Recent advances on bismuth oxyhalides for photocatalytic CO_(2)reduction

Photocatalytic conversion of CO_(2)into fuels such as CO,CH_(4),and CH_(3)OH,is a promising approach for achieving carbon neutrality.Bismuth oxyhalides(BiOX,where X=Cl,Br,and I)are appropriate photocatalysts for this purpose due to the merits of visible-light-active,efficient charge separation,and easy-to-modify crystal structure and surface properties.For practical applications,multiple strategies have been proposed to develop high-efficiency BiOX-based photocatalysts.This review summarizes the development of different approaches to prepare BiOX-based photocatalysts for efficient CO_(2)reduction.In the review,the fundamentals of photocatalytic CO_(2)reduction are introduced.Then,several widely used modification methods for BiOX photocatalysts are systematacially discussed,including heterojunction construction,introducing oxygen vacancies(OVs),Bi-enrichment,heteroatom-doping,and morphology design.Finally,the challenges and prospects in the design of future BiOX-based photocatalysis for efficient CO_(2)reduction are examined.

Polymorphic Pb_(14)O_(8)I_(12) and Pb_(7)O_(4)I_(6) oxyhalides featuring unprecedented[O_(8)Pb_(14)]clusters with broad IR transparency

Wide transmittance range is an essential factor for the design of infrared optical materials.Traditionally,the designs of mid-far infrared crystals have focused on oxygenfree systems of chalcogenides and pnictides.Nevertheless,the introduction of elements with large atomic numbers,such as the lone-pair cation Pb^(2+) and halogen anion I^(-),based on the oxyhalides,can broaden the infrared transmittance range.Thus,two new polymorphs of Pb(Ⅱ)-containing oxyhalides,Pb_(14)O_(8)I_(12)(α-POI)and Pb_(7)O_(4)I_(6)(β-POI),are successfully synthesized via the high-temperature solution method.Interestingly,they crystallize in the same space group,P1,and present unprecedented[O_(8)Pb_(14)]clusters from the perspective of oxocentered[OPb_(4)]basic units.Remarkably,POI exhibits a quite wide transparent range(0.47-16.0μm),which enlightens the oxyhalides with prominent infrared optical properties.Additionally,the first principles calculations show that they have large birefringence(0.139 and 0.108 for α-and β-POI at 1064 nm,respectively),which makes POI promising infrared optical materials.

One-photo excitation pathway in 2D in-plane heterostructures for effective visible-light-driven photocatalytic degradation

Broad-spectrum absorption and highly effective charge-carrier separation are two essential requirements to improve the photocatalytic performance of semiconductor-based photocatalysts.In this work,a fascinating one-photon system is reported by rationally fabricating 2D in-plane Bi_(2)O_(3)/BiOCl(i-Cl)heterostructures for efficient photocatalytic degradation of RhB and TC.Systematic investigations revealed that the matched band structure generated an internal electric field and a chemical bond connection between the Bi_(2)O_(3)and BiOCl in the Bi_(2)O_(3)/BiOCl composite that could effectively improve the utilization ratio of visible light and the separation effectivity of photo-generated carriers in space.The formed interactions at the 2D in-plane heterojunction interface induced the one-photon excitation pathway which has been confirmed by the experiment and DFT calculations.As a result,the i-Cl samples showed significantly enhanced photocatalytic efficiency towards the degradation of RhB and TC(RhB:0.106 min^(-1);TC:0.048 min^(-1))under visible light.The degradation activities of RhB and TC for i-Cl were 265.08 and 4.08times that of pure BiOCl,as well as 9.27 and 2.14 times that of mechanistically mixed Bi_(2)O_(3)/BiOCl samples,respectively.This work provides a logical strategy to construct other 2D in-plane heterojunctions with a one-photon excitation pathway with enhanced performance.

Origin of Bismuth-Rich Strategy in Bismuth Oxyhalide Photocatalysts

Recently,the bismuth-rich strategy via increasing the bismuth content has been becoming one of the most appealing approaches to improve the photocatalytic performance of bismuth oxyhalides.However,insights into the mechanism behind the encouraging experiments are missing.Herein,we report the results of the theory-led comprehensive picture of bismuth-rich strategy in bismuth oxyhalide photocatalysts,selecting Bi_(5)O_(7)X(X=F,Cl,Br,I)as a prototype.First-principle calculations revealed that the strategy enables good n-type conductivity,large intrinsic internal electric field,high photoreduction ability and outstanding harvest of visible light,and particularly ranked the intrinsic activity of this family:Bi_(5)O_(7)F>Bi_(5)O_(7)I>Bi_(5)O_(7)Br>Bi_(5)O_(7)Cl.Designed experiments confirmed the theoretical predictions,and together,these results are expected to aid future development of advanced photocatalysts.

Facile synthesis of hierarchical BiOCl_(x)Br_(1–x) solid solution with enhanced photocatalytic activity

The hierarchical BiOClxBr1–x was synthesized by a simple solvothermal method. The samples were characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM）, UV-visible diffuse reflectance spectroscopy （UV-vis DRS） and Brunauer-Emmett-Teller adsorption method. Compared to pure BiOCl or BiOBr, the BiOClxBr1–x solid solution has enhanced photocatalytic degradation activity for rhodamine B. This phenomenon can be explained to the hierarchical structure, lager specific surface area and appropriate energy gap of the obtained BiOClxBr1–x solid solution. The renewability and stability of photocatalyst were determinated and a possible mechanism of photocatalytic degradation was also proposed.

Pt/Bi_(24)O_(31)Cl_(10) composite nanosheets with significantly enhanced photocatalytic activity under visible light irradiation

Efficient composite semiconductor photocatalysts are highly desirable for the visible-light-driven degradation of organic pollutants. In this study, Bi24O31Cl10 photocatalyst was prepared via a hydrothermal method and modified with Pt nanoparticles (NPs) through a facile deposition procedure. The composite photocatalyst was characterized by X-ray diffraction, transmission electronic microscopy, X-ray photoelectron spectroscopy, UV-vis diffusion reflectance spectroscopy, photoluminescence spectroscopy, and electron spin resonance. The 1.0 wt% Pt/Bi24O31Cl10 photocatalyst showed the highest activity for the degradation of methyl orange under visible light (source: 300 W Xe lamp coupled with a UV-cutoff filter), and the photocatalytic degradation efficiency improved about 2.2 times compared to that of pure Bi24O31Cl10. The composite photocatalyst could maintain most of its activity after four runs of the photocatalytic experimental cycle. This study could provide a novel insight for the modification of other desirable semiconductor materials to achieve high photocatalytic activities.

Three-color upconversion luminescence of rare earth codoped oxyhalide tellurite glasses

The red, green, and blue upconversion properties of Er^3＋/Tm^3＋/Yb^3＋-codoped oxyhalide tellurite glasses were studied under 980 nm LD excitation. The intense red （657 nm）, green （530 and 545 nm）, and blue （476 nm） emissions were simultaneously observed at room temperature. The results showed that the mixed halide modified tellurite glass （TZFCB） had strong upconversion emissions. The effect of halide on upconversion intensity was observed and discussed, and possible upconversion mechanisms were evaluated. The intense red, green, and blue upconversion luminescence of Er^3＋/Tm^3＋/Yb^3＋-codoped oxyhalide tellurite glasses might be a potentially useful material for developing three-dimensional displays applications.

Synthesis, Crystal Structure and Property of Cu Pb_2(OH)_2Cl_3

A new copper（1）-lead（Ⅱ） oxyhalide, CuPb2（OH）2Cl3, has been prepared by hydrothermal reaction and structurally characterized by single-crystal X-ray analysis. The compound crystallizes in tetragonal, space group 14（1）/acd with a = b = 13.77（1）, c = 15.38（1） A, V = 2916.2（2）, Z = 4, Mr = 618.29, Dc = 5.633 g/cm^3,μ = 49.97（2） mm^-1, F（000） = 4192, the final R = 0.0204 and wR = 0.0452 for 757 observed reflections with I 〉 2σ（I）. The structure of CuPb2（OH）2Cl3 contains one-dimensional helical chains built by CuCl4 tetrahedra with comer-sharing along the c-axis, in which the Pb^2＋ and OH^- ions are located at the voids between chains. Optical reflectance spectrum measurements indicate that it is a semiconductor with a band-gap of 3.23 eV.

Tendencies of alloyed engineering in BiOX-based photocatalysts:a state-of-the-art review

Energy-saving and environmentally friendly photocatalysis has emerged as a popular research area in response to issues with energy scarcity and environmental degradation.Due to the unique layer-like structure,BiOX(Cl,Br,I)is frequently used in photocatalysis.However,inherent flaws in BiOX,such as an inappropriate band gap and low carrier separation efficiency,restrict its capacity for photocatalysis.Owing to the tunable grouping layer,alloying engineering is employed to optimize the intrinsic properties of BiOX and alloyed BiOX becomes a promising photocatalytic material.This review describes the structure of BiOX,where tunable halogen layers provide favorable conditions for the implementation of alloying engineering to improve intrinsic properties.The article compares the effects and mechanisms of alloying engineering on the optimization of the energy band structure and carrier behavior of BiOX,and lists various modification methods used to improve the optimization of the intrinsic properties by alloying engineering,including defect engineering,morphology control as well as the synergy between alloying and other modification methods(bismuth-rich strategies,cation doping,construction of heterojunctions and plasma resonance effects).Subsequently,applications of alloyed BiOX in energy and environmental fields are summarized,including contaminant degradation,antibacterial,CO_(2)reduction,nitrogen fixation and organic synthesis.Finally,we summarize the current challenges and future directions of alloyed BiOX.It is expected that this work will provide guidance and assistance for an in-depth study and understanding of the mechanisms of alloying engineering to optimize intrinsic properties and design alloyed BiOX with higher photocatalytic activity.

Regulating the Electronic Structure of Fe^(3+)‑Doped BiOCl_(x)I_(1-x)Solid Solution by an Amidoxime‑Functionalized Fibrous Support for Efficient Photocatalysis

BiOX(X=Cl,I,Br)has attracted intensive interest as a photocatalyst for environmental remediation,but its limited pho-tocatalytic activity versus visible light irradiation restricts its practical application.Herein,a Fe^(3+)-doped BiOCl_(x)I_(1-x)solid solution(Fe-BiOCl_(x)I_(1-x))was synthesized in situ on an amidoxime-functionalized fibrous support via a one-pot solvothermal approach.Comprehensive characterization and DFT calculations indicate that the robust chelated interaction between ami-doxime groups and Fe^(3+)greatly boosts the crystal growth of nanosized Fe-BiOCl_(x)I_(1–x)on the fibrous surface,simultaneously tunes its electronic structure for improved light harvesting and oxygen vacancy creation,and enables the fibrous support to act as an electron sink for efficient charge separation.These synergistic qualities result in high photocatalytic activity for the degradation of organic contaminants,which outperforms that obtained for unsupported Fe-BiOCl_(x)I_(1-x)and other fibrous samples by several times.Our findings highlight the importance of functionalized support design for the development of efficient BiOX photocatalysts under visible light irradiation.

Lactic Acid Assisted Solvothermal Synthesis of BiOClxI1-x Solid Solutions as Excellent Visible Light Photocatalysts

A series of BiOClxI1-x(x=0,0.1,0.3,0.5,0.7,0.9,1.0)photocatalysts was firstly prepared by means of a facile solvothermal route with the help of lactic acid.The measured results show that the morphologies of the as-prepared samples are similar sheets with different thickness and diameters.Thinner nanosheets assembled flower-like BiOCI0.5I0.5 solid solution exhibited the highest photocatalytic activity and stability among the prepared samples for the degradation of methylene blue(MB)and methyl orange(MO)under the illumination of visible light.The excellent photocatalytic properties of BiOCI0.5I0.5 could be attributed to the high specific surface area,the suita-ble band gap energy and the lower recombination rate of the electrons and holes.In addition,catalyst BiOCI0.5I0.5 was further used to degradate a more complicated mixed dye(MCH-RhB+MB)system under visible light,displaying an excellent photocatalytic activity.Finally,the photocatalytic mechanism of catalyst BiOCI0.5I0.5 to degradate colorful dyes was proposed.The trapping experiments of active species indicated that the holes are the main active species for the degradation of the mixed dyes.

Space-confined microwave synthesis of ternary-layered BiOCl crystals with high-performance ultraviolet photodetection

In recent years,two-dimensional(2D)ternary materials have attracted wide attention due to their novel properties which can be achieved by regulating their chemical composition with a very great degree of freedom and adjustable space.However,as for the precise synthesis of 2D ternary materials,great challenges still lie ahead that hinder their further development.In this work,we demonstrated a simple and reliable approach to synthesize 2D ternary-layered BiOCl crystals through a microwave-assisted space-confined process in a short time(<3 minutes).Their ultraviolet(UV)detection performance was analyzed systematically.The photodetectors based on the as-obtained BiOCl platelets demonstrate high sensitivity to 266-nm laser illumination.The responsivity is calculated to be8 A/W and the response time is up to be18 ps.On the other hand,the device is quite stable after being exposed in the ambient air within 3 weeks and the response is almost unchanged during the measurement.The facile and fast synthesis of single crystalline BiOCl platelets and its high sensitivity to UV light irradiation indicate the potential optoelectronic applications of 2D BiOCl photodetectors.

Regulating Built-in Polar States via Atomic Self-Hybridization for Fast Ion Diffusion Kinetics in Potassium Ion Batteries

Potassium ion batteries(PIBs)are of great interest owing to the low cost and abundance of potassium resources,while the sluggish diffusion kinetics of K^(+)in the electrode materials severely impede their practical applications.Here,self-hybridized BiOCl_(0.5)Br_(0.5) with a floral structure is assembled and used as anode for PIBs.Based on the systematic theoretical calculation and experimental analysis,the unbalance of charge distribution between Cl and Br atoms leads to an enhanced built-in electric field and a larger interlayer spacing,which can enhance the K^(+)diffusion.Furthermore,the K^(+)insertion causes the energetic evolution of polar states in the BiOCl_(0.5)Br_(0.5) crystal framework,where the dynamic correlation between the K^(+)and the halogen atoms leads to the formation of hole-like polarons,which significantly improves the K^(+)diffusion and reaction kinetics during the charging/discharging process,giving important implications to design the electrode materials with high electrochemical performance by engineering the interaction between electronic structure and interface.Therefore,the BiOCl_(0.5)Br_(0.5) anode obtains an excellent performance of 171 mAh·g^(-1) at 1 A·g^(-1) over 2000 cycles in PIBs.