Simultaneous removal of cationic and anionic dyes from a complex mixture using a novel composite hydrogel based on pine needles, chitosan, and gelatin.

Following a holistic sustainable approach, we fabricated a biocomposite from pine needles (PNs), with two biopolymers, chitosan (CS) and gelatin (GEL). The biocomposite was used as an effective, regenerable, and reusable adsorbent for the removal of cationic and anionic dyes from their mixture. The cationic dyes chosen were malachite green, methylene blue, and crystal violet; and the anionic dyes were methyl orange and Congo red. The PNs were etherified followed by composite formation with glutaraldehyde-mediated crosslinked network of CS/GEL. Synthesis of composite, i.e. etherified PNs/CS/GEL was confirmed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray (EDX) analysis, and surface charge analysis. The adsorption kinetics studied by different kinetic models, such as pseudo-first-order, pseudo-second-order, and Elovich, followed the Elovich model. Among the three adsorption isotherms (Langmuir, Freundlich, and Temkin) studied, the adsorption followed Langmuir isotherm with maximum adsorption capacity of 307.871 mgg-1 for the mixture of dyes. The reusability studies affirmed the ease of regeneration of the hydrogel for use in multiple cycles. The reported adsorbent is green, low-cost, eco-friendly, and recyclable with a high potential to remove cationic and anionic dyes from their mixture and the real dye-contaminated wastewater.