Due to low cost and low toxicity, manganese oxides have been extensively explored to reduce organic pollutants in wastewater via peroxymonosulfate (PMS) activation; but the development of manganese based catalysts with facile synthesis process at low temperatures and high efficiency is still of significant practical interest. In this paper, a simple room temperature method has been successfully developed to synthesize cryptomelane-type manganese octahedral molecular sieves (OMS-2) from KMnO4 and MnSO4 in the presence of carbon nanotubes (CNTs). The redox reaction between amorphous manganese oxide and CNTs results the decrease of manganese valences and the formation of OMS-2 phase at a low temperature of 25 degrees C. The changes of synthesis time, temperature and CNTs dosage altered the characteristics of the prepared materials. Compared with CNTs, OMS-2 and other manganese oxides hybrids, the synthesized catalysts demonstrated a remarkable efficiency for PMS activation to degrade organic dyes and a superior reusability during ten successive cycles. Sulfate radicals were formed as the active species in the system from the oxidation of low valent Mn species by PMS. This study not only provides a simple method to synthesize OMS-2 at room temperature, but also improves the understanding of PMS activation on manganese-based catalysts for pollutants degradation. (C) 2018 Elsevier Inc. All rights reserved.