Comparative photocatalytic degradation of estrone in water by ZnO and TiO2 under artificial UVA and solar irradiation

Solar photocatalytic decomposition of ethyl paraben in zinc oxide suspensions

“…1b). The higher photocatalytic activity of ZnO compared to P25 has been reported and reviewed elsewhere [20], where azo-dyes and substituted phenols have been employed almost exclusively as the probe compound. Han et al [20], who studied the photocatalytic degradation of estrone under UV-A irradiation, reported that the degradation rate with ZnO was 2-3 times greater than with P25.…”

“…The higher photocatalytic activity of ZnO compared to P25 has been reported and reviewed elsewhere [20], where azo-dyes and substituted phenols have been employed almost exclusively as the probe compound. Han et al [20], who studied the photocatalytic degradation of estrone under UV-A irradiation, reported that the degradation rate with ZnO was 2-3 times greater than with P25. The superior Table 1 Variables of the 2 6 activity of ZnO was mainly attributed to (i) its markedly higher UV absorbance compared to P25 within the wavelength range of 320-385 nm, and (ii) the role of intrinsic defects in the lattice.…”

“…The solution pH dropped slightly from 6.2 to 5.7, which is unlikely to have caused leaching. Han et al [20] reported that the concentration of leached zinc during the photocatalytic degradation of estrone was 5.2 and 8 mg/L after 60 min of reaction at 0.01 and 0.5 g/L ZnO, respectively (in this work, it was 5.8 mg/L after 60 min at 1 g/L ZnO, as seen in Fig. 8); they also found that the extent of dissolution was suppressed by about 50% when the initial solution pH was adjusted to 10.…”

“…The superior Table 1 Variables of the 2 6 activity of ZnO was mainly attributed to (i) its markedly higher UV absorbance compared to P25 within the wavelength range of 320-385 nm, and (ii) the role of intrinsic defects in the lattice. The latter mainly are oxygen vacancies and Zn interstitials, both of which are positively charged and, therefore, they can trap the photogenerated electrons and minimize the rate of electron/hole recombination [20]. Although such defects eventually become neutral, they can participate in ionization reactions releasing again electrons, thus sustaining the redox cycle [20].…”

“…The latter mainly are oxygen vacancies and Zn interstitials, both of which are positively charged and, therefore, they can trap the photogenerated electrons and minimize the rate of electron/hole recombination [20]. Although such defects eventually become neutral, they can participate in ionization reactions releasing again electrons, thus sustaining the redox cycle [20].…”