Accelerated photobleaching of Orange II on novel (H5FeW12O4010H2O)/silica structured fabrics

• Published in: Water research (Oxford) 2004-09, Vol.38 (16), p.3541-3550
• Main Authors: Li, D., Yuranova, T., Albers, P., Kiwi, J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Azo Compounds - chemistry; Azo Compounds - isolation & purification; Benzenesulfonates - chemistry; Benzenesulfonates - isolation & purification; Coloring Agents - chemistry; Coloring Agents - isolation & purification; Exact sciences and technology; Fe-polyoxymetalates in solution; Fe-polyoxymetalates on silica fabrics; Industrial wastewaters; Orange II; Oxidation-Reduction; Photobleaching; Photochemistry; Photodegradation; Pollution; Polymers; Silicon Dioxide; Tungsten - chemistry; Visible light; Wastewaters; Water Purification - methods; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2004.05.005

This study addresses the photobleaching (discoloration) and total organic carbon (TOC) reduction of the non-biodegradable azo-dye Orange II with H5FeW12O40 in homogeneous solution and on H5FeW12O40/silica-structured fabrics in heterogeneous processes. The H5FeW12O40/silica fabric is able to catalyze Orange II bleaching only under light irradiation. In the dark, long-lived intermediates produced in solution were observed to preclude further degradation. The most efficient polytungstate was selected based on the performance during Orange II photobleaching in the presence of H2O2. The H5FeW12O40/silica fabric needed ∼60min to photobleach 85% of an Orange II (0.2mM) solution. The amount of H2O2 and the pH was optimized for the photobleaching of Orange II on the H5FeW12O40/silica fabric. The photobleaching was more efficient as the intensity of the applied light was increased. Repetitive photobleaching cycles of Orange II (0.2mM) on the H5FeW12O40/silica-structured fabric proceeded with the same kinetics, showing the stability of this fabric against oxidative radical attack and the absence of Fe-ions leaching into the solution during Orange II discoloration. The photobleaching times were similar for different concentrations of Orange II suggesting that it is controlled by mass transfer and not by a diffusion-controlled processes. The loading of the silica fabric was determined by elemental analysis to be 7.1% for Fe and 27.2% for W. By electron diffuse spectrometry W-clusters were identified on the silica fabrics and by high-resolution electron microscopy the W-clusters of the catalyst were observed to have sizes between 1 and 2nm. By X-ray photoelectron spectroscopy, it is observed that the W-oxidation state is higher for the unused catalysts than in the catalyst after Orange II photobleaching. This lends support to a photo-assisted Fenton-like mechanism taking place in the H5FeW12O40/ silica-structured fabrics during Orange II decomposition.