A Platform for Ultra-Fast Proton Probing of Matter in Extreme Conditions.

Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art.

Hydrogen-Induced Reduction Improves the Photoelectrocatalytic Performance of Titania.

One of the main challenges to expand the use of titanium dioxide (titania) as a photocatalyst is related to its large band gap energy and the lack of an atomic scale description of the reduction mechanisms that may tailor the photocatalytic properties. We show that rutile TiO single crystals annealed in the presence of atomic hydrogen experience a strong reduction and structural rearrangement, yielding a material that exhibits enhanced light absorption, which extends from the ultraviolet to the near-infrared (NIR) spectral range, and improved photoelectrocatalytic performance. We demonstrate that both magnitudes behave oppositely: heavy/mild plasma reduction treatments lead to large/negligible spectral absorption changes and poor/enhanced (×10) photoelectrocatalytic performance, as judged from the higher photocurrent.

Transition mechanism of the coverage-dependent polymorphism of self-assembled melamine nanostructures on Au(111).

Molecular self-assembled films have recently attracted increasing attention within the field of nanotechnology as they offer a route to obtain new materials. However, careful selection of the molecular precursors and substrates, as well as exhaustive control of the system evolution is required to obtain the best possible outcome. The three-fold rotational symmetry of melamine molecules and their capability to form hydrogen bonds make them suitable candidates to synthesize this type of self-assembled network.

Smart Electrode Surfaces by Electrolyte Immobilization for Electrocatalytic CO Conversion.

The activity and selectivity of molecular catalysts for the electrochemical CO reduction reaction (CORR) are influenced by the induced electric field at the electrode/electrolyte interface. We present here a novel electrolyte immobilization method to control the electric field at this interface by positively charging the electrode surface with an imidazolium cation organic layer, which significantly favors CO conversion to formate, suppresses hydrogen evolution reaction, and diminishes the operating cell voltage. Those results are well supported by our previous DFT calculations studying the mechanistic role of imidazolium cations in solution for CO reduction to formate catalyzed by a model molecular catalyst.

Epitaxial growth and characterization of SnSe phases on Au(111).

Two-dimensional (2D) layered group IV-VI semiconductors attract great interest due to their potential applications in nanoelectronics. Depending on the dimensionality, different phases of the same material can present completely different electronic and optical properties, expanding its applications. Here, we present a combined experimental and theoretical study of the atomic structure and electronic properties of epitaxial SnSe structures grown on a metallic Au(111) substrate, forming almost defect-free 2D layers.

Enabling circular economy by N-recovery: Electrocatalytic reduction of nitrate with cobalt hydroxide nanocomposites on copper foam treating low conductivity groundwater effluents.

Fertilizers play a vital role in the food-energy-water nexus. The traditional method of artificial nitrogen fixation to produce ammonia is a high-energy intensive centralized process that has caused an imbalance of the N-cycle due to the release of N-species to water. Electrocatalytic nitrate reduction (ENR) to ammonia is a promising N-resource recovery alternative that can enable the circular reuse of ammonia in decentralized settings.

On-surface synthesis of metal-organic frameworks: the critical role of the reaction conditions.

Two different metal-organic frameworks with either a honeycomb or Kagome structure were grown on Cu(111) using -aminophenol molecules and native surface adatoms. Although both frameworks are made up from the same chemical species, they are structurally different emphasizing the critical role being played by the reaction conditions during their growth. This work highlights the importance of the balance between thermodynamics and kinetics in the final structure of surface-supported metal-organic networks.

The Role of Metal Adatoms in a Surface-Assisted Cyclodehydrogenation Reaction on a Gold Surface.

Dehydrogenation reactions are key steps in many metal-catalyzed chemical processes and in the on-surface synthesis of atomically precise nanomaterials. The principal role of the metal substrate in these reactions is undisputed, but the role of metal adatoms remains, to a large extent, unanswered, particularly on gold substrates. Here, we discuss their importance by studying the surface-assisted cyclodehydrogenation on Au(111) as an ideal model case.

Electrocatalytic Conversion of CO to Formate at Low Overpotential by Electrolyte Engineering in Model Molecular Catalysis.

An electrolyte engineering strategy was developed for CO reduction into formate with a model molecular catalyst, [Rh(bpy)(Cp*)Cl]Cl, by modifying the solvent (organic or aqueous), the proton source (H O or acetic acid), and the electrode/solution interface with imidazolium- and pyrrolidinium-based ionic liquids (ILs). Experimental and theoretical density functional theory investigations suggested that π -π interactions between the imidazolium-based IL cation and the reduced bipyridine ligand of the catalyst improved the efficiency of the CO reduction reaction (CO RR) by lowering the overpotential, while granting partial suppression of the hydrogen evolution reaction. This allowed tuning the selectivity towards formate, reaching for this catalyst an unprecedented faradaic efficiency (FE -) ≥90 % and energy efficiency of 66 % in acetonitrile solution.

Overcoming barriers for nitrate electrochemical reduction: By-passing water hardness.

Water matrix composition impacts water treatment performance. However, matrix composition impacts have rarely been studied for electrochemical water treatment processes, and the correlation between the composition and the treatment efficiency is lacking. This work evaluated the electrochemical reduction of nitrate (ERN) using different complex water matrices: groundwater, brackish water, and reverse osmosis (RO) concentrate/brine.

On-Surface Thermal Stability of a Graphenic Structure Incorporating a Tropone Moiety.

On-surface synthesis, complementary to wet chemistry, has been demonstrated to be a valid approach for the synthesis of tailored graphenic nanostructures with atomic precision. Among the different existing strategies used to tune the optoelectronic and magnetic properties of these nanostructures, the introduction of non-hexagonal rings inducing out-of-plane distortions is a promising pathway that has been scarcely explored on surfaces. Here, we demonstrate that non-hexagonal rings, in the form of tropone (cycloheptatrienone) moieties, are thermally transformed into phenyl or cyclopentadienone moieties upon an unprecedented surface-mediated retro-Buchner-type reaction involving a decarbonylation or an intramolecular rearrangement of the CO unit, respectively.

Copper-assisted oxidation of catechols into quinone derivatives.

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber-Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface.

Role of the metal surface on the room temperature activation of the alcohol and amino groups of p-aminophenol.

We present a comparative study of the room-temperature adsorption of p-aminophenol (p-AP) molecules on three metal surfaces, namely Cu(110), Cu(111) and Pt(111). We show that the chemical nature and the structural symmetry of the substrate control the activation of the terminal molecular groups, which result in different arrangements of the interfacial molecular layer. To this aim, we have used in-situ STM images combined with synchrotron radiation high resolution XPS and NEXAFS spectra, and the results were simulated by DFT calculations.

Scanning electrochemical microscopy screening of CO electroreduction activities and product selectivities of catalyst arrays.

The electroreduction of CO is one of the most investigated reactions and involves testing a large number and variety of catalysts. The majority of experimental electrocatalysis studies use conventional one-sample-at-a-time methods without providing spatially resolved catalytic activity information. Herein, we present the application of scanning electrochemical microscopy (SECM) for simultaneous screening of different catalysts forming an array.

On-surface Synthesis of a Chiral Graphene Nanoribbon with Mixed Edge Structure.

Chiral graphene nanoribbons represent an important class of graphene nanomaterials with varying combinations of armchair and zigzag edges conferring them unique structure-dependent electronic properties. Here, we describe the on-surface synthesis of an unprecedented cove-edge chiral GNR with a benzo-fused backbone on a Au(111) surface using 2,6-dibromo-1,5-diphenylnaphthalene as precursor. The initial precursor self-assembly and the formation of the chiral GNRs upon annealing are revealed, along with a relatively small electronic bandgap of approximately 1.

On-Surface Driven Formal Michael Addition Produces m-Polyaniline Oligomers on Pt(111).

On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1,4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations.

Differential pulse voltammetric determination of the carcinogenic diamine 4,4'-oxydianiline by electrochemical preconcentration on a MoS based sensor.

An electrochemical sensor for the carcinogen 4,4'-oxydianiline (Oxy) is described. The method is based on the ability of MoS nanosheets to preconcentrate Oxy. A glassy carbon electrode (GCE) was covered, by drop-casting, with MoS nanosheets that were obtained by exfoliation.

Versatile Graphene-Based Platform for Robust Nanobiohybrid Interfaces.

Technologically useful and robust graphene-based interfaces for devices require the introduction of highly selective, stable, and covalently bonded functionalities on the graphene surface, whilst essentially retaining the electronic properties of the pristine layer. This work demonstrates that highly controlled, ultrahigh vacuum covalent chemical functionalization of graphene sheets with a thiol-terminated molecule provides a robust and tunable platform for the development of hybrid nanostructures in different environments. We employ this facile strategy to covalently couple two representative systems of broad interest: metal nanoparticles, via S-metal bonds, and thiol-modified DNA aptamers, via disulfide bridges.

Characterization of LiCoO nanoparticle suspensions by single collision events.

Transient electrochemical experiments associated with the collisions between hydrothermally synthesized LiCoO2 (LCO) nanoparticles/aggregates of different sizes and a polarized gold ultramicroelectrode (UME) were used as a new additive-free analytical tool applied to Li ion insertion compounds. The size of the LCO nanoparticles/aggregates, ranging from 75 to 450 nm, the diffusion coefficient of the LCO nanoparticles/aggregates in suspension (∼8 × 10-9 cm2 s-1), and the Li ion diffusion coefficient within crystalline LCO nanoparticles (∼1.3 × 10-11 cm2 s-1) were estimated from single collision events.

On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate.

The activation, hydrogenation, and covalent coupling of polycyclic aromatic hydrocarbons (PAHs) are processes of great importance in fields like chemistry, energy, biology, or health, among others. So far, they are based on the use of catalysts which drive and increase the efficiency of the thermally- or light-induced reaction. Here, we report on the catalyst-free covalent coupling of nonfunctionalized PAHs adsorbed on a relatively inert surface in the presence of atomic hydrogen.

Electrocatalytic studies on imidazolium based ionic liquids: defining experimental conditions.

The number of publications devoted to studying electrochemical reactions in room temperature ionic liquids (RTILs) is constantly growing, but very few of them have been devoted to defining proper experimental conditions to obtain reproducible electrochemical results. In this work, we demonstrate that the combination of a proper RTIL purification treatment and a filtered Ar gas stream allow us to obtain featureless voltammograms in [C4mim][BF4], [C4mim][NTf2], and [C4m2im][NTf2], which otherwise present signals associated with different types of impurities such as water and some minor electroactive impurities acquired during the RTIL synthesis process. Moreover, we demonstrate that bubbling Ar, or another inert gas, through the electrolyte in order to purge O2 dissolved in RTILs is one of the major sources of water and O2 impurities incorporated in RTILs within the electrochemical cell.

Enantiopure distorted ribbon-shaped nanographene combining two-photon absorption-based upconversion and circularly polarized luminescence.

Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety.

On-Surface Growth Dynamics of Graphene Nanoribbons: The Role of Halogen Functionalization.

On-surface synthesis is a powerful route toward the fabrication of specific graphene-like nanostructures confined in two dimensions. This strategy has been successfully applied to the growth of graphene nanoribbons of diverse width and edge morphology. Here, we investigate the mechanisms driving the growth of 9-atom wide armchair graphene nanoribbons by using scanning tunneling microscopy, fast X-ray photoelectron spectroscopy, and temperature-programmed desorption techniques.

On-Surface Cyclization of ortho-Dihalotetracenes to Four- and Six-Membered Rings.

We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of ortho-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings.