Synthesis of MIL-100 from chemical excess sludge and its TiO2-loaded composite for visible-light-driven catalytic degradation of methylene blue

Abstract

Chemical excess sludge, containing viruses, heavy metals, polycyclic aromatic hydrocarbons, and other components, exhibits high toxicity, making its safe disposal an urgent issue. In this work, MIL-100 (Materials of Institut Lavoisier – 100(iron)) was synthesized using 1,3,5-benzenetricarboxylic acid and iron extracted from excess sludge. Additionally, titanium dioxide was loaded onto MIL-100 via an impregnation–calcination method to form T@MIL-100, and their visible-light-driven photocatalytic activities for methylene blue (MB) degradation were evaluated. The results showed that the synthesized MIL-100 exhibited excellent photocatalytic performance for MB degradation, with a degradation efficiency of 92.44% and a corresponding kinetic constant (k_obs) of 0.97612 h⁻¹. The degradation efficiency of MB over 1%T@MIL-100 was enhanced to 98.42%, and the k_obs value increased to 1.39943 h⁻¹. Quenching experiments further revealed the catalytic mechanism: h⁺ was the dominant active species in the MIL-100 system, while ·O₂⁻ and h⁺ primarily contributed to MB degradation in the T@MIL-100 system. This study provides a low-cost, efficient, and sustainable approach to convert excess sludge into functional metal–organic frameworks (MOFs) and further load TiO₂. This strategy not only promotes the recycling of residual iron in excess sludge to significantly reduce catalyst costs, but also enhances photocatalytic degradation performance, offering an excellent functional material for MB removal.