Investigation of the Influence of Structural Changes in Aqueous Solutions of Phenol on Its Ability to Be Extracted by Fe3O4 Magnetic Nanoparticles

Abstract

The efficiency of accumulating phenol by sorption on Fe₃O₄ magnetic nanoparticles in a static mode in the absence and presence of HCl is evaluated in a wide concentration range (0.0005–10 mmol/L). The most efficient extraction of phenol (53–63%) (4.5 × 10^–4 mol/L) in the absence and presence of HCl additives is observed for the concentrations of ≤0.018 mmol/L. It is established that the efficiency of phenol extraction vaguely depends on pH. Thus, there are concentration ranges for which the extraction efficiency of phenol is slightly higher in the presence of HCl, but there are concentrations (for example, 0.005 or 2–4 mmol/L) for which the degree of extraction and, accordingly, the adsorption values in the presence and absence of HCl are close. Based on the higher value of the correlation coefficient (0.932 versus 0.729), it is established that the kinetics of phenol adsorption on Fe₃O₄ magnetic nanoparticles is better described by the pseudosecond-order model. It is shown that the concentration dependences of the degree of phenol extraction and the adsorption isotherm show nonlinear stepwise behavior (or have well-defined extremes). It is proposed to adhere to systemic concepts when explaining the stepwise behavior of concentration dependences, according to which aqueous solutions are proposed to be considered as complex open nonequilibrium systems that have structural integrity and are characterized by the functional unity of structural components inclined to dynamic self-development due to self-organization and self-renewal. At the same time, it is the self-organization and self-renewal ability that explains the presence of stationary states and jumps (spontaneous transition to a new ordered state) on the concentration dependences of the physicochemical properties of aqueous phenol solutions. A correlation between the efficiency of phenol sorption and structural rearrangements in its aqueous solutions is established. The identified concentration areas are proposed to be associated with the effect of the penetration of phenol molecules into the cavity of the structural network of water molecules, the destruction of the structure of the latter, and the formation of mixed intermolecular associates of phenol with water molecules in different ratios.