# Fabrication of Metal–Organic Framework-Mediated Heterogeneous Photocatalyst Using Sludge Generated in the Classical Fenton Process

## TL;DR

This paper presents a new way to recycle Fenton process sludge into a photocatalyst that efficiently degrades pollutants like methylene blue under visible light.

## Contribution

A novel heterogeneous photo-Fenton catalyst is fabricated from Fenton wastes and MOFs, demonstrating high efficiency and reusability.

## Key findings

- 4-HO-MIL-88-C showed the best performance in methylene blue degradation under visible light.
- The catalyst generates multiple free radicals (singlet oxygen, superoxide, and hydroxyl) during the photo-Fenton process.
- The catalyst maintained over 80% efficiency after five reuse cycles, indicating good stability and reusability.

## Abstract

The sludge produced by the Fenton process contains mixed-valence iron particulates (hereafter called Fenton wastes). Using a solvothermal method, we fabricated a new heterogeneous photo-Fenton catalyst using Fenton wastes and metal–organic frameworks (MOFs). Nanoporous metal carboxylate (MIL-88) MOF impregnated with Fenton waste was functionalized using 2,5-dihydroxyterephthalic acid (x-HO-MIL-88-C, x, concentration of the 2,5-dihydroxyterephthalic acid). The efficiency of x-HO-MIL-88-C was examined under visible light radiation using methylene blue (MB) as an index pollutant. We observed the best catalytic performance for MB degradation by 4-HO-MIL-88-C. In the photo-Fenton process, the simultaneous presence of singlet oxygen, superoxide, and hydroxyl radicals is confirmed by free radical quenching and electron spin resonance spectral data. These free radicals associate with holes in the non-selective degradation of MB. The 4-HO-MIL-88-C catalyst shows good stability and reusability, maintaining over 80% efficiency at the end of five consecutive cycles. This work opens up a new path for recycling Fenton wastes into usable products.