Interfaces and surfaces are where the action happens. Catalysis, molecular recognition, charge transfer, polymerization and many other critical processes take place at the boundary between one medium and another. With the need to integrate new materials into devices, and applications ranging from catalysis to sensors, medicine to self-cleaning surfaces, and displays to lasers, fundamental and applied studies of surface and interface processes and optimization are of critical importance in developing new technology to meet today's challenges. The selection of recent research articles presented below illustrates the vast potential of this field.
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Wet, wet, wet: Surfaces with super-wettability, including three-dimensional, two-dimensional, and one-dimensional materials surfaces can be prepared. By combining different super-wettability properties, novel functional solid/liquid interfacial systems can be generated and integrated into devices for tackling many different problems.
Hydrophilic interface modification of a CoOx-modified Ta3N5 photocatalyst with a magnesia nanolayer significantly improves its water oxidation efficiency under visible light irradiation. The essential roles of the interface modification are proposed to enhance the interfacial coverage of the CoOx/Ta3N5 photocatalyst and to decrease the defect density of Ta3N5 semiconductor. AQE=apparent quantum efficiency.
Elucidation and clarification: The results presented elucidate and clarify the mechanisms occurring at the PDI-8CN2/gold interface: They strongly impact field effect devices. Clarification was achieved as to why the use of substrate/contact treatments, decoupling PDI-8CN2 molecules from the substrate/contacts, is beneficial for devices.
Surface modification: Functionalization of liquid-exfoliated, defect-free, layered 2H-MoS2 was achieved through coordination of metal carboxylate salts by basal-plane sulfur atoms. The surface-coordinated metal center acts as an anchor for ligating organic functionalities. X-ray photoelectron spectroscopy (XPS) provides strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt (see picture).
What a pick! Pickering emulsions are surfactant-free dispersions of two immiscible fluids which are kinetically stabilized by colloidal particles. This review describes recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.
Color tuning: Carbon dots whose peak fluorescence emission wavelengths are tunable across the entire visible spectrum from 400 to 710 nm are synthesized by simple adjustment of reagents and synthesis conditions. They exhibit multicolor emission upon excitation with white light.
SiO2-supported Zr catalyst: The synthesis of the silica-supported azazirconacyclopropane 1 is reported. The application of this compound as well as of its hydrogenated counterpart 2 (see scheme) as catalyst for the hydrogenation of olefins has also been investigated, showing that compound 2 is an efficient catalyst for the conversion of short-chain olefins.
Bridge over nanoparticles: Magnetic and fluorescent assemblies of iron-oxide nanoparticles (NPs) are constructed by threading a viologen-based ditopic ligand, DPV2+, into the cavity of cucurbituril (CB) macrocycles adsorbed on the surface of the NPs (see figure). The resulting viologen-crosslinked iron-oxide nanoparticles exhibit increased porosity, saturation magnetization, and emission properties.
Pushing boundaries: A new method for quantitative and multiplexed measurements of endotoxin–protein binding events using liquid crystals is described.
The production of hydrogen gas by photocatalytic water splitting on silicon nanowires was investigated. It occurs through cleavage of Si-H bonds and formation of Si-OH bonds; the surface dangling bonds have a great impact on charge separation.
Self-assembled DNA nanostructures with precise sizes allowed a programmable “soft lithography” approach to engineer the interfaces of electrochemical DNA sensors. Using millimeter-sized gold electrodes modified with several types of tetrahedral DNA nanostructures of different sizes, it was shown that both the kinetics and thermodynamics of DNA hybridization were profoundly affected.
Stereoselective surfaces: Molecular chirality on a surface induces ring-like aggregates of amyloid Aβ(1–40) on N-isobutyryl-L-cysteine (L-NIBC)-modified gold surface at low concentration, whereas D-NIBC results in rod-like aggregates. The different alignment modes of the β-hairpin are guided by surface chirality through stereoselective recognition enhanced by electrostatic interactions.
Organometallic compounds: Hydride terminated silicon nanocrystals (SiNCs) were functionalized with organolithium reagents. The reaction proceeds at room temperature with short reaction times and gives colloidally stable dispersions. The procedure offers a straightforward way to SiNCs with mixed surface functionalities (see scheme)
A change up: Reported herein is an inverse kinetic solvent isotope effect (KSIE) for the reductive dehalogenation of decabromodiphenyl ethers (deca-BDEs). The transformation under TiO2 photocatalysis involves a proton adduct intermediate which accompanies a hybridization change from sp2 to sp3 for an aromatic carbon atom. The protonation event leads to adsorption of the aromatic halides onto TiO2 with a subsequent electron-transfer reaction to form dehalogenated products.
The metal-assisted chemical etching (MaCE) of Si is systematically investigated. The morphology and crystallographic nature of silver dendrites grown by this method can be significantly modulated by the addition of polyvinylpyrrolidone (PVP).
Shaping up: Ceria nanoparticles (nanoceria) with negligible superoxide dismutase mimetic activity have been identified, and they exert antioxidant effects that are much stronger than expected in human bronchial epithelial cells. The underlying mechanism provides a strategy by which nanoceria of custom size, shape, and surface chemistry can acquire remarkable superoxide-scavenging abilities.
Taking it apart: Chemometrics are used in a two-step process to evaluate time-dependent surface-enhanced Raman spectra, allowing the analysis of reaction kinetics and the identification of short-term spectral variations (see picture).
A direct result: A novel strategy is demonstrated for the direct, spatioselective immobilization of proteins and cells on pristine single-layered graphene sheets through direct photografting and surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate.
Stringent segregation: Superhydrophobic/superoleophilic surfaces and underwater superoleophobic surfaces have been successfully designed, fabricated, and employed in the separation of oil/water-free mixtures and emulsions on the basis of their selective superantiwetting/superwetting properties towards water and oil. Progress, remaining problems, and future challenges in this field are discussed in this Review.
Surface disorder: Monitoring of the oxidation currents of glycerol in sulfuric acid revealed that the electrooxidation of glycerol is highly sensitive to the order of the polycrystalline Pt atoms. The combined responses of disordered single crystals were similar to that of polycrystalline Pt. Changes in the current values of the specific potentials, at which each oxidation takes place, suggest that different ordered domains of Pt independently oxidize glycerol.
Spatial correlation of defects: Oxygen vacancies (VO), the dominant surface defects at TiO2(110), are absent in the vicinity of positively charged subsurface point defects. These point defects, in turn, are located only beyond the nearest subsurface region, which is thus void of any charged defects (see figure).
Tune thin: Core–shell droplets with ultrathin shells are known to be highly stable and are excellent for encapsulation applications. Producing such droplets in a quiescent continuous phase makes the approach easily scalable. An experimental investigation on producing such millimetric structures via microfluidics is presented. The tuning of the shell thickness via surfactant concentrations (see picture) is also discussed.
How large is alcohol surface activity? Reliable surface phase activity coefficients are calculated for ethanol (red symbols) and water (blue symbols) in their mixtures at T=298 K. These surface phase activity coefficients are identical to bulk phase activity coefficients at both ends of the composition scale and take smaller values than those of the equilibrium bulk phase, fulfilling surface phase thermodynamic description.
A tale of two disilenes: The addition of acetonitrile to tetramesityldisilene was examined in order to compare the structures of the molecular adducts with the structures of the acetonitrile adducts formed on the Si(100)-2×1 surface and to provide further insight into the surface chemistry. The reactivity of propionitrile and phenylacetonitrile towards this disilene was also studied to investigate reactivity trends (see scheme).
Sprouting droplets: With increasing time, tubes are observed to sprout from water droplets with rigid membranes formed from colloidal particles trapped on the liquid–liquid interface. This is driven by an internal over-pressure which arises as a result of a minority constituent on the outside of the droplet that preferentially partitions into the water inside the membrane.
Three is company: Multicomponent supramolecular network formation on a Au(111) surface is demonstrated. A hybrid system consisting of covalent and noncovalent hosts was realized when the macrocycle adsorbed in the cavity of a noncovalent host network was used to capture C60 in a spatially repetitive fashion (see figure).
Accessing genomic information: A fast and affordable high-throughput screening method based on surface-enhanced Raman spectroscopy (SERS) is a low-cost and ultrasensitive genotyping strategy for gaining detailed genomic information on DNA duplexes. This method allows recognition of hybridization events, single-base mismatches, and base methylation.
Not as easy as it seems: Benchmarking of the electrocatalytic activity can be unexpectedly very demanding due to experimental issues which are often underestimated.
Liquid, solid, or gel? High-performance electrolytes are important for the success of advanced energy-storage devices. From the view of battery structures and the electrolyte, this Review not only summarizes and discusses the up-to-date development of various electrolyte materials (liquids, solids, and gels), but also emphasizes a comprehensive understanding of electrolyte properties, which is critical for the design of high-performance electrolytes.
Collective action: Molecular crowding in the high-molecular density environment of a 2D peptide monolayer is shown to govern peptide conformation and function. The results show that these collective interactions need to be accounted for in the design and interpretation of experimental studies involving surface-immobilized molecular systems.
Nanoscale gold particles, which are commonly used for the activation of small molecules, have been found to catalytically activate an extended solid oxide. The oxide thus becomes more reactive for solid-state transformations and reactive adsorption processes of relevance in pollutant removal and hydrocarbon processing.
Scratch the surface: An in-depth NMR study of long alkyl chain ligands' interactions with copper nanoparticles is presented (see figure). The effects of the functional head group on the oxidation process of the nanoparticles are investigated.
Perforated liquids: Functionalizing hollow silica spheres with suitable polymer species can produce a porous liquid containing empty silica cavities. Taking advantage of their liquid-like polymeric matrixes as the separation medium and the empty cavities as the gas transport pathway they can function as a promising candidates for gas separation.
Hard graft: An approach to create highly stable diazonium layers grafted on gold and carbon surfaces through a Zn-mediated chemical reduction is reported (see figure). The developed technique resulted in highly stable surfaces, representing a new approach for the controlled, rapid, and potentiostat-free grafting of thin layers of diazonium salts.
Sensitive spintronics: The spintronics applicability of chemically synthesized graphene sheets was found to be extremely sensitive to oxygen. The exceptionally long 140 ns electron spin lifetime is reduced by an order of magnitude by introducing small concentrations of physisorbed O2 onto the graphene surface (see figure; TS=intrinsic spin lifetimes). Our results highlight the importance of chemical environment control and device packing in practical graphene-based spintronic applications.
Utilizing the entrapping and directing effects of a nanocarbon graphitic surface, ionic liquids without cross-linkable groups, which were believed to be unable to be charred under pyrolysis conditions, could form a graphitic layer endowed with highly tailorable surface properties. B, N (blue dots), and C were confirmed to share same hexagonal rings, which provided more designable electronic properties.
Solid-state NMR spectroscopy of selected phosphine oxides adsorbed on silica surfaces establishes the surface mobilities, even of phosphine oxides with high melting points. Crystal structures of the adducts Ph3PO·HOSiPh3 and Cy3PO·H2O indicate that the interactions with silica involve hydrogen bonding of the P=O group to adsorbed water and surface silanol groups (see figure).
Monitoring the interfacial world: A new in situ imaging technology capable of selectively highlighting interfacial self-assembly in real time was developed by employing the unique photophysical properties of aggregation-induced emission (AIE). Application of this technology enabled direct high-contrast visualization of microemulsion evolution, “coffee-ring” formation, and breath-figure dynamics by fluorescence microscopy.
Combined experimental and theoretical approaches resulted in a better understanding of the hydrogenation of CO2 to methanol on copper-based catalysts. These results highlight the important role of the reducible oxide promoter for CO2 activation.
Making changes with visible light: Recent developments in the direct photocatalysis of plasmonic-metal nanoparticles are described, with a focus on the role of the localized surface plasmon resonance (LSPR) effect in plasmonic metals and their applications in organic transformations (see figure). The role of light irradiation in the catalyzed reactions and the light-excited energetic electron reaction mechanisms will be highlighted.
Controllable bioelectrocatalysis: The reversible activation of bioelectrocatalysis by external stimuli at stimuli-responsive supramolecular interfaces integrated with redox enzymes has been established, allowing potential applications in controllable biofuel cells, biosensors, bioelectronic devices, and for energy transduction and information storage. This Minireview outlines the current knowledge and important trends in this area.
Tunnel vision: Recent progress in applying scanning tunneling microscopy (STM) manipulations to regulate the inter-adsorbate and adsorbate–substrate interactions on solid surfaces is reviewed (see figure). This technique has demonstrated a versatile and general method to not only differentiate intermolecular interactions but also construct molecular nanostructures by regulating the adsorbate interactions.
Nanoparticles and macrocycles: Recent literature regarding the combination of supramolecular macrocycles and metal nanoparticles is reviewed, with particular emphasis on the synthesis, surface modification and assembly, as well as the potential applications of the obtained nanocomposites (SERS = surface-enhanced Raman spectroscopy).
Nanoparticles and reactive surfaces: This Minireview provides an overview of selected CO-induced nanostructuring (see scheme). Recent examples of metal-surface and nanoparticle restructuring as a consequence of exposure to CO are discussed and show that nanoscale structures can be obtained under fairly mild conditions. Several cases of mono- and bimetallic compounds are described that show a range of behaviours in relation with the metal–CO interaction strength.
Shine a light on your chemistry! This paper gives an overview of the reactive transient species that are produced in surface waters by sunlight irradiation of photoactive molecules (photosensitizers), such as nitrate, nitrite, and chromophoric dissolved organic matter (CDOM) (see scheme). The main transient species (.OH, CO3−., 1O2, and CDOM triplet states) are involved in the indirect phototransformation of a very wide range of organic pollutants in surface waters.
Diffraction at hard work: Modern heterogeneous catalysis would benefit from a multiscale science approach bridging the molecular world with the macroscopic world. Because of recent breakthroughs in X-ray diffraction methods, including the surface X-ray diffraction of atomically flat model catalysts, X-ray diffraction tomography of catalyst bodies, and X-ray profiling of an active catalyst in a chemical reactor, such an approach is now within reach.
Down to the last detail: Nanostructured solid catalysts were already known in the early 20th century, but their exact structure was unclear. Nowadays, the arrangement of atoms and particles in solids can be manipulated and analyzed down to the atomic scale (see image). The use of specific highly active catalysts enables industrially relevant reactions to be performed at room temperature.
Stick or twist: Recent progress in biointerfaces based on smart-responsive molecules or surface topographies has led to efficient approaches for controlling the adhesive behavior of bacteria.
Polishing up the crystal glasses: An overview of the preparation and characterization of ordered silica films on metal supports is reported. In particular, the specific case of a silica bilayer, which exists in a crystalline and a vitreous variety, is discussed and a model of the vitreous silica structure proposed by William Zachariasen in 1932 is verified. Beyond this, the possibility to prepare the crystalline and the glassy structure on the same support leads to the study of the crystal–glass phase transition in real space (see figure).
The importance of the chemical history of the electrode surface before electrochemical cycling as well as the correlation between interface phenomena, the formation/evolution of an interphase, and the electrochemical behavior of LiFePO4 and LiNi1/2Mn1/2O2 electrodes are investigated by magic-angle-spinning nuclear magnetic resonance, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. These techniques allow the study of interface aging and failure mechanisms.
Not just scratching the surface: Covalently attached monolayers on oxide surfaces are reviewed with an eye to improved robustness, increased functionalization, understanding structural details, and the resulting potential for applications. Such monolayers, provided they are robust enough, provide a way of improving the properties of the bulk oxide material.
Expanding vibrational spectroscopy: Since its first observation in 1973, surface-enhanced Raman scattering (SERS) has developed into a mature vibrational spectroscopic technique. The number of applications in chemistry as well as the material and life sciences is increasing rapidly. This Review summarizes the key concepts behind SERS and provides an overview of current applications in chemistry.
Porefection: Electrochemical transducers based on single stimuli-responsive polymeric nanopores can support a complete set of logic functions. Thermal, chemical, electrical, and optical stimuli are the input signals required to externally tune the pore conductance (i.e. the logical output).
Core of the matter: Key processes in nanostructured dye-sensitized solar cells (DSC) occur at material interfaces containing, for example, oxides, dye molecules, and hole conductors (see picture). The implementation of X-ray-based spectroscopic methods for atomic-level understanding of such properties is reviewed. Examples include energy matching, binding configurations, and molecular orbital composition.
Revealing electrochemistry: Key issues related to the electrochemistry of nanoparticles are being uncovered through innovative techniques capable of relating activity and structure, ultimately at the level of a single nanoparticle. Recent advances in experimental approaches are discussed and assessed, with particular emphasis on those that enhance the fundamental understanding of electrocatalysis and nanoscale electrochemistry.
High in fiber: Carbon fibers (CFs), which are widely utilized in fields ranging from fundamental research to industry, can be functionalized by both thin-layer coating and nanoparticle immobilization (see scheme). In this Minireview, these techniques and some practical applications of functionalized CFs, such as carbon fiber reinforced plastic (CFRP), are overviewed after briefly describing the basic properties of CFs.
Rational design at the nanoscale: Covalent assembly of molecular building blocks is a promising strategy to obtain functional nanostructures in one and two dimensions. This Concept article discusses how computational modeling could be used to obtain design rules that will advance this field towards the predictive design of specific functionalities on specific surfaces (see figure).