Abstract
New hybrid materials – photosensitized nanocomposites containing nanocrystal heterostructures with spatial charge separation, show high response for practically important sub-ppm level NO2 detection at room temperature. Nanocomposites ZnO/CdSe, ZnO/(CdS@CdSe), ZnO/(ZnSe@CdS) were obtained by the immobilization of nanocrystals – colloidal quantum dots (QDs), on the matrix of nanocrystalline ZnO. The formation of crystalline core-shell structure of QDs was confirmed by HAADF-STEM coupled with EELS mapping. Optical properties of photosensitizers have been investigated by optical absorption and luminescence spectroscopy combined with spectral dependences of photoconductivity, which proved different charge localization regimes. Photoelectrical and gas sensor properties of nanocomposites have been studied at room temperature under green light (λmax = 535 nm) illumination in the presence of 0.12 – 2 ppm NO2 in air. It has been demonstrated that sensitization with type II heterostructure ZnSe@CdS with staggered gap provides the rapid growth of effective photoresponse with the increase in the NO2 concentration in air and the highest sensor sensitivity toward NO2. We believe that the use of core-shell QDs with spatial charge separation opens new possibilities in the development of light-activated gas sensors working without thermal heating.
Highlights
Semiconductor metal oxide gas sensors are promising for integration into mobile devices and information networks because of their extremely high sensitivity, stability and miniaturization capability
We investigate photosensitized nanocomposites containing nanocrystalline heterostructures with spatial charge separation as materials for NO2 sensors working at room temperature under photoactivation with visible light and show that such approach significantly improves the photoelectric and sensor properties of the semiconductor oxide
HAADF-STEM images and electron energy loss (EELS) spectra were obtained with a Titan G3 electron microscope operated at 120 kV equipped with a probe aberration corrector and GIF QUANTUM spectrometer
Summary
Semiconductor metal oxide gas sensors are promising for integration into mobile devices and information networks because of their extremely high sensitivity, stability and miniaturization capability Their working principles are based on the chemisorption of molecules from the gas phase and chemical reactions on the surface of the semiconductor metal oxide, which lead to significant changes in the band structure in a narrow near-surface layer and the formation of energy barriers at the solid-gas interface (Bârsan and Weimar, 2001; Sun et al, 2015). The illumination changes the population of surface states by electrons and holes, which affects the concentration of active adsorption centers on the surface of the semiconductor
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