Interband cascade laser absorption sensor for real-time monitoring of formaldehyde filtration by a nanofiber membrane

It is important to reduce the indoor formaldehyde (${\mathrm{H}}_2\mathrm{CO}$) level to improve indoor air quality. To investigate the ${\mathrm{H}}_2\mathrm{CO}$ filtration by a novel nanofiber membrane made from metal-organic frameworks (MOFs), we developed a laser absorption gas sensor for real-time ${\mathrm{H}}_2\mathrm{CO}$ monitoring using a room-temperature interband cascade laser (ICL) emitting at 3.6 µm. Wavelength modulation spectroscopy combined with a multipass gas cell (36 m path length) was implemented to achieve a detection sensitivity of 3 ppb ${\mathrm{H}}_2\mathrm{CO}$ at 1-s averaging time. We custom-designed a permeation ${\mathrm{H}}_2\mathrm{CO}$ generator that produces reference ${\mathrm{H}}_2\mathrm{CO}/{\mathrm{N}}_2$ mixtures with an uncertainty of 6.4% in concentration. With the time-resolved continuous measurements, we observed a high filtration efficiency of 83% for the MOF filter, which, however, decreases linearly to 30% after operating for 3 h. Hence, the ICL-based gas sensor has proved to be a promising technique to assess novel nanomaterials for indoor air purification and pollutant control applications.