Study of Marine Sponges Graphitization during Heat Treatment up to 1200 °C

The results of studies of marine sponge carbonization processes during thermal treatment in an argon atmosphere in the temperature range from room temperature to 1200 °C are presented. The spatial structure, atomic composition of native and carbonized sponges, and their changes during pyrolysis were characterized using a set of methods that are informative at the macro- (thermogravimetric analysis, derivative thermogravimetric analysis, differential scanning calorimetry), micro- (Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy), and nanoscales (X-ray absorption and photoelectron spectroscopy using synchrotron radiation and a sample charge compensation system). Preservation of the 3D architecture at the macro- and microlevels and graphitization of the interfibril medium with the formation of turbostratic graphite at the nanolevel were demonstrated. It was shown that the atomic contents of nitrogen, carbon, and oxygen in the spongin were ~2–3 at.%, ~5 at.%, and ~4 at.%, respectively. The matter concentrated in the space between the spongin fibrils included ~70 at.% carbon and ~11 at.% oxygen, with a large proportion of carbon (~63 at.%) involved in the formation of aromatic and C–C bonds and the remainder in carbon monoxide compounds. After the decomposition of spongin at 400 °C, this substance transformed into turbostratic graphite, preserving the 3D architecture of the original marine sponge as the temperature rose.