Ultrasonic-assisted synthesis of visible-light-induced Bi2MO6 (M=W, Mo) photocatalysts

Developing Z-scheme Bi2MoO6@α-MnO2 beaded core-shell heterostructure in photoelectrocatalytic treatment of organic wastewater

Photoelectrocatalysis (PEC) oxidation technology with the combination of electrocatalysis and photocatalysis is an ideal candidate for treatment of dyeing wastewater containing multifarious intractable organic compounds with high chroma. Constructing high-quality heterojunction photoelectrodes can effectively suppress the recombination of photo-generated carriers, thereby achieving efficient removal of pollution. Herein, a beaded Bi2MoO6@α-MnO2 core-shell architecture with tunable hetero-interface was prepared by simple hydrothermal-solvothermal process. The as-synthesized Bi2MoO6@α-MnO2 had larger electrochemically active surface area, smaller charge transfer resistance and negative flat band potential, and higher separation efficiency of e-/h+ pairs than pure α-MnO2 or Bi2MoO6. It is noteworthy that the as-synthesized Bi2MoO6@α-MnO2 showed Z-scheme heterostructure as demonstrated by the free radical quenching experiments. The optimized Bi2MoO6@α-MnO2-2.5 exhibited the highest degradation rate of 88.64% in 120 min for reactive brilliant blue (KN-R) and accelerated stability with long-term(∼10000s) at the current density of 50 mA cm-2 in 1.0 mol L-1 H2SO4 solution. This study provides valuable insights into the straightforward preparation of heterogeneous electrodes, offering a promising approach for the treatment of wastewater in various industrial applications.

Progressive Insights into Metal-Organic Frameworks and Metal-Organic Framework-Membrane Composite Systems for Wastewater Management

The sustainable management of wastewater through recycling and utilization stands as a pressing concern in the trajectory of societal advancement. Prioritizing the elimination of diverse organic contaminants is paramount in wastewater treatment, garnering significant attention from researchers worldwide. Emerging metal-organic framework materials (MOFs), bridging organic and inorganic attributes, have surfaced as novel adsorbents, showcasing pivotal potential in wastewater remediation. Nevertheless, challenges like limited water stability, elevated dissolution rates, and inadequate hydrophobicity persist in the context of wastewater treatment. To enhance the performance of MOFs, they can be modified through chemical or physical methods, and combined with membrane materials as additives to create membrane composite materials. These membrane composites, derived from MOFs, exhibit remarkable characteristics including enhanced porosity, adjustable pore dimensions, superior permeability, optimal conductivity, and robust water stability. Their ability to effectively sequester organic compounds has spurred significant research in this field. This paper introduces methods for enhancing the performance of MOFs and explores their potential applications in water treatment. It delves into the detailed design, synthesis strategies, and fabrication of composite membranes using MOFs. Furthermore, it focuses on the application prospects, challenges, and opportunities associated with MOF composite membranes in water treatment.

Photocatalytic Reduction of CO2 on a Bi2MoxW1-xO6 Solid Solution with Enhanced Activity

This paper reports on a Bi₂Mo_xW_1-xO₆ solid solution with excellent photocatalytic activity in CO₂ reduction. Under simulated sunlight, the Bi₂Mo_0.25W_0.75O₆ solid solution achieved a CO generation yield of ≤298.2 μmol g^-1 over 3 h, which was 2.1 and 1.5 times larger than those of pristine Bi₂WO₆ and Bi₂MoO₆, respectively. Via an in-depth study of the mechanism, this excellent photocatalytic activity was determinied to be probably due to two major contributions: (1) the formation of oxygen vacancies on the Bi₂Mo_0.25W_0.75O₆ solid solution, which provided more reactive sites for adsorption and activation of CO₂, and (2) modulation of the electronic band structure, which facilitated charge separation. Mechanistic and reaction pathways have been deeply explored and proposed.

Bi2MoO6 nanofilms on the stainless steel mesh by PS-PED method: Photocatalytic degradation of diclofenac sodium as a pharmaceutical pollutant

For the first time, Bi₂MoO₆ nanofilms were successfully synthesized by simultaneous pulse sonication-pulse electrodeposition (PS-PED) on the stainless steel mesh surface. Bismuth molybdate films were formed under various combinations of electrodeposition and sonication (sono-electrodeposition) in continuous and pulse modes. Porous Bi₂MoO₆ films synthesized by PS-PED method and showed the highest efficiency in photocatalytic degradation in comparison with other films. Bi₂MoO₆ film obtained from PS-PED had a thickness of 13.78 nm while, the thickness for the electrodeposition method was 39.52 nm. The high photocatalytic efficiency is attributed to the high surface roughness and low thickness of film synthesized by PS-PED method. Indeed, ultrasound played a key role in the synthesis of films with high surface roughness. On the other hand, shock waves and micro-jets could be dissolved diffusion problems and reduced the dendrite like structures in deposition process. Simultaneous application of pulse modes for both combined methods led to more growth of crystallographic planes. This is due to reaction of ions on the surface in interval relaxation times and produce more nuclei for growth. In order to obtain a high efficiency, response surface methodology was used for optimization of effective variable parameters (t_on, t_off and sonication amplitude) in film preparation.

Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

Controlling the structural organization and crystallinity of functional oxides is key to enhancing their performance in technological applications. In this work, we report a strong enhancement of the structural organization and crystallinity of Bi2WO6 samples synthetized by a microwave-assisted hydrothermal method after exposing them to femtosecond laser irradiation. X-ray diffraction, UV-vis and Raman spectroscopies, photoluminescence emissions, energy dispersive spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy were employed to characterize the as-synthetized samples. To complement and rationalize the experimental results, first-principles calculations were employed to study the effects of femtosecond laser irradiation. Structural and electronic effects induced by femtosecond laser irradiation enhance the long-range crystallinity while decreasing the free carrier density, as it takes place in the amorphous and liquid states. These effects can be considered a clear cut case of surface-enhanced Raman scattering.

High-Throughput Characterization of Structural and Photoelectrochemical Properties of a Bi–Mo–W–O Thin-Film Materials Library

A Bi–W–Mo–O thin-film materials library was fabricated by combinatorial reactive magnetron sputtering. The composition spread was investigated using high-throughput methods to determine crystalline phases, composition, morphology, optical properties, and photoelectrochemical performance. The aurivillius phase (Bi2O2)2+ (BiM(W1−NMoN)M−1O3M+1)2− is the predominantly observed crystal structure, indicating that the thin films in the library are solid solutions. With increasing amounts of Mo ≙ 7–22% the diffraction peak at 2θ = 28° ≙ [131] shifts due to lattice distortion, the photoelectrochemical activity is increasing up to a wavelength of 460 nm with an incident photon to current efficiency (IPCE) of 4.5%, and the bandgap decreases. A maximum photocurrent density of 31 μA/cm2 was measured for Bi31W62Mo7Oz at a bias potential of 1.23 V vs. RHE (0.1 M Na2SO4).

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Effect of pH in the Hydrothermal Preparation of Bi2WO6 Nanostructures

In this study, Bi2WO6 was prepared by the hydrothermal method. The effects of reaction temperature (150/170/200 °C) and reaction time (6/12/24 h) were investigated. The role of strongly acidic pH (1 >) and the full range between 0.3 and 13.5 were studied first. Every sample was studied by XRD and SEM; furthermore, the Bi2WO6 samples prepared at different temperatures were examined in detail by EDX and TEM, as well as FT-IR, Raman and UV-vis spectroscopies. It was found that changing the temperature and time slightly influenced the crystallinity and morphology of the products. The most crystallized product formed at 200 °C, 24 h. The pure, sheet-like Bi2WO6, prepared at 200 °C, 24 h, and 0.3 pH, gradually transformed into a mixture of Bi2WO6 and Bi3.84W0.16O6.24 with increasing pH. The nanosheets turned into a morphology of mixed shapes in the acidic range (fibers, sheets, irregular forms), and became homogenous cube- and octahedral-like shapes in the alkaline range. Their band gaps were calculated and were found to vary between 2.66 and 2.59 eV as the temperature increased. The specific surface area measurements revealed that reducing the temperature favors the formation of a larger surface area (35.8/26/21.6 m2/g belonging to 150/170/200 °C, respectively).

Sonochemical versus hydrothermal synthesis of bismuth tungstate nanostructures: Photocatalytic, sonocatalytic and sonophotocatalytic activities

In the present work, an ultrasound-assisted hydrothermal method was applied as a new approach for the synthesis of Bi₂WO₆ nanostructures. In sonication, a cup horn system as an indirect high intensity sonicator was used. To determine the influence of ultrasonic waves on the morphology, Bi₂WO₆ was also synthesized using the hydrothermal method. The conventional and sonochemical products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR), Raman, photoluminescence (PL), and UV-Vis (UV-Vis) spectroscopies. The XRD patterns confirmed that the sonosynthesized sample has higher crystallinity than the conventional one. The results also showed that ultrasound decreased the particle size and improved the size distribution. In comparison with the hydrothermal sample, the flower like structures formed under sonication have many hollow sites, resulting in higher harvesting and scattering of visible light. The efficiency of resulting nanoparticles in degradation of a binary mixture (RhB/MB) as pollutant was evaluated by photocatalytic, sonocatalytic, and sonophotocatalytic processes. The sono-synthesized sample removed the pollutants four times faster than the hydrothermal sample in sonophocatalytic process. Besides, determining factors including pH, pollutant concentration, temperature, and ultrasound amplitude were optimized in the sonophotocatalytic process.

Bi2MoO6/BiFeO3 heterojunction nanofibers: Enhanced photocatalytic activity, charge separation mechanism and magnetic separability

Uniform Bi₂MoO₆ nanosheets were grown in a high dispersed fashion on electrospun BiFeO₃ nanofibers via a solvothermal technique. The loading amount of Bi₂MoO₆ in the Bi₂MoO₆/BiFeO₃ heterojunction nanofibers could be controlled by adjusting the precursor concentrations in the solvothermal process. The XPS analysis, energy band position calculation and trapping experiments all proved that the Bi₂MoO₆/BiFeO₃ heterojunction is a Z-scheme heterojunction. The Z-scheme Bi₂MoO₆/BiFeO₃ heterojunction had a much higher photocatalytic activity in the visible-light photodegradation of Rhodamine B (RhB) and tetracycline hydrochloride (TC) than pure BiFeO₃ nanofibers or pure Bi₂MoO₆ nanosheets. The enhanced photocatalytic activity was attributed to the formation of Z-scheme Bi₂MoO₆/BiFeO₃ heterojunctions, which could be beneficial to the separation of photogenerated electron-hole pairs. Moreover, the Bi₂MoO₆/BiFeO₃ heterojunction nanofibers could be easily separated under an external magnetic field via the ferromagnetic BiFeO₃. After several cycles, the photocatalytic activity of the Bi₂MoO₆/BiFeO₃ heterojunction no longer significantly decreased suggesting that the Bi₂MoO₆/BiFeO₃ heterojunction is stable. These Z-scheme Bi₂MoO₆/BiFeO₃ heterojunction nanofibers with highly visible-light photocatalytic activity, excellent chemical stability and magnetic separability could be useful in many practical applications.

The controllable fabrication of a novel hierarchical nanosheet-assembled Bi2MoO6 hollow micronbox with ultra-high surface area for excellent solar to chemical energy conversion

In this study, we demonstrated that a novel controllable nano-sheet assembled Bi₂MoO₆ micronbox had higher activity for nitrogen fixation and dye degradation.

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.

Fabrication of porous nanoflake BiMO x (M = W, V, and Mo) photoanodes via hydrothermal anion exchange

Most Bi-based photoelectrodes have suitable band gaps and can effectively promote the water oxidation reaction. However, simple preparation methods for Bi-based binary metal oxides as photoanodes are scarce. This paper describes a simple hydrothermal anion exchange method to synthesize Bi-based binary metal oxides with controlled morphologies. This synthesis process uses BiOI as the template and Bi source, which is eventually converted to Bi-based porous nanoflake photoanodes upon reaction with MO _x (M = W, V, and Mo)-containing precursors. The photoanodes show well-shaped porous nanoflake morphologies and exhibit impressive photoelectrochemical properties compared to Bi-based photoanodes synthesized by conventional methods. These three samples possess long-term stability under solar irradiation and show considerable photocurrent for sulfite oxidation.

Intensification of ultrasound-assisted process for the preparation of spindle-shape sodium zinc molybdate nanoparticles

In the present work, sodium zinc molybdate (SZM) nanoparticles were prepared using conventional and an innovative ultrasound assisted co-precipitation of sodium molybdate, zinc oxide and HNO3 at different temperatures. Prepared product was characterized by XRD, TEM, FT-IR, particle size distribution (PSD), TGA and DTA techniques. TEM analysis shows the spindle-shaped morphology of the formed SZM nanoparticles. The average particle size of SZM nanoparticles is found to be lower in case of sonochemical method (78.3 nm) compared to conventional method (340.2 nm) which is attributed to faster solute transfer rate due to ultrasonic irradiation leading to rapid nucleation and restricted growth of SZM nanoparticles. Further, the kinetics of synthesis of SZM nanoparticles are studied using the sonochemical method at different operating temperature and conventional method at 80°C. It is shown that the rate of reaction is significantly faster at 40°C compared to other temperatures and also conventional method. This can be attributed to intense cavity collapse at lower temperature (low vapour pressure) compared to higher temperature (high vapour pressure) of the reaction mixture.

Synthesis of novel flower-like PtCo–Bi2MoO6 photocatalysts with enhanced visible light photocatalytic performance

A novel PtCo/Bi₂MoO₆ composite photocatalyst was successfully synthesized by loading PtCo alloy nanoparticles via a simple polyol reduction method.

Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials

Bi₂WO₆ and Bi₂WO₆–TiO₂ were synthesized, platinised and evaluated in the photocatalytic reduction of CO₂. The methane yield was greatly improved by platinisation and TiO₂ addition. Blue phosphors enhanced the system stability.

N-type hedgehog-like CuBi2O4 hierarchical microspheres: room temperature synthesis and their photoelectrochemical properties

N-type hedgehog-like CuBi₂O₄ hierarchical microspheres are synthesized at room temperature and show an enhanced photoresponse to visible light, with enhanced light trapping properties derived from the omni-directionally grown nanorods.

Different Surfactants-Assisted Hydrothermal Fabrication and Photocatalytic Properties of Bi2MoO6for Methylene Blue Degradation under Simulated Sunlight Irradiation

Bi2MoO6single-crystallites were synthesized by a simple hydrothermal method in the presence of surfactant sodium dodecyl sulfate (SDS), polyvinyl pyrrolidone (PVP), or cetyl trimethyl ammonium bromide (CTAB). The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) techniques. The photocatalytic activities of the as-fabricated Bi2MoO6samples were measured for the degradation of methylene blue (MB) under the Xe light illumination. It is shown that the introduction of surfactant have a crucial influence on the size and morphology of the Bi2MoO6product. Among the as-fabricated Bi2MoO6samples, the ones derived hydrothermally with CTAB showed outstanding photocatalytic activities for the addressed reaction under simulated sunlight irradiation, attributed to the ultrafine nanocrystals and the higher surface areas.

Production of cerium zinc molybdate nano pigment by innovative ultrasound assisted approach

Ultrasound assisted synthesis of yellow rare earth cerium zinc molybdate anticorrosion nanopigment is presented. This new class of pigment is eco-friendly alternatives to lead, cadmium and chromium pigment as these pigments contains carcinogenic species like Cr(6+) which is responsible for human disease. The synthesis of nanosized cerium zinc molybdate was carried out using cerium nitrate, sodium zinc molybdate as a precursor materials by conventional and ultrasound assisted chemical precipitation method without addition of emulsification agent. XRD, FTIR and elemental analysis confirm the formation of cerium zinc molybdate nanoparticles. The conductivity results indicate that conventional synthesis takes longer time, while in sonochemical technique (US), reaction completes within short period of time. Improved solute transfer rate, rapid nucleation, and formation of large number of nuclei are attributed to presence of cavitation. Saturation of the Ce(3+) ions reaches earlier in case of sonochemical technique which restricts the growth of particles hence smaller size is obtained. The crystallite size of cerium zinc molybdate was found to be 27nm from XRD analysis.