The adsorption of acid orange II (AO7) dye from aqueous solution was examined onto untreated and chemically modified forms (treated with (i) propylamine, (ii) acidic methanol, (iii) formaldehyde and (iv) formic acid with formaldehyde) of brown alga, Stoechospermum marginatum. The adsorption was studied as a function of initial solution pH (2.0–10.0), initial dye concentration (30–90 mg/L), contact time (5–60 min) and biomass dosage (0.2–2.2 g/L) at constant temperature and agitation speed. The kinetic data were well described with the pseudo-second-order model. The results revealed that amine functional groups were mainly responsible for the adsorption of acid orange II dye. The modification of biomass with propylamination enhanced the dye adsorption capacity about two times of the untreated algal biomass. These findings were confirmed by Fourier transform infrared (FT-IR) spectroscopy.

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