噻吩基二维共价有机框架中的拓扑结构诱导局部电荷极化促进光催化制氢

共价有机框架(COFs)是近年来新兴的一类多孔聚合物,在气体吸附、传感器、能源转换和光/电催化等领域表现出较大的应用潜力.然而,欲实现多样化的应用需求常需要对其结构进行合成后改性,这在单一步骤中难以实现.二维亚化学计量共价有机框架(2D-SSCOFs)因其独特的周期性官能团和保持结晶性及孔隙率的能力,成为COFs功能化的新途径.然而,已报道的2D-SSCOFs多具有相同的拓扑结构以及弱电荷极化等问题,限制了其应用潜力.因此,开发具有新颖拓扑结构的2D-SSCOFs对于实现更前沿的功能至关重要.窄带隙噻吩是有机半导体材料的常见单元,它们可以显著地调控共价聚合物骨架的电子和化学环境.本文通过5,5',5''-(苯-1,3,5-三基)三(噻吩-2-甲醛)(TT-3CHO)与4,4',4'',4''-(芘-1,3,6,8-四基)四苯胺(PY-4HN2)的席夫碱缩合反应合成具有大表面积和高结晶度的亚胺连接的新型2D-SSCOF(PTT-COF).噻吩环中2,5位之间的键的弯曲角度使得PTT-COF具有新型的2D亚化学计量拓扑结构,并呈现出非中心对称的优势极化结构.在使用有机空穴传输配体(二茂铁甲醛,FC)精确修饰和Pt作为助催化剂时,PTT-COF-FC体系在可见光照明下表现出较高的析氢产率(79.610 mmol g^(-1) h^(-1)).同时,在420 nm波长的光照下,2 mg的光催化剂表观量子效率达到1.72%.此外,经过24 h循环稳定性测试,PTT-COF-FC体系的活性没有明显下降.为了深入研究PTT-COF-FC体系的高效的产氢机制,通过X射线衍射、红外和固体碳谱等对PTT-COF-FC体系的组成和结构进行分析,确定了PTT-COF-FC的成功合成.通过瞬态吸收、变温荧光和理论计算等研究了材料的激子解离和载流子转移行为.结果表明,得益于独特的富含噻吩的结构设计以及有机空穴传输配体的修饰作用,PTT-COF-FC展现出高效的激子解离和丰富的自由电荷载流子特性.综上所述,本文设计和合成了一种新型PTT-COF光催化材料,其独特的二维亚化学计量拓扑结构和显著的局部电荷极化特性赋予了材料良好的光催化性能.实验和理论研究表明,PTT-COF中的非中心对称拓扑结构和噻吩单元的引入,有效扩展了π离域,进而诱导了局部极化并抑制了激子效应,从而大幅提高了光催化效率.此外,通过二茂铁甲醛的后修饰,结合这些独特的结构特性,PTT-COF在光催化析氢反应中表现出高活性和出色的长期耐久性.本文的研究不仅为设计和构建具有独特结构的新型2D-SSCOF提供新思路,也为构建具有丰富光催化功能的材料开辟了新途径.

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.

Piezoelectric nanofoams with the interlaced ultrathin graphene confining Zn–N–C dipoles for efficient piezocatalytic H_(2) evolution under low-frequency vibration

Unique nanofoams consisting of interweaved ultrathin graphene confining Zn–N–C dipoles (ZnNG) are constructed via calcination of Zn-coordinated precursor.Due to the introduction of local polar Zn–N–C configurations,with hypersensitivity for mechanical stress,the piezoelectricity is created on the nonpiezoelectric graphene,and the hierarchical ZnNG exhibits obvious piezocatalytic activity of water splitting for H_(2) production even under mild agitation.The corresponding rate of H_(2) production is about 14.65 μmol g^(-1)h^(-1).It triggers a breakthrough in piezocatalytic H_(2) evolution under low-frequency vibration,and takes a significant step forward for piezocatalysis towards practical applications.Furthermore,the presented concept of confining atomic polar configuration for engineering piezoelectricity would open up new horizon for constructing new-type piezoelectrics based on both piezoelectric and nonpiezoelectric materials.

Yolk-shell FeSe_(2)@CoSe_(2)/FeSe_(2) heterojunction as anode materials for sodium-ion batteries with high rate capability and stability

Sodium-ion batteries are promising candidates for large-scale grid storage systems and other applications.Their foremost advantage derives from superior environmental credentials,enhanced safety as well as lower raw material costs than lithium-ion batteries.It is still challenging to explore desirable anode material.In this study,FeSe_(2)@CoSe_(2)/FeSe_(2),with a yolk-shell structure was prepared by ion exchange and selenisation.The FeSe_(2)@CoSe_(2)/FeSe_(2)prepared as anode material for sodiumion batteries exhibits excellent rate capability due to the synergistic effect of bimetallic selenides and the interfacial effect of the heterostructure.Moreover,it delivers high performance(510 mAh g^(-1)at 0.2 A g^(-1)),superior rate capa-bility(90%retention at 5 A g^(-1)),and good long-time cycling stability(78%capacity retention after 1800 cycles at a high current density of 2 A g^(-1)).The optimized sodiumion full cell with FeSe_(2)@CoSe_(2)/FeSe_(2)as the anode and Na 3 V 2(PO 4)3 as the cathode still demonstrates excellent performance.Namely,a ca-pacity of 272 mAh g^(-1)(at 1 A g^(-1))within the operating voltage from 1 to 3.8 V can be obtained.This work illustrates the potential of bimetallic selenides with heterostructures for performance enhancement of sodium-ion batteries.

Cs_(3)Bi_(2)B_(9)/BiOBr S-scheme heterojunction for selective oxidation of benzylic C-H bonds

Converting hydrocarbons into aldehydes in a green and environmentally benign way is of great signif-icance in fine chemistry.In this work,all-inorganic Cs_(3)Bi_(2)B_(9) perovskite nanoparticles were uniformly loaded on BiOBr nanosheets via an in-situ growth method,which can selectivity photoactivate aromatic C(sp3)-H bond of toluene to generate benzaldehyde.According to the in-situ X-ray photoelectron spec-troscopy characterization,the photogenerated electrons of BiOBr transfer to Cs_(3)Bi_(2)B_(9) enforced by the in-ternal electric field under light irradiation,resulting in S-scheme heterojunction.Furthermore,theoretical calculations indicate that toluene molecules are inclined to adsorb on the BiOBr surface,subsequently in-volving the oxidation reaction to generate benzyl radical(PhCH_(2)·)by using the energetic holes of BiOBr,while the remaining photoinduced electrons in the conduction band(CB)of Cs_(3)Bi_(2)B_(9) with powerful reduction ability reduce O2 into·O_(2)^(-),which is the vital oxidative active species working on toluene selective oxidation process.Such an unexceptionable charge carrier utilization mode and tendentious ad-sorption behavior of reactants contribute to the optimized Cs_(3)Bi_(2)B_(9)/BiOBr heterojunction with excellent photocatalytic performance,achieving a maximum of 22.5%toluene conversion and 96.2%selectivity to-wards benzaldehyde formation.This work provides a rational photocatalyst heterojunction construction protocol for the selective oxidation of saturated aromatic C-H bonds.

In situ synthesis of flexible Bi_(7)O_(9)I_(3)/carbon paper with enhanced photocatalytic activity

Although Bi_(7)O_(9)I_(3) is an oxygen-rich bismuth oxyiodide with higher photocatalytic activity than BiOI,its applicability for photocatalytic oxidation is limited by the rapid recombination of photogenerated carriers and poor reusability.Depositing Bi_(7)O_(9)I_(3) on flexible macro-sized carbonaceous materials is a promising approach for promoting photogenerated electron migration and improving reusability.In this study,a composite consisting of Bi_(7)O_(9)I_(3) supported on graphitic carbon paper(Bi_(7)O_(9)I_(3)-CP)was synthesized via the in situ transformation of a BiOl-deposited carbon paper precursor(BiOl-CP).The as-prepared Bi_(7)O_(9)I_(3)-CP exhibited higher visible-light-driven photocatalytic activity than both Bi_(7)O_(9)I_(3) and BiOI-CP precursor for phenol removal.The improved photocatalytic activity of Bi_(7)O_(9)I_(3)-CP was attributed to its hierarchical structure and promoted carrier separation,as revealed by photoluminescence,pore structure,and reactive radical analyses.Moreover,owing to its macroscale size and flexibility,the Bi_(7)O_(9)I_(3)-CP composite could be easily operated and reused,which are favorable for practical applications.

Constructing Covalent Triazine Frameworks/N-Doped Carbon-Coated Cu_(2)O S-Scheme Heterojunctions for Boosting Photocatalytic Hydrogen Production

The development of efficient photocatalysts for hydrogen production is crucial in sustainable energy research.In this study,we designed and prepared a Covalent Triazine Framework(CTF)-Cu_(2)O@NC composite featuring an S-scheme heterojunction structure aimed at enhancing the photocatalytic hydrogen production.The light absorption capacity,electron-hole separation efficiency and H_(2)-evolution activity of the composite were significantly enhanced due to the synergistic effects of the nitrogen-doped carbon(NC)layer and the S-scheme heterojunction.Structural and photoelectrochemical characterization of the system reveal that the S-scheme heterojunctions not only enhance the separation efficiency of photogenerated carriers but also maintain the strong redox capabilities to further promote the photocatalytic reactions.Moreover,the NC layer could simultaneously reduce the photocorrosion of Cu_(2)O and promote the electron transfer.Experimental results demonstrate that the CTF-7%Cu_(2)O@NC composite shows outstanding hydrogen-production performance under visible light,achieving 15645μmol∙g^(−1)∙h^(−1),significantly surpassing the photocatalytic activity of pure CTF(2673μmol∙g^(−1)∙h^(−1)).This study introduces a novel approach to the development of efficient and innovative photocatalytic materials,strongly supporting the advancement of sustainable hydrogen energy.

S-scheme photocatalyst Bi2O3/TiO2 nanofiber with improved photocatalytic performance

In this study,a hierarchical Bi2O3/TiO2 fibrous composite was in-situ fabricated on an electrospun TiO2 nanofiber at ambient temperature.In the Bi2O3/TiO2 composite,S-scheme electron migration occurred between Bi2O3 and TiO2.In the photocatalytic degradation of phenol under simulated sunlight,the asprepared Bi2O3/TiO2 nanofibers considerably outperformed Bi2O3 nanoparticles and TiO2 nanofibers.This improvement is contributed by maintaining and effectively utilizing the useful carriers and consuming the useless holes and electrons,realized by the S-scheme heterojunction and hierarchical structure.This study also provides an alternative design fashion for photocatalysts.

Floatable S-scheme photocatalyst for H_(2)O_(2) production and organic synthesis

As an industrial benign oxidant and alternative clean energy carrier for fuel cells,hydrogen peroxide(H_(2)O_(2))becomes the fo-cus of numerous studies.Photocatalytic H_(2)O_(2) synthesis becomes a sustainable protocol[1,2].However,traditional biphase systems suffer from the agglomeration and recycling difficulty of suspended photocatalysts,as well as sluggish delivery of gas reactants,which induces severe charge recombination and slow reaction kinetics[3].

Efficient interfacial charge transfer of BiOCl-In_(2)O_(3) step-scheme heterojunction for boosted photocatalytic degradation of ciprofloxacin

BiOCl as a representative layered bismuth-based photocatalyst with Sillén-structure has aroused wide public concern on photocatalytic degradation.However,the photocatalytic efficiency of pristine BiOCl is currently restricted by its low optical absorption and charge separation efficiency.Herein,step-scheme(S-scheme)heterojunctions of In_(2)O_(3) nanoparticle and BiOCl micron-sheet were constructed by a convenient molten salt method by using a LiNO_(3)-KNO_(3) system.The In_(2)O_(3)-BiOCl heterojunctions exhibit higher optical absorption performance from 380 nm to 700 nm than the pristine BiOCl and enhanced photocatalytic property toward ciprofloxacin(CIP)degradation under Xenon lamp illumination.The sample 20%In_(2)O_(3) -BiOCl showed the highest photodegradation efficiency,attaining 91%removal of CIP within 35 min,which was 39.6 times and 3.2 times higher than that of pristine In_(2)O_(3) and BiOCl,respectively.The improved photodegradation property mainly resulted from the novel S-scheme mechanism,which boosted highly efficient separation of the photo-induced carriers.The photoluminescence spectrometric test and transient photocurrent response results demonstrated that In_(2)O_(3)-BiOCl composite exhibited efficient separation of photo-generated charge carriers.This work would provide new insights into the design of novel S-scheme photocatalytic systems with applicability in photocatalytic water treatment.

Plasmonic TiN nanobelts assisted broad spectrum photocatalytic H_(2) generation

The conversion of solar energy in a wide spectrum region to clean fuel,H_(2),remains a challenge in the field of photocatalysis.Herein,plasmonic TiN nanobelts,as a novel cocatalyst,were coupled with CdS nanoparticles to construct a 0D/1D CdS/TiN heterojunction.Utilization of the localized surface plasmon resonance(LSPR)effect generated from TiN nanobelts was effective in promoting light absorption in the near-infrared region,accelerating charge separation,and generating hot electrons,which can effectively improve the photocatalytic H_(2) generation activity of the 0D/1D CdS/TiN heterojunction over a wide spectral range.Furthermore,owing to the high metallicity and low work function,an ohmic-junction was formed between the CdS and TiN,favoring the transfer of hot electrons generated from TiN nanobelts the CdS nanoparticles,followed by the reaction with water to generate H_(2).Consequently,the 0D/1D CdS/TiN heterojunction demonstrated H_(2) generation activity even under light irradiation at 760 nm,while the pure CdS and Pt nanoparticles modified CdS presented no activity.This work opens a new insight into coupling plasmonic cocatalysts to realize full spectrum H_(2) production.

Effective photocatalytic hydrogen evolution by Ti_(3)C_(2)-modified CdS synergized with N-doped C-coated Cu_(2)O in S-scheme heterojunctions

Photocatalytic hydrogen evolution through water splitting holds tremendous promise for converting solar energy into a clean and renewable fuel source.However,the efficiency of photocatalysis is often hindered by poor light absorption,insufficient charge separation,and slow reaction kinetics of the photocatalysts.In this study,we designed and synthesized a novel S-scheme heterojunction comprising Ti_(3)C_(2)MXene,CdS nanorods,and nitrogen-doped carbon coated Cu_(2)O(Cu_(2)O@NC)core-shell nanoparticles.Ti_(3)C_(2)MXene as a cocatalyst enhances the light absorption and charge transfer of CdS nanorods.Simultaneously,the core-shell Cu_(2)O@NC nanoparticles establish a pathway for transferring photogenerated electrons and create a favorable band alignment for efficient hydrogen evolution.The synergistic effects of Ti_(3)C_(2)MXene and Cu_(2)O@NC on CdS nanorods result in multiple charge transfer channels and improved photocatalytic performance.The optimal hydrogen evolution rate of the Ti_(3)C_(2)-CdS-Cu_(2)O@NC S-scheme heterojunction photocatalyst is 7.4 times higher than that of pure CdS.Experimental techniques and DFT calculations were employed to explore the structure,morphology,optical properties,charge dynamics,and band structure of the heterojunction.The results revealed that the S-scheme mechanism effectively suppresses the recombination of photogenerated carriers and facilitates the separation and migration of photo-generated electrons and holes to the reaction sites.Furthermore,Ti_(3)C_(2)MXene provides abundant active sites essential for accelerating the surface H_(2)-evolution reaction kinetics.The Cu_(2)O@NC core-shell nanoparticles with a large surface area and high stability are closely adhered to CdS nanorods and establish an S-scheme internal electric field with CdS nanorods to drive charge separation.This investigation provides valuable insights into the rational design of CdS-based photocatalysts,enabling efficient hydrogen production by harnessing the robust kinetic driving force provided by the S-scheme heterojunctions.

One-pot synthesis of array-like sulfur-doped carbon nitride with covalently crosslinked ultrathin MoS cocatalyst for drastically enhanced photocatalytic hydrogen evolution

Constructing noble-metal-free loaded catalyst with high-efficiency photocatalytic activity by a simple and scalable method is of profound significance for fundamental research and practical application.Herein,a simple one-pot method was used to synthesize novel samples of array-like sulfur-doped graphitic carbon nitride(SCN)nanosheets with ultrathin MoS2 loading(MS/SCN-x%).The ultrathin MoS2 cocatalyst was evenly distributed on the surface of SCN and was linked to the main catalyst by covalent chemical bonds.Benefited from the multiple advantages of the array-like porous nanosheets structure with rich exposed surface,covalent cross-linking structure,and enhanced visible light absorption,the MS/SCN-2.5%composites drastically improve hydrogen evolution performance,which is superior to original MoS2 nanosheet modified by two-step mixing method,and also rivals with Pt/SCN.The designing strategy of photocatalyst modified by noble-metal-free cocatalyst with covalent bond structure provides fascinating insights into enhanced photocatalytic hydrogen evolution.