Ultrathin and Highly Passivating Silica Shells for Luminescent and Water-Soluble CdSe/CdS Nanorods

Abstract

Microemulsion (water-in-oil) methods enable the encapsulation of individual nanoparticles into SiO spheres. The major drawbacks of this method, when applied for silica encapsulation of anisotropic nanorods (NRs), are spatially unequal silica growth and long reaction times (24 h at least). In this work, various tetraalkoxysilanes [tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), and tetrapropyl orthosilicate (TPOS)] with different alkyl-chain lengths were used as silica precursors in attempt to tune the silanization behavior of CdSe/CdS NRs in a microemulsion system. We find enhanced spatial homogeneity of silica growth with decreasing alkyl-chain length of the tetraalkoxysilanes. In particular, by use of TMOS as the precursor, NRs can be fully encapsulated in a continuous thin (≤5 nm) silica shell within only 1 h reaction time. Surprisingly, the thin silica shell showed a superior shielding ability to acidic environment, even compared to the 30 nm thick shell prepared by use of TEOS. Our investigations suggest that the lower steric hindrance of TMOS compared to TEOS or TPOS strongly promotes homogeneous growth of the silica shells, while its increased hydrolysis rate decreases the porosity of these shells.

Versatile route to core–shell reinforced network nanostructures

“…For the functionalization of nanoparticles with a silica shell, a plethora of methods is described in the literature which are mostly based on the Stöber process. 35 Due to the substrate not being a nanoparticle in solution but rather a macroscopic body (consisting of a network of nanocrystals), methods involving microemulsions 36,37 could not be used. We therefore opted for a synthesis that is similar to the direct coating methods reported, 38,39 with much simpler conditions than the microemulsion routes in terms of the solvent system since no surfactants are employed, see the Experimental section for details.…”

Nanocrystal Aerogels with Coupled or Decoupled Building Blocks

“…To investigate whether the sequence of synthesis steps (namely, network formation and silica coating) influence the physical properties of the resulting nanocrystal aerogels in terms of fluorescence lifetime, the same NRs as those used for the production of the described modified gels were now first surrounded with silica shells according to literature procedures 29 (see the Experimental Methods section and Figure 2b) and subsequently gelated in the presence of further TEOS. This resulted in a silica matrix with singular embedded NRs, which were not in direct contact with each other and should therefore have been decoupled, i.e., they should not have shown increased PL decay times (see also Figure S6 in the Supporting Information).…”

Ripening of Gold Clusters into a Single Domain on Semiconductor Quantum Rods during Langmuir–Blodgett Deposition

“…This finding is in good agreement with previous reports published elsewhere. 33,34 However, the spectrum does not show any typical characteristics of amine groups such as the potential peaks at 1576 and 3300 cm −1 that correspond to the NH 2 scissoring mode and the ν (N−H) stretching mode, respectively. It means although oleylamine was used as a stabilizer for Au 3+ ions during the initial gold cluster attachment on the surface of CdSe/CdS core/shell SNCs, all (or at least majority) of them did not passivate or reside on the surface of SNCs but were removed through the washing process.…”