RSC Mechanochemistry最新文献

Force-activated functional groups in polymers may inform the design of future smart materials in which mechanical events trigger productive chemistry. The availability of such mechanochemically active tools (mechanophores) is perpetually increasing, but the limited understanding of mechanochemical reactivity complicates the identification of new molecular motifs that render reactive groups accessible by force. Here, we expand the chemical scope of our previously reported carbamoyloxime mechanophore motif from latent secondary to tertiary amines by harnessing the reactivity of transient nitrogen-centred radicals formed in the mechanochemical reaction pathway. Carbamoyloximes are modified with an N-pentenyl substituent which undergoes a consecutive intramolecular 5-exo-trig ring-closing reaction with an aminyl radical generated upon force-induced homolytic scission of the mechanophore, thereby enabling the hitherto unexplored mechanochemical activation of latent tertiary amines. We therefore show that carbamoyloxime mechanophores are nitrogen-centred mechanoradical generators expanding the chemical space of polymer mechanochemistry.

The traditional solid or liquid-phase preparation process of clay mineral-based inorganic pigments inevitably involves complex experimental procedures and generation of large volumes of polluting wastewater. To conform to the concept of green chemistry, a cleaner twin screw extrusion followed by high-temperature crystallization technology was developed to prepare low-cost BiVO₄ hybrid pigments based on a natural mixed-dimensional attapulgite clay (MDAPT). It was revealed that the generated shear and extrusion forces during the twin-screw extrusion process effectively promoted the formation of the precursor with the assistance of the colloidal properties of MDAPT. After incorporation of 60 wt% MDAPT, the hybrid pigments obtained at 700 °C presented the best color performance (L^* = 74.76, a^* = 4.24, b^* = 80.84). In view of the synergistic effect of each component, the hybrid pigments served as functional nanofillers for coloring and reinforcing of acrylonitrile-butadiene-styrene (ABS) after being modified with KH-570. At the optimum added amount of 2.75 wt% of hybrid pigments, the tensile strength and bending strength of yellow ABS composites increased by 36.87% and 25.96% compared with that of pure ABS, respectively. Furthermore, it was worth mentioning that incorporation of hybrid pigments also contributed to improving the UV-aging resistance of ABS due to the better absorption and reflection performances of hybrid pigments toward UV and visible light. Therefore, this study is expected to provide a feasible strategy for continuous mechanochemical preparation of low-cost BiVO₄ hybrid pigments for the coloring of ABS with excellent mechanical properties and aging-resistance.

The influence of hydrothermal treatment (HTT) and subsequent mechanochemical treatment (MChT, milling) on the porous and crystalline structure of precipitated zirconium dioxide was studied. It has been established that HTT at 300 °C promotes the transformation of amorphous ZrO₂ into a pure monoclinic phase, as well as the formation of a uniform mesoporous structure which has higher thermal stability. Soft dry milling (300 rpm, 0.5–1 h) of hydrothermally modified monoclinic ZrO₂ causes the introduction of defects into its structure without a noticeable change in the phase composition. The presence of defects is confirmed directly using UV-vis spectra and indirectly by the manifestation of photocatalytic activity of milled samples under visible irradiation. Importantly, it is found that after calcination of milled samples at 500 °C a high fraction of defects remains preserved which opens up the potential of using zirconium dioxide modified in this way as a catalyst or catalytic support with added specific properties offered by defects.

We report an in situ X-ray diffraction study of the mechanochemical ion metathesis between sodium iodide (NaI) and potassium chloride (KCl) to form sodium chloride (NaCl) and potassium iodide (KI) upon ball milling in a shaker mill. The data permit insights into the fundamental processes occurring during mechanochemistry. The reaction proceeds in incremental steps upon ball impact and consequently follows pseudo-zero order kinetics after an induction period needed for mixing and reduction of the sizes of the salt crystals. The total energy input required for full conversion is a constant value irrespective of the shaking frequency. Different shaking frequencies imply different average kinetic energies of the milling balls and thus different energy transfer per impact. The time for the total energy transfer to the powder thus varies as a function of the kinetic energy of the balls and number of impacts. At lower shaking frequency, i.e., at lower kinetic energy of the balls and a lower impact rate, the time required for full conversion is simply longer. The data reported provide strong evidence that pressure generated by the impact of milling balls is the driving force for the metathesis reaction rather than a temperature increase. The observed pseudo-zero order kinetics complies well with periodic pressure pulses driving the salt metathesis reaction.

Mechanochemical approaches to the preparation of chalcogen-bonded cocrystals have not been systematically well-studied. We report here the preparation of six cocrystals and salt cocrystals of chalcogen bond (ChB) donor 3,4-dicyano-1,2,5-telluradiazole using resonant acoustic mixing (RAM). The ChB acceptors employed are tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, 4-methoxypyridine N-oxide, 4-phenylpyridine N-oxide, tetrabutylammonium bromide, and tetrabutylammonium iodide. Acceptor atoms include Cl, Br, I, and O. In all six cases, RAM reproduces the known crystal forms of the ChB products as assessed by powder X-ray diffraction and FTIR spectroscopy. The role of liquid additives is also assessed. The success of RAM in generating ChB products in pure form contrasts with previous efforts to use ball milling for this purpose. We show that ball milling pure 3,4-dicyano-1,2,5-telluradiazole using standard instrumental settings results in amorphization and decomposition in five minutes or less, thereby highlighting the difficulties of using ball milling to generate ChB cocrystals. The design, construction, and implementation of a button operative bot (BOB) to help automate RAM experiments is also described herein. Overall, these results suggest that RAM offers a suitably gentle and tailorable mechanochemical approach for generating known and novel cocrystals.

Copper silver selenide, CuAgSe, was easily and conveniently prepared from Cu, Ag and Se powders in a stoichiometric ratio by one-step solvent-free mechanochemical synthesis after 7 min of milling in a planetary ball mill. The kinetics of the synthesis, along with the structure, morphology, thermal stability, physicochemical, and thermoelectric properties of the product were investigated. The crystal structure, physicochemical properties, and morphology were characterised by X-ray diffraction, particle size distribution analysis, specific surface area measurements, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy. XRD confirmed the crystal structure as a mixture of tetragonal and orthorhombic CuAgSe. Analysis of surface composition revealed partial surface oxidation. Electron microscopy revealed that the nanostructured product consisted of agglomerated particles of irregular shape which formed clusters with a size >20 μm while the mean size of crystallites was 12.1 nm. The mixed crystal structure was also confirmed by selected area diffraction. Thermal analysis clearly indicated a reversible phase transformation. The spark plasma sintering method was applied to prepare a dense CuAgSe pellet for thermoelectric characterization. High-temperature transport properties were examined to assess the potential application of mechanochemically synthesized synthetic eucairite in energy conversion.

Deep understanding of reaction kinetics in mechanochemical conditions is crucial to further advance this field of solid-state chemistry. However, a formidable challenge owing to the complexity of these systems, in particular the kinetic effects of mechanical stress, makes this problem very complex. In this study, we developed a scaling theory to understand the kinetics of mechanochemical reactions by considering convective flows driven by applied mechanical stress, with the assumption that the product behaves as a fluid with the applied mechanical stress in a ball mill. This theory predicts that the rates of mechanochemical reactions are regulated by the dissolution of reactants in the product-rich phase formed between two reactants, and that mechanical force-induced convective flows enhance reaction rates by reducing the thickness of the product-rich phase. This scaling model provides a fundamental approach to understanding the effect of mechanical stress on mechanochemical organic reactions in ball milling.

Na₂CaSnS₄ was prepared by mechanochemical synthesis from a mixture of Na₂S, CaS, and SnS₂. The crystal structure was determined from X-ray powder diffraction data. The chemical composition was confirmed by energy dispersive X-ray spectroscopy, and the ionic conductivity was measured using electrochemical impedance spectroscopy. Na₂CaSnS₄ crystallizes with a rock salt-type structure, space group Fmm, a = 5.6842 (3) Å, V = 183.66 (2) ų, and Z = 1. All the cations are statistically disordered over a unique crystallographic site and are octahedrally coordinated to the sulfur atoms. The ionic conductivity of Na₂CaSnS₄ is 4.2 × 10⁻⁸ S cm⁻¹ (E_a = 0.6 eV) at 33 °C.

Within pharmaceutical research and development, co-crystallization has emerged as a common strategy to modify the physicochemical properties of active pharmaceutical ingredients, tackling a wide array of challenges in drug formulation. Contrasting with conventional solution-based methods that typically consume substantial amounts of solvents and energy, we herein present a more eco-friendly and efficient mechanochemical process for producing co-crystals at kilogram scale. Our study pioneers the use of a drum mill for pharmaceutical co-crystal synthesis, using rac-ibuprofen:nicotinamide as a representative example. Our findings demonstrate the viability of repurposing common industrial milling equipment for potential large-scale production of pharmaceutical co-crystals. With the optimized system and utilizing liquid-assisted grinding techniques, the reaction was completed within 90 min and yielded 99% of pure rac-ibuprofen:nicotinamide co-crystals by simply sieving off the grinding media. Examination of the resulting co-crystals showed minimal metal contamination from abrasion, with levels well within acceptable regulatory standards for daily intake. Our findings underscore the promise of drum mill technology in creating greener processes for large-scale pharmaceutical co-crystal synthesis, paving the way for more sustainable industrial drug manufacturing practices.

This study presents the mechanochemical synthesis of the two K₂Ca(CO₃)₂ polymorphs, fairchildite and buetschliite, from CaCO₃ and K₂CO₃ using a shaker mill. Unlike previous methods requiring high temperatures and prolonged heating, fairchildite, a high-temperature polymorph, is formed initially in all experiments, adhering to Ostwald's rule of stages. Notably, the transformation to the stable buetschliite phase can be achieved by varying milling parameters, particularly frequency and moisture content. The results suggest that pressure, rather than temperature, plays a significant role in this phase transition, with moisture further accelerating the transformation. These findings offer a new, efficient route for the synthesis of these polymorphs, highlighting the critical influence of milling conditions on the reaction pathway.