Synthesis, characterization and photocatalytic activity of MCM-41 mesoporous adsorbents modified with chromium, iron and titanium

ELIAS V; VASCHETTO V; CRIVELLO M; HERRERO E; SAPAG K; CASUSCELLI S; EIMER G

San Pedro

Simposio; Fifth San Luis Symposium on Surfaces, Interfaces and Catalysis.; 2010

Mesoporous adsorbents with MCM-41 structure have been prepared and modified with Cr, Feand Ti by wet impregnation method. Various techniques including XRD, UVvis-DR, ICP and N2adsorption are employed for the adsorbents characterization. All materials presented diffractionpeaks corresponding to the hexagonal arrangement typical of the MCM-41 structure. The surfaceareas were high for all the materials (around 1000 m2/g). Both parameters, the structure orderand surface area, were affected when Cr, Fe and Ti were loaded on the MCM-41 structure. TheUVvis-DR spectrum of pure siliceous MCM-41 does not contain any bands. When this materialwas modified with Cr and Fe the UVvis spectra were completely different. The Cr-modifiedmaterials UVvis-DR spectra present higher absorption in the visible range than the Fe-modified.For both (Cr and Fe-modified mesoporous molecular sieves) the addition of TiO2 furtherenhanced their absorption at longer wavelengths. The adsorbent synthesized were evaluated asphotocatalyst in the Acid Orange 7 (AO7) degradation. Under UVvis radiation the TiO2/Cr/Mphotocatalytic activity was similar to that observed using commercial TiO2 bulk. When onlyvisible radiation was used instead, the catalysts modified with Cr showed significant activity. Inparticular, when TiO2/Cr/M catalyst was used a degradation of about 65% at 5 h of reaction wasachieved. When a semiconductor act as a photo-catalyst a hole-electron par must be created onits surface. Then, this par can interact with hydroxyl and oxygen adsorbed in the surface causingthe organic compound degradation. High energy fotons (!<380 nm) are necessary for electronholepar creation when TiO2 is used as photo-catalyst. The TiO2/Cr/M high activity undervisible light is probably by the heterojunction between the tetrahedrically coordinated Cr(VI)species and the TiO2 particles incorporated on the MCM-41 materials. The Cr(VI) could act asan energy level and could be the responsible for the hole-electron par creation on the surroundingTiO2 with low energy fotons (!<400 nm).