Electrospun Cellulose Acetate/Chitosan Fibers for Humic Acid Removal: Construction Guided by Intermolecular Interaction Study

Humic substance is a ubiquitous class of natural organic matter in soil and aquatic ecosystems, which severely affects the terrestrial and aquatic environments and water-based engineering systems. In our previous work, the adsorption of humic acid (HA) on self-assembled monolayers with different functional groups (OH-SAMs, CH3-SAMs, NH2-SAMs, and COOH-SAM) has been reported, where amino groups exhibited a superior adhesion energy toward HA followed by methyl groups and hydroxyl groups. Therefore, guided by the intermolecular interaction study, chitosan (CS) and cellulose acetate (CA) containing -NH2 and -CH3 groups derived from waste materials were selected to fabricate electrospun fibrous adsorbents for the removal of HA from aqueous solutions in this work. The effect of CA/CS ratios on the structure and adsorption performance of electrospun fibers was investigated in detail. The results revealed that all the samples (CA/CS = 3:1, 1:1, 1:3) showed high adsorption capacities (>152 mg/g) toward HA at pH 4. This was because of the abundant functional groups on the surface of fibers. Especially, the CA/CS 1:1 sample had a uniform fibrous morphology with an average diameter of 335 ± 242 nm, which led to the highest tensile strength of 2.97 ± 0.59 MPa and adsorption capacity of 184.72 mg/g. The adsorption of HA onto CA/CS fibers was nonspontaneous and exothermic in nature. It followed the pseudo-first-order kinetic model and was primarily driven by electrostatic interaction. The adsorption isotherm was better fitted by the Langmuir model. Therefore, this work demonstrates the feasibility to use intermolecular interaction mechanisms to guide the design of functional materials. Moreover, it provides a biodegradable efficient adsorbent that is promising for the applications in water treatment.