(331d) Mesoporous Fe- or Cu-Doped MgO Nanoparticles for Photo-Fenton-like Degradation of Salicylic Acid

Water scarcity combined with its pollution by toxic contaminants is one of the key challenges facing humanity. Among emerging water contaminants, pharmaceuticals and personal care products (PPCPs) have been identified as a rising threat due to their presence in wastewater, surface water, and groundwater. Advanced water treatment techniques, such as microfiltration, reverse osmosis, and advanced oxidation processes (AOPs) have been demonstrated to be highly active toward removing such recalcitrant organic matter. AOPs are of particular interest since they allow for the degradation of organic contaminants that are otherwise recalcitrant and ubiquitous in municipal, industrial, and agricultural wastewater. While the homogeneous Fenton reaction is highly effective, it intrinsically faces two challenges that prevent successful large-scale implementation including (a) the solution pH of ~3 and (b) the waste iron sludge generated. Therefore, research has focused on heterogeneous Fenton catalysts due to their easier separation and reusability, as well as a solution pH closer to the circumneutral which can be discharged into the watershed. This presentation will focus on mesoporous MgO based nanoparticles as photo-Fenton-like catalysts that possesses dual functionality. They both degrade target organic molecules via ROS generation and control the pH near the catalysts thus preventing dissolution and, potentially, loss of iron into the solution. In particular, mesoporous Cu- and Fe-doped MgO nanoparticles were synthesized using a facile sol-gel method and utilized for photo-Fenton-like degradation of salicylic acid (SA). The MgO surface dissolution facilitated an increase in the pH under the reaction conditions that allowed the metal doped MgO catalyst to be active without detectable metal ion leaching. Under simulated solar radiation, salicylic acid, a model compound since it is a common ingredient in nonsteroidal anti-inflammatory drugs (NSAIDs), was completely degraded with an initial rate constant of 0.048 min^-1 at the optimal reaction conditions of 500 ppm loading of 5% Fe-MgO, 20 mM H₂O₂ concentration, and 50 ppm SA concentration. The catalyst was stable over 5 reaction cycles. The Fe-MgO catalyst was shown to have a surface area up to 171 m²/g and contain hematite (Fe₂O₃) nanoparticles with octahedrally coordinated iron catalytic centers, as inferred from diffuse reflectance UV-vis measurements. Post-reaction catalyst characterization showed that some Fe²⁺ was present in the catalyst due to the redox cycle during the chain initiation and propagation steps of the reaction.