Soft-templated formation of double-shelled ZnO hollow microspheres for acetone gas sensing at low concentration/near room temperature

The synthesis of well-defined and complex porous hollow structures via a simple method is still a major challenge. In this work, a unique double-shelled ZnO hollow microsphere with a porous surface is successfully synthesized by a facile soft-templated solvothermal method followed by calcination. The presence of ethylene glycol (EG) as soft template leads to the formation of initial single-layered hollow microspheres and then a time dependent evolution transforms them into uniform ZnO hollow microspheres with tunable shell numbers and void space. When used as sensing materials for detecting acetone, the double-shelled ZnO hollow microsphere sensor exhibits high response toward 100 ppm acetone (101.1) and achieves a rapid response rate and recovery process (within 1/7 s) at 300 degrees C, which are superior over those for ZnO microparticle and single shelled ZnO hollow microsphere. In addition, this sensor exhibits low detection limit (0.5 ppm), low operating temperature (40 degrees C), high selectivity to acetone, and long term stability, suggesting their potential applications as advanced gas sensing materials. Such outstanding gas sensing properties of double-shelled ZnO hollow microsphere is due to the larger Brunauer-Emmett-Teller (BET) surface area (76.11 m(2) g(-1)), porous and double-shelled hollow structure, and excellent capabilities of surface adsorbed oxygen.