Mn-doped ZnO microspheres prepared by solution combustion synthesis for room temperature NH3 sensing

Despite being the most favorable ammonia (NH3) gas sensors, metal oxide semiconductors fail to deliver high selectivity and room temperature (RT) sensing. Tuning the metal oxide with doping is an attractive way of overcoming these disadvantages. Herein, we report Mn-doped ZnO microspheres as promising sensors for highly sensitive and selective RT sensing of NH3. ZnO and 2 wt% Mn-doped ZnO microspheres were synthesized by a low-cost and fast solution combustion synthesis, and their structure, morphology, and gas sensing properties were investigated. Mn-doping resulted in a change in the lattice parameters, an increase in the oxygen vacancies, and surface acidity of ZnO as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Temperature programmed desorption (TPD), respectively. Mn-doped ZnO showed a response (Ra/Rg) of 20.2 in 100 ppm NH3, which is significantly higher than ZnO. The sensor showed high selectivity, three times higher than that of ZnO, and good stability. Improvement in the sensing performance of Mn-doped ZnO is attributed to the increase in the defects and surface acidity with Mn-doping.