Development of prediction models for adsorption properties of chitin and chitosan for micropollutants

Chitin and its derivative, chitosan, are common bioresources and possess well-developed functional groups; therefore, they have been used as adsorbents to remove micropollutants during wastewater treatment. To efficiently use them in the removal process, it is necessary to understand and predict the adsorption properties of chitin and chitosan for micropollutants because there are numerous types of micropollutants. Therefore, we measured the adsorption affinities of raw types of chitin and chitosan for approximately 30 types of micropollutants in neutral or ionic forms. Then, the measured properties were predicted using experimentally determined and theoretically calculated linear free energy relationship (LFER) descriptors. The experimental results revealed that the adsorption affinities depended on the chemical structures of the micropollutants, and of chitin and chitosan possess similar adsorption properties. Next, the relationships between the adsorption affinities of the adsorbents and quantitative structural properties of the adsorbates were analyzed using experimental and in silico calculated LFER descriptors. The results indicated that the experimental descriptors could predict the properties of chitin and chitosan within R2 of 0.832 and 0.827, respectively; moreover, the calculated descriptors could predict the properties of chitin and chitosan within R2 of 0.812 and 0.867, respectively. In addition, since chitin obtained from the red crab contains some impurities, the effect of impurities on adsorption after washing it with methanol and water was investigated. The results showed that the effect of impurities on adsorption was negligible. Using the developed models, based on the measured descriptors, it was identified that the main driving forces of chitin and chitosan were H-bonding donor moment and ionic electrostatic attraction.