“…Since Anipsitakis and Dionysiou first reported that Fe(II) added to a PMS solution could degrade 2,4-dichlorophenol, the Fe(II)/PMS system has received much attention. − The transformation of the target compound in Fe(II)/PMS systems typically exhibits a rapid stage lasting minutes, followed by a much slower stage. ,,, It has been suggested that the rapid stage proceeds via outersphere electron transfer from Fe(II) to PMS to give SO 4 •– or Fe IV =O (reactions or ), which dominates target removal with the final products of SO 4 2– and Fe(III). ,,,, Because the reactivity of Fe(III) toward PMS is too weak to sustain the reaction, ,,, further addition of Fe(II) is required to achieve complete degradation of the target compounds, which results ultimately in generation of excessive iron sludge when the effluent is returned to neutral pH. In addition, the working pH range is limited to the range of 3.0–3.5, the lower end of which is to maintain reactivity and the upper end is to avoid coprecipitation of Fe(III) and Fe(II). , Obviously, improving the reactivity of Fe(III) toward PMS would benefit the development of a sustainable iron-based system in engineering applications. Fe false( normalII false) + normalHSO 5 − → normalSO 4 • − + Fe false( normalIII false) + OH − k 1 a = ( 2.1 − 3.74 ) × 10 4 M − 1 …”