Synthesis of water-soluble Fe-decorated multi-walled carbon nanotubes: A study on thermo-physical properties of ferromagnetic nanofluid

• A direct coupling between carboxylic acids on MWNT surface with amines has been performed.
• Fe ions covalently decorated on the MWCNT surface to impose magnetic property.
• Ferromagnetic MWNT-based water nanofluids were synthesized at different concentrations.
• Thermo-physical and rheological properties of ferromagnetic MWNT-based water nanofluids were investigated.
• A comparison ferromagnetic, covalent and non-covalent nanofluids was performed.

A direct coupling of carboxylic acids-treated multi-walled carbon nanotubes (MWNT) surface with amines is introduced to functionalize MWNT with aspartic acids (Asp). Amide formation has been carried out in the presence of simple zirconium catalysts at 5 mol% loading and then surface functionality groups and morphology of Asp-treated MWNT were studied by infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, and transmission electron microscopy. To impose magnetic property to the surface of MWNT, Fe ions covalently attached through the carboxylic acids group of Asp. This promising method of using a combination of functional iron and Asp based on MWNT was introduced for increasing stability and thermo-physical properties of MWNT-based water nanofluids. MWNT was stably dispersed in aqueous media and in the second phase of study, the ferromagnetic MWNT-based water nanofluids were prepared at different concentrations to estimate the thermo-physical and rheological properties. Density, viscosity, electrical and thermal conductivity behavior of MWNT-based water nanofluids in the presence of ferromagnetic, (Fe), covalent (Asp) and non-covalent (Gum Arabic) functional groups were investigated and promising results obtained. It was found that the rheological and thermo-physical properties of ferromagnetic samples were significantly enhanced compared to the covalent nanofluids and certainly pure water.

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