A straightforward and effective process for coating silver, gold and platinum nanoparticles with functionalized silica shells at room temperature has been developed by A*STAR . Crucially, unlike conventional methods for producing silica-coated metal nanoparticles, this process is based on water and does not employ alcohol, making it both cost-effective and environmentally friendly.
Silica-coated noble metal nanoparticles have attracted great interest because they can be used as catalysts as well as in calorimetric and optical applications. They are typically produced using silane precursors, but these are generally insoluble in water. Consequently, alcohol has to be added to water to facilitate the hydrolysis of these precursors, increasing the cost of production and making the process less green.
Scanning electron microscopy image showing silica-coated silver nanoparticles produced by a simple and effective alcohol-free process (inset shows high-magnification image).
Reproduced, with permission, from Ref. 1 © 2014 Royal Society of Chemistry
Now, a team led by Ming-Yong Han and Shah Kwok Wei at the A*STAR Institute of Materials Research and Engineering has devised an alcohol-free method for producing silica-coated noble metal nanoparticles.
To do this, the team took a commonly used precursor, tetramethoxysilane (Si(OCH₃)₄), and substituted a polar group (mercaptopropyl) for a methoxy group (O–CH3), which resulted in a water-soluble precursor. Then, to enable this precursor to bind directly with the metal nanoparticle surfaces, they functionalized it with a thiol group (–SH).
This process has many advantages. It is straightforward to implement, efficient, universal and easily scalable. Furthermore, since the thickness of the silica shell increases with coating time, shell thickness can be readily controlled up to several tens of nanometers.
By slightly modifying the process, Han and colleagues could also produce nanoparticles that have a high activity for an extremely sensitive spectroscopic technique known as surface-enhanced Raman scattering (SERS) and are promising for highly sensitive detection in analytical and biological applications. SERS is based on the hugely enhanced Raman signal generated when a Raman-active compound is adsorbed on a metal surface. The researchers prepared the fluorescence-free SERS-active nanoparticles by sandwiching Raman-active molecules between the noble metal nanoparticle and the silica shell.
“The simplicity of the silica coating process means it has great potential for coating and protecting the surfaces of various kinds of metal nanoparticles,” explains Han. “Furthermore, the resulting highly negatively charged and SERS-active metal nanoparticles with thiol-functionalized silica shells and surface-protective features are very promising for various applications involving aqueous solutions.”
In particular, Han notes, this water-based route to facile, efficient and functional silica coating of metal nanoparticles at room temperature could be extended to coat metal oxide nanoparticles for green building applications.
 Shah, K. W., Sreethawong, T., Liu, S.-H., Zhang, S.-Y., Tan, L. S. & Han, M.-Y. Aqueous route to facile, efficient and functional silica coating of metal nanoparticles at room temperature. Nanoscale 6, 11273–11281 (2014).
A*STAR Research | ResearchSEA
Atomic structure of ultrasound material not what anyone expected
21.02.2018 | North Carolina State University
Hidden talents: Converting heat into electricity with pencil and paper
20.02.2018 | Helmholtz-Zentrum Berlin für Materialien und Energie
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.
But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...
Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.
The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...
Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters
Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
21.02.2018 | Materials Sciences
21.02.2018 | Health and Medicine
21.02.2018 | Physics and Astronomy