Production of cellulose aerogels from coir fibers via an alkali–urea method for sorption applications

Biodegradable cellulose aerogels have been successfully prepared from coir fibers using a sulfur-free method and NaOH–urea system. Sulfur was avoided during pretreatment because it is environmentally harmful. Interestingly, these pretreatments had a strong effect on the physical properties of the aerogels produced. Good physical properties of the cellulose aerogels were obtained when the Kappa number, i.e., the lignin content, in the pulp was lower than 14.8. NaOH–urea played an important role in transforming cellulose I to cellulose II and crosslinked cellulose to form an aerogel structure. The aerogel had a macroporous structure, ultralight density, high porosity, good durability, and thermal stability. The aerogel was capable of absorbing 22 and 18 times its dry weight in water and oil, respectively. The material also had a high capacity for methylene blue dye adsorption of up to 62 g/g, which was one hundred times higher than that of adsorbents synthesized from the other natural matters. Therefore, the prepared aerogels have potential for various sorption applications. Graphic abstract