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.

In recent years, two-dimensional (2D) plate materials have become the most attractive class of candidate materials with a wide range of potential applications due to their unique structural characteristics and physicochemical properties. Starting from graphene, 2D plate materials have become a large family with many members and diverse categories. Especially in the recent past years, we have made some significant breakthroughs in the field of 2D materials. Langmuir-Blodgett (LB) technology is an advanced technology for preparing ultrathin films with highly ordered molecules by using its unique dynamic interface in the preparation process, which can effectively control and adjust film material with layered nanostructures. With the advancement of LB technology, different thin film materials need to be prepared to realize various functions. This paper summarizes the research progress and future perspectives of LB technology based on 2D materials.