semiconductor gas sensors based on hollow metal oxides: focusing on mof-derived structures

Improving the function of hollow metal oxide nanostructures with various morphologies such as hollow fibres, cubes, cylinders, and hemispheres/spheres has attracted extensive attention due to their wide applications in various areas including gas sensing, catalysts, photocatalysts, and adsorbents. the detection of toxic, pollutant, and flammable gases, using metal oxide semiconductors (mos) is essential for controlling their emissions into indoor and outdoor environments. mos gas sensors are relatively inexpensive and lightweight devices for gas measurement, offering long durability, high sensitivity, and rapid response. given the hollow structure, it is expected that the sensing response in hollow metal oxide nanostructures would be considerably higher than that of similar mos nanoparticles. this is reasonable considering the high surface area and the swift and effective gas transport across the thin, porous shell layer. the main factors determining the sensitivity and response time in hollow metal oxide nanostructures include temperature, humidity, and the presence of interfering gases, which are optimized by tuning the synthesis conditions. this review aims to discuss the advantages and challenges of hollow mos in gas sensing applications, focusing on metal-organic framework derived hollow structures, synthesis methods of hollow nanostructures, and recent advances in gas sensing performance based on hollow mos.