Template-free microwave-assisted synthesis of ZnO hollow microspheres and their application in gas sensing

We report a facile template-free microwave-assisted approach to synthesize ZnO hollow microspheres. Field emission scanning electron microscopic and transmission electron microscopic results revealed that the average dimensions of these hollow microspheres were about 4 μm in diameter and 400 nm in thickness of spherical shell. Interestingly, the “hollowness” of these ZnO spheres could be adjusted by varying the microwave irradiation time. Moreover, various distinct ZnO structures could be obtained by simply changing the amounts of trisodium citrate dihydrate. On the basis of these results, a possible formation mechanism was proposed. Gas sensors were fabricated based on as-prepared hollow spheres, and their gas sensing properties were tested for response to ethanol and methanol.