Kunc Filip, Kodra Oltion, Brinkmann Andreas, Lopinski Gregory P, Johnston Linda J
National Research Council Canada, Ottawa, ON K1A 0R6, Canada.
Nanomaterials (Basel). 2020 Apr 3;10(4):678. doi: 10.3390/nano10040678.
Surface functionalization is a key factor for determining the performance of nanomaterials in a range of applications and their fate when released to the environment. Nevertheless, it is still relatively rare that surface groups or coatings are quantified using methods that have been carefully optimized and validated with a multi-method approach. We have quantified the surface groups on a set of commercial ZnO nanoparticles modified with three different reagents ((3-aminopropyl)-triethoxysilane, caprylsilane and stearic acid). This study used thermogravimetric analysis (TGA) with Fourier transform infrared spectroscopy (FT-IR) of evolved gases and quantitative solution H nuclear magnetic resonance (NMR) for quantification purposes with C-solid state NMR and X-ray photoelectron spectroscopy to confirm assignments. Unmodified materials from the same suppliers were examined to assess possible impurities and corrections. The results demonstrate that there are significant mass losses from the unmodified samples which are attributed to surface carbonates or residual materials from the synthetic procedure used. The surface modified materials show a characteristic loss of functional group between 300-600 °C as confirmed by analysis of FT-IR spectra and comparison to NMR data obtained after quantitative release/extraction of the functional group from the surface. The agreement between NMR and TGA estimates for surface loading is reasonably good for cases where the functional group accounts for a relatively large fraction of the sample mass (e.g., large groups or high loading). In other cases TGA does not have sufficient sensitivity for quantitative analysis, particularly when contaminants contribute to the TGA mass loss. X-ray photoelectron spectroscopy and solid state NMR for selected samples provide support for the assignment of both the functional groups and some impurities. The level of surface group loading varies significantly with supplier and even for different batches or sizes of nanoparticles from the same supplier. These results highlight the importance of developing reliable methods to detect and quantify surface functional groups and the importance of a multi-method approach.
表面功能化是决定纳米材料在一系列应用中的性能及其释放到环境中的归宿的关键因素。然而，使用经过精心优化并通过多方法验证的方法对表面基团或涂层进行量化的情况仍然相对较少。我们已经对一组用三种不同试剂（（3-氨丙基）-三乙氧基硅烷、辛基硅烷和硬脂酸）改性的商用ZnO纳米颗粒上的表面基团进行了量化。本研究使用热重分析（TGA）结合逸出气体的傅里叶变换红外光谱（FT-IR）以及定量溶液¹H核磁共振（NMR）进行定量分析，并使用¹³C固态NMR和X射线光电子能谱来确认归属。对来自同一供应商的未改性材料进行了检查，以评估可能的杂质并进行校正。结果表明，未改性样品存在明显的质量损失，这归因于表面碳酸盐或合成过程中残留的材料。通过对FT-IR光谱的分析以及与从表面定量释放/提取官能团后获得的NMR数据进行比较，证实表面改性材料在300-600°C之间显示出官能团的特征性损失。当官能团占样品质量的比例相对较大时（例如，大基团或高负载量），NMR和TGA对表面负载量的估计之间的一致性相当好。在其他情况下，TGA没有足够的灵敏度进行定量分析，特别是当污染物导致TGA质量损失时。对选定样品进行的X射线光电子能谱和固态NMR为官能团和一些杂质的归属提供了支持。表面基团负载水平因供应商而异，甚至对于来自同一供应商的不同批次或尺寸的纳米颗粒也是如此。这些结果突出了开发可靠方法来检测和量化表面官能团的重要性以及多方法 approach的重要性。 （注：原文中“multi-method approach”未准确翻译，可根据语境灵活处理，这里保留原文供参考）
