Comparison of Cd(II) adsorption properties onto cellulose, hemicellulose and lignin extracted from rice bran

Rice bran, an underutilized by-product obtained from outer rice layers, has received wide interest due to its abundance, eco-friendliness, and low cost. In this research, cellulose, hemicellulose and lignin as the main components of rice bran were fractionated, and their Cd(II) adsorption capacity, behavior and mechanism were further studied. The adsorption capacity of cellulose for Cd(II) was 5.79 mg/g within the equilibrium time of 10 min, which was 1.8 and 3.6 times those of hemicellulose and lignin, respectively. The Cd(II) adsorption onto cellulose exhibited monolayer surface behavior, whilst the heterogeneous adsorption behavior was observed for hemicellulose and lignin. These differences were related to the discrepancy of morphology and chemical composition in three polymers. The multi-hole sticks morphology of cellulose and porous blocky structure of hemicellulose were observed, while lignin showed compact and agglomerated blocky structure. Cellulose had numerous available adsorption sites including the oxygen-containing functional groups, which bonded with Cd(II) driven by chemical interaction. In conclusion, it highlights that cellulose from rice bran has the great potential of being applied as adsorbent for the Cd(II) removal.