Integrating reductive and photocatalytic nanomaterials: Mechanistic insights into the selective adsorption and degradation of cationic contaminants in aqueous environments

Water pollution from industrial discharges and design of sensitive engineering systems surge the need for effective, selective and sustainable remediation technologies. This study investigates the efficacy of nano zero-valent iron (nZVI) versus various photocatalytic nanoparticles (NPs), including titanium dioxide (TiO₂), magnesium oxide (MgO), zinc oxide (ZnO), and cerium oxide (CeO₂) in removing the cationic dye of methylene blue (MB) from water systems. Photocatalytic nanoparticles offer potential advantages due to their high reactivity under UV light, which can degrade complex organic molecules through oxidation processes, whereas nZVI is recognized for its reductive and environmentally friendly capabilities. Here, the interaction dynamics of these NPs with MB was investigated. Briefly, the adsorption rates, degradation efficiency, and the influence of physical and chemical properties on the removal of MB was studied. The interaction mechanism was elucidated by UV–Vis, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FTIR). The results showed while nZVI is an effective reducing adsorbent, it struggles with the stable structure of MB. In a similar response to nZVI, MgO demonstrated superior adsorption capabilities compared to other NPs by over 4 mg/g MB adsorption. The findings suggest that the choice between photocatalytic NPs and nZVI should consider the specific nature of the contaminants and the desired pathway (oxidative vs. reductive) for their removal. This research highlights the importance of engineering nanoparticle applications in water treatment processes. It provides insights into the mechanisms that govern the interaction between NPs and cationic contaminants, crucial for designing more efficient water purification systems.