Polyvinyl Alcohol–Citric Acid: A New Material for Green and Efficient Removal of Cationic Dye Wastewater

The citric acid (CA) cross-linked polyvinyl alcohol (PVA) adsorbent, PVA–CA, was efficiently synthesized and its application to the removal of dyes in water, particularly the cationic dye, methylene blue (MB), was thoroughly investigated. The morphologies and physiochemical characteristics of PVA–CA were fully characterized by SEM, FT-IR, XRD, TGA, BET, and XPS. The effects of contact time, adsorbent dosage, MB concentration, solution pH, and temperature on the adsorption performance were compared using controllable methods. The maximum adsorption capacity of PVA–CA was 709.86 mg g−1 and the removal rate remained high through several adsorption–desorption cycles, demonstrating that such a composite absorbent has a good adsorption performance and recoverability. Further analysis by the density functional theory (DFT) showed that van der Waals interactions, electrostatic interactions and hydrogen bonding interactions between PVA–CA and MB played significant roles in the adsorption mechanism.