Ziyang Lu

Effect of ultrasonic treatment on dispersibility of Fe3O4 nanoparticles and synthesis of multi-core Fe3O4/SiO2 core/shell nanoparticles

Ultrasonic treatment was employed to improve the dispersibility of the Fe3O4 nanoparticles dispersed in aqueous solutions. Electrophoresis and XPS spectra indicate that the ultrasonic treatment can induce the generation of chemisorbed hydroxyl groups and the oxidation of Fe2+ ions on the surface of the magnetic nanoparticles, thus resulting in improved dispersibility of the magnetic nanoparticles. After growth of silica protection layers on the Fe3O4 nanoparticles with different times of ultrasonic treatment, Fe3O4/SiO2 core/shell nanoparticles with different amounts of the magnetic cores were successfully prepared.

Monodisperse magnetizable silica composite particles from heteroaggregate of carboxylic polystyrene latex and Fe3O4 nanoparticles

Monodisperse magnetizable silica composite particles were prepared from heteroaggregates of carboxylic polystyrene latex and Fe(3)O(4) nanoparticles. It was found that the heteroaggregation of the carboxylic latex and Fe(3)O(4) nanoparticles is dependent on the pH of the solution. At low pH value (pH = 2-4), the aggregation proceeds effectively due to opposite charges on the surfaces of the latex and the magnetic nanoparticles. At high pH value (pH>8), no aggregation was observed due to the negative charge on both the surface of the latex and the magnetic nanoparticles. The heteroaggregate of the latex and magnetic nanoparticles was found to be stable in a wide range of pH values, due to the existence of coordination interactions at the interface of the latex and magnetic nanoparticles. After silica layer coating on the heteroaggregate by the Stöber process and removal of the latex by calcination, hollow monodisperse magnetizable silica composite particles are obtained.

Incorporating anionic dyes into silica nanoparticles by using a cationic polyelectrolyte as a bridge

A negatively charged dye, 8-hydroxypyene-1,3,6-sulfonic acid trisodium salt (HPTS), was successfully incorporated into a silica matrix by using a positively charged polyelectrolyte, poly (diallyldimethylammoniumchloride) (PDADMAC) as a bridge. The positive charges of PDADMAC were partially neutralized by HPTS upon the formation of PDADMAC–HPTS complexes. After being introduced into a Stober system and pre-hydrolyzed for a finite time, the surface charge of the complexes was rapidly reversed from positive to negative due to the absorption of the negatively charged silica species on their surface, which was important to avoid flocculation of the complexes and allow the growth of the silica particles. Stability of the complexes and thus the size of resulting particles were tunable by changing either the positive charges of the complexes or the pre-hydrolyzation time of the Stober system. The optical performance of the silica particles was improved and the leakage of the dye from the particles was greatly suppressed due to the electrostatic interaction between the dye and polyelectrolyte.

Unraveling the Growth Mechanism of Silica Particles in the Stöber Method: In Situ Seeded Growth Model

In this work, we investigated the kinetic balance between ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and subsequent condensation over the growth of silica particles in the Stöber method. Our results reveal that, at the initial stage, the reaction is dictated by TEOS hydrolysis to form silanol monomers, which is denoted as pathway I and is responsible for nucleation and growth of small silica particles via condensation of neighboring silanol monomers and siloxane network clusters derived thereafter. Afterward, the reaction is dictated by condensation of newly formed silanol monomers onto the earlier formed silica particles, which is denoted as pathway II and is responsible for the enlargement in size of silica particles. When TEOS hydrolysis is significantly promoted, either at high ammonia concentration (≥0.95 M) or at low ammonia concentration in the presence of LiOH as secondary catalyst, temporal separation of pathways I and II makes the Stöber method reminiscent of in situ seeded growth. This knowledge advance enables us not only to reconcile the most prevailing aggregation-only and monomer-addition models in literature into one consistent framework to interpret the Stöber process but also to grow monodisperse silica particles with sizes in the range 15-230 nm simply but precisely regulated by the ammonia concentration with the aid of LiOH.