The sensitivity and selectivity of semiconductor metal oxides can be effectively improved by transition metal doping and noble metal loading. In this work, Ag-loaded p-type Zn-doped Fe2O3 (Ag@Zn–Fe2O3) nanoparticles were synthesized by a combination of a one-step hydrothermal route and a co-precipitation method. The prepared Ag@Zn–Fe2O3 nanoparticles show a peanut-like structure with a size of about 50–150 nm. The Zn doping and the Ag loading can synergistically improve the response of the Fe2O3 nanoparticles to acetone. At the optimum operating temperature (150 °C), the response of the Ag@Zn–Fe2O3 sensor to 100 ppm acetone is 50.2, which is significantly higher than 8.9 and 25.8 corresponding to Fe2O3 and Zn–Fe2O3, respectively. In addition, the Ag@Zn–Fe2O3 sensor exhibits excellent selectivity, good moisture resistance, and long-term stability to acetone. Meanwhile, the possible mechanism of the improved acetone sensing properties is also discussed.
The effect of noble metal cocatalyst loading on the concentration of surface-reaching photoexcited charges on semiconductors is an interesting and important issue in photocatalysis. Herein, through in situ diffuse-reflectance infrared spectroscopy (DRIFTS), an adsorbate (methanol) surface elementary reaction kinetic analysis method has been exploited to track the concentration of surface-reaching photoholes in a series of Ag/TiO2 nanoparticles with varied Ag loading. The photocatalytic oxidation of adsorbed methanol species on the Ag/TiO2 surface proceeds via first-order reaction kinetics. Thus, the measured reaction rate constants directly reflect the concentration of surface-reaching photoholes under light irradiation. By determining the specific reaction rate constants for methanol oxidation on the Ag/TiO2 surface, we discover that the concentration of surface-reaching photoholes under light irradiation exhibits a volcano-shaped dependence on the Ag loading. Under the optimized Ag loading, it could be found that the concentration of surface-reaching photoholes on Ag/TiO2 surface is nearly 1.5 times greater than that of the pristine TiO2 surface. These results provide, for the first time, unambiguous experimental evidence for the significance of modification with suitable noble metal cocatalysts on regulation of surface-reaching photoexcited charges in semiconductor-based photocatalysis.
For the efficient disposal of organic pollutants and Escherichia coli ( E. coli ) in water, Ag-loaded and Pd-loaded ZnO nanofibers (NFs) were prepared through electrospinning (e-spin), followed by the alcohol-thermal method. The NFs were prepared in membrane form to promote their separation, recovery, and reuse in practical applications. The complete decolorizations of three types of dyes (i.e., azo, triarylmethane, and heterocyclic dyes) were observed when the Ag-loaded or Pd-loaded ZnO nanofiber membrane (NFM) was first applied as photocatalyst under 30-min UV irradiation. The characterization of the catalysts and the decolorization performance of dyes both demonstrated that the optimal loading rates of Ag and Pd were 12% and 6%, respectively. Moreover, the 12%-Ag/ZnO NFM displayed excellent recyclability over five cycles than the 6%-Pd/ZnO NFM. The E. coli disinfection test demonstrated that the photocatalytic inactivation rates with the 12%-Pd/ZnO NFM and the 6%-Ag/ZnO NFM were significantly improved under solar or UV irradiation, and hydroxyl radicals (∙OH) was primarily responsible for the antibacterial performance. Therefore, the presented 12%-Ag/ZnO NFM and 6%-Pd/ZnO NFM can be used for the efficient photocatalytic treatment of dyes and E. coli in water.
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