Unexpected “Hammerlike Liquid” to Pulverize Silica Powders to Stable Sols and Its Application in the Preparation of Sub-10 nm SiO<sub>2</sub> Hybrid Nanoparticles with Chirality

2017-04-30T00:00:00Z (GMT) by Xin-Ling Liu Seiji Tsunega Ren-Hua Jin
Silane coupling agents are well-known as surface modifiers for various kinds of silica (SiO<sub>2</sub>). However, in the present research, it has been found that they can also work as “hammerlike liquid” to pulverize different kinds of bulk amorphous SiO<sub>2</sub> in aqueous systems. This new function was typically clarified by using 3-aminopropyltrimethoxysilane (APS) and bundles of chiral SiO<sub>2</sub> nanofibers (with average diameter of ∼10 nm) as raw materials. By a simple reflux of the mixture of SiO<sub>2</sub> nanofibers and excessive APS in pure H<sub>2</sub>O, the solid-containing mixture turned into a completely clear solution that contained sub-10 nm, amine-modified, and water-soluble hybrid SiO<sub>2</sub> sols (HS-sols). Moreover, this solution showed blue luminescence under ultraviolet irradiation. Furthermore, the circular dichroism and vibrational circular dichroism spectra revealed that the HS-sols are optically active even though the pristine chiral SiO<sub>2</sub> nanofibers were completely destroyed. It was considered that the chirality of SiO<sub>2</sub> nanofibers was due to the asymmetric arrangement of Si and O atoms in chiral domains (<10 nm) on the Si–O–Si network of SiO<sub>2</sub>, and these domains are still preserved in chiral HS-sols. This green method has high potential for the recycling of rich SiO<sub>2</sub> sources to obtain functional SiO<sub>2</sub> nanomaterials with applications such as optical display, imaging, and chiral recognition. Also, it offers a tool for the analysis of the structural properties of SiO<sub>2</sub> on the molecular scale.