Green synthesis of Fe-nanoparticles using pruned tea leaf extract: characterization and use for degradation of dyes from aqueous phase in Fenton-like systems

Green synthesis of nanoparticles (NPs) is considered a highly promising technology for materials. The use of plant-based NPs is the simplest with high reproducibility. Iron nanoparticles (Fe-NPs) were synthesized by pruned tea leaf extract and FeSO4 and were analyzed by XRD, FTIR, XPS, and TEM. The catalytic activity of the Fe-NPs was evaluated for dye degradation under different operating parameters. Kinetc and thermodynamic tests were also conducted to study the reaction behavior. Results showed that the Fe-NPs had an average pore size of 17.9 nm with a surface area of 2.54 m2 g−1. The Fe-NPs contained Fe–O bonds and bioactive substances. The crystalline Fe-NPs were composed of FeOOH, Fe2O3, and α-Fe forms. XPS showed the presence of Fe3+ and Fe2+ in a ratio of 1.78, with Fe2+ accounting for over 64%. TEM revealed the spherical structure with particle size around 34–52 nm. The degradation efficiency of Congo red (CR) surpassed 95% within 30 min for the Fenton-like system, while sole adsorption only achieved 50%. Increasing the solution pH had a significant negative effect. Pseudo-second-order model provided the best fit. Thermodynamic calculations revealed that the catalytic degradation is favorable, spontaneous, and endothermic. Reusability demonstrated that over 95% retention was achieved after five cycles.