Comparison of Microwave-assisted Synthesis and Steglich Thioesterification for the Modification of Nanotubes

Abstract

Organo-modified carbon nanotubes have recently gained the interest of many research groups. The potential for applying a new generation of organo-modified carbon nanotubes in many technological fields reveals the importance of covalent modifications on nanotubes. In this study, using the microwave synthesis method, multi-walled carbon nanotube (MWCNT) thiophenol derivatives were obtained with a thioesterification reaction. For this purpose, MWCNT-COOH was obtained from MWCNT by oxidation, and MWCNT-COCl was synthesized from MWCNT-COOH. The MWCNT-CO-S-(ortho/meta/para-methyl/methoxy-phenyl) (MA1-MA6) compounds were synthesized through both microwave synthesis methods starting with MWCNT-COCl and Steglich ester reaction of MWCNT-COOH. Products were characterized using Fourier Transform-Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), Thermogravimetric Analysis (TGA), and Transmission Electron Spectroscopy (TEM) methods. Furthermore, step numbers, reaction times, and temperatures of obtained molecules, MA1-MA6, were compared. Steglich esterification was found to be the most effective technique for creating these compounds. The photoluminescent characteristics of MWCNT, MWCNT-COOH, and MA1-MA6 compounds were examined. The intensity of the photoluminescence (PL) was found to vary with the location of the functional group. It was detected that the MA2 compound had the highest photoluminescence intensity (6.9x102 a.u.), while the MA1 compound had the second-highest photoluminescence intensity (6.9x102 a.u.). MA1 and MA2 were radiated at low wavelengths of 475-490 nm with high PL values. Possible transitions were n ->pi* transitions, with high PL values obtained because of the oxygen atom in the methoxy group. It is expected that these materials will find use in imaging devices operating at high temperatures, particularly because structures containing methoxy groups exhibit favourable photoluminescence properties.