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.
For recent reviews, see
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).
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).
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
Not as easy as it seems: Benchmarking of the electrocatalytic activity can be unexpectedly very demanding due to experimental issues which are often underestimated.
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.
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.
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.
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).
Taking shape: A Ru3+-mediated synthesis has been developed for unique Pd concave nanostructures which can directly harvest UV-to-visible light for styrene hydrogenation (see figure). The catalytic efficiency under full-spectrum irradiation at room temperature turns out to be comparable to that of the thermally (70 °C) driven reaction. The yields are higher than those obtained using Pd nanocrystals such as nanocubes and octahedrons.
Caught on camera: NaGdF4 nanoparticles coated with ethylenediaminetetraacetic acid (EDTA) chelators functionalized with organic moieties and luminescent dyes were prepared and characterized, and their potential as dual probes for optical/magnetic resonance imaging (MRI) imaging was investigated (see figure).
Sensing Sensibility: A macrocyclic dibenzocoronene tetracarboxdiimide containing two benzo-21-crown-7 groups has been synthesized. It shows liquid-crystalline behavior and selectively binds Pb2+ or K+ to form 1:2 complexes in solution. The complexation leads to a significant increase in fluorescence. The surface organization of discotic columnar structures, in the solid-state, can be controlled by selective ion binding.
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.
Like oil and water: Superoleophobic surfaces with tunable adhesion were obtained by assembling mixed carboxylic acid on nanostructured aluminum substrates. The surface adhesion can be controlled by simply controlling the surface chemical composition (see figure).
More functional: The surface modification of mesoporous silica monoliths through thiol–ene chemistry is reported (see figure). Mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol–gel hydrolysis–polycondensation reaction The different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization.
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).
Going far: Long-distance charge transport is synthetically accessible from double-channel systems, but not from ion-gated or from triple- or single-channel photosystems with central perylenediimide stacks. Hole- rather than electron-transporting perylenediimides and maximized charge separation rather than minimized charge recombination give the best activities (see picture).
Gold nanostars: The relationship between the enhancement by surface-enhanced Raman spectroscopy (SERS) and the localized surface plasmon resonance (LSPR) band is investigated (see picture). The competition between the field enhancement and the optical extinction causes the maximum enhancement factor occurring at a blue-shifted LSPR band from the excitation wavelength rather than at the on-resonance position.
Hold the foam: A surface nanobubble-based diffusion mechanism is proposed that accounts for bubble generation during polymeric foaming in the presence of dispersed nanoparticles. Estimated final bubble sizes in foam are compared with experimentally determined foam morphologies. This simple continuum model gives good agreement between theory and experiment, and can also predict the large difference between nucleating efficiencies of nanoparticles in reactive and nonreactive foaming.
A hive of activity: Tuning the near-surface composition of Ru and Ir elements in a bimetallic oxide by surface segregation results in the formation of a nanosegregated domain (see picture) that balances the stability and activity of surface atoms. A Ru0.5Ir0.5 alloy prepared by this method exhibited a stability four-times higher than the best Ru-Ir oxygen evolution reaction materials, but the same activity.
Cleaner water: Bubble formation at the water–organic solvent interface is dependent on the pH of the medium and the concentration of graphene oxide present. Graphene oxide nanosheets are utilized as carriers for the reactive extraction of methyl green and methyl blue dyes from the aqueous to the organic phase with extraction efficiencies of up to 98.2 and 83.6%, respectively.
A mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads (example in picture: carbon nitride), which were found to catalyze the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF 1183) using formic acid as the hydrogen source and water as the solvent at room temperature. This process is applicable to many nitroarenes without the involvement of high-pressure gases or sacrificial additives.
The transfer of vibrational energy in collisions of an NO molecule with a gold surface proceeds by electron transfer. Thanks to new optical pumping and orientation methods, all molecular degrees of freedom important to this process can be controlled. The probability of the electron-transfer reaction is enhanced by increased translational and vibrational energy as well as by proper orientation of the reactant.
Efficient and generic enantioselective discrimination of various chiral alcohols is achieved by surfaced-enhanced Raman scattering (SERS) spectroscopy. This approach is label-free, does not employ any chiral reagents, and may lead to the development of novel enantiosensing strategies.
Understanding hydrogenation on transition metals: Subsurface hydrogen, Hsub, is shown to significantly influence the stability and the reactivity of the adsorbed hydrogen in two different ways. Calculations on a representative reaction, ethyl hydrogenation, show that it is accelerated on Pd and Pt, but slowed down on Ni and Rh in the presence of Hsub.
Capillary foams are a new class of foams, in which particles and a secondary liquid jointly adsorb at the surface of gas bubbles within a bulk liquid. Particles that adsorb preferentially at the interface of the secondary liquid can mediate its spreading around the gas bubbles. The bubbles are further entrapped in a network of excess secondary-liquid-bridged particles in the primary liquid.
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.
Riding on the surface states highway: First-principles calculations and photoelectrochemical measurements provide a framework for deepened understanding of the oxygen evolution reaction from water splitting on hematite. The reaction takes place on the O-terminated hematite surface via surface states close in energy to the top of the valence band.
Nuked for control: Silver nanoparticles deposited on CeO2-SBA-15 supports possess tunable particle sizes and metal–support interactions (MSIs) when prepared by microwave (MW) irradiation owing to the strong charge polarization of CeO2 clusters (i.e., MW absorption; see figure). The Ag nanoparticle size and MSIs were responsible for the high turnover frequency numbers in ammonia borane dehydrogenation and 4-nitrophenol reduction.
On the surface: The thermal decomposition of organometallic complexes with N-heterocyclic carbene ligands affords Pt nanoparticles that are soluble and stable in water for an indefinite period. The 13C–195Pt coupling observed by solid-state NMR spectroscopy confirms carbene coordination to the nanoparticle surface.
Needle in a haystack: A chip-based electrochemical assay using metal nano-particles (MNPs, see picture) allows simultaneous detection of multiple different biomarkers on the surfaces of cancer cells, enabling discrimination between cancer cells and normal blood cells. As few as two cells captured per electrode can be detected.
Cu-trimer nodes: Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, tetrahydroxybenzene (THB) is shown to dehydrogenate when adsorbed on a Cu(111) surface and form a highly reactive ligand. Density functional calculations confirm that the ligand stabilizes copper adatom trimers and creates a surface coordination network that is a two-dimensional analogue of metal–organic frameworks.
Multifunctional CPPs: Robust and biocompatible coordination polymer nanoparticles (CPPs) with enhanced thermal and colloidal stabilities were obtained by incorporation of carboxyl groups on the amorphous structure. The surface carboxyl groups can be subsequently functionalized, generating a multifunctional nanoplatform for theranostic applications such as drug delivery and imaging (see scheme; EDC=1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; NHS=N-hydroxysuccinimide).
Reversible phase transfer: Octadecyltrimethoxysilane (ODTS) has been used to cap the surfaces of hydrophilic magnetic nanoparticles (NPs), thereby allowing their transfer into nonpolar solution. The resulting hydrophobic magnetic nanoparticles were transferred back into aqueous solution by covering them with a lipid monolayer (see figure; Egg-PC=egg yolk phosphatidylcholine).
Spiky and hollow: By using Ag nanospheres as seeds, hollow Ag–Au nanodendrites can be prepared in 15 s by a combination of a galvanic replacement reaction between Ag and AuCl4−(aq), and a AuCl4−(aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) in water. Owing to their sharp tips, the Ag–Au nanodendrites were effective substrates for surface-enhanced Raman scattering (SERS) detection of 4-mercaptopyridine and rhodamine 6G.
Si prefers alcohol: Low-temperature hydrosilylation led to a preferential surface grafting of the Si-O-C linkage instead of the classic Si-C linkage when reacted with an alcohol carrying a short bifunctional alkyne (see figure). Even in the presence of another alkyne competitor (trifluoroalkyne) at equimolar concentration, the Si-O-C bond remained the dominant linkage to the silicon surface through nucleophilic reaction.
Explosive sensing: A structural mechanism that takes into account both the special conformation of oligophenyleneethynylene molecules at a thin-film surface and antenna effects enabled by exciton migration is presented (see figure). This mechanism explains why these crystallized fluorescent films exhibit excellent sensing properties toward nitroaromatic vapors despite the fact that they are nonporous.
Two birds with one stone! Xanthates and peroxides are used as radical precursors to graft various functions at the reduced graphene oxide surface. The developed method allows a double functionalization by both xanthate and peroxide radicals to be performed in one single step. The versatility of the method is highlighted by the grafting of seven xanthates and four peroxides. The resulting material shows no visible structural damage and long-lasting dispersibility.
Sourcing luminescence: Imidazolium–silica-based nanoparticle networks (INNs) have been synthesized and characterized (see picture). A molecular model for the imidazolium–silica network is presented and described. The presence of water near the silica surface and its influence on the position of the counteranions in the INN has been shown.
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.
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.
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.
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).
To expand the utilization of cellulose beyond its traditional uses, it is necessary to modify the surface of the fibers. This paper summarizes the modification of cellulose by controlled polymerization methods such as ATRP, RAFT, ROP, and ROMP. The combination of the excellent properties of cellulose with functional polymers creates new materials of great potential in advanced material applications.
In this review, a brief introduction to surface modification using poly(N-vinylpyrrolidone) and its copolymers and their potential biomedical applications is presented. Some perspectives on future research in the areas are also discussed.