Synthesis of core-shell ZIF-8@α-Fe2O3 nanorods and improvement of selectivity for ammonia gas

Uniform and dense α-Fe 2 O 3 nanorods were directly synthesized on the ceramic tube substrate by hydrothermal method, and then a layer of porous and dense ZIF-8 film was hydrothermally grown and coated on the surface of α-Fe 2 O 3 nanorods after immersion in ligand solution and high-temperature treatment. Then the core-shell ZIF-8 @ α-Fe 2 O 3 nanorods were obtained. The elements, composition, surface morphology, and crystal structure of the samples were analyzed by XPS, SEM, TEM, and XRD. These results indicate that the width of the rod-shaped α-Fe 2 O 3 was between 20 and 40 nm while the rod-shaped α-Fe 2 O 3 coated with a layer of dense porous ZIF-8 was between 50 and 80 nm. The gas sensing results reveal that compared with pure α-Fe 2 O 3 nanorods, ZIF-8 @ α-Fe 2 O 3 had a great improvement in gas selectivity (11.7), response value (136.9 for ammonia gas of 50 ppm at 280 ℃). The working process and gas sensing mechanism of the ZIF-8 @ α-Fe 2 O 3 were discussed and it demonstrates that ZIF-8 not only plays a screen role in the gas-sensitive response process, but also increases the sensitivity by adsorbing oxygen molecules. It proved that the direct growth of ZIF-8 @ α-Fe 2 O 3 on the ceramic tube provides a more effective way to improve the gas response and selectivity. • The core-shell ZIF-8@α-Fe 2 O 3 nanorods are directly grown on the Al 2 O 3 tubes via hydrothermal method. • ZIF-8@α-Fe 2 O 3 had a great improvement in gas selectivity, response value, response and recovery time. • For all of the testing gases in this experiment, only NH 3 molecules can pass through the gate of ZIF-8 smoothly.