Spatially confined redox chemistry in periodic mesoporous hydridosilica-nanosilver grown in reducing nanopores

Periodic mesoporous hydridosilica, PMHS, is shown for the first time to function as both a host and a mild reducing agent toward noble metal ions. In this archetypical study, PMHS microspheres react with aqueous Ag(I) solutions to form Ag(0) nanoparticles housed in different pore locations of the mesostructure. The dominant reductive nucleation and growth process involves SiH groups located within the pore walls and yields molecular scale Ag(0) nanoclusters trapped and stabilized in the pore walls of the PMHS microspheres that emit orange-red photoluminescence. Lesser processes initiated with pore surface SiH groups produce some larger spherical and worm-shaped Ag(0) nanoparticles within the pore voids and on the outer surfaces of the PMHS microspheres. The intrinsic reducing power demonstrated in this work for the pore walls of PMHS speaks well for a new genre of chemistry that benefits from the mesoscopic confinement of Si-H groups.     

Sub-nanometer precision modification of the optical properties of three-dimensional polymer-based photonic crystals

We present a convenient post-fabrication technique to precisely tune the optical properties of polymer-based three-dimensional photonic crystals with sub-nanometer precision. Conventional air-plasma etching is utilized to modify the filling fraction of direct laser written polymer photonic crystals beyond the wavelength-imposed limits. Tuning of the optical properties is monitored in transmission and reflection spectroscopy. A simple model for the etching process is proposed and found to be in good agreement with the experimental observations.     

Polymer-like conformation and growth kinetics of Bi2S3 nanowires

One-dimensional inorganic crystals (i.e., crystalline nanowires) are one of the most intensely investigated classes of materials of the past two decades. Despite this intense effort, an important question has yet to be answered: do nanowires display some of the unique characteristics of polymers as their diameter is progressively decreased? This work addresses this question with three remarkable findings on the growth and form of ultrathin Bi(2)S(3) nanowires. (i) Their crystallization in solution is quantitatively describable as a form of living step-growth polymerization: an apparently exclusive combination of addition of "monomer" to the ends of the nanowires and coupling of fully formed nanowires "end-to-end", with negligible termination and initiation. (ii) The rate constants of these two main processes are comparable to those of analogous processes found in polymerization. (iii) The conformation of these nanowires is quantitatively described as a worm-like conformation analytically analogous to that of semiflexible polymers and characterized by a persistence length of 17.5 nm (shorter than that of double-stranded DNA) and contour lengths of hundreds of micrometers (longer than those of most synthetic polymers). These findings do not prove a chemical analogy between crystals and polymers (it is unclear if the monomer is a molecular entity tout court) but demonstrate a physical analogy between crystallization and polymerization. Specifically, they (i) show that the crystallization of ensembles of nanoscale inorganic crystals can be conceptually analogous to polymerization and can be described quantitatively with the same experimental and mathematical tools, (ii) demonstrate that one-dimensional nanocrystals can display topological characteristics of polymers (e.g., worm-like conformation in solution), (iii) establish a unique experimental model system for the investigation of polymer-like topological properties in inorganic crystals, and (iv) provide new heuristic guidelines for the synthesis of polymer-like nanowires.     

Mechanical stability enhancement by pore size and connectivity control in colloidal crystals by layer-by-layer growth of oxide

Control of the pore size and connectivity of micro-sphere colloidal crystal lattices has been achieved by a layer-by-layer growth of silica using atmospheric pressure room temperature chemical vapour deposition of silica, a method which largely increases the mechanical stability of the lattice without disrupting its long range order.     

Synthetic self-propelled nanorotors

Self-powered completely synthetic nanorotors have been prepared from barcoded gold-nickel nanorods having the gold end anchored to the surface of a silicon wafer; constant velocity circular movements are observed when hydrogen peroxide fuel is catalytically decomposed to oxygen at the unattached nickel end of the nanorod.