately ten times enhancement) without any sacrificial agents or cocatalysts, being one of the best CO₂ reduction photocatalysts in the gas-solid system reported so far. This work provides an integrated solution to governing charge movement behavior on the basis of collaborative polarization from bulk and surface.

Bi spheres SPR-coupled Cu2O/Bi2MoO6 with hollow spheres forming Z-scheme Cu2O/Bi/Bi2MoO6 heterostructure for simultaneous photocatalytic decontamination of sulfadiazine and Ni(II)

Environmental problem on the coexistence of organic pollutants and heavy metals in surface waters has become increasingly serious. Few relative researches have focused on their simultaneous decontamination. Herein, a ternary plasmonic Z-scheme Cu₂O/Bi/Bi₂MoO₆ heterojunction was synthesized via two-step route followed by a wet-impregnation, where Bi spheres coupled with Cu₂O particles were anchored on the surface of Bi₂MoO₆ with hollow microflower spheres. The composites were characterized via various measurements. The excellent photocatalytic activity of Cu₂O/Bi/Bi₂MoO₆ displayed in single sulfadiazine (SDZ) oxidation or Ni(II) reduction, and their simultaneous removal. The degradation pathway for SDZ was investigated via LC-MS and Gaussian theory. DFT and FDTD calculations confirmed the electronic structural characteristics in the Cu₂O/Bi/Bi₂MoO₆ heterostructure and the induced electric field enhancement around nearly touching Bi spheres. A possible photodegradation mechanism of the as-prepared photocatalyst was elucidated via combining scavenger experiments with EPR technique. The results suggested h⁺, •O₂^- and •OH all participated in SDZ oxidation, which verified that Z-Scheme electron transfer was major manner in Cu₂O/Bi/Bi₂MoO₆, while •O₂^- and e^-acted on Ni(II) reduction. The improved photocatalytic activity of Cu₂O/Bi/Bi₂MoO₆ could be ascribed to the unique Z-scheme electron transfer among Cu₂O, Bi and Bi₂MoO₆, particularly SPR and local electric field near Bi spheres.

Graphene quantum dot modified Bi2WO6 with enhanced photocatalytic activity by reinforcing the charge separation

The GQDs/BWO composites consisting of size-controllable GQDs and Bi₂WO₆ nanosheets were synthesized, and they exhibited an excellent photocatalytic activity.

Facile synthesis of a direct Z-scheme BiOCl–phosphotungstic acid heterojunction for the improved photodegradation of tetracycline

A one-step hydrothermal approach for synthesizing BiOCl–phosphotungstic acid (BiOCl–HPW) heterojunctions is proposed. The prepared BiOCl–HPW heterojunction exhibited good stability and photocatalytic activity.

A composite of single-crystalline Bi2WO6 and polycrystalline BiOCl with a high percentage of exposed (00l) facets for highly efficient photocatalytic degradation of organic pollutants

A composite of single-crystalline Bi₂WO₆ and polycrystalline BiOCl with a high percentage of exposed (00l) facets was fabricated by the molten salt method (MSM) in the presence of polytetrafluoroethylene (PTFE).

Construction of the Bi2WO6/Bi4V2O11 heterojunction for highly efficient visible-light-driven photocatalytic reduction of Cr(vi)

Bi₂WO₆/Bi₄V₂O₁₁ heterojunctions constructed by anchoring Bi₄V₂O₁₁ nanocrystals onto Bi₂WO₆ nanoflakes exhibit excellent photocatalytic Cr(vi) reduction activity and cycling stability under visible light irradiation.

Controlled formation of a flower-like CdWO4–BiOCl–Bi2WO6 ternary hybrid photocatalyst with enhanced photocatalytic activity through one-pot hydrothermal reaction

Flower-like CdWO₄–BiOCl–Bi₂WO₆ ternary hybrid photocatalyst shows enhanced photocatalytic activity due to dye sensitization and its cascade structure.

Facile one-step hydrothermal synthesis of noble-metal-free hetero-structural ternary composites and their application in photocatalytic water purification

The development of heterostructured and metal decorated photocatalysts using a relatively simple, efficient and economical one-step strategy is crucial for commercial applications.

A novel Nb2O5/Bi2WO6 heterojunction photocatalytic oxidative desulfurization catalyst with high visible light-induced photocatalytic activity

A novel Nb₂O₅/Bi₂WO₆ heterojunction catalyst was synthesized and applied in PODS of DBT. It shows higher activity than pure Nb₂O₅ and Bi₂WO₆ in visible light induced PODS of DBT, in which holes and superoxide radicals are the main reactive species.

Facile Fabrication of Bi2WO6/Ag2S Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Performances

In this report, a novel photocatalyst based on Bi2WO6/Ag2S heterostructures was prepared by a 3-mercaptopropionic acid (MPA)-assisted route at room temperature. Compared to bare Bi2WO6 and Ag2S nanoparticles, the as-formed Bi2WO6/Ag2S heterostructures exhibit enhanced photocatalytic activity for the degradation of rhodamine B (Rh B) under visible-light irradiation. This kind of enhancement in the photocatalytic activity is considered to be the synergistic effects of both the effective electron-hole separation and expansion of the light-absorption range. The pH of the solution is of vital importance to the photocatalytic activity of the as-formed Bi2WO6/Ag2S heterostructures. Under low pH value, the photosensitization process is suppressed, while under higher pH value, the photosensitization process is favored. The mechanism of the photocatalytic process was proposed by the active-species-trapping experiments, indicating that the photogenerated holes (h(+)) play a crucial role in the degradation of Rh B under visible light. The enhanced photocatalytic performance of this heterostructure makes it a promising material for the treatment of dye-containing wastewater.

MoS2 nanodot decorated In2S3 nanoplates: a novel heterojunction with enhanced photoelectrochemical performance

MoS2 nanodot decorated In2S3 nanoplates were successfully synthesized via a modified one-pot method. The In2S3/MoS2 heterojunction nanocomposite exhibits superior optical and photoelectrochemical performance to the bare ones, owing to the synergistic effect.

Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity

We report the synthesis and photoelectrochemical assessment of phase pure tetragonal matlockite structured BiOX (where X = Cl, Br, I) films.

We report the synthesis and photoelectrochemical assessment of phase pure tetragonal matlockite structured BiOX (where X = Cl, Br, I) films. The materials were deposited using aerosol-assisted chemical vapour deposition. The measured optical bandgaps of the oxyhalides, supported by density functional theory calculations, showed a red shift with the increasing size of halide following the binding energy of the anion p-orbitals that form the valence band. Stability and photoelectrochemical studies carried out without a sacrificial electron donor showed the n-type BiOBr film to have the highest photocurrent reported for BiOBr in the literature to date (0.3 mA cm^–2 at 1.23 V vs. RHE), indicating it is an excellent candidate for solar fuel production with a very low onset potential of 0.2 V vs. RHE. The high performance was attributed to the preferred growth of the film in the [011] direction, as shown by X-ray diffraction, leading to internal electric fields that minimize charge carrier recombination.

Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light

A new mesoporous silica protected plasmonic photocatalyst, Au/BiOCl@mSiO2, was prepared by a modified AcHE method and a subsequent UV light induced photodeposition process. The surfactant-free heterojunction allows the electrons spontaneously flow from Au to nearby BiOCl surface, leading to the accumulation of positive charges on Au surface, and negative charges on Bi species under visible light. Au/BiOCl@mSiO2 exhibits high visible light photocatalytic efficiency in complete oxidation of aqueous formaldehyde and Rhodamin B. We showed that a positive relationship exists between the LSPR effect and rate enhancements, and leads to a hypothesis that the metallic Au LSPR enhances the photocatalytic rates on nearby semiconductors by transferring energetic electrons to BiOCl and increasing the steady-state concentration of active OH species by a multi-electron reduction of molecular oxygen. The OH species is the main oxidant in photocatalytic transformations, whose intensity is greatly enhanced in the dye-involving systems due to the synergetic effect between LSPR and dye sensitization processes. In addition, the mesoporous SiO2 shell not only inhibits the over growth of BiOCl nanocrystals within the silica frameworks, but also protects the dissolution of chloride or Au species into aqueous solution, which ultimately makes the Au/BiOCl@mSiO2 catalysts rather stable during photocatalysis.

Fabrication of Wide-Range-Visible Photocatalyst Bi2WO6-x nanoplates via Surface Oxygen Vacancies

Bi2WO6 as a high visible-light-driven catalyst has been aroused broad interest. However, it can only be excitated by the light with λ < 450 nm and the solar energy utilization need to be improved. Here, the wide-range-visible photoresponse Bi2WO6-x nanoplates were fabricated by introducing surface oxygen vacancies through the controllable hydrogen reduction method. The visible photoresponse wavelength range is extended from 450 nm to more than 600 nm. In addition, the photocatalytic activity of Bi2WO6-x is also increased and is 2.1 times as high as that of pristine Bi2WO6. The extending of the photoresponse range and the enhancement of the photoactivity both can be attributed to the surface-oxygen-vacancy states. This is because surface-oxygen-vacancy states generated above and partly overlapping of with the valence band (VB) will result in the rising of valence band maximum (VBM), thus broadening the VB width. This approach is proposed to develop many types of wide-range-visible optical materials and to be applicable to many narrow and wide bandgap materials.

Ag nanoparticles/hematite mesocrystals superstructure composite: a facile synthesis and enhanced heterogeneous photo-Fenton activity

The synergistic effect of the unique superstructure and the Ag loading resulted in the effective separation of charge carriers and excellent photo-Fenton performance of Ag/hematite mesocrystals.

Accessible fabrication of Bi2MoO6/BiOCl for effectively conducting thermally-responsive catalytic decontamination of model pollutants

Bi₂MoO₆/BiOCl (BMB) with thermally-responsive catalytic properties was synthesized by a one-step hydrothermal approach.

Deposition of silver nanoparticles onto two dimensional BiOCl nanodiscs for enhanced visible light photocatalytic and biocidal activities

Silver modified 2D BiOCl showed excellent photocatalytic performance in degrading sulfanilamide and presented good antibacterial efficiency under visible light irradiation.

Facile synthesis of a visible light α-Fe2O3/BiOBr composite with high photocatalytic performance

Novel α-Fe₂O₃/BiOBr composites were synthesized by a simple in hydrolysis method for the first time, which showed enhanced photocatalytic performance for the photocatalytic degradation of organic dyes under visiblelight irradiation.

Exploring the effects of nanocrystal facet orientations in g-C₃N₄/BiOCl heterostructures on photocatalytic performance

Effective separation and migration of photogenerated electron-hole pairs are two key factors to determine the performance of photocatalysts. It has been widely accepted that photocatalysts with heterojunctions usually exhibit excellent charge separation. However, the migration process of separated charges in the heterojunction structures has not been fully investigated. Herein, photocatalysts with heterojunctions are constructed by loading g-C3N4 nanoparticles onto BiOCl nanosheets with different exposed facets (BOC-001 and BOC-010). The g-C3N4 nanoparticles with decreasing size and increasing zeta potential could induce stronger coupling and scattering in the heterojunction. The relationship between the crystal facet orientation in the BiOCl nanosheets and charge separation/effective migration behaviours of the materials is investigated. The visible light photocatalytic activity of the composites is evaluated by methyl orange (MO) and phenol degradation experiments, and the results show that ng-CN/BOC-010 composites exhibit higher photocatalytic performance than that of ng-CN/BOC-001 composites. Both photoelectrochemical and fluorescence emission measurements indicate that the different exposed facets in ng-CN/BiOCl composites could induce the migration of the photogenerated electrons in different ways, but do not significantly alter the separation efficiencies. The separated electrons in ng-CN/BOC-010 undergo a shorter transport distance than that of ng-CN/BOC-001 to reach the surface reactive sites. The study may suggest that the crystal facet orientation in polar semiconductors is a critical factor for designing highly efficient heterojunction photocatalysts.

Enhanced photocatalytic activity of α-Fe2O3/Bi2WO6 heterostructured nanofibers prepared by electrospinning technique

One-dimensional α-Fe₂O₃/Bi₂WO₆ heterostructured nanofibers with the diameter of about 300–500 nm were successfully prepared by using a simple and straightforward protocol combining an electrospinning technique with a sintering process.

Synthesis of Ag2CO3/Bi2WO6 heterojunctions with enhanced photocatalytic activity and cycling stability

Novel hierarchical Ag₂CO₃/Bi₂WO₆ heterojunction photocatalysts were prepared and they exhibited excellent photocatalytic activity and outstanding cycling performance for the degradation of rhodamine B (RhB) dye under visible light irradiation.

Photocatalytic property of a Bi2O3 nanoparticle modified BiOCl composite with a nanolayered hierarchical structure synthesized by in situ reactions

Bi₂O₃ nanoparticle modified BiOCl nanosheets with a nanolayered hierarchical structure synthesized by in situ reactions exhibit high photocatalytic performance.

Photoelectric activity of a Bi₂O₃/Bi₂WO₆-xF₂x heterojunction prepared by a simple one-step microwave hydrothermal method

NH4F/Bi2WO6 powders were prepared by a simple one-step microwave hydrothermal method at different reaction temperatures, using Bi(NO3)3·5H2O and Na2WO4·2H2O as raw materials and NH4F as an additive agent. Their photoelectric activities were also investigated via the degradation of Rhodamine B (RhB). The results indicate that when the reaction temperature increases to 220 and 240 °C, the orthorhombic Bi2WO6 phase with space group Pca21 and cubic Bi2O3 phase with space group Pn3̅m appear. Raman spectroscopy, SEM, TEM, and XPS results also confirm the existence of a Bi2O3/Bi2WO6-xF2x heterojunction at higher temperature. Greater than 95% photodegradation of RhB under the exposure of simulated sunlight is achieved within 90 min with the Bi2O3/Bi2WO6-xF2x heterojunction prepared at 220 °C, which displays remarkably promoted photocatalytic activities. The electrochemical impedance spectra and photocurrent results also prove that efficient charge separation and better electron transport properties are achieved by the Bi2O3/Bi2WO6-xF2x heterojunction film prepared at 220 °C. In addition, the mechanism of the crystal growth and formation of the p-n junction between p-type Bi2O3 and n-type Bi2WO6 were also discussed.

Enhancement of visible photocatalytic performances of a Bi2MoO6–BiOCl nanocomposite with plate-on-plate heterojunction structure

A visible-light-sensitive Bi₂MoO₆–BiOCl heterojunction photocatalyst was synthesized via a hydrothermal process.