CoFe2O4 nano-crystallines were prepared by a hydrothermal method at 120–220 °C. CoFe2O4 sensors were fabricated from the CoFe2O4 nano-crystallines and their gas sensing properties were investigated. Spinel CoFe2O4 nano-crystallines could be obtained when the pH value was in the range of 8–14, and the morphology of the particles obtained under different conditions was almost spherical. The CoFe2O4 nano-crystallines obtained at a pH of 8–10 exhibited n-type response to gases at low temperatures and p-type response to gases at high temperatures, while CoFe2O4 nano-crystallines obtained at a pH of 11–14 exhibited p-type response to gases. It was found that the sensor based on the CoFe2O4 nano-crystallines prepared at 180 °C for 48 h (pH 8) exhibited good performance, characterized by high responses to dilute C2H5OH and very low responses to petrol, C6H6 and C6H5CH3 when operating at 150 °C. If there was no ethanol in the atmosphere, the sensor based on nano-CoFe2O4 (180 °C, 48 h, pH 8) could be used to detect triethylamine at 190 °C. The sensor is a promising candidate for practical detector for dilute C2H5OH and triethylamine.

Ethanol gas sensor based on CoFe2O4 nano-crystallines prepared by hydrothermal method

Production of single phase nano size NiFe2O4 particles using sol–gel auto combustion route by optimizing the preparation conditions

Size and crystallinity-dependent magnetic properties of copper ferrite nano-particles

Formaldehyde is a hazardous indoor volatile organic pollutant, thus selective and precise detection at a low concentration level is crucial. In this paper, NiO/NiFe2O4 nanocomposites were prepared through a simple two-step hydrothermal route and their gas sensing performances were investigated. SEM and TEM results showed that the composite products were NiO nanotetrahedrons decorated with numerous separated NiFe2O4 nanoparticles on the outer layer surface. XPS characterization confirmed that the as formed NiFe2O4 exhibited a p-type conductivity due to the hole transfer between Ni3+ and Ni2+ and therefore p-p isotype heterojunctions formed in the composite products. The element ratio of Fe to Ni was optimized to gain higher gas-sensing performance through adjusting the feeding amount of Fe3+ in the synthesis process. As a consequence, the gas sensor based on the sample NiFe-0.008 showed the highest response of 33.3–200 ppm formaldehyde vapor at 240 °C and a low detection limit of 200 ppb. The composite sensor also showed short response/recovery time and good long term stability. The enhanced gas sensing properties to formaldehyde can be attributed to the unique tetrahedral morphology and p-p heterojunction structure, which can provide more active sites and signiﬁcantly enlarge resistance variation. This work will provide a new perspective of p-p heterojunction for the practical application in formaldehyde gas sensor.

S.S Bellad

Papers

Substrate temperature dependent properties of sprayed CoFe2O4 ferrite thin films