Abstract Carbon materials with unique sp 2 ‐hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom‐up” strategy by pyrolysis of graphitic carbon nitride (g‐C 3 N 4 ) (or other carbon/nitrogen (C, N)‐enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon‐based catalysts with tunable morphologies, including carbon nano‐balls, carbon nanotubes, nitrogen/sulfur (S, N) doped‐carbon nanosheets, and single‐atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric‐gas chromatography‐mass spectrometry measurements indicates that the release of C─N‐related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g‐C 3 N 4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon‐based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses.
Nanorods of MoO3 are accessible in gram quantities from MoO3·2H2O via a flexible one-step solvothermal reaction. Several hours of treatment in water at 180 °C are sufficient to convert the starting material quantitatively into rods with diameters around 100 nm and microscale lengths. The formation of MoO3 rods proceeds in both neutral ionic and acidic media within a wide parameter window encompassing reaction temperatures between 90 and 180 °C and time scales ranging from several hours to 7 d. The rod morphology can be tuned by selecting a proper additive, and the nanorods withstand heating to 400 °C. Furthermore, the reaction pathways in various solvothermal media were investigated and both intermediate molybdic acids and the bulk nanorod products were characterized by means of EXAFS spectroscopy.
We introduce the novel Co4O4 complex [CoII4(hmp)4(μ-OAc)2(μ2-OAc)2(H2O)2] (1) (hmp = 2-(hydroxymethyl)pyridine) as the first Co(II)-based cubane water oxidation catalyst. Monodentate acetate and aqua ligands lend the flexible environment of 1 closest resemblance to photosystem II among its tetranuclear mimics to date. Visible-light-driven catalytic activity of 1 increases with pH value through aqua ligand deprotonation. The Co(II) core combines robustness and stability with flexibility through a new type of water-oxidation mechanism via mobile ligands.
Although the {CaMn4O5} oxygen evolving complex (OEC) of photosystem II is a major paradigm for water oxidation catalyst (WOC) development, the comprehensive translation of its key features into active molecular WOCs remains challenging. The [Co(II)3Ln(hmp)4(OAc)5H2O] ({Co(II)3Ln(OR)4}; Ln = Ho-Yb, hmp = 2-(hydroxymethyl)pyridine) cubane WOC series is introduced as a new springboard to address crucial design parameters, ranging from nuclearity and redox-inactive promoters to operational stability and ligand exchange properties. The {Co(II)3Ln(OR)4} cubanes promote bioinspired WOC design by newly combining Ln(3+) centers as redox-inactive Ca(2+) analogues with flexible aqua-/acetate ligands into active and stable WOCs (max. TON/TOF values of 211/9 s(-1)). Furthermore, they open up the important family of 3d-4f complexes for photocatalytic applications. The stability of the {Co(II)3Ln(OR)4} WOCs under photocatalytic conditions is demonstrated with a comprehensive analytical strategy including trace metal analyses and solution-based X-ray absorption spectroscopy (XAS) investigations. The productive influence of the Ln(3+) centers is linked to favorable ligand mobility, and the experimental trends are substantiated with Born-Oppenheimer molecular dynamics studies.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The predictive hydrothermal synthesis of polyoxometalates (POMs) is an important challenge for their targeted production and for the design of new POM motifs and organic−inorganic POM materials. In this context, the systematic fluorination of POMs remains to be fully explored. Therefore, the structure-directing influence of cation pairs on the primary and secondary structure of polyoxofluoromolybdates(VI) is explored in the present study. In the first step, new types of mixed alkali difluorooctamolybdates ((M, M′)Mo8O26F2·nH2O; M, M′ = K−Cs) illustrate how the choice of the alkali cations controls the resulting structure type. This structure-directing potential of the cations is investigated in terms of electrostatic calculations. The concept of cation pairs as structural "spacers" and "scissors" is then applied to construct new secondary structures from the recently discovered [Mo6O18F6]6− and [Mo7O22F3]5− fluoromolybdate anions. The use of selected bicyclic organic cations (asn = 1-azoniaspiro[4,4]nonane; adu = 1-azonia-4,9-dioxaspiro[5,5]undecane) led to the new organic−inorganic fluoromolybdates asn2Na4Mo6O18F6·6H2O, adu3Na3Mo6O18F6·3H2O and adu4NaMo7O22F3·4H2O. The steering effect of the organic cations in the formation of the layered organic−inorganic structures is compared for all three compounds with respect to their potential as building blocks for constructing POM-based materials.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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