Chitosan polymer/ functionalised rambutan peel using carboxylic acid: process optimisation using Box-Behnken Design for brilliant green dye removal

Herein, effective removal of brilliant green dye from the water was achieved using eco-friendly and sustainable adsorbent (CHA/RP-CA) derived from chitosan (CHA) and functionalised rambutan (Nephelium lappaceum L.) peel using carboxylic acid (citric acid, CA). Using Box-Behnken Design (BBD), the adsorption variables, A: CHA/RP-CA dosage (0.02–0.08 g), B: pH (4–10), and C: contact duration (10–40 min), were modelled and optimised. The BBD model's results showed that the ideal adsorption variables for maximum BG removal (93.68%) were pH ~ 10, CHA/RP-CA dose = 0.066 g, and contact duration = 39 min. Pseudo-first-order and Freundlich models agreed with the experimental results of BG adsorption by CHA/RP-CA. With an adsorption capacity of 439.5 mg/g for CHA/RP-CA, the created biomaterial demonstrated a strong ability to adsorb BG. Several interactions, including Yoshida H-bonding, electrostatic, n-π, and H-bonding, are involved in the cationic dye adsorption process on the CHA/RP-CA. This study encourages the development of sustainable adsorbents from waste biomass and biopolymers for effectively removing dyes from wastewater. Multiple Sustainable Development Goals (SDGs) are met by the current endeavour, including SDG 6 (Clean Water and Sanitation), SDG 12 (Responsible Consumption and Production), SDG 13 (Climate Action), and SDG 14 (Life Below Water).