Model sta 409 pc

The contents of CNT and Fe were evaluated by thermo-gravimetric analysis (TGA, Netzsch Model STA 409 PC, heating rate of 10 °C min⁻¹ and a constant air flow of 20 mL min⁻¹). The structural features of CNTs and CNCs were characterized by high resolution transmission electron microscopy (HR-TEM, JEOL-2010F, accelerating voltage of 200 kV), and Raman spectroscopy (Raman, Bruker Senterra R200-L, excitation wavelength of 532 nm). The functional groups were determined by X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi). The specific surface area of the sample was calculated using the Brunauer–Emmett–Teller method (BET, TriStar 3000 V6.05 A).

The samples were dispersed in ethanol and poured onto grids for observation. The morphologies of the samples were investigated using transmission electron microscopy (TEM) with an acceleration voltage of 200 kV (JEOL 2100, Japan). N₂ adsorption–desorption isotherms were recorded with an ASAP 2400 physisorption instrument made by Micromeritics Corporation (UNITED STATES). Prior to measurement, all samples were dried under vacuum at 333 K for 24 h. Pore size distribution was calculated by the BJH method. Fourier transform infrared spectra (FT-IR) of the samples were collected by the KBr pellet technique on a Nicolet 370 infrared spectrophotometer in the range 500–4000 cm⁻¹. Thermo gravimetric analysis (TGA) curves were recorded in air flow on a Netzsch Model STA 409PC instrument with a heating rate of 20 K min⁻¹ from room temperature to 973 K using α-Al₂O₃ as the standard material. The acidity strength of catalyst was determined by Hammett acidity function method combined with UV-visible spectroscopy (Shanghai Tianmei Co. Ltd, China). 4-Nitroaniline was chosen as the basic indicator and CCl₄ was chosen as the solvent.