Biosorption of Acid Black 1 (AB1) onto brown macroalgae, Nizamuddina zanardinii, was investigated. The effects of different parameters including pH, biomass loading, dye concentration, temperature, and salinity on the biosorption capacity were studies. The result at equilibrium was successfully described by the Freundlich model, and the estimated biosorption capacity was 29.79 mg/g. The kinetic of biosorption at different agitation speeds (70–180 rpm) and particle sizes (56–500 lm) were evaluated by pseudo-second- order, pseudo-first-order, and intraparticle diffusion kinetic models. The results showed that the pseudo-second-order model could be used as a successful model for the biosorption kinetics. Thermodynamics of sorption was investigated at different temperatures from 283 to 313 K. The negative values of Gibbs free energy, DG0, and positive value of enthalpy, DH0, confirm the possibility of the biosorption process and the spontaneous nature of the biosorption. A decrease in particle size of N. zanardinii biomass increased AB1 biosorption capacity. Furthermore, addition of NaCl (0–40 g/L) resulted in minor improvement in the dye biosorption. Role of different functional groups on the surface of biomass for biosorption of AB1 was investigated using FTIR.

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