An impedimetric ammonia sensor based on nanostructured α-Fe ₂ O ₃

An impedimetric sensor has been developed for the detection of ammonia vapour using a highly crystalline α-Fe2O3 synthesized by a solution combustion method. The as-prepared α-Fe2O3 requires annealing at 600 °C for 2 h to obtain high crystallinity and good purity. The material is characterized by XRD, FT-IR, SEM and AFM. AC impedance data reveal a systematic variation in charge transfer resistance with respect to ammonia concentration. A linear calibration between sensitivity and ammonia concentration is obtained in the concentration range from 100 to 1000 ppm. The sensor has a sensitivity (%) of about 33 with a response and recovery time of 40 and 50 s, respectively, at 100 ppm of ammonia. The sensor can be described by an equivalent circuit having two resistance and two capacitance components parallel to each other. α-Fe2O3 is found to show a higher sensitivity to ammonia in comparison to other vapours like acetone, methanol, ethanol, propanol and butanol.