Application of a biowaste of fish (Labeo rohita) scale for the removal of methyl orange from aqueous solutions: optimization of sorption conditions by response surface method and analysis of adsorption mechanism

Abstract

Methyl orange, an anionic dye, is injurious to health and the environment which must be treated before discharging. The processed fish (Labeo rohita) scales were characterized by scanning electron microscope (SEM), the attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FT-IR), and BET surface area analyzer. The BET surface area and pore diameter were observed to be 192 m² g⁻¹ and 44 nm, respectively. Influences of parameters such as pH, temperature, and concentration of adsorbent were studied by response surface methodology and analysis of variance (ANOVA) to optimize methyl orange dye uptake in adsorption process by fish scale. The influences of factors on adsorption capacity followed the order (initial concentration ˃ temperature ˃ pH). The fish scale attained a high sorption capacity (Langmuir capacity of 520 mg g⁻¹ at pH 5.3, 283 K) towards methyl orange. The thermodynamics analyses implied that the physisorption was an exothermic and spontaneous process (ΔG⁰ = negative, ΔH⁰ = −9.17 kJ mol⁻¹ and ΔS⁰ = + 0.03 J mol⁻¹ K⁻¹). The interaction of fish scale biosorbent with methyl orange dye was also explored with the assistance of a mechanistic pathway. The results indicate that the fish scale could be employed as an effective biosorbent for the removal of methyl orange dye from aqueous solution.