In order to understand the degradation pathway and intermediates that are formed during photocatalytic process for phenol decomposition, LC–MS analysis (Fig. 10) is carried out on supernatant obtained after 100 min from reactor. The chromatographic pattern of the colorless supernatant (Fig. 10a) revealed the presence of two compounds at 2.129 and 2.457 retention times while their corresponding masses (m/e) are found to be 146.06 and 370.12, respectively. Such a degradation of phenol can be explained on the basis of Advanced Oxidation Processes (AOPs) promoted by heterogeneous photocatalyst through oxidative mineralization of most of the organic pollutants. This process involves [38]: (a) absorption of efficient photons by ZnO–clay nanocomposite, (b) oxygen adsorption followed by generation of superoxide radicals, (c) generation of [H] atoms through photoelectrons, (d) formation of hydroxyl radicals from transient hydrogen peroxide and (e) oxidation of organic molecule via successive attack of OH• radicals. Two oxidative reagents are usually found to be associated with such photo-degradation process, namely, photo-produced holes h+ “Photo-Kolbe” and the OH• radicals, which are highly reactive and degrading but non-selective agents. Moreover, the reductive process also takes place through photo-generated hydrogen atom from water.
In order to understand the degradation pathway and intermediates that are formed during photocatalytic process for phenol decomposition, LC–MS analysis (Fig. 10) is carried out on supernatant obtained after 100 min from reactor. The chromatographic pattern of the colorless supernatant (Fig. 10a) revealed the presence of two compounds at 2.129 and 2.457 retention times while their corresponding masses (m/e) are found to be 146.06 and 370.12, respectively. Such a degradation of phenol can be explained on the basis of Advanced Oxidation Processes (AOPs) promoted by heterogeneous photocatalyst through oxidative mineralization of most of the organic pollutants. This process involves [38]: (a) absorption of efficient photons by ZnO–clay nanocomposite, (b) oxygen adsorption followed by generation of superoxide radicals, (c) generation of [H] atoms through photoelectrons, (d) formation of hydroxyl radicals from transient hydrogen peroxide and (e) oxidation of organic molecule via successive attack of OH• radicals. Two oxidative reagents are usually found to be associated with such photo-degradation process, namely, photo-produced holes h+ “Photo-Kolbe” and the OH• radicals, which are highly reactive and degrading but non-selective agents. Moreover, the reductive process also takes place through photo-generated hydrogen atom from water.
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