Conductometric sensor for ammonia and ethanol using gold nanoparticle-doped mesoporous TiO2

Abstract

We describe uniform and high-temperature-stable mesoporous TiO 2 beads functionalized with gold nanoparticles (AuNPs-TiO 2 ) for use in conductometric sensing of gases and organic vapors. The size of the interconnected main mesopores of the TiO 2 beads ranges from 8 to 15 nm, and the AuNPs have diameters between 8 and 10 nm. The mesoporous TiO 2 beads are formed during calcination while the structure-directing template agent is removed. Monodispersed AuNPs are formed by reduction in-situ and are placed inside the mesoporous TiO 2 framework. This prevents aggregation of the AuNPs even at 500°C. The materials were characterized by UV-vis spectroscopy, scanning and transmission electron microscopy, nitrogen adsorption-desorption, and X-ray diffraction. Comb-type gold electrodes were then fabricated on an alumina substrate and are shown to display excellent properties in terms of sensing ammonia, ethanol, methanol or acetone. The sensitivity (defined as the ratio of resistivities under vapor and air) of a typical AuNPs(0.5 %)-TiO 2 gas sensor for ethanol reached up to 5.65 at above 600 ppm at 75°C. Response time and recovery times (t 90 ≤20 s) are faster than (or comparable to) other metal-doped TiO 2 sensors, and working temperatures are much lower. An interesting observation was made in that the changes in the conductivity of the sensor change with temperature. The sensor prepared with AuNPs(0.5 %)-TiO 2 is of the p-type (in its response to ammonia gas) at 45°C, but becomes n-type at 20°C. Obviously, rather slight changes in temperature lead to a complete change in the direction of the conductometric signal change. This may provide a new aspect in terms of selective and highly sensitive detection of ammonia at ambient and slightly elevated temperatures.

Plasma‐polymerized cyclohexane coatings for ethanol and ammonia vapors sensing

“…In this case, for ethanol sensing, CH 10 operating at 100°C was good and CH 7.5 operating at 100°C is suitable for ammonia sensing. The interaction of alcohol and reducing gases with sensing film were entirely different and thus led to such results 14 . The flow of ethanol and ammonia vapors on the sensor film and its simultaneous reaction 15 with the polymerized CH by the adsorption and interaction processes gave rise to variation in the senor response.…”

A Highly Sensitive Toluene and Xylene QCM Nanosensor Using Nanoporous MIL‐101(Cr) as a Sensing Layer

“…They are classified based on their working principles into electrochemical, [5] optical, [6] mass (acoustic), electrical, and other types. Mass sensors can be divided into quartz crystal microbalances (QCM) [7] and surface acoustic waves (SAW), [8] and electrical sensors can be classified into metal oxide semiconductors (MOS), [9] capacitors, [10] and resistors. [11] Nowadays scientists are eager to explore small amounts of chemical compounds in reactions.…”

Freestanding flexible, pure and composite form of reduced graphene oxide paper for ammonia vapor sensing

“…The SnO 2 -reduced graphene oxide based porous film has been reported to be an effective gas sensor material with tunable sensitivity through UV irradiation 18 . Various methods used for ammonia sensing include colorimetric sensing 19 , conductometric sensing 20 , electrochemical sensing 21 , direct detection of ammonium ion by means of oxygen electrocatalysis 22 , resistance based sensing 23–25 , impedance analysis 26 and Keithley electrometer sensing 27 . The gas sensing by impedance analysis is simple and compact experimental set-up compared with other methods.…”