Abstract
Magnetite (\(\hbox {Fe}_{3}\hbox {O}_{4}\)) nanoparticles with different particle sizes (9.9–29.1 nm) were prepared by using the aerial oxidation method under light irradiation with various wavelengths at room temperature. The photocatalytic degradation of orange II using \(\hbox {Fe}_{3}\hbox {O}_{4}\) nanoparticles as photocatalysts was evaluated. Experimental results showed that the particle sizes of \(\hbox {Fe}_{3}\hbox {O}_{4}\) nanocrystals decreased gradually with the decreasing wavelengths of light irradiation. With the decrease in the size of the samples, the \(\hbox {Fe}_{3}\hbox {O}_{4}\) nanoparticles exhibited a large surface area and high adsorption. Furthermore, the small-particle-sized \(\hbox {Fe}_{3}\hbox {O}_{4}\) sample could cause an appropriate red shift of the spectra and promote the decomposition of \(\hbox {H}_{2}\hbox {O}_{2}\), and produce high-content \(^{\bullet }\hbox {OH}\) radicals, which lead to an improvement of photodegradation efficiency of orange II.