Nano-scale spatial confinement can alter chemistry at mineral-water interfaces. These nano-scale confinement effects can lead to anomalous fate and transport behavior of aqueous metal species. When a fluid resides in a nanoporous environments (pore size under 100 nm), the observed density, surface tension, and dielectric constant diverge from those measured in the bulk. To evaluate the impact of nano-scale confinement on the adsorption of copper (Cu2+), we performed batch adsorption studies using mesoporous silica. Mesoporous silica with the narrow distribution of pore diameters (SBA-15; 8, 6, and 4 nm pore diameters) was chosen since the silanol functional groups are typical to surface environments. Batch adsorption isotherms were fit with adsorption models (Langmuir, Freundlich, and Dubinin-Radushkevich) and adsorption kinetic data were fit to a pseudo-first-order reaction model. We found that with decreasing pore size, the maximum surface area-normalized uptake of Cu2+ increased. The pseudo-first-order kinetic model demonstrates that the adsorption is faster as the pore size decreases from 8 to 4 nm. We attribute these effects to the deviations in fundamental water properties as pore diameter decreases. In particular, these effects are most notable in SBA-15 with a 4-nm pore where the changes in water properties may be responsible for the enhanced Cu mobility, and therefore, faster Cu adsorption kinetics.

中文翻译：

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铜（II）在中孔二氧化硅上的吸附：纳米级限制作用。

纳米级的空间限制可以改变矿泉水界面的化学性质。这些纳米级的限制作用会导致水性金属物种的异常命运和运输行为。当流体驻留在纳米多孔环境中（孔径小于100 nm）时，观察到的密度，表面张力和介电常数与大块中测量的密度，表面张力和介电常数不同。为了评估纳米级限制对铜（Cu2 +）吸附的影响，我们使用中孔二氧化硅进行了批量吸附研究。选择具有窄孔径分布的中孔二氧化硅（SBA-15； 8、6和4 nm孔径），因为硅烷醇官能团对于表面环境是典型的。批量吸附等温线适用于吸附模型（Langmuir，Freundlich，（Dubinin-Radushkevich）和吸附动力学数据拟合到拟一级反应模型。我们发现，随着孔径的减小，Cu2 +的最大表面积归一化吸收量增加。拟一级动力学模型表明，随着孔径从8 nm减小到4 nm，吸附更快。我们将这些影响归因于随着孔径的减小基本水属性的偏差。尤其是，这些效应在具有4nm孔的SBA-15中最为明显，其中水性质的变化可能是导致铜迁移率提高的原因，因此，铜的吸附动力学更快。拟一级动力学模型表明，随着孔径从8 nm减小到4 nm，吸附更快。我们将这些影响归因于随着孔径的减小基本水属性的偏差。尤其是，这些效应在具有4nm孔的SBA-15中最为明显，其中水性质的变化可能是导致铜迁移率提高的原因，因此，铜的吸附动力学更快。拟一级动力学模型表明，随着孔径从8 nm减小到4 nm，吸附更快。我们将这些影响归因于随着孔径的减小基本水属性的偏差。尤其是，这些效应在具有4nm孔的SBA-15中最为明显，其中水性质的变化可能是导致铜迁移率提高的原因，因此，铜的吸附动力学更快。