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Photocatalytic properties of disordered birnessite-like Mn oxides deposited on the zeolite Y surface is investigated. Synthesis was carried out by ion-exchanging Mn 2 + along with M 2 + = Ba 2 + , Sr 2 + , Ca 2 + , Mg 2 + into zeolite, followed by precipitation of nanosized Mn oxides on the zeolite surface after reaction with KMnO 4 . These samples are labeled M 2 + MnO x -Y, and they were treated with K + to prepare KMnO x -Y(M 2 + ). XRD, XPS, Raman, and electron microscopy provided information on the comparative structural features for M 2 + MnO x -Y and KMnOx-Y(M 2 + ).Photocatalytic water oxidation using these samples was evaluated using Ru(bpy) 3 2 + -S 2 O 8 2À system. The catalytic activity of KMnOx-Y(M 2 + ) is higher than M 2 + MnO x -Y, for comparable Mn loadings, and forms the interesting observation in this paper. For M 2 + MnO x -Y, the catalytic activity normalized to the Mn content followed the order: Ba 2 + > Sr 2 + > Ca 2 + > Mg 2 + and is possibly reflection of the lower Mn loadings, which leads to smaller MnO x crystallites.[a] S.

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By employing laser pulses at various wavelengths for nanosecond flash photolysis, a comprehensive time-resolved study has been performed on transient azomethine ylides photogenerated from several 2,3-diphenyl aziridines in fluid solutions under three different conditions, namely, by direct 266 nm excitation, under reversible electron-transfer sensitization by 1,4-dicyanonaphthalene singlet excited state, and via energy transfer from acetone triplet. Under each of the three conditions of photoexcitation, azomethine ylides are readily formed as transient species, characterized by broad, structureless absorption spectra with maxima at 470-500 nm and mostly complex decay kinetics in μs-ms time domain. Under acetone triplet sensitization, a second, shorter-lived transient species with absorption maximum at ∼360 nm is observed to grow and decay in the same time range as that of the growth of ylides. This species has been identified as the ring-opened precursor ylide triplet. The azomethine ylides are practically nonquenchable by oxygen, except that under acetone triplet sensitization in air-saturated acetonitrile, their decay is significantly enhanced. The latter is explained in terms of quenching through dipolarophilic reaction with singlet oxygen. A value of 1.6 × 10(9) M(-1) s(-1) has been estimated for the rate constant for reaction between singlet oxygen and ylide from trans-2,3-diphenylaziridine. We also report rate constants, in the range 2 × 10(3) to 4 × 10(9) M(-1) s(-1), for the quenching of azomethine ylides by two dipolarophiles, namely, maleic anhydride and dimethyl acetylene dicarboxylate. The dipolarophilic reactivity of ylides carrying bulky substituents on the N atom is relatively subdued. Acetic acid proved to be a modest quencher of ylides with rate constants close to 10(6) M(-1) s(-1).

Study of manganese oxides for electrocatalytic and photocatalytic oxidation of water is an active area of research. The starting material in this study is a high-surface-area disordered birnessite-like material with K + in the interlayers (KMnOx). Upon ion-exchange with Fe 3+ , the disordered layer structure collapses (Fe(IE)MnOx), and the surface area is slightly increased. Structural analysis of the Fe(IE)MnOx included examination of its morphology, crystal structure, vibrational spectra, and manganese oxidation states. Using the Ru(bpy) 3 2+ –persulfate system, the dissolved and headspace oxygen upon visible light photolysis with highly dispersed Fe(IE)MnOx was measured. The photocatalytic activity for O 2 evolution of the Fe(IE)MnOx was three times better than KMnOx, with the highest rate being 9.3 mmol O 2 mol Mn –1 s –1 . The improvement of the photocatalytic activity was proposed to arise from the increased disorder and interaction of Fe 3+ with the MnO 6 octahedra. As a benchmark, colloidal IrO 2 was a better photocatalyst by a factor of ∼75 over Fe(IE)MnOx.