Role of hexamethylenetetramine in ZnO-cellulose nanocomposite enabled UV and humidity sensor

Spherical nanoparticles and short nanorods of ZnO nanocrystals were grown on cellulose fibers by a simple one pot aqueous chemical bath deposition technique using hexamethylenetetramine (HMT) as the surfactant. The role of surfactant on UV and humidity sensing properties of ZnO-cellulose nanocomposite (ZCN) has been investigated. The structure, morphology and composition of the ZCNs were investigated by X-rays diffraction, field emission scanning electron microscopy and thermogravimetric analysis, respectively. The morphology, shape and size of the ZCN were analyzed by a transmission electron microscopy. The optical properties were investigated by diffuse reflectance spectroscopy (DRS). The band gap values of the composites, obtained from DRS, were in the range of 3.22-3.24 eV. The ZCN synthesized with 0.9 wt% of HMT showed a very high response to ultraviolet (UV) light, characterized by a large increase in the photocurrent under UV illumination. Due to UV illumination, the surface photocurrent recorded from a pellet of the above nanocomposite powder increased from 7.416x10(-7) A to 3.161x10(-5) A in 8 s. The ON to OFF ratio of the photocurrent (I-UV/I-Dark) was 42.624, whereas the response and recovery times were 8 s and 10 s, respectively. The humidity sensing properties of the nanocomposite powder were studied in the relative humidity (RH) range 40-90% and a sensitivity of 4.487 M Omega/%RH was recorded for the powder synthesized at optimized condition. The high ON/OFF ratio, short response and recovery time imply the importance of the material as a good UV sensor, whilst the notable sensitivity of the material promises for efficient humidity sensing applications.