Hypothesis

Sodium adsorption on silica surfaces depends on the solution counter-ion. Here, we use NaOH solutions to investigate basic environments.

Simulations

Sodium adsorption on hydroxylated silica surfaces from NaOH solutions were investigated through molecular dynamics with a dissociative force field, allowing for the development of secondary molecular species.

Findings

Across the NaOH concentrations (0.01 M − 1.0 M), ∼50% of the Na⁺ ions were concentrated in the surface region, developing silica surface charges between − 0.01 C/m² (0.01 M NaOH) and − 0.76 C/m² (1.0 M NaOH) due to surface site deprotonation. Five inner-sphere adsorption complexes were identified, including monodentate, bidentate, and tridentate configurations and two additional structures, with Na⁺ ions coordinated by bridging oxygen and hydroxyl groups or water molecules. Coordination of Na⁺ ions by bridging oxygen atoms indicates partial or complete incorporation of Na⁺ ions into the silica surface. Residence time analysis identified that Na⁺ ions coordinated by bridging oxygen atoms stayed adsorbed onto the surface four times longer than the mono/bi/tridentate species, indicating formation of relatively stable and persistent Na⁺ ion adsorption structures. Such inner-sphere complexes form only at NaOH concentrations of > 0.5 M. Na⁺ adsorption and lifetimes have implications for the stability of silica surfaces.

中文翻译：

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NaOH溶液与二氧化硅表面的相互作用

假设

钠在二氧化硅表面的吸附取决于溶液的抗衡离子。在这里，我们使用NaOH解决方案来研究基本环境。

模拟

通过具有解离力场的分子动力学研究了钠在NaOH溶液中对羟基化二氧化硅表面的吸附，从而发展了次级分子。

发现

在整个NaOH浓度（0.01 M-1.0 M）中，约50％的Na ⁺离子集中在表面区域，在-0.01 C / m ²（0.01 M NaOH）和-0.76 C / m ²之间形成二氧化硅表面电荷。（1.0 M NaOH）归因于表面位点去质子化。鉴定了五个内层吸附复合物，包括单齿，双齿和三齿构型以及两个其他结构，其中Na ⁺离子通过桥连氧和羟基或水分子来协调。的Na的协调⁺通过桥接氧原子离子的Na指示的部分或完全掺入⁺离子进入二氧化硅表面。停留时间分析表明，Na ⁺通过桥接氧原子配位的离子比单/双/三齿物种保持吸附在表面的时间长四倍，表明形成了相对稳定和持久的Na ⁺离子吸附结构。此类内球络合物仅在> 0.5 M的NaOH浓度下形成。Na ^+的吸附和寿命对二氧化硅表面的稳定性有影响。