Investigating the charge transfer mechanism of ZnSe QD/COF S-scheme photocatalyst for H_(2)O_(2) production by using femtosecond transient absorption spectroscopy

Hydrogen peroxide(H_(2)O_(2))has gained widespread attention as a versatile oxidant and a mild disin-fectant.Here,an electrostatic self-assembly method is applied to couple ZnSe quantum dots(QDs)with a flower-like covalent organic framework(COF)to form a step-scheme(S-scheme)photocata-lyst for H_(2)O_(2)production.The as-prepared S-scheme photocatalyst exhibits a broad light absorption range with an edge at 810 nm owing to the synergistic effect between the ZnSe QDs and COF.The S-scheme charge-carrier transfer mechanism is validated by performing Fermi level calculations and in-situ X-ray photoelectron and femtosecond transient absorption spectroscopies.Photolumi-nescence,time-resolved photoluminescence,photocurrent response,electrochemical impedance spectroscopy,and electron paramagnetic resonance results show that the S-scheme heterojunction not only promotes charge carrier separation but also boosts the redox ability,resulting in enhanced photocatalytic performance.Remarkably,a 10%-ZnSe QD/COF has excellent photocatalytic H_(2)O_(2)-production activity,and the optimal S-scheme composite with ethanol as the hole scavenger yields a H_(2)O_(2)-production rate of 1895 mol g^(-1)h^(-1).This study presents an example of a high-performance organic/inorganic S-scheme photocatalyst for H_(2)O_(2)production.

Fabrication of g-C_(3)N_(4) nanosheet/Bi_(5)O_(7)Br/NH_(2)-MIL-88B(Fe)nanocomposites:Double S-scheme photocatalysts with impressive performance for the removal of antibiotics under visible light

Novel graphitic carbon nitride(g-C_(3)N_(4))nanosheet/Bi_(5)O_(7)Br/NH_(2)-MIL-88B(Fe)photocatalysts(denoted as GCN-NSh/Bi_(5)O_(7)Br/FeMOF,in which MOF is metal–organic framework)with double S-scheme heterojunctions were synthesized by a facile solvothermal route.The resultant materials were examined by X-ray photoelectron spectrometer(XPS),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),photoluminescence spectroscopy(PL),Fourier transform infrared spectroscopy(FT-IR),UV-Vis diffuse reflection spectroscopy(UV-vis DRS),photocurrent density,electrochemical impedance spectroscopy(EIS),and Brunauer–Emmett–Teller(BET)analyses.After the integration of Fe-MOF with GCN-NSh/Bi_(5)O_(7)Br,the removal constant of tetracycline over the optimal GCN-NSh/Bi_(5)O_(7)Br/Fe-MOF(15wt%)nanocomposite was promoted 33 times compared with that of the pristine GCN.The GCN-NSh/Bi_(5)O_(7)Br/Fe-MOF(15wt%)nanocomposite showed superior photoactivity to azithromycin,metronidazole,and cephalexin removal that was 36.4,20.2,and 14.6 times higher than that of pure GCN,respectively.Radical quenching tests showed that·O_(2)-and h+mainly contributed to the elimination reaction.In addition,the nanocomposite maintained excellent activity after 4 successive cycles.Based on the developed n–n heterojunctions among n-GCN-NSh,n-Bi_(5)O_(7)Br,and n-Fe-MOF semiconductors,the double S-scheme charge transfer mechanism was proposed for the destruction of the selected antibiotics.

In situ fabrication of Bi_(2)Se_(3)/g-C_(3)N_(4)S-scheme photocatalyst with improved photocatalytic activity

Bismuth selenide(Bi_(2)Se_(3))is an attractive visible-light-responsive semiconductor that can absorb a full range of visible and near-infrared light.However,its poor redox capacity and rapid carrier recombination limit its application in photocatalytic oxidation.In this study,we adopted Bi_(2)Se_(3)as the couple part of graphitic carbon nitride(g-C_(3)N_(4))to construct a Bi_(2)Se_(3)/g-C_(3)N_(4)composite photocatalyst.Through in situ fabrication,the self-developed Bi2O3/g-C_(3)N_(4)precursor was transformed into a Bi_(2)Se_(3)/g-C_(3)N_(4)heterojunction.The as-prepared Bi_(2)Se_(3)/g-C_(3)N_(4)composite exhibited much higher visible-light-driven photocatalytic activity than pristine Bi_(2)Se_(3)and g-C_(3)N_(4)in the removal of phenol.The enhanced photocatalytic activity was ascribed to the S-scheme configuration of Bi_(2)Se_(3)/g-C_(3)N_(4);this was confirmed by the energy-level shift,photoluminescence analysis,computational structure study,and reactive-radical testing.In the S-scheme heterojunction,photo-excited electrons in the conduction band of g-C_(3)N_(4)migrate to the valence band of Bi_(2)Se_(3)and combine with the excited holes therein.By consuming less reactive carriers,the S-scheme heterojunction can not only effectively promote charge separation,but also preserve more reactive photo-generated carriers.This property enhances the photocatalytic activity.

S-Scheme photocatalyst TaON/Bi_(2)WO_(6) nanofibers with oxygen vacancies for efficient abatement of antibiotics and Cr(VI):Intermediate eco-toxicity analysis and mechanistic insights

Enlightened by natural photosynthesis,developing efficient S-scheme heterojunction photocatalysts for deleterious pollutant removal is of prime importance to restore environment.Herein,novel TaON/Bi_(2)WO_(6) S-scheme heterojunction nanofibers were designed and developed by in-situ growing Bi_(2)WO_(6) nanosheets with oxygen vacancies(OVs)on TaON nanofibers.Thanks to the efficiently spatial charge disassociation and preserved great redox power by the unique S-scheme mechanism and OVs,as well as firmly interfacial contact by the core-shell 1D/2D fibrous hetero-structure via the in-situ growth,the optimized TaON/Bi_(2)WO_(6) heterojunction unveils exceptional visible-light photocatalytic property for abatement of tetracycline(TC),levofloxacin(LEV),and Cr(Ⅵ),respectively by 2.8-fold,1.0-fold,and 1.9-fold enhancement compared to the bare Bi_(2)WO_(6),while maintaining satisfactory stability.Furthermore,the systematic photoreaction tests indicate Ta-ON/Bi_(2)WO_(6) has the high practicality in the elimination of pollutants in aquatic environment.The degradation pathway of tetracycline and intermediate eco-toxicity were determined based on HPLC–MS combined with QSAR calculation,and a possible photocatalytic mechanism was elucidated.This work provides a guideline for designing high-performance TaON-based S-scheme photocatalysts with defects for environment protection.

All-organic covalent organic frameworks/perylene diimide urea polymer S-scheme photocatalyst for boosted H_(2) generation

Conjugated covalent organic frameworks(COFs)hold great promise in photocatalytic hydrogen evolution owing to their high crystallinity,large surface area,and distinct structure.However,COFs exhibit poor charge separation.Therefore,investigating highly effective COF-based photocatalysts is crucial.For the first time,conjugated COF/perylene diimide urea polymer(PUP)all-organic heterostructure with S-scheme interfacial charge-transfer channels was successfully developed and manufactured via in situ coupling of the two-dimensional triazine-based imine-linked COF(denoted as TATF-COF)with PUP.The optimal photocatalytic hydrogen-evolution rate of 94.5 mmol h^(-1) g^(-1) for TATF-COF/PUP is 3.5 times that of pure TATF-COF and is comparable to or even higher than that of the previously reported COF-based photocatalysts,resulting in an apparent quantum efficiency of up to 19.7%at 420 nm.The improved directional S-scheme charge transfer driven by the tuned built-in electric field and enhanced oxidation and reduction reaction rates of the photogenerated carriers contribute synergistically to the boosted photocatalytic H_(2) evolution.Experiments and theoretical studies reveal plausible H_(2) evolution and spatial S-scheme charge-separation mechanisms under visible-light irradiation.This study provides advanced methods for constructing all-organic S-scheme high-efficiency photocatalysts by the modulation of band structures.

Chalcogenide-based S-scheme heterojunction photocatalysts

The unique photocatalytic mechanism of S-scheme heterojunction can be used to study new and efficient photocatalysts.By carefully selecting semiconductors for S-scheme heterojunction photocatalysts,it is possible to reduce the rate of photogenerated carrier recombination and increase the conversion efficiency of light into energy.Chalcogenides are a group of compounds that include sulfides and selenides(e.g.,CdS,ZnS,Bi_(2)S_(3),MoS_(2),ZnSe,CdSe,and CuSe).Chalcogenides have attracted considerable attention as heterojunction photocatalysts owing to their narrow bandgap,wide light absorption range,and excellent photoreduction properties.This paper presents a thorough analysis of S-scheme heterojunction photocatalysts based on chalcogenides.Following an introduction to the fundamental characteristics and benefits of S-scheme heterojunction photocatalysts,various chalcogenide-based S-scheme heterojunction photocatalyst synthesis techniques are summarized.These photocatalysts are used in numerous significant photocatalytic reactions,in-cluding the reduction of carbon dioxide,synthesis of hydrogen peroxide,conversion of organic matter,generation of hydrogen from water,nitrogen fixation,degradation of organic pollutants,and sterilization.In addition,cutting-edge characterization techniques,including in situ characterization techniques,are discussed to validate the steady and transient states of photocatalysts with an S-scheme heterojunction.Finally,the design and challenges of chalcogenide-based S-scheme heterojunction photocatalysts are explored and recommended in light of state-of-the-art research.

Recent progress in CdS-based S-scheme photocatalysts

Photocatalytic technology with sunlight as driving force can convert solar energy into other energy sources for storage and further use.Cadmium sulfide(CdS),as a typical reducing semiconductor of metal sulfides,represents an interesting research hotspot in photocatalysis due to its suitable bandgap(2.4 eV)for utilizing visible light and strong reducing ability for inducing surface catalytic reactions.Unfortunately,the photocatalytic performance of CdS is still limited by its fast carrier recombination and serious pho-tocorrosion.So far,CdS semiconductor has been widely developed as a typical reducing photocatalyst in constructing novel S-scheme heterojunction to overcome the above drawbacks.In this review,the de-sign concepts,basic principles,and charge transfer characteristics of CdS-based S-scheme heterojunction photocatalysts have been comprehensively introduced.Several advanced and effective characterization methods for studying the mechanism of CdS-based S-scheme heterojunction are analyzed in detail.Fur-thermore,we also summarize the typical applications of CdS-based S-scheme heterojunctions for water splitting,CO_(2) reduction,pollutant degradation,etc.Eventually,according to the current investigation sta-tus,some drawbacks in the current synthetic strategy,mechanism exploration,and application prospect of CdS-based S-scheme heterojunction are proposed,which need to be addressed by further expansion and innovative research.

Rational construction of CuFe_(2)O_(4)@C/Cd_(0.9)Zn_(0.1)S S-scheme heterojunction photocatalyst for extraordinary photothermal-assisted photocatalytic H_(2) evolution

Rational design of photocatalyst to maximize the use of sunlight is one of the issues to be solved in photocatalysis technology.In this study,the CuFe_(2)O_(4)@C/Cd_(0.9)Zn_(0.1)S(CFO@C/CZS)S-scheme photocatalyst with photothermal effect was synthesized by ultrasonic self-assembly combined with calcination.The dark CFO@C absorbed visible light and partly converted into heat to promote the hydrogen evolution reaction.The presence of heterojunctions inhibited the photogenerated electron-hole recombination.The graphite-carbon layer provided a stable channel for electron transfer,and the presence of magnetic CFO made recycle easier.Under the action of photothermal assistance and heterojunction,the hydrogen evolution rate of the optimal CFO@C/CZS was 80.79 mmol g^(-1) h^(-1),which was 2.55 times and 260.61 times of that of pure CZS and CFO@C,respectively.Notably,the composite samples also exhibit excellent stability and a wide range of environmental adaptability.Through experimental tests and first-principles simulation calculation methods,the plausible mechanism of photoactivity enhancement was proposed.This work provided a feasible strategy of photothermal assistance for the development of heterojunction photocatalysts with distinctive hydrogen evolution.

Self-assembled S-scheme In_(2.77)S_(4)/K^(+)-doped g-C_(3)N_(4)photocatalyst with selective O_(2) reduction pathway for efficient H_(2)O_(2) production using water and air

The development of an efficient artificial H_(2)O_(2) photosynthesis system is a challenging work using H_(2)O and O_(2) as starting materials.Herein,3D In_(2.77)S_(4) nanoflower precursor was in-situ deposited on K^(+)-doped g-C_(3)N_(4)(KCN)nanosheets using a solvothermal method,then In_(2.77)S_(4)/KCN(IS/KCN)het-erojunction with an intimate interface was obtained after a calcination process.The investigation shows that the photocatalytic H_(2)O_(2) production rate of 50IS/KCN can reach up to 1.36 mmol g^(-1)h^(-1)without any sacrificial reagents under visible light irradiation,which is 9.2 times and 4.1 times higher than that of KCN and In_(2.77)S_(4)/respectively.The enhanced activity of the above composite can be mainly attributed to the S-scheme charge transfer route between KCN and In_(2.77)S_(4) according to density functional theory calculations,electron paramagnetic resonance and free radical capture tests,leading to an expanded light response range and rapid charge separation at their interface,as well as preserving the active electrons and holes for H_(2)O_(2) production.Besides,the unique 3D nanostructure and surface hydrophobicity of IS/KCN facilitate the diffusion and transportation of O_(2) around the active centers,the energy barriers of O_(2) protonation and H_(2)O_(2) desorption steps are ef-fectively reduced over the composite.In addition,this system also exhibits excellent light harvesting ability and stability.This work provides a potential strategy to explore a sustainable H_(2)O_(2) photo-synthesis pathway through the design of heterojunctions with intimate interfaces and desired reac-tion thermodynamics and kinetics.

Facet-dependent CuO/{010}BiVO_(4)S-scheme photocatalyst enhanced peroxymonosulfate activation for efficient norfloxacin removal

Rapid recombination of charge carriers and sluggish Cu^(2+)/Cu^(+)conversion rate in Cu-based photocatalysts hinder the improvement of the peroxymonosulfate(PMS)activation efficiency.Herein,a novel S-scheme system was successfully built through hydrothermal and in-situ calcination methods to activate PMS for norfloxacin(NOR)degradation,which combined CuO with BiVO_(4)(BVO)containing surface heterojunc-tion.The UV-vis spectra manifested that BVO displayed excellent visible light absorption performance after compounding with CuO,and the light absorption threshold of CuO/BVO was about 600 nm.Thanks to the existence of surface heterojunction in BVO,the photoinduced electrons,and holes would trans-fer to{010}and{110}facets,respectively.The construction of S-scheme heterojunction further facilitated the accumulation of electrons on CuO,thus realizing the spatial separation of charge carriers.In addi-tion,the electrons gathered on the CuO expedited the Cu^(2+)/Cu^(+)cycle,thereby improving the activation efficiency of PMS.On this basis,the NOR removal capacity of 5CuO/BVO composites was obviously en-hanced,which was 3.65 and 2.45 times that of CuO and BVO.Moreover,the influence of ambient pH and PMS dosage on the photocatalytic performance of CuO/BVO was investigated.Through the analysis of NOR degradation pathways and degradation products,it was found that the toxicity threat of NOR to the environment was reduced during the degradation process.According to the XPS results,forming the S-scheme heterojunction accelerated the Cu^(2+)/Cu^(+)redox cycle during the PMS activating process.Meanwhile,photoluminescence(PL)and time-resolved photoluminescence(TRPL)analysis demonstrated that the CuO/BVO composites exhibited eminent ability for charge separation.The possible mechanism of charge transfer was assumed by exploring reactive species and the energy band structure of catalysts.To sum up,this research provides a new perspective on boosting PMS activation to purify antibiotics in water.

Review on inorganic-organic S-scheme photocatalysts

The inorganic-organic S-scheme heterojunction photocatalyst demonstrates exceptional light absorption capacity,high photogenerated charge separation efficiency,and remarkable redox ability,while also inheriting diverse advantages of both inorganic and organic semiconductors.This paper provides a comprehensive review of recent advances in photocatalysis in relation to the inorganic-organic S-scheme heterojunction photocatalyst.Firstly,the fundamental aspects and benefits of the S-scheme heterojunction photocatalyst are outlined,followed by a discussion of several synthetic techniques for producing the inorganic-organic S-scheme heterojunction photocatalyst,as well as various advanced characterization methods that can verify the S-scheme heterojunction photocatalyst in both steady-state and transient processes.The impact of the inorganic-organic S-scheme heterojunction photocatalyst is illustrated with examples in fields such as carbon dioxide reduction,water splitting for hydrogen production,hydrogen peroxide synthesis,nitrogen fixation,organic pollutant degradation,organic transformation,and sterilization.Finally,suggestions are presented for designing the inorganic-organic S-scheme heterojunction photocatalyst and enhancing its photocatalytic performance.Undoubtedly,the inorganic-organic Sscheme heterojunction photocatalyst has emerged as a prominent and promising technology in the field of photocatalysis.

Enhanced antibiotic degradation performance of Cd_(0.5)Zn_(0.5)S/Bi_(2)MoO_(6) S-scheme photocatalyst by carbon dot modification

S-scheme heterojunction engineering is an effective strategy to attain distinctive photocatalysts.Herein,a carbon dots modulated S-scheme hetero-structured photocatalyst of Cd_(0.5)Zn_(0.5)S nanoparticles/Bi_(2)MoO_(6) microspheres/carbon dots (CZCBM),aiming to conquer the photo-corrosion and strengthen the photocatalytic property of Cd_(0.5)Zn_(0.5)S,was developed via a facile solvothermal route.Under visible light,the optimal CZCBM-2 affords a 1.8-,1.5-,or 0.6-time reinforcement in the oxytetracycline degradation rate constant compared to Bi_(2)MoO_(6),Cd_(0.5)Zn_(0.5)S or Cd_(0.5)Zn_(0.5)S/Bi_(2)MoO_(6),which is credited to the strengthened visible-light response,increased reactive sites,and efficient dissolution of photo-carriers with optimal redox capacity because of the co-effect of carbon dots and S-scheme heterostructure.Significantly,the photo-corrosion of Cd_(0.5)Zn_(0.5)S is significantly suppressed and CZCBM-2 affords superior stability and reusability during cycling tests.Besides,CZCBM-2 can be well adapted to various environments.The toxicology appraisement unravels the decreased eco-toxicity of most intermediates compared to oxytetracycline.Lastly,an S-scheme charge transfer mechanism with carbon dots as electron reservoir in CZCBM is deduced,which uncloses that •O_(2)− and h+ dominantly account for oxytetracycline eradication and detoxification.This study demonstrates the design of unique carbon dots favored S-scheme heterostructures as an effective “Two Birds with One Stone” strategy to achieve high anti-photo-corrosion performance and reinforced photocatalytic performance of sulfides.

BiOBr/COF S-scheme photocatalyst for H_(2)O_(2) production via concerted two-electron pathway

Constructing step-scheme(S-scheme)heterojunctions has become a popular strategy for efficient pho-tocatalytic H_(2)O_(2) generation.Herein,we in situ grew BiOBr nanosheets(NSs)on a Schiff-base covalent organic framework(COF)with largeπ-conjugated structures to prepare S-scheme BiOBr/COF photocat-alysts for H_(2)O_(2) synthesis.The highest photocatalytic H_(2)O_(2) production performance of the composite sample constituting the S-scheme heterojunction is 3749μmol g−1 h−1,which was 1.85 and 27 times the rates of COF and BiOBr,respectively.The construction of S-scheme heterojunction contributed to ef-ficient carrier transfer and separation in space and enhanced redox power.Moreover,the lying-down O_(2)-adsorption configuration on the COF surface favors the concerted two-electron O_(2) reduction process,which greatly reduced the reduction potential requirement for O_(2)-to-H_(2)O_(2) conversion.The synergy be-tween the S-scheme heterojunction and the unique O_(2)-COF interaction boosted photocatalytic H_(2)O_(2) pro-duction activity.

Cu/TiO_(2) Photocatalysts for CO_(2) Reduction: Structure and Evolution of the Cocatalyst Active Form

Extensive work on a Cu-modified TiO_(2) photocatalyst for CO_(2) reduction under visible light irradiation was conducted. The structure of the copper cocatalyst was established using UV-vis diff use refl ectance spectroscopy, high-resolution transmis- sion electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. It was found that copper exists in different states (Cu 0 , Cu^(+) , and Cu^(2+) ), the content of which depends on the TiO_(2) calcination temperature and copper loading. The optimum composition of the cocatalyst has a photocatalyst based on TiO_(2) calcined at 700℃ and modified with 5 wt% copper, the activity of which is 22 μmol/(h·g cat ) (409 nm). Analysis of the photocatalysts after the photocatalytic reaction disclosed that the copper metal on the surface of the calcined TiO_(2) was gradually converted into Cu_(2) O during the photocatalytic reaction. Meanwhile, the metallic copper on the surface of the noncalcined TiO_(2) did not undergo any trans- formation during the reaction.

Enhancing Photocatalytic Hydrogen Evolution through Electronic Structure and Wettability Adjustment of ZnIn_(2)S_(4)/Bi_(2)O_(3) S-Scheme Heterojunction

The production of renewable fuels through water splitting via photocatalytic hydrogen production holds significant promise.Nonetheless,the sluggish kinetics of hydrogen evolution and the inadequate water adsorption on photocatalysts present notable challenges.In this study,we have devised a straightforward hydrothermal method to synthesize Bi_(2)O_(3)(BO)derived from metal‐organic frameworks(MOFs),loaded with flower-like ZnIn_(2)S_(4)(ZIS).This approach substantially enhances water adsorption and surface catalytic reactions,resulting in a remarkable enhancement of photocatalytic activity.By employing triethanolamine(TEOA)as a sacrificial agent,the hydrogen evolution rate achieved with 15%(mass fraction)ZIS loading on BO reached an impressive value of 1610μmol∙h^(−1)∙g^(−1),marking a 6.34-fold increase compared to that observed for bare BO.Furthermore,through density functional theory(DFT)and ab initio molecular dynamics(AIMD)calculations,we have identified the reactions occurring at the ZIS/BO S-scheme heterojunction interface,including the identification of active sites for water adsorption and catalytic reactions.This study provides valuable insights into the development of high-performance composite photocatalytic materials with tailored electronic properties and wettability.

Rational Design and Construction of a CdS QDs/lnVO_(4) Atomic-Layer(110)/(110)Facet S-Scheme Heterojunction for Highly Efficient Photocatalytic Degradation of C_(2)H_(4)

Exploring high efficiency S-scheme heterojunction photocatalysts with strong redox ability for removing volatile organic compounds from the air is of great interest and importance.However,how to predict and regulate the transport of photogenerated carriers in heterojunctions is a great challenge.Here,density functional theory calculations were first used to successfully predict the formation of a CdS quantum dots/InVO_(4)atomic-layer(110)/(110)facet S-scheme heterojunction.Subsequently,a CdS quantum dots/InVO_(4)atomic-layer was synthesized by in-situ loading of CdS quantum dots with(110)facets onto the(110)facets of InVO_(4)atomic-layer.As a result of the deliberately constructed built-in electric field between the adjoining facets,we obtain a remarkably enhanced photocatalytic degradation rate for ethylene.This rate is 13.8 times that of pure CdS and 13.2 times that of pure InVO_(4).In-situ irradiated X-ray photoelectron spectroscopy,photoluminescence and time-resolved photoluminescence measurements were carried out.These experiments validate that the built-in electric field enhanced the dissociation of photoexcited excitons and the separation of free charge carriers,and results in the formation of S-scheme charge transfer pathways.The reaction mechanism of the photocatalytic C_(2)H_(4)oxidation is investigated by in-situ electron paramagnetic resonance.This work provides a mechanistic insight into the construction and optimization of semiconductor heterojunction photocatalysts for application to environmental remediation.

Amplified internal electric field of Cs_(2)CuBr_(4)@WO_(3-x)S-scheme heterojunction for efficient CO_(2)photoreduction

Heterojunction construction,especially S-scheme heterojunction,represents an efficient universal strategy to achieve high-performance photocatalytic materials.For further performance stimulation of these well-designed heterojunctions,modulating the interfacial internal electric field(IEF)to steer dynamic charge transfer represents a promising approach.Herein,we realized the precise regulation of Fermi level(E_(F))of the oxidation semiconductor(mesoporous WO_(3-x))by tailoring the concentration of oxygen vacancies(V_(O)),maximizing the IEF intensity in Cs_(2)CuBr_(4)@WO_(3-x)(CCB@WO_(3-x))S-scheme heterojunction.The augmented IEF affords a robust driving force for directional electron delivery,leading to boosted charge separation.Hence,the developed CCB@WO_(3-x)S-scheme heterojunction demonstrated outstanding photocatalytic CO_(2)reduction performance,with the electron consumption rate(Relectron)up to 390.34μmol g^(-1)h^(-1),which is 3.28 folds higher than that of pure CCB.An in-depth analysis of the S-scheme electron transfer mode was presented via theoretical investigations,electron spin resonance(ESR),photo-irradiated Kelvin probe force microscopy(KPFM),and in-situ X-ray photoelectron spectroscopy(XPS).Finally,the CO_(2)photoconversion route was explored in detail using in-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and DFT theoretical calculations.

Vacancy engineering mediated hollow structured ZnO/ZnS S-scheme heterojunction for highly efficient photocatalytic H_(2) production

Designing a step-scheme(S-scheme)heterojunction photocatalyst with vacancy engineering is a reliable approach to achieve highly efficient photocatalytic H_(2)production activity.Herein,a hollow ZnO/ZnS S-scheme heterojunction with O and Zn vacancies(VO,Zn-ZnO/ZnS)is rationally constructed via ion-exchange and calcination treatments.In such a photocatalytic system,the hollow structure combined with the introduction of dual vacancies endows the adequate light absorption.Moreover,the O and Zn vacancies serve as the trapping sites for photo-induced electrons and holes,respectively,which are beneficial for promoting the photo-induced carrier separation.Meanwhile,the S-scheme charge transfer mechanism can not only improve the separation and transfer efficiencies of photo-induced carrier but also retain the strong redox capacity.As expected,the optimized VO,Zn-ZnO/ZnS heterojunction exhibits a superior photocatalytic H_(2) production rate of 160.91 mmol g^(-1)h^(-1),approximately 643.6 times and 214.5 times with respect to that obtained on pure ZnO and ZnS,respectively.Simultaneously,the experimental results and density functional theory calculations disclose that the photo-induced carrier transfer pathway follows the S-scheme heterojunction mechanism and the introduction of O and Zn vacancies reduces the surface reaction barrier.This work provides an innovative strategy of vacancy engineering in S-scheme heterojunction for solar-to-fuel energy conversion.

Molten salt construction of core-shell structured S-scheme CuInS_(2)@CoS_(2) heterojunction to boost charge transfer for efficient photocatalytic CO_(2) reduction

Weak redox ability and severe charge recombination pose significant obstacles to the advancement of CO_(2) photoreduction.To tackle this challenge and enhance the CO_(2) photoconversion efficiency,fabricating well-matched S-scheme heterostructure and establishing a robust built-in electric field emerge as pivotal strategies.In pursuit of this goal,a core-shell structured CuInS_(2)@CoS_(2)S-scheme heterojunction was meticulously engineered through a two-step molten salt method.This approach over the CuInS_(2)-based composites produced an internal electric field owing to the disparity be-tween the Fermi levels of CoS_(2) and CuInS_(2) at their interface.Consequently,the electric field facili-tated the directed migration of charges and the proficient separation of photoinduced carriers.The resulting CuInS_(2)@CoS_(2) heterostructure exhibited remarkable CO_(2) photoreduction performance,which was 21.7 and 26.5 times that of pure CuInS_(2) and CoS_(2),respectively.The S-scheme heterojunc-tion photogenerated charge transfer mechanism was validated through a series of rigorous anal-yses,including in situ irradiation X-ray photoelectron spectroscopy,work function calculations,and differential charge density examinations.Furthermore,in situ infrared spectroscopy and density functional theory calculations corroborated the fact that the CuInS_(2)@CoS_(2) heterojunction substan-tially lowered the formation energy of *COOH and *CO.This study demonstrates the application potential of S-scheme heterojunctions fabricated via the molten salt method in the realm of ad-dressing carbon-related environmental issues.

Mg-doped SrTaO_(2)N as a visible-light-driven H_(2)-evolution photocatalyst for accelerated Z-scheme overall water splitting

Perovskite SrTaO_(2)N is one of the most promising narrow-bandgap photocatalysts for Z-scheme overall water splitting.However,the formation of defect states during thermal nitridation severely hinders the separation of charges,resulting in poor photocatalytic activity.In the present study,we successfully synthesize SrTaO_(2)N photocatalyst with low density of defect states,uniform morphology and particle size by flux-assisted one-pot nitridation combined with Mg doping.Some important parameters,such as the size of unit cell,the content of nitrogen,and microstructure,prove the successful doping of Mg.The defect-related carrier recombination has been significantly reduced by Mg doping,which effectively promotes the charge separation.Moreover,Mg doping induces a change of the band edge,which makes proton reduction have a stronger driving force.After modifying with the core/shell-structured Pt/Cr_(2)O_(3)cocatalyst,the H_(2)evolution activity of the optimized SrTaO_(2)N:Mg is 10 times that of the undoped SrTaO_(2)N,with an impressive apparent quantum yield of 1.51%at 420 nm.By coupling with Au-FeCoO_(x)modified BiVO_(4)as an O_(2)-evolution photocatalyst and[Fe(CN)_(6)]_(3)−/[Fe(CN)_(6)]_(4)−as the redox couple,a redox-based Z-scheme overall water splitting system is successfully constructed with an apparent quantum yield of 1.36%at 420 nm.This work provides an alternative way to prepare oxynitride semiconductors with reduced defects to promote the conversion of solar energy.