Diamond nanoparticles (DNPs), also known as nanodiamonds, have attracted significant interest in recent years due to a number of potential applications. Their particular usage requires proper surface engineering. In this work, DNPs with a nominal diameter of 5 nm were treated using underwater pulsed streamer corona discharge. A reactor with a needle-to-plate electrode system was employed. The electrolytic conductivity of aqueous DNPs suspensions (0.37 g l(-1)) was adjusted by NaCl to 100 and 500 mu S cm(-1). The discharge-treated particles predominantly formed several mm long filaments consisting of agglomerates with submicron diameter, independent of the solution conductivity and the treatment time. The treatment of DNPs decreased the sp(2)-bonded carbon atoms, as evaluated by XPS for more conductive solution. For both solutions, oxidation of the DNP surface was observed. FTIR measurements showed evolution of new bands at 800-950 cm(-1) and 1261 cm(-1), which were attributed to the formation of epoxides via the attack of HO2 center dot radicals on surface C=C double bonds.
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