Semiconductor photocatalysis under natural sunlight is an emergent area in contemporary materials research, which has attracted considerable attention toward the development of catalysts for environmental remediation using solar energy. A series of five-layer Aurivillius-phase perovskites, Bi 5 ATi 4 FeO 18 (A = Ca, Sr, and Pb), are synthesized for the first time. Rietveld refinements of the powder X-ray diffraction data indicated orthorhombic structure for the Aurivillius phases with Fe largely occupying the central octahedral layer, whereas the divalent cations (Ca, Sr, and Pb) are statistically distributed over the cubo-octahedral A-sites of the perovskite. The compounds with visible-light-absorbing ability ( E g ranging from ∼2.0 to 2.2 eV) not only exhibit excellent collective photocatalytic degradation of rhodamine B–methylene blue (MB) and rhodamine B–rhodamine 6G mixture at pH 2 but also show almost 100% photocatalytic selective degradation of MB from the rhodamine B–MB mixture at pH 11 under natural solar irradiation. The selectivity in the alkaline medium is believed to originate from the combined effect of the photocatalytic degradation of MB by the Aurivillius-phase perovskites and the photolysis of MB. Although a substantial decrease in MB adsorption from the mixed dye solution (MB + RhB) together with slower MB photolysis at the neutral pH makes the selective MB degradation sluggish, the compounds showed excellent photocatalytic degradation activity and chemical oxygen demand removal efficacy toward individual RhB (at pH 2) and MB (at pH 11) under sunlight irradiation. The catalysts are exceptionally stable and retain good crystallinity even after five successive cyclic runs without any noticeable loss of activity in both the acidic and alkaline media. The present work provides an important insight into the development of layered perovskite photocatalysts for collective degradation of multiple pollutants and selective removal of one or multiple pollutants from a mixture. The later idea may open up new possibilities for recovery/purification of useful chemical substances from the contaminated medium through selective photocatalysis.

Developing highly efficient catalysts for chemoselective oxidation of methane to methanol under mild conditions is a grand challenge. We report the successful design and synthesis of a heterogeneous single-site cobalt hydroxide catalyst [Ce-UiO-Co­(OH)] supported by the nodes of a cerium metal–organic framework (Ce-UiO-66 MOF), which is efficient in partial methane oxidation using hydrogen peroxide at 80 °C, giving an extraordinarily high methanol yield of 2166 mmol gcat –1 in 99% selectivity with a turnover number of 3250. The Ce-UiO-Co catalyst is significantly more active and selective than its iso-structural zirconium analogue Zr-UiO-Co in methane to methanol conversion. Experimental and computational studies suggest the formation of the CoIII(η2-hydroperoxide) intermediate coordinating with one μ4-O– and two neutral carboxylate oxygens of Ce4+ oxo nodes within the pores of Ce-UiO-66, which undergoes σ-bond metathesis with the methane C–H bond in the turnover limiting step of the catalytic cycle. The significantly lower activation energy of Ce-UiO-Co than Zr-UiO-Co is due to the highly electron-deficient nature of the cobalt ion of the Co­(η2-O2H) species supported by the Ce-UiO nodes, which promotes facile C–H activation of methane via σ-bond metathesis. This MOF-based catalyst design holds promise in developing molecular electrophilic abundant metal catalysts for chemoselective functionalization of saturated hydrocarbons.

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The overall photocatalytic activity shown by a semiconductor photocatalyst stems from a complex interplay of several critical factors that includes light absorption, carrier recombination dynamics, charge transfer resistance, lifetime of...

We report a metal-organic framework (MOF) supported monoligated phosphine-cobalt complex, which is an active heterogeneous catalyst for aromatic CÀ H borylation and alkene hydroboration. The mono(phosphine)-Co catalyst (MOFÀ PÀ Co) was prepared by metalation of a porous triarylphosphine-functionalized MOF (MOFÀ P) with CoCl 2 followed by activation with NaEt 3 BH. The MOF catalyst has a broad substrate scope with excellent functional group tolerance to afford arene-and alkylboronate esters in excellent yields and selectivity. MOFÀ PÀ Co gave a turnover number (TON) of 30,000 and could be recycled and reused at least 13 times in arene CÀ H borylation. Importantly, the attempt to prepare the homogeneous control (Ph 3 PÀ Co) using triphenylphosphine was unsuccessful due to the facile disproportionation reactions or intermolecular ligand exchanges in the solution. In contrast, the site isolation of the active mono(phosphine)-Co species within the MOF affords the robust and coordinatively unsaturated metal complexes, allowing to explore their catalytic properties and the reaction mechanism.