Yee Hwa Sehlleier

Electrostatic Self-Assembly Enabling Integrated Bulk and Interfacial Sodium Storage in 3D Titania-Graphene Hybrid

Room-temperature sodium-ion batteries have attracted increased attention for energy storage due to the natural abundance of sodium. However, it remains a huge challenge to develop versatile electrode materials with favorable properties, which requires smart structure design and good mechanistic understanding. Herein, we reported a general and scalable approach to synthesize three-dimensional (3D) titania-graphene hybrid via electrostatic-interaction-induced self-assembly. Synchrotron X-ray probe, transmission electron microscopy, and computational modeling revealed that the strong interaction between titania and graphene through comparably strong van der Waals forces not only facilitates bulk Na+ intercalation but also enhances the interfacial sodium storage. As a result, the titania-graphene hybrid exhibits exceptional long-term cycle stability up to 5000 cycles, and ultrahigh rate capability up to 20 C for sodium storage. Furthermore, density function theory calculation indicated that the interfacial Li+, K+, Mg2+, and Al3+ storage can be enhanced as well. The proposed general strategy opens up new avenues to create versatile materials for advanced battery systems.

Surface functionalization of microwave plasma-synthesized silica nanoparticles for enhancing the stability of dispersions

Abstract Gas phase-synthesized silica nanoparticles were functionalized with three different silane coupling agents (SCAs) including amine, amine/phosphonate and octyltriethoxy functional groups and the stability of dispersions in polar and non-polar dispersing media such as water, ethanol, methanol, chloroform, benzene, and toluene was studied. Fourier transform infrared spectroscopy showed that all three SCAs are chemically attached to the surface of silica nanoparticles. Amine-functionalized particles using steric dispersion stabilization alone showed limited stability. Thus, an additional SCA with sufficiently long hydrocarbon chains and strong positively charged phosphonate groups was introduced in order to achieve electrosteric stabilization. Steric stabilization was successful with hydrophobic octyltriethoxy-functionalized silica nanoparticles in non-polar solvents. The results from dynamic light scattering measurements showed that in dispersions of amine/phosphonate- and octyltriethoxy-functionalized silica particles are dispersed on a primary particle level. Stable dispersions were successfully prepared from initially agglomerated nanoparticles synthesized in a microwave plasma reactor by designing the surface functionalization.

Functionalization of SiO2 nanoparticles and their superhydrophobic surface coating

Silica (SiO2) nanoparticles synthesized from the gas phase in a microwave plasma reactor were dispersed in organic solvents and subsequently chemically modified with silane coupling agents (SCAs) to reduce agglomeration. A transparent and stable dispersion of silica nanoparticles in toluene could be achieved after functionalization with octyltriethoxysilane (OTES). FTIR measurements indicated that the concentration of free hydroxyl groups on the nanoparticle surface was notably decreased. Nanodispersions of functionalized silica particles with several SCAs were prepared and coated onto glass substrates. The resulting highly hydrophilic/hydrophobic glass substrates were investigated by water contact angle measurements. As a result, the hydrophobically OTES-functionalized silica nanoparticles in toluene showed an average diameter of 28 nm and remained for more than eight weeks.