On The Action of Ozone on Single-Wall Carbon Nanohorns (SWCNH)

Abstract

Single-Wall Carbon Nanohorns (SWCNH) were ozonized with two different methodologies in batch and in continuous. The oxidation degree of SWCNH was determined by the FT-IR spectroscopy which is also able to detect the presence of secondary ozonide groups. The thermal treatment of the ozonized SWCNH at 350°C under N₂ caused the decomposition of the secondary ozonide groups as evidenced by FT-IR spectroscopy. Furthermore ozonized SWCNH were studied by differential scanning calorimetry (DSC). The typical exothermal decomposition of the ozonides was observed with DSC but at higher temperatures than usual and with an activation energy of 120 kJ/mol. Based on the decomposition heat released, about 4–5 secondary ozonide groups per each SWCNH were estimated. Fully ozonized SWCNH are easily and completely dispersible in distilled water giving a brown solution and lowering the pH to 5.9. Electronic absorption spectra of these solutions are reported. The water dispersions of ozonized SWCNH are able to reduce Ag⁺ ions to silver nanoparticles but the resulting colloidal solution is unstable and flocculate.

Keywords:

• SWCNH
• ozonization
• secondary ozonides
• thermal decomposition
• FT-IR
• DSC
• colloidal solution
• silver ions reduction