Organic functionalization of thermally reduced graphene oxide nanoplatelets by adsorption: structural and morphological characterization

Abstract

Adsorption of chlorinated poly(ethylene-co-vinyl acetate)-g-maleic anhydride copolymer and in situ-generated polyaniline (PANI) on thermally reduced graphene oxide (TRGO) platelets was studied in the current study. The adsorption was characterized structurally and morphologically through thermogravimetric analysis, differential scanning calorimetry (DSC), elemental analysis, infra-red and Raman spectroscopy, X-ray diffraction and microscopy. The amount of copolymer adsorption reached a plateau of 0.22 g per g of TRGO, when the initial copolymer to TRGO weight ratio of 1 was used. In the case of PANI modification, much higher extent of adsorption of 0.92 g/g of TRGO (without reaching plateau) was observed due to in situ polymer synthesis and the absence of any steric hindrance to the chains. Shift in the DSC melting transition temperatures of copolymer also indicated that some change in the polymer chain morphology took place after immobilization of polymer on TRGO. PANI modification led to significant reduction in peak melting point from 175C to 140 °C owing to the hindrance in polymer crystallization. The basal plane spacing in the TRGO platelets increased the copolymer adsorption as the 0 0 1 basal plane diffraction shifted from 27° 2Θ for pristine TRGO to 22.5° 2Θ for modified TRGO. For the PANI modified TRGO, no diffraction signal corresponding to TRGO was observed due to extensive adsorption of polymer on the surface. A much thicker polymer phase wrapping the TRGO platelets was observed for PANI modified TRGO. This was also observed through EFTEM and EDX, where the presence of Cl and N (along with other atoms) indicated layer of copolymer and PANI, respectively on the surface of the platelets. EELS analysis also confirmed the semi-crystalline nature of the modified TRGO resulting from the adsorption of semi-crystalline polymers on TRGO. The adsorption approaches used in the study demonstrate successful generation of the functional nanomaterials with tunable extent of surface coverage and potential of employing diverse surface modifications.