Search Results (511)

2,5-bis(hydroxymethy)lfuran (BHMF), a renewable compound with extensive industrial applications, can be obtained by selective hydrogenation of the C=O group of 5-hydroxymethylfurfural (HMF), a platform molecule derived from lignocellulosic biomass. In this work, we perform kinetic modeling of the selective liquid-phase hydrogenation of HMF to BHMF over a Cu/SiO₂ catalyst prepared by precipitation–deposition (PD) at a constant pH. Physicochemical characterization, using different techniques, confirms that the Cu/SiO₂–PD catalyst is formed by copper metallic nanoparticles of 3–5 nm in size highly dispersed on the SiO₂ surface. Before the kinetic study, the Cu/SiO₂-PD catalyst was evaluated in three solvents: tetrahydrofuran (THF), 2-propanol (2-POH), and water. The pattern of catalytic activity and BHMF yield for the different solvents was THF > 2-POH > H₂O. In addition, selectivity to BHF was the highest in THF. Thus, THF was chosen for further kinetic study. Several experiments were carried out by varying the initial HMF concentration (C⁰_HMF) between 0.02 and 0.26 M and the hydrogen pressure (P_H2) between 200 and 1500 kPa. In all experiments, BHMF selectivity was 97–99%. By pseudo-homogeneous modeling, an apparent reaction order with respect to HFM close to 1 was estimated for a C⁰_HMF between 0.02 M and 0.065 M, while when higher than 0.065 M, the apparent reaction order changed to 0. The apparent reaction order with respect to H₂ was nearly 0 when C⁰_HMF = 0.13 M, while for C⁰_HMF = 0.04 M, it was close to 1. The reaction orders estimated suggest that HMF is strongly absorbed on the catalyst surface, and thus total active site coverage is reached when the C⁰_HMF is higher than 0.065 M. Several Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were proposed, tested against experimental data, and statistically compared. The best fitting of the experimental data was obtained with an LHHW model that considered non-competitive H₂ and HMF chemisorption and strong chemisorption of reactant and product molecules on copper metallic active sites. This model predicts both the catalytic performance of Cu/SiO₂-PD and its deactivation during liquid-phase HMF hydrogenation. Full article

Series of pyrene-labeled diols (Py₂-DOs) and polyols (Py-POs) were synthesized by coupling a number (n_PyBA) of 1-pyrenebutyric acids to diols and polyols to yield series of end-labeled linear (n_PyBA = 2) and branched (n_PyBA > 2) oligomers, respectively. Pyrene excimer formation (PEF) between an excited and a ground-state pyrene was studied for the Py₂-DO and Py-PO samples by analyzing their fluorescence spectra and decays in tetrahydrofuran, dioxane, N,N-dimethylformamide, and dimethyl sulfoxide. Global model-free analysis (MFA) of the pyrene monomer and excimer fluorescence decays yielded the average rate constant (<k>) for PEF. After the calculation of the local pyrene concentration ([Py]_loc) for the Py₂-DO and Py-PO samples, the <k>-vs.-[Py]_loc plots were linear in each solvent, with larger and smaller slopes for the Py₂-DO and Py-PO samples, respectively, resulting in a clear kink in the middle of the plot. The difference in slope was attributed to a bias for PEF between pyrenes close to one another on the densely branched Py-PO constructs resulting in lower apparent [Py]_loc and <k> values. This study illustrated the ability of PEF to probe how steric hindrance along a main chain affects the dynamic encounters between substituents in multifunctional oligomers such as diols and polyols. Full article

Delivering of hydrophobic drugs by polymeric nanoparticles is an intensively investigated research and development field worldwide due to the insufficient solubility of many existing and potential new drugs in aqueous media. Among polymeric nanoparticles, micelles of biocompatible amphiphilic block copolymers are among the most promising candidates for solubilization, encapsulation, and delivery of hydrophobic drugs to improve the water solubility and thus the bioavailability of such drugs. In this study, amphiphilic ABA triblock copolymers containing biocompatible hydrophilic hyperbranched (dendritic) polyglycerol (HbPG) outer and hydrophobic poly(tetrahydrofuran) (PTHF) inner segments were synthesized using amine-telechelic PTHF as a macroinitiator for glycidol polymerization. These hyperbranched–linear–hyperbranched block copolymers form nanosized micelles with 15–20 nm diameter above the critical micelle concentration. Coagulation experiments proved high colloidal stability of the aqueous micellar solutions of these block copolymers against temperature changes. The applicability of block copolymers as drug delivery systems was investigated using curcumin, a highly hydrophobic, water-insoluble, natural anti-cancer agent. High and efficient drug solubilization up to more than 3 orders of magnitude to that of the water solubility of curcumin (>1500-fold) is achieved with the HbPG-PTHF-HbPG block copolymer nanomicelles, locating the drug in amorphous form in the inner PTHF core. Outstanding stability of and sustained curcumin release from the drug-loaded block copolymer micelles were observed. The in vitro bioactivity of the curcumin-loaded nanomicelles was investigated on U-87 glioblastoma cell line, and an optimal triblock copolymer composition was found, which showed highly effective cellular uptake and no toxicity. These findings indicate that the HbPG-PTHF-HbPG triblock copolymers are promising candidates for advanced drug solubilization and delivery systems. Full article

Ion interactions with molecular structures give insights into physicochemical processes in the cosmos, radiation damage, plasma, combustion, and biomass conversion reactions. At the atomic scale, these interactions lead to excitation, ionization, and dissociation of the molecular components of structures found across all these environments. Furan, cyclic aromatic ether (C₄H₄O), serves as a gas-phase deoxyribose analog and is crucial for understanding key pathways in renewable biomass conversion, as its derivatives are versatile molecules from lignocellulosic biomass degradation. Therefore, collisions of H₃⁺ and C⁺ ions with gas-phase furan molecules were investigated in the 50–1000 eV energy range, exploiting collision-induced emission spectroscopy. High-resolution fragmentation spectra measured at 1000 eV for both cations reveal similar structures, with C⁺ collisions resulting in more significant furan fragmentation. Relative cross-sections for product formation were measured for H₃⁺ + C₄H₄O collisions. Possible collisional processes and fragmentation pathways in furan are discussed. These results are compared with those for tetrahydrofuran and pyridine to illustrate how the type and charge of the projectile influence neutral fragmentation in heterocyclic molecules. Full article

A separable bamboo-like carbon nanotube-based catalyst was prepared by the spherfication method using sodium alginate and nickel. The spheres were carbonized and then decorated with palladium nanoparticles before they were tested in nitrobenzene hydrogenation. The test was repeated with five different commonly used solvents (methanol, ethanol, isopropanol, tetrahydrofuran, and acetonitrile). According to the results, polar solvents showed a significantly higher aniline yield than the more apolar solvents and exceptional results were reported for ethanol (~100%). The catalyst was reused two more times (four hours each) to check the Pd leaching where the spheres kept their shape (despite the high mechanical friction caused by the mixer) and only a relatively low Pd amount was lost (5.48 rel.%). The catalyst was easily retrievable. Full article

Poly(3,3-bis(azidomethyl)oxetane(BAMO)-tetrahydrofuran(THF)) copolymer (PBT) and ammonium perchlorate (AP) are critical components of solid rocket propellants, where their interfacial bonding mechanisms and temperature-dependent mechanical properties are pivotal to propellant reliability. In this study, density functional theory (DFT) calculations were employed to evaluate the adsorption energies between common AP crystal surfaces and PBT units, identifying the most energetically favorable adsorption configurations. The atomic configurations and charge transfer characteristics at the PBT-AP interface were systematically analyzed. Molecular dynamics (MD) simulations were further conducted to determine the thermally stable operating range of the PBT-AP system. The results reveal a strong temperature dependence of mechanical performance, with viscous failure mechanisms and damage thresholds during static tensile processes investigated across varying temperatures. Notably, mechanical properties remain stable below 60 °C but deteriorate significantly above this temperature. This study elucidates the influence of a PBT-AP interfacial microstructure and temperature on mechanical performance and tensile fracture damage boundaries, providing crucial insights for the design, formulation, and safe application of PBT-based solid rocket propellants. Full article

Hydrate-based gas separation (HBGS) is a new method for extracting helium from helium-rich natural gas (HNG). The ethane in HNG affects the thermodynamic equilibrium hydrate formation pressure (Peq), and Peq is crucial to the application of HBGS for extracting helium. In this work, the Peq of the HNGs with different ethane contents (0.5 mol%, 1.0 mol%, and 10 mol%) and the solutions with different tetrahydrofuran (THF) contents (5 wt%, 10 wt%, and 19 mol%) at different temperatures were experimentally investigated through the isothermal pressure search method. Ethane and THF have a competitive effect on hydrate formation. A new thermodynamic model was proposed to predict the Peq of different HNG–THF solution systems. The effect of ethane on Peq can be quantitatively described, and the Peq of HNGs can be accurately predicted by the model in this work. The average relative deviation of the model for predicting Peq of HNGs in different THF aqueous solution systems is less than 3%. The results of this study can guide the operating conditions for the optimization of extracting helium from HNGs by the HBGS process. Full article

Deep coal seams in the Junggar Basin, China, have demonstrated high gas yields due to enhanced pore structures resulting from hydraulic fracturing. However, raw coal samples inadequately represent these stimulated reservoirs, and acquiring fractured core samples post-stimulation is impractical. To address this, a novel and operable laboratory method has been developed to fabricate porosity-enhanced synthetic coal plugs that better simulate deep coalbed methane reservoirs. The fabrication process involves crushing lignite and separating it into three particle size fractions (<0.25 mm, 0.25–1 mm, and 1–2 mm), followed by mixing with a resin-based binder system (F51 phenolic epoxy resin, 650 polyamide, and tetrahydrofuran). These mixtures are molded into cylindrical plugs (⌀50 mm × 100 mm) and cured. This approach enables tailored control over pore development during briquette formation. Porosity and pore structure were comprehensively assessed using helium porosimetry, mercury intrusion porosimetry (MIP), and micro-computed tomography (micro-CT). MIP and micro-CT confirmed that the synthetic plugs exhibit significantly enhanced porosity compared to raw lignite, with pore sizes and volumes falling within the macropore range. Specifically, porosity reached up to 27.84%, averaging 20.73% and surpassing the typical range for conventional coal briquettes (1.89–18.96%). Additionally, the resin content was found to strongly influence porosity, with optimal levels between 6% and 10% by weight. Visualization improvements in micro-CT imaging were achieved through iodine addition, allowing for more accurate porosity estimations. This method offers a cost-effective and repeatable strategy for creating coal analogs with tunable porosity, providing valuable physical models for investigating flow behaviors in stimulated coal reservoirs. Full article

Diblock copolymers (BCP) consisting of poly(methyl methacrylate) (PMMA) and poly(1H,1H,2H,2H-perfluorodecyl methacrylate) (PsfMA) blocks are employed as templates for controlled dispersion and localization of multi-walled carbon nanotubes (MWCNT). Short MWCNT are modified with perfluoroalkyl groups to increase the compatibility between MWCNT and the semifluorinated (PsfMA) phase and to promote a defined arrangement of MWCNT in the BCP morphology. Thin BCP and BCP/MWCNT composite films are prepared by dip-coating using tetrahydrofuran as solvent with dispersed MWCNT. Atomic force microscopy, scanning and transmission electron microscopy reveal a strong tendency of the BCP to form micelle-like domains consisting of a PMMA shell and a semifluorinated PsfMA core, embedded in a soft phase, containing also semifluorinated blocks. MWCNT preferentially localized in the embedding phase outside the micelles. Perfluoroalkyl-modification leads to significant improvement in the dispersion of MWCNT, both in the polymer solution and the resulting nanocomposite film due to increased interaction of MWCNT with the semifluorinated side chains in the soft phase outside the micelle domains. As a result, reliable electrical conductivity is observed in contrast to films with non-modified MWCNT. Thus, well-dispersed, modified MWCNT provide a defined electrical conduction path at the micrometer level, which is interesting for applications in electronics and vapor sensing. Full article

Due to the widespread utilization of biodegradable plastics (such as polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT)) as alternatives to traditional plastics such as PE and PP, the disposal of the end-of-use biodegradable plastic products mixed with other waste has increasingly become an issue. This study investigated the co-pyrolysis characteristics, kinetic features, product formation, and synergistic effects of common biodegradable plastics (PLA and PBAT) and kitchen waste (KW) at different mass ratios, using TGA-FTIR-GC/MS. The findings revealed that the addition of KW significantly lowered the pyrolysis temperature. For the PLA and KW with a 2:1 mass ratio, the activation energy decreased by approximately 35 kJ/mol compared to PLA pyrolysis alone. The production of lactide increases significantly, while the formation of aldehydes and CO decreases. Moreover, the co-pyrolysis of KW and PBAT reduces the formation of harmful substances such as tetrahydrofuran and cyclopentanone. This study provides valuable insights into the pyrolysis process of mixed biodegradable plastic waste, offering a better approach for the disposal of similar forms of waste and resource recovery scenarios. Full article

In this study, we examined the oxidation of (E)-2-hydroxy-1-naphthaldehyde oxime with lead tetraacetate in tetrahydrofuran that produced novel (E)-7a,8,9,10-tetrahydro-12H-naphtho[1,2-e]pyrrolo[2,1-b][1,3]oxazin-12-one oxime and 1-(pyrrolidin-1-yl)naphtho[1,2-d]isoxazole and known 7a,8,9,10-tetrahydro-12H-naphtho[1,2-e]pyrrolo-[2,1-b][1,3]oxazin-12-one in 15, 18, and 10% yields, respectively. The oxime is partially hydrolyzed to its corresponding ketone. Modifying the oxidants and reaction conditions did not improve the product yields. Based on previous studies in our laboratory, we proposed that the reactions proceed via the formation of an o-naphthoquinone nitrosomethide intermediate; 1D and 2D NMR, HRMS, IR, and UV-VIS spectra provided information that supported the structure of the products. Full article

In our research aimed at replacing precious transition metals like platinum with abundant base metals such as nickel for efficient triplet emitters, we synthesized and studied Ni(II) complexes [Ni(L^NHR)Cl]. These complexes containing the N^C^N cyclometalating dipyridyl-phenide ligand, equipped with pending H-bonding amine groups (NH(C₆H₅) (L^NHPh) and NH(C₆H₅CH₂), ClL^NHBn). Molecular structures determined from experimental X-ray diffractometry and density functional theory (DFT) calculations in the ground state showed marked deviation of the Cl⁻ coligand (ancillary ligand) from the ideal planar coordination, with τ₄ values of 0.35 and 0.33, respectively, along with hydrogen bonding interactions of the ligand NH function with the Cl⁻ coligand. The complexes exhibit long-wavelength absorption bands at approximately 425 nm in solution, with the experimental spectra being accurately reproduced through time-dependent density functional theory (TD-DFT) calculations. Vibrationally structured emission profiles and steady-state photoluminescence quantum yields of 30% for [Ni(L^NHPh)Cl] and 40% for [Ni(L^NHBn)Cl] (along with dual excited state lifetimes in the ns and in the ms range) were found in frozen 2-methyl-tetrahydrofuran (2MeTHF) glassy matrices at 77 K. Furthermore, within a poly(methyl methacrylate) matrix, the complexes showed emission bands centered at around 550 nm within a temperature range from 6 K to 300 K with lifetimes similar to 77 K. Based on TD-DFT potential scans along the metal–ligand (Ni–N) coordinate, we found that in a rigid environment that restricts the geometry to the Franck-Condon region, either the triplet T₅ or the singlet S₄ state could contribute to the photoluminescence. Full article

3,3-Bis (azide methyl) oxy-butyl ring (BAMO)-tetrahydrofuran (THF) copolyethers (PBT) are some of the most promising energetic binders. In this paper, the methods of synthesis of PBT binders are reviewed, and the research progress in PBT binders and PBT-based solid propellants in terms of their thermal and combustion behavior, curing and rheology properties, energy and aging properties, and mechanical and safety performances are systematically summarized. The problems and shortcomings of PBT binders in the application of solid propellants and their thriving trends are pointed out, providing support for speeding up the practical application of PBT binders in high-energy solid propellants. Full article

The rearrangement of a total of 56 members of 22 series of orthogonally protected N-alkyl arylsulphonamides of general structure 4-XC₆H₄SO₂NR¹CO₂R² [X = H, CH₃, F, Cl, Br, CH₃O, CN, CF₃ or C(CH₃)₃; R¹ = CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂ or CH₂CH(CH₃)₂; R² = CH₃, C₂H₅ or C(CH₃)₃] when treated with lithium di-isopropylamide in tetrahydrofuran at −78 °C has been studied. The competition between directed ortho metalated rearrangement, to form 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ and the production of a substituted saccharin, is strongly influenced by the size of R¹ and R², especially in the series with X = CH₃. When R¹ = CH₃ or to a lesser degree, C₂H₅, formation of the saccharin competes to a significant extent, especially when the migrating group is CO₂CH₃ or CO₂C₂H₅. In contrast, when R¹ is a larger alkyl group, particularly if it is branched at either the α- or β-carbon atom [CH(CH₃)₂ or CH₂CH(CH₃)₂], the increased steric hindrance essentially prevents cyclisation, thus facilitating rearrangement to 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ in high yield. The size of the migrating CO₂R² group also exerts an effect on the competition between the reactions: when R² = C(CH₃)₃, clean rearrangement is possible even when R¹ = CH₃ in each series of X. These results have implications for further elaboration and rearrangement of 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ in order to prepare substituted saccharins containing a 6-CO₂R³ group. Full article

The total activity coefficient is exploited to study the deviation of a solution from the hypothetical ideal solution. It is proven for a solution that the curve of the total activity coefficient and all curves of activity coefficients of components will intersect at the stationary point of the total activity coefficient curve. It is found for the negative (positive) deviation binary solutions studied here that the magnitudes of the total activity coefficient at the minimum (maximum) point of the total activity coefficient curve becomes bigger as the intermolecular attraction of the solute and solvent become weaker. Furthermore, the shape of the total activity coefficient curve, as well as the molar concentration of its stationary point, are dependent on the intermolecular attraction of components in the solution. Finally, for the negative solution of tetrahydrofuran + 1,1,2,2-tetrachloroethane and the positive-deviation solution of ethyl isobutyrate + 1-butanol, the effects of pressure on the total activity coefficient of the negative and positive solutions are investigated. Full article