Ultra-sensitive near-infrared fiber-optic gas sensors enhanced by metal-organic frameworks

Abstract

ABSTRACT We demonstrate ultra-sensitive near-infrared (NIR) fiber-optic gas sensors enhanced by metal-organic framework (MOF) Cu-BTC (BTC=benzene-1,3,5- tricarboxylate), which is coated on a single-mode optical fiber. For the first time, we obtained high-resolution NIR spectroscopy of CO 2 adsorbed in MOF without seeing any rotational side band. Real-tim e measurement showed different response time depending on the concentration of CO 2 , which is attributed to the complex adsorption and desorption mechanism of CO 2 in Cu-BTC. The lowest detection limit of CO 2 we achieved is 20 ppm with only 5-cm long Cu-BTC film. Keywords: Gas sensing, Near-infrared, Metal-organic framework 1. INTRODUCTION Gas sensing plays pivotal roles in many applications including safe ty management of petrochemical industry[1], study of atmospheric science[2] and exhaust gas mon itoring for combustion engines[3], to name a few. There are numerous gas sensing technologies available that allow trace-level detection of various gases[1, 4-9]. Among them, optical sensors using infrared (IR) absorption spectroscopy[4, 7, 8, 10] sta nds out due to the high de tection specificity. IR spectroscopy relies on the optical absorption of molecular vibration bands, which represent the signatures of various gas molecules. Therefore, IR absorption spectroscopy is widely used as a simple and reliable technique for both detection and identificatio n of hazardous and greenhouse gases. In addition, IR sensors have minimal drift, fast response, long lifetime, and can be conducted in real time and in situ without disturbing the target system. The principle of infrared absorption gas sensing is based on Beer-Lambert law: (1) where I is the transmitted light intensity, I