Ultrahigh Sensitivity of Au/1D α-Fe2O3 to Acetone and the Sensing Mechanism

Hematite (alpha-Fe2O3) is a nontoxic, stable, versatile material that is widely used in catalysis and sensors. Its functionality in sensing organic molecules such as acetone is of great interest because it can result in potential medical applications. In this report, microwave irradiation is applied in the preparation of one-dimensional (ID) alpha-FeOOH, thereby simplifying our previous hydrothermal method and reducing the reaction time to just a few minutes. Upon calcination, the sample was converted to porous alpha-Fe2O3 nanorods, which were then decorated homogeneously by fine Au particles, yielding Au/1D alpha-Fe2O3 at nominally 3 wt% Au. After calcination, the sample was tested as a potential sensor for acetone in the parts per million range and compared to a similarly loaded Pt sample and the pure 1D alpha-Fe2O3 support. Gold addition results in a much enhanced response whereas Pt confers little or no improvement. From tests on acetone in the 1-100 ppm range in humid air, Au/1D alpha-Fe2O3 has a fast response, short recovery time, and an almost linear response to the acetone concentration. The optimum working temperature was found to be 270 degrees C, which was judged to be a compromise between the thermal activation of lattice oxygen in hematite and the propensity for acetone adsorption. The surface reaction was investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and a possible sensing mechanism is proposed. The presence of Au nanoparticles is believed to promote the dissociation of molecular oxygen better in replenishing 0 vacancies, thereby increasing the instantaneous supply of lattice oxygen to the oxidation of acetone (to H2O and CO2), which proceeds through an adsorbed acetate intermediate. This work contributes to the development of next-generation sensors, which offer ultrahigh detection capabilities for organic molecules.