A facile method for preparation of uniformly decorated-spherical SnO2 by CuO nanoparticles for highly responsive toluene detection at high temperature

We reported a facile preparation of a uniform decoration of spherical n-type SnO2 by p-type CuO nanopa rticles as well as their utilization for enhanced performance on toluene gas detection.CuO nanoparticles and spherical SnO2 were synthesized by a facile non-hydrolytic solvothermal reaction,which could easily control their morphology.A uniform CuO nanoparticles decoration onto spherical SnO2 was achieved by a simple sonication and vigorous stirring at room tempe rature.We revealed orga nic solvents used in the oxide synthesis had a considerable influence on its surface charge that was beneficial for a uniformly electrostatic self-decoration between positively charged p-type CuO nanoparticles and negatively charged n-type spherical SnO2.Interestingly,CuO was partially reduced to Cu metal during high concentration of toluene exposure destroying p-n contact and developing new metal-semiconductor contact so-called ohmic junction,resulting in extraordinarily responsive and selective to toluene gas at 400℃as compared to a single p-CuO and n-SnO2.It was also found that the amount of particle decoration had an influence on sensor response and resistance.The optimum amount of CuO nanoparticle decoration was0.1 mmol on 0.5 mmol SnO2.The re s ponse(S=Ra/Rg)and selectivity of CuO/S nO2 based material toward the exposure of 75 ppm toluene had reached to such high as 540 and 5,respectively.The effect of p-n heterojunction and metal-semiconductor contact on the gas sensing mechanism of p-type CuO/n-type SnO2 was discussed.Furthermore,by decorating with CuO nanoparticles,CuO/SnO2 morphology was well-maintained after gas sensing evaluation demonstrated its excellency for high temperature toluene gas sensor application.

Ordered mesoporous NiFe_2O_4 with ultrathin framework for low-ppb toluene sensing

Highly sensitive and selective detection against specific target gases, especially at low-ppb （part per bil- lion） level, remain a great number of challenges in gas sensor applications. In this paper, we first present an ordered mesoporous NiFe204 for highly sensitive and selective detection against low-ppb toluene. A series of mesoporous NiFe204 materials were synthesized by templating from mesoporous silica KIT-6 and its framework thickness was reduced from 8.5 to 5 nm by varying the pore size of KIT-6 from 9.4 to 5.6 nm, accompanied with the increase of the specific surface area from 134 to 216 m^2 g^-1. The ordered mesoporous NiFe2O4 with both ultrathin framework of 5 nm and large specific surface area of up to 216 m^2 g^-1 exhibits a highest response （Rgas/Ralr-1 = 77.3） toward 1,000 ppb toluene at 230℃ and is nearly 7.3 and 76.7 times higher than those for the NiFe204 replica with thick framework and its bulk counter- part respectively, which also possesses a quite low limit of detection （〈2 ppb）, and good selectivity.