Suman Pokhrel

Humidity-sensing properties of ZnCr2O4–ZnO composites

Abstract The preparation of ZnCr2O4 was carried out by the high-temperature solid-state method with the reaction of Cr2O3 and ZnO at 900 °C. Experimental results on the composites made from different mole ratios of ZnCr2O4 and ZnO for electrical and humidity-sensing properties are described. The sintered polycrystalline disks of the composites were subjected to DC electrical conductivity measurements over the temperature range 330–500 K from which the activation energies were determined. The composites were identified by powder X-ray diffraction (XRD). The scanning electron microscopy (SEM) studies were carried out to study the surface structure of the sensor materials. The composites were subjected to DC resistance measurements as a function of relative humidity in the range of 5–98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor Sf (R5%/R98%) measured at 298 K revealed that ZCZO-21 has the highest humidity sensitivity, greater than 6.5×103; however, ZCZO-11, ZCZO-32, and ZCZO-14 have lower sensitivity but better linear trend. The response and recovery characteristics for ZCZO-21 and ZCZO-11 were assessed.

Preparation, characterization, and X-ray structure analysis of diethylenetriammonium tetrathiomolybdate

The interaction of H2S gas with aqueous ammonium heptamolybdate solution in the presence of diethylenetriamine (dien) led to the formation of diethylenetriammonium tetrathiomolybdate crystals. The elemental analyses, UV-Visible, IR, and 1H NMR spectra suggested the presence of organic cation and (MoS4)2− moiety. The 1H NMR revealed the presence of two sets of symmetrical A2X2 multiple patterns. The compound crystallizes in the monoclinic system with space group Pn, a = 7.196(6), b = 7.532(3), c = 11.525(10) Å, α = 90°, β = 90.17(3)°, γ = 90°, V = 624.78(8) Å3, and Z = 2, wR1 = 0.0261 and wR2 = 0.0698. The structure consists of tetrahedral tetrathiomolybdate anions, which form an extended three-dimensional network in the solid state with Mo–S⋅⋅⋅H–N hydrogen bonding with the organic cation.