CaO–SnO2 nanocrystalline composites with rod-like structures had been fabricated through an efficient and facile electrospinning approach, followed by appropriate thermal treatment in ambient conditions. The morphology of CaO–SnO2 composite nanorods consisted of fine grain sized SnO2 nanoparticles. The 2 at% CaO–SnO2 L-NRs (loose nanorod structure) do not array closely in the center of the nanorods, showed a unique nanocrystalline structure and exhibit excellent sensing properties with high response and good selectivity at room temperature, by using NOx as a probe molecule. Moreover, 2 at% CaO–SnO2 L-NRs revealed a favourable linear relationship in the whole NOx detection region. The high response of 2 at% CaO–SnO2 L-NRs may be attributed to one-dimensional loose nanostructures for every SnO2 nanoparticle which overlapping and being connected with four or more adjacent grains through necks can adsorb a NOx molecule. The necks stabilized at the ideal size which enhances electron ‘‘injection’’ in the depleted inter-crystal boundaries and the large number of sensing activity sites (chemisorbed oxygen: O−, O2−, O2−). Furthermore, the joining of nanocrystals by annealing can improve the conduction of electrons. The 2 at% CaO–SnO2 L-NRs showed excellent sensitivity characteristics to NOx even at the level less than 10 ppb. The excellent gas sensing properties can be a reference for the preparation of other semiconductors for sensor applications.
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