Facile synthesis of CaO-SnO2 nanocrystalline composite rods by electrospinning method with enhanced gas sensitive performance at room temperature

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-, O-2-). 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.