Immobilization of halogenated porphyrins and their copper complexes in MCM-41: Environmentally friendly photocatalysts for the degradation of pesticides

MCM-41 immobilized (ship-in-a-bottle) meso-tetrakis(2-fluorophenyl)porphyrin, TFPP@MCM-41, and meso-tetrakis(2,6-dichlorophenyl)porphyrin, TDCPP@MCM-41, and the corresponding copper metal complexes, CuTFPP@MCM-41 and CuTDCPP@MCM-41, were successfully synthesized by the condensation of pyrrole with the desired benzaldehydes, using the nitrobenzene method, in the absence or presence of copper salt, respectively. Their characterization was performed by DRS-UV–vis, luminescence, EPR, ATR-FTIR spectroscopies, PXRD, TG/DTA, nitrogen adsorption analysis and elemental analysis. All the immobilized porphyrins TFPP@MCM-41, TDCPP@MCM-41, CuTFPP@MCM-41 and CuTDCPP@MCM-41 were tested in the photodegradation of 2,4,6-trimethylphenol and TFPP@MCM-41 showed the best performance. The studies were extended to the photodegradation of pesticides fenamiphos and diuron using TFPP@MCM-41 as photocatalyst and the photoproducts were identified by LC–MS. Mechanistic studies, using furfuryl alcohol as singlet oxygen trap revealed that there was no involvement of this species in the photodegradation of the above mentioned pesticides and the identified photoproducts are consistent with a radical mechanism. An efficient photolysis of the pesticides after 5 h, in aerated aqueous solutions, was observed with TFPP@MCM-41 with no loss of the photocatalytic activity over recycling. These heterogeneous photocatalysts with no significant decomposition of the porphyrin make them promising candidates for water treatment.