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. 2025 Jul 10;10(28):30985-30995.
doi: 10.1021/acsomega.5c03914. eCollection 2025 Jul 22.

Role of Solvents in Iron Nanoparticle Synthesis: Analyzing Water and 1‑Methyl-2-Pyrrolidone with Green Tea Extract as a Reducing Agent

Nikhil Kumar Daimari  1 , Ashish Gogoi  1 , Rajib Biswas  1 , Nirmal Mazumder  2
Affiliations

Role of Solvents in Iron Nanoparticle Synthesis: Analyzing Water and 1‑Methyl-2-Pyrrolidone with Green Tea Extract as a Reducing Agent

Nikhil Kumar Daimari et al. ACS Omega. .

Abstract

The choice of solvent in the synthesis of nanoparticles plays a pivotal role in influencing the nucleation and growth kinetics of nanoparticles. Deionized water (DI) due to its cost-effectiveness, low toxicity, and ability to dissolve precursor salts effectively makes an ideal solvent medium, while aprotic organic solvents such as N-methyl-2-pyrrolidone (NMP) with high dipole moment also demonstrate their efficacy as dual solvent-reducing agents. Herein, this study aims to explore the effect of different solvent media on the biosynthesis of iron nanoparticles (FeNPs) and their impact on the optical, structural, and morphological properties. Green tea extract acts as a reducing agent aiding in stable nanoparticle formation by surface capping with active phytochemical functional groups. The synthesized FeNPs were characterized using ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), zeta sizer, and Fourier transform infrared (FTIR) spectroscopy. The appearance of absorption peaks affirmed ligand-to-metal charge transfer and double exciton transitions undergoing in the optical structure of the nanoparticles. XRD analysis confirmed the formation of a mixed-phase hematite (α-Fe2O3) and maghemite (γ-Fe2O3) nanostructure with rhombohedral and cubic lattices. Morphological studies by FESEM specify high-yield synthesis of FeNPs with mean particle size of 52.20 ± 14.65 and 51.77 ± 13.82 nm for DI and NMP, respectively. The oxidation of NMP solvent molecules also functioned as a coreducing agent for the reduction of metal Fe species allowing the growth of FeNPs at ambient room temperature. The effectiveness of NMP in FeNPs synthesis highlights its potential as a practical route for producing iron-based nanomaterials while revealing key aspects of solvent-nanoparticle interactions.

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Figures

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Schematic representation of (A) preparation of green tea extract and (B) biosynthesis process of FeNPs in different solvents.
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UV–visible spectrum of green tea extract and FeNPs in solvent DI and NMP. The inset displays the broad absorption band.
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Tauc plots for (A) direct transition and (B) indirect transition in biosynthesized FeNPs in DI solvent.
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Tauc plots for (A) direct transition and (B) indirect transition in biosynthesized FeNPs in NMP solvent.
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XRD spectra of FeNPs in (A) DI and (B) NMP solvents.
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FESEM images of biosynthesized FeNPs in (A) DI solvent, (B) NMP solvent, and (C, D) their corresponding particle size distribution profile. Values are presented as mean ± standard deviation.
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EDX spectra of biosynthesized FeNPs in (A) DI and (B) NMP solvents.
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Measurements from zeta sizer showing the size of biosynthesized FeNPs in (A) DI solvent and (B) NMP solvent.
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FTIR spectra of green tea extract and biosynthesized FeNPs.
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