Orange II (C16H11N2NaO4S) from Sigma Aldrich was used as a model azo dye. A 1 L jar test reactor was used in the experiment. 0.3 mM Orange II solution (58.6 mg/L as TOC)was added to initiate the reaction between nZVI and H2O2. The pH was adjusted by adding 0.1 MNaOH or 0.1 M H2SO4 solution. Hydrogen peroxide solution (28 w/w%, Duksan Pure Chemicals Co. Ltd) was diluted with deionized water.