Magnetic characterization study of gadolinium chelate modified multi-walled carbon nanotubes, graphene oxide and reduced graphene oxide: a comparative study

Abstract

The carbon nanotubes are characterized by interesting physical properties, which resulting from the strong carbon – carbon covalent sp2 bond. Their properties derived from the 1Dstructure. The surface modification of carbon nanotubes can stretched their application in many sectors. However, the functionalization of carbon nanotubes involving oxidative reflux is known, and popularly used for the introduction of chemical functionality along the surface and ends of carbon nanotubes. The volatile method invariably results in an unpredictable degree of chemical functionalization of carbon nanotube surfaces, variable lattice order, and potentially introduces chemically different nanoscale environments. This study focuses on a predictable approach towards the functionalization of multi-walled carbon nanotubes (MWCNTs); aimed at manipulating the degree and chemical nature of functionalization by controlling oxidative reaction temperatures, with a view to incorporate a magnetic complex on the nanotube surface via ternary complex formation. Our findings indicate functionalization occurs at temperatures as low as 55°C. However, the chemical nature of the attached functional groups varies with increasing temperature – understanding the latter is essential for the attachment of metal complexes to carbon nanotubes. Investigation of the functionalized MWCNTs using spectroscopic techniques elucidates the prevailing chemical nature of the nanotube surface that suggests carboxylate functionality, is replaced at higher temperatures, by the formation of hydroxyl moieties. This observation is substantiated through deconvolution of D and G phonon modes of recorded Raman spectra, corroborated by Zeta potential studies and analysis of acid-base titration data. Attachment of the Gadolinium complex of dietheylenetriaminepentaaccetic acid, [GdDTPAH2], to a functionalized-MWCNT is confirmed by chemical analysis using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES), which shows the percentage of gadolinium varying in the range of 5% to 6% in the samples. The acquisition of magnetic data reveals the antiferromagnetic interaction and possibly an anisotropic exchange bias. The magnetic properties show a distinct temperature dependence, this includes a change in slope of the saturation moment, which increases to a point of non-saturation as the temperature decreases. This is an indication that there is a competing magnetic phase different to the ferromagnetism. It is also revealed that high surface modification of multi-walled carbon nanotubes using Gd-DTPA, increases excitation level of gadolinium electron in the material. In addition, Carbonyl group have been introduced onto graphene single layer surface via Modified Hummers method. Sodium nitrate and potassium permanganate used as oxidant reactants. L-ascorbic acid used to produce reduced graphene oxide. Lower concentration of carboxylic group on reduced graphene oxide influenced the magnetic and electronic properties of the sample. Magnetic environment affect electronic transport properties of the reduced and graphene oxide. The magnetic data indicates paramagnetic behavior with impurities showing slight slope in the range of zero field. Consequently, it is also displayed the surface modification of graphene oxide and reduced graphene oxide using magnetic molecule Gd-DTPA accompanied with increases excitation of gadolinium electron in their orbital. Those complexes can be used to increase or decrease the relaxation times of carbon-13 nuclei in NMR spectrometry