Green vegetable waste composited with chitosan as a bioadsorbent for effective removal of methylene blue dye from water: Insight into physicochemical and adsorption characteristics

In the current work, green vegetable waste (lettuce leaves, Swiss chard stems, and cucumber peel) was functionalized using sulfuric acid (H₂SO₄) and subsequently composited with chitosan to develop a biocomposite (starting now, CHT/GVW-HS) for effectively removing methylene blue (MB) dye from water. The adsorption variables, including CHT/GVW-HS dosage (0.03–0.09 g), removal time (10–90 min), and pH (4–10), were optimized using Box-Behnken Design (BBD). The BBD model's findings indicate that the ideal values for achieving maximum removal of MB (98.57 %) are a pH of approximately 10, a dose of CHT/GVW-HS of 0.065 g, and a contact duration of 88 min. The experimental results of MB adsorption by CHT/GVW-HS were in agreement with pseudo-first-order and the Freundlich models. The biomaterial exhibited a high adsorption capacity of 296.83 mg/g for CHT/GVW-HS, indicating its strong ability to adsorb MB. The adsorption route of MB on the CHT/GVW-HS involves various interactions like electrostatic, n-π, Yoshida H-bonding, and H-bonding. The study promotes the production of sustainable adsorbents using waste biomass and biopolymers to efficiently eliminate dyes from wastewater. The current work contributes to several Sustainable Development Goals (SDGs), such as Life Below Water, Clean Water and Sanitation, Climate Action, and Responsible Consumption and Production.