In this study, a newly emerging oxidant nanoscale calcium peroxide (nCaO(2)) was synthesized to degrade 2,4-dichlorophenol (2,4-DCP). nCaO(2) was prepared from nanoscale Ca(OH)(2) and H2O2 and confirmed to be less than 150 nm in diameter and 62.23 m(2) . g(-1) in specific surface area (SSA). For treating 2,4-DCP, the optimal ratio between Ca(OH)(2) and H2O2 was 1:5. Compared with conventional CaO2, nCaO(2) was found to be more efficient for destructing 2,4-DCP. 2,4-DCP was completely degraded in 5 d by nCaO(2) while only 75.0% 2,4-DCP was destructed by conventional CaO2. The effects of solution pH and water matrix, including SO42-, HCO3- and humic acid (HA) were examined. The reactive species in nCaO(2) system was investigated by photoluminescence (PL) technique and the quenching experiments. Results showed that hydroxyl radical (OH center dot) was the dominant reactive species for destructing 2,4-DCP. The major oxidation products identified in this study were 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), phenol and benzoquinone (BQ). Our works gave an important insight into the use of nCaO(2) to degrade some organic contaminants which might provide some references for the application of nCaO(2) in chlorophenols contaminated groundwater remediation. (C) 2016 Elsevier B.V. All rights reserved.