Wang et al. [27] reported a study based on the relative between particle size and photocatalytic
activity of samples. It was found that the higher particle size and lower surface area (21 nm, 70 m2/g) as
well as lower particle size and higher surface area (6 nm, 253 m2/g) of the sample were unfavorable for its
photocatalytic activity and the samples with intermediate grain size and surface area (11 nm, 157 m2/g)
showed the highest photocatalytic activity.