A 2D honeycomb coordination polymer of [Cd(TMA)]n (H2TMA = 3-thiophenemalonic acid) for humidity sensing applications

Abstract Humidity sensor is of prime importance to monitor and control moisture sensitive environments for human life and industrial manufacturing. Compared with traditional materials of oxides and polymers, research of humidity sensors using coordination polymers (CPs) is still in the initial stage yet an appealing option. Here, we successfully synthesized a new CP with formula of [Cd(TMA)]n (named as CdTMA, H2TMA = 3-thiophenemalonic acid) through a facile acetone diffusion method at room temperature. This CdTMA crystalized in a two-dimensional (2D) honeycomb-like lamellar structure is explored as impedimetric humidity sensing material. The CdTMA based sensor takes the advantages of high sensitivity, good repeatability, fast response as well as narrow hysteresis loop. It is worth mentioning that the sensor enjoys sensitivity of as high as 1.28 × 104 with response time as short as 12 s switching from 11% relative humidity (RH) to 97% RH at room temperature. Finally, the humidity sensing mechanism has been discussed through complex impedance analysis, and the interaction between water molecules and CdTMA at different RH is further visualized by schematic diagrams.