Ultrathin and highly passivating silica shells for luminescent and water-soluble CdSe/CdS nanorods

TL;DR

This study develops a rapid, uniform, and highly passivating silica shell coating for CdSe/CdS nanorods using TMOS, significantly improving encapsulation efficiency and environmental stability compared to traditional methods.

Contribution

It demonstrates that using TMOS enables ultrathin, homogeneous silica shells in just 1 hour, enhancing protection and solubility of nanorods.

Findings

TMOS yields more uniform silica shells than TEOS or TPOS.

Ultrathin silica shells (≤5 nm) provide superior acid resistance.

Reaction time reduced to 1 hour with TMOS.

Abstract

Microemulsion (water-in-oil) methods enable the encapsulation of individual nanoparticles into SiO2 spheres. The major drawbacks of this method, when applied for silica encapsulation of anisotropic nanorods (NRs), are a spatially unequal silica growth and long reaction times (24 h at least). In this work, various tetra-alkoxysilanes (tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS) and tetrapropyl orthosilicate (TPOS)) with different alkyl-chain lengths were used as the silica precursors in attempt to tune the silanization behavior of CdSe/CdS NRs in a microemulsion system. We find an enhanced spatial homogeneity of the silica growth with decreasing alkyl-chain length of the tetra-alkoxysilanes. In particular, by using TMOS as the precursor, NRs can be fully encapsulated in a continuous thin ($\le$ 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 using TEOS. Our investigations suggest that the lower steric hindrance of TMOS compared to TEOS or TPOS strongly promotes the homogeneous growth of the silica shells while its increased hydrolysis rate leads decreases the porosity of these shells.