Eco-Friendly Anionic Surfactant for the Removal of Methyl Red from Aqueous Matrices

This study aimed to evaluate the methyl red (MR) removal efficiency from aqueous matrices using an eco-friendly anionic surfactant (a calcium surfactant, or CaSF), obtained from frying oil residue. Data obtained by infrared spectroscopy revealed several functional groups that favor the capture of the dye by chemisorption by forming hydrogen bonds and covalent interactions. The kinetic testing results fit the pseudo-second order model, reaching equilibrium in 30 min. Adsorption was greatly influenced by temperature. The Langmuir isotherm was the one best fitting the process at 20 °C, while the Dubinin–Radushkevich isotherm fitted it better at higher temperatures. Under optimized conditions, the maximal MR adsorption capacity of CaSF reached 53.59 mg·g−1 (a removal rate of 95.15%), proving that the adsorbent at hand can be an excellent alternative for the removal of undesirable levels of MR present in aqueous matrices.