Characterization of Oreochromis niloticus fish scales and assessment of their potential on the adsorption of reactive blue 5G dye

• RB5G dye sorption process by the Oreochromis niloticus fish scales was assessed.
• An elevated sorption capacity comparable to conventional adsorbents was observed.
• Fish scales adsorbent is mainly composed by collagen and hydroxyapatite.
• Hydroxyapatite leaching simultaneous to adsorption process at acidic media.
• Amide groups present at collagen are mainly responsible for RB5G dye adsorption.

In this work, the physicochemical and morphological characterization of fish scales and an evaluation of their adsorption of reactive blue 5G (RB5G) dye were performed. The analysis of N2 physisorption, pHZPC, SEM–EDX, XRD and FTIR was carried out. Adsorption experiments were performed in batch and closed system. From N2 physisorption studies, we obtained values of the specific surface area, total pore volume and average pore diameter as 2.6 m2 g−1, 0.003 cm3 g−1 and 20.6 Å, respectively. The pHZPC was estimated as 7.6. The presence of hydroxyapatite and collagen fibres in the structure of the scales was observed in SEM–EDX, XRD and FTIR results. Furthermore, leaching of mineral phase mainly occurs during the adsorption process in acid medium (pH 2), although, in neutral and alkaline media (pH 7 and 10), it is less pronounced. The FTIR spectra indicate that the amides functional groups from collagen structure are responsible for RB5G dye adsorption. Comparing the RB5G dye uptake at different initial pH values (2, 7, 10), a higher capacity was achieved in acidic medium. The equilibrium adsorption data of RB5G dye at pH 2 showed a maximum capacity of 241.20 mg g−1 with fast kinetics.

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