New methylene blue incorporated in mordenite zeolite as humidity sensor material

Our experimental observation shows that new methylene blue (NMB) incorporated in H-mordenite zeolite can serve as an excellent candidate for optical humidity sensing. New methylene blue was incorporated into H-mordenite zeolite by ion exchange reaction in aqueous phase. The dye solid was characterized by diffuse reflectance spectroscopy (DRS). The mechanism of the sensor is based on the protonation and deprotonation of the dye molecules which are associated with the desorption and adsorption of water molecules by zeolite, respectively. The measurement was carried out at seven fixed humidity points in the range of 6-98% relative humidity. The sensor showed a linear response range from 6 to 95% relative humidity, good stability and reversibility. The sensor operates both in 632 nm and 590 nm bands. The sensor demonstrates relatively fast response and recovery times about 1 min in the direction of adsorption and about 2 min in the direction of desorption of water. (c) 2006 Elsevier B.V. All rights reserved.