Strong nano size effect of titanium silicalite (TS-1) zeolites for electrorheological fluid

Abstract

A rapid seeded growth was observed on nanosized (50–100 nm) titanium silicalite-1 (TS-1) zeolites (denoted as nano-TS-1) with a recovered mother liquid. Only 3–8 h were required to synthesize the zeolites with a yield above 80% at 393–423 K in a hydrothermal condition. Such a high efficiency is superior to the conventional synthesis, which produces the sub-micron (100–200 nm) TS-1 within 8–36 h without any seeding effect by the mother liquid. The synthesis of the nano-TS-1 was relatively insensitive to the synthesis condition, though dependent on the seeding effect, water content, and titanium precursors. A possible explanation is proposed for the formation of the MFI type TS-1 zeolites based on the ESI-MS spectra analysis on the synthesis gel. The basic building units (BBU), composed of the active SiO2 species, especially the monomer silicic acid, were firstly induced to the polymerization and formed the special secondary building units (SBU), including certain critical SimOn species for constructing. These SBUs were assembled to mfi cages (as a compositing building unit) and pentasil-type chains, fabricated as a MFI-type crystal. The recovered mother liquid not only provided certain amount of SBU-type SixOy species that accelerated the nucleation and formation of the zeolites, but also intensified the super-saturation of the active SiO2 species that would favor the nanosized zeolites. Such nanoscale size endows the TS-1 zeolites with large external surface area (148 m2/g) and zeta potential value (−47 mV), accounting for the novel dispersion of the nanoparticles. The composition of TiO2/SiO2 in the nano-particles created superior electro rheological properties to those of the conventional sub-micron TS-1 zeolites.