# Coffee Waste as a Green Precursor for Iron Nanoparticles: Toward Circular, Efficient and Eco-Friendly Dye Removal from Aqueous Systems

## TL;DR

This study shows how coffee waste can be used to create iron nanoparticles that efficiently remove dyes from water in an eco-friendly way.

## Contribution

The novel use of spent coffee waste as a green precursor for synthesizing iron nanoparticles for dye removal is introduced.

## Key findings

- Nanoparticles achieved 100% dye removal efficiency under optimized conditions.
- Coffee waste polyphenols effectively act as reducing agents for nanoparticle synthesis.
- The method supports circular economy and sustainable water remediation.

## Abstract

In this study, the use of spent coffee waste as a green precursor of polyphenolic compounds, which are subsequently employed as reducing agents for the synthesis of zero-valent iron nanoparticles (nZVI) aimed at the efficient removal of dyes from aqueous systems, has been investigated. The nanoparticles, generated in situ in the presence of controlled amounts of hydrogen peroxide, were applied in the removal of organic dyes—including methylene blue, methyl orange, and orange G—through a heterogeneous Fenton-like catalytic process. The synthesized nZVI were thoroughly characterized by nitrogen adsorption at 77 K, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and powder X-ray diffraction (XRD). A statistical design of experiments and response surface methodology were employed to evaluate the effect of polyphenol, Fe(III), and H2O2 concentrations on dye removal efficiency. Results showed that under optimized conditions, a 100% removal efficiency could be achieved. This work highlights the potential of nZVI synthesized from agro-industrial waste through sustainable routes as an effective solution for water remediation, contributing to circular economy strategies and environmental protection.