The anodic mineralization/incineration of toxic organic substrates in aquatic media is an important goal in industrial electrochemistry, whose achievements in synthesis and energetics already greatly contribute to the reduction of the environmental impact in chemical production of goods and in energy conversion. Electrochemical incineration of organic pollutants can be attempted by direct or indirect oxidation. Recently, degradation of organophosphorous pesticides has been under study since they are extensively used and have shown to be environmentally persistent. Therefore, electrochemical oxidation of methamidophos (O,S,dimethylphosphor amidothioate: C2H8N02PS), an organophosphorous pesticide, has been studied at Pb/PbO2, Ti/SnO2 and diamond (BDD) anodes. In this work, the electrooxidation of methamidophos was canied out on these anodic materials at 30°C in sodium sulphate aqueous media under different pH conditions and at different current densities of electrolysis. According to reverse phase HPLC studies using UVVis detection, it was found that at pH 2.0 and using a Pb/PbO2 electrode, the concentration of methamidophos decreases from 50 ppm to non-detectable concentrations (less than 5 ppm) during the first 40 minutes of reaction, whereas Ti/SnO2 and diamond are less efficient towards methamidophos oxidation. In basic media (pH 8.5), it was observed that pH decreases as a consequence of hydrogen ions formation. FTIR studies based on attenuated total reflectance (ATR) lead us to confirm that aqueous formaldehyde (IR bands: 1028, 1218, 1368, 1740,2910, and 2971 cm-1), was the main product of reaction when using a Pb/PbO2 anode at pH 2.0 and at 20 mA/cm2. Under the same conditions, SnO2 shows poor formaldehyde production compared to Pb/PbO2, while BDD does not show this species formation. However, FTIR/ATR studies on diamond electrolyses performed at pH 12.0 and at 20 mA/cm2 show the appearance of carbon dioxide (IR bands: 2361 and 2338 cm-1) and phosphate (IR strong bands: 3005 and 1006 cm-1) spectra, which suggest a direct mineralization step of methamidophos.
Electrochemical oxidation of methamidophos in aqueous solutions: Role of electrode material
MARTINEZ, Carlos Alberto;FERRO, Sergio;DE BATTISTI, Achille;
2008
Abstract
The anodic mineralization/incineration of toxic organic substrates in aquatic media is an important goal in industrial electrochemistry, whose achievements in synthesis and energetics already greatly contribute to the reduction of the environmental impact in chemical production of goods and in energy conversion. Electrochemical incineration of organic pollutants can be attempted by direct or indirect oxidation. Recently, degradation of organophosphorous pesticides has been under study since they are extensively used and have shown to be environmentally persistent. Therefore, electrochemical oxidation of methamidophos (O,S,dimethylphosphor amidothioate: C2H8N02PS), an organophosphorous pesticide, has been studied at Pb/PbO2, Ti/SnO2 and diamond (BDD) anodes. In this work, the electrooxidation of methamidophos was canied out on these anodic materials at 30°C in sodium sulphate aqueous media under different pH conditions and at different current densities of electrolysis. According to reverse phase HPLC studies using UVVis detection, it was found that at pH 2.0 and using a Pb/PbO2 electrode, the concentration of methamidophos decreases from 50 ppm to non-detectable concentrations (less than 5 ppm) during the first 40 minutes of reaction, whereas Ti/SnO2 and diamond are less efficient towards methamidophos oxidation. In basic media (pH 8.5), it was observed that pH decreases as a consequence of hydrogen ions formation. FTIR studies based on attenuated total reflectance (ATR) lead us to confirm that aqueous formaldehyde (IR bands: 1028, 1218, 1368, 1740,2910, and 2971 cm-1), was the main product of reaction when using a Pb/PbO2 anode at pH 2.0 and at 20 mA/cm2. Under the same conditions, SnO2 shows poor formaldehyde production compared to Pb/PbO2, while BDD does not show this species formation. However, FTIR/ATR studies on diamond electrolyses performed at pH 12.0 and at 20 mA/cm2 show the appearance of carbon dioxide (IR bands: 2361 and 2338 cm-1) and phosphate (IR strong bands: 3005 and 1006 cm-1) spectra, which suggest a direct mineralization step of methamidophos.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
