In this study, degradation of Malachite green (MG) (10 mg/L) by Potassium persulphate (KPS) (1 g/L), and KPS in presence of (1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) nickel(II) perchlorate (complex1), (200 mu M), was investigated by spectrophotometric and HPLC methods. KPS alone had ability to degrade MG. Interestingly, rate of degradation of MG was enhanced upon addition of complex1. Degradation was effective at pH range of 3-9 and was found to be dependent on initial concentration of KPS, complexl, MG, and pH. Degradation of MG by KPS was not significantly affected in presence of Ni(II) ions whereas in presence of Fe(II) ions degradation was incomplete. Ability of KPS to reduce TOC increased in presence of complex1. Transformation products were analysed by LC-ESI-MS. Finally, treatment of MG with complex1 and KPS resulted in removal of antibacterial activity of MG under in vitro conditions. (C) 2012 Elsevier B.V. All rights reserved.