Synthesis of Fe3O4 Nanoparticles Using Lichen (Collema ABU01502) Extract and their Application in the Removal of 4-Nitrophenol from Aqueous Solution

Abstract

In this study, magnetite (Fe₃O₄) nanoparticles were successfully synthesized via a green and sustainable route using Collema lichen (ABU01502) extract as a natural reducing and capping agent, and their application in the removal of 4-nitrophenol (4-NP) from aqueous solution was systematically investigated. Fourier Transform Infrared (FTIR) spectroscopy confirmed the presence of bio-derived functional groups (–OH, C=O, C–O, and aromatic moieties) on the nanoparticle surface alongside the characteristic Fe–O vibration around 580 cm⁻¹, indicating successful formation of magnetite with biomolecular capping. SEM and TEM analyses showed that the nanoparticles were almost spherical and had some agglomeration. The sizes of the particles ranged from 10.0 to 28.5 nm. UV–Vis spectroscopy showed a broad absorbance between 300 and 800 nm, consistent with the optical behavior of Fe₃O₄ nanoparticles. Batch adsorption experiments demonstrated that 4-NP removal efficiency strongly depended on pH, temperature, contact time, and adsorbent dosage, with removal efficiencies ranging from approximately 4 % to 55 % prior to optimization. Response Surface Methodology (RSM) based on a 2⁴ factorial design yielded a highly significant predictive model (F = 37.10, p = 0.0063) with a high coefficient of determination (R² = 0.9933). Optimal conditions (pH 8.0, 60 °C, 180 min, and 4 g L⁻¹ adsorbent dosage) resulted in a maximum 4-NP removal of 74.93 % and a desirability of 1.0. Adsorption equilibrium was best described by the Langmuir isotherm (R² = 0.9942), with a monolayer adsorption capacity of 49.75 mg g⁻¹ and a favorable separation factor (Rᴸ = 0.095). These findings demonstrate that lichen-mediated Fe₃O₄ nanoparticles are efficient, magnetically recoverable, and environmentally benign adsorbents for nitrophenol-contaminated water treatment.