Catalytic degradation of Orange II by UV-Fenton with hydroxyl-Fe-pillared bentonite in water

Although homogeneous photo-Fenton system is a very efficient method for organic wastewater treatment, it suffers from costly pH adjustment as well as difficult separation of catalysts from aqueous in practical application. Through cation exchange reaction, hydroxyl-Fe-pillared bentonite (H-Fe-P-B) was successfully prepared as a solid catalyst for UV-Fenton to degrade non-biodegradable azo-dye Orange II. Compared with raw bentonite, the content of iron, interlamellar distance and external surface area of H-Fe-P-B increased remarkably. H-Fe-P-B had good photosensitivity and catalyst reactivity. And the catalytic activity of H-Fe-P-B for H2O2 came from hydroxyl-Fe between sheets rather than Fe3+ or Fe2+ in tetrahedral or octahedral sheets of bentonite. In UVA–H2O2 system, H2O2 could destroy the azo bond of excited Orange II molecules but could not effectively mineralize it. After 120 min treatment, 83% discoloration was obtained while only 2% of TOC was removed. When H-Fe-P-B was used as catalyst, a significant degradation of Orange II was observed at the same condition as UVA–H2O2 system. Almost 100% discoloration and more than 60% TOC removal of Orange II could be achieved after 120 min treatment. Because of the strong surface acidity and the electronegativity of H-Fe-P-B, the pH range of this catalyst in the Orange II discoloration could be extended up to 9.5. And this catalyst showed good stability during Orange II degradation in water in wide range of pH (3.0–9.5). These results indicated that the H-Fe-P-B was a promising catalyst for UV-Fenton system.