Efficient removal of toxic dyes malachite green and fuchsin acid from aqueous solutions using Pullulan/CMC hydrogel

Abstract

Interest in removing dyes from industrial wastewater via surface adsorption has grown significantly in recent years. Hydrogels are promising adsorbents for dye removal due to their simple synthesis and convenient application. Herein, we reported PA/CMC hydrogel synthesized from Pullulan (PA) and Carboxymethyl cellulose (CMC) with epichlorohydrin (ECH) as the crosslinker via chemical crosslinking. The characterization of the PA/CMC hydrogels involves employing various techniques such as Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX analysis). PA/CMC hydrogel removes toxic dyes such as Malachite green (MG) and Fuchsin acid (FA) dyes from water. PA/CMC hydrogel exhibits maximum adsorption capacities (qmax) for MG and FA of 1816.99 and 1937.00 mg/g, respectively. The maximum removal efficiencies of MG and FA were found to be 96.88 % and 94.25 %, respectively, at 30 °C and pH 9, with an adsorbent amount of 0.30 gm and dye content of 50 mg/L, with MG necessitating a contact time of 120 min and FA requiring 160 min. The adsorption mechanism of the PA/CMC hydrogels for MG and FA dyes is plausible due to electrostatic attraction, hydrogen bonding, and π-π interactions. These results indicated that the adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherm conformed to the Langmuir model. Even after undergoing five cycles, the PA/CMC-gel maintains strong removal capabilities, highlighting its remarkable reusability and structural integrity.