Quercus robur acorn peel as a novel coagulating adsorbent for cationic dye removal from aquatic ecosystems

Oak acorn peel (OP) was used in natural form for the removal of cationic dyes, methylene blue (MB), acridine orange (AO) and malachite green (MG) from aqueous solutions. OP removed 60–97% of 600 mg L^-1 dyes at wide ranging pH (2–10). Adsorption equilibriums were attained within 3 h. Sorbent (5 g L^-1) adsorption capacity was 109.43, 115.92 and 111.85 mg g^-1 for MB, AO and MG, respectively. Adsorption kinetics was described using pseudo-second-order model. Equilibrium adsorption data were interpreted by Langmuir and Freundlich isotherms. Dye removal was by coagulation-coupled adsorption. Coagulation was due to the formation of complexes between the dye molecules and OP polyphenols that led to the deposition of precipitated flocs.