Electrical and humidity-sensing properties of flexible metal-organic framework M050(Mg) and KOH/M050 and AuNPs/M050 composites films

A commercial metal-organic framework (MOF) of Basosiv M050 and its composite materials potassium hydroxide/M050 (KOH/M050) and Au nanoparticles/M050 (AuNPs/M050) were coated on a polyethylene terephthalate (PET) substrate to form novel flexible impedance-type humidity sensors. The electrical properties of M050 to which were added various amounts of KOH or AuNPs were studied in detail as functions of relative humidity (RH). The contributions of the KOH or the AuNPs to the humidity-sensing (linearity and sensitivity) properties and flexibility were thus elucidated. The M050 and composites of KOH/M050 and AuNPs/M050 films that were coated on PET substrates were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-vis spectroscopy and infrared spectrometry. The sensor that was made of KOH/M050 film with 0.05 M added KOH exhibited high flexibility, the highest sensitivity, acceptable linearity, a short response time, a low temperature coefficient and long-term stability. The humidity-sensing mechanism of the KOH/M050 film was explained using complex impedance spectra.