Research on Chemical Intermediates最新文献

Carbon points in lignin were prepared by hydrothermal method at 180 °C for 12 h. Carbon points with diameters of 1–5 nm were observed by transmission electron microscopy. The prepared lignin carbon point solution was put into the synthesis system of Mil-125(Ti) derivative porous titanium dioxide (M–TiO₂) with 10, 15 and 20 mL, respectively, at 150 °C and 48 h to obtain CQDs/M–TiO₂ composite photocatalyst series. Through a series of characterization and analysis of its structure and morphology, it is proved that the carbon point is successfully recombined with Mil-125(Ti) derivative porous titanium dioxide (M–TiO₂). Through ultraviolet–visible-near-infrared diffuse reflection and flat band potential analysis, we determined that CQDs can improve the light absorption range of porous titanium dioxide (M–TiO₂), a derivative of Mil-125(Ti), and calculated the band structure of the material. It is proved that CQDs and Mil-125(Ti) derivative porous titanium dioxide(M–TiO₂) constitute a type I heterojunction. Photoelectrochemical analysis shows that CQDs/M–TiO₂ composite catalyst has better separation and transport efficiency than M–TiO₂ photogenerated electrons and holes. The photocatalytic hydrogen production activity test at a wavelength of > 380 nm showed that the hydrogen production rate of CQDs-15/M–TiO₂ composite reached 6715 μmol/h g, which was 5.6 times that of M–TiO₂ alone (1200 μmol/h g).

The current research work impasses on the fabrication of the best-fitted electrocatalyst for efficient and improved oxygen electrolysis process. The mesoporous CuO@N-doped carbon nanostructures were formulated using energy efficient low temperature synthesis method which is simple as well as economical. The mesoporous nanostructure of the electrocatalyst resembles the porous structure which is responsible for increase in higher anodic oxidative reactions which in turn increases the ratio of the electron charge transfer between the interfaces and of the catalyst as well. Experimental analysis revealed outstanding performance metrics, with the CuO@N-doped carbon nanostructures demonstrating a low overpotential of 350 mV at a current density of 10 mA/cm² and a Tafel slope of 87 mV dec⁻¹. The electrocatalyst was also found to be significantly stable for the oxygen evolution process (OER) in the actual industrial applications.

Single-atom catalysts (SACs), with advantages of high catalytic activity, high stability and high selectivity, have displayed a perfect performance in electro- chemically sensing small biological molecules. However, SACs were in scare case to be employed in electroanalysis on dihydroxybenzene isomers. Hence, high- temperature pyrolysis-derived Cu-based single-atom catalyst (Cu-SAC) was obtained and then was observed to own an outstanding property on detecting dihydroxybenzene isomers. Cu-SAC exhibited a large specific surface area and highly dispersed active sites that were uniformly distributed on N-doped porous carbon characterized by XRD, SEM, TEM, HAADF-STEM, XPS and BET. The electrochemical sensor based on Cu-SAC demonstrated a wide detection range of 1–100 μM and the significant sensitivity for the simultaneous measurement of hydroquinone (HQ) and catechol (CC) under optimal conditions. The detection limits for both isomers were around 0.11 μM for HQ and 0.33 μM for CC, respectively. Additionally, this sensor was successfully utilized to identify HQ and CC in a tap water sample.

An efficient method has been developed for the Biginelli synthesis of 3,4-dihydropyrimidin-2(1H)-one analogues by three component reaction of aryl aldehyde, aceto acetic ester and urea/thiourea under the influence of catalytic amount of Crown Ether Complex Cation Ionic Liquid (CECIL) [18-C-6 K]₂[CO₃] under solvent free reaction. This crucial Biginelli transformation in combination with [18-C-6 K]₂[CO₃] catalytic material are offered many advantages for the world of synthetic organic chemistry such as ecofriendly approach, simple thermal condition, easy workup procedure, without use of toxic organic solvents, short reaction time and good yield of the products.

Graphical abstract

Synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives using [18-C-6 K]₂[CO₃]

Micelles, a unique structural arrangement, function as nano-dimensional vessels in organic reactions, facilitating numerous catalytic transformations in water. This comprehensive study aims to explore the potential impact of two anionic surfactants (sodium dodecylsulphate or SDS or SC₁₂S and sodium tetradecylsulphate or STS or SC₁₄S) having dissimilar alkyl chain lengths and the hydrophobicity of the aliphatic alcohols (propanol and pentanol) as well on the overall kinetic profile of the oxidation study. The SDS micellar medium significantly encourages the reaction rate compared to STS micellar media. In the case of aliphatic alcohols with varying hydrophobicity, the same kind of rate is observed as with surfactants: (k_obs)_SDS-Propanol ~ 13-folds > (k_obs)_SDS-Pentanol ~ 11-folds > (k_obs)_STS-Propanol ~ 2.4-folds > (k_obs)_STS-Pentanol ~ 2-folds. The rate of the reaction improves as the aliphatic alcohol and surfactant hydrophobicity reduces. Herein, the effectiveness of micellar catalysis is greatly influenced by the surface charge of the micelle and surfactant-alcohol hydrophobic interaction. The kinetic observations are elucidated with conductometry, fluorometry, UV–Vis spectroscopy, FT-IR, ¹H-NMR, DLS, FESEM, TEM, and Zeta potential analysis. The Piszkiewicz’s kinetic model has also been applied to enlighten the linear rate acceleration in both micellar media.

The dicyandiamide/phthalic acid (DCDA/PA) precursor with molecular assembly strategy was prepared by hydrothermal treatment the mixture of dicyandiamine and phthalic acid, in which some of the amines were bound by phthalic acid through hydrogen bonding interactions, and the carbon nitride (CN) photocatalyst was further prepared by thermal polymerization. The results showed that the new chemical structure formed by the interaction of melamine cyanurate and phthalic acid through hydrogen bonding could hinder the intermolecular collision chances during the calcination process of DCDA/PA precursor, which made the polymerization reaction difficult to be carried out, and the CN photocatalysts with irregular layered stacking structure were formed. In addition, the presence of more amino groups in the CN-0.3 structure can effectively improve the separation efficiency of its photogenerated charge carriers, and after simulated visible light irradiation for 60 min, the photocatalytic activity presented by CN-0.3 for MB was 2.72 times higher than that of pristine g-C₃N₄.

The catalytic performance of gallium-modified FAU (Ga-FAU) zeolite on the ethane-to-aromatics (ETA) process was studied by a two-layer ONIOM (our Own N-layered Integrated molecular Orbital and molecular Mechanics) method implemented in Gaussian software. The whole ETA mechanism includes two pathways: ethane dehydrogenation to ethylene and ethylene aromatization. Four different Ga models ([GaH₂]⁺, [GaH]²⁺, [GaO]⁺, and Ga⁺) have been used over the Ga-FAU zeolite. For the ethane dehydrogenation, the order of reactivity is [GaH]²⁺ > [GaH₂]⁺ > [GaO]⁺ > Ga⁺. We selected the [GaH₂]⁺ site to study the ethylene aromatization. On the [GaH₂]⁺ model, the ethane dehydrogenation could take place through both the stepwise pathway (three steps) and the concerted pathway. The three-step pathway is more favorable than the concerted pathway. The rate-determining step of ethylene aromatization is the dehydrogenation of cyclohexene cation. The ethylene aromatization proceeds more slowly than the ethane dehydrogenation due to the higher energy barrier, and thus, the ethylene molecule should be the major product in the whole ETA process on Ga-FAU. The differential charge density (DCD), reduced density gradient (RDG), and local orbital locator (LOL) were employed to analyze the direction of electron migration and the nature of interactions in different TS fragments. The RDG analysis suggests that except for attractive force, there is strong spatial repulsive interaction between fragments that are close in distance, especially in organic carbon ring. The LOL maps indicate that partial covalent interactions often exist in the region where the chemical bonds are forming or breaking. The DCD plots reveal the variation of electron densities of different TS fragments. The electrons always migrate from the fragments with the negative DCD values to the fragments with the positive DCD values.

Graphical abstract

The mechanistic study of the gold-catalyzed cycloisomerization of alcohols or amine tethered-vinylidenecyclopropanes has been performed using high-level DFT calculations to find the reasons for the observed selectivity of the products. Two possible pathways were observed, in the first product, during the cyclization process, the vinylidenecyclopropane moiety converts to methylidenecyclopropane-containing product (P1) via an ionic (non-carbene) intermediate, and in the second product, converts to cyclobutene-containing product (P2) via a carbene intermediates. In all six examined derivatives (containing different alkyl groups at C1 allenic carbon) P2 was the major product by both thermodynamic (the more stability of P1 than P2) and kinetic (the smaller barrier for producing P2 versus P1) criteria in both gas phase and solvent (THF, using PCM model) media. However, in the derivatives with low-strain allenic group (R), I1 (which leads to P1) is more stable than I3 intermediates (which leads to P2) by 0.6–4.2 kcal/mol in the gas phase and 1.0–3.1 kcal/mol in the solvent and the derivatives with high-strain allenic group, I3 is more stable than I1 by 2.1–2.5 kcal/mol in the gas phase and 3.5–4.2 kcal/mol in the solvent. Therefore, both gas phase and solvent data show that because of the different hindrance between the alkyl group and gold cation complex, the selectivity of the reaction is yielded by the favorability of I1 or I3 intermediates. Interestingly, another evidence was provided by atomic charges in the reactants using NBO calculations. These calculations showed that when the atomic charge of C1 allenic carbon was higher than C3, the gold cation prefers to produce I1, leading to P1, and when the atomic charge of C3 allenic carbon was higher than C1, the gold cation prefers to produce I2, leading to P2.

Design of TiO₂ photocatalyst and mesoporous silica composites were carried out for application to water purification. Two different types of precursors (titanium ammonium oxalate and ammonium hexafluorotitanate) for anchoring of TiO₂ on mesoporous silica were adopted for comparative studies to show the roles of chemical constituents in both precursors. In the utilization of ammonium hexafluorotitanate, hydrophobic nature on the surface of mesoporous silica as well as the high crystallinity and visible light absorption performance of TiO₂ were achieved by the co-existence of fluorine and nitrogen during the decomposition of precursors to TiO₂ at elevated temperature. Based on these fascinating functions of composite photocatalyst, good photocatalytic activity was realized in the degradation of phenol in water under UV light (λ > 290 nm) irradiation. This composite photocatalyst also exhibited photocatalytic activity even under visible light (λ > 420 nm) irradiation.

Several copper (II) complexes derived from organic ligands [benzo[b]oxazole] acetonitrile] within the intracrystalline structure of ZSM-5 (Si/Al = 38) through direct synthesis under autogenous pressure are reported. Cu^II-BOA/ZSM-5 complexes were characterized by elemental analysis, XRD, FT-IR, UV–Vis, DTA/TGA, and N₂ adsorption. XRD patterns of the encapsulated complexes suggest that the zeolite framework has not collapsed during encapsulation. Until the crystallinity reaches 0.05 Cu^II-BOA/Z, the crystallinity rises monotonically, followed by a decrease as the complex concentration increases. Additionally, the encapsulated copper (II) complex reduced both its surface area and pore volume relative to the parent zeolite, suggesting that the Cu^II-BOA complex is encapsulated inside it. Among the catalysts examined, encapsulated-0.05Cu^II-BOA/Z showed maximum conversion (26%) and selectivity (90%) toward phenol. Density functional theory (B3LYP-6-31G(d)) was performed to study the effect of the interaction mode of complex with zeolite. The NLOs manners were elucidated via 1st and 2nd hyper polarizabilities. The charge transport mechanism was anticipated using ionization potential (IP) and bond dissociation enthalpy (BDE), which were subsequently employed to examine the autoxidation characteristics.