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.
