Microtubular α-Fe2O3/Fe2(MoO4)3 heterostructure derived from absorbent cotton for enhanced ppb-level H2S gas-sensing performance

Highlights: • Microtubular α-Fe₂O₃/Fe₂(MoO₄)₃ heterostructure was simply prepared by using as absorbent cotton biotemplate. • The FFMO sensor possesses the highest sensitivity to 10 ppm H₂S rather than reported Fe₂(MoO₄)₃-based sensors. • The response time of 3 s to 10 ppm H₂S is the fastest in reported Fe₂(MoO₄)₃-based sensors. • The detection limit of 50 ppb is the lowest in reported Fe₂(MoO₄)₃-based sensors. -- Abstract: Microtubular α-Fe₂O₃/Fe₂(MoO₄)₃ heterostructure (FFMO) was massively prepared by facile immersion-calcination method with absorbent cotton being employed as template, which is formed by a great number of cross-linking nanoparticles. In comparison with the pure iron molybdate (FMO) microtubules, the small-sized α-Fe₂O₃ nanocrystals evenly attached to the surface of FMO particles, increasing the specific surface area of FFMO composites and forming broad hierarchical pores. Gas-sensing measurement indicates that the sensor fabricated from FFMO heterostructure presents response of 12.69 toward 10 ppm H₂S, being about 2.2 times larger than that of pure FMO-based sensor. And the working temperature also reduces from 170 °C to 133 °C. In particular, the FFMO composite exhibits the fastest response (T_res = 3 s) and the lowest detection limit (50 ppb) to H₂S gas among all reported FMO-based sensors. Such rapid response and highly sensitive to trace H₂S are dominantly assigned to the synergism of the inherent properties of multistage-pores microtubule, n-n heterojunction, surface adsorbed oxygen, as well as the generation of metastable iron sulfide induced by lattice oxygen. In addition, the gas-sensing mechanism of the sensor is also studied in detail.