In this work, we
successfully prepared three different mesoporous
NiO nanostructures with preferential (111) planes using three different
solvents–water, a water–ethanol mixture, and a water–ethylene
glycol mixture. The NiO nanosheets prepared from the water–ethylene
glycol mixture and denoted as NiO-EG showed a nanosheet morphology
thinner than 10 nm, whereas the water–ethanol and water samples
were 30–40 nm and above 100 nm thick, respectively. The NiO-EG catalyst was found to exhibit a high catalyzing ability to activate
peroxymonosulfate (PMS) for decoloring dyes, by which 94.4% of acid
orange 7 (AO7) was degraded under the following reaction conditions:
AO7 = 50 mg/L, catalyst = 0.2 g/L, PMS = 0.8 g/L, pH = 7, and 30 min
reaction time. The dye degradation rate was investigated as a function
of the catalyst dosage, pH, and dye concentration. According to quenching
experiments, it was found that SO4•–, HO•, and
O2•– were the dominant radicals for AO7 degradation, and oxygen vacancies
played a significant role in the generation of radicals. High surface
area, thin flaky structure, rich oxygen vacancies, fast charge transport,
and low diffusion impedance all enhanced the catalytic activity of
NiO-EG, which exhibited the highest degradation ability due to its
abundant accessible active sites for both adsorption and catalysis.