Thermodynamics and kinetic analysis of carbon nanofibers as nanozymes.

Abstract

Purpose: Evaluation of structural features, thermodynamics and kinetic properties of carbon nanofibers (CNFs) as artificial nanoscale enzymes (nanozyme).

Methods: Synthesis of CNFs was done using chemical vapor deposition, and transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and energy-dispersive x-ray spectroscopy (EDX) were used to provide information on the morphology, elemental monitoring and impurity assay of the CNFs. The thermal features of the CNFs were evaluated using differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) derivative and TGA. The calculated thermo-physical parameters were melting temperature (Tm), weight loss maximum temperature (T_max ) and enthalpy of fusion (ΔH_fusion ). Catalytic activity was assayed by a 4-aminoantypyrine (4-AAP)-H₂O₂ coupled colorimetric system by UV-visible spectroscopy.

Results: FE-SEM and TEM analysis demonstrated parallel graphitic layers and uniformity of atomic orientation and morphology. The EDX spectra approved carbon element as major signal and presence of partial Ti as impurities of CNFs during CVD process. The DTA thermogram showed the endothermic process had a maximum temperature of 82.27°C at -15.48 mV and that thermal decomposition occurred at about 200°C. The TGA-differential gravimetric analysis thermogram showed that T_max was 700°C. The DSC heat flow curve showed a melting temperature (Tm) of 254.52°C, ΔH_fusion of 3.84 J^.g^-1, area under the curve of 58.58 mJ and T_e (onset) and T_f (end set) temperatures of 246.60°C and 285.67°C, respectively. The peroxidase activity of the CNFs obeyed the Michaelis-Menten equation with a double-reciprocal curve and the calculated K_m, K_cat and V_max kinetic parameters.

Conclusion: CNFs as peroxidase nanozymes are intrinsically strong and stable nanocatalysts under difficult thermal conditions. The peroxidase activity was demonstrated, making these CNFs candidates for analytical tools under extreme conditions.