Hallmarks of mechanochemistry: from nanoparticles to technology

Structural and luminescence characterization of β-Ga2O3 nanopowders obtained via high-energy ball milling

β-Ga2O3 nanocrystals have been successfully obtained by the high-energy ball milling method. The obtained nanocrystalline powders have been characterized using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and luminescent spectroscopy. X-ray diffraction patterns show a single gallium oxide structure formed in the milling process with a small amount of α-Ga2O3 phase. The grains of irregular shape were identified with the TEM technique. HRTEM images confirmed the formation of the β-Ga2O3 nanocrystals with a size distribution of 50–80 nm. Three luminescence bands peaked at about 2.52, 2.91, and 3.26 eV were observed in photoluminescence spectra. The gradual blue shift of the emission maxima at the excitation in the fundamental absorption edge under the different milling conditions was detected.

From Inert to Catalytically Active Milling Media: Galvanostatic Coating for Direct Mechanocatalysis

The inert milling balls, commonly utilized in mechanochemical reactions, were coated with a layer of Pd and utilized as catalyst in the direct mechanocatalytic Suzuki reaction. With high yields (>80 %), the milling balls can be recycled multiple times in the absence of any solvents, ligands, catalyst-molecules and -powders, while utilizing as little as 0.8 mg of Pd per coated milling ball. The coating sequence, the support material, and the layer thickness were examined towards archiving high catalyst retention, low abrasion and high conversion. The approach was transferred to the coating of milling vessels revealing the interplay between catalytically available surface area and the mechanical energy impact in direct mechanocatalysis.

Application of a Method for Measuring the Grindability of Fine-Grained Materials by High-Speed Milling

This article deals with the development of an alternative method for determining the grindability index of fine-grained materials. This method is inspired by the commercially used VTI method (also known as RTI after the Russian Thermal Energy Institute), which was widely used in Central and Eastern Europe in coal grinding. The disadvantage of the VTI method is that it uses a specific grinding device that otherwise has no other use and nowadays is no longer commonly available. Through the new method, high-energy grinding was performed using a commercially available planetary mill on silicate materials such as limestone, feldspar, corundum, and quartz. The effectiveness of the method was verified on clinker as a representative of widely used materials. The deviation between the grindability index calculated by the origin VTI method and the new developed method was on average approximately 8%; in the case of clinker grinding, it was only 3%. The results showed that the VTI method could be replaced by a new method that uses a modern available planetary mill and laser granulometry to determine the grindability index. The result is a new classification of materials according to their grindability indexes, which is based on the original VTI method.

Shape memory polymer composites (SMPCs) using interconnected nanowire network foams as reinforcements

Shape memory polymers (SMPs), although offer a suite of advantages such as ease of processability and lower density, lag behind their shape memory alloy counterparts, in terms of mechanical properties such as recovery stress and cyclability. Reinforcing SMPs with inorganic nanowires and carbon nanotubes (CNTs) is a sought-after pathway for tailoring their mechanical properties. Here, inorganic nanowires also offer the added advantage of covalently binding the fillers to the surrounding polymer matrices via organic molecules. The SMP composites (SMPCs) thus obtained have well-engineered nanowire-polymer interfaces, which could be used to tune their mechanical properties. A well-known method of fabricating SMPCs involving casting dispersions of nanowires (or CNTs) in mixtures of monomers and crosslinkers typically results in marginal improvements in the mechanical properties of the fabricated SMPCs. This is owed to the constraints imposed by the rule-of-mixture principles. To circumvent this limitation, a new method for SMPC fabrication is designed and presented. This involves infiltrating polymers into pre-fabricated nanowire foams. The pre-fabricated foams were fabricated by consolidating measured quantities of nanowires and a sacrificial material, such as (NH₄)₂CO₃, followed by heating the consolidated mixtures for subliming the sacrificial material. Similar to the case of traditional composites, use of silanes to functionalize the nanowire surfaces allowed for the formation of bonds between both the nanowire-nanowire and the nanowire-polymer interfaces. SMPCs fabricated using TiO₂nanowires and SMP composed of neopentyl glycol diglycidyl ether and poly(propylene glycol) bis(2-aminopropyl ether) (Jeffamine D230) in a 2:1 molar ratio exhibited a 300% improvement in the elastic modulus relative to that of the SMP. This increase was significantly higher than SMPC made using the traditional fabrication route. Well-known powder metallurgy techniques employed for the fabrication of these SMPCs make this strategy applicable for obtaining other SMPCs of any desired shape and chemical composition.

Resolving puzzles of the phase-transformation-based mechanism of the strong deep-focus earthquake

Deep-focus earthquakes that occur at 350–660 km are assumed to be caused by olivine → spinel phase transformation (PT). However, there are many existing puzzles: (a) What are the mechanisms for jump from geological 10⁻¹⁷ − 10⁻¹⁵ s⁻¹ to seismic 10 − 10³ s⁻¹ strain rates? Is it possible without PT? (b) How does metastable olivine, which does not completely transform to spinel for over a million years, suddenly transform during seconds? (c) How to connect shear-dominated seismic signals with volume-change-dominated PT strain? Here, we introduce a combination of several novel concepts that resolve the above puzzles quantitatively. We treat the transformation in olivine like plastic strain-induced (instead of pressure/stress-induced) and find an analytical 3D solution for coupled deformation-transformation-heating in a shear band. This solution predicts conditions for severe (singular) transformation-induced plasticity (TRIP) and self-blown-up deformation-transformation-heating process due to positive thermomechanochemical feedback between TRIP and strain-induced transformation. This process leads to temperature in a band, above which the self-blown-up shear-heating process in the shear band occurs after finishing the PT. Our findings change the main concepts in studying the initiation of the deep-focus earthquakes and PTs during plastic flow in geophysics in general.

The developed theory for coupled deformation, plastic strain-induced phase transformation, transformation-induced plasticity, and self-blown-up deformation-transformation-heating in shear band explains the main puzzles of deep-focus earthquakes.

Nanomilling-driven volumetric changes in multiparticulate As4S4-bearing nanocomposites recognized with a help of annihilating positrons

Employing positron annihilation lifetime (PAL) spectroscopy, nanomilling-driven volumetric changes driven are identified in multiparticulate nanocomposites of As4S4–ZnS–Fe3O4 system, considered in transitions between their respective hierarchical derivatives from triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) to biparticulate (1⋅As4S4/1⋅Fe3O4, 1⋅As4S4/4⋅ZnS) and monoparticulate (As4S4) ones. Unconstrained three-component PAL spectra of nanocomposites are parameterized in terms of positron-Ps trapping conversion obeying x3-x2-CDA (coupling decomposition algorithm). Coexistence of nanocrystalline nc-β-As4S4 and amorphous a-AsS phase is shown to be crucial feature of these nanocomposites, the latter being generated continuously due to reamorphization of initial disordered phase and/or vitrification of nc-β-As4S4 phase. The inverse positron-to-Ps trapping conversion prevails in transition from biparticulate (1⋅As4S4/1⋅Fe3O4) and monoparticulate (As4S4) nanocomposites (both dominated by trapping in As4S4-bearing sub-system) to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared positron traps being vacancy defects in a-As–S matrix, and Ps-decay sites formed instead being triple junctions between amorphized nc-β-As4S4 grains. The normal Ps-to-positron-trapping conversion prevails in transition from biparticulate (1⋅As4S4/4⋅ZnS) nanocomposite dominated by positron trapping in ZnS sub-system to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared Ps-decay sites being triple junctions between amorphized nc-β-As4S4 grains, and positron traps formed instead being vacancy-type defects in the packing of the finest ZnS crystallites (~ 2–3 nm).

Properties of CuFeS2/TiO2 Nanocomposite Prepared by Mechanochemical Synthesis

CuFeS₂/TiO₂ nanocomposite has been prepared by a simple, low-cost mechanochemical route to assess its visible-light-driven photocatalytic efficiency in Methyl Orange azo dye decolorization. The structural and microstructural characterization was studied using X-ray diffraction and high-resolution transmission electron microscopy. The presence of both components in the composite and a partial anatase-to-rutile phase transformation was proven by X-ray diffraction. Both components exhibit crystallite size below 10 nm. The crystallite size of both phases in the range of 10-20 nm was found and confirmed by TEM. Surface and morphological properties were characterized by scanning electron microscopy and nitrogen adsorption measurement. Scanning electron microscopy has shown that the nanoparticles are agglomerated into larger grains. The specific surface area of the nanocomposite was determined to be 21.2 m^2·g^-1. Optical properties using UV-Vis and photoluminescence spectroscopy were also investigated. CuFeS₂/TiO₂ nanocomposite exhibits strong absorption with the determined optical band gap 2.75 eV. Electron paramagnetic resonance analysis has found two types of paramagnetic ions in the nanocomposite. Mössbauer spectra showed the existence of antiferromagnetic and paramagnetic spin structure in the nanocomposite. The CuFeS₂/TiO₂ nanocomposite showed the highest discoloration activity with a MO conversion of ~ 74% after 120 min irradiation. This study has shown the possibility to prepare nanocomposite material with enhanced photocatalytic activity of decoloration of MO in the visible range by an environmentally friendly manner.

A greener approach towards the synthesis of N-heterocyclic thiones and selones using the mechanochemical technique

This manuscript describes the synthesis of N-heterocyclic thiones and selones of a variety of imidazolium salts involving an eco-friendly and solventless ball-milling technique. The products have been isolated in almost quantitative yield, involving a minimum quantity of solvents only for the isolation of products by column chromatography, and in some cases for purification purposes. Both mono- and bisimidazolium salts afforded N-heterocyclic thiones and selones. The methodology is found to be superior in terms of reaction time, yield and energy efficiency as compared to conventional solution-state reactions.

Mechanical Activation by Ball Milling as a Strategy to Prepare Highly Soluble Pharmaceutical Formulations in the Form of Co-Amorphous, Co-Crystals, or Polymorphs

Almost half of orally administered active pharmaceutical ingredients (APIs) have low solubility, which affects their bioavailability. In the last two decades, several alternatives have been proposed to modify the crystalline structure of APIs to improve their solubility; these strategies consist of inducing supramolecular structural changes in the active pharmaceutical ingredients, such as the amorphization and preparation of co-crystals or polymorphs. Since many APIs are thermosensitive, non-thermal emerging alternative techniques, such as mechanical activation by milling, have become increasingly common as a preparation method for drug formulations. This review summarizes the recent research in preparing pharmaceutical formulations (co-amorphous, co-crystals, and polymorphs) through ball milling to enhance the physicochemical properties of active pharmaceutical ingredients. This report includes detailed experimental milling conditions (instrumentation, temperature, time, solvent, etc.), as well as solubility, bioavailability, structural, and thermal stability data. The results and description of characterization techniques to determine the structural modifications resulting from transforming a pure crystalline API into a co-crystal, polymorph, or co-amorphous system are presented. Additionally, the characterization methodologies and results of intermolecular interactions induced by mechanical activation are discussed to explain the properties of the pharmaceutical formulations obtained after the ball milling process.

Sr2TiO4 Prepared Using Mechanochemical Activation: Influence of the Initial Compounds’ Nature on Formation, Structural and Catalytic Properties in Oxidative Coupling of Methane

Methane oxidative coupling (OCM) is considered a potential direct route to produce C2 hydrocarbons. Layered perovskite-like Sr2TiO4 is a promising OCM catalyst. Mechanochemical activation (MA) is known to be an environmentally friendly method for perovskite synthesis. Sr2TiO4 were synthesized using MA of the mixtures containing SrCO3 or SrO and TiO2 or TiO(OH)2 and annealing at 900 and 1100 °C. XRD and FT-IRS showed that MA leads to the starting component disordering and formation of SrTiO3 only for SrO being pronounced when using TiO(OH)2. After annealing at 900 °C, Sr2TiO4 was mainly produced from the mixtures of SrCO3 or SrO and TiO(OH)2. The single-phase Sr2TiO4 was only obtained from MA products containing SrCO3 after calcination at 1100 °C. The surface enrichment with Sr was observed by XPS for all samples annealed at 1100 °C depending on the MA product composition. The OCM activity of the samples correlated with the surface Sr concentration and the ratio of the surface oxygen amount in SrO and perovskite (Oo/Op). The maximal CH4 conversion and C2 yield (25.6 and 15.5% at 900 °C, respectively), and the high long-term stability were observed for the sample obtained from (SrCO3 + TiO2), showing the specific surface morphology and optimal values of the surface Sr concentration and Oo/Op ratio.

Date Fruit (Phoenix dactylifera L.) Cultivar Extracts: Nanoparticle Synthesis, Antimicrobial and Antioxidant Activities

The pharmaceutical research sector’s inability to produce new drugs has made it difficult to keep up with the rate at which microbial resistance is developing. Recently, nanotechnology and its combinations with natural products have been the saviors against multidrug resistant bacteria. In the present investigation, different Egyptian and Saudi date cultivars were extracted and then phytochemically analyzed and tested for possible antimicrobial activities against multidrug resistant (MDR) microbes. The results revealed that extract of the flesh of fresh “Hayany” fruit (Egyptian date) showed the highest antimicrobial activity, with high levels of phenolic, flavonoid, and tannin concentrations (538.578 µg/mL, 28.481 µg/mL, and 20.888 µg/mL, respectively) and high scavenging activity, with an IC50 reaching 10.16 µg/mL. The highest synergistic activity was found between fresh “Hayany” fruit extract and amikacin. Novel nano-fresh fruit of “Hayany” date extract was synthesized using a ball-milling technique. The vesicle size was 21.6 nm, while the PDI and zeta potential were 0.32 and +38.4 mV, respectively. The inhibition zone diameters of nano-fresh fruit of “Hayany” date extract/amikacin reached 38 mm and 34 mm, with complete microbial eradication after 9 h and 6 h, against Candida albicans and Staphylococcus aureus, respectively. In conclusion, date fruit extract could be used as a candidate bioactive compound in the fight against infectious diseases.

Ternary and Quaternary Nanocrystalline Cu-Based Sulfides as Perspective Antibacterial Materials Mechanochemically Synthesized in a Scalable Fashion

Twelve Cu-based ternary (Cu-Me₁-S, Me₁ = Fe, Sn, or Sb) and quaternary (Cu-Me₂-Sn-S, Me₂ = Fe, Zn, or V) nanocrystalline sulfides are shown as perspective antibacterial materials here. They were prepared from elemental precursors by a one-step solvent-free mechanochemical synthesis in a 100 g batch using scalable eccentric vibratory ball milling. Most of the products have shown strong antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria. For instance, stannite Cu₂FeSnS₄ and mohite Cu₂SnS₃ were the most active against E. coli, whereas kesterite Cu₂ZnSnS₄ and rhodostannite Cu₂FeSn₃S₈ exhibited the highest antibacterial activity against S. aureus. In general, stannite has shown the best antibacterial properties out of all the studied samples. Five out of twelve products have been prepared using mechanochemical synthesis for the first time in a scalable fashion here. The presented synthetic approach is a promising alternative to traditional syntheses of nanomaterials suitable for biological applications and shows ternary and quaternary sulfides as potential candidates for the next-generation antibacterial agents.

Controlling Nonlinear Dynamics of Milling Bodies in Mechanochemical Devices Driven by Pendular Forcing

Understanding the dynamics of milling bodies is key to optimize the mixing and the transfer of mechanical energy in mechanochemical processing. In this work, we present a comparative study of mechanochemical reactors driven by harmonic pendular forcing and characterized by different geometries of the lateral borders. We show that the shape of the reactor bases, either flat or curved, along with the size of the milling body and the elasticity of the collisions, represents relevant parameters that govern the dynamical regimes within the system and can control the transition from periodic to chaotic behaviors. We single out possible criteria to preserve target dynamical scenarios when the size of the milling body is changed, by adapting the relative extent of the spatial domain. This allows us to modulate the average energy of the collisions while maintaining the same dynamics and paves the way for a unifying framework to control the dynamical response in different experimental conditions. We finally explore the dynamical and energetic impact of an increasingly asymmetric mechanical force.

Micrococcus lylae MW407006 Pigment: Production, Optimization, Nano-Pigment Synthesis, and Biological Activities

Simple Summary

The global crisis of increased mortality rates due to the emergence of antimicrobial resistance and cancers has increased researchers’ efforts to find new, potent solutions through implementing natural products in the pharmaceutical industry. The present investigation produced echinenone (yellowish-orange pigment) from Micrococcus lylae MW407006 with potent pharmacological activities. A response surface methodology statistical design was used to optimize the biomass production, pigment concentration, and antimicrobial activity. The Spearman correlation coefficient was assessed, which indicated a strong linear relationship between biomass production, pigment concentration, and antimicrobial activity. Nano-echinenone was physically synthesized through the ball-milling technique. The synthesized nano-echinenone showed higher pharmacological activities (antimicrobial, antioxidant, and antitumor activities) in comparison with the crude pigment. The significantly high selectivity index of the synthesized nano-echinenone proved its safety and paved the way for its possible use in the pharmaceutical industry.

Abstract

Bacterial pigments (e.g., melanin and carotenoids) are considered to be among the most important secondary metabolites due to their various pharmacological activities against cancer and microbial resistance. Different pigmented bacterial strains were isolated from soil samples from El Mahmoudiyah governance and screened for their antimicrobial activity. The most promising pigment producer was identified as Micrococcus lylae MW407006; furthermore, the produced pigment was identified as echinenone (β-carotene pigment). The pigment production was optimized through a central composite statistical design to maximize the biomass production, pigment concentration, and the antimicrobial activity. It was revealed that the most significant fermentation parameters were the glucose (as a carbon source) and asparagine (as a nitrogen source) concentrations. Nano-echinenone was synthesized using the ball milling technique, characterized, and finally assessed for potential antimicrobial, antioxidant, and antitumor activities. The data revealed that the synthesized nano-echinenone had higher antimicrobial activity than the crude pigment. The cytotoxic potency of echinenone and nano-echinenone was investigated in different cell lines (normal and cancer cells). The inhibition of cell proliferation and induction of cell death was observed in Caco-2 and Hep-G2 cells. The data proved that nano-echinenone is a suitable candidate for use as a safe antimicrobial and anti-hepatocellular-carcinoma agent.

Mechanochemically assisted persulfate activation for the facile recovery of metals from spent lithium ion batteries

A novel mechanochemically assisted persulfate activation method was proposed in this study to enhance the leaching of valuable metals from lithium-ion batteries by combining ball-milling, advanced oxidation processes and sucrose reduction. By optimizing leaching parameters including temperature, pH, milling time and solid-to-liquid ratio, high leaching efficiencies of 97.1%, 94.0%, 87.6% and 93.8% can be achieved for Li, Ni, Co and Mn respectively. In the mechanochemical process, the breakage of covalent bonds in cathode material is facilitated by free radicals generated from zero valent iron activated ammonia persulfate as well as mechanochemical activation. To further explore the role of free radicals, the mechanism of ammonia persulfate activation by zero valent iron was elucidated, and SO₄^•- was identified as the dominant reactive oxygen species in the mechanochemical process. Meanwhile, the synergistic effect of mechanochemically driven crystal dissolution and sulfate radical facilitated bond cleavage was revealed by ab initio molecular dynamics simulation. Moreover, the released metal was reduced by sucrose to a lower valent state of high solubility to promote transfer to the aqueous phase during the subsequent leaching process with dilute sulfuric acid. In this work, the insight on the mechanism of mechanochemical processes strengthened by free radicals may provide an inspiration for the recovery of valuable metals from LIBs.

Decoupling the Chemical and Mechanical Strain Effect on Steering the CO2 Activation over CeO2-Based Oxides: An Experimental and DFT Approach

Doped ceria-based metal oxides are widely used as supports and stand-alone catalysts in reactions where CO2 is involved. Thus, it is important to understand how to tailor their CO2 adsorption behavior. In this work, steering the CO2 activation behavior of Ce-La-Cu-O ternary oxide surfaces through the combined effect of chemical and mechanical strain was thoroughly examined using both experimental and ab initio modeling approaches. Doping with aliovalent metal cations (La3+ or La3+/Cu2+) and post-synthetic ball milling were considered as the origin of the chemical and mechanical strain of CeO2, respectively. Experimentally, microwave-assisted reflux-prepared Ce-La-Cu-O ternary oxides were imposed into mechanical forces to tune the structure, redox ability, defects, and CO2 surface adsorption properties; the latter were used as key descriptors. The purpose was to decouple the combined effect of the chemical strain (εC) and mechanical strain (εM) on the modification of the Ce-La-Cu-O surface reactivity toward CO2 activation. During the ab initio calculations, the stability (energy of formation, EOvf) of different configurations of oxygen vacant sites (Ov) was assessed under biaxial tensile strain (ε > 0) and compressive strain (ε < 0), whereas the CO2-philicity of the surface was assessed at different levels of the imposed mechanical strain. The EOvf values were found to decrease with increasing tensile strain. The Ce-La-Cu-O(111) surface exhibited the lowest EOvf values for the single subsurface sites, implying that Ov may occur spontaneously upon Cu addition. The mobility of the surface and bulk oxygen anions in the lattice contributing to the Ov population was measured using 16O/18O transient isothermal isotopic exchange experiments; the maximum in the dynamic rate of 16O18O formation, Rmax(16O18O), was 13.1 and 8.5 μmol g-1 s-1 for pristine (chemically strained) and dry ball-milled (chemically and mechanically strained) oxides, respectively. The CO2 activation pathway (redox vs associative) was experimentally probed using in situ diffuse reflectance infrared Fourier transform spectroscopy. It was demonstrated that the mechanical strain increased up to 6 times the CO2 adsorption sites, though reducing their thermal stability. This result supports the mechanical actuation of the "carbonate"-bound species; the latter was in agreement with the density functional theory (DFT)-calculated C-O bond lengths and O-C-O angles. Ab initio studies shed light on the CO2 adsorption energy (Eads), suggesting a covalent bonding which is enhanced in the presence of doping and under tensile strain. Bader charge analysis probed the adsorbate/surface charge distribution and illustrated that CO2 interacts with the dual sites (acidic and basic ones) on the surface, leading to the formation of bidentate carbonate species. Density of states (DOS) studies revealed a significant Eg drop in the presence of double Ov and compressive strain, a finding with design implications in covalent type of interactions. To bridge this study with industrially important catalytic applications, Ni-supported catalysts were prepared using pristine and ball-milled oxides and evaluated for the dry reforming of methane reaction. Ball milling was found to induce modification of the metal-support interface and Ni catalyst reducibility, thus leading to an increase in the CH4 and CO2 conversions. This study opens new possibilities to manipulate the CO2 activation for a portfolio of heterogeneous reactions.

Mechanochemically synthesized Al-Fe (oxide) composite with superior reductive performance: Solid-state kinetic processes during ball milling

Recently, mechanical ball milling (BM), a simple and green powder processing method, has been successfully applied to improve the performance of zero-valent metals (ZVMs) for efficient water treatment. However, until now BM is still regarded as a "black box" in which the processes of the solid-state reaction during activation remain unclear. In this paper, firstly, FeSO₄·7H₂O crystal was used to activate and modify inert microscale zero-valent aluminum (mZVAl) by BM to synthesize Al-Fe (oxide)^bm composite that showed superior reactivity in reductive removal of various contaminants and excellent reusability, which may be mainly ascribed to the newly formed iron oxide layer on mZVAl by mechanochemical reaction. At the same time, the formation of iron oxides on mZVAl was closely related to BM parameters. Further kinematic analysis revealed that the occurrence of mechanochemical reaction depended on the impact energy and input energy, which BM speed and BM time were two main factors determining reaction extent on the premise that the precursors were full dose. Moreover, kinetic fitting uncovered the solid-state reaction mechanism between mZVAl and FeSO₄·7H₂O conformed to three-dimensional diffusion and phase boundary reaction models. This study ponders deeply upon the mechanochemical process and solid reaction mechanism during the preparation of Al-Fe (oxide)^bm composite, which deepens comprehensions of material synthesis procedures by BM and promotes applications of ZVM-based composite in polluted water or wastewater treatment.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Mechanochemical synthesis of catalysts and reagents for water decontamination: Recent advances and perspective

This paper aims to provide insights on mechanochemistry as a green and versatile tool to synthesize advanced materials for water remediation. In particular, mechanochemical methodologies for preparation of reagents and catalysts for the removal of organic pollutants are reviewed and discussed, focusing on those materials that, directly or indirectly, induce redox reactions in the contaminants (i.e., photo-, persulfate-, ozone-, and Fenton-catalysts, as well as redox reagents). Methods reported in the literature include surface reactivity enhancement for single-component materials, as well as multi-component material design to obtain synergistic effects in catalytic efficiency and/or reactivity. It was also amply demonstrated that mechanochemical surface activation or the incorporation of catalytic/reactive components boost the generation of reactive species in water by accelerating charge transfer, increasing superficial active sites, and developing pollutant absorption. Finally, indications for potential future developments in this field are debated.

Exploring the ancient chemistry of mercury

This paper explores the chemistry of mercury as described in ancient alchemical literature. Alchemy's focus on the knowledge and manipulation of natural substances is not so different from modern chemistry's purposes. The great divide between the two is marked by the way of conceptualizing and recording their practices. Our interdisciplinary research group, composed of chemists and historians of science, has set off to explore the cold and hot extraction of mercury from cinnabar. The ancient written records have been perused in order to devise laboratory experiments that could shed light on the material reality behind the alchemical narratives and interpret textual details in a unique perspective. In this way, it became possible to translate the technical lore of ancient alchemy into the modern language of chemistry. Thanks to the replication of alchemical practices, chemistry can regain its centuries-long history that has fallen into oblivion.

Chemical effects induced by the mechanical processing of granite powder

Starting from 1970s, the use of mechanical forces to induce chemical transformations has radically changed vast areas of metallurgy and materials science. More recently, mechanochemistry has expanded to core sectors of chemistry, showing the promise to deeply innovate chemical industry while enhancing its sustainability and competitiveness. We are still far, however, from unveiling the full potential of mechanical activation. This study marks a step forward in this direction focusing on the chemical effects induced on the surrounding gaseous phase by the mechanical processing of granite. We show that fracturing granite blocks in oxygen can result in the generation of ozone. The refinement of coarse granite particles and the friction between fine ones are also effective in this regard. Combining experimental evidence related to the crushing of large granite samples by uniaxial compression and the ball milling of coarse and fine granite powders, we develop a model that relates mechanochemical ozone generation to the surface area effectively affected by fracture and frictional events taking place during individual impacts. We also extend the investigation to gaseous phases involving methane, oxygen, benzene and water, revealing that chemical transformations occur as well.

Operando acoustic analysis: a valuable method for investigating reaction mechanisms in mechanochemistry

We present a new operando approach for following reactions taking place in mechanochemistry, relying on the analysis of the evolution of the sound during milling. We show that differences in sound can be directly correlated to (physico)chemical changes in the reactor, making this technique highly attractive and complementary to others for monitoring mechanochemical reactions. Most notably, it can provide unique information on the actual movements of the beads within the milling jars, which opens new avenues for helping rationalize mechanochemical processes.

Surface and Bulk Chemistry of Mechanochemically Synthesized Tohdite Nanoparticles

Aluminum oxides, oxyhydroxides, and hydroxides are important in different fields of application due to their many attractive properties. However, among these materials, tohdite (5Al2O3·H2O) is probably the least known because of the harsh conditions required for its synthesis. Herein, we report a straightforward methodology to synthesize tohdite nanopowders (particle diameter ∼13 nm, specific surface area ∼102 m2 g-1) via the mechanochemically induced dehydration of boehmite (γ-AlOOH). High tohdite content (about 80%) is achieved upon mild ball milling (400 rpm for 48 h in a planetary ball mill) without process control agents. The addition of AlF3 can promote the crystallization of tohdite by preventing the formation of the most stable α-Al2O3, resulting in the formation of almost phase-pure tohdite. The availability of easily accessible tohdite samples allowed comprehensive characterization by powder X-ray diffraction, total scattering analysis, solid-state NMR (1H and 27Al), N2-sorption, electron microscopy, and simultaneous thermal analysis (TG-DSC). Thermal stability evaluation of the samples combined with structural characterization evidenced a low-temperature transformation sequence: 5Al2O3·H2O → κ-Al2O3 → α-Al2O3. Surface characterization via DRIFTS, ATR-FTIR, D/H exchange experiments, pyridine-FTIR, and NH3-TPD provided further insights into the material properties.

Structural and Optical Characterization of Mechanochemically Synthesized CuSbS2 Compounds

One of the areas of research on materials for thin-film solar cells focuses on replacing In and Ga with more earth-abundant elements. In that respect, chalcostibite (CuSbS₂) is being considered as a promising environmentally friendly and cost-effective photovoltaic absorber material. In the present work, single CuSbS₂ phase was synthesized directly by a short-duration (2 h) mechanochemical-synthesis step starting from mixtures of elemental powders. X-ray diffraction analysis of the synthesized CuSbS₂ powders revealed a good agreement with the orthorhombic chalcostibite phase, space group Pnma, and a crystallite size of 26 nm. Particle-size characterization revealed a multimodal distribution with a median diameter ranging from of 2.93 μm to 3.10 μm. The thermal stability of the synthesized CuSbS₂ powders was evaluated by thermogravimetry and differential thermal analysis. No phase change was observed by heat-treating the mechanochemically synthesized powders at 350 °C for 24 h. By UV-VIS-NIR spectroscopy the optical band gap was determined to be 1.41 eV, suggesting that the mechanochemically synthesized CuSbS₂ can be considered suitable to be used as absorber materials. Overall, the results show that the mechanochemical process is a viable route for the synthesis of materials for photovoltaic applications.

Assessment of recycling methods and processes for lithium-ion batteries

This review discusses physical, chemical, and direct lithium-ion battery recycling methods to have an outlook on future recovery routes. Physical and chemical processes are employed to treat cathode active materials which are the greatest cost contributor in the production of lithium batteries. Direct recycling processes maintain the original chemical structure and process value of battery materials by recovering and reusing them directly. Mechanical separation is essential to liberate cathode materials that are concentrated in the finer size region. However, currently, the cathode active materials are being concentrated at a cut point that is considerably greater than the actual size found in spent batteries. Effective physical methods reduce the cost of subsequent chemical treatment and thereafter re-lithiation successfully reintroduces lithium into spent cathodes. Some of the current challenges are the difficulty in controlling impurities in recovered products and ensuring that the entire recycling process is more sustainable.

Confinement-Induced Catalytic Dissociation of Hydrogen Molecules in a Scanning Tunneling Microscope

The catalytic scission of single chemical bonds has been induced by the nanoscale confinement in a scanning tunneling microscope (STM) junction. Individual hydrogen molecules sandwiched between the STM tip and a copper substrate can be dissociated solely by the reciprocating movement of the tip. The reaction rate depends sensitively on the local molecular environment, as exemplified by the effects of a nearby carbon monoxide molecule or a gold adatom. Detailed mechanisms and the nature of the transition states are revealed by density functional theory (DFT) calculations. This work provides insights into chemical reactions at the atomic scale induced by localized confinement applied by the STM tip. Furthermore, a single diatomic molecule can act as a molecular catalyst to enhance the reaction rate on a surface.

Mechanochemical Transformations of Biomass into Functional Materials

Biomass is one of the promising alternatives to petroleum-derived materials and plays a major role in our fight against climate change by providing renewable sources of chemicals and materials. Owing to its chemical and structural complexity, the transformation of biomass into value-added products requires a profound understanding of its composition at different scales and innovative methods such as combining physical and chemical processes. In this context, the use of mechanochemistry in biomass valorization is currently growing owing to its potentials as an efficient, sustainable, and environmentally friendly approach. This review highlights the latest advances in the transformation of biomass (i. e., chitin, cellulose, hemicellulose, lignin, and starch) to functional materials using mechanochemical-assisted methods. We focused here on the methodology of biomass processing, influencing factors, and resulting properties with an emphasis on achieving functional materials rather than breaking down the biopolymer chains into smaller molecules. Opportunities and limitations associated this methodology were discussed accordingly for future directions.

Mechanically activated calcium carbonate and zero-valent iron composites for one-step treatment of multiple pollutants

The growing presences of conventional and emerging contaminants make the wastewater treatment increasingly difficult and expensive on a global scale. ZVI tends to be an expectable material for the detoxification of some difficult contaminants such as chlorinated solvents and nitroaromatics. In this work, together use with calcium carbonate (CaCO₃), which serves as a green supporter to ZVI and also direct participant toward the purification process, has been carried out by cogrinding to give a synergistic effect, particularly for treating multiple pollutants including both inorganic and organic compositions. Based on a set of analytical methods of XRD, FTIR, SEM, XPS, and other test methods, the activation mechanism of the ball milling process and the removal performances of the prepared composites were examined. The results prove that the mechanically activated calcium carbonate and ZVI composite samples exhibited extremely high removal capacity on a variety of pollutants contaminated water. The decolorization of azo dyes is mainly attributed to the breaking of chromogenic functional group nitrogen and nitrogen double bonds, and the removal mechanism of aromatic series occurs through a hydrogenation substitution reaction. As to the inorganic pollutant removals, besides the efficient heavy metal ion precipitations, phosphate and fluoride ions are co-precipitated through the formation of fluorapatite to achieve a simultaneous and synergistic removal effect. Under the optimal reaction conditions, the concentration of PO₄^3- is reduced from 250 to 0 mg/L, and that of F^- is reduced from 51.07 to 1.20 mg/L. The prepared composite sample of ZVI rand calcium carbonate allowed simultaneous removals of both inorganic and organic pollutants, simplifying the remediation process of complicated multiple contaminations.

Metal-Catalyzed Organic Reactions by Resonant Acoustic Mixing

We demonstrate catalytic organic synthesis by Resonant Acoustic Mixing (RAM): a mechanochemical methodology that does not require bulk solvent or milling media. Using as model reactions ruthenium-catalyzed ring-closing metathesis and copper-catalyzed sulfonamide-isocyanate coupling, RAM mechanosynthesis is shown to be faster, operationally simpler than conventional ball-milling, while also providing the first example of a mechanochemical strategy for ruthenium-catalyzed ene-yne metathesis. Reactions by RAM are readily and directly scaled-up without any significant changes in reaction conditions, as shown by the straightforward 200-fold scaling-up of the synthesis of the antidiabetic drug Tolbutamide, from hundreds of milligrams directly to 30 grams.

A Unique Mechanochemical Redox Reaction Yielding Nanostructured Double Perovskite Sr2FeMoO6 With an Extraordinarily High Degree of Anti-Site Disorder

Strontium ferromolybdate, Sr2FeMoO6, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation via a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that Sr2FeMoO6 can be mechanosynthesized at ambient temperature in air directly from its precursors (SrO, α-Fe, MoO3) in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity. The mechanically induced evolution of the Sr2FeMoO6 phase and the far-from-equilibrium structural state of the reaction product are systematically monitored with XRD and a variety of spectroscopic techniques including Raman spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. The unique extensive oxidation of iron species (Fe0 → Fe3+) with simultaneous reduction of Mo cations (Mo6+ → Mo5+), occuring during the mechanosynthesis of Sr2FeMoO6, is attributed to the mechanically triggered formation of tiny metallic iron nanoparticles in superparamagnetic state with a large reaction surface and a high oxidation affinity, whose steady presence in the reaction mixture of the milled educts initiates/promotes the swift redox reaction. High-resolution transmission electron microscopy observations reveal that the mechanosynthesized Sr2FeMoO6, even after its moderate thermal treatment at 923 K for 30 min in air, exhibits the nanostructured nature with the average particle size of 21(4) nm. At the short-range scale, the nanostructure of the as-prepared Sr2FeMoO6 is characterized by both, the strongly distorted geometry of the constituent FeO6 octahedra and the extraordinarily high degree of anti-site disorder. The degree of anti-site disorder ASD = 0.5, derived independently from the present experimental XRD, Mössbauer, and SQUID magnetization data, corresponds to the completely random distribution of Fe3+ and Mo5+ cations over the sites of octahedral coordination provided by the double perovskite structure. Moreover, the fully anti-site disordered Sr2FeMoO6 nanoparticles exhibit superparamagnetism with the blocking temperature T B = 240 K and the deteriorated effective magnetic moment μ = 0.055 μ B per formula unit.

Mechanochemical Preparation, Characterization and Biological Activity of Stable CuS Nanosuspension Capped by Bovine Serum Albumin

The biocompatible nanosuspension of CuS nanoparticles (NPs) using bovine serum albumin (BSA) as a capping agent was prepared using a two-stage mechanochemical approach. CuS NPs were firstly synthetized by a high-energy planetary ball milling in 15 min by milling elemental precursors. The stability of nanoparticles in the simulated body fluids was studied, revealing zero copper concentration in the leachates, except simulated lung fluid (SLF, 0.015%) and simulated gastric fluid (SGF, 0.078%). Albumin sorption on CuS NPs was studied in static and dynamic modes showing a higher kinetic rate for the dynamic mode. The equilibrium state of adsorption was reached after 90 min with an adsorption capacity of 86 mg/g compared to the static mode when the capacity 59 mg/g was reached after 2 h. Then, a wet stirred media milling in a solution of BSA was introduced to yield the CuS-BSA nanosuspension, being stable for more than 10 months, as confirmed by photon cross-correlation spectroscopy. The fluorescent properties of the nanosuspension were confirmed by photoluminescence spectroscopy, which also showed that tryptophan present in the BSA could be closer to the binding site of CuS than the tyrosine residue. The biological activity was determined by in vitro tests on selected cancer and non-tumor cell lines. The results have shown that the CuS-BSA nanosuspension inhibits the metabolic activity of the cells as well as decreases their viability upon photothermal ablation.

In Situ Analytical Methods for the Characterization of Mechanochemical Reactions

The interest in mechanochemical reactions and their fields of application have increased enormously in recent times. Mechanically activated reactions offer the advantage of cost-efficiency as well as environmentally friendly syntheses routes. In contrast to thermally induced processes, the energy transfer via the milling media takes place on a local scale. This leads to unique reaction pathways, which often also result in the formation of metastable phases. For the understanding of reaction pathways on a mechanistic level, it is very important to follow the processes taking place in the grinding jar during milling. Besides the measurement of pressure and temperature changes during a mechanochemical reaction, in situ high energy synchrotron X-ray powder diffraction and Raman spectroscopy experiments have been successfully implemented over the last 10 years. This review will highlight the developments which were achieved in the field of in situ monitoring of mechanochemical reactions and their input to the understanding of mechanochemistry.

Mechanistic Insights on the Mechanosynthesis of Phenytoin, a WHO Essential Medicine

In recent years, mechanochemistry has enriched the toolbox of synthetic chemists, enabling faster and more sustainable access to new materials and existing products, including active pharmaceutical ingredients (APIs). However, molecular-level understanding of most mechanochemical reactions remains limited, delaying the implementation of mechanochemistry in industrial applications. Herein, we have applied in situ monitoring by Raman spectroscopy to the mechanosynthesis of phenytoin, a World Health Organization (WHO) Essential Medicine, enabling the observation, isolation, and characterization of key molecular-migration intermediates involved in the single-step transformation of benzil, urea, and KOH into phenytoin. This work contributes to the elucidation of a reaction mechanism that has been subjected to a number of interpretations over time and paints a clear picture of how mechanosynthesis can be applied and optimized for the preparation of added-value molecules.

Potassium at the Origins of Life: Did Biology Emerge from Biotite in Micaceous Clay?

Intracellular potassium concentrations, [K+], are high in all types of living cells, but the origins of this K+ are unknown. The simplest hypothesis is that life emerged in an environment that was high in K+. One such environment is the spaces between the sheets of the clay mineral mica. The best mica for life’s origins is the black mica, biotite, because it has a high content of Mg++ and because it has iron in various oxidation states. Life also has many of the characteristics of the environment between mica sheets, giving further support for the possibility that mica was the substrate on and within which life emerged. Here, a scenario for life’s origins is presented, in which the necessary processes and components for life arise in niches between mica sheets; vesicle membranes encapsulate these processes and components; the resulting vesicles fuse, forming protocells; and eventually, all of the necessary components and processes are encapsulated within individual cells, some of which survive to seed the early Earth with life. This paper presents three new foci for the hypothesis of life’s origins between mica sheets: (1) that potassium is essential for life’s origins on Earth; (2) that biotite mica has advantages over muscovite mica; and (3) that micaceous clay is a better environment than isolated mica for life’s origins.