Dye Modification of Nanofibrous Silicon Oxide Membranes for Colorimetric HCl and NH₃ Sensing

Abstract

Colorimetric sensors for monitoring and visual reporting of acidic environments both in water and air are highly valuable in various fields, such as safety and technical textiles. Until now solgel based colorimetric sensors are usually non-flexible bulk glass or thin film sensors. Large area, flexible sensors usable in strong acidic environments are not available. Therefore, in this study organically modified silicon oxide nanofibrous membranes are produced by combining electrospinning and sol-gel technology. Two pH-indicator dyes are immobilized in the nanofibrous membranes: Methyl Yellow via doping, Methyl Red via both doping and covalent bonding. This resulted in sensor materials with a fast response time and high sensitivity for pHchange in water. The covalent bond between dye and the sol-gel network showed to be essential to obtain a reusable pH-sensor in aqueous environment. Also a high sensitivity was obtained for sensing of HCl and NH3 vapors, including a memory function allowing visual read-out up to 20 minutes after exposure. These fast and reversible, large area flexible nanofibrous colorimetric sensors are highly interesting for use in multiple applications such as protective clothing and equipment. Moreover, the sensitivity to biogenic amines was demonstrated, offering potential for control and monitoring of food quality.

Silica Nanofibrous Membranes for the Separation of Heterogeneous Azeotropes

“…When stored at room temperature (RT, 20 °C) and 65% relative humidity (RH), the hydrophobic/hydrophilic switch is observed after 4 months (right region of Figure ). In the case of an RH of 90%, the membrane is superhydrophilic within 21 d . The lower the relative humidity, the longer the hydrophobic nature lasts.…”

TiO2 functionalized nanofibrous membranes for removal of organic (micro)pollutants from water

“…The silica nanofibers can change their hydrophilicity in time [31]. Therefore, both hydrophobic and hydrophilic samples were dip-coated, which resulted in a significant difference in TiO2 loading (Figure 2 f,g and Table 1).…”

Colorimetric Nanofibers as Optical Sensors

“…Therefore, it is beneficial to not restrict colorimetric sensor design to organic polymers, but broaden their applicability by producing sensors from ceramic nanofibers. By combining stimuli‐sensitive dyes, the advantageous properties of nanofibers and the high temperature and chemical resistance of ceramic sol‐gel based materials, we designed an advanced colorimetric sensor with a unique combination of properties based on dye‐doping of silica nanofibers . In contrast to the usually non‐flexible bulk glass or thin film sensors, our designed large‐area ceramic nanofibrous sensors were flexible.…”

“…TEOS‐APTES ceramic nanofibers doped with the dye Methyl Red show visual responsivity towards biogenic amines (right). Adapted with permission . Copyright 2016, WILEY‐VCH Verlag GmbH & Co.…”