Gas-Sensing Mechanism of Silica with Photonic Bandgap Shift

Convective assembly of silica colloidal particles inside photonic integrated chip-based microfluidic systems for gas sensing applications

Optofluidics is a new field of modern science that stands at the interface of microfluidics and photonics and has good prospects for application in gas sensors. Microfluidics offers a promising platform for tuning and assembling monolayer structures that are used as sensitive layers for gas detection. Herein, we evaluate the concept of monolayer formation on a silicon nitride substrate enabling a surface coverage up to 59% through a microfluidic convective assembly and couple it with a photonic integrated chip to probe gas sensing performance.

Programmable Color in a Free-Standing Photonic Microgel Film with Ultra-Fast Response

In this work, a free-standing microgel film with programmable and angle-independent structural color is prepared via a simple but effective method. Dried poly(styrene-N-isopropylacrylamide-acrylic acid) (pStNIPAAmAA) microgels were stabilized by inter-microgel crosslinking, and thus, only microgels were used to build the optical hydrogel. The free-standing microgel film displayed tunable structural color by the swelling/deswelling of the microgels under external stimuli, such as temperature, pH, ionic strength, and organic solvent. Moreover, the structural color of the film is angle-independent for the disordered microgel arrays. It is worth noting that programmable color stripes which have the panther chameleon's ability to change skin color are successfully fabricated by patterning microgels with different thermoresponsivities. More importantly, the microgel film has an ultrafast response to temperature (1.41 s from 20 to 40 °C) and pH (2.24 s from pH 8.3 to pH 2.0), much faster than that of most optical materials reported in previous studies.

Highly Selective Gas Sensor Based on Hydrophobic Silica Decorated with Trimethoxyoctadecylsilane

Trimethoxyoctadecylsilane (OTMS) was successfully used to decorate mesoporous silica with a self-assembly method to enhance the relative gas selectivity. A quartz crystal microbalance was employed to measure the gas-sensing properties. The content of OTMS was the crucial factor that greatly affected the adsorption capacity (q) of silica, which could be converted to relative selectivity (S) to study the sensing mechanism. With increasing OTMS content, q was far higher for small-molecule gases compared to volatile organic compounds (VOCs), which could be explained by the polarity of the bonding objects, and S reached a maximum value of 45.71%. When exposed to VOCs, S was always greater than 0 among the three alcohols. The sensing mechanisms of undecorated silica and OTMS-decorated silica were quite different; the three-state mechanism was proposed to explain the sensing mechanism of OTMS-decorated silica. When exposed to small-molecule gases, the atoms that bonded with carbon atoms on OTMS greatly influenced q. With increasing OTMS content, the bonding energy of OTMS with CO₂ was far less than that with other molecules, resulting in a relative selectivity as high as 38.69%. Furthermore, macroperformance and microproperties were combined in three-dimensional coordinates, which could be applied to predict the sensing performance of silica.

A new synthesis methodology for SiO2 gel-based nanostructures and their application for elimination of dye pollutants

A new procedure for preparation of a high specific surface area silica-based nanostructure and its copper-containing active photocatalyst is described.