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.

Ultrahigh Charge Separation Achieved by Selective Growth of Bi4O5I2 Nanoplates on Electron-Accumulating Facets of Bi5O7I Nanobelts

Ultrahigh charge separation was observed in Bi₄O₅I₂/Bi₅O₇I two-dimensional (2D)/one-dimensional (1D) hierarchical structures (HSs) constructed by selective growth of 2D monocrystalline Bi₄O₅I₂ nanoplates on the electron-accumulating (100) facet of 1D monocrystalline Bi₅O₇I nanobelts. In addition to the presence of type-II heterojunction between Bi₄O₅I₂ and Bi₅O₇I elementary entities in 2D/1D HSs, the type-II (100)/(001) surface heterojunction in Bi₅O₇I nanobelt substrates was also confirmed by means of density functional theory (DFT) calculations and selective photoreduction/oxidation deposition experiments. The synergistic effect of two kinds of heterojunctions in Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs endowed them with ultrahigh charge carrier separation and transfer characteristics. In contrast with the control sample (BB40-C) constructed by growing Bi₄O₅I₂ nanoplates on whole four sides of Bi₅O₇I nanobelts, Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs demonstrated significantly enhanced charge transfer between Bi₅O₇I nanobelt substrates and Bi₄O₅I₂ nanoplates, owing to respective electron and hole accumulations on (100) and (001) facets of Bi₅O₇I substrates caused by (100)/(001) surface heterojunction. The enhanced separation behavior was successfully verified by steady/transient-state photoluminescence, electrochemical techniques, and photocatalytic degradation experiments. Based on the above effective charge separation of Bi₄O₅I₂/Bi₅O₇I 2D/1D HSs as well as the routine advantages for 2D/1D HSs, such as the excellent charge transport in monocrystalline elementary entities, much higher specific surface area, and enhanced light absorption by multiple reflections, the optimal BB40 HSs demonstrated ultrahigh photocatalytic performance than the control samples, whose apparent rates for Rhodamine B [or tetracycline hydrochloride (TC)] degradation were 7.1 (2.9 for TC), 10.3 (4.7 for TC), and 2.2 (1.7 for TC) times those of pristine Bi₅O₇I nanobelts, Bi₄O₅I₂ nanoplates, and BB40-C, respectively. It is hoped that this crystal facet selection during the heterostructure construction in this work could provide a new strategy or some enlightenment for the exploration of highly active 2D/1D HSs or other-dimensional heterostructure nanomaterials applied in the fields of photocatalysts, solar cells, sensors, and others.

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.

Fabrication and Photocatalytic Property of Novel SrTiO3/Bi5O7I Nanocomposites

The novel SrTiO3/Bi5O7I nanocomposites were successfully fabricated by a thermal decomposition approach. The as-prepared samples were characterized by XRD, XPS, SEM, EDS, FTIR, DRS and PL spectra. The results show that the SrTiO3/Bi5O7I nanocomposites are composed of perovskite SrTiO3 nanoparticles and tetragonal Bi5O7I nanorods. The SrTiO3/Bi5O7I nanocomposites exhibit an excellent photocatalytic performance for the degradation of RhB solution under simulated solar light irradiation, which is superior to that of pristine Bi5O7I and SrTiO3. In particular, the 30 wt% SrTiO3/Bi5O7I nanocomposite is found as the optimal composites, over which the dye degradation reaches 89.6% for 150 min of photocatalysis. The photocatalytic degradation rate of the 30 wt% SrTiO3/Bi5O7I nanocomposite is found to be 3.97 times and 12.5 times higher than that of bare Bi5O7I and SrTiO3, respectively. The reactive species trapping experiments suggest that [Formula: see text] and holes are the main active species responsible for the RhB degradation. In addition, the PL spectra elucidate the effective separation of photoinduced electron-hole pairs. Further, the possible photocatalytic mechanism of the SrTiO3/Bi5O7I nanocomposites is also elucidated based on the experimental evidences.

Intensive photocatalytic activity enhancement of Bi5O7I via coupling with band structure and content adjustable BiOBrxI1-x

Band structure and component content are the key factors for determining the activity of semiconductor heterojunction. In this study, a novel Bi₅O₇I/BiOBr_xI_1-x heterostructure was synthesized by a simple hydrobromic (HBr) acid etching method through transforming partial of Bi₅O₇I to I^- ion doped BiOBr (BiOBr_xI_1-x) at room temperature without adding extra dopant. Both the band structure and component content of Bi₅O₇I/BiOBr_xI_1-x alter with the additive HBr acid. The Bi₅O₇I/BiOBr_xI_1-x (S3.0) sample exhibits the best photocatalytic activity, 6 times higher than that of pure Bi₅O₇I, for the degradation of methyl orange under visible-light (λ > 420 nm). The activity enhancement of Bi₅O₇I/BiOBr_xI_1-x is primarily ascribed to the improved separation efficiency of photocharges, originated from the adjustable band structure and component content. The significant findings of this paper provide a facile way to construct highly efficient semiconductor heterojunction via playing the synergetic effect of adjustable band structure and component content for purifying organic pollutants in wastewater.

Three-dimensional Ag2O/Bi5O7I p-n heterojunction photocatalyst harnessing UV-vis-NIR broad spectrum for photodegradation of organic pollutants

Ag₂O nanoparticles-loaded Bi₅O₇I microspheres forming a three dimensional Ag₂O/Bi₅O₇I p-n heterojunction photocatalyst with wide-spectrum response were synthesized in this study. The results of transmission electron microscopy observations revealed that the Ag₂O nanoparticles with the diameter of ca. 10-20nm were distributed on the surfaces of Bi₅O₇I nanosheets. The as-synthesized Ag₂O/Bi₅O₇I exhibited an excellent wide-spectrum response to wavelengths ranging from ultraviolet (UV) to near-infrared (NIR), indicating its potential for effective utilization of solar energy. Compared with pure Bi₅O₇I, the Ag₂O/Bi₅O₇I composite also demonstrated excellent photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution under visible LED light irradiation. Among samples, the 20% Ag₂O/Bi₅O₇I composite photocatalyst showed the highest photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution. In addition, the 20% Ag₂O/Bi₅O₇I composite also exhibited a photocatalytic activity for the degradation of Bisphenol A under NIR light irradiation. The improved photocatalytic activity is attributed to the formation of a p-n heterojunction between Ag₂O and Bi₅O₇I, allowing the efficient utilization of solar energy (from UV to NIR) and high separation efficiency of photogenerated electron-hole pairs. The present work is desirable to explore a possible avenue for the full utilization of solar energy.

Synthesis of one-dimensional Bi2O3–Bi5O7I heterojunctions with high interface quality

One-dimensional Bi₂O₃–Bi₅O₇I heterostructures with high interface quality were first synthesized by calcining of BiOI–Bi(OHC₂O₄)·2H₂O precursors. And the obtained Bi₂O₃–Bi₅O₇I heterostructures exhibit outstanding photocatalytic activity for degrading methyl orange and phenol with high concentration.

ZnO–TiO2 composites and ternary ZnTiO3 electrospun nanofibers: the influence of annealing on the photocatalytic response and reusable functionality

By using understanding from the construction of composites to ternary-phased 1D NFs, we design a layout for ZnO–TiO₂ composite and ZnTiO₃ electrospun NFs with different band structures as a function of the annealing temperature with the possibility of defect states.

Controllable synthesis and photoreduction performance towards Cr(vi) of BiOCl microrods with exposed (110) crystal facets

BiOCl microrod exposed (110) facets was synthesized via a simple hydrothermal method using sodium citrate as capping agent. It exhibits outstanding photoreduction performance towards Cr(vi) at neutral and acid condition.

Facet-Dependent Photocatalytic N2 Fixation of Bismuth-Rich Bi5O7I Nanosheets

Bismuth-rich bismuth oxyhalides (Bi-O-X; X = Cl, Br, I) display high photocatalytic reduction activity due to the promoting conduction band potential. In this work, two Bi₅O₇I nanosheets with different dominant facets were synthesized using either molecular precursor hydrolysis or calcination. Crystal structure characterizations, included X-ray diffraction patterns (XRD), field emission electron microscopy and fast Fourier transformation (FFT) images, showed that hydrolysis and calcination resulted in the dominant exposure of {100} and {001} facets, respectively. Photocatalytic data revealed that Bi₅O₇I-001 had a higher activity than Bi₅O₇I-100 for N₂ fixation and dye degradation. Photoelectrochemical data revealed that Bi₅O₇I-001 had higher photoinduced carrier separation efficiency than Bi₅O₇I-100. The band structure analysis also used to explain the underlying photocatalytic mechanism based on the different conduction band position. This work presents the first report about the facet-dependent photocatalytic performance of bismuth-rich Bi-O-X photocatalysts.

Visible/near-IR-light-driven TNFePc/BiOCl organic-inorganic heterostructures with enhanced photocatalytic activity

Although semiconductor photocatalysis has been reported for more than 40 years, the spectral response is still focused on the region of UV-Visible and it is seldom extended to more than 600 nm. In this work, visible/near-IR-light-driven 2,9,16,23-tetranitrophthalocyanine iron (FeTNPc)/bismuth oxychloride (BiOCl) organic-inorganic heterostructures have been synthesized by a two-step solvothermal method. The obtained products were characterized by X-ray diffraction, Fourier transform infrared spectra, scanning electron and transmission microscopy, energy dispersive X-ray spectrometer, UV-vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption, and electrochemical measurements. The photocatalytic activity for the decomposition of methyl orange and bisphenol A solution can be significantly improved under visible/near-IR-light irradiation. Through detecting the main oxidative species by trapping experiments, the results show holes and ˙O2(-) radicals are majorly and minorly responsible for photodegradation respectively. What's more, the FeTNPc/BiOCl composite photocatalyst still retained the photocatalytic activity after three cycle measurements.

Room temperature synthesis of Bi4O5I2 and Bi5O7I ultrathin nanosheets with a high visible light photocatalytic performance

Bi₄O₅I₂ and Bi₅O₇I ultrathin nanosheets with a high visible-light photocatalytic activity for phenol degradation are prepared via a facile route at room temperature.

Synthesis of BiOI/Bi4O5I2/Bi2O2CO3 p–n–p heterojunctions with superior photocatalytic activities

The formation of p–n heterojunctions among BiOI, Bi₄O₅I₂ and Bi₂O₂CO₃ enhances the charge transfer and separation of the photogenerated carriers and photocatalytic activity.