Alkylamine-Integrated Metal–Organic Framework-Based Waveguide Sensors for Efficient Detection of Carbon Dioxide from Humid Gas Streams

Metal–organic framework (MOF)-based chemical sensors have recently been demonstrated to be highly selective, sensitive, and reversible for CO2 sensing across a range of platforms including optical fiber and surface acoustic wave-based sensors. However, interference of water molecules is a primary issue in CO2 sensing systems based upon MOF layers due to cross-sensitivity, stability of MOF-based materials in humid conditions, and associated baseline drift over the lifetime of sensors. Herein, we develop a simple approach of alleviating the negative effect of water vapor to the optical fiber sensor by using alkylamine (i.e., oleylamine) to form a protective hydrophobic layer on the surface of MOFs for improving water stability. Alkylamine-modification of a MOF-coated optical fiber sensor provides a reversible and stable sensing response to a wide range of CO2 concentrations while also enhancing the CO2 sensitivity of the sensor under wet conditions. The FT-IR and breakthrough studies on the oleylamine-modified MOF confirm that the water vapor does not adversely impact the intrinsic CO2 sorption capacities. Thus, this simple stratrgy for enhancing the CO2/H2O selectivity in the MOF sorbent could also be useful for improving CO2 capture/separation performance in flue gas stream.