Decolorization of organic dyes by zero-valent iron in the presence of oxalic acid and influence of photoirradiation and hexavalent chromium

• Fe0/OA/DO is more effective in decolorization of MB than Fe0/EDTA/DO.
• Photo-assisted Fe0/OA/DO is effective in decolorization of OII.
• OII and Cr(VI) can be simultaneously removed in photo-assisted Fe0/EDTA/DO.

In the present study, zero-valent iron (Fe0) film coated on indium tin oxide (ITO)-coated glass substrate was prepared with electrodeposion. Decolorization of methylene blue (MB) and orange II (OII) by the Fe0 film in the presence of oxalic acid (OA) and dissolved oxygen (DO) and the influence of photoirradiation and hexavalent chromium (Cr(VI)) has been investigated. The newly developed Fe0/OA/DO system is more effective in decolorization of MB than its EDTA counterpart, and is of a strong stability in prolonged use. Operating parameters such as pH and OA concentration have significant influence on the decolorization rate for MB in this system, and lower pH value and higher OA concentration are favorable. The low decolorization rate for OII can be dramatically enhanced by introduction of photoirradiation into the system. Coexistence of Cr(VI) has an opposite influence on decolorization of MB and OII in the photo-assisted Fe0/OA/DO system. In the latter case, Cr(VI) promotes the decolorization of OII, and itself can also be reduced, which allows effective simultaneous removal of OII and Cr(VI) from a mixed solution. Several mechanisms involved in decolorization of MB and OII have also been discussed.

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