Gas-Responsive and Self-Powered Visual Composite Langmuir–Blodgett Films for Ultrathin Gas Sensors

Abstract

The complex and variable environments are challenging the development of related detection and analysis. Ammonia (NH3) and hydrogen chloride (HCl) gases are both commonly used in industry, but they are considered to be toxic and corrosive substances that can threaten human health and the environment. Therefore, it is necessary here to develop a convenient, sensitive, and reliable sensor device for acid–alkali gas detection. Herein, we propose the synthesis strategy of an ultrathin film gas sensor based on the pH-responsive, self-powered, and visible composite Langmuir–Blodgett (LB) films. In our work, the LB films with nanometric thicknesses are obtained based on the sensitive materials of two novel carbazole structural sensitizers (abbreviated as CS-35 and CS-37) and several dye molecules. The composite LB films are formed with Carbazole samples and dye molecules through hydrogen bonding, π–π stacking, synergistic electrostatic interactions, and hydrophobic interactions, existing as J-aggregate or H-aggregate. The formation of high-quality and uniform Langmuir films is confirmed with transmission electron microscope (TEM), UV–vis spectrum, atomic force microscopy (AFM), and other measurements. In addition, based on the simple protonation and deprotonation, the prepared LB films can be assembled into a visual sensor for the response of pH gases. The response is confirmed by the study of ultraviolet spectroscopy and electrical output in vertical contact separation mode, which potentially unlocks a sustainable future for the application of ultrathin self-powered gas sensors.

Interaction Modes in Pressure-Induced Molecular Nanoarchitectonics of the Alkylated Azobenzene Monolayer: Interfacial Analyses and Molecular Dynamic Simulation

“…In the literature, different types of azobenzene surfactants are reported ,− with different polar anchoring groups and different lengths of alkyl tail groups . They show different values for the collapse pressure (π c ), limiting area ( A 0 ), elastic modulus (| E |), surface potential (Δ V ), etc., depending on molecule–molecule and molecule–water interactions at the air–water interface.…”

Recent Progress in the Applications of Langmuir–Blodgett Film Technology

“…These substances pose risks to both human health and environmental integrity. Li et al [ 28 ] proposed a synthesis method for ultra-thin film gas sensors utilizing pH-responsive, self-supplied, and visible composite LB films. As shown in Figure 4 a,b, two new carbazole structure sensitizers and several dye molecules were used as sensitizing materials to prepare nano-thick films using LB technology.…”

“…Gas sensors equipped with LB films derived from various subphases of ( d ) Azo, ( e ) Methyl Orange (MO), and ( f ) Congo Red (CR) subjected to HCl and NH 3 gases. Reprinted with permission from [ 28 ]. Copyright 2022, American Chemical Society.…”

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

“…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 …”