The photochemically assisted Fenton reaction (photo-Fenton) is important because it may be particularly effective for the degradation of harmful organic compounds in the environment using solar light. The purpose of the present study was to determine the effectiveness of hydroxy Fe/Al-intercalated montmorillonites (Fe/Al-Mt) as photo-Fenton catalysts. In particular, different Fe/Al molar ratios were of interest as a means to vary catalytic activity. Intercalation was achieved via an ion-exchange method and brilliant orange X-GN was the test compound for photodegradation by hydrogen peroxide (H2O2) under visible-light irradiation (γ < 420 nm) in the presence of Fe/Al-Mt. The Fe/Al-Mt materials obtained were characterized by powder X-ray diffraction, N2 adsorption/desorption, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopic analysis, and ultraviolet-visible spectroscopy. The decoloration performance of Fe/Al-Mt was investigated using different experimental parameters, including the synthesis method, the Fe/Al molar ratio of the intercalating solution, the catalyst dosage, the H2O2 dosage, and the pH. The results of photo-Fenton reaction showed that the photocatalytic activity of Fe/Al-Mt was enhanced significantly by the extent of hydroxy Al/Fe intercalation. For optimal reaction conditions, 99.92% degradation efficiency of X-GN was achieved after 140 min of reaction. To obtain further information on the visible-light-assisted photo-Fenton process, a high-performance liquid chromatography-mass spectrometry method was applied to indentify the intermediate products and a degradation pathway was proposed.

The chemical, textural and structural transformations of Al13-intercalated montmorillonite, resulting from the depolymerization of the interlamellar Al13 polycations by Na salicylate solutions, were studied. Nitrogen gas adsorption shows a dramatic decrease in specific surface area from 493 to 39 m2g–1, due to the loss of microporosity. Modelling of small-angle X-ray scattering (SAXS) curves shows that the final product contains two phases: a Na-exchanged swelling phase accounting for 40% of the clay, and a fixed interlayer distance (20.8 Å ) phase accounting for 60% of the clay. The Al remaining in the clay galleries (45% of the initial Al) is composed of 13% Al13– and 87% hexacoordinated Al, probably Al(OH)03 and oligomeric Al-salicylate complexes, as shown by 27Al NMR. The instability of Al13-intercalated montmorillonite towards organic ligands is related to the hydration shell of the tridecamer, revealed by SAXS. These results focus on the necessity to take into account the presence of organic ligands in natural media when using materials such as Al13-intercalated clays.