Nickle ion surface engineered MOF derived α-Fe2O3 octahedrons for high efficiency toluene detection with high moisture resistance and long-term stability

Metal-organic framework derivatives have become very promising candidates for gas sensors due to their advantages of large specific surface area, many surface active sites, and tunable properties. Meanwhile, Ni ion doping is an effective technique to enhance the moisture resistance of sensing materials. Inspired by this, in this work, we have successfully synthesized porous octahedral structures of Ni-Fe2O3 derived from metal-organic frameworks by in situ doping, in which the Ni contents were 0.4, 0.5 and 0.6 mol%, respectively. Notably, Ni doping changes the conductive type of Fe2O3 from n-type to p-type with a significant decrease in resistance. At the same time, the sensing performance of Fe2O3 octahedrons for volatile organic compound gases, especially toluene, is greatly improved. The 0.5 mol% Ni doped Fe2O3 sensor showed the highest response to toluene at 225°C (100 ppm, 47), which is five times higher than the pristine Fe2O3 (response 9.5). In addition, the sensor demonstrated fast response and recovery time (20 s/40 s), low detection limit (200 ppb), high moisture tolerance (98% RH, 47), and long-term stability of over 60 days. The main reason for the exceptional performance of Ni doped Fe2O3 sensors is its special porous octahedral structure, and more importantly, the change of carrier type of the sensing material after Ni doping and the substantial increase of oxygen vacancies, and the catalytic effect of Ni ions.