Nanostructured Particles, Crystals, Composites and Assemblies


1. Pore Fabrication in Various Silica-based Nanoparticles by Controlled Etching


We developed a​ novel method based on controlled etching to fabricate nanopores on preformed silica nanoparticles (<100 nm in diameter). The obtained monodisperse nanoporous particles could form highly stable homogeneous colloidal solution. Fluorescent silica nanoparticles and magnetic silica-coated γ-Fe2O3 nanoparticles were investigated as examples to illustrate that this strategy could be generally applied to various silica-based functional nanoparticles. The results indicated that this method was effective for generating pores on these nanoparticles without altering their original functionalities. The obtained multifunctional nanoparticles would be useful for many biological and biomedical applications. These porous nanoparticles could also serve as building blocks to fabricate three-dimensionally periodic structures that have the potential to be used as photonic crystals.



2. One-Step Preparation of Zeolite Silicalite-1 Microspheres with Adjustable Macroporosity


A facile one-step method was developed for the preparation of zeolite silicalite-1 (or ZSM-5) microspheres without the need of pre-synthesizing zeolite nanocrystals. Zeolite nanocrystals (~100 nm) were formed and spontaneously assembled into uniform micrometer-sized (3−5 μm) spheres. The obtained microspheres possess significant textual porosity (up to 0.24 cm3/g), which can be adjusted by simply adding different amounts of styrene in the synthesis. The zeolite microspheres are useful for enzyme immobilization, and the enzyme loading is proportional to the textual porosity.

  • Jia Hua and Yu Han*, Chem. Mater., 21 (2009) 2344-2348​
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3. Site-specific growth of Au particles on ZnO nanopyramids under ultraviolet illumination
In this work, wurtzite ZnO nanocrystals with unique “pyramid” morphology were firstly prepared via solvothermal synthesis. It was determined that the ZnO nanopyramids are grown along the polar c-axis with the vertexes pointing to the [001] direction. When the mixture of ZnO nanopyramids and Au precursor (HAuCl(4)) was exposed to ultraviolet (UV) illumination. The obtained Au/ZnO nanocomposite showed significantly enhanced photocatalytic activity as compared to the bare ZnO nanopyramids. First-principles based calculations demonstrate that the Au particles can accommodate photoelectrons and thus facilitate the charge separation.​

  • Kexin Yao, Xin Liu, Lan Zhao, Huachun Zeng*, Yu Han*, Nanoscale 3 (2011), 4195-4200
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4. Mechanistic investigation into the spontaneous linear assembly of gold nanospheres
By encapsulating aggregates of Au nanospheres in shells of polystyrene-block-poly(acrylic acid), we prevent the dissociation and aggregation typically associated with the drying of solution samples on TEM/SEM substrates. In our study of the salt-induced aggregation of 2-naphthalenethiol-functionalized Au nanospheres in DMF, the trapping of the solution species under various experimental conditions permits new insights in the mechanism thereof. We provide evidence that the spontaneous linear aggregation in this system is a kinetically controlled process and hence the long-range charge repulsion at the “transition state” before the actual contact of the Au nanospheres is the key factor. Thus, the charge repulsion potential (i.e. the activation energy) a nanosphere must overcome before attaching to either end of a nanochain is smaller than attaching on its sides, which has been previously established. This factor alone could give rise to the selective end-on attachment and lead to the linear assembly of originally isotropic Au nanospheres.

    (A–F) TEM images of AuNSn@PSPAA prepared using [NaCl] of (a) 0 mM; (b) 0.44 mM; (c) 0.55 mM; (d) 0.66 mM; (e) 0.77 mM; (f) 0.88 mM​
  • Miaoxin Yang, Gang Chen, Yunfeng Zhao, Georg Silber, Yong Wang, Shuangxi Xing, Yu Han* and Hongyu Chen*, “Mechanistic investigation into the spontaneous linear assembly of gold nanospheres” Phys. Chem. Chem. Phys., 12 (2010), 11850-1186