A Review: Photocatalysts Based on BiOCl and g-C3N4 for Water Purification

Many organic pollutants are discharged into the environment, which results in the frequent detection of organic pollutants in surface water and underground water. Some of the organic pollutants can stay for a long time in the environment due to their recalcitrance. Advanced oxidation processes (AOPs) can effectively treat the recalcitrant organic compounds in water. Photocatalysis as one of the AOPs has attracted a lot of interest. BiOCl and g-C3N4 are nice photocatalysts. However, their catalytic activity should be further improved for industrial utilization. The construction of heterojunction between the two different components is deemed as an efficient strategy for developing a highly efficient photocatalyst. As a typical type-II heterojunction, g-C3N4/BiOCl heterojunctions showed better photocatalytic performance. To date, the g-C3N4/BiOCl composites were mainly studied in the field of water purification. The photoactivity of the pristine catalysts was greatly enhanced by the combination of the two materials. However, three kinds of proposed mechanisms were used to explain the improvement of the g-C3N4/BiOCl heterojunctions. But few researchers tried to explain why there were three different scenarios employed to explain the charge transfer. According to the articles reviewed, no direct evidence could indicate whether the band structures of the heterojunctions based on BiOCl and g-C3N4 were changed. Therefore, many more studies are needed to reveal the truth. Having a clearer understanding of the mechanism is beneficial for researchers to construct more efficient photocatalysts. This article is trying to start a new direction of research to inspire more researchers to prepare highly effective photocatalysts.

Engineering Z-scheme TiO2-OV-BiOCl via oxygen vacancy for enhanced photocatalytic degradation of imidacloprid

The development and application of photocatalysts with strong redox ability to degrade refractory pesticides is the key to eliminating pesticide contamination. In this work, we develop a facile, time-saving, and surfactant-assisted method to fabricate a new Z-scheme heterojunction based on TiO2/BiOCl. This photocatalyst is rich in oxygen vacancy defects (TiO2-OV-BiOCl), and displays an excellent photocatalytic degradation performance for imidacloprid (IMD), and a possible degradation pathway of IMD is provided. The surfactant F127 plays an essential role in regulating the oxygen vacancy defects (OVDs) of TiO2-OV-BiOCl, where the OVD mainly exists in 5 layer BiOCl ultrathin nanosheets. Free radical trapping experiments demonstrate that the introduction of an OVD in BiOCl as a 'charge mediator' changes the charge-transfer mode from a type-II mechanism to a Z-scheme mechanism. The formation of a Z-scheme heterojunction leads to an excellent light utilization and higher separation efficiency of photogenerated charge carriers with a prolonged lifetime compared to those of BiOCl and TiO2/BiOCl. This work highlights the critical role of an OVD in the construction of a Z-scheme heterojunction of TiO2/BiOCl, and it can be applied to construct efficient photocatalytic systems for pesticide degradation.

Modulating formation rates of active species population by optimizing electron transport channels for boosting the photocatalytic activity of a Bi2S3/BiO1−xCl heterojunction

Bi₂S₃/BiO_1−xCl heterojunction with OVs can regulate PS to produce ASP through optimizing ETCs and modulating ASP formation rates by cooperation of OVs with IEF to hinder the invalid consumption of ASP and significantly enhance the catalytic efficiency.

Eco-friendly synthesis and photocatalytic application of flowers-like ZnO structures using Arabic and Karaya Gums

Flowers-like ZnO structures were synthesized using Arabic Gum (AGZnO) or Karaya Gum (KGZnO). The AGZnO and KGZnO were characterized by X-ray diffractometry, Fourier Transformed Infrared, Scanning Electron Microscopy, Photoluminescence, nitrogen adsorption/desorption and diffuse reflectance techniques. The materials were tested in the discoloration of Methylene Blue (MB) dye under visible light and scavenger studies were also performed. The toxicity of the MB irradiated was investigated in bioassays with Artemia salina. The structural characterization demonstrated the formation of hexagonal ZnO. All samples presented flower-like morphology with presence of mesopores identified by BET method. The optical properties indicated band gap of 2.99 (AGZnO) and 2.76 eV (KGZnO), and emission in violet, blue and green emissions also were observed. The KGZnO demonstrated better photocatalytic performance than the AGZnO, and scavenger studies indicated that OH radicals are the main species involved in the degradation of the pollutant model. The photodiscoloration of MB solution did not demonstrate toxicity. Therefore, KGZnO is a promising material for photocatalysis application.

Surface-state-induced upward band bending in P doped g-C3N4 for the formation of an isotype heterojunction between bulk g-C3N4 and P doped g-C3N4: photocatalytic hydrogen production

The staggered type heterojunction with g-C₃N₄ based nanomaterials has received much attention owing to its change in chemical potential between two semiconductors.

Application of BiOX Photocatalysts in Remediation of Persistent Organic Pollutants

Bismuth oxyhalides have recently gained attention for their promise as photocatalysts. Due to their layered structure, these materials present fascinating and highly desirable physicochemical properties including visible light photocatalytic capability and improved charge separation. While bismuth oxyhalides have been rigorously evaluated for the photocatalytic degradation of dyes and many synthesis strategies have been employed to enhance this property, relatively little work has been done to test them against pharmaceuticals and pesticides. These persistent organic pollutants are identified as emerging concerns by the EPA and effective strategies must be developed to combat them. Here, we review recent work directed at characterizing the nature of the interactions between bismuth oxyhalides and persistent organic pollutants using techniques including LC-MS/MS for the determination of photocatalytic degradation intermediates and radical scavenging to determine active species during photocatalytic degradation. The reported investigations indicate that the high activity of bismuth oxyhalides for the breakdown of persistent organic pollutants from water can be largely attributed to the strong oxidizing power of electron holes in the valence band. Unlike conventional catalysts like TiO2, these catalysts can also function in ambient solar conditions. This suggests a much wider potential use for these materials as green catalysts for industrial photocatalytic transformation, particularly in flow chemistry applications.

Synthesis of a BiOCl1−xBrx@AgBr heterostructure with enhanced photocatalytic activity under visible light

We present a facile approach to preparing a BiOCl_1−xBr_x@AgBr heterostructure using a two-step solvothermal method. Multiple characterisation techniques have been employed to investigate its morphology, structure, optical and electronic properties and photocatalytic performance. The photocatalytic activity of the BiOCl_1−xBr_x@AgBr heterostructure was sufficiently evaluated by adopting Reactive Blue KN-R as the target organic pollutant under visible light irradiation. The as-prepared BiOCl_1−xBr_x@AgBr exhibited much higher photocatalytic activity than BiOCl_1−xBr_x and BiOCl, which was ascribed to the movement of photogenerated electrons from AgBr to BiOCl_1−xBr_x, resulting in effective charge separation and transfer. Moreover, the modification of BiOCl_1−xBr_x with AgBr broadened the light absorption range, making the composite suitable for visible light excitation. The excellent photocatalytic performance provides potential opportunities to utilize BiOCl_1−xBr_x@AgBr for environmental purification and organic pollution treatment of water.

BiOCl_1−xBr_x nanosheets are covered by a thin layer of AgBr that forms BiOCl_1−xBr_x@AgBr heterostucture with high photocatalytic activity.

Photoelectrochemical sensing of bisphenol a based on graphitic carbon nitride/bismuth oxyiodine composites

Graphitic carbon nitride/bismuth oxyiodine composites with excellent photoelectrochemical performance had been designed for sensitive PEC monitoring platform of bisphenol A.

Bi(iii) immobilization inside MIL-101: enhanced photocatalytic performance

Bi(iii) particles were immobilized into the cages of mesoporous chromium oxoterephthalate MIL-101. The material obtained possesses enhanced photocatalytic activity in comparison with bulk BiOCl synthesized under the same conditions.

BiOBr/BiOF composites for efficient degradation of rhodamine B and nitrobenzene under visible light irradiation

BiOBr/BiOF (BF) composites were successfully synthesized via a facile one-step hydrothermal method for the first time. The structures, morphologies and photocatalytic performances of BF composites were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and electrochemical impedance spectroscopy respectively. The results show that the BF composites exhibit enhanced photocatalytic performances in the degradation of RhB and nitrobenzene with maximum degradation rates of 100% (25min) and 94% (300min) under visible light irradiation, respectively. The improved photocatalytic performance is mainly ascribed to the small crystalline size and the reduced electron-hole pair recombination with the presence of BiOF in the composites. Furthermore, the photodegradation mechanism was investigated and the h⁺ and OH radicals are suggested to be the main active species for photocatalytic degradation of RhB and nitrobenzene.