Chemistry of Materials最新文献

Layered ternary (MnX₂Te₄)(X₂Te₃)_n (X = Bi or Sb, n = 0–3) tellurides are intensely studied as perspective magnetic topological insulators: MnBi₂Te₄ and MnBi₄Te₇ demonstrate the quantum anomalous Hall effect up to several Kelvin. To enlarge the temperature range for this quantum behavior, the materials require a net magnetization and a high Curie temperature, T_C. Recently, we found that Mn enrichment and Mn/Sb site intermixing increase the T_C from 30 K in MnSb₂Te₄ to 58 K in Mn_2.01(1)Sb_1.19(1)Te₄. Here, we synthesize the utmost manganese-rich members of this materials family, with an average Mn content of 28–32 at. % and the record T_C = 65–73 K nearing the liquid-nitrogen threshold. By combining single-crystal X-ray diffraction, ab initio modeling and bulk DC magnetization, we pinpoint the relationship between the lattice symmetry and the magnetic order. The trigonal Mn_1.90(1)Sb_1.39(1)Te₄ phase with manganese atoms in the van der Waals gap hosts the highest-T_C ferrimagnetic state. We get the first insights into its electronic structure and topological nature by ab initio modeling using density functional theory. Initiated by the filling of the van der Waals gap, the compound mimics a structural transition from a trigonal (sp. gr. R3̅m) to a cubic lattice (sp. gr. Fm3̅m), which is reminiscent of the structural polymorphism of the Ge–Sb–Te thermoelectrics.

Atomic layer deposition (ALD), with its precise process control and conformality, has recently gained interest for synthesizing transition metal sulfides like MoS₂, which have varied applications in low-dimensional electronics and electrocatalysts. Hydrogen sulfide (H₂S) has been used in many sulfide ALD processes; however, H₂S is a toxic gas that requires expensive containment and abatement measures for shipping, installation, and storage. Herein, we report a PEALD process capable of synthesizing MoS₂ without H₂S. This process utilizes a Mo precursor commonly used in ALD, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is a liquid that is significantly less hazardous and expensive than H₂S. It was found that the TBDS-based PEALD process results in layered, stoichiometric MoS₂ with limited contamination. The TBDS-based PEALD process was also analyzed via mass spectrometry to determine the mechanistic roles of each reactant. Apparently, H₂ plasma removes ligands from the chemisorbed Mo precursor, which allows TBDS to sulfurize the top layer, producing H₂S and isobutene as byproducts. MoS₂ films deposited via the TBDS-based process possessed fewer yet taller out-of-plane growths and similar crystal grain diameter (∼10 nm) and electrical resistivity (13.6–15.5 Ω·cm for 3 nm thick films) compared to films made with H₂S. Thus, the TBDS-based process is a suitable and safer alternative to the H₂S-based process for large-area synthesis of layered MoS₂.

Conferring adsorptive properties to 3D printed materials by functionalizing thermoplastic polymers with metal–organic framework (MOF) materials paves the way for fused deposition modeling (FDM) 3D printing. However, to maintain the flexibility of the filament for printing, a low MOF loading mass (<10 wt %) must be maintained, which undesirably reduces the adsorption capability of the printed materials. In this study, 50 wt % HKUST-1 MOF is loaded into polyethylene glycol dimethyl ether (PEGDME) plasticized polylactic acid (PLA) to form a composite (HK@PLA–PEG-50). The high mass loading is achieved by the introduction of PEGDME as a plasticizer and the preparation of a homogeneous composite slurry. Without the post-printing process, the printed sorbent material with a high surface area of 547 m² g^–1 (49% relative to that of the originally prepared HKUST-1) has a CO₂ adsorption capacity of 37.7 cm³ g^–1 at 1 atm and 298 K, with a removal efficiency of 93.4% for 18 mg L^–1 methylene blue (MB) solution. These results prove that HKUST-1 in the filament exhibits adsorption ability without hindrance from the polymer portion, which resulted from the high mass loading of HKUST-1 and led to the interconnection between the particles, thereby avoiding the blocking effect of the PLA polymer. This study demonstrates a promising method for preparing high-mass-loading HKUST-1 composite materials for FDM 3D printing and opens up the possibility of loading other MOF materials with unique properties into polymers for diverse applications.

Transition metal (TM) oxides, particularly manganese oxide spinels, are promising cathode materials for next-generation rechargeable batteries, offering reversible intercalation of multivalent ions, such as Mg²⁺, at high voltages and energy storage capacities potentially higher than conventional Li-ion cathodes. However, repeated electrochemical cycling of these oxide cathodes with Mg²⁺ can lead to irreversible structural changes, causing capacity fade and voltage losses. In this study, we utilize in situ transmission electron microscopy (TEM), including aberration-corrected scanning transmission electron microscopy (STEM) imaging and electron energy-loss spectroscopy (EELS), to examine the electronic and structural changes in MgCr_1.5Mn_0.5O₄ under electron beam exposure. We find that electron beam irradiation induces Mn migration in both the bulk and surface regions of the nanocrystals, leading to the formation of a MnO phase on the crystal surface, with the dynamics of this formation captured at the atomic scale. These results demonstrate the potential for in situ TEM to capture the atomic-scale dynamics of cation migration during the structural changes previously observed in battery cathodes throughout electrochemical cycling. Our study identifies the causes of unwanted secondary phase formation in multivalent spinel oxide cathodes, attributing it to phase separation and TM-ion diffusion.

Developing an efficient catalyst that can reduce CO to economically viable products provides a pathway to achieve carbon neutrality. For this purpose, we introduce and characterize boron phosphide nanotubes, a class of materials that allow one to reach a goal without costly and toxic metal atoms. The tubular configuration imparts a confining effect, facilitating CO adsorption and catalytic reduction into ethanol. By calculating the transition state conditions under different charging and using grand canonical potential kinetics, we establish the transition state energy barriers in the system at different electrochemical potentials. We further elucidate the kinetics and mechanism of the entire reaction process at the microkinetics level and predict the onset potential to be -0.30 V with the Tafel slope of 93.69 mV/dec. Finally, we demonstrate control over concentrations of the products and intermediate species by the choice of pH and the applied potential. The characterized material class and established chemical mechanisms guide design of electrocatalysts for producing multicarbon products.

Developing an efficient catalyst that can reduce CO to economically viable products provides a pathway to achieve carbon neutrality. For this purpose, we introduce and characterize boron phosphide nanotubes, a class of materials that allow one to reach a goal without costly and toxic metal atoms. The tubular configuration imparts a confining effect, facilitating CO adsorption and catalytic reduction into ethanol. By calculating the transition state conditions under different charging and using grand canonical potential kinetics, we establish the transition state energy barriers in the system at different electrochemical potentials. We further elucidate the kinetics and mechanism of the entire reaction process at the microkinetics level and predict the onset potential to be −0.30 V with the Tafel slope of 93.69 mV/dec. Finally, we demonstrate control over concentrations of the products and intermediate species by the choice of pH and the applied potential. The characterized material class and established chemical mechanisms guide design of electrocatalysts for producing multicarbon products.

Melt-quenched glasses from zeolitic imidazolate frameworks (ZIFs), a subset of metal–organic frameworks (MOFs) constructed from imidazolate linkers and divalent metal ions, represent a novel class of porous materials with potential applications in gas separation, optics, and as battery materials. Volumetric adsorption studies in combination with high-pressure ¹³C in situ NMR spectroscopy of CO₂ have emerged as promising tools to investigate the textural properties of porous materials, including ZIFs. However, CO₂ is not inert. It can chemically bind to Lewis basic sites present in the pores, thus changing the identity of CO₂. Here, we use this property to investigate dangling linker defects in crystalline ZIFs and their corresponding glasses or mechanochemically amorphized derivatives before and after exposure to ¹³C-enriched CO₂ at high pressure via solid-state NMR spectroscopy. Dangling linkers in the porous materials are visualized spectroscopically via carboxylation at their non-coordinating N atoms, forming carbamates. We observe that the carboxylation reaction of dangling linkers is much more pronounced in ZIF glasses than in the crystalline parent compounds, substantiating that the glasses feature a considerably higher concentration of such defects. Quantitative ¹³C NMR spectroscopy reveals that approximately 1% of the imidazolate-type linkers are carboxylated in glasses, whereas the amount of the carboxylated linkers is about seven times lower in the pristine ZIFs. These findings offer structural insight into the defects of ZIF glasses and bear significant practical implications for applications ranging from gas separation to catalysis.