Degradation of azo dye Acid Orange 7 in water by Fe0/granular activated carbon system in the presence of ultrasound

Degradation of azo dye Acid Orange 7 (AO7) was investigated using zero-valent iron/granular activated carbon (Fe0/GAC) in the absence and presence of ultrasound (US). The AO7 degradation efficiency by Fe0/GAC was dramatically enhanced by ultrasound, ultrasound alone had a little effect on the degradation. Effects of Fe0/GAC ratios and initial pH values on AO7 degradation were studied in the US-Fe0/GAC system. The degradation followed the pseudo-first-order kinetics model. The pseudo-first-order rate constant of AO7 degradation by Fe0/GAC was 8.74 × 10−3 min−1 while that by US-Fe0/GAC was 3.91 × 10−2 min−1. A significant synergetic effect was observed between US and Fe0/GAC. Ultrasound swept the reactive intermediates or products from Fe0 surface, and thereby the surface of Fe0 was cleaned and reactivated. Granular activated carbon was added as cathode to increase the unit of internal batteries and enhance the current efficiency of the internal electrolysis. The suitable Fe0/GAC ratio (v/v) for the degradation of AO7 in the presence of ultrasound was 1:1. The degradation was highly dependent on pH, and a decrease of the initial pH values from 12.0 to 4.0 led to the increase of degradation efficiencies. Sulfanilamide was proved as the main residual degradation product in the solution by the analysis of high-performance liquid chromatograms.