Aqueous foam loaded TiO₂ nano-catalysts for promoting photodegradation of methylene blue

In this work, the photodegradation of methylene blue was investigated by constructing a novel photocatalysis reactor, which was filled with aqueous foam. Nanoscale TiO₂ particles were used as photocatalyst. In order to obtain stable foam phase, cetyl trimethyl ammonium bromide (CTAB) was used as the frother, and its suitable initial concentration in the feeding solution was 0.20 g/L. Under the suitable conditions of loading liquid volume 200 mL, initial concentration of TiO₂ nano-catalysts in the feeding solution 5.0 g/L, inner diameter of foam column 18 mm, aperture diameter of gas distributor 125 μm, and circulating velocity of bulk solution 500 mL/h, the maximum degradation percentage of methylene blue was 97.6 ± 1.2%. Atomic force microscopy (AFM) analysis suggested that the entrainment effect of rising bubbles and the circulation flow of bulk solution inside the aqueous foam did not cause the conspicuous aggregation of TiO₂ nano-catalysts under the suitable conditions, but their surface roughness decreased. Meanwhile, foam entrainment had not a significant impact on the polydispersity of TiO₂ nano-catalysts. In contrast to the photodegradation of methylene blue in aqueous solution, the photocatalysis process using aqueous foam is the intensity of light received by TiO₂ nano-catalyst increases, and irradiation period is less. This work is expected to provide new insight into the rational design of photocatalysis reactor, to facilitate the harmless treatment of dyestuff wastewater.