Controllable Synthesis of Various CaCO₃ Morphologies Based on a CCUS Idea

A novel, green, and economic CaCO₃ synthesis method using a CO₂-storage material (CO₂SM) was developed based on the strategy of carbon capture, utilization, and storage (CCUS). In this process, CO₂SM was used as both a CO₂ source and a crystal modifier to regulate and control the crystallization of CaCO₃. 1,4-Butanediol (BDO) and/or 1,2-ethanediamine (EDA) from CO₂SM played unexpected roles as a surfactant, structure-directing agent, and/or pH modulator. The effects of CO₂SM concentrations, reaction temperatures, and reaction times were systematically investigated. Pure calcite (bundle-like and dumbbell-like) and pure vaterite (oblate spheroid and snowball-like) CaCO₃ products were obtained. Moreover, the CO₂SM was recycled to prepare same crystal phase CaCO₃ upon the addition of an appropriate amount of Ca­(OH)₂ with 120 g·L^–1 CO₂SM concentration

<i>A</i>‑Site-Doping Enhanced <i>B</i>‑Site Ordering and Correlated Magnetic Property in La_2–<i>x</i>Bi_<i>x</i>CoMnO₆

A series of Bi-doped La_2–<i>x</i>Bi_<i>x</i>CoMnO₆ double perovskite oxides are synthesized, and the impact of doping on crystal structures and magnetic properties is investigated comprehensively. X-ray photoelectron spectroscopy and Raman spectrum analyses reveal that ordering of Co and Mn ions at <i>B</i>-site is gradually improved with the rise of Bi concentration. Meanwhile, magnetic disordering is suppressed greatly by showing larger magnetic moments. Structurally, the Rietveld refinement shows that the bonds are elongated, while the bond angles are shrunken after doping, giving rise to lowered Curie temperature. We also observe a large negative zero-field-cooling magnetization, which is attributed to the formation of spin antiparallel or canted ferromagnetic domains and clusters that are separated by the antiphase boundaries. First-principles calculations confirm the enhanced Co–Mn ordering upon Bi doping by taking into account both the ordering and disordering configurations of La₂CoMnO₆, LaBiCoMnO₆, and Bi₂CoMnO₆. Moreover, we find a spin-state transition in the antisite Co ions from high-spin (Co²⁺-t_2g⁵e_g²) to low-spin state (Co³⁺-t_2g⁶e_g⁰), which is consistent with the increased total magnetic moments by the Bi doping

General Synthesis of MOF Nanotubes via Hydrogen-Bonded Organic Frameworks toward Efficient Hydrogen Evolution Electrocatalysts

The application scope of metal–organic frameworks (MOFs) can be extended by rationally designing the architecture and components of MOFs, which can be achieved via a metal-containing solid templated strategy. However, this strategy suffers from low efficiency and provides only one specific MOF from one template. Herein, we present a versatile templated strategy in which organic ligands are weaved into hydrogen-bonded organic frameworks (HOFs) for the controllable and scalable synthesis of MOF nanotubes. HOF nanowires assembled from benzene-1,3,5-tricarboxylic acid and melamine via a simple sonochemical approach serve as both the template and precursor to produce MOF nanotubes with varied metal compositions. Hybrid nanotubes containing nanometal crystals and N-doped graphene prepared through a carbonization process show that the optimized NiRuIr alloy@NG nanotube exhibits excellent electrocatalytic HER activity and durability in alkaline media, outperforming most reported catalysts. The strategy proposed here demonstrates a pioneering study of combination of HOF and MOF, which shows great potential in the design of other nanosized MOFs with various architectures and compositions for potential applications