Simulated sunlight photodegradation of 2-mercaptobenzothiazole by heterogeneous photo-Fenton using a natural clay powder

The efficiency of 2-mercaptobenzothiazole (MBT) degradation by heterogeneous photo-Fenton process using local natural clay powder (NCP) is described. Experiments were conducted at natural pH with a batch reactor equipped with a medium-pressure Hg lamp emitting mainly at 366 nm. The natural clay was characterized by SEM-EDS, UV-vis diffuse reflectance spectroscopy, XRF and XRD analysis. The specific BET surface area of the clay was 30.2 m2 g−1.The photodegradation of MBT follows first order (for direct photolysis) and pseudo-first order kinetics (for photocatalysis). Direct photolysis of MBT showed a negligible effect both upon 254 and 365 nm irradiation, while 42.5% and 62% of MBT was eliminated in three hours under 310 nm irradiation in the presence of H2O2 and under sunlight irradiation (using NCP), respectively. Kinetic runs carried out with 5.0·10−5 M MBT and 0.5 g L−1clay showed both higher MBT conversion and photodegradation rate at basic pH (10) and in oxygen saturated media. The presence of oxalic acid and H2O2 significantly enhanced MBT photodegradation. The photodegradation of MBT is mainly attributed to reaction with HO, leading to different intermediates that have been identified by HPLC-MS. A reaction mechanism is proposed. The highest TOC removals were obtained using UVA at low pHs (2.6), and in the absence of O2 with 68% and 65% TOC removal respectively in two hours, whereas MBT transformation is faster (t½ = 7 min) and higher (90%) at pH = 10. The obtained results strongly support the use of natural clay rich in iron oxides as inexpensive, clean and efficient photocatalysts for water pollutants abatement using heterogeneous photo-Fenton process.