Nonlinear kinetics and isotherm study of acid red 183 removal using chitosan and chitosan‐enhanced urea–formaldehyde resin

Abstract In this study, we synthesized a new biocomposite, chitosan‐modified urea–formaldehyde resin (UF/Chi), as a potential adsorbent for removing the dye Acid Red 183 (AR183) from aqueous solutions. Characterization of chitosan and the UF/Chi composite was performed using scanning electron microscopy, X‐ray diffraction, Fourier transform infrared (FTIR) spectroscopy, non‐isothermal thermogravimetric analysis, differential thermal gravimetry and the Brunauer–Emmett–Teller (BET) method. The results showed that the UF/Chi composite has a rough surface and macropores, resulting in a slightly higher specific surface area ( S BET ) of 6 m 2 g −1 compared to chitosan, which has S BET of less than 5 m 2 g −1 . FTIR spectroscopy validated the interaction between chitosan and UF during in situ synthesis. The UF/Chi composite showed greater thermal stability, with a degradation onset ( T 5% = 92.1 °C) occurring later than for chitosan ( T 5% = 61.1 °C). Thermodynamic studies revealed that the adsorption of AR183 on both chitosan and the UF/Chi composite is spontaneous. Adsorption kinetics indicated that the double exponential model best fitted the UF/Chi composite and chitosan, followed by the Elovich model. The Sips isotherm model was optimal for adsorption on both sorbents. The processes are both physical and chemical. Maximum adsorption capacities were 24.2571 mg g −1 for the UF/Chi composite ( c = 50 mg dm −3 , pH = 6.27, adsorbent dosage 100 mg, T = 25 °C) and 196.5018 mg g −1 for chitosan ( c = 300 mg dm −3 , pH = 6.27, adsorbent dosage 75 mg, T = 25 °C). These results suggest that both materials effectively remove AR183 dye from aqueous media. © 2026 Society of Chemical Industry.