Real-time monitoring of CO2 gas using inverse opal photonic gel containing Poly(2-(dimethylamino)ethylmethacrylate

With the rapid progression of global climate changes and air pollution in recent years, there has been growing interest in the sensing and monitoring of CO₂ gas. In the present study, an inverse opal photonic gel (IOPG) colorimetric sensor is demonstrated that is capable of real-time monitoring of CO₂ gas in an open system without the necessity of a power supply. The IOPGs are fabricated via the opal-templated photo-polymerization of monomer mixtures of hydroxyethyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) or 2-(dimethylamino)propyl methacrylamide (DMAPMAm), followed by template removal. When the IOPG sensor is immersed in water with a steady flow of mixed CO₂/N₂ gas at various ratios, the CO₂ molecules dissolve in the water and are converted to carbonate anions, which subsequently bind to the amino groups of pDMAEMA to build up osmotic pressure, thus leading to swelling of the IOPG. A comparison of the sensing and recovery capabilities of the two types of IOPG indicates that the pDMAEMA-containing IOPG exhibits a limit of detection below 1.2%, and 2.6 times faster CO₂ desorption kinetics compared to the pDMAPMAm-containing IOPG. The swelling behavior of the CO₂-responsive IOPG is rigorously investigated at various pH values, and temperatures by analyzing the reflectance spectra of the IOPG in the visible wavelength range. The usefulness of the pDMAEMA-IOPG as a real-time CO₂ sensor was confirmed by applying it to various carbonated drinks.