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1.
J Phys Chem A ; 128(18): 3635-3645, 2024 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-38662914

RESUMO

High-field magic angle spinning (MAS) dynamic nuclear polarization (DNP) is becoming a common technique for improving the sensitivity of solid-state nuclear magnetic resonance (SSNMR) by the hyperpolarization of nuclear spins. Recently, we have shown that gamma irradiation is capable of creating long-lived free radicals that are amenable to MAS DNP in quartz and a variety of organic solids. Here, we demonstrate that ball milling is able to generate millimolar concentrations of stable radical species in diverse materials such as polystyrene, cellulose, borosilicate glass, and fused quartz. High-field electron paramagnetic resonance (EPR) was used to obtain further insight into the nature of the radicals formed in ball milled quartz and borosilicate glass. We further show that radicals generated in quartz by ball milling can be used for solid-effect DNP. We obtained 29Si DNP enhancements of approximately 114 and 33 at 110 K and room temperature, respectively, from a sample of ball milled quartz.

2.
Nanoscale Adv ; 3(14): 4065-4071, 2021 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-36132842

RESUMO

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.

3.
Nat Commun ; 11(1): 3005, 2020 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-32532971

RESUMO

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.

4.
Chem Commun (Camb) ; 54(89): 12574-12577, 2018 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-30272084

RESUMO

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.

5.
Chem Commun (Camb) ; 49(10): 972-4, 2013 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-23128845

RESUMO

For the first time a metal hydride has been used for the preparation of a metal-organic framework. MIL-78 has been synthesized by the solid-state mechanochemical reaction between yttrium hydride and trimesic acid. The process does not involve solvents and does not generate liquid by-products, thus proving the viability of the solid-state approach to the synthesis of MOFs.


Assuntos
Compostos Organometálicos/síntese química , Ácidos Tricarboxílicos/química , Ítrio/química , Estrutura Molecular , Compostos Organometálicos/química
6.
ACS Nano ; 3(3): 527-36, 2009 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-19243128

RESUMO

Self-assembled monolayer (SAM) structures and properties are dominated by two interactions: those between the substrate and adsorbate and those between the adsorbates themselves. We have fabricated self-assembled monolayers of m-1-carboranethiol (M1) and m-9-carboranethiol (M9) on Au[111]. The two isomers are nearly identical geometrically, but calculated molecular dipole moments show a sizable difference at 1.06 and 4.08 D for M1 and M9 in the gas phase, respectively. These molecules provide an opportunity to investigate the effect of different dipole moments within SAMs without altering the geometry of the assembly. Pure and co-deposited SAMs of these molecules were studied by scanning tunneling microscopy (STM). The molecules are indistinguishable in STM images, and the hexagonally close-packed adlayer structures were found to have ((square root of 19) x (square root of 19))R23.4 degrees unit cells. Both SAMs display rotational domains without the protruding or depressed features in STM images associated with domain boundaries in other SAM systems. Differing orientations of molecular dipole moments influence SAM properties, including the stability of the SAM and the coverage of the carboranethiolate in competitive binding conditions. These properties were investigated by dynamic contact angle goniometry, Kelvin probe force microscopy, and grazing incidence Fourier transform infrared spectroscopy.

7.
Phys Chem Chem Phys ; 7(6): 1310-4, 2005 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-19791349

RESUMO

The paper discusses some unresolved issues in the solid state chemistry of alkali metal aluminohydrides (alanates) relevant to high-capacity hydrogen storage. Analysis of experimental data available in chemical and materials science literature suggests a one-step mechanism for the thermal decomposition of both pure and Ti-doped aluminohydrides. Most likely, the presence of a titanium hydride phase in the catalyst is responsible for the catalytic effect of Ti-additives. Furthermore, ball-milling promotes chemical and phase transformations of solid alanates by enhancing mass transfer in the material and creating high-pressure spots where pressure-driven chemical reactions can take place.

8.
Chem Commun (Camb) ; (15): 1606-7, 2002 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-12170804

RESUMO

Cis-(Ph3P)2PtCl2 and cis-(Ph3P)2PtCO3 were prepared mechanochemically from solid reactants in the absence of a solvent; cis-(Ph3P)2PtCl2 was obtained in 98% yield after ball-milling of polycrystalline PtCl2 and Ph3P; the mechanically induced solid-state reaction of cis-(Ph3P)2PtCl2 with an excess of anhydrous K2CO3 produced cis-(Ph3P)2PtCO3 in 70% yield; the formation of transition metal complexes as a result of mechanochemical solvent-free reactions has been confirmed by means of solid-state 31P MAS NMR spectroscopy, X-ray powder diffraction and differential thermal analysis.

9.
Chem Commun (Camb) ; (7): 724-5, 2002 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-12119692

RESUMO

Phosphonium salts have been prepared during high-energy ball-milling of triphenylphosphine with solid organic bromides; the reactions occur at ambient conditions without a solvent; in the case of 2-bromo-2-phenylacetophenone the reaction in a solution usually produces a mixture containing both the C-phosphorylated and O-phosphorylated compounds, while the solvent-free mechanically induced transformation results in the thermodynamically favorable C-phosphorylated product; the occurrence of the observed transformations during mechanical processing of solid reactants is confirmed by the solid-state 31P NMR spectroscopy and X-ray powder diffraction.


Assuntos
Compostos Organofosforados/síntese química , Química Farmacêutica/métodos , Resíduos Industriais/prevenção & controle , Mecânica
10.
J Am Chem Soc ; 124(22): 6244-5, 2002 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-12033845

RESUMO

We describe the nearly quantitative preparation of phosphorus ylides and the Wittig reaction occurring in the solid sate during high-energy mechanochemical processing. Initial insights into the details of the discovered chemical transformations indicate that high-energy mechanical processing supports the interaction of reacting centers by breaking crystallinity of the reactants and by providing mass transfer without a solvent.

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