Catalytic degradation of dyes using activated MIL-100(Fe) metal-organic framework

Abstract

Improperly treated wastewater can be harmful to human health and aquatic ecosystems due to residual pollutants with aromatic compounds, such as dyes and pharmaceuticals, being particularly difficult to degrade. Dyes are attractive probes for other more toxic compounds, as they are widely available and have many functional groups that are present in other pollutants. Many treatment methods are used for this application, such as the homogeneous Fenton process involving the reaction between iron salt and an oxidant, but such catalysts are often non-recoverable. Iron-based metal-organic frameworks (MOFs) are the focus of this work due to their stabilization of iron that could allow them to react in a Fenton-like process with less leaching. MIL-100(Fe) is part of a reportedly water-stable series of MOFs, and in this work is synthesized as a catalyst for the degradation of several dyes, with a focus on methylene blue (MB) dye. In its as-synthesized state, MIL-100(Fe) does not greatly improve MB degradation rates relative to a non-MOF control. Thermal activation under vacuum at conditions of 493 K and 393 K, as well as “fresh” non-activated MIL-100(Fe), are compared, with activation conditions improving both MB adsorption and degradation rates. The leaching of active species into solution is also explored, with differences in rates batch-to-batch after MOF removal.