Citric Acid-crosslinked Cellulosic Hydrogel from Sugarcane Bagasse: Preparation, Characterization, and Adsorption Study

In this work, citric acid (CIT) is proposed as a harmless alternative to epichlorohydrin (ECH) for crosslinking in the synthesis of cellulose hydrogels. Sugarcane bagasse was utilized as a source of cellulose fibers. Cellulose fibers were disintegrated using the solvent-dissolution method before forming a gel-like solution. Subsequently, CIT was added to initiate crosslinking, and the behavior was evaluated by adding various amounts of citric acid (0, 20, 30, and 40 wt%). Cellulose hydrogel with a good mechanical strength (10 mm penetration depth) was obtained from crosslinking using 40 wt% of CIT (HCIT-4), which is comparable to ECH-cross-linked hydrogel (HECH) that has a penetration depth of 8 mm. A proper amount of CIT molecules allows the crosslinking of the cellulose fibers into the hydrogel. The FT-IR analysis reveals a C-O-C band blue-shifting for HCIT-4 compared to HECH, with a gap difference of 82 cm-1. The crystallinity from XRD patterns of HCIT-4 is comparable to that of HECH, which confirms that CIT can be used as a substitute for ECH. The adsorption ability was evaluated against methylene blue dye, the isotherm and kinetic adsorption models for the adsorption system were determined. Freundlich and pseudo-second-order models correlate well to isotherm and kinetics data, suggests that the adsorbent possesses heterogeneous surface sites which adsorption controlled by chemisorption. The prepared HCIT-4 was able to remove 24.88 mg methylene blue/g of the hydrogel at 70 °C, meanwhile HECH only able to remove 12.01 mg/g. The adsorption capacity was increased when adsorption temperature increased, suggesting endothermic behavior.