Iron–doped bismuth oxybromides as visible-light-responsive Fenton catalysts for the degradation of atrazine in aqueous phases

Pesticides and its degradation products,being well–known residues in soil,have recently been detected in many water bodies as pollutants of emerging concerns,and thus there is a contemporary demand to develop viable and cost–effective techniques for the removal of related organic pollutants in aqueous phases.Herein,a visible-light-responsive Fenton system was constructed with iron–doped bismuth oxybromides(Fe–BiOBr)as the catalysts.Taking the advantage of sustainable Fe(Ⅲ)/Fe(Ⅱ)conversion and optimized H_(2)O_(2)utilization,the optimal Fe–BiOBr–2 catalyst showed an excellent atrazine removal efficiency of 97.61%in 120 min,which is superior than the traditional homogeneous Fenton and the majority of heterogeneous processes documented in the literature.In this photo–Fenton system,hydroxyl(·OH)and superoxide(·O_(2)^(-))radicals were dominant active species contributed to the oxidative degradation of atrazine.Due to the production of various active radicals,five degradation pathways were proposed based on the identification of intermediates and degradation products.Overall,this work not only demonstrates a fundamental insight into creating highly efficient and atom economic photo-Fenton systems,but also provides a complementary strategy for the treatment of organic pollutants in water.

Thermal Stability, Microstructure and Photocatalytic Activity of the Bismuth Oxybromide Photocatalyst

Flake BiOBr was first prepared by a solution method at room temperature. Then, the produced BiOBr was calcined at different temperatures. It was found that BiOBr is not a stable compound. It transforms to plate-like Bi24031Brll at around 750 ℃ and the formed Bi24O31Br11 can further convert to rod-like a-Bi203 at around 850℃. The prepared compounds were characterized with X-ray diffraction （XRD）, N2 physical adsorption, scanning electron microscopy （SEM）, and UV-Vis diffuse reflectance spectra （DRS）, respectively. The photocatalytic activity of the produced bismuth oxybromides was evaluated by photocatalytic decomposition of acid orange Ⅱ under both visible light （λ〉420 nm） and UV light （λ=365 nm） irradiation. Results show that these compounds have different band gaps and different photocatalytic properties. The band gap energies of the as-prepared samples were found to be 2.82, 2.79, 2.60 and 3.15 eV for BiOBr, BiOBr/Bi24O31Br, Bi24O31Br, and a-Bi2O3, respectively. Under both UV light and visible light irradiation, the photocatalytic activity follows the order： BiOBr/Bi24O31Br mixture 〉 BiOBr 〉 Bi24031Br〉a-Bi2O3. The change in photocatalytic activity could be attributed to the different light absorption ability and microstructures of the photocatalysts.

High-performance UV detectors based on 2D CVD bismuth oxybromide single-crystal nanosheets

Two-dimensional(2D)ternary wide-bandgap semiconducting materials have great potential in power device,flexible electronic device,short-wavelength light emitting diodes(LEDs)and photodetectors due to the controllable bandgap,strong light-material interaction,and controlled freedom degree of stoichiometry variation.However,it is still a great challenge to precisely control the growth of high-quality 2D ternary wide-bandgap semiconducting materials due to the variety of components,which hinders their development for practical applications.In this work,high-quality 2D ternary bismuth oxybromide single-crystal nanosheets with a high yield were prepared by space-confined chemical vapor deposition(CVD)method.The devices based on 2D ultrathin BiOBr single-crystal nanoflakes show a high UV detecting performance including low dark current(Idark)of 1.46pA and high re s ponsivity(R),external quantum efficiency(EQE)and detectivity(D*)of 14.96 A W-1,5460%,and 5.74 × 10^10 Jones,respectively,as well as fast response process(τrise=80 ms,τdecay=40 ms).The excellent UV performance can be ascribed to the photogating effect by trapped states,which endow it with great potential for high-performance UV detectors.

Self-adaptive bulk/surface engineering of Bi_(x)O_(y)Br_(z) towards enhanced photocatalysis:Current status and future challenges

The bulk/surface states of semiconductor photocatalysts are imperative parameters to maneuver their performance by significantly affecting the key processes of photocatalysis including light absorption,separation of charge carrier,and surface site reaction.Recent years have witnessed the encouraging progress of self-adaptive bulk/surface engineered Bi_(x)O_(y)Br_(z) for photocatalytic applications spanning various fields.However,despite the maturity of current research,the interaction between the bulk/surface state and the performance of Bi_(x)O_(y)Br_(z) has not yet been fully understood and highlighted.In this regard,a timely tutorial overview is quite urgent to summarize the most recent key progress and outline developing obstacles in this exciting area.Herein,the structural characteristics and fundamental principles of Bi_(x)O_(y)Br_(z)for driving photocatalytic reaction as well as related key issues are firstly reviewed.Then,we for the first time summarized different self-adaptive engineering processes over Bi_(x)O_(y)Br_(z)followed by a classification of the generation approaches towards diverse Bi_(x)O_(y)Br_(z)materials.The features of different strategies,the up-to-date characterization techniques to detect bulk/surface states,and the effect of bulk/surface states on improving the photoactivity of Bi_(x)O_(y)Br_(z)in expanded applications are further discussed.Finally,the present research status,challenges,and future research opportunities of self-adaptive bulk/surface engineered Bi_(x)O_(y)Br_(z)are prospected.It is anticipated that this critical review can trigger deeper investigations and attract upcoming innovative ideas on the rational design of Bi_(x)O_(y)Br_(z)-based photocatalysts.

Substrate-dependent photoreactivities of BiOBr nanoplates prepared at different pH values

In this study,we showed that BiO Br nanoplates prepared at different pH values have substratedependent photocatalytic activities under visible-light irradiation. The BiO Br nanoplates synthesized at pH 1（BOB-1） degraded salicylic acid more effectively than did those obtained at pH 3（BOB-3）,but the order of their photocatalytic activities in rhodamine B（RhB） degradation were reversed. Electrochemical Mott–Schottky and zeta-potential measurements showed that BOB-1 had a more positive valence band and lower surface charge,leading to superior photocatalytic activity in salicylic acid degradation under visible light. However,BOB-3 was more powerful in RhB degradation because larger numbers of superoxide radicals were generated via electron injection from the excited RhB to its more negative conduction band under visible-light irradiation; this was confirmed using active oxygen species measurements and electron spin resonance analysis. This study deepens our understanding of the origins of organic-pollutant-dependent photoreactivities of semiconductors,and will help in designing highly active photocatalysts for environmental remediation.

Surface defect and lattice engineering of Bi_(5)O_(7)Br ultrathin nanosheets for efficient photocatalysis

The effective separation and migration of photogenerated charge carriers in bulk and on the surface of photocatalysts will significantly promote photocatalytic efficiency.However,the synchronous regulation of photocharges on both counts is challenging.Herein,the simultaneous separation of bulk and surface photocharges is conducted to enhance photocatalytic activity by coupling the surface defects and lattice engineering of bismuth oxybromide.The depth-modulated Bi_(5)O_(7)Br ultrathin nanosheets with an abundance of bismuth in the crystal structure increased the internal electric field,which propelled the separation and migration of photocharges from bulk to the surface.Creation of oxygen vacancies(OVs)on the nanosheet surface forms local electric fields,which can stimulate the migration of charges to active sites on the catalyst surface.Therefore,the OV-assembled Bi_(5)O_(7)Br nanosheets demonstrated enhanced photocatalytic degradation efficiency under simulated solar-light illumination.This study proved the possibility of charge governing via electric field modulation based on an integrated strategy.