title: Iron in non-hydroxyl radical mediated photochemical processes for dye degradation: Catalyst or inhibitor?
abstract: The acetylacetone (AA) mediated photochemical process has been proven as an efficient approach for decoloration. For azo dyes, the UV/AA process was several to more than ten times more efficient than the UV/H2O2 process. Iron is one of the most common elements on the earth. It is well known that iron can improve the UV/H2O2 process through thermal Fenton and photo-Fenton reactions. What will be the role of iron in the UV/AA process? Could iron-AA complexes act as photocatalysts in environmental remediation? To answer these questions, the photo-degradation of an azo dye, Acid Orange 7 (AO7), was conducted under the variant combinations of AA with iron species in both ionic (Fe2+, Fe3+) and complex (Fe(AA)3) forms. The pseudo-first-order decoloration rate constants of AO7 in these photochemical processes followed such an order: UV/Fe(II)/AA<UV/Fe(III)/AA<UV/Fe(AA)3<UV/AA. The results demonstrate that iron species, in either ionic or complex form, acts as an inhibitor rather than a catalyst in the UV/AA process. Based on spectroscopic analysis, the inner filter effect of iron and the competition between Fe(III) and AA for the complexation with AO7 were attributed to the inhibition effect of iron on the UV/AA process. The understanding of the role of iron provides insight into the practical application of the UV/AA process.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Bingdang
authors.initials: B
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China. Electronic address: sjzhang@nju.edu.cn.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Xuchun
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, MD 21218-2686, United States.
authors.forename: Xitong
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Bingcai
authors.initials: B
authors.lastname: Pan
mesh_terms: D001391:Azo Compounds / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D001557:Benzenesulfonates / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D002384:Catalysis; D004396:Coloring Agents / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D056831:Coordination Complexes / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D010422:Pentanones / Q000737:chemistry*; D055668:Photochemical Processes; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D004396:Coloring Agents; D056831:Coordination Complexes; D005290:Ferric Compounds; D005296:Ferrous Compounds; D010422:Pentanones; D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; C008790:acetylacetone; D006861:Hydrogen Peroxide; D007501:Iron; C014722:2-naphthol orange
keywords: Acetylacetone; Catalyst; Photodegradation; UV/Fenton; UV/H(2)O(2)