Synthesis, Testing, and Characterization of a Novel Nafion Membrane with Superior Performance in Photoassisted Immobilized Fenton Catalysis

Abstract

A new type of Nafion/Fe structured membrane ensuring faster kinetics, higher efficiency, and mechanical properties has been prepared and will be compared in its performance with the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane during the abatement of model organic compounds. During the casting of the laboratory Nafion sample, the iron ions were introduced directly into the Nafion oligomer solution. This novel laboratory Nafion/Fe was tested as an immobilized catalyst in the degradation of several toxic pollutants showing a faster photoassisted degradation kinetics and a wider effective photocatalytic pH range compared to the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane. When carrying out Ar ion sputtering of the 50 topmost catalyst layers, evidence is presented by X-ray photoelectron spectroscopy that Fe ions are found in the inner Nafion layers and seem to be responsible for the immobilized photoassisted Fenton processes leading to the degradation of 4-chorophenol (4-CP) taken as a model organic pollutant for the degradation process reported in this study. In the laboratory sample, the iron oxy/hydroxy Nafion moiety undergoes a transition to a more stable Nafion/Fe species during 4-CP degradation as determined by X-ray diffraction. This more stable form shows a higher iron dispersion and crystallinity compared to the fresh sample and is stabilized by the Nafion matrix avoiding the formation of separate iron phases. By infrared absorption (Fourier transform infrared), evidence is presented for the band of akaganeite-like species at 870 cm(-1) on the laboratory Nafion/Fe sample. This band disappears after 4-CP degradation because of the formation of the more highly dispersed iron species. Sputtering experiments show a decrease of F-containing groups in the laboratory Nafion/Fe samples closer to the catalyst upper layer while the amounts of Fe, C, and in particular O species increase in the topmost layer(s). In particular, the oxygenated species develop in the Nafion/Fe up to approximately 50 A below the catalyst surface. These species remain stable during the long-term Nafion/Fe degradation of 4-CP. Dynamo-mechanical analysis performed on laboratory Nafion/ Fe membrane samples revealed that these membranes possessed a greater mechanical modulus and resistance than the commercial Dupont 117 Nafion membrane.

Heterogeneous Fenton Catalyst for the Efficient Removal of Azo Dyes in Water

“…The process can be conducted both homogeneously [1]- [5] and heterogeneously [6]- [25]. Despite its proven efficiency, advanced oxidation processes have some disadvantages, such as production of sludge with a high content in iron and iron deactivation by the formation of complexing agents.…”

“…For these purposes, various supports such as nafion [6], zeolite [7]- [11], silica [12], clay [13], resins, and activated carbon [14] [15] have been used to prepare novel heterogeneous Fenton catalysts. In heterogeneous phase, the physical steps in addition to chemical changes take place on the surface of the catalyst at the active sites where mass transfer limited adsorption of reactant molecules occurs.…”

Decolorization of KN-R catalyzed by Fe-containing Y and ZSM-5 zeolites

“…But it has the shortcoming that Fe ions remain in the treated water, and additional step is needed to remove them. Efforts have been made to develop heterogeneous Fenton-like catalysts to overcome this shortcoming, which include supported Fe ions, clusters or oxides [3][4][5][6][7][8][9][10]. Mesoporous molecular sieves have drawn much attention due to their great surface area, high uniformity and easily controllable pore size.…”

Study on Sono-Photocatalytic Degradation of POPs: A Case Study Hydrating Polyacrylamide in Wastewater

“…Therefore, a lot of effort has been made in developing heterogeneous photo-Fenton catalysts. For example, Parra et al prepared Nafion/Fe structured membrane catalyst and used it in the photo-assisted immobilized Fenton degradation of 4-chorophenol (Parra et al, 2004). However, Nafion/Fe structured membrane catalyst is much expensive for practical use.…”