NO₂ and NH₃ detection using work function measurement of solvothermal synthesised ZnO–NiO nanocomposites: a case study

Work function measurement using Kelvin probe method has been demonstrated as an effective and novel approach towards detection of NH₃ and NO₂ gases using ZnO–NiO based nanocomposites. For this the nanocomposites were synthesised in different compositions using the solvothermal method. Formation of ZnO–NiO nanocomposites was confirmed using XRD and EDS studies. It is found that the nanoparticle morphology of NiO changes with different percentages of Zn addition. The work function of the sensing film was found to decrease and increase upon exposure to NH₃ (1.51) and NO₂ (1.18) gases owing to the reducing and oxidising nature of the test gases. Of the different composites, Zn_0.75Ni_0.25O exhibited highest sensor response towards the test gases. The increased response is attributed to the nanostructured morphology of the nanocomposite and the formation and collapse of the p-n heterojunction formed between p-type NiO and n-type ZnO. Besides, incorporation of NiO enhances the oxygen adsorption on the sensor surface assigned to the Ni²⁺ ions getting readily oxidised to Ni³⁺. Our results clearly suggest that the work function measurements could also be used as an effective way for NO₂ and NH₃ detection.