Search Results (268)

In this work, we report a novel mechanochemical synthesis method for the synthesis of quinoxaline derivatives—a spiral gas–solid two-phase flow approach, which enables the efficient preparation of quinoxaline compounds. Compared to conventional synthetic methods, this approach eliminates the need for heating or solvents while significantly reducing reaction time. The structures of the synthesized compounds were characterized using nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV–Vis) absorption spectroscopy, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and high-performance liquid chromatography (HPLC). Using the synthesis of 2,3-diphenylquinoxaline (1) as a model reaction, the synthetic process was investigated with UV–Vis spectroscopy. The results demonstrate that when the total feed amount was 2 g with a carrier gas pressure of 0.8 MPa, the reaction completed within 2 min, achieving a yield of 93%. Furthermore, kinetic analysis of the reaction mechanism was performed by monitoring the UV–Vis spectra of the products at different time intervals. The results indicate that the synthesis of 1 follows the A4 kinetic model, which describes a two-dimensional diffusion-controlled product growth process following decelerated nucleation. Full article

Mechanochemical and transition-metal-catalyzed reactions of alkynes, exhibiting significant advantages like short reaction time, solvent-free, high yield and good selectivity, were considered to be green and sustainable pathways to access functionalized molecules and obtained increasing attention due to the superiorities of mechanochemical processes and the reactivities of alkynes. The ball milling and CuI-catalyzed Sonogashira coupling of alkyne and aryl iodide avoided the use of common palladium catalysts. The mechanochemical Rh(III)- and Au(I)-catalyzed C–H alkynylations of indoles formed the 2-alkynylated and 3-alkynylated indoles selectively. The mechanochemical and copper-catalyzed azide-alkyne cycloaddition (CuAAC) between alkynes and azides were developed to synthesize 1,2,3-triazoles. Isoxazole could be formed through ball-milling-enabled and Ru-promoted cycloaddition of alkyne and hydroxyimidel chloride. In this review, the generation of mechanochemical and transition-metal-catalyzed reactions of alkynes was highlighted. Firstly, the superiority and application of transition-metal-catalyzed reactions of alkynes were briefly introduced. After presenting the usefulness of green chemistry and mechanochemical reactions, mechanochemical and transition-metal-catalyzed reactions of alkynes were classified and demonstrated in detail. Based on different kinds of reactions of alkynes, mechanochemical and transition-metal-catalyzed coupling, cycloaddition and alkenylation reactions were summarized and the proposed reaction mechanisms were disclosed if available. Full article

This study explores the enhanced photocatalytic performance of boron-doped zinc oxide (ZnO) nanoparticles synthesized via a scalable mechanochemical route. Utilizing X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), the structural and morphological properties of these nanoparticles were assessed. Specifically, nanoparticles with 1 wt%, 2.5 wt%, and 5 wt% boron doping were analyzed after calcination at temperatures of 500 °C, 600 °C, and 700 °C. The obtained results indicate that 1 wt% B-ZnO nanoparticles calcined at 700 °C show superior photocatalytic efficiency of 99.94% methyl orange degradation under UVA light—a significant improvement over undoped ZnO. Furthermore, the study introduces a predictive model using the artificial neural network (ANN) technique, developed in Python, which effectively forecasts photocatalytic performance based on experimental conditions with R² = 0.9810. This could further enhance wastewater treatment processes, such as heterogeneous photocatalysis, through ANN-guided optimization. Full article

Despite significant advances in understanding neuronal development, a fully quantitative framework that integrates intracellular mechanisms with environmental cues during axonal growth remains incomplete. Here, we present a unified biophysical model that captures key mechanochemical processes governing axonal extension on micropatterned substrates. In these environments, axons preferentially align with the pattern direction, form bundles, and advance at constant speed. The model integrates four core components: (i) actin–adhesion traction coupling, (ii) lateral inhibition between neighboring axons, (iii) tubulin transport from soma to growth cone, and (iv) orientation dynamics guided by substrate anisotropy. Dynamical systems analysis reveals that a saddle–node bifurcation in the actin adhesion subsystem drives a transition to a high-traction motile state, while traction feedback shifts a pitchfork bifurcation in the signaling loop, promoting symmetry breaking and robust alignment. An exact linear solution in the tubulin transport subsystem functions as a built-in speed regulator, ensuring stable elongation rates. Simulations using experimentally inferred parameters accurately reproduce elongation speed, alignment variance, and bundle spacing. The model provides explicit design rules for enhancing axonal alignment through modulation of substrate stiffness and adhesion dynamics. By identifying key control parameters, this work enables rational design of biomaterials for neural repair and engineered tissue systems. Full article

This work investigated the structural response and phase transformation dynamics of silica-bearing cherts subjected to high-temperature processing (up to 1400 °C) and prolonged mechanochemical activation. Through a combination of X-ray diffraction (XRD) with Rietveld refinement, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and transmission electron microscopy (HRTEM), we trace the crystallographic pathways of quartz, moganite, tridymite, and cristobalite under controlled thermal and mechanical stress regimes. The experimental results demonstrated that phase behavior is highly dependent on intrinsic properties such as initial phase composition, impurity presence, and crystallinity. Heating at 1400 °C induced irreversible conversion of quartz, moganite, and tridymite into cristobalite. Samples enriched in cristobalite and tridymite exhibited notable increases in crystallinity, whereas quartz-dominant samples showed either stability or a decline in structural order. Rietveld analyses underscored the critical influence of microstrain and crystallite size on thermal resilience and phase persistence. Thermal profiles revealed by DSC and TGA expose overlapping processes including polymorphic transitions, minor phase dehydration, and redox-driven changes, likely associated with trace components. Mechanochemical processing resulted in partial amorphization and the emergence of phases such as opal and feldspar minerals (microcline, albite, anorthite), interpreted as the product of lattice collapse and subsequent reprecipitation. Heat treatment of chert leads to a progressive rearrangement and recrystallization of its silica phases: quartz collapses around 1000 °C before recovering, tridymite emerges as an intermediate phase, and cristobalite shows the greatest crystallite size growth and least deformation at 1400 °C. These phase changes serve as markers of high-temperature exposure, guiding the identification of heat-altered lithic artefacts, reconstructing geological and diagenetic histories, and allowing engineers to adjust the thermal expansion of ceramic materials. Mechanochemical results provide new insights into the physicochemical evolution of metastable silica systems and offer valuable implications for the design and thermal conditioning of silica-based functional materials used in high-temperature ceramics, glasses, and refractory applications. From a geoarchaeological standpoint, the mechanochemically treated material could simulate natural weathering of prehistoric chert tools, providing insights into diagenetic pathways and lithic degradation processes. Full article

Nd–Fe–B permanent magnets are vital for numerous key technologies in strategic sectors such as renewable energy production, e-mobility, defense, and aerospace. Accordingly, the demand for rare earth elements (REEs) enormously increases in parallel to a significant uncertainty in their supply. Thus, research and innovative studies are focus on the investigation of sustainable solutions to the problem and a closed-loop value chain. The present study is based on two benign-by-design approaches aimed at decreasing the recycling loop span by preparing standardized batches of EoL Nd–Fe–B materials to be treated separately depending on their properties, as well as using mechanochemical method for waste processing. The previously reported benefits of both direct recycling and mechanochemistry include significant improvements in processing metrics, such as energy use, ecological impact, technology simplification, and cost reduction. Waste-sintered Nd–Fe–B magnets from motorbikes were collected, precisely sorted, selected, and pre-treated. The study presents a protocol of resource-efficient recycling through mechanochemical processing of non-oxidized sintered EoL magnets, involving the extraction of Nd₂Fe₁₄B magnetic grains and refining the material’s microstructure and particle size after 120 min of high-energy ball milling in a zirconia reactor. The recycled material preserves the main Nd₂Fe₁₄B magnetic phase, while an anisotropic particle shape and formation of a thin Nd/REE-rich layer on the grain surface were achieved. Full article

In this investigation, a novel process for the synthesis of nano-ZrO₂ powders based on high-temperature mechanochemical technology (HTMT) in a short process is proposed and HTMT nano-ZrO₂ enhancement mechanism as an additive on the properties of B₄C ceramics was systematically investigated. ZrO(OH)₂ was used as a precursor, and ZrO₂-B₄C composites were prepared by optimizing the ball milling temperature and time in combination with the hot-press sintering technique. The results demonstrated that the high-temperature mechanical force causes the transition temperature of ZrO₂ from monoclinic to tetragonal crystal system to be decreased to 500 °C. The ZrO₂ treated by high-temperature ball milling at 600 °C/6 h exhibits lower microstress, higher crystallinity, and a particle size of only about 9.12 nm. HTMT nano-ZrO₂ effectively controls the size of in situ generated ZrB₂ particles in B₄C ceramics, reduces interfacial porosity and grain coarsening, and promotes densification of B₄C ceramics compared to commercially available nano-ZrO₂. With the addition of 4 wt% HTMT nano-ZrO₂, the composite showed optimal comprehensive properties: relative density of 99.75% (2.57 g/cm³), fracture toughness of 4.74 MPa/m^1/2, flexural strength of 266.61 MPa, Vickers hardness of 31.14 GPa, and fracture mode with mixed mechanism of through-crystallization and along-crystallization. Full article

The synthesis of calcium carbonate (CaCO₃) nanoparticles has gained an increasing interest due to their improved properties and diverse industrial applications. Among various synthesis techniques, the mechanochemical synthesis process has emerged as a promising route for nano-CaCO₃ synthesis. A high-energy ball mill is required for synthesizing nano-CaCO₃, whereas post-milling heat treatment facilitates completing the reaction that remains incomplete during milling. Post-milling heat treatment may also influence the properties of synthesized CaCO₃, which has not yet been thoroughly investigated. This study investigated the influence of post-milling heat treatment on the polymorphs, micromorphology, and particle size distribution of CaCO₃. The results indicated that the heat treatment of the as-milled powder enhanced the homogeneity of crystal polymorphs while maintaining the particle sizes within the nano-range (<100 nm). X-ray diffraction (XRD) analysis identified two polymorphs (vaterite and calcite) in samples obtained from different milling intensities. However, after heat treatment, all vaterite transformed into calcite. A bimodal particle size distribution was observed in CaCO₃ nanoparticles and was influenced by both the milling and heating intensities. It was observed that 60 min heat applied to 30 min as-milled powder was enough to produce nano-CaCO₃ (<50 nm) where the percentage of larger particles (<250 nm) became negligible (~1%). Micromorphology images confirmed the transformation of crystal polymorphs and the reduction in particle size. Full article

This study investigates the mechanochemical transformation of commercial vermiculites from Uganda and China, processed for 30 minutes (30 min), 8 hours (8 h), and 24 hours (24 h). Structural and textural modifications were analyzed using X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area measurements, and scanning electron microscopy (SEM). Characterization via X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area measurements, and scanning electron microscopy (SEM) revealed substantial structural and textural modifications. Crystallinity decreased significantly, from 66.37% to 3.47% in the Ugandan sample, whereas the three mixed-phase Chinese samples exhibited greater structural resilience, with final crystallinity ranging from 3.82% to 6.30%. Mechanochemical treatment induced mineral phase transformations, including hydrobiotite formation in the Ugandan sample and Fe₃Si, quartz, moganite, and NaMgH₃ in the Chinese samples. Particle size reduced significantly, reaching submicrometric dimensions after 24 h, with C1 showing the smallest mean size (0.39 µm). BET analysis showed an initial increase in specific surface area, peaking at 31.83 m²/g for C1 after 8 h, followed by a decrease due to pore collapse. The optimal treatment time varied by sample, with 30 min maximizing adsorption in C2 and C3, while 8 h was most effective for C1. These findings highlight mechanochemical treatment as a viable method for tuning vermiculite properties for applications in adsorption, catalysis, and composite materials. Full article

The goal of this work was to prepare modified titanium dioxide catalysts applicable for self-cleaning and disinfecting surfaces, possessing both antibacterial and photocatalytic activity in the visible-light region, via green and affordable synthesis. For this purpose, silverization was chosen due to its antibacterial and electron-capturing effects, and to achieve efficient visible-light excitation, urea was used as a precursor for nitrogen doping. Mechanochemical activation with grinding, as an environmentally friendly process, was applied for the catalyst modification under various conditions, such as the amounts of the modifying substances, the milling time, the ratio of the weights of the material to be ground, and the grinding balls. The photocatalytic activity in the UV and visible range was tested in suspensions with oxalic acid and coumarin as model compounds. The antibacterial effect was measured by the bioluminescence of Vibrio fischeri bacteria. The highest photocatalytic activity in the visible range was observed with the nitrogen-doped titanium dioxide (N-TiO₂) prepared with 10% urea. Silveration of N-TiO₂ (up to 0.2%) decreased photocatalytic activity while improving the antibacterial efficiency. To maximize both effects, mechanical mixtures of the separately modified catalysts (N-TiO₂ and Ag-TiO₂) were also examined in different ratios. The 1:1 mixture provided the optimum combination. Full article

The microwave heating of silicon carbide is induced at a specific frequency of 2.45 GHz, leading to rapid heating within a temperature range of several hundred degrees Celsius. In this study, a mechanochemical curing process using iodine was employed to cure polycarbosilane (PCS), followed by the addition of carbon nanotubes (CNTs) to produce mixed polymer powders. The effects of the CNT addition on the microstructure, crystalline structure, and microwave heating properties were investigated. The findings indicated that the incorporation of CNTs generally led to a reduction in the number of micropores; however, when the CNT concentration exceeded 10 wt%, the aggregation of CNTs became evident. In terms of microwave heating properties, the sample containing 0.1 wt% CNTs achieved the highest temperature, whereas samples with a higher CNT content demonstrated a heating limit of approximately 500 °C. Remarkably, post-processing of the specimens with 10 wt% CNTs enabled rapid heating to approximately 1800 °C within 4 s of microwave exposure. Full article

In the search for technologies and materials to improve the safety and efficacy of active ingredients used in treating diseases, layered double hydroxides (LDHs) have been proposed as drug carriers since they can enhance the effects of active ingredients and even reduce toxicity. Doxorubicin (DOX) is one of the most widely used and studied antitumor drugs due to its broad spectrum; however, due to its low plasma bioavailability and slow systemic clearance, only a small fraction of the drug reaches and acts on the tumor, so LDHs have been proposed as vehicles to solve these disadvantages. The most used method to load the drug is incubating LDH particles in DOX solutions. In this work, two additional methods, co-precipitation, and mechanochemical reaction, were explored to evaluate the structural stability of the vehicle and the amount of DOX retained by LDHs structured by magnesium/aluminum and zinc/aluminum cations, which are the two most common compositions to design materials for biomedical applications. The zinc/aluminum LDH structure degraded in the loading process, whereas the magnesium/aluminum LDH particles were stable against the three loading processes. The mechanochemical procedure, a green and sustainable technology, loaded the highest content of DOX. Full article

Natural zeolites (NatZ) are widely available, porous, crystalline aluminosilicate minerals that are commonly used as cost-effective adsorbents in water treatment processes. Despite their efficiency in removing various heavy metal ions from wastewater, NatZ show relatively low affinity toward Ni²⁺ and Cr³⁺ ions. This study aimed to develop composite adsorbents based on NatZ and hydroxyapatite using two methods, hydrothermal and mechanochemical, and their adsorption properties for the removal of Ni²⁺ and Cr³⁺ ions from aqueous solutions were investigated. X-ray powder diffraction and scanning electron microscopy analyses confirmed that under hydrothermal conditions, needle-like hydroxyapatite crystals were formed on the surface of NatZ, while the zeolite structure remained unchanged. Compared to the mechanochemically prepared sample, this adsorbent showed higher efficiency, binding 6.91 mg Ni²⁺/g and 16.95 mg Cr³⁺/g. Adsorption kinetics of the tested cations in both cases can be described by a pseudo-second-order model (R² is higher than 0.95 for all adsorbents). It is concluded that the presence of hydroxyapatite on the zeolite surface significantly improves the adsorption performance of NatZ, demonstrating its potential for the removal of heavy metal ions in wastewater treatment. Full article

After attending both the “Decade to Educate in the Sustainable Development and the Agenda 30 of the UNESCO” and the “ACS GCI Pharmaceutical Roundtable”, which focused on sustainable chemistry, in this article, a green chemistry contribution to the Kamal Qureshi protocol is offered; thus, DIM^® and several of its analogs (3,3′-diindolylmethanes) were suitably produced under the green chemistry protocol. In the first stage, the substrate indol-3-yl carbinol was evaluated using mechanochemistry (the best mode) in comparison to other activating methods (near-infrared and microwave electromagnetic irradiation and ultrasound), wishing to highlight the employment of both TAFF^®, an excellent and well-characterized natural catalyst (bentonitic clay), and acetone, a green solvent, in addition to the analysis of the procedures in real-time. In the second stage, the mechanochemical methodology was extended to produce a set of fifteen DIMs, in the last stage, the use of a green metric exhibited the greenness of the approach, with it being important to highlight that, to our knowledge, after a search in the literature, this is the first time that the process has been evaluated to demonstrate its greenness. Full article

This study examines the effects of thermal (1000 °C), hydrothermal (100 °C), mechanochemical (ambient T), and microwave (~100 °C) treatments on three types of Chinese vermiculites, one with lower potassium content than the others. The goal was to obtain materials with enhanced properties related to specific surface areas. The response of the vermiculites to treatments and their physicochemical properties were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTG), and textural characterization via the BET method. XRD analyses showed similar mineral composition in treated and untreated samples, but the treatments affected the intensity and width of phase reflections, altering crystallinity and structural order, as well as the proportions of vermiculite, hydrobiotite, and phlogopite. Thermogravimetric analysis revealed two mass loss stages: water desorption (from 25 °C to about 250 °C) and recrystallization or dehydroxylation (above 800 °C). The isotherms indicated mesoporous characteristics, with hydrothermally CO₂-treated samples having the highest specific surface area and adsorption capacity. The samples with vermiculite, hydrobiotite, and phlogopite generally showed moderate to high specific surface area (S_BET) values, and mechanochemical treatments significantly increase S_BET and pore volume (V_p) in the vermiculite and hydrobiotite samples. Crystallinity affects S_BET, average V_p, and average pore size, and its monitoring is crucial to achieve the desired material characteristics, as higher crystallinity can reduce S_BET but improve mechanical strength and thermal stability. This study highlights the influence of different treatments on vermiculite properties, providing valuable insights into their potential applications in various fields (such as thermal insulation in vehicles and aircraft, and the selective adsorption of gases and liquids in industrial processes, improving the strength and durability of building materials like cement and bricks). Full article