Coupling visible light sono-photocatalysis and sono-enhanced ultrafiltration processes for continuous flow degradation of dyestuff using N-doped titania nanoparticles

Sono-photocatalysis has potential to increase the efficiency of both sonolysis and photocatalysis processes. On the other hand, in the sono-enhanced membrane separation processes the ultrasonic waves are able to clean the membrane surface, inhibit its fouling and enhance the separation efficiency. In this work, visible-light sono-photocatalysis and sono-enhanced membrane separation processes were coupled in a one pot/hybrid reactor for continuous flow removal of a dyestuff from water. First, N-doped titania sono-photocatalyst and microporous polyvinylidene fluoride membrane were prepared and characterized. Then, the hybrid reactor was set for the dyestuff degradation. The effect of operational variables including N-doped titania dosage, pH, retention time, visible-light power, radical scavengers and inorganic oxidants on the degradation efficiency was investigated. An enhancement in the degradation efficiency was observed by adding inorganic oxidants and increasing the retention time and visible light power. However, the degradation efficiency was decreased by increasing pH and adding organic and inorganic radical scavengers. 750 mg/L was the optimum N-doped titania dosage. The efficiency of the hybrid process was higher than other probable processes and the synergistic effect between photocatalysis and sonolysis was 23.51%. Main intermediates of dyestuff degradation were identified and a plausible degradation pathway was proposed using GC-MS analysis.