An excellent-responding ethanol sensor with quasi p–n heterojunction based on the composite material of Fe3O4 and Cu2O

Mesoporous and hollow nanostructures are ideal gas sensing materials due to their large surface-to-volume ratio. In this work, we have successfully synthesized mesoporous ferroferric oxide (Fe3O4) and hollow truncated octahedron cuprous oxide (Cu2O). The quasi p–n heterojunction material (Fe3O4@Cu2O) could be prepared by grind and sonication of the mixture of Fe3O4 and Cu2O with one-step method. The composite material exhibits excellent gas sensing property, which is similar to heterojunction material. The Fe3O4@Cu2O-based gas sensor has a higher sensitivity and a lower detection limit than the gas sensor based on only n-type (Fe3O4) or p-type (Cu2O) semiconductor. A detection limit as low as 100 ppb to ethanol and a rapid response within 5 s are achieved under the optimal conditions. We propose an assumption that the quasi p–n heterojunction material, in which electrons transferring from the n-type semiconductor filled with electrons to the p-type semiconductor full of vacancies, can accelerate the speed of electron transportation like a bridge to connect two semiconductors. This simple and economical preparation method for the heterojunction sensing materials may be a significant step towards practical application of gas sensors.