Iron-rich industrial sludge-derived metal organic framework for enhanced photoelectrochemical degradation of methylene blue

The escalating discharge of textile effluents, burdened with persistent dyes such as methy­lene blue (MB), has become a significant global concern. In this study, a surface-engineered iron sludge, denoted as IMS-MOF, was synthesized by modifying iron-rich industrial metal sludge (IMS) to enhance its performance in photoelectrochemical degradation of MB. The IMS-MOF was synthesized via a hydrothermal method, utilizing IMS as the metal ion source and 1,3,5-tricarboxylic acid (BTC) as ligand. Characterization results revealed that IMS-MOF exhibited an increase in surface area (50.34 m² g-1), and porosity (0.27 cm³ g-1) compared to IMS (36.56 m² g-1, 0.19 cm³ g-1). Additionally, the MOF process induced a morphological transition from densely agglomerated particles with rough surface features to well-defined, rod-shaped crystalline structures, characteristic of metal-organic frameworks, thereby sig­nificantly enhancing the specific surface area and active site accessibility. This structural rear­rangement led to a significant increase in the specific surface area and facilitated enhanced access to the active sites within the framework. The band gap reduction in IMS-MOF enhanced its photocatalytic activity under UV light irradiation. Photoelectrochemical degradation studies showed that IMS-MOF achieved higher MB removal efficiency than IMS, with over 90 % MB degradation within a specific contact time. The adsorbent exhibits good adsorption performance over a broad pH range (5-11). By scavenging tests of free radicals generated, hydroxy radicals (·OH) and superoxide radicals (·O2-) were indicated as the reactive oxygen species in the photoelectrochemical degradation. Although IMS-MOF showed a 15.1 % decrease after 10 cycles, it still possessed reusability and stability, indicating that it is qualified for textile wastewater treatment in practice.