Abstract
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.
Highlights
The encapsulation of plasmonic nanosystems in silica structures, especially gold nanoparticles (AuNPs), has attracted tremendous attention over the last two decades [1,2] since the thermal and mechanical robustness and optical transparency of this material make it an ideal candidate to expand the applications of metal nanoparticles
We looked at the basic routes employed for the synthesis of a family of mesoporous materials discovered in 1992 [37] by researchers at the Mobil Research and Development Corporation called M14S, which includes three different discrete structures: MCM-48, MCM-50, and MCM-41
Mesoporous silica-coated AuNPs were successfully synthesised through a simple strategy that enables control over the crystallinity, pore order and position of the AuNPs
Summary
The encapsulation of plasmonic nanosystems in silica structures, especially gold nanoparticles (AuNPs), has attracted tremendous attention over the last two decades [1,2] since the thermal and mechanical robustness and optical transparency of this material make it an ideal candidate to expand the applications of metal nanoparticles. This is because the silicate salts are soluble in water and charged in alkaline solution; they may interact with the positively charged head groups of the surfactant molecules before the hydrolysis of TEOS begins In light of this effect, a method to manipulate the direction of the silica growth and its crystallinity by controlling the amount of silicate would be of enormous help, being further exploited to confer specific directionality to the synthesis of hybrid Au@SiO2 NPs. Here, we report a simple one-pot reaction methodology that increases the crystallinity of the MCM-41 and allows control over the position of the AuNPs within the mesoporous silica nanostructures upon addition of a small amount of sodium silicate, offering the possibility of realising Janus NPs based on mesoporous silica-coated AuNPs
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
