Synthesis of α-Anderson Polyoxometalates-Porphyrin polymeric hybrid as an efficient photosensitizer

Abstract

New metalloporphyrin, [N6O8ZnC54H46](DiT-Zn@DiPP) and its polymeric hybrid with polyoxometalate (POM), [{N(C4H9)4}3n{C54H40N6O26MnMo6Zn}.H2O]n (poly(DiT-DiPP@ADP), bearing covalently linked AD-POM and metalloporphyrin (DiT-Zn@DiPP) subunit in an alternative manner, have been synthesized and rigorously characterized through elemental analysis, FT-IR, UV–visible, 1H NMR spectra, fluorescence studies and cyclic voltammetry. The adsorption and photodegradation efficiency of polymer [{N(C4H9)4}3n{C54H40N6O26MnMo6Zn}.H2O]n has been studied comparatively to previously synthesized POM-porphyrin hybrid ([N(C4H9)4]3[C98H68N10O26MnMo6Zn2].5H2O) T-TriPP@ADP, containing one AD-POM sandwiched between two metalloporphyrin (T-Zn@TriPP) subunit. For the measurement of extent of adsorption and adsorption nature, Langmuir and Freundlich isotherm models have been used. The values of n calculated from Freundlich adsorption isotherm indicate the physical adsorption of cationic dyes (RhB and MB) on both catalysts (poly(DiT-DiPP@ADP) and T-TriPP@ADP). The values of RL calculated from the Langmuir isotherm model also show the favorable adsorption of dyes on the poly(DiT-DiPP@ADP) and T-TriPP@ADP. Both poly(DiT-DiPP@ADP) and T-TriPP@ADP show remarkable photocatalytic degradation of dyes, however poly(DiT-DiPP@ADP) show more photodegradation efficiency in comparison to T-TriPP@ADP due to its polymeric structure. Due to the polymeric nature of poly(DiT-DiPP@ADP) there is a remarkable fluorescence quenching (93 %) in poly(DiT-DiPP@ADP) relative to DiT-Zn@DiPP, indicating more transfer of electrons from DiT-Zn@DiPP to AD-POM moiety within poly(DiT-DiPP@ADP). The LUMO position of poly(DiT-DiPP@ADP) (−3.68 eV) is higher as compared to LUMO of AD-POM (−3.82 eV) which is considered to be accountable for electronic transfer from porphyrin to POM moiety within hybrid. The resulting excited electrons that are produced due to light irradiation during photocatalytic experiment are responsible for production of active species (h+, 1O2, OH●, O2–●) from water and dissolved oxygen. The experimental data for photodegradation is well fitted in first order linear equation as values of correlation constant (R2), for poly(DiT-DiPP@ADP) catalyst are 0.98, 0.96, 0.98 (MB), 0.97, 0.99, 0.98 (RhB) and for T-TriPP@ADP catalyst are 0.97, 0.99, 0.99 (MB), 0.95, 0.99, 0.99 (RhB), indicating pseudo first order reaction.