Influence of interfacial, thermodynamic and hydrophobic parameters on Acid Red 57 removal by ionic micellar flocculation

Most dyes are complex organic molecules that are highly resistant to degradation and may cause severe damage to live organisms and photosynthetic activities. In this respect, the aim of the present study was to assess the influence of interfacial, thermodynamic and hydrophobic parameters on Acid Red 57 removal from aqueous media by ionic micellar flocculation using surfactants sodium dodecanoate (C12), sodium tetradecanoate (C14) and sodium hexadecanoate (C16). The results demonstrate that an increase in the hydrophobic nature of the surfactant provokes different Krafft (Tkrafft) temperature and critical micelle concentration behaviors, and the greater the hydrophobicity the higher the solubilization temperature and lower the concentration needed for micelle formation. It was also found that long-chain surfactants cause an increase in the area of the polar part of the surfactant and change the micelle shape from lamellar (C12, C14) to cylindrical (C16), interfering in the solubilization capacity of the micelles. Micelle diameter determination aimed at demonstrating that the dye is solubilized inside the micelles via hydrophobic interactions. The dye removal tests showed that an increase in surfactant concentration improves process efficiency, surfactant C12 exhibiting the best dye removal indices (around 90%). Thermodynamic parameters showed that ionic micellar flocculation is exothermic and non-spontaneous.