Chemphyschem最新文献

Hydroxyanions and oxyanions can overcome electrostatic repulsion between like charges to form supramolecular architectures whose formation is driven by non-covalent interactions such as hydrogen bonds and halogen bonds (HaB). We report here a ¹²⁷I solid-state nuclear magnetic resonance (SSNMR) study of a series of six organic periodates including compounds which feature I ⋅ ⋅ ⋅ O HaB between pairs of IO₄ ^- anions and control samples which do not feature HaB. ¹²⁷I SSNMR spectra of powdered samples acquired under stationary conditions at 9.4, 11.7, and 21.1 T are simulated using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian to provide the isotropic chemical shift, ¹²⁷I nuclear quadrupolar coupling constant (C_Q), and quadrupolar asymmetry parameter for each compound. One of the HaB compounds, 4-(pyrrolidin-1-yl)pyridinium periodate, is characterized by the largest C_Q(¹²⁷I) value measured to date for a periodate anion, 52.70 MHz. Control organic periodates which do not have HaBs have C_Q(¹²⁷I) values that are much lower than those seen in the halogen-bonded systems, thereby easily differentiating between these two sets of compounds. The C_Q(¹²⁷I) values for those compounds featuring only halogen-bonded periodate anions correlate with the shear strain of the anion, which may be attributed to the influence of the HaB on the local geometry. More rigorous correlations between structure and the ¹²⁷I NMR data are confounded by the presence of dynamics in some of the samples.

Stabilized lithium isotopes (⁶Li, ⁷Li) play an important role in related fields such as energy and defense. With the advancement of nuclear technology, the demand for lithium isotopes is expected to increase significantly. Although the separation of lithium amalgam is effective, it poses greater pollution risks. Therefore, it is very important to establish an efficient, green and sustainable lithium isotope separation method. Lithium isotopes are extremely difficult to isolate, but the discovery of their differences in migration (diffusion) rates, optical excitation, magnetic field response, and chemical binding has enable their potential separation lithium isotopes. Among the various lithium isotope separation methods developed, electrochemical migration stands out as a technique with industrial potential due to its high single-stage separation factor. Hence, this paper focuses on the research progress of lithium isotope separation methods with significant industrial potential. It elucidates the merits and challenges of various techniques, explores key obstacles to their industrialization. Finally, a method for separating lithium isotopes using solid electrolytes is described in the context of lithium-ion battery technology and related research on lithium isotope separation. Despite being in its infancy, this method warrants further research and experimentation.

The selectivity of acetylene hydrogenation by the Rh single-atom catalyst (SAC) supported on HY zeolite was investigated using density functional theory (DFT) and a 5/83T quantum mechanics/molecular mechanics (QM/MM) embedded cluster model. The calculated activation barrier (ΔG^≠) for the oxidative addition of dihydrogen to the Rh metal center (15.9 kcal/mol) is lower in energy than that for the σ-bond metathesis of dihydrogen to the Rh-C bond (22.7 kcal/mol) and the Rh-O bond (28.4 kcal/mol). The activation barriers of the oxidative addition of subsequent dihydrogen molecules are significantly higher than that of the oxidative addition of the first dihydrogen molecule. These findings align with the experimentally observed activity and selectivity of the atomically dispersed Rh catalyst supported on HY zeolite. Natural bond orbital (NBO), molecular orbital (MO) and fuzzy bond order analyses were used to examine the interaction between the Rh metal center and acetylene versus ethylene ligands. The occupancies of the Rh lone pairs, π-bonding and π*-antibonding orbitals of acetylene and ethylene are consistent with the expected stronger interaction between the Rh metal center and acetylene compared to ethylene on the HY zeolite support.

Thin metal-organic framework films grown in a layer-by-layer manner have been the subject of growing interest. Herein we investigate one of the most popular frameworks, the type HKUST-1. Firstly, we show a special synthesis procedure resulting in quick but optically perfect growth. This enables the synthesis of films of excellent optical quality within a short timeframe. Secondly and most importantly, we address the known, but not fully understood observation that the expected growth rate of one monolayer per cycle is strongly exceeded, e. g. by a factor of 4. This is an often-ignored inconsistency in the literature. We offer a growth model using a reconstruction process in every cycle leading to a deterministic reconstruction-by-reconstruction (RbR) cycle growth with a 4-times higher growth rate. It represents an up-to-now hidden chemical assembly mechanism.

The composition of the saturated vapors of two platinum complexes with the macrocyclic ligands 5,10,15,20-tetraphenylporphyrin (PtTPP) and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (PtTF₅PP) and their structures were determined by synchronous gas-phase electron diffraction/mass spectrometry (GED/MS). These porphyrin complexes are those with the heaviest metal atom in the coordination cavity that have been structurally investigated in the gas phase. The mass spectra confirm the presence of a single molecular form of each, PtTPP (T=629 K) and PtTF₅PP (T=597 K). Their structures can serve as references for related complexes in the crystalline state or solutions. Differences between the geometries of PtTPP and PtTF₅PP in the crystalline and gaseous states include a significant deformation of the tetrapyrrole macrocycle in solid PtTPP. The experimental Pt-N bond lengths of both complexes are in agreement with quantum chemical calculations (DFT/B97D/ECP(Pt)) taking into account relativistic effects. The effect of lanthanide contraction is evident from the similarity of the Pd-N and Pt-N internuclear distances of analogous compounds. The strong electron density transfer from the porphyrin backbone to the metal ion and the resulting low effective positive charge on the platinum atom, studied by NBO and QTAIM methods, helps to rationalize the high catalytic activity of such platinum compounds.

The CO₂-assisted oxidative dehydrogenation (ODH) of light alkanes offers a promising route for converting underutilized resources into valuable chemical feedstocks while addressing environmental challenges associated with CO₂ emissions. CO₂ plays a dual role in ODH by acting as a mild oxidant that enhances product selectivity and catalyst stability while preventing carbon deposition through the Reverse Water-Gas Shift (RWGS) and Boudouard reactions. The review has elucidated a variety of catalyst design and optimization strategies that may guide the future development of novel CO₂-assisted ODH catalysts with improved alkane conversion, superior alkene selectivity, and long-term stability. It provides a comprehensive analysis of the structural characteristics, catalytic performances, and reaction mechanisms of typical catalysts, including transition metal catalysts (e. g., Cr-based, Co-based, V-based), metal oxide catalysts (e. g., Ga-based, In-based), noble metal catalysts (e. g., Pt-based, Ru-based), and bimetallic catalysts. Special attention is given to the structure-performance relationship of these catalysts, emphasizing how changes in promoters, supports, and morphology affect critical properties such as redox behavior, acidity-basicity balance, dispersion of active components, and catalyst-support interactions. Finally, future research directions and perspectives for the CO₂-assisted ODH of ethane and propane are proposed, with a focus on advancing catalyst design and optimization strategies. This review aims to serve as a comprehensive reference for researchers exploring the potential of CO₂-assisted ODH in promoting sustainable production of light alkenes.

We have explored the thermodynamics and microkinetic aspects of oxygen evolution catalysis on low loading of Ir(111) on nitrogen-doped graphene at constant potential. The electronic modification induced by N-doping is the reason for the reduced overpotential of OER. The N-induced defect in the charge density is observed with increasing charge-depleted region around the Ir atoms. The lattice contraction shifts the d-band center away from the Fermi level, which increases the barrier for OH* and O* formation on Ir(111) supported on NGr (Ir(111)@NGr). Thus, highly endothermic O* formation reduces the OOH* formation, which is the potential determining step. For comparison, all electronic and binding energy calculations were also performed against Ir NP supported on Gr (Ir(111)@Gr). The stepwise potential-dependent activation barrier ( $G_a$ ) was obtained using the charge extrapolation method. The third step remains the RDS in all ranges of water oxidation potentials. The potential dependent $G_a$ is further applied to the Eyring rate equation to obtain the current density ( $j_{OER}$ ) and correlation between $j_{OER}$ and pH dependence, i. e., OH^- concentration. The microkinetic $j_{OER}$ progression leads to a Tafel slope value of 30 mV dec^-1 at pH=14.0, requiring ${\eta }_{kinetic}=0.33V$ .

Nitrogen reduction reaction (NRR) as a promising approach to ammonia synthesis has received much attention in recent years. Molybdenum disulfides (MoS₂), as one of the most potential candidates for NRR, are extensively investigated. However, the inert basal plane limits the application of MoS₂. Herein, by using density functional theory (DFT) calculations, we constructed edge-exposed MoS₂ and different kinds of basal plane defects, including anti-site, sulfur vacancy and pore defects, to systematically investigate their influence on the NRR performance. The thermodynamically calculated results revealed that the NRR on edge-exposed MoS₂, anti-site defects, sulfur vacancy with three sulfur atoms missing (S_3V) and porous defect (D) exhibit great catalytic activity with low limiting potentials. The calculated limiting potentials are -0.43 and -0.47 V at armchair and zigzag edge MoS₂, -0.42 and -0.44 V at anti-site defects, -0.49 and -0.67 V at S_3V and D. However, by inspecting the thermodynamic properties of the hydrogen evolution reaction, we proposed that the zigzag-end MoS₂ and anti-site defects exhibit a better NRR selectivity compared to armchair-end MoS₂, S_3V and D. Electronic structure calculations reveals that the edge-exposed and basal plane defective MoS₂ can improve the conductivity of the material by reducing the band gap. Donation-backdonation mechanism can effectively promote the activation of nitrogen molecule. Our results pave the way to understanding the defective effects of the MoS₂ inertness plane for NRR and designing high-performance NRR catalysts.

This study investigates the coupling of mercury sulfide (HgS) and copper oxide (CuO) nanoparticles with metal-organic frameworks (MOFs) as a support material for enhancing the electrocatalytic oxygen evolution reaction (OER). The integration of HgS and CuO into the MOF framework aims to leverage the unique electronic and structural properties of both the nanoparticles and the MOFs to improve catalytic performance. Metal-organic frameworks (MOFs), particularly ZIF-67, are investigated for their potential to catalyze water-splitting reactions due to their high porosity and large specific surface areas. The strategic incorporation of HgS and CuO into ZIF-67 significantly enhances its electrocatalytic properties, resulting in remarkable performance metrics: a low overpotential of 246 mV at 10 mA/cm², a Tafel slope of 123 mV/dec, an expanded electrochemical active surface area (ECSA) of 23.56 cm², and a reduced charge transfer resistance of 34.86 Ω. This integration enhances porosity and increases active surface area, which is crucial for improved catalytic performance. This investigation introduces an innovative methodology for fabricating highly efficient electrocatalysts, positioning HgS/CuO/ZIF-67 as a promising candidate for oxygen evolution reactions in alkaline media. The findings highlight the potential of this novel nanocomposite in future clean energy applications, particularly in the realm of water-splitting technologies.

TiO₂ is widely studied as an efficient UV-light photocatalyst for organic compound degradation through reactive oxygen species (ROS) generation. TiO₂ can be modified to show photocatalytic activity under visible light illumination by combining with visible-light absorbing metal oxides. Here, we investigated Co₃O₄/TiO₂ composite materials as visible-light absorbing photocatalysts, with various weight loadings of Co₃O₄, for the decolorization of wastewater pollutant indigo carmine. Under green LED light, 1.4 wt% Co₃O₄/TiO₂ showed the highest decolorization rate compared to other weight loadings and bare TiO₂. While UV-Vis spectroscopy indicated that Co₃O₄/TiO₂ composite materials and bare TiO₂ cause similar dye decolorization behavior, NMR spectroscopy showed that after 24 h, reaction products were present in the reaction mixture for 1.4 wt% Co₃O₄/TiO₂, while TiO₂ showed no reaction products. The lack of photocatalytic activity of Co₃O₄/zeolite and other Co₃O₄/oxide composite materials suggests a synergistic effect between Co₃O₄ and TiO₂, where a small amount of Co₃O₄ enables TiO₂ to utilize visible light without compromising the surface area available for ROS creation. Lastly, we emphasize the need to be cautious when drawing conclusions regarding the dye degradation, since we showed that decolorization does not necessarily equate to full degradation, using a unique combination of UV-Vis and nuclear magnetic resonance spectroscopy.