论文部分内容阅读
开发低成本的半导体光催化剂以实现可见光下高效、持久的光催化分解水产氢化是一个非常具有挑战性的课题.近年来,1D MnxCd1-xS纳米结构由于载流子扩散路径短,长径比高,具有优异的光吸收、电荷分离和H2析出活性,而广泛地应用在光催化H2析出应用中.然而,单一的MnxCd1-xS光催化剂仍然存在着一些缺点,如光生电子-空穴对的快速复合和量子效率低等.为了进一步促进光生电荷载流子的分离和H2释放动力学,采用原位溶剂热法合成了Mn0.2Cd0.sS纳米棒(MCS NRs)和Ti3C2 MXene纳米片(NSs)之间的1D/2D肖特基异质结.采用各种表征方法深入地研究了金属Ti3C2 MXene NSs在Mn0.2Cd0.8S纳米棒上促进光催化H2进化的关键作用和潜在机制.通过X射线衍射(XRD)、透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)、元素分布图和X射线光电子能谱(xPs)等测试手段,证实成功地构建了低成本的肖特基杂质结,并将其应用于光催化产氢反应中.此外,在Na2SO3和Na2S混合牺牲剂溶液中,进行了光催化析氢反应.优化后的1 D/2D肖特基异质结的最高析氢速率为15.73 mmol·g-1·h-1,比纯MCS NRs (2.34 mmol·g-1·h-1)高6.72倍.在420 nm处获得了19.6％的表观量子效率(AQE).稳定性测试结果表明,二元光催化剂具有良好的光催化稳性性及广阔的应用前景.更有趣的是,紫外-可见漫反射光谱、光致发光(PL)光谱、瞬态光电流响应和极化曲线谱都清楚地证实了MCS NRs和Ti3C2 MXene纳米片之间的有效电荷分离.线性扫描伏安法(LSV)也表明,MXene助催化剂的加入可以显著降低纯MCS NRs的过电位,证实2D Ti3C2 NSs可以作为电子导电桥梁,改善H2析出动力学.总之,金属Ti3C2 MXene NSs和MCS NRs之间的2D/1D杂化肖特基异质结不仅可以大大改善光生电子和空穴的分离,而且可以减少H2析出过电位,从而显著提高光催化产氢活性.希望本文的研究能为低成本肖特基异质结的构建提供新的思路,为光催化H2生产的实际应用提供参考.“,”Sustainable photocatalytic H2 evolution has attracted extensive attention in recent years because it can address both energy shortage and environmental pollution issues.In particular,metal sulfide solid-solution photocatalysts have been widely applied in photocatalytic hydrogen generation owing to their excellent light harvesting properties,narrow enough band gap,and suitable redox potentials of conduction and valance bands.However,it is still challenging to develop low-cost and high-efficiency sulfide solid-solution photocatalysts for practical photocatalytic hydrogen evolution.Recently,1D MnxCd1-xS nanostructures have shown superior light absorption,charge separation,and H2-evolution activity owing to their shortened diffusion pathway of carriers and high length-to-diameter ratios.Thus,1D MnxCd1-xS nanostructures have been applied in photocatalytic H2 evolution.However,a single MnxCd1-xS photocatalyst still has some disadvantages for photocatalytic H2 evolution,such as the rapid recombination of photogenerated electron-hole pairs and low quantum efficiency.Herein,to further boost the separation of photogenerated charge carriers and H2-evolution kinetics,an in situ solvothermal method was used to synthesize the 1D/2D Schottky-based heterojunctions between the Mn0.2Cd0.8S nanorods (MCS NRs) and Ti3C2 MXene nanosheets (NSs).Furthermore,various characterization methods have been used to investigate the crucial roles and underlying mechanisms of metallic Ti3C2 MXene NSs in boosting the photocatalytic H2 evolution over the Mn0.2Cd0.8S nanorods.X-ray Diffraction (XRD),Transmission Electron Microscope (TEM),High Resolution Transmission Electron Microscopy (HRTEM),element mapping images,and X-ray Photoelectron Spectroscopy (XPS) results clearly demonstrate that hybrid low-cost Schottky-based heterojunctions have been successfully constructed for practical applications in photocatalytic H2 evolution.Additionally,the photocatalytic hydrogen evolution reaction (HER) was also carried out in a mixed solution of Na2SO3 and Na2S using as the sacrificial agents.The highest hydrogen evolution rate of the optimized 1D/2D Schottky-based heterojunction is 15.73 mmol·g-1·h-1,which is 6.72 times higher than that of pure MCS NRs (2.34 mmol·g-1·h-1).An apparent quantum efficiency of 19.6％ was achieved at 420 nm.The stability measurements of the binary photocatalysts confirmed their excellent photocatalytic stability for practical applications.More interestingly,the UV-Vis diffuse reflection spectra,photoluminescence (PL) spectrum,transient photocurrent responses,and Electrochemical Impedance Spectroscopy (EIS)Nyquist plots clearly confirmed the promoted charge separation between the MCS NRs and Ti3C2 MXene NSs.The linear sweep voltammetry also showed that the loading of MXene cocatalysts could greatly decrease the overpotential of pure MCS NRs,suggesting that the 2D Ti3C2 NSs could act as an electronic conductive bridge to improve the H2-evolution kinetics.In summary,these results show that the 2D/1D hybrid Schottky-based heterojunctions between metallic Ti3C2 MXene NSs and MCS NRs can not only improve the separation of photogenerated electrons and holes but also decrease the H2-evolution overpotential,thus resulting in significantly enhanced photocatalytic H2 generation.We believe that this study will inspire new ideas for constructing low-cost Schottky-based heterojunctions for practical applications in photocatalytic H2 evolution.