Carbon microtubes derived from self-rolled chitosan acetate films and graphitized by joule heating

Herein, a fast and efficient approach is proposed to obtain carbon microtubes with graphitic structure. The precursor tubes are formed via self-rolling of chitosan acetate (CA) biopolymer films in water. The self-rolling capacity is imparted to the CA films by heating them at 150 °C on a hot plate for several minutes in the ambient atmosphere. The resulting differential swelling of the top and bottom layers of the films in water generates the bending moment. The amorphous carbon microtubes are produced in Ar atmosphere via thermal treatment of chitosan acetate microtubes at 900 °C. Carbon/oxygen ratio increases from 1.2 for the pristine chitosan tube to 5.3 after the pyrolysis process. Finite electrical conductivity of the so-prepared tubes (σ ≈ 1 · 10³ S · m⁻¹) allows their consecutive treatment by joule heating. The current-induced graphitization of the tubes at 2500 °C is confirmed by TEM, Raman spectroscopy and XRD techniques. Electrical conductivity of tubes raised in course of the treatment to (σ ≈ 1.8 · 10⁴ S · m⁻¹). In joule-heated tubes, the carbon/oxygen ratio increases to 9.4.