Highly active iron-containing silicotungstate catalyst for heterogeneous Fenton oxidation of 4-chlorophenol

Polyoxometalates (POMs) have been a class of attractive redox catalysts and photocatalysts, but so far, there have been few reports on application of POMs in Fenton (or Fenton-like) oxidation processes. In this context, an iron-containing silicotungstate (Fe(III)AspSiW) was synthesized using ferric chloride (FeCl3, Fe-III), aspartic acid (C4H7NO4, Asp) and silicotungstic acid (H4SiW12O40 center dot xH(2)O, SiW) as raw materials and employed as a heterogeneous catalyst for Fenton oxidizing 4-chlorophenol (4-CP). The chemical formula of Fe(III)AspSiW is speculated as [Fe(C4H5NO4)](3.5)H(0.5)SiW(12)O(40 center dot)14H(2)O with Keggin-structured SiW12O404- anion. The FeIIIAspSiW catalyst showed high activity for oxidation of 4-CP by H2O2 ranging from acidic to circumneutral pHs under both the dark and irradiated conditions. Besides, the catalyst also exhibited good regenerability without significant performance drop. The catalytic mechanism in non-irradiated system was related to the Fenton-like catalysis of ferric iron in Fe(III)AspSiW. Moreover, the enhanced degradation of 4-CP under irradiation was attributed to the synergistic effect of Fenton-like catalysis of ferric iron and photocatalysis of SiW12O404- anions in FeIIIAspSiW.