The excess fluoroquinolones (FQs) discharged into the aquatic environment due to human activities must be removed cost-effectively. In an article published in the Journal of Cleaner Production, the authors fabricated an environment-friendly dealkaline lignin-grafted Fe₃O₄ nanoparticles (Fe₃O₄@DAL) for the removal of fluoroquinolone antibiotics.

Multiple interactions between Fe₃O₄@DAL and FQs facilitate their facile removal. The authors confirmed the nanoparticle’s superior adsorption and reusability and highlighted the application of degraded Fe₃O₄@DAL nanoparticles as fertilizers.

Nanoparticles in Removal of FQs

The presence of environmental contaminants (ECs) is a problem affecting the ecosystem and human health. Antibiotics are one of the alarming ECs leading to drug resistance and long-term indirect effects on the ecosystem. Among antibiotics, FQs are amphiphilic antibacterial drugs widely used in animal husbandry and agriculture. The excess FQs discharged into water bodies must be removed to avoid drug resistance and protect the environment.

Among various techniques employed to remove ECs from waterbodies, adsorption by adsorbents gained considerable attention due to its cost-efficiency, facile operation, high efficiency, and less secondary pollution.

Lignin is a natural polymer that is abundantly available in nature. It is an aromatic biopolymer with an amphiphilic molecular structure, hydrophobic three-dimensional network, and polar groups on the surface. Due to the advantages such as good stability, biodegradability, cost-efficiency, and renewability, lignin has a potential adsorbent of FQs in wastewater.

Magnetic nanoparticles combine the advantages of nanotechnology and magnetic separation. Under an external magnetic field, the magnetic nanoparticles can be separated easily without filtration or centrifugation. Additionally, these magnetic nanoparticles are cost-effective, recyclable, and can be applied to large-volume samples.

Fe₃O₄@DAL Nanoparticles

In the present work, the authors fabricated the amino-functionalized Fe₃O₄ nanoparticles (Fe₃O₄-NH₂) using a solvothermal method. Later, they grafted dealkaline lignin (DAL) onto the Fe₃O₄-NH₂ nanoparticles through an amide reaction at room temperature.

The authors characterized the as prepared Fe₃O₄@DAL and investigated their properties. They explored the adsorption mechanism using Fourier transform infrared spectroscopy (FTIR). The current work sets an example for natural polymer’s application in wastewater treatment, paving the way for environmental protection and energy conservation.

Fe₃O₄@DAL was used to remove FQs including lomefloxacin (LOM), pefloxacin (PEF), enrofloxacin (ENR), and difluoxacin (DIF) from water, through multiple interactions.

Research Findings

The results obtained from transmission electron microscopy (TEM) and X-Ray diffraction (XRD) studies of Fe₃O₄@DAL reveal the bright central area and dark periphery, suggesting the hollow structure of the nanoparticle. The selected area electron diffraction (SAED) pattern of nanoparticles confirmed its multi-crystalline nature with bright spots and diffuse circles. The nitrogen (N₂) adsorption-desorption isotherm of Fe₃O₄@DAL revealed a type-IV isotherm indicating a mesoporous structure.

FTIR spectra revealed a broad band at 3266-centimeter inverse, indicating the presence of a hydroxyl (OH) functional group. The peaks for carboxyl (O-C=O), phenylic C=C, and benzene ring derivatives -CH were found at 1419, 1507, and 861-centimeter inverse, respectively. Moreover, the peaks at 1595 and 1548-centimeter inverse corresponds to carbonyl (C=O) stretching of amide I bond and N-H bending of amide II bond, respectively, corroborating the grafting of DAL on the surface of Fe₃O₄-NH2 via amide reaction.

Thermal curves of Fe₃O₄@DAL revealed excellent thermal stability due to the carbon elements. The nanoparticle showed two thermal degradation ranges due to loss of bound water molecules and thermolysis of organic components such as methoxy, hydroxyl, and carboxyl groups that get decomposed easily.

Based on the removal efficiency and uptake capacity (q_e) values, the authors selected Fe3O4@DAL adsorbent concentration as 2.5 grams per liter to remove FQs. They also confirmed that the adsorbent has good tolerance to salt ions dispersed in water.

The maximum adsorption capacity (q_max) of Fe₃O₄@DAL towards LOM, PEF, DIF, and ENR antibiotics were analyzed, confirming an order of DIF > ENR > PEF > LOM.

Conclusion

In the present work, the authors prepared an eco-friendly and cost-effective magnetic lignin-based Fe₃O₄@DAL nanoadsorbent, using a facile amidation reaction to eliminate FQs from water bodies. The as-prepared Fe₃O₄@DAL nanoparticles facilitate the adsorption of four FQs.

The FQs adsorption on the nanoparticles was spontaneous, endothermic, and exhibited entropy augment behavior. The electrostatic force, hydrogen-bonding, and π-π interaction between nanoparticles and FQs lead to the excellent performance of Fe₃O₄@DAL.

The prepared nanoparticles catalyze the oxidative degradation of FQs through pseudo-second order reaction through charge transfer, exhibiting reusability and stability. The degraded nanoparticles are applied as fertilizers in forestry and agriculture.

The life cycle assessment (LCA) revealed that Fe₃O₄@DAL has minimal effect on the environment throughout its life cycle. The authors anticipate that future studies will explore the composite photocatalyst strategy on the Fe₃O₄@DAL nanomaterial in combination with green energy to catalyze the degradation of antibiotics.