Carboxylmethyl cellulose produced from wood sawdust for improving properties of sodium alginate hydrogel in dye adsorption

Cellulose-based materials have shown immense potential for diverse applications because of its attractive properties such as excellent mechanical properties, rich hydroxyl groups for modification, and natural properties with recyclability, nontoxicity, biocompatibility, biodegradability, and environmental friendliness. This study aimed to optimize cellulose extraction from wood sawdust using deep eutectic solution (DES) treatments for the preparation of carboxymethyl cellulose (CMC) and to evaluate the application of CMC in sodium alginate (SA) microgel for dye adsorption. Cellulose extractions were optimized in reduced chemical treatment conditions with high cellulose contents (88.19 %), and selectively increased lignin removal (87.23 %). The analyses by SEM, XRD, and FT-IR revealed that carboxymethylation was successfully transformed into CMC to facilitate the significantly improved water solubility and swelling ability. The TGA curve of CMC showed a higher thermal stability (residual weight of 52 % at 300 °C) compared to unmodified cellulose due to the decomposition of the amorphous regions during the carboxymethylation. The combined biodegradable SA and water-soluble CMC composite microgels were successfully fabricated via cross-linking with calcium chloride using a microfluidic approach. The incorporation of CMC into SA microgel had enhanced mechanical properties, adsorption capacities of 160.87 and 141.48 mg/g, and adsorption–desorption efficiencies of 96.84 % and 95.41 % for crystal violet and trypan blue respectively after five cycles. The adsorption processes of both dyes can be described by Sips adsorption isotherms and pseudo-second-order kinetic models, verifying the chemical interaction-assisted process. This simple green CMC/SA adsorbent has the potential to significantly enhance the adsorption capacity of dye removal from wastewater.