Adsorption Study of Protein onto Gallic Acid Modified Fe3O4 Nanoparticles

In recent years, Fe3O4 nanoparticles have been widely developed as adsorbents for various applications. However, their hydrophobic surface limits their application in polar systems, necessitating surface modifications to enhance adsorption. In this study, gallic acid was employed to modify Fe3O4 nanoparticles, as its carboxyl and phenolic hydroxyl groups can provide sites for protein adsorption. The research aims to determine the optimal pH, adsorption capacity, isotherm models, and thermodynamic parameters for bovine serum albumin (BSA) adsorption, as a model protein, onto gallic acid-modified and unmodified Fe3O4 nanoparticles using batch experiments. The experiments varied pH (3.6–5.6), initial BSA concentrations (0.50–1.75 mg/L), and temperatures (30–50 °C). FTIR analysis confirmed successful modification through the presence of C=O stretching bonds, while BSA adsorption was indicated by the appearance of amide groups and transmission electron microscopy (TEM) observations. Maximum adsorption was achieved at pH 4.8, in the vicinity of BSA isoelectric point. The Langmuir isotherm model best described the adsorption process for all adsorbents. Thermodynamic analysis showed that BSA adsorption was spontaneous and endothermic with increased randomness, as evidenced by negative Gibbs free energy, along with positive enthalpy and entropy values. Surface modification with gallic acid enhanced BSA adsorption capacity to 68.49 mg/g compared to 34.84 mg/g for unmodified Fe3O4 at 50 °C.