Interdisciplinary Centre for Nanostructured Materials and Interfaces and Dept of Physics, Università degli Studi di Milano, Milano, Italy.
PLoS One. 2013 Jul 16;8(7):e68655. doi: 10.1371/journal.pone.0068655. Print 2013.
We report on the systematic investigation of the role of surface nanoscale roughness and morphology on the charging behaviour of nanostructured titania (TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces have been characterized by direct measurement of the electrostatic double layer interactions between titania surfaces and the micrometer-sized spherical silica probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a colloidal probe provides well-defined interaction geometry and allows effectively probing the overall effect of nanoscale morphology. By using supersonic cluster beam deposition to fabricate nanostructured titania films, we achieved a quantitative control over the surface morphological parameters. We performed a systematical exploration of the electrical double layer properties in different interaction regimes characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness Rq, the correlation length ξ and the Debye length λD. We observed a remarkable reduction by several pH units of IEP on rough nanostructured surfaces, with respect to flat crystalline rutile TiO2. In order to explain the observed behavior of IEP, we consider the roughness-induced self-overlap of the electrical double layers as a potential source of deviation from the trend expected for flat surfaces.
我们系统地研究了表面纳米级粗糙度和形态对纳米结构二氧化钛（TiO2）表面在水溶液中带电行为的影响。通过在 NaCl 水溶液电解质中直接测量 TiO2 表面和原子力显微镜中微米级球形二氧化硅探针之间的静电双层相互作用，来表征等电点（IEP）。使用胶体探针提供了明确定义的相互作用几何形状，并允许有效地探测纳米形貌的整体效果。通过使用超音速团束沉积来制造纳米结构 TiO2 薄膜，我们实现了对表面形貌参数的定量控制。我们在不同的相互作用区域中进行了系统的探索，这些区域的特征纳米长度比为：表面均方根粗糙度 Rq、相关长度 ξ 和德拜长度 λD。与平晶金红石 TiO2 相比，我们观察到粗糙纳米结构表面的 IEP 显著降低了几个 pH 单位。为了解释观察到的 IEP 行为，我们考虑了粗糙度引起的电双层自重叠，这是偏离平面表面预期趋势的潜在原因。
