A Novel Heterostructure of BiOI Nanosheets Anchored onto MWCNTs with Excellent Visible-Light Photocatalytic Activity

Improvement of Photocatalytic Performance by Building Multiple Heterojunction Structures of Anatase-Rutile/BiOI Composite Fibers

In this study, multiple heterojunction structures of anatase-rutile/Bismuth oxyiodide (BiOI) composite fibers are designed by the combined method of electrospinning and hydrothermal techniques. The influence of different Ti/Bi atomic ratios ([Ti/Bi]) on the nanostructures and photocatalytic properties are investigated. It is found that the morphology of BiOI covered on the TiO₂ fiber surface changed with [Ti/Bi] from nanosheets to submicron spheres structures. Additionally, the crystallization of the composite fibers including the phases of anatase, rutile, and BiOI is identified, theses phases are in close contact with each other, and the interfacial effects are helpful to form the multiple heterojunctions which lead to blue shifts on the chemical state of Ti. The absorption of visible light has been improved by compositing BiOI on TiO₂, while the band gap values of the composite fibers are significantly reduced, which can enhance the generation and separation of electrons and holes. For the case of [Ti/Bi] = 1.57, the photodegradation rate of anatase-rutile/BiOI composite fibers is about 12 times that of pure TiO₂. For the photocatalytic mechanism, the synergistic s-type heterojunctions increase the content of active oxides which have a positive effect on the degradation rate.

New generation advanced nanomaterials for photocatalytic abatement of phenolic compounds

Nowadays, organic pollutants create severe problems worldwide. Phenolic compounds are the harmful pollutants that are developed from industrial effluents, thus causing several environmental problems. Low-cost materials show good potential capabilities for removal of phenolic compounds but are not so effective, so modification is required. New generation nanocatalysts are thought to be excellent for phenol removal. Removal of phenolic pollutants by photodegradation may lead to the decrement of these problematic groups. In this review, (i) a new generation of catalysts for the removal of phenolic compounds is discussed, (ii) nanocatalysts for photodegradation processes, and (iii) the mechanisms involved in photodegradation processes are also discussed. It is noticeable from the analysis that new generation catalysts for photodegradation processes have been demonstrated for high removal abilities of irrefutable phenolic compounds. Finally, future perspectives are also given in this article for the further development of next-generation catalysts.

Fabrication of a Heterobinuclear Redox Cycle to Enhance the Photocatalytic Activity of BiOCl

La3+ and Ni2+-doped BiOCl were prepared by sol–gel method and characterized by physicochemical and spectroscopic techniques. Their photocatalytic performances were investigated by the degradation of gentian violet under visible light. The results indicated that the co-doping of Ni and La significantly enhanced the photocatalytic performance of BiOCl. The photodegradation efficiency of LaNiBiOCl reached 95.5% in 105 min, which was 1.5 times that of BiOCl. This significant enhancement in photocatalytic activity was mainly attributed to the effective capture and transfer of photogenerated electrons between heterobinuclear La and Ni redox cycle, which benefited the photodegradation of active h+ and the formation of active •O2−. Furthermore, the photodegradation activity did not show an obvious drop after five recycles, indicating that LaNiBiOCl was a promising semiconductor photocatalyst for the degradation of gentian violet.

Recent advances in bismuth oxyhalide photocatalysts for degradation of organic pollutants in wastewater

Photocatalysis has been considered as an environmental-friendly strategy for degradation of organic pollutants to the nontoxic products of H2O and CO2. Compared to metal oxide semiconductors, BiOX (X = Cl, Br and I) photocatalysts exhibit some advantages, such as, unique layered structure, good chemical stability and superior photocatalytic activity. This review provides an overview on the controllable synthesis of BiOX-based photocatalysts and their application in photodegradation of organic pollutants. Firstly, the controllable synthesis of BiOX is introduced, including hydrothermal, solvothermal, hydrolysis, precipitation, two-phase methods, ultrasonic/microwave-assisted methods, and physical methods. Then, the doping and surface modification of BiOX are summarized, including non-metal doping, metal doping, dual doping, and the modification by introducing surface terminations or carriers. In addition, the heterojunctions of BiOX/BiOY and BiOX/Bi m O n X z are introduced. At last, the promising research trends of BiOX-based photocatalysts are put forward. The main purpose is providing practical guidelines for developing high-performance BiOX photocatalysts.

Enhanced photodegradation of doxycycline (DOX) in the sustainable NiFe2O4/MWCNTs/BiOI system under UV light irradiation

In this study, a magnetic NiFe₂O₄/MWCNTs/BiOI composite were fabricated and applied for enhanced and sustainable photocatalytic degradation of doxycycline (DOX) under UV light irradiation. The as-synthesized material was characterized by a series of techniques and its photocatalytic property was assessed via a couple of batch tests. With the pH at 3.0 and NiFe₂O₄/MWCNTs/BiOI loading of 1.5 g L^-1, the DOX degradation (at 45 mg L^-1) efficiency could achieve 92.18% with the reaction rate constant k of 0.0072 min^-1. The high mineralization of DOX suggests the strong oxidation of both the parent pollutant and the intermediary products in the ternary catalyst system. DRS spectra indicated that compared with BiOI, the introduction of NiFe₂O₄ and MWCNTs reduces the band gap energy of the NiFe₂O₄/MWCNTs/BiOI. The quenching test illustrates that h⁺, OH and O₂^- all functioned in the developed photocatalytic system, where O₂^- and h⁺ play the dominant roles in DOX degradation. The more efficient electron-h⁺ separation and more oxidizing species induced by UV light resulted in the significant improvement of DOX abatement in the developed coupling system compared with that on either BiOI or NiFe₂O₄/MWCNTs. The magnetic property of NiFe₂O₄/MWCNTs/BiOI enables its easy separation of the solid catalyst from the reaction solution and the sustainable application in the photocatalysis. Based on the intermediates of DOX decomposition identified by UPLC-MS, the possible degradation routes were proposed accordingly.

Facile fabrication of Fe-doped Nb2O5 nanofibers by an electrospinning process and their application in photocatalysis

It is of top priority to develop highly efficient visible-light photocatalysts to realize the practical applications of photocatalysis in industry. Niobium pentoxide (Nb2O5) is considered as a potentially attractive candidate for the visible-light-driven photodegradation of organic pollutants. In an effort to enhance its photocatalytic activity, Fe-doped Nb2O5 nanofibers with various Fe contents (the molar ratios of Fe to Nb were 0.005/1, 0.01/1, 0.03/1 or 0.05/1) were successfully prepared by an electrospinning method. The structural features, morphologies, and optical properties of the as-prepared samples were investigated. Photocatalytic activities of the samples were evaluated through degradation of Rhodamine B (RhB) under visible light irradiation. All the prepared Fe-doped Nb2O5 nanofibers exhibited much higher activities for degrading RhB solution than the pristine Nb2O5 nanofibers, and the maximum degradation yield of 98.4% was achieved with the nanofibers (Fe to Nb: 0.03/1) under visible light irradiation for 150 min. The photocatalytic degradation rate fitted a pseudo-first-order equation, and the rate constants of reactions with Fe-doped Nb2O5 nanofiber (the molar ratios of Fe to Nb were 0.03/1) or pure Nb2O5 nanofiber were 0.0282 min-1 and 0.0019 min-1, respectively. Doping Fe ions into the nanofibers enhanced the absorption within the visible-light range and reduced the photo-generated electron-hole pair recombination, and thus improved the photocatalytic activity. These attractive properties suggest that the Fe-doped Nb2O5 nanofibers have great potential for applications in the future to solve pollution issues.

Facile fabrication of hierarchical p-Ag2O/n-Nb2O5 heterojunction microspheres with enhanced visible-light photocatalytic activity

Constructing p-n heterojunction is an efficient strategy to improve the photocatalytic efficiency. Here, we report a hierarchical Ag2O/Nb2O5 heterojunction composite as a novel and efficient visible-light driven photocatalyst. Hierarchical Nb2O5 microspheres were prepared by a hydrothermal method, and then the in situ growth of Ag2O nanoparticles on their surfaces was realized by a simple deposition method. Structural and textural features of the Ag2O/Nb2O5 composites were investigated, revealing that Ag2O nanoparticles were well distributed on the surface of Nb2O5 microspheres. Photocatalytic degradation of rhodamine B (RhB) was significantly enhanced by Ag2O/Nb2O5 photocatalysts under visible light. The optimal Ag/Nb molar ratio was determined to be 0.15 : 1, which yielded a 21.8 times faster degradation rate constant than plain Nb2O5 microspheres and had excellent stability for at least 4 catalytic cycles. The superior photocatalytic performance of Ag2O/Nb2O5 photocatalyst can be ascribed to the hierarchical superstructure as well as the heterojunction between Ag2O and Nb2O5, which facilitated the separation of photogenerated charge carriers. This work has potential application in the future for solving environmental pollution.

Solvothermal synthesis of multiwall carbon nanotubes/BiOI photocatalysts for the efficient degradation of antipyrine under visible light

Antipyrine (ANT), as a widely used relieve headache, fever anti-inflammatory pharmaceutical in medical treatment, is difficult to be removed completely in water. The application of photocatalytic removal of ANT is restricted to UV light irradiation (<5% of solar energy), and the degradation pathways of ANT require more theoretical evidence. In this study, a series of three dimensions (3D) hierarchical structure multiwall carbon nanotubes/bismuth oxyiodide (MWCNTs/BiOI) photocatalysts were systematically designed and firstly applied to remove ANT through visible light (>43% of solar energy) induced photodegradation. Consequently, the as-prepared MWCNTs/BiOI photocatalysts presented superior photocatalytic activities on ANT degradation with respect to that of BiOI under 60 min visible light irradiation (100% vs 82.2%). Especially, the enhanced photocatalytic mechanism on ANT was analyzed by morphology, optical and photo-electrochemical properties. Results revealed that the designed 3D micro-mesoporous structure could promote the diffusion of photogenerated electron-hole pairs, and the utilization of photoelectrons could be efficiently improved by MWCNTs (1.5 times). Furthermore, based on radicals scavenging experiments, the photogenerated hole (h⁺) and superoxide radical (O₂^-) were demonstrated as the dominant active species in ANT photocatalytic oxidation process. The photodegradation pathways of ANT were proposed with the calculation of frontier electron densities (FEDs) and the analysis of LC-MS/MS. This study presents a feasible approach for the high efficiency removal of trace pharmaceuticals under visible light photocatalytic process.

Ag₂CO₃ Decorating BiOCOOH Microspheres with Enhanced Full-Spectrum Photocatalytic Activity for the Degradation of Toxic Pollutants

The development of excellent full-spectrum photocatalysts is of vital significance to its practical application in environmental remediation. Herein, flower-like Ag₂CO₃/BiOCOOH type I heterostructures were prepared via a facile method and exhibited powerful photocatalytic activity by removing various toxic pollutants (rhodamine B, methyl blue, and tetracycline hydrochloride) under simulated sunlight irradiation. The boosted photocatalytic performance is attributed to the expanded range of the absorption spectrum and alleviated separation rate of the photo-induced electrons and holes. The photoluminescence spectra and trapping experiment were applied to clarify the photocatalytic reaction mechanism of Ag₂CO₃/BiOCOOH. The holes and •O₂⁻ were detected as the dominant reactive species involved in pollutant degradation. This work provides a novel full-spectrum-driven photocatalyst of Ag₂CO₃/BiOCOOH, which could effectively degrade toxic pollutants under simulated sunlight.

Facile Synthesis of Bi2MoO6 Microspheres Decorated by CdS Nanoparticles with Efficient Photocatalytic Removal of Levfloxacin Antibiotic

Developing high-efficiency and stable visible-light-driven (VLD) photocatalysts for removal of toxic antibiotics is still a huge challenge at present. Herein, a novel CdS/Bi2MoO6 heterojunction with CdS nanoparticles decorated Bi2MoO6 microspheres has been obtained by a simple solvothermal-precipitation-calcination method. 1.0CdS/Bi2MoO6 has stronger light absorption ability and highest photocatalytic activity with levofloxacin (LEV) degradation efficiency improving 6.2 or 12.6 times compared to pristine CdS or Bi2MoO6. CdS/Bi2MoO6 is very stable during cycling tests, and no appreciable activity decline and microstructural changes are observed. Results signify that the introduction of CdS could enhance the light absorption ability and dramatically boost the separation of charge carriers, leading to the excellent photocatalytic performance of the heterojunction. This work demonstrates that flower-like CdS/ Bi2MoO6 is an excellent photocatalyst for the efficient removal of the LEV antibiotic.

Hierarchical heterostructures of Bi2MoO6 microflowers decorated with Ag2CO3 nanoparticles for efficient visible-light-driven photocatalytic removal of toxic pollutants

Developing highly active and durable visible-light-driven photocatalysts for the degradation of toxic pollutants is of vital significance. Herein, Ag₂CO₃ nanoparticles were in situ formed on Bi₂MoO₆ microflowers to produce Ag₂CO₃/Bi₂MoO₆ heterostructures via a facile procedure. The morphologies, phases, chemical compositions, and optical properties of Ag₂CO₃/Bi₂MoO₆ were examined by multiple characterization techniques. The Ag₂CO₃/Bi₂MoO₆ heterostructures exhibited substantially improved performance in the removal of industrial dyes (rhodamine B (RhB), methyl orange (MO), and methyl blue (MB)), and the antibiotic tetracycline hydrochloride (TC), compared with bare Bi₂MoO₆ and Ag₂CO₃ under visible-light irradiation. The enhancement of activity was attributed to the high charge-separation capacity, which results from the matched band alignment of the two components. The cycling experiments showed a good durability of Ag₂CO₃/Bi₂MoO₆. Holes were found to be the dominant active species accounting for the pollutant degradation. This compound is a promising candidate for wastewater treatment.

Biofabricated BiOI with enhanced photocatalytic activity under visible light irradiation

In the recent past, there has been a large-scale utilization of plant extracts for the synthesis of various photocatalysts. The biofabrication technology eliminates the usage of harmful chemicals and serves as an eco-friendly approach for environmental remediation. Herein, a comparative analysis between bismuth oxyiodide synthesized via Azadirachta indica (neem) leaf extract (BiOI-G) and without leaf extract (BiOI-C) has been envisaged. The BiOI-G and BiOI-C samples were characterized by spectral and microscopic techniques, which revealed that the Azadirachta indica assisted BiOI-G attained enhanced features over BiOI-C such as narrower band gap, large surface area, porosity, increased absorption range of visible light and effectual splitting of the photogenerated e--h+ pairs. Benefiting from these enhanced features, BiOI-G degraded methyl orange (MO), rhodamine B (RhB), and benzotriazole (BT) at a significantly higher rate in comparison to BiOI-C. The degradation rate of MO, RhB and BT by BiOI-G was observed to be 1.3, 1.25 and 1.29 times higher in comparison to BiOI-C. Moreover, BiOI-G displayed high stability upto five cycles of the photocatalytic activity, which endow its effectiveness as a highly-efficient green photocatalyst.

Graphene Oxide/BiOCl Nanocomposite Films as Efficient Visible Light Photocatalysts

A novel graphene oxide/BiOCl (GO/BiOCl) nanocomposite film was prepared via a spread coating method. In visible-light photocatalytically degrading Rhodamine B (RhB) experiments, 2 wt% GO/BiOCl could degrade 99% of RhB within 1.5 h and the rate constant was 12.2 times higher than that of pure BiOCl. The degradation efficiency still kept at 80% even after 4 recycles, evidencing the relatively good recyclability. The enhancement was attributed to the improvement of visible light adsorption and charge separation. Holes and superoxide radicals· O2- played a major role as reactive species. The values of conduction band and valence band for GO and BiOCl were calculated and a new photocatalytic mechanism of GO/BiOCl nanocomposite was proposed.

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.

Ag3VO4 Nanoparticles Decorated Bi2O2CO3 Micro-Flowers: An Efficient Visible-Light-Driven Photocatalyst for the Removal of Toxic Contaminants

Semiconductor-based photocatalysis is of great potential for tackling the environmental pollution. Herein, a novel hierarchical heterostructure of Bi₂O₂CO₃ micro-flowers in-situ decorated with Ag₃VO₄ nanoparticles was developed by a facile method. Various characterization techniques have been employed to study the physical and chemical property of the novel catalyst. The novel catalyst was utilized for the photocatalytic removal of industrial dyes (rhodamine B, methyl orange) and tetracycline antibiotic under visible-light irradiation. The results indicated that Ag₃VO₄/Bi₂O₂CO₃ heterojunctions showed a remarkably enhanced activity, significantly higher than those of bare Ag₃VO₄, Bi₂O₂CO₃, and the physical mixture of Ag₃VO₄ and Bi₂O₂CO₃ samples. This could be ascribed to an enhanced visible-light harvesting capacity and effective separation of charge carriers by virtue of the construction of hierarchical Ag₃VO₄/Bi₂O₂CO₃ heterojunction. Moreover, Ag₃VO₄/Bi₂O₂CO₃ also possesses an excellent cycling stability. The outstanding performance of Ag₃VO₄/Bi₂O₂CO₃ in removal of toxic pollutants indicates the potential of Ag₃VO₄/Bi₂O₂CO₃ in real environmental remediation. Highlights Novel architectures of Ag₃VO₄ nanoparticles modified Bi₂O₂CO₃ micro-flowers were constructed.Novel Ag₃VO₄/Bi₂O₂CO₃ exhibited excellent photocatalytic activity and stability.Ag₃VO₄/Bi₂O₂CO₃ heterojunctions significantly promote the charge separation.

Renewable biomass derived porous BCN nanosheets and their adsorption and photocatalytic activities for the decontamination of organic pollutants

In this work, the preparation, characterization and removal capabilities of a novel biomass derived BC and its BCN nanocomposites are described. Possessing hierarchically porous structures, extremely large surface areas and special chemical bonds, porous BCN nanosheets have demonstrated advantages in terms of their adsorption and photocatalytic activities. The adsorption and photocatalytic activities of the as-prepared catalysts were evaluated by the degradation of RhB. The best results exhibited 97% and 95% decomposition of RhB which were obtained by using porous BCN-40 nanosheets within 120 min at 25 °C under UV light and visible light (>420 nm) irradiation respectively. The rate constant of the porous BCN-40 nanosheets for the degradation of RhB was more 16 times than that of pure h-BN. Besides, the porous BCN nanosheets showed remarkable cycling stability, maintaining a high photocatalytic activity up to 94% after 5 cycles. Furthermore, the degradation mechanisms of RhB and the photocatalytic mechanism have been explained in this paper.

Ag2WO4 nanorods decorated with AgI nanoparticles: Novel and efficient visible-light-driven photocatalysts for the degradation of water pollutants

To develop efficient and stable visible-light-driven (VLD) photocatalysts for pollutant degradation, we synthesized novel heterojunction photocatalysts comprised of AgI nanoparticle-decorated Ag2WO4 nanorods via a facile method. Various characterization techniques, including XRD, SEM, TEM, EDX, and UV-vis DRS were used to investigate the morphology and optical properties of the as-prepared AgI/Ag2WO4 catalyst. With AgI acting as the cocatalyst, the resulting AgI/Ag2WO4 heterostructure shows excellent performance in degrading toxic, stable pollutants such as rhodamine B (RhB), methyl orange (MO) and para-chlorophenol (4-CP). The high performance is attributed to the enhanced visible-light absorption properties and the promoted separation efficiency of charge carriers through the formation of the heterojunction between AgI and Ag2WO4. Additionally, AgI/Ag2WO4 exhibits durable stability. The active species trapping experiment reveals that active species (O2•- and h+) dominantly contribute to RhB degradation. The AgI/Ag2WO4 heterojunction photocatalyst characterized in this work holds great potential for remedying environmental issues due to its simple preparation method and excellent photocatalytic performance.