Multiwalled carbon nanotubes@pectin/κ-carrageenan-based nanocomposite biohydrogel prepared by gamma irradiation for efficient methylene blue dye sequestration

Abstract

This study addresses the critical issue of removing toxic dyes from industrial wastewater to protect the environment and human health. To address this challenge, a bio-based composite hydrogel was synthesized using gamma irradiation, 20 kGy, incorporating multiwalled carbon nanotubes@pectin/κ-carrageenan/polyacrylic acid (MWCNTs PC/KC/PAAc) for removing methylene blue (MB) dye from aqueous solutions. The prepared composites underwent characterization through Fourier-transform infrared spectroscopy, x-ray diffraction, and thermogravimetric analyses. Brunauer–Emmett–Teller analysis demonstrated a significant increase in surface area upon the addition of MWCNTs. Specifically, the surface area increased from 342.5 m2 g−1 for PC/KC/PAAc to 689.5 m2 g−1 when 0.175 wt% of MWCNTs were added. Also, scanning electron microscopy and atomic force microscopy were utilized to examine the surface topography of PC/KC/PAAc and MWCNTs@PC/KC/PAAc. The results reveal that at 0.175 wt% of MWCNTs, there was a more uniform surface topography with well-distributed MWCNTs within the matrix. In the adsorption study of MB dye, it was found that the highest MB removal efficiency was achieved at pH 11, with values of 68.21% and 96% for PC/KC/PAAc and MWCNTs@PC/KC/PAAc, respectively. Furthermore, upon studying the effect of MWCNTs (%), the results showed that the removal (%) of PC/KC/PAAc was 68.21 ± 1.02%, and this percentage increased rapidly with the addition of MWCNTs, reaching a maximum of 96 ± 0.85% when 0.175 (wt%) of MWCNTs was added. Isotherm and kinetic modeling demonstrated that MB adsorption follows the Freundlich isotherm for PC/KC/PAAc and the Redlich–Peterson isotherm for MWCNTs@PC/KC/PAAc, both following a pseudo-second-order kinetics model. In addition, from AFM data, after MB removal, the height increased significantly from 322 nm for PC/KC/PAAc to 810 nm for MWCNTs@PC/KC/PAAc (0.175 wt%), indicating a substantially higher adsorption of MB by MWCNTs@PC/KC/PAAc.