Waste cotton sheets (WCS) are promising cellulose sources due to their high content of cellulose and large amount of disposal every year, which could be recycled and employed as low-cost structural materials. The present work aims at investigating the efficacy of hydrogel adsorbents prepared from regenerated WCS as the carriers of activated carbon (AC) for treating the dye-contaminated water. Activated WCS was directly dissolved in lithium chloride/ N , N -dimethylacetamide (LiCl/DMAc) solvent and then regenerated into cellulose hydrogels, which were employed as three-dimensional biodegradable matrices for loading an extremely high content of AC (up to 5000%). The morphology and properties of resultant adsorbents were studied in detail. The results showed that different washing methods and contents of AC and cellulose had obvious effects on water contents, mechanical properties, and adsorption capacities of AC/WCS hydrogels. Especially, the hydrogels containing high AC content washed by gradient ethanol solvent exhibited outstanding compressive strengths of up to 3.0 MPa at 60% strain, while the adsorption capacity of 5000%AC/0.3CS toward a model dye methylene blue (MB, initial concentration of 200 mg/L) reached 174.71 mg/g at pH 6.9 and 35 °C. This was comparable to the adsorption capacity of original AC powders, while no AC powders were released from hydrogels to water. The adsorption of MB followed the Dubinin–Astakhov model and pseudo-first-order mechanism. Thermodynamic studies showed the spontaneous and endothermic nature of the overall physical adsorption process. Therefore, this work demonstrates the feasibility to recycle WCS into biodegradable carriers of functional compounds, and the AC/regenerated cellulose hydrogels have a high potential as a promising adsorbent with low-cost and convenient separation for dye removal from wastewater.

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, CH 3 -SAMs, NH 2 -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 -NH 2 and -CH 3 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.