Immobilizing Ionic Liquids onto Functionalized Surfaces for Sensing Volatile Organic Compounds

Abstract

Herein, a highly sensitive volatile organic compound (VOC) gas sensor is demonstrated using immobilized ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, onto surfaces functionalized by the quaternary ammonium group −N+R, −COOH, and −NH2, i.e., N+–IL, COOH–IL, and NH2–IL, respectively. These functional groups ensure highly tunable interactions between the IL and surfaces, efficiently modulating the electrical resistance of the immobilized IL upon exposure to acetone and toluene. The immobilized IL to both acetone and toluene displays significant electronic resistance changes at a concentration of 150 ppm, falling in the order NH2–IL > N+–IL > COOH–IL for acetone while COOH–IL > NH2–IL > N+–IL for toluene. A better gaseous sensing ability is achieved in COOH–IL for toluene than acetone, while this does not hold in the case of NH2–IL and N+–IL surfaces because of the completely different ion structuring of the IL at these functionalized surfaces. The accelerated ion mobility in the IL that is immobilized onto functionalized surfaces is also responsible for the strong gaseous sensing response, which is demonstrated further by the atomic force microscopy-measured smaller friction coefficient. This is highly encouraging and suggests that ILs can be immobilized by a network formed by surface functionalization to easily and cheaply detect VOCs at ppm concentrations.

Effect of Electrode Surface Chemistry on Ion Structuring of Imidazolium Ionic Liquids

“…The third layer on the Au–NH 2 surface is also composed of the “cation–anion” pairs and so on. The difference in cation and anion layers formed closest to the Au–COOH and Au–NH 2 surfaces is due to their completely different interaction energies: the cation–COOH interaction energy is stronger than cation–NH 2 , while that is weaker for anion–COOH than anion–NH 2 . Note that due to the existence of these −COOH and −NH 2 functional groups, the detected ion layering thickness of the IL from the force–distance curves is not exactly equal to but very close to the theoretical cation or anion size, indicating that the films of the grafted −COOH and −NH 2 layers act as good networks to support the IL, as illustrated in the left-bottom corners of Figure e.…”

“…The difference in cation and anion layers formed closest to the Au−COOH and Au−NH 2 surfaces is due to their completely different interaction energies: the cation− COOH interaction energy is stronger than cation−NH 2 , while that is weaker for anion−COOH than anion−NH 2 . 56 Note that due to the existence of these −COOH and −NH 2 functional groups, the detected ion layering thickness of the IL from the force−distance curves is not exactly equal to but very close to the theoretical cation or anion size, indicating that the films of the grafted −COOH and −NH 2 layers act as good networks to support the IL, as illustrated in the left-bottom corners of Figure 4e. Previous studies revealed that the number of layering structures decreases with increasing molecular flexibility for conventional molecular liquids, as flexible molecules can pack effectively without layering.…”

Enhanced Acetone-Sensing Properties of Pt-Decorated In2O3 Hollow Microspheres Derived from Pt-Embedded Template

“…Additionally, it should be emphasized that intermediate organic matter may be formed during the sensing process and then adsorbed on the sensing layer. In this scenario, Pt would serve as a good catalyst for disrupting C–C bonds by deconstructing these intermediate species and promoting their faster desorption. , …”

“…In this scenario, Pt would serve as a good catalyst for disrupting C−C bonds by deconstructing these intermediate species and promoting their faster desorption. 49,51 ■…”

Influence of Volatile Organic Compound Adsorption on the Characteristics of Organic Field-Effect Transistors and Rules for Gas-Sensing Measurements

“…Volatile organic compounds (VOCs) are widely used as additives and solvents in industry and daily life. Most VOCs are toxic, carcinogenic, and combustible, seriously threatening human health and safety. − Therefore, the detection of VOCs in the atmosphere is essential. Organic semiconductors (OS) have recently received increasing attention in gas sensors because of their potential applications in flexible and wearable electronics. − In addition, organic semiconductors are genius for VOC gas-sensing applications because the precise organic synthesis can tailor functional groups for the specific binding of VOC analytes, leading to the prospect of simplifying gas sensors with enhanced responsivity and selectivity …”