Figure 5: Photocatalytic & gas-sensing performance of as-prepared ZnO nanocrystals.
(a) Photodegradation of MO over ZnO nanocrystals under simulated sunlight irradiation. (b) SPV spectra of ZnO nanocrystals obtained using different heat treatments. (c) Cycling runs for photodegradation of MO over ZnO-300/100–650/200 under simulated sunlight irradiation. The normalized concentration of MO aqueous solution is monitored by measuring the absorbance at 464 nm. (d) Real-time response curves of sensors based on different ZnO nanocrystals to NO2 with concentrations ranging from 5 to 25 ppm under 365 nm light irradiation at room temperature. (e) Reproducibility of sensor performance based on ZnO-300/100–650/200 response to 25 ppm NO2 under 365 nm light irradiation at room temperature. (f) Selectivity of the sensor based on ZnO-300/100–650/200 with presence of interference gases (25 ppm) under 365 nm light irradiation at room temperature. (g) Schematic of the catalytic reaction mechanism of ZnO-300/100–650/200 under simulated sunlight irradiation: (1) Generation of electron-hole pairs under UV irradiation, (2) dye molecules’ excitation by visible light, (3) recombination of photo-generated electrons and holes in the bulk, (4) recombination of photo-generated electrons and holes caused by grain-boundary defects, (5) surface oxygen vacancy-induced separation of electron-hole pairs, (6) electron injection from excited dye molecules into the surface and CB of ZnO, (7) formation of ROS, (8) degradation of dye molecules.
