Mechanistic impact of sodium nitrate on the characteristics of MWCNTS oxidation and potential application on methylene blue adsorption from wastewater

Abstract

Effect of oxidizing agents on plastic waste derived multi-walled carbon nanotubes (MWCNTs) was investigated in this study. It was investigated whether a single oxidizing agent is sufficient for the desired oxidation or if the use of multiple agents is required. Typically, the modified Hummers method employs several oxidizing agents such as H₂SO₄, NaNO₃, H₂O₂, and KMnO₄, contributing to increased production costs and posing challenges for scalability. The investigation focused on the presence or absence of NaNO₃ while altering the ratio of KMnO₄ and reaction time. The synthesized materials were analysed using UV–VIS spectrophotometry and FTIR. The shifted peaks of the XRD pattern were analysed for the surface modification of the MWCNTOs surfaces with the degree of oxidation. Surface morphology of the samples was obtained using FESEM and found comparable changes with the degree of oxidation. The percentage of Methylene Blue (MB) dye removal was examined using oxidized samples, and the impact of oxidation on the efficacy of dye adsorption was investigated. The results showed that maximum 79% removal occurred for lowest oxidised MWCNTs compared to others as maximum oxidation leads to agglomeration of particles. The Freundlich isotherm and pseudo 1st order reaction order models exhibited optimal compatibility with pristine MWCNTs. In contrast, Langmuir and pseudo 2nd order kinetics models demonstrated superior fitment with oxidized MWCNTs. This suggests a transition in the adsorption phenomenon from physisorption to chemisorption.