The role of water in the photocatalytic degradation of acetonitrile and toluene in gas-solid and liquid-solid regimes

• Format: Article
• Language: English
• Published: Hindawi Limited 2006-01-01
• Series: International Journal of Photoenergy
• Online Access: http://www.hindawi.com/GetArticle.aspx?doi=10.1155/IJP/2006/39182

<p>Photocatalytic degradation of acetonitrile and toluene was carried out both in gas-solid and in liquid-solid regimes by using commercial <mml:math alttext="${ext{TiO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>TiO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> samples (Merck and Degussa P25). The investigation was mainly aimed to study the influence of water present in the reaction environment on the mechanism and degradation rate of two probe molecules. In gas-solid regime, the reacting mixture consisted of toluene or acetonitrile, oxygen, nitrogen, and water vapour. The main degradation product of toluene was <mml:math alttext="${ext{CO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>CO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> with small amounts of benzaldehyde. In the presence of water vapour, the activity of <mml:math alttext="${ext{TiO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>TiO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> Merck remained stable but greatly decreased if water was absent. <mml:math alttext="${ext{TiO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>TiO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> Degussa P25 continuously deactivated, even in the presence of water vapour. With both catalysts, the photodegradation products of acetonitrile were <mml:math alttext="${ext{CO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>CO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> and HCN; the activity was stable and was independent of the presence of water vapour in the reacting mixture. The production of HCN represents a drawback of acetonitrile photocatalytic degradation but the elimination of HCN is not actually a problem. In liquid-solid regime, the main intermediates of toluene photodegradation were <mml:math alttext="$p$"> <mml:mi>p</mml:mi> </mml:math>-cresol and benzaldehyde; traces of pyrogallol and benzyl alcohol were also found. Benzoic acid, hydroquinone, and trans, trans muconic acid were detected only when <mml:math alttext="${ext{TiO}}_{ext{2}} $"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>TiO</mml:mtext> </mml:mrow> <mml:mtext>2</mml:mtext> </mml:msub> </mml:mrow> </mml:math> Merck was used. The photodegradation products of acetonitrile were cyanide, cyanate, formate, nitrate, and carbonate ions.</p>