Nanoclustered Pd decorated nanocrystalline Zn doped SnO2 for ppb NO2 detection at low temperature

Nanoclustered Pd (2 mol%) was used to decorate Zn doped SnO2 (10 mol% Zn) in order to increase its sensing performances. Zn doped SnO2 built from nanoparticles was prepared by a hydrothermal method using a nonionic surfactant -Brij52 and Tripropylamine (TPA) as co-templates. The presence of well-dispersed Zn2+ ions in the SnO2 matrix leads to a nonstoichiometric surface. Pd was deposited by subsequent wet impregnation using hydrazine as reducing agent. The as obtained powders were deposited as thick layers onto commercial substrates, in order to obtain the sensitive structures. The coexistence of a mixture of valence states (Pd-0, Pd2+ and Pd4+) was highlighted on the surface of the as prepared layers. Several aspects have been followed regarding the Zn and Pd dispersion into the SnO2 matrix: the large scale and low scale morphology (SEM and TEM/HRTEM) in relation with the synthesis route, the obtained crystallographic phases (XRD, SAED) and the way in which the Zn2+ ions are inserted into the SnO2 structure (XRD, XPS, EPR), the spatial distribution of the added chemical elements, Zn and Pd (SEM, STEM, EDS). All these morphological and structural aspects, as well as the Pd surface chemistry, have been correlated with the sensing properties of the nanostructured materials under controlled gas atmosphere. Through this study, we could harvest the specific role of the aforementioned loadings towards selective detection of low NO2 concentrations, between 350 ppb to 5 ppm, at low operating temperature of 100 degrees C, for infield conditions.