Synthesis and cationic dye biosorption properties of a novel low-cost adsorbent: coconut waste modified with acrylic and polyacrylic acids.

Coconut waste (CW), a novel, low cost adsorbent, has been utilized for the removal of methylene blue (MB) dye from an aqueous solution. CW was chemically modified with acrylic (AcA) and polyacrylic acids (PAcA) using different modification methods, such as esterification with AcA, chemically grafting of PAcA, and plasma-enhanced chemical vapor deposition (PECVD) coating with PAcA. CW-based adsorbents were used in the experiments to study MB adsorption probability, and their activities were compared. The adsorption behavior of MB onto the adsorbents was investigated with respect to parameters such as sorbent dosage (0.5-4 g/L), pH (2-10), initial dye concentration (50-250 mg/L), and temperature (22-65 °C). The time taken of AcA modified CW (CW-AcA), PAcA-grafted CW (CW-PAcAgrafted), and PAcA-coated CW (CW-PAcAcoated) for the removal of 94.6%, 97.7%, and 91.0% of MB from 50 mg/L of dye solution is 180 min. Characterization of CW-based adsorbents was achieved using SEM, XRD, BET, XPS, and FT-IR analysis. The adsorption fitted the Langmuir model, and the adsorption kinetics were consistent with a pseudosecond-order kinetics model. The results obtained from the maximum adsorption capacity (qmax) for AcA-, PAcAcoated-, and PAcAgrafted-CWs were 138.88, 136.98, and 98.03 mg/g at adsorbent dose of 0.1 g/50 mL for initial dye concentration of 200 mg/L, 22 ± 1 °C, and pH 10:10:8.