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A new family of heterostructured transition-metal dichalcogenides (TMDCs) with incommensurate (“misfit”) spatial arrangements of well-defined layers was prepared from structurally dissimilar single-phase 2H-MoS2 and 1T-HfS2 materials. The experimentally observed heterostructuring is energetically favorable over the formation of homogeneous multi-principle element dichalcogenides observed in related dichalcogenide systems of Mo, W, and Ta. The resulting three-dimensional (3D) heterostructures show semiconducting behavior with an indirect band gap around 1 eV, agreeing with values predicted from density functional theory. Results of this joint experimental and theoretical study open new avenues for generating unexplored metal-dichalcogenide heteroassemblies with incommensurate structures and tunable physical properties.

Three-dimensional heterostructures are usually created either by assembling two-dimensional building blocks into hierarchical architectures or using stepwise chemical processes that sequentially deposit individual monolayers. Both approaches suffer from a number of issues, including lack of suitable precursors, limited reproducibility, and poor scalability of the preparation protocols. Therefore, development of alternative methods that enable preparation of heterostructured materials is desired. We create heterostructures with incommensurate arrangements of well-defined building blocks using a synthetic approach that comprises mechanical disassembly and simultaneous reordering of layered transition-metal dichalcogenides, MX2, and non-layered monochalcogenides, REX, where M = Ta, Nb, RE = Sm, La, and X = S, Se. We show that the discovered solid-state processes are rooted in stochastic mechanochemical transformations directed by electronic interaction between chemically and structurally dissimilar solids toward atomic-scale ordering, and offer an alternative to conventional heterostructuring. Details of composition–structure–properties relationships in the studied materials are also highlighted., 3D heterostructures offer properties that are inaccessible in bulk single-phase solids, but synthetic approaches are limited. The authors use mechanochemical reshuffling of binary precursors and subsequent annealing to design structurally aligned misfit heterostructures with well-defined atomic arrangements.

A new mixed alkali metal–aluminum borohydride LiAl(BH4)2Cl2 has been prepared via mechanochemical synthesis from the 2LiBH4–AlCl3 mixture. Structural characterization, performed using a combination of X-ray powder diffraction and solid-state NMR methods, indicates that the LiAl(BH4)2Cl2 phase adopts a unique 3D framework and crystallizes in an orthorhombic structure with the space group C2221, a = 11.6709(6) Å, b = 8.4718(4) Å, c = 7.5114(3) Å. The material shows excellent dehydrogenation characteristics, where hydrogen evolution starts at Tons = 70 °C, releasing approximately 2 wt.% of nearly pure (99.8 vol.%) hydrogen and a very small amount (~0.2 vol.%) of diborane. When compared to halide-free mixed alkali metal–aluminum borohydrides, the presence of Al‒Cl bonding in the LiAl(BH4)2Cl2 structure likely prevents the formation of Al(BH4)3 upon decomposition, thus suppressing the formation of diborane.

The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH4-SiS2 (x = 2–8), where M = Li or Na, were investigated using gas sorption analysis, powder X-ray diffraction, and infrared and solid-state NMR spectroscopic methods. The 2LiBH4:1SiS2 system forms an amorphous product that releases ca. 4.3 wt % of H2 below 385 °C with a Tonset of 88 °C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5 wt % of H2 at 385 °C under 160 bar pressure. The H2 release from materials with varying LiBH4:SiS2 ratios peaks at 8.2 wt % for the 6LiBH4:1SiS2 composition, with a reversible hydrogen storage capacity of 2.4 wt %. The H2 desorption capacities of the Li-containing systems surpass those of Na-containing systems. Solid-state NMR studies indicate that products of mechanochemical reactions in the LiBH4 SiS2 system consist of one-dimensional chains of edge-sharing SiS4/2 tetrahedra in which the non-bridging S-ends are terminated with Li+, which are further coordinated to the [BH4]− anions. A variety of possible polymorphs in the Li Si S-(BH4) composition space have been identified using first principles and thermodynamic modeling that supports the likelihood of formation of such novel complexes.

Three metal-organic framework (MOF) compounds, Ln0.5Gd0.5{C6H3(COO)3}; Ln = Eu, Tb, and Dy with a MIL-78 structure, have been synthesized by a solvent-free mechanochemical method from stoichiometric mixtures of benzene 1,3,5-tricarboxylic acid, C6H3(COOH)3, also known as trimesic acid, and the respective lanthanide carbonates, Ln2(CO3)3·xH2O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln0.5Gd0.5) shows the characteristic red, green, and yellow luminescence of Eu3+, Tb3+, and Dy3+, respectively. Efficient intramolecular energy transfer from the ligand triplet state to the excited states of Ln3+ ions can be observed. The lifetimes and quantum yields of these compounds are studied and discussed in detail. Among the three compounds, the Tb3+ containing compound shows the longest lifetime and highest quantum yield due to a smaller contribution from non-radiative decay pathways and better matching of the lowest triplet energy level of the benzenetricarboxylate ligand and the resonance level of Tb3+.

Solid-state mechanochemical synthesis of alane (AlH3) starting from sodium hydride (NaH) and aluminum chloride (AlCl3) has been achieved at room temperature. The transformation pathway of this solid-state reaction was controlled by a stepwise addition of AlCl3 to the initial reaction mixture that contained sodium hydride in excess of stoichiometric amount. As in the case of previously investigated LiH–AlCl3 system, complete selectivity was achieved whereby formation of unwanted elemental aluminum was fully suppressed, and AlH3 was obtained in quantitative yield. Reaction progress during each step was investigated by means of solid-state NMR and powder X-ray diffraction, which revealed that the overall reaction proceeds through a series of intermediate alanates that may be partially chlorinated. The NaH–AlCl3 system presents some subtle differences compared to LiH–AlCl3 system particularly with respect to optimal concentrations needed during one of the reaction stages. Based on the results, we postulate that high local concentrations of NaH may stabilize chlorine-containing derivatives and prevent decomposition into elemental aluminum with hydrogen evolution. Complete conversion with quantitative yield of alane was confirmed by both SSNMR and hydrogen desorption analysis.

Alkali metal monohydrides, AH (A = Li–Cs) have been synthesized in quantitative yields at room temperature by reactive milling of alkali metals in the presence of hydrogen gas at 200 bar or less. The mechanochemical approach reported here eliminates problems associated with the malleability of alkali metals — especially Li, Na, and K — and promotes effective solid–gas reactions, ensuring their completion. This is achieved by incorporating a certain volume fraction of the corresponding hydride powder as a process control agent, which allows continuous and efficient milling primarily by coating the surface of metal particles, effectively blocking cold welding. Formation of high-purity crystalline monohydrides has been confirmed by powder X-ray diffraction, solid-state NMR spectroscopy, and volumetric analyses of reactively desorbed H2 from as-milled samples. The proposed synthesis method is scalable and particularly effective for extremely air-sensitive materials, such as alkali and alkaline earth metal hydrides. The technique may also be favorable for production in continuous reactors operating at room temperature, thereby reducing the total processing time, energy consumption and, hence, the cost of production of these hydrides or their derivatives and composites.

Increasing demand for lithium-ion batteries (LIBs) that serve as power source for diverse electronic devices, electrical propulsion systems and other applications, calls for economical and environmentally benign recycling of spent LIBs and recovery of critical elements such as Co and Li from rapidly growing volumes of battery wastes. The presented study explores mechanochemical extraction of Co and Li from lithium cobaltate (LiCoO2), which serves as cathode material in commercial LIBs. Our investigation reveals that solvent-free mechanochemical processing can successfully convert pure, reagent grade LiCoO2 into metallic Co and Li-derivatives that are suitable for the further recovery of Li. We also show that the proposed approach can be successfully applied to reclaiming these critical elements from commercial LIBs. Due to its magnetic nature, metallic Co is easy to separate from non-magnetic components of mechanochemically generated powder mixtures using an appropriate magnetic separation technique, while Li can be reclaimed as Li2CO3 after an additional liquid-phase processing. The recovery rates achieved during our experiments with pure LiCoO2 are ∼90% for Co and ∼70% for Li.

Transition metal dichalcogenides combining multiple principal elements in their structures are synthesized via mechanochemical exfoliation and spontaneous reassembly of binary precursors into 3D-heterostructures that are converted into single-phase layered materials by high-temperature reactive fusion. Physical and chemical events enabling these transformations are summarized in the form of a conceivable reaction mechanism.