Lead-Free Cs3 Bi2 Br9 Perovskite as Photocatalyst for Ring-Opening Reactions of Epoxides

Herein, an innovative approach was developed by using stable, lead-free halide perovskite for solar-driven organic synthesis. The ring-opening reaction of epoxides was chosen as a model system for the synthesis of value-added β-alkoxy alcohols, which require energy-intensive process conditions and corrosive, strong acids for conventional synthesis. The developed concept included the in situ preparation of Cs₃ Bi₂ Br₉ and its simultaneous application as photocatalyst for epoxide alcoholysis under visible-light irradiation in air at 293 K, with exceptional high activity and selectivity ≥86 % for β-alkoxy alcohols and thia-compounds. The Cs₃ Bi₂ Br₉ photocatalyst exhibited good stability and recyclability. In contrast, the lead-based perovskite showed a conversion rate of only 1 %. The origin of the unexpected catalytic behavior was attributed to the combination of the photocatalytic process and the presence of suitable Lewis-acidic centers on the surface of the bismuth halide perovskite photocatalyst.

Serpentinization: Connecting Geochemistry, Ancient Metabolism and Industrial Hydrogenation

Rock⁻water⁻carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe₃O₄) plus H₂. The hydrogen can generate native metals such as awaruite (Ni₃Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H₂ and CO₂ under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate-intermediates of the acetyl-CoA pathway, the most ancient pathway of CO₂ fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni⁰ in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO₂-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase-the only enzyme on Earth that reduces N₂-is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe₃O₄ and H₂, the catalyst and reductant for industrial CO₂ hydrogenation and for N₂ reduction via the Haber⁻Bosch process. In both industrial processes, an Fe₃O₄ catalyst is matured via H₂-dependent reduction to generate Fe₅C₂ and Fe₂N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways.

A CsPbBr3 /TiO2 Composite for Visible-Light-Driven Photocatalytic Benzyl Alcohol Oxidation

Halide perovskites have attracted great attention in the fields of photovoltaics, LEDs, lasers, and most recently photocatalysis, owing to their unique optoelectronic properties. The all-inorganic halide perovskite CsPbBr₃ /TiO₂ composite material catalyzes selective benzyl alcohol oxidation to benzaldehyde under visible-light illumination. The catalyst, which is prepared by a facile wet-impregnation method, shows very good selectivity towards benzaldehyde (>99 % at 50 % conversion). Action spectra and electron spin resonance (ESR) studies reveal that photoexcited electrons formed within CsPbBr₃ upon visible-light illumination take part in the reaction via reduction of oxygen to form superoxide radicals. The detailed post-catalysis characterization by UV/Vis and X-ray photoelectron spectroscopy, X-ray diffraction, and high-angle annular dark-field scanning transmission electron microscopy studies further demonstrated the good stability of CsPbBr₃ in terms of morphology and crystal structure under the reaction conditions. This study sheds light on promising new photocatalytic applications of halide perovskites.

Coffee-Waste Templating of Metal Ion-Substituted Cobalt Oxides for the Oxygen Evolution Reaction

A facile and scalable method using coffee waste grounds as a hard template has been developed to fabricate nanostructured Co₃ O₄ for the oxygen evolution reaction (OER). Co₃ O₄ incorporating metals with different valences (M/Co=1:4; M=Cu, Ni, Fe, Cr, and W) were also prepared with similar sheet-like structures comprising nanosized crystallites. After detailed characterization by X-ray diffraction, electron microscopy, and nitrogen sorption, the oxides were employed as OER electrocatalysts. Substitution of octahedral and tetrahedral sites of the spinel structure with divalent and trivalent transition metals (Cu, Ni, Fe, and Cr) increased the activity of Co₃ O₄ for the OER, whereas incorporation of hexavalent W led to formation of a second crystal phase and significantly higher electrocatalytic performance. Furthermore, this method is easily scaled up for mass production of Co₃ O₄ with the same nanostructure, which is highly desirable for large-scale application.

Structural effects on optoelectronic properties of halide perovskites

This review gives a perspective on different synthetic methodologies for the preparation of halide perovskites and highlights the structural effects on their optoelectronic properties.

Promoting effect of solvent on Cu/CoO catalyst for selective glycerol oxidation under alkaline conditions

Cu/CoO catalysts were employed for the selective oxidation of glycerol in the aqueous phase under basic conditions.

Iron-Induced Activation of Ordered Mesoporous Nickel Cobalt Oxide Electrocatalyst for the Oxygen Evolution Reaction

Herein, ordered mesoporous nickel cobalt oxides prepared by the nanocasting route are reported as highly active oxygen evolution reaction (OER) catalysts. By using the ordered mesoporous structure as a model system and afterward elevating the optimal catalysts composition, it is shown that, with a simple electrochemical activation step, the performance of nickel cobalt oxide can be significantly enhanced. The electrochemical impedance spectroscopy results indicated that charge transfer resistance increases for Co₃O₄ spinel after an activation process, while this value drops for NiO and especially for CoNi mixed oxide significantly, which confirms the improvement of oxygen evolution kinetics. The catalyst with the optimal composition (Co/Ni 4/1) reaches a current density of 10 mA/cm² with an overpotential of a mere 336 mV and a Tafel slope of 36 mV/dec, outperforming benchmarked and other reported Ni/Co-based OER electrocatalysts. The catalyst also demonstrates outstanding durability for 14 h and maintained the ordered mesoporous structure. The cyclic voltammograms along with the electrochemical measurements in Fe-free KOH electrolyte suggest that the activity boost is attributed to the generation of surface Ni(OH)₂ species that incorporate Fe impurities from the electrolyte. The incorporation of Fe into the structure is also confirmed by inductively coupled plasma optical emission spectrometry.

Selective glycerol oxidation over ordered mesoporous copper aluminum oxide catalysts

Ordered mesoporous Cu–Al₂O₃ catalysts were employed for the selective oxidation of glycerol into value-added products. Co-solvents such as ethanol, 1-propanol, and tert-butanol strongly improve the reaction kinetics.

Spent Tea Leaf Templating of Cobalt-Based Mixed Oxide Nanocrystals for Water Oxidation

The facile synthesis of nanostructured cobalt oxides using spent tea leaves as a hard template is reported. Following an impregnation-calcination and template removal pathway, sheetlike structures containing nanosized crystallites of Co₃O₄ are obtained. Co₃O₄ incorporated with Cu, Ni, Fe, and Mn (M/Co = 1/8 atomic ratio) are also prepared, and the materials are thoroughly characterized using X-ray diffraction, electron microscopy, and N₂ sorption. The method is applicable to several commercial tea leaves and is successfully scaled up to prepare over 7 g of Co₃O₄ with the same nanostructure. The oxides are then tested for electrochemical water oxidation, and Cu, Ni, and Fe incorporations show beneficial effect on the catalytic activity of Co₃O₄, achieving performance comparable to levels from benchmark electrocatalysts. These data suggest that tea leaf templating can be utilized as a facile and promising approach to prepare nanostructured functional catalyst.

Preparation of Organometal Halide Perovskite Photonic Crystal Films for Potential Optoelectronic Applications

Herein, a facile method for the preparation of organometal halide perovskite (OHP) thin films in photonic crystal morphology is presented. The OHP photonic crystal thin films with controllable porosity and thicknesses between 2 μm and 6 μm were prepared on glass, fluorine-doped tin oxide (FTO), and TiO2 substrates by using a colloidal crystal of polystyrene microspheres as a template to form an inverse opal structure. The composition of OHP could be straightforwardly tuned by varying the halide anions. The obtained OHP inverse opal films possess large ordered domains with a periodic change of the refractive index, which results in pronounced photonic stop bands in the visible light range. By changing the diameter of the polystyrene microspheres, the position of the photonic stop band can be tuned through the visible spectrum. This developed methodology can be used as blueprint for the synthesis of various OHP films that could eventually be used as more effective light harvesting materials for diverse applications.