Santana Vega Marina, Guerrero Martínez Andrés, Cucinotta Fabio
School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
Departamento de Química Física, Universidad Complutense de Madrid, Avenida Complutense s/n, 28040 Madrid, Spain.
Nanomaterials (Basel). 2019 Mar 3;9(3):348. doi: 10.3390/nano9030348.
Hybrid materials prepared by encapsulation of plasmonic nanoparticles in porous silica systems are of increasing interest due to their high chemical stability and applications in optics, catalysis and biological sensing. Particularly promising is the possibility of obtaining gold@silica nanoparticles (Au@SiO₂ NPs) with Janus morphology, as the induced anisotropy can be further exploited to achieve selectivity and directionality in physical interactions and chemical reactivity. However, current methods to realise such systems rely on the use of complex procedures based on binary solvent mixtures and varying concentrations of precursors and reaction conditions, with reproducibility limited to specific Au@SiO₂ NP types. Here, we report a simple one-pot protocol leading to controlled crystallinity, pore order, monodispersity, and position of gold nanoparticles (AuNPs) within mesoporous silica by the simple addition of a small amount of sodium silicate. Using a fully water-based strategy and constant content of synthetic precursors, cetyl trimethylammonium bromide (CTAB) and tetraethyl orthosilicate (TEOS), we prepared a series of four silica systems: (A) without added silicate, (B) with added silicate, (C) with AuNPs and without added silicate, and (D) with AuNPs and with added silicate. The obtained samples were characterised by transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and UV-visible spectroscopy, and kinetic studies were carried out by monitoring the growth of the silica samples at different stages of the reaction: 1, 10, 15, 30 and 120 min. The analysis shows that the addition of sodium silicate in system B induces slower MCM-41 nanoparticle (MCM-41 NP) growth, with consequent higher crystallinity and better-defined hexagonal columnar porosity than those in system A. When the synthesis was carried out in the presence of CTAB-capped AuNPs, two different outcomes were obtained: without added silicate, isotropic mesoporous silica with AuNPs located at the centre and radial pore order (C), whereas the addition of silicate produced Janus-type Au@SiO₂ NPs (D) in the form of MCM-41 and AuNPs positioned at the silica⁻water interface. Our method was nicely reproducible with gold nanospheres of different sizes (10, 30, and 68 nm diameter) and gold nanorods (55 × 19 nm), proving to be the simplest and most versatile method to date for the realisation of Janus-type systems based on MCM-41-coated plasmonic nanoparticles.
通过将等离子体纳米颗粒封装在多孔二氧化硅体系中制备的杂化材料，因其高化学稳定性以及在光学、催化和生物传感领域的应用而越来越受到关注。特别有前景的是获得具有两面神形态的金@二氧化硅纳米颗粒（Au@SiO₂ NPs）的可能性，因为诱导的各向异性可进一步用于在物理相互作用和化学反应性中实现选择性和方向性。然而，目前实现此类体系的方法依赖于基于二元溶剂混合物以及不同浓度的前驱体和反应条件的复杂程序，其可重复性仅限于特定类型的Au@SiO₂ NPs。在此，我们报告了一种简单的一锅法方案，通过简单添加少量硅酸钠，可实现介孔二氧化硅内金纳米颗粒（AuNPs）的结晶度、孔有序性、单分散性和位置的可控。使用完全水基策略以及合成前驱体十六烷基三甲基溴化铵（CTAB）和正硅酸四乙酯（TEOS）的恒定含量，我们制备了一系列四种二氧化硅体系：（A）不添加硅酸盐，（B）添加硅酸盐，（C）有AuNPs且不添加硅酸盐，以及（D）有AuNPs且添加硅酸盐。通过透射电子显微镜（TEM）、小角X射线散射（SAXS）和紫外可见光谱对所得样品进行了表征，并通过监测反应不同阶段（1、10、15、30和120分钟）二氧化硅样品的生长进行了动力学研究。分析表明，体系B中硅酸钠的添加导致MCM - 41纳米颗粒（MCM - 41 NP）生长较慢，因此与体系A相比具有更高的结晶度和更明确的六方柱状孔隙率。当在CTAB包覆的AuNPs存在下进行合成时，得到了两种不同的结果：不添加硅酸盐时，得到各向同性的介孔二氧化硅，AuNPs位于中心且具有径向孔有序性（C），而添加硅酸盐则产生了MCM - 41形式的两面神型Au@SiO₂ NPs（D），且AuNPs位于二氧化硅 - 水界面。我们的方法对于不同尺寸（直径为10、30和68 nm）的金纳米球和金纳米棒（55×19 nm）具有良好的可重复性，被证明是迄今为止实现基于MCM - 41包覆的等离子体纳米颗粒的两面神型体系最简单、最通用的方法。
