Raman spectroscope

Morphological analysis was performed using SEM (S-4800, Hitachi, Tokyo, Japan). The Raman and PL measurement were performed using a confocal Raman spectroscope (inVia, Renishaw, WUE, UK) with a 488-nm laser. The bonding characteristic was measured using XPS (Sigma Probe, Thermo VG Scientific, MA, USA).

The pore volume, surface area, and pore diameter of the MWCNTs were evaluated using an ASAP 2020 adsorption analyzer (Micromeritics, Norcross, GA, USA) at −196 °C. An X-ray diffractometer (X’pert Pro System, PANalytical, Malvern, UK) with Cu Kα radiation was employed to observe the crystalline phase of the MWCNTs. A field-emission scanning electron microscope (JEOL JSM-6700F, Akishima, Tokyo, Japan) and a transmission electron microscope (JEOL JEM-1200CX II, Akishima, Tokyo, Japan) were used to examine their morphological features. A Fourier transmission infrared spectroscope (FTIR-8300, Shimadzu, Nakagyo-ku, Kyoto, Japan) was employed to examine the functional groups of the MWCNTs. Graphitization was assessed using a confocal Raman spectroscope (Renishaw, Gloucestershire, UK) with 632 nm He–Ne laser excitation. The stability of the MWCNTs before and after modification was examined using a thermogravimetric analyzer (Mettler Toledo, OH, USA, model TGA/SDTA851e). The surface elements on the MWCNTs were analyzed using an X-ray photoelectron spectroscope (Esca Lab 250Xi, Thermo Scientific, Waltham, MA, USA). The C1s peak at 284.60 eV was employed to calibrate the binding energy. The amounts of metallic impurities in the MWCNTs were determined using an inductively coupled plasma–mass spectrometer (ICP-MS) (Konton Plasmakon, Eching, Germany, model S-35).