A dual ammonia-responsive sponge sensor: preparation, transition mechanism and sensitivity

Abstract

PDMS-PU (polydimethylsiloxane-polyurethane) sponge decorated with In(OH)3 (indium hydroxide) and BCP (bromocresol purple) particles is shown to be a room-temperature ammonia sensor with high sensitivity and excellent reproducibility; it can accomplish real-time detection and monitoring of ammonia in the surrounding environment. The superhydrophobic and yellowish In(OH)3-BCP-TiO2-based ammonia-responsive (IBT-AR) sponge changes to a purple superhydrophilic one when exposed to ammonia. Notably, after reacting with ammonia, the sponge can recover its original wettability and color after heating in air. The wettability, color and absorption signal of IBT-AR sponge have been measured for sensing ammonia using the water contact angle, macroscopic observation and UV-vis absorption spectrometry, respectively. The minimum ammonia concentrations that can be detected by the sponge wettability, color and absorption signal are 0.5%, 1.4 ppm and 50 ppb, respectively. This kind of sponge with smart wettability and color is a promising new ammonia detector.

An Ammonia Sensor Using an Unadorned Bromocresol Layer

“…However the response is not linear with concentration. This nonlinearity has also been seen elsewhere for the ammonia responsive sponge [10], the cellulose based smart xerogel [14] and the sol gel system [9]. When a tube with CaO is introduced into the stream of gas, the signal is decreased which indicates that water does play a role in the response.…”

“…The appearance of a peak at 1590 cm -1 is indicative of the presence of a carbonyl in keeping with the mechanism predicted theoretically [24] shown in Figure 5. The transformation of conjugation in the mechanism is in keeping with the colour change unlike other proposed mechanisms [10]. NH 4 + acts as counterion to the dianionic form in the solid state.…”

“…However, these comprise layers which function at high temperatures or are quite complex to fabricate. A complex polydimethylsiloxanepolyurethane sponge decorated with In(OH) 3 and bromocresol purple changed colour and wettability on exposure to ammonia [10]. A surface plasmon resonance based fibre optic sensor based on BCP coatings sputtered on either silver or gold on a silica fibre responded to ammonia up to 150 ppm NH 3 [11].…”