Gas sensors based on membrane diffusion for environmental monitoring

Over the last few decades, gas membrane diffusion has been applied to elaborate chemical analyses, leading to the development of a series of gas sensing techniques for environmental monitoring. This work reviews the gas sensors that incorporate the gas membrane diffusion mechanism with either electrochemical or optical transducers, and concludes the theoretical relationship between the detection signal and the mass transfer parameters across the membrane, such as membrane thickness, gas diffusion coefficient and driving force. It also envisages that, with the availability of modern electronic and computing technology, the in-situ membrane diffusion rate of a target species is proportional to its real-time concentration in the sample and can be readily measured. Such a measuring principle is promising in developing the next generation of gas sensors based on membrane diffusion to achieve real-time and continuous monitoring of important trace gases (e.g. CO2, SO2, NH3) in the natural environment (water, soil and air).