Mechanochemical Reaction Research Articles

FeN4 active sites generated on dipyridylpyridazine functionalized reduced graphene oxide for high-performance air electrode in a Zn-air battery

The growing global electricity demand requires the development of cost-effective energy conversion and storage systems, integrating inexpensive, eco-friendly, and high-efficiency catalysts. Oxygen reduction reaction (ORR) is considered crucial process to achieve high-power-density fuel cells and Zn-air batteries (ZABs). The latter have attracted the attention of scientific community due to its high theoretical energy density, reliable safety and low-cost. However, several limitations must be overcome, designing ORR catalysts thought versatile and economical synthetic routes. In this sense, the non-noble iron–nitrogen-carbon materials (FeNC) have been reported as the most potential candidates for attaining superior activity toward ORR in substitution of the high-priced commercial Pt-C catalysts. Herein, Diels-Alder surface adducts based on dipyridylpyridazine units have been created along 2D surface of reduced graphene oxide (rGO) nanosheets for the controlled generation of FeN4 active sites at the edges through successive solvent-free mechanochemical reactions and an additional thermal treatment. The optimized catalyst provided high content of pyridinic-N, graphitic-N and Fe2+ species, contributing to the excellent activity delivered as electrocatalyst for ORR processes. In addition, a flooded ZAB assembled with this material as cathodic/air electrode exhibited excellent specific capacities of 4.94 and 2.77 A·h·g−1 at -1 and -5 mA, respectively, improving the catalytic performance obtained for the 10 wt% Pt-C benchmark electrocatalyst.

Lead recovery from waste CRT funnel glass by mechanochemical reaction with reductive Al powder

The safe disposal of waste cathode ray tubes (CRTs) has always been a serious problem due to the stable microstructure of toxic lead (Pb) located in glass. Thousands of researches have been trying to explore environmental and efficient ways to dispose of waste CRTs. To recycle lead from waste CRT funnel glass effectively, a mechanochemical reduction method has been developed in this research. Aluminum was used as a reductant, and the hydrochloric acid solution was used in the leaching process to separate lead from the solution. After mechanochemical ball milling with aluminum, lead ion in CRT funnel glass was transferred into nano-sized element lead. Lead recovery from CRT funnel glass increased significantly as compared to non-activated leaded glass. Approximately 40 % of lead was leached after mechanical activation without aluminum, while over 96 % of lead in the CRT funnel glass could be recovered after mechanochemical reduction with aluminum. Lead chloride (PbCl2) can be recycled from the leaching solution after cooling crystallization. Nano-sized Pb formation and the structural changes of leaded CRT funnel glass by mechanochemical reduction process contributed to obvious improvement in lead recovery. This research provided a high-efficiency and feasible approach for recovering lead in form of PbCl2 crystal from leaded glass.

Mechanosynthesis of Fullerotetrahydroquinolines by Copper-Mediated sp3 C–H Functionalization of N,N-Dimethylanilines with [60]Fullerene

AbstractAn efficient mechanochemical copper-mediated coupling reaction of [60]fullerene with para- or meta-substituted N,N-dimethylanilines under solvent-free and ambient conditions has been developed. The present protocol provides N-methylfullerotetrahydroquinolines containing electron-withdrawing or electron-donating groups on the phenyl ring in a short reaction time and at room temperature. This reaction occurs through copper-mediated sp3 C–H functionalization of N,N-dimethylanilines under ball-milling conditions. In addition, a representative fullerotetrahydroquinoline has been applied in a perovskite solar cell device.

EFFECT OF MECHANOCHEMICAL PROCESSING PARAMETERS ON ETHOXYLATION OF BENZOIC ACID DERIVATIVES

The regularities of ethoxylation of benzoic acid derivatives during interaction with polyethylene glycol through mechanochemical solid-phase synthesis in a vibrating apparatus have been studied. The conditions for carrying out mechanochemical reactions to increase the conversion degree of initial reagents into reaction products are analysed. The products of ethoxylation are characterized by IR spectroscopy, acid-base potentiometric titration, tensiometry, and dilatational rheology. It has been established that the degree of starting reagents conversion into ethoxylation products depends on the nature of the substituent and its position in the benzene ring. The degree of conversion into reaction products is higher for ortho-substituted derivatives of benzoic acid. It is shown that the salts of ethoxylated derivatives of benzoic acid exhibit pronounced surfactant properties at the air - solution interface.

Mechanochemical Metal‐free N‐Sulfonyl Transfer Reaction: Expedient Synthesis of N‐Sulfonyl Amidines

AbstractAn operationally simple mechanochemical reaction between iminoiodinanes with numerous cyclic 2°‐amines such as morpholine, piperidine, pyrrolidine, thiomorpholine, N‐Boc diazepine and N‐Boc piperazine has been reported to afford N‐sulfonyl amidines in moderate to excellent yield. The N‐sulfonyl transfer reaction happens in a ball mill apparatus (RETSCH 400™) with three 5 mm stainless steel (ss) balls in a 5 mL stainless steel (ss) reaction jar with 2‐methyl tetrahydrofuran as liquid assisted grinding auxiliary (LAG). This metal catalyst‐base free synthesis with minimal solvents (as LAGs) demonstrated an efficient N‐sulfonyl transfer reaction from iminoiodinanes. N‐sulfonyl amidines are ubiquitous building blocks present in natural products and drug intermediates. Control experiments and computational studies based on density functional theory (DFT) calculations were performed to gain deeper insight into the mechanism.

Enhanced mechanical properties of poly(vinyl chloride) using hexene‐doping graphitic nanoplatelets

AbstractHexene‐doping graphitic nanoplatelets (HxGNs), as a new filler, have extraordinary properties (e.g., hexene‐functionalization, wedge‐shaped pore, high specific surface areas, and so on), and interfacial interactions with hydrophobic polymers. Thus, the HxGNs sufficiently increase the mechanical properties of poly(vinyl chloride) (PVC). HxGN@PVC_X nanocomposites can be prepared easily with a solution casting method because the HxGNs are well dispersed in tetrahydrofuran. The tensile strength, Young's modulus, toughness, and strain‐to‐failure of HxGN@PVC_5 nanocomposites increase by approximately 33.1%, 27.3%, 58.6%, and 40.5%, respectively, compared with pure PVC. Especially, the low toughness of PVC, which hinders practical applications, has been greatly improved. The improved performance is from the outstanding properties of the HxGNs and the excellent interfacial interactions between the HxGNs and PVC chain. As a result, HxGNs as a filler act as a reinforcing agent and plasticizer for the PVC matrix.Highlights The performance of the HxGN@PVC_5 nanocomposites is increased. The HxGN into PVC matrix is effective to overcome the disadvantages of PVC. A mechanochemical reaction can make graphitic nanoplatelets with specific groups. Graphitic nanoplatelets with specific groups can be used as new filler.

Mechanochemical Release of Fluorophores from a “Flex‐activated” Mechanophore

AbstractOptical force probes that can release force‐dependent and visualized signals with minimal changes in the polymer main chains under mechanical load are highly sought after but currently limited. In this study, we introduce a flex‐activated mechanophore (FA) based on the Diels–Alder adduct of anthracene and dimethyl acetylenedicarboxylatea that exhibits turn‐on mechanofluorescence. We demonstrate that when FA is incorporated into polymer networks or in its crystalline state, it can release fluorescent anthracenes through a retro‐Diels–Alder mechanochemical reaction under compression or hydrostatic high pressure, respectively. The flex‐activated mechanism of FA is successfully confirmed. Furthermore, we systematically modulate the force delivered to the mechanophore by varying the crosslinking density of the networks and the applied macroscopic pressures. This modulation leads to incremental increases in mechanophore activation, successive release of anthracenes, and quantitative enhancement of fluorescence intensity. The exceptional potential of FA as a sensitive force probe in different bulk states is highlighted, benefiting from its unique flex‐activated mode with highly emissive fluorophore releasing. Overall, this report enriches our understanding of the structures and functions of flex‐activated mechanophores and polymeric materials.

Mechanochemical Release of Fluorophores from a "Flex-activated" Mechanophore.

Optical force probes that can release force-dependent and visualized signals with minimal changes in the polymer main chains under mechanical load are highly sought after but currently limited. In this study, we introduce a flex-activated mechanophore (FA) based on the Diels-Alder adduct of anthracene and dimethyl acetylenedicarboxylatea that exhibits turn-on mechanofluorescence. We demonstrate that when FA is incorporated into polymer networks or in its crystalline state, it can release fluorescent anthracenes through a retro-Diels-Alder mechanochemical reaction under compression or hydrostatic high pressure, respectively. The flex-activated mechanism of FA is successfully confirmed. Furthermore, we systematically modulate the force delivered to the mechanophore by varying the crosslinking density of the networks and the applied macroscopic pressures. This modulation leads to incremental increases in mechanophore activation, successive release of anthracenes, and quantitative enhancement of fluorescence intensity. The exceptional potential of FA as a sensitive force probe in different bulk states is highlighted, benefiting from its unique flex-activated mode with highly emissive fluorophore releasing. Overall, this report enriches our understanding of the structures and functions of flex-activated mechanophores and polymeric materials.

Thermally Stable Photomechanical Molecular Hinge: Sterically Hindered Stiff-Stilbene Photoswitch Mechanically Isomerizes.

Molecular photoswitches are extensively used as molecular machines because of the small structures, simple motions, and advantages of light including high spatiotemporal resolution. Applications of photoswitches depend on the mechanical responses, in other words, whether they can generate motions against mechanical forces as actuators or can be activated and controlled by mechanical forces as mechanophores. Sterically hindered stiff stilbene (HSS) is a promising photoswitch offering large hinge-like motions in the E/Z isomerization, high thermal stability of the Z isomer, which is relatively unstable compared to the E isomer, with a half-life of ca. 1000 years at room temperature, and near-quantitative two-way photoisomerization. However, its mechanical response is entirely unexplored. Here, we elucidate the mechanochemical reactivity of HSS by incorporating one Z or E isomer into the center of polymer chains, ultrasonicating the polymer solutions, and stretching the polymer films to apply elongational forces to the embedded HSS. The present study demonstrated that HSS mechanically isomerizes only in the Z to E direction and reversibly isomerizes in combination with UV light, i.e., works as a photomechanical hinge. The photomechanically inducible but thermally irreversible hinge-like motions render HSS unique and promise unconventional applications differently from existing photoswitches, mechanophores, and hinges.

Novel Floating Adsorbent for Water Treatment: Organically Modified Layered Alkali Silicate by Facile Mechanochemical Reaction.

Adsorption serves as an effective way to collect (remove) contaminants from aqueous solution. In the present study, a novel floating adsorbent was designed through surface modification of a layered alkali silicate (octosilicate) using a silane coupling reagent (chlorodimethyl[3-(2,3,4,5,6-pentafluorophenyl)propyl]silane) to collect metal ions from water. By conducting the grafting by solvent-free mechanochemical reaction at room temperature, the external surface of octosilicate was modified to be hydrophobic while preserving the ion exchange capability in the interlayer space. Characterizations of XRD, IR, SEM, TGA, 29Si MAS NMR, and 19F MAS NMR confirmed the successful grafting at the external surface of octosilicate particles. The modified silicate demonstrated buoyancy at the air-water interface, facilitating the concentration of methylene blue, Ni2+, and Pb2+ from aqueous solutions. The adsorbed amounts of metal ions on the floating adsorbent were greater than those reported for the common nonfloating adsorbents (zeolites, clays, and clay minerals).

The Role of Crystalline Intermediates in Mechanochemical Cyclorhodation Reactions Elucidated by in-Situ X-ray Powder Diffraction and Computation.

The occurrence of crystalline intermediates in mechanochemical reactions might be more widespread than previously assumed. For example, a recent study involving the acetate-assisted C-H activation of N-Heterocycles with [Cp*RhCl2 ]2 by ball milling revealed the formation of transient cocrystals between the reagents prior to the C-H activation step. However, such crystalline intermediates were only observed through stepwise intervallic ex-situ analysis, and their exact role in the C-H activation process remained unclear. In this study, we monitored the formation of discrete, stoichiometric cocrystals between benzo[h]quinoline and [Cp*RhCl2 ]2 by ball milling using in-situ synchrotron X-ray powder diffraction. This continuous analysis revealed an initial cocrystal that transformed into a second crystalline form. Computational studies showed that differences in noncovalent interactions made the [Cp*RhCl2 ]2 unit in the later-appearing cocrystal more reactive towards NaOAc. This demonstrated the advantage of cocrystal formation before the acetate-assisted metalation-deprotonation step, and how the net cooperative action of weak interactions between the reagents in mechanochemical experiments can lead to stable supramolecular assemblies, which can enhance substrate activation under ball-milling conditions. This could explain the superiority of some mechanochemical reactions, such as acetate-assisted C-H activation, compared to their solution-based counterparts.

Surface Modification of Kraft Lignin by Mechanochemical Processing with Sodium Percarbonate.

In this article, we present a novel one-pot mechanochemical reaction for the surface activation of lignin. The process involves environmentally friendly oxidation with hydrogen peroxide, depolymerization of fractions with high molecular mass, and introduction of new carbonyl functions into the lignin backbone. Kraft lignin was ground with sodium percarbonate and sodium hydroxide in a ball mill at different time intervals. Analyses by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), size exclusion chromatography (SEC), dynamic vapor sorption (DVS), and small-angle X-ray scattering (SAXS) showed significant improvements. After only 5 min of reaction, there was a 47% reduction in mass-average molecular weight and an increase in carboxyl functionalities. Chemical activation resulted in an approximately 2.8-fold increase in water adsorption. Principal component analysis (PCA) provided further insight into the correlations between IR spectra and SAXS parameters.

Ultrasound-responsive copolymeric micelles prepared by RAFT polymerization using a difunctional spiropyran-based RAFT agent: Investigation of mechanochromism kinetics, responsivities, and enhanced spiropyran mechanoactivation within micelles

An in-depth investigation of the ultrasonic response of mechanophores containing weak covalent bonds within nanosized aggregates is vital for ultrasound imaging, drug delivery, and sensors. In this work, well-defined amphiphilic block SP-[poly(methyl methacrylate-b-N-isopropylacrylamide)]2SP-[p(MMA-b-NIPAM)]2 (P1) and amphiphilic random, SP-[poly(methyl methacrylate-r-N-isopropylacrylamide)]2SP-[p(MMA-r-NIPAM)]2 (P2) copolymers with SP mechanophore embedded at midpoint polymer chain are prepared by RAFT (reversible addition-fragmentation chain transfer) polymerization using a pre-synthesized novel functional bi (trithiocarbonate) and spiropyran (SP)-based RAFT reagent. Both P1 and P2 copolymers self-assemble in spherical micelles in AcCN/water mixed solvents, and several assemblies with different water contents are fabricated. The structural differentiation between block P1 and random P2 dominates the inverse influence of water content on the aggregate sizes of micelles. Under ultrasound irradiation, the SP mechanophore is activated within both micelles, and the amount of activated SP mechanophore increases progressively with prolonged sonication time. For P1, the mechanochemical reaction (mechanochromism) kinetics in an aggregated state and a single chain state are different, while that of P2 micelles and liner are similar, inferred to be associated with the structure difference between both micelles. The mechanoactivation of SP mechanophore within micelles in AcCN/water mixed solvents is higher than in dissolved state due to the micellization of P1 and P2, entangling the hydrophobic PMMA segments and partially swelling in the micellar core. Moreover, an increase in the medium's dielectric constant around the core's SP is also observed, promoting the SP mechanoactivation. This approach may provide a new strategy for preparing novel mechanophore-centered amphiphilic copolymers with colorful structures and high hydrophilicity. These can self-aggregate into nanoparticles in aqueous or mixed solutions, exhibiting effective effects of ultrasonic responsiveness. We expect this work to push forward the in-depth studies on the ultrasonic responsive mechanism of assembly and help open new research avenues into the mechanochemical reactions within nanosized aggregates.

Optical and Photocatalytic Properties of Cobalt-Doped LuFeO3 Powders Prepared by Oxalic Acid Assistance.

B-site cobalt (Co)-doped rare-earth orthoferrites ReFeO3 have shown considerable enhancement in physical properties compared to their parent counterparts, and Co-doped LuFeO3 has rarely been reported. In this work, LuFe1-xCoxO3 (x = 0, 0.05, 0.1, 0.15) powders have been successfully prepared by a mechanochemical activation-assisted solid-state reaction (MAS) method at 1100 °C for 2 h. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies demonstrated that a shrinkage in lattice parameters emerges when B-site Fe ions are substituted by Co ions. The morphology and elemental distribution were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The UV-visible absorbance spectra show that LuFe0.85Co0.15O3 powders have a narrower bandgap (1.75 eV) and higher absorbance than those of LuFeO3 (2.06 eV), obviously improving the light utilization efficiency. Additionally, LuFe0.85Co0.15O3 powders represent a higher photocatalytic capacity than LuFeO3 powders and can almost completely degrade MO in 5.5 h with the assistance of oxalic acid under visible irradiation. We believe that the present study will promote the application of orthorhombic LuFeO3 in photocatalysis.

Direct Synthesis of Fluorinated Carbon Materials via a Solid‐State Mechanochemical Reaction Between Graphite and PTFE

AbstractFluorinated carbon materials (FCMs) have received significant attention, because of their exceptional stability, which is associated with the strong C‐F bonding, the strongest among carbon single bonds. However, the fluorination of carbon materials requires extremely toxic and moisture‐sensitive reagents, which makes it inapplicable for practical uses. Here, a straightforward and relatively safe method are reported for the scalable synthesis of FCMs, by mechanochemical depolymerization of polytetrafluoroethylene (PTFE) and fragmentation of graphite. The resultant FCMs are evaluated as anode materials for lithium‐ion batteries (LIBs). An optimized FCM delivered capacities as high as 951.6 and 329.3 mAh g −1 at 0.05 and 10 A g −1, respectively. It also demonstrated capacity retention as high as 76.6% even after 1000 cycles at 2.0 A g −1.

Monodisperse Cyclic Polymer Mechanochemistry: Scission Kinetics and the Dynamic Memory Effect with Ultrasonication and Ball-Mill Grinding.

A series of monodisperse cyclic and linear poly(d,l-lactide)s (c-PLA and l-PLA, respectively) were prepared with various degrees of polymerization (DP) using an iterative convergent synthesis approach. The absence of a molecular weight distribution provided us a chance to study their mechanochemical reactivity without obstructions arising from the size distribution. Additionally, we prepared l- and c-PLAs with identical DPs, which enabled us to attribute differences in scission rates to the cyclic polymer architecture alone. The polymers were subjected to ultrasonication (US) and ball-mill grinding (BMG), and their degradation kinetics were explored. Up to 9.0 times larger scission rates were observed for l-PLA (compared to c-PLA) with US, but the difference was less than 1.9 times with BMG. Fragmentation requires two backbone scission events for c-PLA, and we were able to observe linear intermediates (formed after a single scission) for the first time. We also developed a new method of studying the dynamic memory effect in US by characterizing and comparing the daughter fragment molecular weight distributions of l- and c-PLAs. These results provide new insights into the influence of the cyclic polymer architecture on mechanochemical reactions as well as differences in reactivity observed with US and BMG.

Inducing Magnetic Properties with Ferrite Nanoparticles in Resins for Additive Manufacturing.

Additive manufacturing and nanotechnology have been used as fundamental tools for the production of nanostructured parts with magnetic properties, expanding the range of applications in additive processes through tank photopolymerization. Magnetic cobalt ferrite (CoFe2O4) and barium ferrite (BaFe12O19) nanoparticles (NPs) with an average size distribution value (DTEM) of 12 ± 2.95 nm and 37 ± 12.78 nm, respectively, were generated by the hydroxide precipitation method. The dispersion of the NPs in commercial resins (Anycubic Green and IRIX White resin) was achieved through mechanochemical reactions carried out in an agate mortar for 20 min at room temperature, with limited exposure to light. The resulting product of each reaction was placed in amber vials and stored in a box to avoid light exposure. The photopolymerization process was carried out only at low concentrations (% w/w NPs/resin) since high concentrations did not result in the formation of pieces, due to the high refractive index of ferrites. The Raman spectroscopy of the final pieces showed the presence of magnetic NPs without any apparent chemical changes. The electron paramagnetic resonance (EPR) results of the pieces demonstrated that their magnetic properties were maintained and not altered during the photopolymerization. Although significant differences were observed in the dispersion process of the NPs in each piece, we determined that the photopolymerization did not affect the structure and superparamagnetic behavior of ferrite NPs during processing, successfully transferring the magnetic properties to the final 3D-printed piece.

Structure analysis and electrical properties of 10PbTiO3─10Fe2O3─30V2O5─50B2O3 via high energy mechanochemical technique

A non-conventional mechanochemical processing technique was used to prepare fine-grain of mixed iron and vanadium oxides with a lead titanate system at boron oxide matrix. The structures of the ball milled samples were analyzed at different milling times and temperatures. After 30h of mechanical milling, the vanadium peaks completely disappeared, and partially supersaturated solid solution was formed. The average crystallite size of the 30h milled sample calculated from XRD patterns decreases rapidly from 3.72 μm to 69.4 nm while the crystallite size of the 50h was 26.3 nm. The DSC curve confirms the mechanochemical reactions. Metastable phases of lead vanadium oxide obtained after heat treatment with average crystallite size 65 nm in a non-crystalline matrix. The conductivity of the heat-treated samples increases with increasing heating temperature. The conductivity of all the prepared samples was found to be consistent with small polaron hopping, Mott’s theory which confirmed by studying the power law behavior of its AC conductivity. The AC conductivity increases with increasing temperature and frequency.

Mechanosynthesis and electrical conductivity of undoped and calcium-substituted GdAlO3 perovskites

Gadolinium aluminate (GdAlO3) and its calcium-substituted derivates (Gd1-xCaxAlO3-δ; x = 0.05, 0.10 and 0.15) are prepared via one-step mechanochemical processing of simple oxide precursors at ambient temperature. The mechanochemical reaction is accompanied by Gd2O3 phase transformation. The as-prepared and sintered materials are characterized by X-ray diffraction and scanning electron microscopy. Sintering at 1450 °C resulted in relatively porous ceramics (with density <90 % of theoretical value) except Gd0.85Ca0.15AlO3-δ. The electrical conductivity of the sintered samples was investigated by impedance spectroscopy at 350–1000 °C in air. Undoped GdAlO3 ceramics exhibit low conductivity, ∼10−6 S/cm at 800 °C. Acceptor-type substitution of 5 at % of gadolinium by calcium results in ∼3 orders of magnitude increase in both total and bulk conductivity associated with a substantial enhancement in oxygen-ionic transport. Further doping has a limited effect on the electrical transport properties, and electrical conductivity remains nearly composition-independent in the range x = 0.05–0.15. Grain boundaries are demonstrated to have a significant contribution to the total resistivity of prepared calcium-substituted Gd1-xCaxAlO3-δ ceramics with grain sizes in the range of 1.1–1.5 µm.

Mechanochemical Reactions from Individual Impacts to Global Transformation Kinetics

AbstractTypically induced by the mechanical processing of powders in ball mills, mechanochemical transformations are considered to result from the application of mechanical force to solid reactants. However, the undeniable deep connection between the dynamic compaction of powders during impacts and the overall transformation degree has yet to be disclosed. In the present work, we show that the square planar bis(dibenzoylmethanato)NiII coordination compound undergoes trimerization when its powder experiences even a single ball impact. Based on systematic experiments with individual ball impacts and analysis by Raman spectroscopy, we provide here quantitative mapping of the transformation in the powder compact and deduce bulk reaction kinetics from multiple individual impacts.