Zeolite membranes for highly selective formaldehyde sensors

Abstract

A major challenge in gas sensing (e.g. breath analysis, indoor air quality monitoring, etc.) is the accurate detection of trace-level species in complex mixtures. While modern chemical gas sensors can be extremely compact, inexpensive and highly sensitive, their success is still limited by selectivity. Here, we combine sensors with highly selective zeolite membranes pre-separating gas mixtures. Zeolites – broadly applied in catalysis and gas separation – effectively separate molecules based on kinetic diameter, sorption and diffusion characteristics. Therefore, zeolite membranes are suitable filters for gas sensors removing undesired species from mixtures like exhaled breath. As proof-of-concept, a zeolite Mobile-Five (MFI)/Al2O3 membrane is placed upstream a highly sensitive but non-selective Pd-doped SnO2 sensor. Their combination exhibits exceptional selectivity (>100) for formaldehyde (down to 30ppb) at 90% relative humidity, outperforming most state-of-the-art detectors by more than an order of magnitude. This novel concept is readily extendable to other tracers, as many combinations of widely tunable microporous membranes and gas sensors can be realized in this modular sensing device. This could enable a new class of highly sensitive and selective portable breath detectors or compact indoor air monitors.