Butyl acrylate/TiO2–copolymer hybrid one-dimensional photonic crystal–based colorimetric sensor for detection of C6–C16 n-alkanes of kerosene in adulterated diesel

Diesel fuel, which is widely used in engines, generators, and industrial equipment, is often adulterated with kerosene. The use of adulterated diesel fuel reduces the performance and durability of diesel–fuel-powered engines, causes environmental pollution, and promotes tax evasion. However, detecting kerosene in diesel using a high-precision instrumental technique such as gas chromatography with flame ionization detection is difficult because both diesel and kerosene contain C6–C16 paraffins. In this study, we developed a simple and reliable colorimetric sensor to detect various volumetric fractions of kerosene in diesel. A novel 15-layered one-dimensional photonic crystal (1D PC) was prepared using a photo-crosslinked butyl acrylate (BA)–based copolymer [P(BA-co-BPA)] as the low-refractive-index material and a photo-crosslinked copolymer–TiO2 hybrid (Ti70) as the high-refractive-index material. The P(BA-co-BPA) layers swelled to a greater extent in smaller-sized C6–C16 n-alkanes than in the larger ones. Consequently, the reflection colors of P(BA-co-BPA)/Ti70 PC underwent a greater red shift from the sky-blue color of the pristine state as the swelling increased from the C16 to the C6 n-alkanes. When immersed in pure diesel, the 1D PC exhibited a green color, which underwent a greater red shift as the volume fraction of kerosene increased from 10% (∼limit of colorimetric detection) to 100% in the kerosene + diesel mixtures. The 1D PC reached saturation within 45 min and changed color from the sky-blue corresponding to the pristine state to greenish yellow, yellow, yellow-orange, orange, and reddish orange in 10%, 20%, 30%, 50–70%, and 100% kerosene, respectively. Moreover, it exhibited recyclability in five swelling/deswelling cycles in diesel and kerosene. We expect that these findings will promote the development of simple and state-of-the-art 1D PC sensors.