Title : Assessment of the production of hydroxyl radical using nano zero-valent iron embedded in a meso-porous silica matrix
Zero-Valent Iron (Fe0) has been shown to detoxify water by creating hydroxyl radicals through Fenton-like reactions combined with hydrogen peroxide (H2O2) to get rid of organic contaminants. Nano-sized zero-valent iron (n/ZVI) in combination with oxidants and UV radiation, has been reported can increase the Fenton reaction rate and make water detox more effective. In this work, the production of reactive oxygen species, particularly hydroxyl radicals, was assessed for the heterogeneous photo-assisted Fenton-like reaction using nZVI embedded in a mesoporous silica matrix, hydrogen peroxide, and UV-A radiation. The experiments consisted of preparing a 10 µM solution of N, N-dimethyl-p-nitrosoaniline (pNDA, used as HO• radical probe) in 100 mL of water and adding the silica-embedded nZVI at three different loads (21 mg/L to 24 mg/L) with or without H2O2, and/or UV-A radiation (λmax= 365 nm). The absorbance of the pNDA was measured and compared to that of clear, deionized water. The trials consisted of using immobilized nZVI alone, immobilized nZVI/H2O2, and immobilized nZVI/H2O2/UV. The best conditions for hydroxyl radicals production measured as pNDA bleaching were by the combination of immobilized nZVI/H2O2/UV despite nZVI, UV-A radiation and hydrogen peroxide alone were capable of bleaching pNDA to a certain extent. The use of the H2O2/UV system reached a plateau for hydroxyl radical production after 20 min of reaction. Two kinetic models were proposed to fit experimental data for the different reaction conditions tested and the obtained results were capable of fitting experimental data fairly good meaning that the proposed reaction mechanisms may occur within the reaction mixture to some extent. This novel material was found with interesting capabilities to produce reactive oxygen species, particularly hydroxyl radicals, under photoassisted conditions and high potential for further photocatalytic applications in water treatment.