Stabilization of Silica Gel against Hydrolysis by Doping with F^(-) or Zr(Ⅳ)

Silica gel (SG) was synthesized via acidification of sodium silicate solution then doped with Fˉ or Zr(IV) in molar ratios of F/Si 3/100, and Zr/Si 0.75/100 and 3.75/100 and sintered at 500°C, 800°C and 1000°C. The samples were investigated by X-ray diffractometry, infrared absorption and Raman spectra, surface area measurement, and inductively coupled plasma-optical emission spectrometry-monitored silica hydrolysis. All samples are mesoporous with BET surface areas 181.5 - 523.9 m2·gˉ1. The surface area of the silica samples decreases as the sintering temperature increases. The hydrolysis process of silica decreases as the sintering temperature increases and as the surface area decreases. The pH and the type of buffer solution affect the hydrolysis of silica samples due to a SN2 reaction mechanism favored in basic media using ammonia buffer. Zr(IV) increases the stability of silica samples against the hydrolysis as confirmed by the structural investigation, surface area and silica hydrolysis. Fˉ observably decreases the silica hydrolysis process when presenting on the surface of SG.

Electrospun carbon nanofibre-assisted patterning of metal oxide nanostructures

This work establishes carbon nanofibre-mediated patterning of metal oxide nanostructures,through the combination of electrospinning and vapor-phase transport growth.Electrospinning of a suitable precursor with subsequent carbonization results in the patterning of catalyst gold nanoparticles embedded within carbon nanofibres.During vapor-phase transport growth,these nanofibres allow preferential growth of one-dimensional metal oxide nanostructures,which grow radilly outward from the nanofibril axis,ielding a hairy caterpilr-ike morphology.The synthesis of metal oxide caterpilars is demonstrated using zinc oxide,indium oxide,and tin oxide.Source and substrate temperatures play the most crucial role in determining the morphology of the metal oxide caterpillars,whereas the distribution of the nanofibres also has a significant impact on the overall morphology.Introducing the current methodology with near-field electrospinning further facilitates user-defined custom patterning of metal oxide caterpllr-like structures.

Laser-induced hierarchical carbon patterns on polyimide substrates for flexible urea sensors

Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen,known as the pyrolysis process,is often employed to convert micro and nano patterned polymers into carbon structures,which are subsequently used as device components.Pyrolysis is performed at≥900℃,which entails substrate materials with a high thermal stability that excludes flexible,polymeric substrates.We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide(Kapton)sheets in the micrometer to millimeter scale by inducing a localized,rapid pyrolysis,for the fabrication of flexible devices.Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section.The material is obtained using various combinations of laser parameters and pyrolysis environment(oxygen-containing and inert).Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters,primarily fluence and power.A photothermal carbonization mechanism based on the plume formation is proposed.Further,laser carbon is used for the fabrication of enzymatic,pH-based urea sensors using two approaches:(i)direct urease enzyme immobilization onto carbon and(ii)electrodeposition of an intermediate chitosan layer prior to urease immobilization.This flexible sensor is tested for quantitative urea detection down to 10^(−4) M concentrations,while a qualitative,color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters.Laser carbon is suitable for a variety of other flexible electronics and sensors,can be conveniently integrated with an external circuitry,heating elements,and with other microfabrication techniques such as fluidic platforms.