Synthesis of silica-coated ZnO nanocomposite : the resonance structure of polyvinyl pyrrolidone (PVP) as a coupling agent

Abstract The preparation of silica-coated ZnO nanocomposite using polyvinyl pyrrolidone (PVP) as a coupling agent was investigated. Transmission electron microscopy analysis revealed that silica has been deposited on the surface of PVP-capped ZnO nanoparticles as a continuous thin layer. Two-dimensional correlation analysis based on the time-dependent UV–vis spectra was introduced to study the interaction governing the deposition of silica on to PVP-capped ZnO. Strong hydrogen bonds formed between the amphiphilic PVP molecules and silica in the silicacoated PVP-capped ZnO composites. The reduced photocatalytic activity of silica-coated ZnO nanoparticles will enhance their performance as durable, safe, and nonreactive UV blockers in plastics, paints, and coating for outdoor textile and timber products.

Nanocrystalline titanium to mesoporous anatase with high bioactivity

In present study, the formation of bioactive anatase on bulk titanium (Ti) by hybrid surface mechanical attrition treatment (SMAT) is reported. A commercial pure Ti plate first underwent SMAT in a vacuum for 1 h to produce a nanocrystalline layer with a thickness of about 30 µm, and then the nanocrystalline Ti (30 nm) was transformed into mesoporous anatase with a grain size 10 nm by chemical oxidation and calcination. The mesoporous anatase showed excellent bioactivity while being soaked in simulated body fluid, which could be attributed to the unique nanostructure on the SMAT Ti surface.

Diatoms : self assembled silica nanostructures, and templates for bio/chemical sensors and biomimetic membranes

In this review we highlight recent advances in the understanding of biosilica production, biomodification of diatom frustules and their subsequent applications in bio/chemical sensors, and as a model membrane for filtration and separation.

Double-layer and hydration forces measured between silica sheets subjected to various surface treatments

Force measurements between silica surfaces in aqueous solutions of NaCl are reported. Silica is prepared with one of three surface treatments: (i) flaming, (ii) exposure to steam for 150 h, and (iii) brief exposure to ammonia vapor. Analysis of electrical double-layer interactions indicates that the surface density of silanol groups increases with steam treatment, and that exposure to ammonia etches the surface slightly and renders it porous. The force at short range is dominated by a strong repulsion which is attributed to hydration of the surface. The hydration component of the force is not significantly affected by the surface treatments, nor by electrolyte concentration over the range investigated (up to 0.1 M).

Measuring surface forces to explore surface chemistry : mica, sapphire and silica

In this paper measurements of the forces acting between two solid surfaces separated by a thin liquid film are discussed. By investigating these forces in a range of different liquids and solutions, it is possible to acquire an understanding of the surface properties of the solid material. The surface of mica has been studied extensively in this way, and the results obtained are reviewed to illustrate how the surface force measurements can give surface chemical information. Recent measurements on two other materials, sapphire and silica, which are of greater practical interest are also discussed.

Photoreactive azido-containing silica nanoparticle/polycation multilayers : durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C–H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.

An illustration of the physical robustness of silica monolithic rod columns

A commercial silica monolithic rod column (100 × 4.6 mm) was cut into smaller sections using a saw. Each time a section was cut from the column, the performance of the remaining intact monolith was retested. No significant change in the performance of the bed was recorded following the removal of 40 mm of the column in three separate cut sections. The work illustrates that monoliths are extremely robust and that they can be remodelled to different lengths if required, or a blocked section of the column (i.e. inlet) could be removed in much the same manner as for GC columns.