| Summary: | Herein, chitosan (CS) and watermelon seed shell (WSS) were blended to yield a new biocomposite (CS/WSS) via sonication with an ultrasonic bath of 40 kHz for 25 min at 20 W. Thus, CS/WSS adsorbent was applied for the removal of reactive orange 16 dye (RO16) from the aqueous environment. The CS/WSS characteristics were evaluated using XRD, SEM–EDX, FTIR, and pHpzc methods. The adsorption efficiency of CS/WSS with the RO16 dye was optimized using a Box-Behnken design (BBD). The three independent experimental parameters include the CS/WSS dosage (A 0.02–0.1 g/100 mL), contact time (B 10–60 min), and RO16 solution pH (C 4–10). The kinetics of adsorption analysis validates that the adsorption of RO16 with the CS/WSS biocomposite adopts a pseudo-second-order (PSO) adsorption profile. In addition, the Freundlich and Langmuir isotherm models were assessed to obtain best-fit results for the isotherm profiles. The maximum adsorption capacity of CS/WSS biocomposite (qmax) for RO16 was found to be 158.6 mg/g in an acidic pH environment at pH 4 and 25 °C. The mechanism of RO16 adsorption onto the CS/WSS biocomposite surface has several contributions that include electrostatic forces, hydrogen bonding, n-π and π -π interactions. Thus, the CS/WSS biocomposite exhibits favourable RO16 dye removal in aqueous media. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
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