Preparation of cellulose-based composite hydrogels for the removal of methylene blue

Abstract

The discharge of dyes, including methylene blue (MB), contributes to environmental pollution. Adsorption is one of the most widely used techniques for removing colorants from water, with hydrogels being the materials that have attracted the most attention due to their excellent adsorption capacity. In this work, hydrogels composed of cellulose/pectin/starch were synthesized to remove MB dissolved in water. For the characterization of the hydrogel, Fourier-Transform Infrared, Thermogravimetry/Differential Thermal Analysis, XRD, and Scanning Electron Microscopy techniques were applied. At pH 9, the maximum swelling capacity (326.1%) of the hydrogel and the maximum MB removal percentage (37.05%) were obtained. The Weber-Morris diffusion kinetic model indicated that other adsorption mechanisms exist in addition to the diffusion process of MB through the hydrogel pores. Temkin's model better described the adsorption process, therefore an interaction between the adsorbate and the adsorbent surface is assumed, while the MB adsorption kinetics at pH 5 followed a pseudo-first-order model; and at pH 7 and pH 9, they followed a pseudo-second-order model.