Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials
Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials
复制标题
DOI：
10.1021/jacs.9b05509
复制
发表时间：
2019-10-02
影响因子：
15
通讯作者：
Rossini, Aaron J.
中科院分区：
文献类型：
--
作者：
Hanrahan, Michael P.;Chen, Yunhua;Rossini, Aaron J.
表面表征对于理解原子级结构如何影响半导体纳米颗粒（NPs）的化学和物理性质至关重要。固态核磁共振光谱（NMR）是一种潜在的强有力的技术，用于表征纳米粒子的表面，但它受到了不良的灵敏度。动态核极化表面增强NMR光谱（DNP SENS）先前已被证明，以提高1-2个数量级的表面选择性固态NMR实验的灵敏度。用于NP上的DNP SENS实验的已建立的样品制备需要在介孔二氧化硅上稀释NP。使用六方氮化硼（h-BN）分散纳米粒子加倍DNP增强和绝对灵敏度相比，标准协议与介孔二氧化硅。或者，将NP沉淀为粉末，将它们与h-BN混合，然后用自由基溶液浸渍粉末状混合物，通过增加最终样品中NP的浓度，导致灵敏度进一步提高4倍。与先前建立的DNP SENS程序相比，这种修改的程序提供了NMR灵敏度的9倍改进，使得能够在CdS，Si和Cd 3 P2 NP上进行具有挑战性的同源和异源2D NMR实验。这些实验允许NMR信号从表面，地下和核心网站进行观察和分配。例如，我们证明了在CdS NP上获得DNP增强的2D Cd-113-Cd-113相关NMR实验和官能化Si NP的天然各向同性丰度2D C-13-Si-29 HETCOR。这些实验提供了一个关键的理解NP表面结构。
Surface characterization is crucial for understanding how the atomic-level structure affects the chemical and photophysical properties of semiconducting nanoparticles (NPs). Solid-state nuclear magnetic resonance spectroscopy (NMR) is potentially a powerful technique for the characterization of the surface of NPs, but it is hindered by poor sensitivity. Dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) has previously been demonstrated to enhance the sensitivity of surface-selective solid-state NMR experiments by 1-2 orders of magnitude. Established sample preparations for DNP SENS experiments on NPs require the dilution of the NPs on mesoporous silica. Using hexagonal boron nitride (h-BN) to disperse the NPs doubles DNP enhancements and absolute sensitivity in comparison to standard protocols with mesoporous silica. Alternatively, precipitating the NPs as powders, mixing them with h-BN, and then impregnating the powdered mixture with radical solution leads to further 4-fold sensitivity enhancements by increasing the concentration of NPs in the final sample. This modified procedure provides a factor of 9 improvement in NMR sensitivity in comparison to previously established DNP SENS procedures, enabling challenging homonuclear and heteronuclear 2D NMR experiments on CdS, Si, and Cd3P2 NPs. These experiments allow NMR signals from the surface, subsurface, and core sites to be observed and assigned. For example, we demonstrate the acquisition of DNP-enhanced 2D Cd-113-Cd-113 correlation NMR experiments on CdS NPs and natural isotropic abundance 2D C-13-Si-29 HETCOR of functionalized Si NPs. These experiments provide a critical understanding of NP surface structures.