Photocatalytic Degradation of Crystal Violet on Cu, Zn Doped BiVO4 Particles

Fabrication of codoped photocatalysts is a developing area of research. Herein, we explore the visible light photocatalytic properties of Cu, Zn codoped BiVO4 particles. Doping lower valent cations (Cu and Zn) makes the BiVO4 surface more acidic and enables us to target the basic crystal violet (CV) dye. The adopted hydrothermal protocol of synthesis results in the formation of Cu-Zn codoped monoclinic BiVO4 particles. Undoped monoclinic BiVO4, prepared by the same protocol, showed significant formation of oxygen vacancies. XPS analyses confirm the coexistence of Cu2+/Cu+ and Zn2+ dopants. Increased dopant percentage reduced oxygen vacancies. XRD indicates that Cu2+/Cu+ or Zn2+ dopants generally substitute Bi3+ in BiVO4. All photocatalysis activities for CV degradation are reported under near-neutral pH conditions. A typical codoped BiVO4 photocatalyst with 1% Zn and 2% Cu demonstrated the best CV degradation photocatalytic activity. The activity of this Zn, Cu codoped photocatalyst is better than that of pure, Zn-doped, and Cu-doped BiVO4 samples. Active species trapping experiments indicated the possible photocatalysis mechanism. The photocatalysts exhibited appropriate recyclability and photostability.

Graphene-based photocatalysts for degradation of organic pollution

Compared with the traditional wastewater treatment technology, semiconductor photocatalysis is a rapidly emerging environment-friendly and efficient Advanced Oxidation Process for degradation of refractory organic contaminants. Single-component semiconductor photocatalysts exhibit poor photocatalytic performance and cannot meet the requirements of wastewater treatment. The combination of semiconductor photocatalysts and Graphene can effectively improve the photocatalytic activity and stability of semiconductor photocatalysts. This review focuses on the synergistic effect of several types of semiconductors with Graphene for photocatalytic degradation of organic pollutants. After a brief introduction of the photodegradation mechanism of semiconductor materials and the basic description of Graphene, the synthesis, characterization and degradation performance of various Graphene-based semiconductor photocatalysts are emphatically introduced.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts

Bi₅O₇I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi₅O₇I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi₅O₇I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi₅O₇I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi₅O₇I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi₅O₇I were also developed to further boost the efficiency of Bi₅O₇I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi₅O₇I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

Construction of 1T-MoS2 quantum dots-interspersed (Bi1-x Fe x )VO4 heterostructures for electron transport and photocatalytic properties

The present study reports trigonal phase molybdenum disulfide quantum dots (MoS2/QDs)-decorated (Bi1-x Fe x )VO4 composite heterostructures. Initially, (Bi1-x Fe x )VO4 heterostructure nanophotocatalysts were synthesized through the hydrothermal method decorated with 1T-MoS2 via a sonication process. 1T-MoS2@(Bi1-x Fe x )VO4 heterostructures were characterized in detail for phase purity and crystallinity using XRD and Raman spectroscopy. The Raman mode evaluation indicated monoclinic, mixed monoclinic-tetragonal and tetragonal structure development with increasing Fe concentration. For physiochemical properties, SEM, EDX, XPS, PL, EPR, UV-visible and BET techniques were applied. The optical energy band gaps of 1T-MoS2@(Bi1-x Fe x )VO4 heterostructures were calculated using the Tauc plot method. It shows a blue shift initially within a monoclinic structure then a red shift with an increase of Fe concentration. 1T-MoS2@(Bi40Fe60)VO4 with 2 wt% of 1T-MoS2-QDs carrying a mixed phase exhibited higher photocatalytic activity. The enhanced photocatalytic activity is attributed to the higher electron transportation from (Bi1-x Fe x )VO4 surface onto 1T-MoS2 surface, consequently blocking the fast electron-hole recombination within (Bi1-x Fe x )VO4. 1T-MoS2 co-catalyst interaction with (Bi1-x Fe x )VO4 enhanced the light absorption in the visible region. The close contact of small 1T-MoS2-QDs with (Bi1-x Fe x )VO4 develops a high degree of crystallinity, with fewer defects showing mesoporous/nanoporous structures within the heterostructures which allows more active sites. Herein, the mechanism involved in the synthesis of heterostructures and optimum conditions for photocatalytic degradation of crystal violet dye are explored and discussed thoroughly.

Bi2O3/BiVO4@graphene oxide van der Waals heterostructures with enhanced photocatalytic activity toward oxygen generation

The van der Waals (vdW) integration enables to create heterostructures with intimate contact and bring new opportunities. However, it is not confined to layered materials but can also be generally extended to 3D materials. Multidimensional Bi₂O₃/BiVO₄@graphene oxide (GO) van der Waals heterostructures are synthesized by one-pot wet chemistry method. Bi₂O₃/BiVO₄ composite nanoparticles are self-assembled with GO framework by vdW interaction to form vdW heterostructures, in which GO framework allows short electron transport distance and rapid charge transfer and provides massive reactive sites. Such self-assembled heterostructures show a superior high photoactivity towards oxygen evolution with an enhanced oxygen generation rate of 1828 µmol h^-1 g^-1, nearly 3 times than that of pure BiVO₄, attributed to the accelerated charge separation and transfer processes of Bi₂O₃/BiVO₄@GO vdW heterostructures. This study indicates that our strategy provides a new avenue towards fabricating multi-dimensional vdW heterostructures and inspiring more innovative insights in oxygen evolution field.

Influence of the Chemical Compositions of Bismuth Oxyiodides on the Electroreduction of Carbon Dioxide to Formate

Bismuth oxyiodides with varying chemical compositions were fabricated to effectively electrochemical reduce CO₂ to formate. Bi₅ O₇ I and Bi₇ O₉ I₃ nanosheets assemble irregularly, and BiOI nanosheets form a sphere-like structure. Compared with BiOI and Bi₇ O₉ I₃ , Bi₅ O₇ I exhibits an excellent Faradaic efficiency of 89 % for formate production with the partial current density of 13.2 mA/cm² at -0.89 V vs. RHE owing to the elevated amounts of Bi metal sites reduced from Bi³⁺ during electrolysis. The partial current densities of formate on BiOI were higher than those on Bi₇ O₉ I₃ which is attributed to the higher iodine content. The synergistic effect of bismuth and iodine of bismuth oxyiodides is responsible for their electrocatalytic properties during CO₂ reduction in aqueous solutions.

Bismuth-rich bismuth oxyiodide microspheres with abundant oxygen vacancies as an efficient photocatalyst for nitrogen fixation

A combined bismuth-rich and defect introduction strategy was used to prepare the H-Bi₅O₇I with abundant oxygen vacancies, which can effectively yield ammonia under visible light without any organic scavengers or noble-metal cocatalysts.

In situ preparation of g-C3N4/Bi4O5I2 complex and its elevated photoactivity in Methyl Orange degradation under visible light

A graphite carbon nitride (g-C₃N₄) modified Bi₄O₅I₂ composite was successfully prepared in-situ via the thermal treatment of a g-C₃N₄/BiOI precursor at 400°C for 3 hr. The as-prepared g-C₃N₄/Bi₄O₅I₂ showed high photocatalytic performance in Methyl Orange (MO) degradation under visible light. The best sample presented a degradation rate of 0.164 min^-1, which is 3.2 and 82 times as high as that of Bi₄O₅I₂ and g-C₃N₄, respectively. The g-C₃N₄/Bi₄O₅I₂ was characterized by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (DRS), electrochemical impedance spectroscopy (EIS) and transient photocurrent response in order to explain the enhanced photoactivity. Results indicated that the decoration with a small amount of g-C₃N₄ influenced the specific surface area only slightly. Nevertheless, the capability for absorbing visible light was improved measurably, which was beneficial to the MO degradation. On top of that, a strong interaction between g-C₃N₄ and Bi₄O₅I₂ was detected. This interplay promoted the formation of a favorable heterojunction structure and thereby enhanced the charge separation. Thus, the g-C₃N₄/Bi₄O₅I₂ composite presented greater charge separation efficiency and much better photocatalytic performance than Bi₄O₅I₂. Additionally, g-C₃N₄/Bi₄O₅I₂ also presented high stability. •O₂^- and holes were verified to be the main reactive species.

Bi4O5I2/nitrogen-doped hierarchical carbon (NHC) composites with tremella-like structure for high photocatalytic performance

BiOI is a visible photocatalyst towards organic pollutant. In this work, biomass waste (withered typha grass) was used to fabricate nitrogen-doped hierarchical carbon (NHC) by an one-step carbonization route. Then NHC provided a good carrier to load the BiOI semiconductor materials by a green simple co-precipitation method, after adding NaOH solution, the irregular microspheres BiOI/NHC was gradually etched by OH^- to form the tremella-like Bi₄O₅I₂/NHC. The well-defined tremella-like Bi₄O₅I₂/NHC invested adequate interface and high particular surface range (S_BET: 66 m² g^-1), which is higher than pure BiOI (22 m² g^-1) and Bi₄O₅I₂ (17 m² g^-1). Multiple synergistic effects, such as high S_BET can give more dynamic destinations, the special tremella-like structure can assimilate more reflected occurrence light of other nanosheets, low I content can increase the conduction/valence band gap of semiconductor materials and NHC can act as an electron acceptor, making as-prepared Bi₄O₅I₂/NHC composite ideal candidates for photocatalysis. The degradation rate of Bi₄O₅I₂/NHC reaches up to 87.4% of methyl orange in 2 h, which is about 2 times higher than BiOI and Bi₄O₅I₂. Therefore, this work gives a technique to link NHC derived from biomass waste to Bi₄O₅I₂ with highly-efficiency photocatalytic performance.

Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts

Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.

BiOCl facilitated photocatalytic degradation of atenolol from water: Reaction kinetics, pathways and products

Atenolol (ATL), a kind of largely used beta-blockers, has been widely detected in the aquatic environment, which could cause adverse impact on human beings. In this study, bismuth oxychloride (BiOCl) photocatalyst was synthesized and applied to remove ATL in the aqueous system under simulated natural light. Emphasis was laid on the reaction kinetics and the impact of natural organic matter (NOM) (0-20 mg/L). Possible transformation pathways were systematically investigated based on identification of reaction products via liquid chromatography-mass spectrometry (LC-MS). As a consequence, BiOCl presents highly photocatalytic efficiency yielding up to nearly 100% ATL conversion after 60 min of interaction, together with fairly high photostability evidenced by considerably efficient removal of ATL after 10 catalytic cycles. Four kinds of possible products are detected using LC-MS in the process of reaction, indicating possible transformation ways of ATL photocatalysis. NOM has an inhibiting impact on the removal of ATL and influences the products distribution. This study provides an emerging nanocatalyst for ATL photodegradation and could eventually lead to development of novel methods to control pharmaceutical contamination in water.

A bismuth oxide/graphene oxide nanocomposite membrane showing super proton conductivity and low methanol permeability

Proton exchange membrane fuel cells are still limited as state-of-art proton exchange membranes perform poorly at high and low temperature and are easily damaged by harsh electrochemical conditions such as reactive peroxide species. One effective solution to this issue is to develop new types of proton conductive materials that are capable of working in a broad temperature range. A simple vacuum-assisted filtration method is employed to obtain a well-ordered new proton-conducting membrane by immobilizing nanosized bismuth oxide clusters [H6Bi12O16] (NO3)10·6(H2O) {H6Bi12O16} onto graphene oxide (GO) supports (named as {H6Bi12O16}/GO). {H6Bi12O16}/GO is stable in acidic media and has high proton conductivity over the temperature range from -40 to 80 °C. The proton conductivity of the {H6Bi12O16}/GO membrane is 0.564 S cm-1 at 80 °C in aqueous solution (in plane), and 0.1 S cm-1 at 80 °C and 97% RH (out of plane), respectively. Without loss of high proton conductivity, the membrane also exhibited 100-fold lower methanol permeability than a Nafion 117 membrane. Moreover, {H6Bi12O16}/GO displayed good catalytic decomposition of hydrogen peroxide and superior humidity response and recovery properties. These advantages mean that {H6Bi12O16}/GO holds great promise as a solid-state electrolyte that can potentially be applied in energy conversion devices in the future.

Band gap engineering of BiOI via oxygen vacancies induced by graphene for improved photocatalysis

A reduced graphene oxide–bismuth iodide oxide (rGO–BiOI) composite was prepared by a thermal reduction method.

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Green synthesis of catalytic gold/bismuth oxyiodide nanocomposites with oxygen vacancies for treatment of bacterial infections

We have developed a simple and green solution for the synthesis of catalytic gold-doped bismuth oxyiodide (Au/BiOI) nanocomposites at room temperature from an aqueous mixture of gold ions, bismuth ions, and iodide ions. Au nanoparticles (NPs) were formed in situ and doped into BiOI nanosheets. The oxygen vacancies generated in BiOI give rise to its oxidase-like activity, and Au doping facilitated the reaction leading to a 4-fold higher oxidase-like activity of the Au/BiOI nanocomposite. The Au/BiOI nanocomposites showed wide spectrum antimicrobial activity not only against non-multidrug-resistant E. coli, K. pneumoniae, S. enteritidis, S. aureus, and B. subtilis bacteria, but also against multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The gold doping reduced the minimal inhibitory concentration value by ∼2000-fold for the Au/BiOI nanocomposite, in comparison with only BiOI nanoparticles. The bactericidal property of the Au/BiOI nanocomposite arose from the combined effect of the disruption of the bacterial membrane through a strong interaction of the nanocomposite with the bacteria and the generation of reactive oxygen species. Also, the Au/BiOI nanocomposite is highly biocompatible, which has been demonstrated in vitro by analysis of cytotoxicity and hemolysis, and in vivo by evaluating ocular tissue responses. Furthermore, intrastromal administration of Au/BiOI nanocomposites can effectively alleviate S. aureus-induced bacterial keratitis in rabbits, suggesting a significant disinfectant benefit in preclinical studies. The Au/BiOI nanocomposites show great potential for the inactivation of bacterial pathogens in an aqueous environment and treatment of bacterial infection-induced diseases.

Synthesis of Zn3(VO4)2/BiVO4 heterojunction composite for the photocatalytic degradation of methylene blue organic dye and electrochemical detection of H2O2

In this study, a Zn₃(VO₄)₂/BiVO₄ heterojunction nanocomposite photocatalyst was prepared using a hydrothermal route with different molar concentration ratios.

Heavy pnictogen chalcohalides: the synthesis, structure and properties of these rediscovered semiconductors

Heavy pnictogen chalcohalides offer various shades from the same palette, like “Paysage” by Nicolas de Staël. Their versatility and tunability lead to a new world of possible applications.

Visible light assisted photocatalytic degradation of crystal violet dye and electrochemical detection of ascorbic acid using a BiVO4/FeVO4 heterojunction composite

A highly pure BiVO₄/FeVO₄ heterojunction nanocomposite photocatalyst was synthesized by a facile hydrothermal method. The simple and economical manufacturing process allows easier industrial scale-up and the results contribute to the design of more effective photocatalysts.

Investigation on enhanced photocatalytic degradation of bisphenol A with bismuth oxyiodide catalyst using response surface methodology

In this study, Bi₇O₉I₃ photocatalyst was successfully synthesized via a simple and rapid microwave irradiation method. The characterization of prepared photocatalysts was determined by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The photocatalytic performance was determines by the degradation of bisphenol A (BPA) under xenon lamp illumination. The Bi₇O₉I₃ catalyst exhibited superior photocatalytic performance and the first-order kinetic rate constant of Bi₇O₉I₃ was about 4.2 times greater than that of BiOI. The enhanced photocatalytic activity was associated with surface morphology, suitable band gap energy and low recombination rate of electron–hole pairs. Furthermore, the photocatalytic efficiency of BPA with Bi₇O₉I₃ was systematically investigated using a three factor, three level Box–Behnken experimental design and response surface methodology (RSM). A quadratic polynomial model was proposed. Experimental and predicted values exhibited a good correlation with a predicted R² value of 0.9016. A relative significance study of three independent variables showed that catalyst dosage had the most significant positive effect on the degradation of BPA, followed by initial concentration of BPA and pH value. The prepared Bi₇O₉I₃ is a promising photocatalyst for practical application in organic pollutant decomposition.

Bi₇O₉I₃ was synthesized via a microwave irradiation method and the influence of different parameters on BPA degradation was investigated using a response surface methodology.