Copolymer-Based Photonic Crystal Sensor for Discriminative Detection of Liquid Benzene, Toluene, Ethylbenzene, and Xylene

Photonic crystals (PCs) with adjustable optical properties have received increasing attention in research of colorimetric sensors for volatile organic compounds (VOCs). Herein, a high-sensitive copolymer-based 1DPC sensor comprising poly(styrene-ethylene glycol dimethacrylate-acrylic acid) (P(St-EGDMA-AA)) and TiO2 is designed for visual detecting and discriminating liquid aromatic VOCs–benzene, toluene, ethylbenzene, and xylene (BTEX). The functional multilayered and porous sensor quickly and reversibly varies its color from violet to red of different shades and reaches a response balance within 1.0, 1.5, 8.0, and 12.0 s when immersed in benzene, toluene, ethylbenzene, and xylene, respectively, realizing rapid discriminative detection of these aromatic compounds. When the PC sensor is applied to aromatic hydrocarbon–ethanol binary mixtures, its photonic stopband position redshifts first and blueshifts afterward with the increase of the concentration of the aromatic hydrocarbon, and this phenomenon can be explained by the “cosolvency effect”. Notably, introduction of a third component–water to the binary system greatly affects the optical properties of the sensor even at low concentration of the aromatic hydrocarbon. With potential utility, these photonic materials are promising as portable, economical, and visually detectable aromatic hydrocarbon sensors for environment quality monitoring.