Hybrid sp2/sp3 nanodiamonds as heterogeneous metal-free ozonation catalysts in water

Abstract

There is a growing interest from academia and industry in metal-free heterogeneous catalysts as an alternative to current non-sustainable transition metal catalysts. Herein we report a comprehensive study on the development of hybrid nanodiamonds with a diamond core and defective graphitic shells with different sp2/sp3 ratios as metal-free ozonation catalysts. A volcano-type trend relationship between the catalytic activities with respect to the sp2/sp3 ratio was found. The most active nanodiamond pyrolysed at 1100 °C for 1 h exhibits a unique sp2/sp3 configuration together with an optimum amount of oxygen and nitrogen functional groups. O3 is catalytically transformed into hydroperoxyl radicals and 1O2 species. The catalytic activity of the spent hybrid nanodiamonds can be recovered by a simple annealing in an inert atmosphere that reconstitutes the defective sp2/sp3 hybrid nanodiamond. This study exemplifies the possibility of tailoring the physico-chemical properties of commercial nanodiamonds for the development of active metal-free ozonation catalysts.