Ultrasonic-assisted fabrication of montmorillonite-lignin hybrid hydrogel: Highly efficient swelling behaviors and super-sorbent for dye removal from wastewater

Abstract

A novel hybrid hydrogel was synthesized from grafting of acrylamide and N-isopropyl acrylamide onto lignin by incorporation of montmorillonite under ultrasonic irradiation (lignin-g-p(AM-co-NIPAM)/MMT). The hydrogel was characterized by electron microscopy-energy dispersion spectrometer (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and mechanical strength analysis. The results showed that the hybrid hydrogel displayed thinner pore walls, better thermal stability and mechanical strength after hybriding with montmorillonite. The hydrogel was employed for the removal of methylene blue from the aqueous solution, and it exhibited good swelling–deswelling property. The initial swelling kinetic was Fickian type diffusion and the whole swelling process was good fit for Schott's pseudo-second order model. The adsorption process was found to be highly pH and temperature dependent and followed the pseudo-second-order rate model. The equilibrium adsorption data were found to fit well to the Langmuir and Freundlich models, with an optimum adsorption value of 9646.92mgg−1. The hydrogel presented excellent regeneration capacity and was successfully used for five cycles of adsorption–desorption. In summary, the hydrogel has shown its potential as an environment friendly and efficient adsorbent for the adsorption of dyes from wastewater.