Sp2 Carbon Research Articles

Enantio‐ and Z‐Selective δ‐Hydroarylation of Aryl‐Substituted 1,3‐Dienes via Rh‐Catalyzed Conjugate Addition

AbstractMetal‐catalyzed enantioselective conjugate arylations of electron‐poor alkenes are highly selective processes for C(sp2)−C(sp3) bond formation. δ‐Selective hydroarylations of electron‐poor 1,3‐dienes are less well developed and reactions that deliver high enantioselectivity while giving single alkene isomer products are elusive. Here we report the Rh‐catalyzed δ‐arylation of aryl‐substituted 1,3‐dienes that gives nearly exclusive Z‐1,4‐addition products (generally with >95 : 5 positional and geometrical selectivity). This remote functionalization provides access to chiral diarylated alkenes from readily available precursors poised for further functionalization, including in the synthesis of bioactive molecules. Mechanistic studies suggest that protonolysis of a Rh‐allyl intermediate generated by diene insertion into a Rh‐aryl is the turnover limiting step and occurs by an inner‐sphere proton transfer pathway.

A deeper orbital hybridization because of more unpaired electrons in d orbital resulted in a better catalytic performance

Previous reports usually co-doping various additional transition metals to improve the NH3-SCR performance of V/TiO2 catalyst. However, seldom work understood the so-called enhancement from an atom scale. This work first selected nine elements (Me) mainly from a same VIB family or a same fourth period, and compared them in transition states of MeV/TiO2 during NH3-SCR. The dehydrogenation step of adsorbed NH3 resulted to be the key step and W substitution got the lowest dehydrogenation energy of 1.29 eV. After estimating the key atoms, the total width of Me-O-V hybridization followed the order of 1.7 eV (WV/TiO2) > 1.3 eV (V/TiO2) > 1.1 eV (CoV/TiO2) > 0.9 eV (LaV/TiO2). The deeper hybridization was attributed to a shorter Me-O-V bond. Both V and W were in a high-spin state while Co and La were in a low-spin state. Moreover, W atom had four semi full d orbitals, bigger than that (three) of V, which were more conducive to electron transfer, and resulting in the biggest overlapping of atomic orbitals. The above prediction was consistent with the afterward experimental result, in which MeV/TiO2 showed a NH3-SCR conversion order of 81 % (WV/TiO2) > 59 % (V/TiO2) > 41 % (CoV/TiO2) > 2 % (LaV/TiO2) at 300 °C. The main result of this work is in favor of designing an effective catalyst from the atom scale.

A novel synthesis route with large-scale sublattice asymmetry in boron doped graphene on Ni(111)

One of the promising ways to functionalize graphene is incorporation of heteroatoms in carbon sp2 lattice, as it is proven to be an efficient and versatile method for controllably tuning chemistry of graphene. We present unique, contamination-free method for selectively doping graphene with B dopants, which are incorporated in layer from a reservoir created in the bulk of Ni(111) single crystal, during standard CVD growth process, leading to clean, versatile and efficient method for creating B-doped graphene. We combine experimental (STM, XPS) and theoretical (DFT, simulated STM) studies to understand structural and chemical properties of substitutional B dopants. Along with previously reported substitutional B in fcc sites, we have observed, for the first time, two more defects, namely substitutional B in top sites and interstitial B in octahedral subsurface sites. Extensive STM investigations confirm presence of low and high concentration regions of B dopants in as-prepared B-doped graphene, indicating non-uniform boron incorporation. Among two substitutional sites, no preference is observed in low-concentration B-doped regions, whereas in high B concentration regions, one of the sublattices is preferred for incorporation, along with alignment of defects. This generates an asymmetric sublattice doping in as-grown B-doped graphene, which is theoretically predicted to result in notable band gap.

Understanding the Competition Mechanism between Na2O and CaO for the Formation of the Initial Layer of Zhundong Coal Ash

The contents of alkali and alkaline earth metals are higher in Zhundong coal, and there are serious problems of slagging and fouling during the combustion process. Therefore, it is of great significance to reveal the mechanism of slagging and fouling in the boiler of Zhundong coal. In this paper, first-principle calculations based on density functional theory are used to study the competition mechanism of alkaline metal oxides during the combustion process in Zhundong coal by establishing the Na2O(110)/CaO(100)-SiO2(100) double-layer interface model. The results show that the bond lengths of the surface of Na2O(110) and CaO(100) with SiO2(100) after adsorption were generally lengthened and the value of bond population became smaller, which formed a stable binding energy during the reaction. The electron loss of Na is 0.05 e, the electron loss of Ca is 0.03 e, and the electron loss of Na2O is greater than that of CaO. The charge transfer on the surface of Na2O with SiO2 is obviously higher than that of CaO and the orbital hybridization on the surface of CaO with SiO2 is weaker than that on the surfaces of Na2O with SiO2. Na2O is easier to react with SiO2 than CaO. The adsorption energies on the surface of Na2O and CaO with SiO2 are −5.56 eV and −0.72 eV, respectively. The adsorption energy of Na2O is higher than that of CaO, indicating that Na2O is more prone to adsorption reactions and formation of Na-containing minerals and other minerals, resulting in more serious slagging. In addition, the XRD analyses at different temperatures showed that Na-containing compounds appeared before Ca-containing ones, and the reaction activity of Na2O is stronger than that of CaO in the reaction process. The experimental results have good agreement with the calculation results. This provides strong evidence to reveal the slagging and fouling of Zhundong coal.

Rare Earth Single-Atom Catalysis for High-Performance Li-S Full Battery with Ultrahigh Capacity.

Lithium-sulfur (Li-S) batteries have many advantages but still face problems such as retarded polysulfides redox kinetics and Li dendrite growth. Most reported single atom catalysts (SACs) for Li-S batteries are based on d-band transition metals whose d orbital constitutes active valence band, which is inclined to occur catalyst passivation. SACs based on 4f inner valence orbital of rare earth metals are challenging for their great difficulty to be activated. In this work, we design and synthesize the first rare earth metal Sm SACs which has electron-rich 4f inner orbital to promote catalytic conversion of polysulfides and uniform deposition of Li. Sm SACs enhance the catalysis by the activated 4f orbital through an f-d-p orbital hybridization. Using Sm-N3C3 modified separators, the half cells deliver a high capacity over 600 mAh g-1 and a retention rate of 84.3 % after 2000 cycles. The fabricated Sm-N3C3-Li|Sm-N3C3@PP|S/CNTs full batteries can provide an ultra-stable cycling performance of a retention rate of 80.6 % at 0.2 C after 100 cycles, one of the best full Li-S batteries. This work provides a new perspective for the development of rare earth metal single atom catalysis in electrochemical reactions of Li-S batteries and other electrochemical systems for next-generation energy storage.

Rare Earth Single‐Atom Catalysis for High‐Performance Li−S Full Battery with Ultrahigh Capacity

AbstractLithium‐sulfur (Li−S) batteries have many advantages but still face problems such as retarded polysulfides redox kinetics and Li dendrite growth. Most reported single atom catalysts (SACs) for Li−S batteries are based on d‐band transition metals whose d orbital constitutes active valence band, which is inclined to occur catalyst passivation. SACs based on 4f inner valence orbital of rare earth metals are challenging for their great difficulty to be activated. In this work, we design and synthesize the first rare earth metal Sm SACs which has electron‐rich 4f inner orbital to promote catalytic conversion of polysulfides and uniform deposition of Li. Sm SACs enhance the catalysis by the activated 4f orbital through an f‐d‐p orbital hybridization. Using Sm‐N3C3 modified separators, the half cells deliver a high capacity over 600 mAh g−1 and a retention rate of 84.3 % after 2000 cycles. The fabricated Sm‐N3C3‐Li|Sm‐N3C3@PP|S/CNTs full batteries can provide an ultra‐stable cycling performance of a retention rate of 80.6 % at 0.2 C after 100 cycles, one of the best full Li−S batteries. This work provides a new perspective for the development of rare earth metal single atom catalysis in electrochemical reactions of Li−S batteries and other electrochemical systems for next‐generation energy storage.

The Peptide Bond: Resonance Increases Bond Order and Complicates Fragmentation.

The enhancement of the peptide bond order by a resonance in the lone pair of N and the π-bond of CO is analyzed. A decomposition of the bond order in terms of localized molecular orbitals is developed and applied to the peptide bond. A combination of two rotations of hybrid orbitals is proposed to improve the boundary treatment in the fragment molecular orbital method. The developed approach is applied to peptide bonds, and it is found crucial to retain the π orbital in the variational space of both fragments across the boundary. The interaction energies between conventional amino acid residues in Trp-cage (1L2Y) are discussed.

A facile electrospinning strategy to prepare cost-effective carbon fibers as a self-supporting anode for lithium-ion batteries

Carbon materials with fibrous morphology and enhanced mechanical properties have shown to be promising materials as self-supporting anode materials for lithium-ion batteries (LIBs). In this study, coal-based carbon fibers (CFs) with favorable flexibility and superior tensile strength were prepared from lignite and coal derivatives such as coal-based humic acid and coal tar pitch via electrospinning in the assistance of polyacrylonitrile. All these coal-based CFs have an 1D dense fibrous microstructure with controllable diameter and appreciable specific surface area with enriched in O/N-containing groups by rationally choosing the precursor type. The organic macromolecules enriched aromatic ring in lignite and coal derivatives cross-link with linear polyacrylonitrile molecular chains to form a more solid three-dimensional (3D) network framework under the conditions of electrospinning and carbonization. Such 3D microstructure not only can significantly improve the flexibility and tensile strength of coal-based CFs, but also can increase the content of graphite-like microcrystalline carbon (sp2 carbon) in carbon fibers, thereby improving the electrical conductivity. Due to the smaller molecular structure, coal tar pitch can be more easily combined with polyacrylonitrile by electrostatic force. The CFs derived from coal tar pitch (CTP-CFs) exhibited the largest average diameter (156.2 nm), a higher microporous surface area (2.6 m2·g−1), higher pyrrole nitrogen and contained reasonable proportions of amorphous carbon (sp3 carbon) and sp2 carbon. As a consequence, among the various derived coal-based CFs applied as self-supporting anode materials for LIBs, CTP-CFs showed the highest first reversible capacity (770.8 mAh·g−1 at 20 mA·g−1) and excellent cycling performance with capacity retention rate of 89.1 % after 200 cycles. This work paves a new strategy to prepare CFs as flexible self-supporting anodes for LIBs from low-cost carbon precursors that can be rationally chosen to further tune the property of the CFs.

Effect of temperature on the friction behavior and mechanism of DLC film in CO2 foam fracturing environment

Diamond-like carbon (DLC) film is considered to be an attractive candidate material for reducing friction and wear in oil and gas equipment due to its low friction and high wear resistance. This study investigated the evolution of friction interfaces and tribochemical reaction at three different temperatures through reactive molecular dynamics simulations. The results reveal that the synergistic effect of atomic transfer layer and chemical passivation of DLC film leads to the decrease of friction force with increasing ambient temperature. The cumulative atomic transfer layer with increasing ambient temperature also contributes to the increase of wear amount, while the atomic lattice transition dominates friction temperatures. More importantly, the phenomenon of increased sp3 carbon atoms in DLC film is also temperature dependent.

Immobilization of gaseous As2O3 on γ-Fe2O3 (001) surface by forming monodentate and bidentate complexes: Insight from DFT study

Coal combustion is one primary anthropogenic emission source of atmospheric arsenic. Ferromagnetic γ-Fe2O3 has been regarded as an effective and promising immobilization sorbent for As2O3(g) in flue gas with good magnetic properties. The reported mechanism explorations about gaseous arsenic capture in flue gas by density functional theory (DFT) are mainly based on forming one chemical bond between arsenic and sorbent. Recent studies demonstrated that multidentate arsenic complexes could be formed with iron oxides in solution. However, the possible formation pathway of multidentate complexes between gaseous As2O3 and γ-Fe2O3 was not been reported yet. This is the first study to investigate the thermodynamics and quantum mechanics of bidentate complexes between As2O3(g) and γ-Fe2O3 (001) by DFT. Three kinds of arsenic bidentate complexes were discovered at γ-Fe2O3 (001) surface, including “2 O to 2 Feoct”, “2 O to Fetet & Feoct,” and “As & O to 2 Feoct,” which were named as configuration A, B and C, respectively. Configuration B, “2 O to Fetet & Feoct”, showed the lowest adsorption energy (Eads) among the three kinds of bidentate complexes. The Mulliken population analysis further confirmed the electron transfer between the atoms of newly formed chemical bonds in bidentate configurations. In addition, the projected density of states (PDOS) analysis exhibiting resonance peaks also showed the formation of hybrid orbitals. The criteria for the determination of bidentate complexes were also proposed. The results evidence a convincing conclusion that monodentate and bidentate complexes with stable chemical bonds can be formed when As2O3(g) is immobilized by γ-Fe2O3 (001).

Unveiling the Potential of Haloalkenes as Electron Density Acceptors.

We report herein, by means of structural and computational analyses, a comprehensive study of the capability of differently substituted haloalkenes to behave as electron density acceptors in noncovalent interactions. The nature of these interactions between haloalkenes and Lewis bases highly depends on the number and nature of the halogen atoms bound to the carbon-carbon double bond. When hydrogen bonds, which generally dominate for mono- and dihaloalkenes, cannot be formed, we observe the establishment of attractive interactions in which an sp2 carbon atom, belonging to an acyclic C=C double bond, plays the role of the Lewis acid via its π* antibonding orbital.

Insight into the influence of X (X = Cu, Mg and Zn) alloying on the mechanical and electronic properties of orthorhombic Ti3Sn compound by first-principles investigation

The mechanical properties and electronic structures of X (X = Cu, Mg and Zn) alloyed orthorhombic Ti3Sn compounds have been carried out by using first-principles calculations. It is revealed from formation energy that the all X-alloyed compounds are thermodynamically stable. According to the results of site occupancy energy, the X atom prefers to occupy the Ti 8g site of orthorhombic Ti3Sn compound. The calculated single crystal elastic constants showed that Ti47Sn16CuTi8g and Ti47Sn16ZnTi8g possess the largest resistance to shear deformation in (100) crystal plane and the most compressible compound along c-axis, respectively. It is found that the mechanical properties of Cu-alloyed orthorhombic Ti3Sn compound are stronger than that of Mg- and Zn-alloyed. It can be revealed from electronic structures that the Ti–Sn, Ti–Cu and Cu–Sn covalent bonds in Ti47Sn16CuTi8g are attributed to the hybridization of Cu-3d, Ti-3d and Sn-5p orbitals, while some ionic bonds and antibonding states are existed in Ti47Sn16MgTi8g and Ti47Sn16ZnTi8g.

Carbon-doped carbon nitride with improved photocatalytic performance for visible-light-driven Giese reaction

In recent research, there has been significant focus on developing highly efficient photocatalysts for forming C(sp3)-C(sp3) bonds. In this study, a series of carbon-doped carbon nitride (C-CN-x) materials were synthesized through molecular self-assembly and thermal polymerization. The introduction of carbon atoms was found to modulate the band gap, specific surface area, and photoelectric properties of the C-CN-x catalysts. These catalysts were applied in the conjugate addition reaction of 1,3-dioxolane with electron-deficient olefins under blue light irradiation. Among them, C-CN-2 exhibited the highest photocatalytic activity with a yield of 91 %. Remarkably, a comparable yield was achieved under sunlight exposure. Furthermore, a detailed investigation into the reaction mechanism was conducted. This study provided valuable insights into the design and development of highly efficient photocatalysts for C(sp3)-C(sp3) bond formation, with potential applications in organic synthesis and green chemistry.

The Triceptide Maturase OscB Catalyzes Uniform Cyclophane Topology and Accepts Diverse Gly-Rich Precursor Peptides.

Triceptides are a class of ribosomally synthesized and post-translationally modified peptides defined by an aromatic C(sp2) to Cβ(sp3) bond. The Gly-rich repeat family of triceptide maturases (TIGR04261) are paired with precursor peptides (TIGR04260) containing a Gly-rich core peptide. These maturases are prevalent in cyanobacteria and catalyze cyclophane formation on multiple Ω1-X2-X3 motifs (Ω1 = Trp and Phe) of the Gly-rich precursor peptide. The topology of the individual rings has not been completely elucidated, and the promiscuity of these enzymes is not known. In this study, we characterized all the cyclophane rings formed by the triceptide maturase OscB and show the ring topology is uniform with respect to the substitution at Trp-C7 and the atropisomerism (planar chirality). Additionally, the enzyme OscB demonstrated substrate promiscuity on Gly-rich precursors and can accommodate a diverse array of engineered sequences. These findings highlight the versatility and implications for using OscB as a biocatalyst for producing polycyclophane-containing peptides for biotechnological applications.

One-pot synthesis of platinum-samarium dendritic nanocrystals with tunable elemental compositions for efficient electrocatalytic methanol oxidation via f-d hybridization interaction

Metallic doping is widely recognized as an effective approach to modulate the intrinsic electronic structure of platinum (Pt)-based electrocatalysts, thereby enhancing their performance in fuel cells. Recent progress mainly focused on doping metals from d-block or p-block of the periodic table to promote d-d or p-d hybridization interactions, while f-block metals, such as rare earth metals, have received less attention. In this study, samarium (Sm)-doped Pt nanocrystals with a dendritic nanoparticle morphology were synthesized with precise control over their elemental composition. The key to achieving this unique morphology was the co-reduction of halide-free Pt and Sm precursors by glucose in the presence of cetyltrimethylammonium chloride (CTAC) in N-oleyl-1,3-propyldiamine (OPDA) at an elevated temperature. When employed as an electrocatalyst for the methanol oxidation reaction (MOR) in an alkaline medium, the optimized Pt86.4Sm13.6 nanodendrites/C exhibited nearly a 7-fold increase in specific activity, accelerated reaction kinetics, and enhanced long-term durability compared to commercial Pt/C. This improved electrocatalytic activity is attributed to the unconventional f–d hybridization interactions, which weaken CO binding and reduce the CO poisoning effect. The f-d hybridization interactions were further elucidated by density functional theory (DFT) calculations, which showed that the stronger interaction between OH and Sm-doped Pt(111) surface exhibits a benefit to combine with CO to form COOH and then release CO2, affirming the critical role of Sm-doping in improving the MOR activity. This research offers a viable strategy for creating rare earth metal-doped bimetallic nanocrystals with controlled morphology and may be extended to the rational design of high-performance fuel cell electrocatalysts based on f-d orbital hybridization.

Investigation of the usage of carbon-based two dimensional materials in lithium sulfide (Li–S) batteries

After the synthesis of graphene (Gr), the other two-dimensional (2D) allotropes of carbon based materials have been predicted theoretically or synthesized by experimentally. Two of these nanomaterials are graphyne (Gy) and graphdiyne (Gdy) which are close relatives of Gr and can be synthesized in bulk. While carbon atoms in Gr bonds with sp2 bonds, Gy and Gdy comprise sp and sp2 hybridized carbon atoms with high degrees of π conjugation that features uniformly distributed pores. So, these intrinsic nanopores add distinction to Gy and Gdy with respect to the Gr especially for energy storage applications. Nowadays, the researchers are studying to improve the storage capacity of Lithium-ion batteries (LIBs). However, Lithium–Sulfur (Li–S) batteries can store approximately five times more energy in terms of energy density compared to LIBs. In this study, we have systematically investigated the lithium polysulfides (LixSy; 1≤x≤2,1≤ y ≤ 8) adsorbed on Gr, Gy and Gdy monolayers by means of density functional theory (DFT) calculations. Our results reveal that, the presence of sp bonds and the size of nanopores in the structure extremely affect the adsorption energy of small sized LixSy clusters. However, the adsorption energies obtained with increasing the size of LixSy clusters are almost similar in Gr, Gy and Gdy monolayers. The diffusion barrier energy values obtained for LixSy clusters indicate that the migration of clusters on Gr may be easy but it is hard on Gdy and especially on Gy due to the pore networks in the structures acting as traps to anchor the LixSy clusters. In addition, we have investigated the double adsorption of LixSy clusters on Gr, Gy and Gdy structures to search the shuttle effect. It can be reported that LixSy clusters do not bind each others and do not create long polysulfide chains, which is not requested.

Selective Adsorption of Sr(II) from Aqueous Solution by Na3FePO4CO3: Experimental and DFT Studies.

The efficient segregation of radioactive nuclides from low-level radioactive liquid waste (LLRW) is paramount for nuclear emergency protocols and waste minimization. Here, we synthesized Na3FePO4CO3 (NFPC) via a one-pot hydrothermal method and applied it for the first time to the selective separation of Sr2+ from simulated LLRW. Static adsorption experimental results indicated that the distribution coefficient Kd remained above 5000 mL·g-1, even when the concentration of interfering ions was more than 40 times that of Sr2+. Furthermore, the removal efficiency of Sr2+ showed no significant change within the pH range of 4 to 9. The adsorption of Sr2+ fitted the pseudo-second-order kinetic model and the Langmuir isotherm model, with an equilibrium time of 36 min and a maximum adsorption capacity of 99.6 mg·g-1. Notably, the adsorption capacity was observed to increment marginally with an elevation in temperature. Characterization analyses and density functional theory (DFT) calculations elucidated the adsorption mechanism, demonstrating that Sr2+ initially engaged in an ion exchange reaction with Na+. Subsequently, Sr2+ coordinated with four oxygen atoms on the NFPC (100) facet, establishing a robust Sr-O bond via orbital hybridization.

Palladium-catalyzed Suzuki-Miyaura cross-couplings of stable glycal boronates for robust synthesis of C-1 glycals

C-1 Glycals serve as pivotal intermediates in synthesizing diverse C-glycosyl compounds and natural products, necessitating the development of concise, efficient and user-friendly methods to obtain C-1 glycosides is essential. The Suzuki-Miyaura cross-coupling of glycal boronates is notable for its reliability and non-toxic nature, but glycal donor stability remains a challenge. Herein, we achieve a significant breakthrough by developing stable glycal boronates, effectively overcoming the stability issue in glycal-based Suzuki–Miyaura coupling. Leveraging the balanced reactivity and stability of our glycal boronates, we establish a robust palladium-catalyzed glycal-based Suzuki-Miyaura reaction, facilitating the formation of various C(sp2)-C(sp), C(sp2)-C(sp2), and C(sp2)-C(sp3) bonds under mild conditions. Notably, we expand upon this achievement by developing the DNA-compatible glycal-based cross-coupling reaction to synthesize various glycal-DNA conjugates. With its excellent reaction reactivity, stability, generality, and ease of handling, the method holds promise for widespread appication in the preparation of C-glycosyl compounds and natural products.

Exploring enhanced CFC gas adsorption on Pt decorated graphene-modified sheets: A density functional theory investigation

The potential of Pt-decorated graphene and Pt-decorated graphene doped with N and S as efficient absorbent and gas sensors for chlorofluorocarbons (CFCs) is examined here using density functional theory (DFT) calculations. Pt-decorated graphene is an incredible material with many applications being investigated because of its amazing properties. We study the structural properties, charge transfer, interaction distance, and orbital hybridization in both pristine and graphene-doped with N and S. We perform extensive electronic investigations that include evaluations of the density of states, frontier molecular orbitals, and non-covalent interactions to gain a deeper knowledge of the interactions of the CFC molecules. Our findings reveal a physisorption interaction between CFC molecules and Pt-decorated graphene, which yields an adsorption energy of −0.50 eV. However, Pt-decorated graphene and Pt-decorated graphene doped with N and S exhibit adsorption energies of −0.70 eV and −0.55 eV, respectively, signifying chemisorption behaviour. It suggests that this material can be used as a CFC gas sensor.

Ab Initio Electronic, Magnetic, and Optical Properties of Fe Phthalocyanine on Cr2O3(0001).

The organic molecules adsorbed on antiferromagnetic surfaces can produce interesting interface states, characterized by charge transfer mechanisms, hybridization of molecular-substrate orbitals, as well as magnetic couplings. Here, we apply an ab initio approach to study the adsorption of Fe phthalocyanine on stoichiometric Cr2O3(0001). The molecule binds via a bidentate configuration forming bonds between two opposite imide N atoms and two protruding Cr ones, making this preferred over the various possible adsorption structures. In addition to the local modifications at these sites, the electronic structure of the molecule is weakly influenced. The magnetic structure of the surface Cr atoms shows a moderate influence of molecule adsorption, not limited to the atoms in the close proximity of the molecule. Upon optical excitation at the onset, electron density moves toward the molecule, enhancing the ground state charge transfer. We investigate this movement of charge as a mechanism at the base of light-induced modifications of the magnetic structure at the interface.