Graunke Thorsten, Schmitt Katrin, Raible Stefan, Wöllenstein Jürgen
Laboratory for Gas Sensors, Department of Microsystems Engineering-IMTEK, University of Freiburg, Georges-Köhler-Allee 102, 79110 Freiburg, Germany.
ams Sensor Solutions Germany GmbH, Gerhard-Kindler-Str. 8, 72770 Reutlingen, Germany.
Sensors (Basel). 2016 Sep 28;16(10):1605. doi: 10.3390/s16101605.
In this paper we report on how to increase the selectivity of gas sensors by using fluoropolymer membranes. The mass transport of polar and non-polar gases through a polymer membrane matrix was studied by systematic selection of polymers with different degrees of fluorination, as well as polymers whose monomers have ether groups (-O-) in addition to fluorine groups (-F). For the study, a set of application-relevant gases including H₂, CO, CO₂, NO₂, methane, ethanol, acetone, and acetaldehyde as well as various concentrations of relative humidity were used. These gases have different functional groups and polarities, yet have a similar kinetic diameter and are therefore typically difficult to separate. The concentrations of the gases were chosen according to international indicative limit values (TWA, STEL). To measure the concentration in the feed and permeate, we used tin-dioxide-based metal oxide gas sensors with palladium catalyst (SnO₂:Pd), catalytic sensors (also SnO₂:Pd-based) and thermal conductivity sensors. This allows a close examination of the interdependence of diffusion and physicochemical operating principle of the sensor. Our goal is to increase the selectivity of gas sensors by using inexpensive fluoropolymer membranes. The measurements showed that through membranes with low polarity, preferably non-polar gases are transported. Furthermore, the degree of crystallization influences the permeability and selectivity of a polymer membrane. Basically the polar polymers showed a higher permeability to water vapor and polar substances than non-polar polymer membranes.
在本文中，我们报告了如何通过使用含氟聚合物膜来提高气体传感器的选择性。通过系统地选择不同氟化程度的聚合物，以及除氟基团（-F）外单体还含有醚基（-O-）的聚合物，研究了极性和非极性气体在聚合物膜基质中的质量传输。为了进行这项研究，使用了一组与应用相关的气体，包括H₂、CO、CO₂、NO₂、甲烷、乙醇、丙酮和乙醛，以及各种浓度的相对湿度。这些气体具有不同的官能团和极性，但具有相似的动力学直径，因此通常难以分离。气体浓度根据国际指示限值（时间加权平均容许浓度、短时间接触容许浓度）进行选择。为了测量进料和渗透物中的浓度，我们使用了带有钯催化剂的二氧化锡基金属氧化物气体传感器（SnO₂:Pd）、催化传感器（同样基于SnO₂:Pd）和热导率传感器。这使得能够仔细研究传感器扩散与物理化学工作原理之间的相互依存关系。我们的目标是通过使用廉价的含氟聚合物膜来提高气体传感器的选择性。测量结果表明，通过低极性的膜，优先传输的是非极性气体。此外，结晶度会影响聚合物膜的渗透性和选择性。基本上，极性聚合物对水蒸气和极性物质的渗透性高于非极性聚合物膜。
