Revealing the Molecular Identity of Defect Sites on PbS Quantum Dot Surfaces with Redox-Active Chemical Probes
Revealing the Molecular Identity of Defect Sites on PbS Quantum Dot Surfaces with Redox-Active Chemical Probes
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DOI：
10.1021/acs.chemmater.1c00520
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发表时间：
2021-03-16
影响因子：
8.6
通讯作者：
Dempsey, Jillian L.
中科院分区：
文献类型：
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作者：
Hartley, Carolyn L.;Dempsey, Jillian L.
半导体量子点（QD）表面的缺陷限制了这些有前途的材料的应用。然而，使用化学方法合理钝化这些位点的努力受到缺乏对表面缺陷的分子水平理解的限制。在本文中，我们报告了氧化还原活性化学探针（E度' = -0.48至-1.9V vs Fe+/0）与光谱工具（核磁共振（NMR）、X射线光电子能谱（XPS）和UV-vis-NIR）结合的应用，以深入了解PbS QD表面缺陷的分子水平性质和反应性。首先，铅离子为基础的陷阱协调油酸配体进行了研究，通过反应与外层还原剂，其中减少的Pb 2+离子的亚群促进配体置换。我们观察到这种反应性和量子点大小之间的相关性，其中最小的配体位移发生在小量子点（2.6 nm），但高达约。15%的配体被更大的QD（>4 nm）取代。还原剂的强度也具有显著影响;在QD尺寸保持恒定的情况下，更有效的还原剂比温和的还原剂诱导更高程度的配体置换。最后，硫族化合物为基础的缺陷（二硫化物）询问与选择性三烷基膦试剂。量子点与膦探针的反应性的比较表明，大PbS量子点具有比小量子点更大比例的天然二硫键缺陷。总的来说，这项工作产生洞察到的身份，可能的结构环境和目标缺陷位点的还原电位，从而提供了一个详细的图片和路线图钝化常见的量子点表面缺陷。
Defects arising on the surfaces of semiconductor quantum dots (QDs) limit the applications of these otherwise promising materials. Efforts to rationally passivate these sites using chemical methods, however, are limited by a lack of molecular-level understanding of surface defects. Herein, we report the application of redoxactive chemical probes (E degrees' = -0.48 to -1.9 V vs Fe+/0) coupled with spectroscopic tools (nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR) to gain insight into the molecular-level nature and reactivity of defects at PbS QD surfaces. First, Pb ion-based traps coordinated by oleate ligands are studied by reaction with outer-sphere reductants, wherein reduction of a subpopulation of Pb2+ ions promotes ligand displacement. We observe a correlation between this reactivity and QD size, wherein minimal ligand displacement occurs in small QDs (2.6 nm) but up to ca. 15% of ligands are displaced with larger QDs (>4 nm). The strength of the reductant also has a significant impact; with QD size held constant, more potent reductants induce a higher extent of ligand displacement than mild reductants. Finally, chalcogenide-based defects (disulfides) are interrogated with selective trialkylphosphine reagents. Comparison of QD reactivity with phosphine probes reveals that large PbS QDs possess a greater proportion of native disulfide defects than small QDs. Collectively, this work yields insight into the identities, likely structural environments and reduction potentials of targeted defect sites, thus providing a detailed picture-and roadmap for passivation-of common QD surface defects.