Near-infrared absorption gas sensing with metal-organic framework on optical fibers

Abstract

Despite significant advantages in terms of portability and cost, near-infrared (NIR) gas sensing still remains a great challenge due to its relatively weak overtone absorption from the fundamental vibrational bond absorption at the mid-IR frequency. In this paper, we demonstrated ultra-sensitive NIR gas sensing for carbon dioxide (CO2) at 1.57μm wavelength through nanoporous Cu-BTC (BTC=benzene-1,3,5-tricarboxylate) metal-organic framework (MOF) coated single-mode optical fiber. For the first time, we obtained high-resolution NIR spectroscopy of CO2 sorbed in MOF without seeing any rotational side band, indicating that the tightly confined gas molecules in the MOF pores do not have any freedom of rotation. Real-time measurement of the mixed gas flow of CO2 and Ar showed different response time depending on the concentration of CO2, which is attributed to the complex sorption mechanism of CO2 in Cu-BTC MOF. Most importantly, we realized ultra-low detection limit of CO2 (<20ppm) with only 5cm long Cu-BTC MOF thin film coated on single-mode optical fibers.