A novel green synthesis of zero valent iron nanoparticles (NZVI) using three plant extracts and their efficient application for removal of Cr(VI) from aqueous solutions

- Zero valent iron nanoparticles (NZVI) were synthesized via green synthesis method.
- Rosa, Thymus, and Urtica dioica extracts were used to produce novel NZVI.
- Differences in Fe NPs synthesized were observed by characterization.
- The synthesized TV-Fe, UD-Fe and RD-Fe showed high adsorption capacity of 459 mg/g.
- For 1 min contact time, Cr(VI) removal was 94.8%, 83.4% and 86.8% for RD, UD and TV.

In the present study, NZVI particles were synthesized from the plant extracts including Rosa damascene (RD), Thymus vulgaris (TV), and Urtica dioica (UD). The FTIR arspectshowed that polyphenols, proteins and organic acids which serve as reducing and stabilizing agents play a significant role in the synthesis of NPs and reduce the possibility of aggregation of NPs compared to chemical techniques of NPs synthesis. The amount and type of compounds in plant extracts affect the structure and also agglomeration of NPs after adsorption process. Based on the results, the highest removal efficiency occurred at pH 2. With increase in contact time and amount of dose, the percentage removal increases. Inversely, increase of initial concentration of Cr(VI) decreases the removal efficiency of the contaminant. These nanoparticles have a high adsorption capacity. Accordingly, by applying a dose of 0.2 g/l and contact time of 10 min, the three NPs yielded >90% removal efficiency. Also, for 1 min contact time, the percentage removal was 94.87%, 83.48% and 86.8% for RD-Fe, UD-Fe and TV-Fe, respectively. By an increase to 25 min, the removal percentage reached to 100% for TV-Fe and UD-Fe. Moreover, 30 min was required to remove Cr(VI) completely by RD-F.

FTIR spectra analysis (400-4000 cm−1) for synthesized nanoparticles before adsorption are shown in the figure. In this figure, the most distinguishable peaks are shown for the NPs which are coded separately. All synthesized nanoparticles have relatively same peaks. In range between wave number 3400 and 3430 cm−1, the highest peak was appeared in region A which corresponds to polyphenols. These peaks show the prominent phenolic functional groups in FTIR analysis. The second strong peak in region E in the range of 1126-1190 cm−1, corresponds to carbonyl group which shows heterocyclic compounds resulting from proteins of plant extracts. Accordingly, the FTIR spectra of NPs exhibited another prominent peak in region C between 1628 cm−1 and 1640 cm−1. This peak corresponds to resonance absorption of the CC in alkene groups belonging to the family of no-saturated hydrocarbon compounds. Another strong peak is observed in region G within the range of 615-617 cm−1, indicating aromatic compounds of alkanes. Other peaks can also be seen in regions F and D, which all correspond to organic, aromatic compounds, an also derivations of these compounds including polyphenols, alcohol or terpenoids, proteins and organic acids in plant extracts. According to the Fig, the intensity of peaks corresponding to TV-Fe is stronger than other synthesized NPs in almost all peaks, while for RD-Fe NPs the relationship is opposite. This shows the difference between stabilizing and reducing agents in extracts of different plants. The intensity of RD-Fe peak in region E is less than other NPs due to the presence of NPs which inhibit aggregation.62