Facile and Green Synthesis of Carboxylated Cellulose Nanocrystals as Efficient Adsorbents in Wastewater Treatments

A simple and eco-friendly Fe²⁺/H₂O₂ oxidation of microcrystalline celluloses (MCCs) to prepare cellulose nanocrystals (CNCs) with high carboxylation content is proposed. The effects of reaction times on the morphology, microstructure, and chemical and thermal properties of isolated carboxylated CNCs were investigated. The oxidative decomposition of Fe²⁺/H₂O₂ solution of MCC yielded CNCs with a size of 92–140 nm in length and 19–23 nm in width. The CNCs extracted at 6 h possessed the highest carboxyl content (2.2 mmol/g) with a zeta potential of −41 mV and a thermal decomposition temperature of greater than 325 °C. These CNCs are efficient adsorbents for dyes (methylene blue) and metal ions (copper ion) found in wastewater, with removal rates of up to 95.6 and 82.3%, respectively.