当量子点邂逅光催化
本期导读：
本期文献精选向大家快递几篇用量子点作催化剂进行光催化的文章。关于光催化的重要性和美好愿景，就无需小编BB了。“号子”里这么多催化大神，肯定早就熟知了其中的“猫腻”。
量子点能够吸收可见光，必然就有人拿它来试试光催化。但是系统的研究量子点作为光催化剂的可能性，肯定不仅仅是因为量子点能吸收可见光。个人认为一个很重要的原因是量子点合成体系完善，可调控性强，而且具有尺寸效应。这些特点弥补了传统多相催化剂的不足。传统多相催化剂，合成方法比较粗糙（浸渍浸渍、焙烧焙烧，完事）。从而导致可调控性差，比如尺寸，形貌，晶型等。相比而言，量子点材料的液相合成已经发展成熟，其对材料的控制已经十分精细，比如可以通过控制大小来调节吸收和发射波长；各种形貌的调控也较为简单；晶型的调控也不难实现。
首先分享一篇综述：
Semiconductor nanostructures that can effectively serve as light-responsive photocatalysts have been of considerable interest over the past decade. This is because their use in light-induced photocatalysis can potentially address some of the most serious environmental and energy-related concerns facing the world today. Oneimportant application is photocatalytic hydrogen production from water undersolar radiation. It is regarded as a clean and sustainable approach to hydrogen fuel generation because it makes use of renewable resources (i.e., sunlight and water), does not involve fossil fuel consumption, and does not result in environmental pollution or green house gas emission. Another notable applicationis the photocatalytic degradation of nonbiodegradable dyes, which offers aneffective way of ridding industrial wastewater of toxic organic pollutantsprior to its release into the environment. Metal oxide semiconductors (e.g.,TiO2) are the most widely studied class of semiconductor photocatalysts. Their nanostructured forms have been reported to efficiently generate hydrogen from water and effectively degrade organic dyes under ultraviolet-light irradiation. However, the wide band gap characteristic ofmost metal oxides precludes absorption of light in the visible region, which makes up a considerable portion of the solar radiation spectrum. Meanwhile,nanostructures of cadmium chalcogenide semiconductors (e.g., CdS), with their relatively narrow band gap that can be easily adjusted through size control and alloying, have displayed immense potential as visible-light-responsive photocatalysts, but the intrinsic toxicity of cadmium poses potential risks tohuman health and the environment.
Indeveloping new nanostructured semiconductors for light-driven photocatalysis, it is important to choose a semiconducting material that has a high absorptioncoefficient over a wide spectral range and is safe for use in real-world settings. Among the most promising candidates are the multinary chalcogenide semiconductors (MCSs), which include the ternary I-III-VI2 semiconductors(e.g., AgGaS2, CuInS2, and CuInSe2) and the quaternary I2-II-IV-VI4 semiconductors (e.g., Cu2ZnGeS4, Cu2ZnSnS4, and Ag2ZnSnS4). These inorganic compounds consist of environmentally benign elemental components, exhibit excellent light-harvesting properties, and possess band gap energies that are well-suited for solar photon absorption. Moreover, the band structuresof these materials can be conveniently modified through alloying to boost their ability to harvest visible photons. In this Account, we provide a summary of recent research on the use of ternary I-III-VI2 and quaternary I2-II-IV-VI4 semiconductor nanostructures for light-induced photocatalytic applications, with focus on hydrogen productionand organic dye degradation. We include a review of the solution-based methods that have been employed to prepare multinary chalcogenide semiconductor nanostructures of varying compositions, sizes, shapes, and crystal structures, which are factors that are known to have significant influence on thephotocatalytic activity of semiconductor photocatalysts. The enhancement of photocatalytic performance through creation of hybrid nanoscale architecturesis also presented. Lastly, views on the current challenges and future directions are discussed in the concluding section.
该综述围绕多元素（I‐III-VI2&I2‐II-IV-VI4）量子点的光催化展开。为什么不是以经典的CdSe或者CdS作为研究对象？回答很简单，因为这两者里面都有Cd。文中首先介绍这类量子点的合成方法，以及如何实现成分控制、尺寸控制、形貌控制和晶面控制。紧接着介绍了量子点和金属纳米粒子复合结构材料的协同作用。最后总结这类材料在产氢和染料降解方面的应用。
通过成分控制可以进行能带工程。比如ZnS的带宽太宽不能吸收可见光，CuInS2的导带底不足以将H2O还原成H2。然而通过合金可以很好的解决这些问题。尺寸调节则更为重要，尺寸越小、比表面积越大、催化活性位点越多。但是并非越小越好，因为尺寸小，表面缺陷多，使得光生激子容易被捕获。形貌和晶型在光催化同样重要，文中指出一维量子点材料有利于电子和空穴的分离。
下面这篇是李亚栋院士近期发在JACs上的一篇通讯。他们合成了一种复合结构的量子点纳米棒（Cu1.94S−ZnxCd1−xS）。这种纳米材料具有出色的光催化效果。文章的亮点在于材料的“试得其用”，即发挥了组分调控的优势，又展现了特殊形貌的长处，还有好文章不可缺少的理论计算。Cu1.94S吸收近红外光、ZnxCd1-xS吸收可见光，两者结合拓宽了吸光范围，同时两者纳米尺度的结合利于电子和空穴的分离。再掺点贵金属Pt，产氢效率一路飙升。具体牛B到什么程度，各位去看原文吧。
In this Communication, we present the integration of synergetic designs into high-quality, well-defined Cu1.94S–ZnxCd1–xS heteronanorods (0 ≤ x ≤ 1) for enhanced photocatalytic hydrogen evolution. These heteronanorods possess two light absorbers, intimate heterointerfaces, tunable band gaps over a wide range, and uniformone-dimensional morphology. As verified by experimental and density functional theory studies, these heteronanorods with continuous composition adjustmentfully exploit the benefits of both interfacial charge separation and optimized band alignments. Even without any cocatalysts, Cu1.94S–Zn0.23Cd0.77S heteronanorods exhibit efficient hydrogen production activity (7735 μmol h–1 g–1)under visible-light irradiation (λ > 420 nm), representing a 59-fold enhancement compared with the pristine CdS catalyst. Meanwhile, deposition of a Pt cocatalyst on the Cu1.94S–ZnxCd1–xS surface substantially enhances the hydrogen production performance (13 533 μmolh–1 g–1) with an apparent quantum efficiency of 26.4% at 420 nm, opening up opportunities to promote the overall photocatalytic performance using rationally designed nanostructures.
虽然量子点材料作为光催化剂具有众多优点和长处，但是同样存在巨大的挑战。其中一个重要问题是：目前溶液相合成的量子点并不是单纯的无机材料，其表面包袱有一层有机配体。所以量子点催化剂其实是有机无机的复杂结构材料。有机配体的引入导致体系变得复杂很多。第一：导致能级结构发生变化，特别是表面能级，同时配体自身的能级对量子点也会有影响。第二：配体可能会限制光生激子的转移。所以如何测试量子点在催化剂中的实际氧化还原电势显得尤为重要。
第三篇文章介绍了通过potentiometric method 的方法测试量子点的氧化还原电势和其费米能级的位置。具体内容和原理，欢迎大家阅读原文哦。
A potentiometric method for measuring redox potentials of colloidal semiconductor nanocrystals (NCs) is described. Fermi levels of colloidal ZnO NCs are measured in situ during photodoping, allowing correlation of NC redox potentials and reduction levels. Excellent agreement is found between electrochemical and optical redox-indicator methods. Potentiometry is also reported for colloidal CdSe NCs, which show more negative conduction-band-edge potentials than in ZnO. This difference is highlighted by spontaneous electron transfer from reduced CdSe NCs to ZnO NCs in solution, with potentiometry providing a measure of the inter-NC electron-transfer driving force. Future applications of NC potentiometry are briefly discussed.
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用量子点来做光催化，这件事你怎么看？靠谱么？