Carbon-modified BiVO4 microtubes embedded with Ag nanoparticles have high photocatalytic activity under visible light

Facile Hydrothermal Synthesis of BiVO4/MWCNTs Nanocomposites and Their Influences on the Biofilm Formation of Multidrug Resistance Streptococcus mutans and Proteus mirabilis

This study utilized a simple hydrothermal technique to prepare pure BiVO4 and tightly bound BiVO4/multiwalled carbon nanotubes (MWCNTs) nanocomposite materials. The surfactant was employed to control the growth, size, and assembly of BiVO4 and the nanocomposite. Various techniques including X-ray diffraction (XRD), Ultraviolet-visible (UV-vis), photoluminescence (PL), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were utilized to analyze and characterize BiVO4 and the BiVO4/MWCNTs nanocomposite. Through XRD analysis, it was found that the carbon nanotubes were effectively embedded within the lattice of BiVO4 without generating any separate impurity phase and had no influence on the BiVO4 monoclinic structure. TEM images confirmed the presence of MWCNTs within BiVO4. Furthermore, adding MWCNTs in the BiVO4/MWCNTs nanocomposite resulted in an effective charge transfer transition and improved carrier separation, as evidenced by PL analysis. The introduction of MWCNTs also led to a significant reduction in the optical band gap due to quantum effects. Finally, the antibacterial activity of pure BiVO4 and the BiVO4/MWCNTs nanocomposite was assessed by exposing Proteus mirabilis and Streptococcus mutans to these materials. Biofilm inhibition and antibiofilm activity were measured using a crystal violet assay and a FilmTracer LIVE/DEAD Biofilm Viability Kit. The results demonstrated that pure BiVO4 and BiVO4/MWCNTs effectively inhibited biofilm formation. In conclusion, both pure BiVO4 and BiVO4/MWCNTs are promising materials for inhibiting the bacterial biofilm during bacterial infections.

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.

Synergistic removal of organic pollutants from water by CTF/BiVO4 heterojunction photocatalysts

Herein, a series of covalent triazine framework/bismuth vanadate (CTF/BiVO₄) heterojunction catalysts were prepared using the hydrothermal method. The mechanism of the CTF/BiVO₄ heterojunction photocatalyst in the system was examined to provide a theoretical basis for constructing a high-efficiency photocatalysis composite system for removing organic pollutants from water. Compared with CTF and BiVO₄ catalysts alone, composite materials have been shown to have significantly higher degradation efficiencies against organic pollutants in water. Moreover, the degradation effect was found to be optimal when the mass ratio of CTF to BiVO₄ was 1:1 (1-CTF/BiVO₄). On the basis of physicochemical characterization results, it was concluded that the effective construction of CTF/BiVO₄ composite photocatalyst material systems and the formation of type II heterojunction structures between CTF and BiVO₄ effectively promote the separation of photogenerated carriers and increase the interface charge transfer efficiency.

Facile Preparation of a Bispherical Silver-Carbon Photocatalyst and Its Enhanced Degradation Efficiency of Methylene Blue, Rhodamine B, and Methyl Orange under UV Light

The combination of organic and inorganic materials is attracting attention as a photocatalyst that promotes the decomposition of organic dyes. A facile thermal procedure has been proposed to produce spherical silver nanoparticles (AgNPs), carbon nanospheres (CNSs), and a bispherical AgNP-CNS nanocomposite. The AgNPs and CNSs were each synthesized from silver acetate and glucose via single- and two-step annealing processes under sealed conditions, respectively. The AgNP-CNS nanocomposite was synthesized by the thermolysis of a mixture of silver acetate and a mesophase, where the mesophase was formed by annealing glucose in a sealed vessel at 190 °C. The physicochemical features of the as-prepared nanoparticles and composite were evaluated using several analytical techniques, revealing (i) increased light absorption, (ii) a reduced bandgap, (iii) the presence of chemical interfacial heterojunctions, (iv) an increased specific surface area, and (v) favorable band-edge positions of the AgNP-CNS nanocomposite compared with those of the individual AgNP and CNS components. These characteristics led to the excellent photocatalytic efficacy of the AgNP-CNS nanocomposite for the decomposition of three pollutant dyes under ultraviolet (UV) radiation. In the AgNP-CNS nanocomposite, the light absorption and UV utilization capacity increased at more active sites. In addition, effective electron-hole separation at the heterojunction between the AgNPs and CNSs was possible under favorable band-edge conditions, resulting in the creation of reactive oxygen species. The decomposition rates of methylene blue were 95.2, 80.2, and 73.2% after 60 min in the presence of the AgNP-CNS nanocomposite, AgNPs, and CNSs, respectively. We also evaluated the photocatalytic degradation efficiency at various pH values and loadings (catalysts and dyes) with the AgNP-CNS nanocomposite. The AgNP-CNS nanocomposite was structurally rigid, resulting in 93.2% degradation of MB after five cycles of photocatalytic degradation.

Synthesis of Ce0.1La0.9MnO3 Perovskite for Degradation of Endocrine-Disrupting Chemicals under Visible Photons

The UN Environmental Protection Agency has recognized 4-n-Nonylphenol (NP) and bisphenol A (BPA) as among the most hazardous chemicals, and it is essential to minimize their concentrations in the wastewater stream. These industrial chemicals have been witnessed to cause endocrine disruption. This report describes the straightforward hydrothermal approach adopted to produce Ce0.1La0.9MnO3 (CLMO) perovskite’s structure. Several physiochemical characterization approaches were performed to understand the Ce0.1La0.9MnO3 (CLMO) perovskite crystalline phase, element composition, optical properties, microscopic topography, and molecular oxidation state. Here, applying visible photon irradiation, the photocatalytic capability of these CLMO nanostructures was evaluated for the elimination of NP and BPA contaminants. To optimize the reaction kinetics, the photodegradation of NP and BPA pollutants on CLMO, perovskite was studied as a specification of pH, catalyst dosage, and initial pollutant concentration. Correspondingly, 92% and 94% of NP and BPA pollutants are degraded over CLMO surfaces within 120 and 240 min, respectively. Since NP and BPA pollutants have apparent rate constants of 0.0226 min−1 and 0.0278 min−1, respectively, they can be satisfactorily fitted by pseudo-first-order kinetics. The decomposition of NP and BPA contaminants is further evidenced by performing FT-IR analysis. Owing to its outstanding photocatalytic execution and simplistic separation, these outcomes suggest that CLMO is an intriguing catalyst for the efficacious removal of NP and BPA toxicants from the aqueous phase. This is pertinent for the treatment of endocrine-disrupting substances in bioremediation.

Carbon hollow matrix anchored by isolated transition metal atoms serving as a single atom cocatalyst to facilitate the water oxidation kinetics of bismuth vanadate

Here, nitrogen doped carbon hollow matrix anchored by isolated transition metal atoms (M@NC, M = Fe, Co or Ni) are firstly utilized as new single atom cocatalysts (SACCs) to enhance the PEC performance of Mo, W ions co-doped BiVO₄ (Mo, W: BVO) through a simple spin-coating method. It is found that Mo, W: BVO modified with Fe@NC exhibits higher photocurrent density than the one decorated with Co@NC or Ni@NC due to the relatively low redox potential of Fe³⁺/Fe²⁺ (0.77 V vs SHE). During the photoelectrochemical (PEC) process, the Fe²⁺ ions are easier to accept the photogenerated holes of BVO and be oxidized to Fe³⁺ ions. Then, Fe³⁺ ions are reduced to Fe²⁺ again by accepting the electrons of water, and evolve oxygen simultaneously. Hence, Fe@NC could facilitate the water oxidation kinetics through the redox cycle of Fe ions and promote the charge separation efficiency by capturing the photogenerated holes. Theoretical calculations demonstrate that the deposition of Fe atoms make NC negatively charged, which is conducive to receiving the photogenerated holes. As a result, Mo, W: BVO/Fe@NC exhibits higher photocurrent density (3.2 mA/cm² vs RHE) than other BVO-based samples. This work opens up a new application field of SACCs serving as OER cocatalysts, and may provide a universal strategy to construct the efficient PEC photoelectrodes.

Strong Light-Matter Interactions in Au Plasmonic Nanoantennas Coupled with Prussian Blue Catalyst on BiVO4 for Photoelectrochemical Water Splitting

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO₄ ) nanostructures, yielding Au-capped BiVO₄ (Au-BiVO₄ ). The formation of multiple size/dimension Au capping islands provides strong light-matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO₄ (through the excitation of Fabry-Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub-band-gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au-BiVO₄ /PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO₄ photoanode was obtained as 190 μA cm^-2 , whereas it was boosted to 295 μA cm^-2 and 1800 μA cm^-2 for Au-BiVO₄ and Au-BiVO₄ /PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic-based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs.

An integrating photoanode consisting of BiVO4, rGO and LDH for photoelectrochemical water splitting

The photoanode of BiVO₄/rGO/NiFe-LDH was fabricated by a facile electrodeposition method, and it showed excellent photoelectrochemical properties for solar water splitting, benefitting from the formation of heterojunctions and the decoration of rGO.

Bismuth vanadate-based semiconductor photocatalysts: a short critical review on the efficiency and the mechanism of photodegradation of organic pollutants

The number of publications on photocatalytic bismuth vanadate-based materials is constantly increasing. Indeed, bismuth vanadate is gaining stronger interest in the photochemical community since it is a solar-driven photocatalyst. However, the efficiency of BiVO₄-based photocatalyst under sunlight is questionable: in most of the studies investigating the photodegradation of organic pollutants, only few works identify the by-products and evaluate the real efficiency of BiVO₄-based materials. This short review aims to (i) present briefly the principles of photocatalysis and define the photocatalytic efficiency and (ii) discuss the formation of reactive species involved in the photocatalytic degradation process of pollutants and thus the corresponding photodegradation mechanism could be determined. All these points are developed in a comprehensive discussion by focusing especially on pure, doped, and composite BiVO₄. Therefore, this review exhibits a critical overview on different BiVO₄-based photocatalytic systems with their real efficiency. This is a necessary knowledge for potential implementation of BiVO₄ materials in environmental applications at larger scale than laboratory conditions.

Visible-light-induced Ag/BiVO4 semiconductor with enhanced photocatalytic and antibacterial performance

An Ag-loaded BiVO₄ visible-light-driven photocatalyst was synthesized by the microwave hydrothermal method followed by photodeposition. The photocatalytic performance of the synthesized samples was evaluated on a mixed dye (methylene blue and rhodamine B), as well as bisphenol A in aqueous solution. Similarly, the disinfection activities of synthesized samples towards the Gram-negative Escherichia coli (E. coli) in a model cell were investigated under irradiation with visible light (λ ≥ 420 nm). The synthesized samples have monoclinic scheelite structure. Photocatalytic results showed that all Ag-loaded BiVO₄ samples exhibited greater degradation and a higher mineralization rate than the pure BiVO₄, probably due to the presence of surface plasmon absorption that arises due to the loading of Ag on the BiVO₄ surface. The optimum Ag loading of 5 wt% has the highest photocatalytic performance and greatest stability with pseudo-first-order rate constants of 0.031 min^-1 and 0.023 min^-1 for the degradation of methylene blue and rhodamine B respectively in a mixture with an equal volume and concentration of each dye. The photocatalytic degradation of bisphenol A reaches 76.2% with 5 wt% Ag-doped BiVO₄ within 180 min irradiation time. Similarly, the Ag-loaded BiVO₄ could completely inactivate E. coli cells within 30 min under visible light irradiation. The disruption of the cell membrane as well as degradation of protein and DNA exhibited constituted evidence for antibacterial activity towards E. coli. Moreover, the bactericidal mechanisms involved in the photocatalytic disinfection process were systematically investigated.

Preparation and Characterization of Mo Doped in BiVO₄ with Enhanced Photocatalytic Properties

Molybdenum (Mo) doped BiVO₄ was fabricated via a simple electrospun method. Morphology, structure, chemical states and optical properties of the obtained catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), N₂ adsorption–desorption isotherms (BET) and photoluminescence spectrum (PL), respectively. The photocatalytic properties indicate that doping Mo into BiVO₄ can enhance the photocatalytic activity and dark adsorption ability. The photocatalytic test suggests that the 1% Mo-BiVO₄ shows the best photocatalytic activity, which is about three times higher than pure BiVO₄. Meanwhile, 3% Mo-BiVO₄ shows stronger dark adsorption than pure BiVO₄ and 1% Mo-BiVO₄. The enhancement in photocatalytic property should be ascribed to that BiVO₄ with small amount of Mo doping could efficiently separate the photogenerated carries and improve the electronic conductivity. The high concentration doping would lead the crystal structure transformation from monoclinic to tetragonal phase, as well as the formation of MoO₃ nanoparticles on the BiVO₄ surface, which could also act as recombination centers to decrease the photocatalytic activity.

One-step synthesis of composite material MWCNT@BiVO4 and its photocatalytic activity

In this research, a composite material (MWCNT@BiVO₄) was prepared using a one step hydrothermal method.

Preparation of a Microspherical Silver-Reduced Graphene Oxide-Bismuth Vanadate Composite and Evaluation of Its Photocatalytic Activity

A novel Ag-reduced graphene oxide (rGO)-bismuth vanadate (BiVO₄) (AgGB) ternary composite was successfully synthesized via a one-step method. The prepared composite was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Brunauer-Emmett-Teller (BET) surface area measurement, Raman scattering spectroscopy, and ultraviolet-visible diffuse-reflection spectroscopy (UV-vis DRS). The results showed that bulk monoclinic needle-like BiVO₄ and Ag nanoparticles with a diameter of approximately 40 nm formed microspheres (diameter, 5–8 μm) with a uniform size distribution that could be loaded on rGO sheets to facilitate the transport of electrons photogenerated in BiVO₄, thereby reducing the rate of recombination of photogenerated charge carriers in the coupled AgGB composite system. Ag nanoparticles were dispersed on the surface of the rGO sheets, which exhibited a localized surface plasmon resonance phenomenon and enhanced visible light absorption. The removal efficiency of rhodamine B dye by AgGB (80.2%) was much higher than that of pure BiVO₄ (51.6%) and rGO-BiVO₄ (58.3%) under visible light irradiation. Recycle experiments showed that the AgGB composite still presented significant photocatalytic activity after five successive cycles. Finally, we propose a possible pathway and mechanism for the photocatalytic degradation of rhodamine B dye using the composite photocatalyst under visible light irradiation.

Flexible Tricolor Flag-liked Microribbons Array with Enhanced Conductive Anisotropy and Multifunctionality

Anisotropically conductive materials are important components in subminiature devices. However, at this stage, some defects have limited practical applications of them, especially low anisotropic degree and high cost. Here, we report novel tricolor flag-liked microribbons array prepared by electrospinning technique. The tricolor flag-liked microribbons array is composed of parallel microribbons, and each microribbon consists of three different regions, just like tricolor flag. The tricolor flag-liked microribbons array is only electrically conductive in the direction parallel to the microribbons, whereas in the perpendicular and thickness directions are insulative. The electrical conductivity along parallel direction reaches up to 8 orders of magnitude higher than that along perpendicular direction. The degree of anisotropy in present study is increased by 2 orders of magnitude than that of the anisotropically conductive material in references reported before. Besides, other functions can be conveniently assembled into tricolor flag-liked microribbons array to realize multifunctionality. Owing to the high electrical anisotropy and multifunctionality, tricolor flag-liked microribbons array will have important applications. Furthermore, a universal technique to prepare microribbons with three functional regions has been established for fabricating excellent multifunctional materials.

One-dimensional Bi2O3 QD-decorated BiVO4 nanofibers: electrospinning synthesis, phase separation mechanism and enhanced photocatalytic performance

In this work, we design and successfully fabricate novel Bi₂O₃ quantum dot (QD)-decorated BiVO₄ nanofibers by electrospinning. Furthermore, it exhibits enhanced photocatalytic activities by promoting the separation of photoinduced electrons and holes.

Nanostructured bismuth vanadate-based materials for solar-energy-driven water oxidation: a review on recent progress

Water oxidation is the key step for both photocatalytic water splitting and CO₂ reduction, but its efficiency is very low compared with the photocatalytic reduction of water. Bismuth vanadate (BiVO₄) is the most promising photocatalyst for water oxidation and has become a hot topic for current research. However, the efficiency achieved with this material to date is far away from the theoretical solar-to-hydrogen conversion efficiency, mainly due to the poor photo-induced electron transportation and the slow kinetics of oxygen evolution. Fortunately, great breakthroughs have been made in the past five years in both improving the efficiency and understanding the related mechanism. This review is aimed at summarizing the recent experimental and computational breakthroughs in single crystals modified by element doping, facet engineering, and morphology control, as well as macro/mesoporous structure construction, and composites fabricated by homo/hetero-junction construction and co-catalyst loading. We aim to provide guidelines for the rational design and fabrication of highly efficient BiVO₄-based materials for water oxidation.

Highly dispersed palladium nanoparticles anchored on UiO-66(NH₂) metal-organic framework as a reusable and dual functional visible-light-driven photocatalyst

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of about 3-6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH₂) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH₂) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(vi) compared with UiO-66(NH₂) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron-hole pairs. More significantly, the Pd@UiO-66(NH₂) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(vi) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts.