Tunable visible light enhanced triethylamine adsorption on pH dependent ZnO nanostructures: An investigation by scanning Kelvin probe

In this work, we reported the effect of adsorption of volatile organic compounds on surface potential of zinc oxide nanostructures synthesized at four different pH (5, 7, 9, and 11) at 80°C about 45 min. For all zinc oxide nanostructures, the contact potential difference was determined by exposing ethanol, n-hexane, and triethylamine under dark and visible light in ambient air environment using scanning Kelvin probe with surface photovoltage module. X-ray diffraction studies revealed that the crystallite size decreased with an increase in pH. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy studies showed that the shift in pH resulted in multiple morphologies ranging from dumbbells to nanocones decorated nanorods. Photoluminescence, Raman spectra and surface photovoltage measurements revealed the presence of defects (oxygen and zinc vacancies) that enhanced the photosensitivity of zinc oxide nanostructures in the visible region. Out of all samples, the zinc oxide nanostructures obtained at pH 9 and 11 have demonstrated ∼ 3 times enhanced photovoltage towards triethylamine.