Rotureau Elise, Rocha Luciana S, Goveia Danielle, Alves Nuno G, Pinheiro José Paulo
Université de Lorraine, CNRS, LIEC, Nancy, France.
Centro Interdisciplina de Quimica do Algarve (CIQA), Departamento de Quimica e Bioquimica (DQB)/Faculdade de Ciencia e Tecnologia (FCT), University of Algarve, Faro, Portugal.
Front Chem. 2020 Dec 16;8:614574. doi: 10.3389/fchem.2020.614574. eCollection 2020.
Silica oxides nano- and microparticles, as well as silica-based materials, are very abundant in nature and industrial processes. Trace metal cation binding with these bulk materials is generally not considered significant in speciation studies in environmental systems. Nonetheless, this might change for nanoparticulate systems as observed in a previous study of Pb(II) with a very small SiO particle (7.5 nm diameter). Besides, metal binding by those nanoparticles is surprisingly characterized by a heterogeneity that increases with the decrease of metal-to-particle ratio. Therefore, it is interesting to extend this study to investigate different trace metals and the influence of the nanoparticle size on the cation binding heterogeneity. Consequently, the Cd(II), Pb(II), and Zn(II) binding by two different sized SiO nanoparticles (Ludox LS30 and TM40) in aqueous dispersion was studied for a range of pH and ionic strength conditions, using the combination of the electroanalytical techniques Scanned Stripping ChronoPotentiometry and Absence of Gradients and Nernstian Equilibrium Stripping. The coupling of these techniques provides the free metal concentration in the bulk (AGNES) and information of the free and complex concentration at the electrode surface for each Stripping Chronopotentiometry at Scanned deposition Potential (SSCP). A recent mathematical treatment allows the reconstruction of a portion of the metal to ligand binding isotherm with the included heterogeneity information using the full SSCP wave analysis. In this work, we observed that the Zn(II) binding is homogeneous, Cd(II) is slightly heterogeneous, and Pb(II) is moderately heterogeneous, whereas the results obtained with the 7.5 nm diameter nanoparticle are slightly more heterogeneous than those obtained with the one of 17 nm. These findings suggest that the Zn(II) binding is electrostatic in nature, and for both Cd(II) and Pb(II), there should be a significant chemical binding contribution.
二氧化硅纳米颗粒和微米颗粒以及硅基材料在自然界和工业过程中非常丰富。在环境系统的形态研究中，痕量金属阳离子与这些块状材料的结合通常被认为并不重要。然而，正如之前对非常小的二氧化硅颗粒（直径7.5纳米）进行的铅（II）研究中所观察到的那样，对于纳米颗粒系统而言，情况可能会有所不同。此外，那些纳米颗粒对金属的结合令人惊讶地具有异质性，且这种异质性会随着金属与颗粒比例的降低而增加。因此，扩展这项研究以探究不同的痕量金属以及纳米颗粒尺寸对阳离子结合异质性的影响是很有意思的。为此，使用电分析技术扫描溶出计时电位法以及无梯度和能斯特平衡溶出法的组合，研究了两种不同尺寸的二氧化硅纳米颗粒（Ludox LS30和TM40）在水相分散体系中对镉（II）、铅（II）和锌（II）的结合情况，研究范围涵盖了一系列pH值和离子强度条件。这些技术的结合提供了本体中的游离金属浓度（AGNES），以及每次扫描沉积电位溶出计时电位法（SSCP）时电极表面的游离和络合浓度信息。最近的一种数学处理方法允许使用完整的SSCP波分析，利用包含的异质性信息重建部分金属与配体的结合等温线。在这项工作中，我们观察到锌（II）的结合是均匀的，镉（II）的结合略有异质性，铅（II）的结合具有中等异质性，而直径7.5纳米的纳米颗粒所得到的结果比直径17纳米的纳米颗粒所得到的结果异质性略高。这些发现表明，锌（II）的结合本质上是静电作用，而对于镉（II）和铅（II）而言，应该存在显著的化学结合作用。
