Enhanced room temperature sensitivity of undoped HfO2 nanoparticles towards formaldehyde gas

Abstract

Hafnium oxide (HfO 2 ) nanoparticulate powders were synthesized via a single step sol gel route using citric acid and ethylene glycol as chelating agent and polymerizing agent, respectively. In order to burn off the volatile components and produce crystalline HfO 2 nanoparticles, the powders were calcined at moderately high temperatures ranging from 500 to 800 °C for 1 h each. The crystal structures of the nanoparticles were ascertained by powder X-ray diffraction. The nanocrystals in powder form had monoclinic structure and preferred orientation of the nanocrystals along (−111) direction was evident. The morphologies of the HfO 2 nanopowders were studied by Field Emission Scanning Electron Microscope (FESEM). Morphologies of the nanopowder were observed to change with calcination temperatures. The optical properties of the HfO 2 nanoparticles were evaluated by UV-Vis Diffuse Reflectance Spectroscopy (DRS). A small change in the band gap energy of HfO 2 nanoparticles was observed with a change in the calcination temperature. In order to study the electrical and gas sensing properties of HfO 2 nanoparticles, the powders were pressed into pellets with 12.0 mm diameter and 1.5 mm thickness. Gas sensing properties of HfO 2 pellets were investigated by exposing them to formaldehyde gas inside closed chambers. The sensitivity of HfO 2 towards formaldehyde gas initially increased with an increase in the calcination temperature due to increased porosity and decreased resistance of the HfO 2 pellet. The HfO 2 powder calcined at 700 °C showed highest sensitivity of 91.2% towards 264 ppm formaldehyde gas. The sensitivity declined with further increase in the calcination temperature because the HfO 2 pellet became less porous thereby. Selectivity of the HfO 2 sensor was tested with three volatile organic compound gases: acetone, ethanol and formaldehyde. Highest response was recorded for the formaldehyde gas.

Buteinylated-hafnium oxide bionanoparticles for electrochemical sensing of wogonin

“…39 The band gap of HfO 2 was determined to be 5.2 eV, attributed to the electronic transition of the valence band to the conduction band for monoclinic HfO 2 NPs. 40 Likewise, the band gap of HfO 2 –B was found to be 4.6 eV, which was significantly decreased due to the oxygen vacancies and distortions in the intrinsic surface effect of HfO 2 after the incorporation of butein. The observed shift in the band gap value (0.6 eV) leads to the improvement of conductivity and high electron transfer capability suitable for electrochemical sensor applications.…”