Enhanced isoprene gas sensing performance based on p-CaFe2O4/n-ZnFe2O4 heterojunction composites

Isoprene, a toxic volatile organic compound, is harmful to the human body. It is of great application value to develop gas sensing materials for the effective detection of isoprene. In this work, the CaFe2O4, ZnFe2O4 and CaFe2O4/ZnFe2O4 composites are successfully synthesized by hydrothermal approach. Especially, the CaFe2O4/ZnFe2O4-50% presents porous walnut-like structure and exhibits the superior gas sensing properties to isoprene, including a high response to 30 ppm isoprene (S=19.50), low working temperature (200 °C) and fast response-recovery time (~72–35 s). Moreover, the CaFe2O4/ZnFe2O4-50% based sensor also achieves good selectivity, excellent humidity resistance, long-term stability and LOD as low as 0.12 ppb. Further analysis demonstrates that the outstanding gas sensing properties of CaFe2O4/ZnFe2O4-50% can be attributed to the improvement of electron-hole (e--h+) separation rate, the decrease of charge transfer resistance, the high content of OV, large BET surface area, the narrowed band gap and the formation of CaFe2O4/ZnFe2O4 p-n heterojunctions. These results indicate that appropriate CaFe2O4 coupled with ZnFe2O4 to form CaFe2O4/ZnFe2O4 is a promising strategy to achieve a superior isoprene gas sensor.