Bond Splitting Research Articles

Facile heterolytic bond splitting of molecular chlorine upon reactions with Lewis bases: Comparison with ICl and I2

AbstractFormation of molecular complexes and subsequent heterolytic halogen‐halogen bond splitting upon reactions of molecular Cl2 with nitrogen‐containing Lewis bases (LB) are computationally studied at M06‐2X/def2‐TZVPD and for selected compounds at CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz levels of theory. Obtained results are compared with data for ICl and I2 molecules. Reaction pathways indicate, that in case of Cl2∙LB complexes the activation energies for the heterolytic Cl‐Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl2 molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X2∙Py with formation of [XPy2]+… contact ion pairs in the gas phase is slightly endothermic in case of Cl2 and I2, but slightly exothermic in the case of ICl. Formation of {[ClPy2]+…}2 dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor‐stabilized Cl+ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor‐stabilized Cl+ species is viable alternative to the homolytic Cl‐Cl bond breaking.

Retrofitting performance of precast UHPC jackets and NSM GFRP bars in pre-damaged RC columns with deficient lap splices

Fiber-reinforced polymer (FRP) jackets and the near surface-mounted (NSM) technique have been widely used to improve the seismic performance of intact reinforced concrete (RC) columns with deficient lap splices. For damaged lap-spliced RC columns, use of ultra-high-performance concrete (UHPC) jackets is more powerful in eliminating the bond splitting failure and recovering the stiffness than FRP jackets. This study proposed an L-shape precast steel-reinforced UHPC (PR-UHPC) jacket to improve the retrofit performance of conventional cast-in-place (CIP) and precast UHPC jackets. Further, PR-UHPC jackets were combined with NSM GFRP bars to develop an innovative method. Cyclic loading tests were performed on three three-fourths scaled deficient lap-spliced RC columns. One intact column was directly retrofitted with PR-UHPC jackets, while the other two were first damaged and then retrofitted with PR-UHPC jackets and the combination of PR-UHPC jackets and NSM GFRP bars, respectively. To investigate the effects of UHPC details and NSM bar types, a previous study on lap-spliced RC columns retrofitted with CIP plain UHPC jackets and NSM steel bars was incorporated. The test results indicate that the retrofitted columns failed with rebar fracture, and plastic hinge shifting was prevented. The peak load, effective yield stiffness, and ultimate drift ratio of the retrofitted columns were 29∼50 %, 37∼39 %, and 126∼165 % higher than those of the unretrofitted columns, respectively. NSM GFRP bars outperformed steel bars in terms of residual drift ratio control. The numerical model well predicted the cyclic behavior by addressing the pre-damage effect and the actual confinement of PR-UHPC jackets. The parametric study revealed that the increase of PR-UHPC jacket width effectively improved the strength and stiffness, while the pre-damage degree had a minor effect. The recommended UHPC jacket height for the present columns was 2.5 times the plastic hinge length. Finally, a design method was developed for the UHPC jacket width.

Experimental Study on the Bonding Performance between Shaped Steel and High-Strength Concrete

The integration of steel fibers into high-strength concrete (HSC) offers a solution to address the brittleness and limited ductility typically associated with conventional HSC structures. To investigate the bonding properties between shaped steel and high-strength concrete with steel fiber (SFRC), thirteen tests of the shaped steel/SFRC specimens are conducted to explore the effects of various factors such as steel fiber volume ratio, concrete strength grade, reinforcement ratio, steel embedment depth, and cover thickness on bond–slip behavior. Three distinct failure modes, such as pushout failure, bond splitting, and yielding failure of steel, are identified during the pushout tests. Three different types of bond strength, such as the initial bond strength, the ultimate bond strength, and the residual bond strength, are observed from the load–slip curves between the shaped steel and concrete. By incorporating nonlinear spring elements, a numerical model for accurately simulating the bond performance between the shaped steel and SFRC specimens is developed. The bond strength between the shaped steel and concrete increase as the concrete strength, cover thickness, steel fiber volume ratio, and stirrup ratio increase, while it decreases as the steel embedment depth increases. A model for the bond strength between shaped steel and SFRC is developed, and it agrees well with the test data.

A review on retrofitting concrete members with near‐surface mounted‐fiber reinforced polymer composites

AbstractIn an era flooded with a multitude of studies investigating the performance of concrete structures retrofitted using fiber‐reinforced polymer (FRP) materials, this review addresses the critical need for a comprehensive overview of the retrofitting of concrete members using near‐surface mounted (NSM)‐FRP composites, aiming to save time and effort while providing engineers and research community with valuable resources relevant to the field. This review focuses on the key factors influencing both the flexural and shear retrofitting processes of reinforced concrete (RC) beams, such as the percentage, type, size and geometry of NSM‐FRP reinforcement, as well as groove design, groove‐filling materials and beam depth. Moreover, the paper explores the failure modes associated with each retrofitting type, for example, debonding failures, shear/flexural failure and rupture of steel or NSM‐FRP reinforcement, to name a few. The review also delves into the bond behavior of NSM‐FRP‐bonded joints, examining factors, such as the bonded length, surface texture of NSM‐FRP reinforcement and type of bonding agent, which would affect the bond behavior and strength of the joints. The failure mechanisms associated with the bonded joints, such as interfacial bond failure, FRP rupture and splitting of the adhesive cover, are also highlighted. Finally, this compilation aims to guide engineers and researchers by offering a critical and comprehensive database for optimal designs, further development and suggesting future research directions.

Multicomponent metal nanoparticles supported on nickel foam for efficient catalytic decomposition of vaporized hydrogen peroxide

Residual high-concentration vaporized hydrogen peroxide (VHP) after disinfection poses a significant threat to human health and the disinfection space. The considerable concerns make it necessary to develop efficient catalysts for VHP decomposition. In this work, three-dimensional (3D) porous Ni foam (NF)-based multicomponent nanocomposites were fabricated via a facile in-situ hydrothermal method. The effect of the composition and content of elements on the catalytic decomposition of VHP was studied. The AlCrFePt0.64/NF catalyst exhibits the best catalytic performance among all catalysts and requires only 59 min to reduce the VHP concentration from 250 ppm to 1 ppm. Furthermore, the AlCrFePt0.64/NF shows superior stability and no obvious change in VHP decomposition performance after ten recycling tests. The decomposition of VHP follows a pseudo-first-order kinetics rate law. The catalytic decomposition mechanism of VHP proceeds through O-O splitting and consecutive H-transfer reactions. The enhanced catalytic activity of the AlCrFePt0.64/NF is ascribed to the synergetic effect of noble-metal Pt and transition metals, which leads to the presence of initially larger amounts of surface O* and HO* species, and lower activation energy of the O-O bond splitting.

Ion recognition enables fast Mg–Cl bond dissociation kinetics and better Mg plating/stripping reversibility

Rechargeable Mg-metal batteries hold considerable promise for renewable energy storage and utilization. However, the Mg stripping/plating processes suffer from sluggish ion pairs dissociation kinetics, resulting in poor rate and cycle properties. In this work, an efficient skeleton host containing dissimilar coupling elements with varied electronegativity has been designed to promote interfacial reaction kinetics by accelerating the Mg–Cl bond dissociation process. As a proof-of-concept prototype, the N/O-doped cobalt nanoparticles embedded in carbonaceous polyhedrons has been synthesized via facile high temperature annealing of zeolitic imidazolate framework-67 (ZIF-67). The exposed electron-rich N/O sites and electron-deficient Co sites can regulate the adsorbing structure configuration of [Mg-Cl]+ complex ions by selectively bonding with the Mg2+ and Cl– through chemical coordination linkage, respectively. The elongated bond length from 2.596 Å to 2.679 Å and the weakened bond strength are beneficial for the complex ions dissociation, leading to better charge transfer kinetics. In addition, the better magnesiophilic property accompanied by the conductive and porous permeable three-dimensional architecture realizes the homogeneous electrodeposition of Mg and improved electrode kinetics. The decreased overpotential has been verified in both magnesium organohaloaluminates electrolyte (from 290 mV to 189 mV) and conventional Mg(TFSI)2-based electrolyte (from 600 mV to 200 mV). The designed skeleton host also exhibits excellent long cycle lifespan above 2300 h and extra-high average Coulombic efficiency of 99.65 % within 700 cycles. The accelerated bond splitting strategy enables improved metal-anode reversibility, which is also insightful to high concentrated or other electrolyte systems that contain abundant ion pairs or aggregates.

Structural and life cycle assessments of recycled aggregate concrete beams incorporating industrial hemp fibers

AbstractAs a sustainable concrete material, hemp and recycled aggregate concrete (HRAC) is produced by partial replacement of natural coarse aggregates (NCA) with recycled concrete coarse aggregates (RCA) and industrial hemp fibers. The objective of the reported research was to investigate the structural performance of reinforced concrete beams prepared with HRAC and designed to fail in flexure, shear, or bond splitting modes of failure, and to compare that performance with companion control beams cast with conventional concrete. The significance stems for the fact that no previous research is reported on mixtures using such a combination of hemp fibers and RCA. Test results indicated that HRAC beams with 0.75% volumetric percentage hemp fibers and 50% RCA replacement had comparable peak load capacities to the control beams with no RCA and no fibers, with ±4% difference for all tested modes of failure. Additionally, the fracture energy of the HRAC beam was higher than the control beam by 3.6%, 17.9%, and 14.4% for the flexure, shear, and bond modes of failure, respectively. Moreover, a life cycle analysis (LCA) was considered to compare HRAC mix with conventional concrete mix in terms of the environmental aspects. LCA results indicated that HRAC is a sustainable concrete, specifically with respect to structural performance and lower environmental impact.

Role of Substrate Binding Interactions on DNA Repair by Photolyase.

The repair of the cyclobutane pyrimidine dimer (CPD) lesion in DNA by photolyase is determined by its initial recognition, and the catalytic efficiency depends on a series of intermolecular electron-transfer (ET) processes. Here, we investigated the repair of a CPD structural isomer, replacing the deoxyribose with a pyranose sugar on the 5' site, and found a loss in binding efficiency and repair quantum yield. Using femtosecond spectroscopy, we characterized all elementary repair steps and observed a systemic slowdown of the four intermolecular ET reactions and the second bond splitting. Our observations and molecular dynamics simulations suggest that the sugar replacement disrupts the lesion binding configuration, weakening the electronic coupling between the cofactor and lesion and altering the stability of lesion intermediates. These findings highlight how the CPD photolyases have utilized the structural features of the CPD lesion and optimized its interactions with the cofactor and key active-site residues to maximize repair yields.

Ultra-small PdAuIr nanoparticles on amine-functionalized porous organic polymers for efficient dehydrogenation from FA at room temperature

Formic acid (FA) is a prospective hydrogen storage agent, which has attracted much attention for its low toxicity and stability and plays a significant role in the comprehensive implementation of the hydrogen economy. In this regard, it is very important to utilize additive free FA dehydrogenation, for which few heterogeneous catalysts are available. Herein, we report ultra-small PdAuIr nanoparticles (NPs) supported on amine-based amorphous porous organic polymers (POPs), which exhibit excellent FA dehydrogenation activity with an initial total turnover number (TOF) of 9635 h−1 without additives at room temperature and apparent activation energy (Eaapp) of 36.5 kJ/mol. The results show that the excellent performance can be attributed to the synergistic effect of trimetallic alloys and strong metal-support interaction effect (SMSI), as well as to the amine groups (-NH2) grafted on POPs which facilitates the O–H bond splitting on FA. Overall, the simple and efficient synthetic strategy provides a new method for the selective dehydrogenation of FA.

Development length and bond behavior of lap-spliced reinforcement in Ultra-high performance concrete beams

Ultra-high performance concrete (UHPC) is a new composite material that can significantly improve bond performance with steel bars. There is insufficient research on UHPC bond behavior under actual stress within structural members, which is critical for structure safety and economy. In this paper, 17 lap-spliced beams were tested to simulate flexural member bond conditions. The test parameters included UHPC compressive strength, cover depth, fiber content, splice length and stirrups in the spliced region. All specimens failed by the UHPC cover splitting crack. The beam without fiber experienced brittle splitting failure, while the beams with fibers experienced ductile splitting failure. The test results showed that increasing UHPC strength and cover depth could increase bond strength. The bond strength increased linearly with fiber content from 0% to 3% but decreased with 4% fiber content. Bond strength decreased linearly with splice length. Transverse reinforcement in the lap splice effectively improved bond strength; however, when the additional confinement reaches a limit, the increase in stirrups no longer improves UHPC bond stress. The experimental study established a formula for predicting UHPC bond splitting strength, considering the influence of the above parameters. The maximum limit of bond strength contributed by the stirrup was obtained. Finally, the development length calculation model applicable to UHPC was established by modifying the NC theory method. The proposed model was compared with current design methods, and the predicted values of the proposed model were closest to the experimental values.

Assessing Combinations of B(C6 F5 )3 and N2 -Derived Molybdenum Nitrido Complexes for Heterolytic Bond Activation.

Two different dinitrogen-derived molybdenum nitrido complexes varying by their geometry, ligand spheres and oxidations states were shown to engage their N ligand in dative bonding with the strong Lewis acid B(C6 F5 )3 . The stable adducts were assessed for frustrated Lewis pair-type heterolytic E-H bond splitting of hydrosilanes (E=Si) and HB(C6 F5 )2 . Whereas Si-H bond activation was achieved, HB(C6 F5 )2 was shown to substitute B(C6 F5 )3 in a quantitative or equilibrated fashion, depending on the nature of the nitrido complex. No B-H bond splitting was observed. Thermodynamics of these reactions, computed by DFT, are in agreement with the experimental outcomes.

Adsorbed Enolate as the Precursor for the C–C Bond Splitting during Ethanol Electrooxidation on Pt

Ethanol is a promising alternative fuel to methanol for direct alcohol fuel cells. However, the complete electrooxidation of ethanol to CO2 involves 12 electrons and C-C bond splitting so that the detailed mechanism of ethanol decomposition/oxidation remains elusive. In this work, a spectroscopic platform, combining SEIRA spectroscopy with DEMS, and isotopic labeling were employed to study ethanol electrooxidation on Pt under well-defined electrolyte flow conditions. Time- and potential-dependent SEIRA spectra and mass spectrometric signals of volatile species were simultaneously obtained. For the first time, adsorbed enolate was identified with SEIRA spectroscopy as the precursor for C-C bond splitting during ethanol oxidation on Pt. The C-C bond rupture of adsorbed enolate led to the formation of CO and CHx ad-species. Adsorbed enolate can also be further oxidized to adsorbed ketene at higher potentials or reduced to vinyl/vinylidene ad-species in the hydrogen region. CHx and vinyl/vinylidene ad-species can be reductively desorbed only at potentials below 0.2 and 0.1 V, respectively, or oxidized to CO2 only at potentials above 0.8 V, and thus they poison Pt surfaces. These new mechanistic insights will help provide design criteria for higher-performing and more durable electrocatalysts for direct ethanol fuel cells.

Ultrafast repair dynamics of CPD photolesion isosteres by DNA photolyase.

UV-B rays from sunlight can cause damage to DNA by inducing photolesions, two major forms being the cyclobutane pyrimidine dimer (CPD) and a less frequently formed 6-4 pyrimidine pyrimidone (64PP) photoproduct. Photolyases (PLs) are flavoenzymes which identify these photolesions and repair them using blue light. CPD PLs utilize 10 ultrafast elementary steps, including 7 electron transfer (ET) steps, to complete the photorepair cycle and modulate the quantum repair yield1. This can be influenced by the interplay between various molecular factors at the active site: amino acid residues, the bound substrate, solvation activity and plasticity/flexibility. Here, we have utilized a combination of steady-state kinetic studies, ultrafast laser spectroscopy and molecular dynamics simulations to approach the role of chemical properties of the substrate and binding configuration. We have measured the binding constants, quantum repair yields and ultrafast reaction rates of each elementary step involved for photorepair of 3 novel CPD isosteres (CPD1 and CPD2: 5’-Thymine<>Toluene-3’ adducts2; CPD3: T<>T dimer with 5’ pyranose sugar instead of furanose) by EcPL. We have found that EcPL can repair all 3 isosteres, despite weaker binding, albeit with lower repair yields. The enzyme utilizes universally conserved pathways to repair the isosteres. The binding configuration and redox properties of the substrate may play a direct role in modulating the reaction rates of intermolecular ET and intramolecular bond splitting steps in the repair photocycle, which in turn determines their overall repair quantum yield.

Carbon Surface-Influenced Heterogeneity of Ni and Co Catalytic Sites as a Factor Affecting the Efficiency of Oxygen Reduction Reaction.

Highly porous carbon black and micro/mesoporous activated carbon were impregnated with cobalt and nickel nitrates, followed by heat treatment at 850 °C in nitrogen. Detailed information about chemistry and porosity was obtained using XPS, XRD, TEM/EDX, and nitrogen adsorption. The samples were used as ORR catalysts. Marked differences in the performance were found depending on the type of carbon. Differences in surface chemistry and porosity affected the chemistry of the deposited metal species that governed the O2 reduction efficiency along with other features of the carbon supports, including electrical conductivity and porosity. While dissociating surface acidic groups promoted the high dispersion of small metal species, carbon reactivity with oxygen and acidity limited the formation of the most catalytically active Co3O4. Formation of Co3O4 on the highly conductive carbon black resulted in an excellent performance with four electrons transferred and a current density higher than that on Pt/C. When Co3O4 was not formed in a sufficient quantity, nickel metal nanoparticles promoted ORR on the Ni/Co-containing samples. The activity was also significantly enhanced by small pores that increased the ORR efficiency by strongly adsorbing oxygen, which led to its bond splitting, followed by the acceptance of four electrons.

Highly Strained Arene-Fused 1,2-Diborete Biradicaloid.

The stepwise reduction of a doubly cyclic alkyl(amino)carbene (CAAC)-stabilized 2,3-bis(dibromoboryl)naphthalene enables the isolation of the corresponding mono- and bis(boryl) radicals (one- and two-electron reduction), a 2π-aromatic 1,2-diborete (four-electron reduction), which shows biradical character in the solid-state EPR spectrum, and its cyclic bis(alkylidene)diboron dianion (six-electron reduction). The X-ray crystallographic analysis of the diborete shows a highly strained and twisted four-membered ring with a formal cis-diborene motif featuring a very elongated B-B double bond. Calculations based on DFT and multireference approaches reveal that the diborete possesses an open-shell singlet biradicaloid ground state, which is slightly energetically preferred to its EPR-active triplet-state congener. The addition of CO to the diborete resulted in B-B bond splitting and the formation of the corresponding closed-shell singlet, doubly Lewis base-stabilized bis(borylene), whereas a twofold γ insertion of phenyl azide generates a 1,3-bis(diazenyl)-1,3,2,4-diazadiboretidine.

Investigation of Interfacial Bonding Properties of Polyurethane Concrete and Cement Concrete/Steel Reinforcement

To solve the problem that the repair material of the bridge's expansion joint anchorage area is prone to debonding from the other bridge components, polyurethane concrete was designed and prepared, and the bonding performance of polyurethane concrete was tested by the bond splitting test, bond direct shear test, bond oblique shear test, and steel reinforcement pull-out test. The results show that the interfacial bond strength of polyurethane concrete and cement concrete can be improved by increasing the interfacial roughness. The bond splitting strength increases by up to 91.4%, the bond direct shear strength increases by up to 55.2%, and the bond oblique shear strength increases by up to 28.9%. The bond strength between polyurethane concrete and cement concrete are minimally influenced by temperature. An increase in the diameter of the reinforcement or the length of the bonded anchorage can increase the ultimate pull-out strength of the polyurethane concrete and the steel reinforcement. Polyurethane concrete is a novel composite material with excellent bonding performance with cement concrete and steel reinforcement, which can be widely used in practical projects, such as repairing bridge expansion joint anchorage areas in the future.

Experimental study of the relationship between bond strength of aggregates interface and microhardness of ITZ in concrete

• A research on the acquisition of macro-mechanical data of the ITZ in the meso-mechanical calculation of concrete. • The mechanical properties of the ITZ with different mix ratios were measured, the relationship between the bond strength and the microhardness of the ITZ in concrete is established. • A two-parameter linear relationship between the splitting tensile strength of the interface bond and the age and the W/B ratio was established. • The priority order of the calculated value of the interface strength in the numerical analysis of concrete meso-mechanics is proposed. The problem of taking macro-mechanical data of the interface between aggregates and slurry in the calculation of meso-mechanics of concrete was studied in this paper. Through a systematic standard interface test study where the interfacial bond splitting tensile strength method and the interfacial transition zone (ITZ) microhardness method were used, mechanical properties were investigated at macro-scale (bond strength), and followed by ITZ microhardness at meso-scale, moreover the relationships between macro- and meso-mechanical properties were established. The results show that interfacial bond splitting strength of aggregates-slurry gradually increases with increasing hydration age and decreases with increasing water-binder ratio; the ITZ thickness decreases and the ITZ microhardness valley value increases with the extension of curing age. There is a certain correlation between macro-scale mechanical strength of interface and meso-scale mechanics of ITZ. There is a significant linear relationship between the splitting tensile strength of the interface bond and the splitting tensile strength of the cement slurry, so the interface strength can be calculated according to the splitting tensile strength of the slurry substrate. The interfacial bond splitting tensile strength and ITZ microhardness valley have different degrees of correlation. The interfacial bond splitting tensile strength has a particularly significant linear relationship with the microhardness value of the cement paste substrate. Therefore, the calculation value of the interface strength in the numerical analysis of concrete micromechanics should preferably adopt the linear relationship formula with the microhardness of the cement paste substrate.

Interstitial Hydrogen Atom Modified PdPt Nanosheets for Efficient Ethanol Electro-oxidation with High C–C Bond Cleavage Selectivity

Direct ethanol fuel cells (DEFCs) are a type of promising portable power source with low environmental pollution and high energy density. However, the further commercialization of DEFCs is hindered by the incomplete oxidation of ethanol on the electrocatalysts. Herein, we report a successful synthesis of ultrathin PdPtH nanosheets (NSs) for the first time by the in situ formation of interstitial hydrogen atoms accompanied by wet-chemical coreduction of Pd and Pt precursors. The PdPtH NSs possess selectivity of 15.1% related to C–C bond splitting for ethanol complete oxidation to CO2 through the C1 pathway at a low potential, while the contrast selectivity is 4.8% for Pt black, 9.2% for commercial Pd black, and 11.7 for PdH NSs, respectively. Accordingly, the PdPtH NSs exhibited enhanced catalytic activity in comparison to the counterparts. The mass activity toward ethanol oxidation reaction (EOR) of the PdPtH NSs is 5.2 times and 87 times higher than that of commercial Pd and commercial Pt, respectively. The structure stability and growth mechanism of the PdPtH NSs were also investigated. The results of in situ Fourier transform infrared spectra revealed a stronger C–C bond cleavage ability and CO stripping shows the better antipoisoning properties of the PdPtH NSs arising from the cooperation of the PdPt alloy with interstitial H atoms.

A High-Valent Ru-PCP Pincer Catalyst for Hydrogenation of Carbonyl and Carboxyl Compounds under Molecular Hydrogen.

Low-valent metals traditionally dominate the domain of catalytic hydrogenation. However, metal-ligand cooperating (MLC) catalytic systems, operating through heterolytic H-H bond splitting by a Lewis acidic metal and a basic ligand site, do not require an electron-rich metal. On the contrary, high-valent metals that induce weaker back donation facilitate heterolytic bond activation. Here we report, for the first time, the efficient hydrogenation of carbonyl and carboxyl compounds under molecular hydrogen catalyzed by a structurally well-defined RuIV catalyst bearing a bifunctional PCP pincer ligand. The catalyst exhibits reactivity toward molecular hydrogen superior to that of the low-valent analog and allows hydrogen activation even at room temperature.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions