Intelligent Environmental Sensing: Fabrication of Switchable, Reusable, and Highly Sensitive Gas Sensors with Spiropyran-Grafted Anodic Aluminum Oxide Templates

Abstract

Monitoring undesired pH deviations in the surroundings is one of the most pervasive issues of environment and industry, and developing efficient, economical, portable, and reusable membranes for pH monitoring is urgently needed. Herein, we report novel smart nanomembranes (SNMs) that are made up of anodic aluminum oxide (AAO) templates grafted with spiropyran molecules. The ultraviolet and visible light responses of the SNMs under acid vapors are investigated. Under UV irradiation, the ring-closed spiropyran on the AAO templates transform to ring-opened merocyanine, which contains phenolate oxygen and can be further protonated by acids. Such a protonation process not only shows evident color changes but also endows SNMs with pH-responsive properties, which are further investigated by UV-vis diffuse reflectance spectroscopy. Furthermore, to demonstrate the pH-responsive properties of the SNM, common volatile acids such as hydrochloric acid, nitric acid, formic acid, and acetic acid are tested. The SNM shows conspicuous sensibility, reusability, and reversibility during the processes of irradiation, protonation, and deprotonation. Therefore, the newly developed SNM can be an excellent alternative to the existing pH sensors for the detection of pH variations in environment and industry.