Adsorption and Catalytic Activation of the Molecular Oxygen on the Metal Supported h-BN

The single metal atom (Ni, Pd, Pt) anchored on defective hexagonal boron nitride for oxidative desulfurization

Single-atom catalysts (SACs) have attracted great attention for various chemical reactions because of their strong activity, high metal utilization ratio, and low cost. Here, by using the density functional theory (DFT) method, the stability of a single VIII-group metal atom (M = Ni, Pd, Pt) anchored on the defective hexagonal boron nitride (h-BN) sheet and its possible application in oxidative desulfurization (ODS) are investigated. Calculations show that the stability of the single M atom embedded in the h-BN surface with B and N vacancies is strikingly enhanced compared to that on the perfect h-BN surface. The catalytic activities of the defective h-BN-supported single metal atom are further studied by the activation of molecular oxygen and subsequent oxidation of dibenzothiophene (DBT). O2 is activated to the super-oxo state with large interaction energies on three M/VN surfaces. However, among the three M/VB surfaces, only Pt/VB performs efficient activation of O2. The oxidation of DBT proceeds in two steps; the rate-determining step is the initial step, in which activated O2 oxidizes DBT to produce sulfoxide. By comparing the energy barrier in the first reaction step, both Ni/VN and Pt/VB are revealed as promising candidates for the ODS reaction.

Oxygen-Induced Dissociation of a Single Water Molecule in Confined 2-D Layers: A Semiempirical study

Semiempirical quantum mechanical methods provides a middle ground between a computationally demanding full ab initio quantum chemistry calculations and force-field calculations in application to molecule-surface interactions. In this study, PM7 semiempirical method is used to evaluate adsorption energy values of X@h-BN monolayer [X= O, OH, and H 2 O] followed by a mechanistic study of oxygen-induced water dissociation on a free-standing h-BN monolayer. Based on oxygen adsorption configurations, two reaction pathways for water dissociation are studied that yield two distinct configurations of double OH-functionalized h-BN monolayer. We then investigated the effect of a cover layer graphene on these proposed mechanistic pathways by placing the graphene cover layer on the top of the h-BN monolayer and continuously tuning the separation ( d Gr/h-BN ) between these two layers.

Enhanced Catalytic Activity of Boron Nitride Nanotubes by Encapsulation of Nickel Wire Toward O2 Activation and CO Oxidation: A Theoretical Study

Perfect boron nitride (BN) nanotubes are chemically inert, and hardly considered as catalysts. Nevertheless, metal wire encapsulated BN nanotubes show extraordinarily high chemical activity. We report nickel (Ni) nanowire encapsulated BN(8.0) and BN(9.0) nanotubes toward O2 activation and CO oxidization on the basis of first-principles calculations. Our results suggest that Ni wire encapsulated BN(8.0) and BN(9.0) nanotubes can easily adsorb and activate O2 molecules to form peroxo or superoxo species exothermically. Meanwhile, superoxo species are ready to react with CO molecules forming OCOO intermediate state and finally yielding CO2 molecules. Meanwhile, the rate-limiting step barrier is only 0.637 eV, implying excellent performance for CO oxidation on Ni nanowire encapsulated BN nanotubes. Furthermore, encapsulation of nickel wire improves the catalytic activity of BN nanotubes by facilitating electron transfer from Ni wire to BN nanotubes, which facilitates the adsorption of highly electronegative O2 molecules and subsequent CO oxidation. This study provides a practical and efficient strategy for activating O2 on a metal encapsulated BN nanotube toward CO oxidation.

The influence of an interfacial hBN layer on the fluorescence of an organic molecule

We investigated the ability of a single layer of hexagonal boron nitride (hBN) to decouple the excited state of the organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) from the supporting Cu(111) surface by Raman and fluorescence (FL) spectroscopy. The Raman fingerprint-type spectrum of PTCDA served as a monitor for the presence of molecules on the surface. Several broad and weak FL lines between 18,150 and 18,450 cm^-1 can be detected, already from the first monolayer onward. In contrast, FL from PTCDA on a bare Cu(111) surface is present only from the second PTCDA layer onward. Hence, a single layer of hBN decouples PTCDA from the metal substrate to an extent that a weak radiative FL decay of the optical excitation can occur. The different FL lines can be ascribed to different environments of the adsorption sites, namely molecules adsorbed at surface defects, in large ordered domains, and located in the second layer.

Oxygen Functionalization of Hexagonal Boron Nitride on Ni(111)

The interaction of single-layer hexagonal boron nitride (h-BN) on Ni(111) with molecular oxygen from a supersonic molecular beam led to a covalently bonded molecular oxygen species, which was identified as being between a superoxide and a peroxide. This is a rare example of an activated adsorption process leading to a molecular adsorbate. The amount of oxygen functionalization depended on the kinetic energy of the molecular beam. For a kinetic energy of 0.7 eV, an oxygen coverage of 0.4 ML was found. Near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy revealed a stronger bond of h-BN to the Ni(111) substrate in the presence of the covalently bound oxygen species. Oxygen adsorption also led to a shift of the valence bands to lower binding energies. Subsequent temperature-programmed X-ray photoelectron spectroscopy revealed that the oxygen boron bonds are stable up to approximately 580 K, when desorption, and simultaneously, etching of h-BN set in. The experimental results were substantiated by density functional theory calculations, which provided insight to the adsorption geometry, the adsorption energy and the reaction pathway.

Hexagonal Boron Nitride Functionalized with Au Nanoparticles-Properties and Potential Biological Applications

Hexagonal boron nitride is often referred to as white graphene. This is a 2D layered material, with a structure similar to graphene. It has gained many applications in cosmetics, dental cements, ceramics etc. Hexagonal boron nitride is also used in medicine, as a drug carrier similar as graphene or graphene oxide. Here we report that this material can be exfoliated in two steps: chemical treatment (via modified Hummers method) followed by the sonication treatment. Afterwards, the surface of the obtained material can be efficiently functionalized with gold nanoparticles. The mitochondrial activity was not affected in L929 and MCF-7 cell line cultures during 24-h incubation, whereas longer incubation (for 48, and 72 h) with this nanocomposite affected the cellular metabolism. Lysosome functionality, analyzed using the NR uptake assay, was also reduced in both cell lines. Interestingly, the rate of MCF-7 cell proliferation was reduced when exposed to h-BN loaded with gold nanoparticles. It is believed that h-BN nanocomposite with gold nanoparticles is an attractive material for cancer drug delivery and photodynamic therapy in cancer killing.

Synthesis of armchair graphene nanoribbons from the 10,10'-dibromo-9,9'-bianthracene molecules on Ag(111): the role of organometallic intermediates

We investigate the bottom-up growth of N = 7 armchair graphene nanoribbons (7-AGNRs) from the 10,10′-dibromo-9,9′-bianthracene (DBBA) molecules on Ag(111) with the focus on the role of the organometallic (OM) intermediates. It is demonstrated that DBBA molecules on Ag(111) are partially debrominated at room temperature and lose all bromine atoms at elevated temperatures. Similar to DBBA on Cu(111), debrominated molecules form OM chains on Ag(111). Nevertheless, in contrast with the Cu(111) substrate, formation of polyanthracene chains from OM intermediates via an Ullmann-type reaction is feasible on Ag(111). Cleavage of C–Ag bonds occurs before the thermal threshold for the surface-catalyzed activation of C–H bonds on Ag(111) is reached, while on Cu(111) activation of C–H bonds occurs in parallel with the cleavage of the stronger C–Cu bonds. Consequently, while OM intermediates obstruct the Ullmann reaction between DBBA molecules on the Cu(111) substrate, they are required for the formation of polyanthracene chains on Ag(111). If the Ullmann-type reaction on Ag(111) is inhibited, heating of the OM chains produces nanographenes instead. Heating of the polyanthracene chains produces 7-AGNRs, while heating of nanographenes causes the formation of the disordered structures with the possible admixture of short GNRs.

Corrugation in the Weakly Interacting Hexagonal-BN/Cu(111) System: Structure Determination by Combining Noncontact Atomic Force Microscopy and X-ray Standing Waves

Atomically thin hexagonal boron nitride (h-BN) layers on metallic supports represent a promising platform for the selective adsorption of atoms, clusters, and molecular nanostructures. Specifically, scanning tunneling microscopy (STM) studies revealed an electronic corrugation of h-BN/Cu(111), guiding the self-assembly of molecules and their energy level alignment. A detailed characterization of the h-BN/Cu(111) interface including the spacing between the h-BN sheet and its support-elusive to STM measurements-is crucial to rationalize the interfacial interactions within these systems. To this end, we employ complementary techniques including high-resolution noncontact atomic force microscopy, STM, low-energy electron diffraction, X-ray photoelectron spectroscopy, the X-ray standing wave method, and density functional theory. Our multimethod study yields a comprehensive, quantitative structure determination including the adsorption height and the corrugation of the sp² bonded h-BN layer on Cu(111). Based on the atomic contrast in atomic force microscopy measurements, we derive a measurable-hitherto unrecognized-geometric corrugation of the h-BN monolayer. This experimental approach allows us to spatially resolve minute height variations in low-dimensional nanostructures, thus providing a benchmark for theoretical modeling. Regarding potential applications, e.g., as a template or catalytically active support, the recognition of h-BN on Cu(111) as a weakly bonded and moderately corrugated overlayer is highly relevant.

Atomically Thin Hexagonal Boron Nitride Nanofilm for Cu Protection: The Importance of Film Perfection

Outstanding protection of Cu by high-quality boron nitride nanofilm (BNNF) 1-2 atomic layers thick in salt water is observed, while defective BNNF accelerates the reaction of Cu toward water. The chemical stability, insulating nature, and impermeability of ions through the BN hexagons render BNNF a great choice for atomic-scale protection.

Enhanced selective oxidation of h-BN nanosheet through a substrate-mediated localized charge effect

First-principles calculations reveal a spatially confined enhancement in the chemical reactivity of h-BN sheets towards O₂, mediated via a substrate-induced charge effect.

Defective Hexagonal Boron Nitride Nanosheet on Ni(111) and Cu(111): Stability, Electronic Structures, and Potential Applications

Defective hexagonal boron nitride nanosheets (h-BNNSs) supported by Ni(111) and Cu(111) surfaces have been systematically studied in this work by first-principles methods. The calculation results show that various defects play an important role in enhancing the stability of h-BNNS/metal heterostructure. Importantly, significant electron transfer through the interface between metal substrate and h-BNNS to the defect sites can make h-BNNS more catalytically active. Using the oxygen reduction reaction (ORR) as a probe, it is shown that the binding energies of O2*, OH*, OOH*, and O* on h-BNNS/Cu(111) with a boron vacancy (VB) are quite similar to those observed on the Pt(111) surface, suggesting inert h-BNNS materials with defects can be functionalized by metal surfaces to become catalytically active for the ORR process. On the other hand, the reaction mechanism of CO oxidation on Ni(111) and Cu(111) supported h-BNNS with VB is systematically investigated. The h-BN/Cu(111) catalyst with a VB precovered by a CO species exhibits catalytic capacity for CO oxidation with a lower energy barrier compared with that on h-BN/Cu(111) without any defect. While on Ni(111) supported h-BNNS with a N vacancy, the defect site turns to be dominated by O2 and the energy barrier is significantly increased, indicating its dependence on the type of defect. This work will provide information for designing h-BN-based catalysts in heterogeneous catalysis.

From Graphene Nanoribbons on Cu(111) to Nanographene on Cu(110): Critical Role of Substrate Structure in the Bottom-Up Fabrication Strategy

Bottom-up strategies can be effectively implemented for the fabrication of atomically precise graphene nanoribbons. Recently, using 10,10'-dibromo-9,9'-bianthracene (DBBA) as a molecular precursor to grow armchair nanoribbons on Au(111) and Cu(111), we have shown that substrate activity considerably affects the dynamics of ribbon formation, nonetheless without significant modifications in the growth mechanism. In this paper we compare the on-surface reaction pathways for DBBA molecules on Cu(111) and Cu(110). Evolution of both systems has been studied via a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and theoretical calculations. Experimental and theoretical results reveal a significant increase in reactivity for the open and anisotropic Cu(110) surface in comparison with the close-packed Cu(111). This increased reactivity results in a predominance of the molecular-substrate interaction over the intermolecular one, which has a critical impact on the transformations of DBBA on Cu(110). Unlike DBBA on Cu(111), the Ullmann coupling cannot be realized for DBBA/Cu(110) and the growth of nanoribbons via this mechanism is blocked. Instead, annealing of DBBA on Cu(110) at 250 °C results in the formation of a new structure: quasi-zero-dimensional flat nanographenes. Each nanographene unit has dehydrogenated zigzag edges bonded to the underlying Cu rows and oriented with the hydrogen-terminated armchair edge parallel to the [1-10] direction. Strong bonding of nanographene to the substrate manifests itself in a high adsorption energy of -12.7 eV and significant charge transfer of 3.46e from the copper surface. Nanographene units coordinated with bromine adatoms are able to arrange in highly regular arrays potentially suitable for nanotemplating.

A Cu(111) supported h-BN nanosheet: a potential low-cost and high-performance catalyst for CO oxidation

CO oxidation on h-BNNS/Cu(111).