Covalent Surface Modification of Oxide Surfaces

A valence tautomeric cobalt-dioxolene complex with an anchoring group for prospective chemical grafting to metal oxides

Here, we synthesized a valence tautomeric cobalt-dioxolene complex featuring a protected anchoring group. At room temperature, the complex reveals a nearly pure low-spin-Co(iii)-catecholate state in the solid state, but a nearly pure high-spin-Co(ii)-semiquinonate state in toluene solution. Thermal switchability of the complex in solution and in the solid state is investigated.

Helix-sense-selective surface grafting polymerization for preparing optically active hybrid microspheres

Chiral hybrid micro/nanomaterials have attracted great interest and have been extensively studied due to their intriguing properties and promising applications which cannot be achieved with each of the single components.

Highly Fluorinated Barium Titanate Nanoparticle Dispersion for Fabrication of Lithographically Patterned Thin Films

We report the synthesis, characterization, and photopatterning of high-k inorganic nanoparticles that are covered with highly fluorinated carboxylic acid and, as a result, are solution-processable in fluorous liquids. Barium titanate (BTO) nanoparticles, 7–8 nm in diameter, were prepared under solvothermal conditions and were surface-modified with perfluoroalkyl ether-type carboxylic acid molecules via ligand-exchange reactions. Thin films with a high dielectric constant (9.27 at 1 kHz) were achieved by spin-coating homogeneous solutions of BTO nanoparticles in a fluorous solvent (HFE-7500). Additionally, electron-beam lithography and photolithography were applied to the thin films of BTO nanoparticles, yielding BTO patterns with scales of 300 nm and 5 μm, respectively. Thus, an approach for a chemically non-damaging solution process of inorganic materials for device implementation was successfully demonstrated.

Thiazolocatechol: Electron-Withdrawing Catechol Anchoring Group for Dye-Sensitized Solar Cells

Anchoring groups adopting a five-membered bidentate chelating are attractive to realize high power conversion efficiency (η) and long-term durability in dye-sensitized solar cells (DSSCs). In this regard, we chose catechol as an anchoring group that can adopt the chelating. However, the DSSCs with catechol-based sensitizers have never exceeded an η-value of 2 %. These poor photovoltaic performances may be associated with the electron-donating ability of the hydroxy groups in catechol. Considering these, we envisioned that fusing an electron-withdrawing thiazole moiety with a catechol anchoring group would improve its photovoltaic performance. Herein, we report a push-pull porphyrin sensitizer ZnPTC with a thiazolocatechol anchoring group. The DSSC with ZnPTC exhibited η=4.87 %. This value is the highest ever reported for catechol-anchor based DSSCs. Meanwhile, the long-term cell durability was not improved, although the robust anchoring properties were attained under harsh conditions.

Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions

The electrochemical grafting of the “in-situ” prepared diazopyridinium salt have permitted the attachment of pyridine moieties onto platinum and glassy carbon surfaces. The modification of the electrode surfaces is observed by a redox probe. The ability of the film for the complexation of copper (II) ions is demonstrated by square wave voltammetry. After 45 min accumulation of copper (II) ions onto the grafted electrode surfaces, the electrode signal obtained by square wave voltammetry measurement served to discriminate the adsorbed heavy metal ions. Such measurements showed that the grafted pyridine has the ability to display complexing behavior toward some heavy metal ions. DFT calculations support a strong binding of the pyridine moieties onto the Pt surface. The most favorable complexation mode of copper (II) ions as suggested from DFT is the bidentate complex. This strategy is vital in constructing a wide range of different electrochemical sensors.

The influence of the grafted aryl groups on the solvation properties of the graphyne and graphdiyne - a MD study

The mechanism of the adsorption and grafting of diazonium cations onto the surface of graphyne and graphdiyne was investigated using Density Functional Theory (DFT). The adsorption energy (both in vacuum and water as solvent) of the phenyl diazonium cation was evaluated at three different positions of the graphyne and graphdiyne surface. Moreover, the lowest energy adsorption sites were used to calculate and plot Non-covalent Interactions (NCI). The Bond Dissociation Energy (BDE) results (up to 66 kcal/mol) for the scission of the phenyl group support the remarkable stability of the grafted layer. As both of these materials are non-dispersible in aqueous solution, in this work through the use of Molecular Mechanics (MM) and Molecular Dynamics (MD) we explored also the effect of the grafted substituted aryl groups derived from aryldiazonium salts onto the solvation properties of these materials.

Mixed Ligand Shell Formation upon Catechol Ligand Adsorption on Hydrophobic TiO2 Nanoparticles

Modifying the surfaces of metal oxide nanoparticles (NPs) with monolayers of ligands provides a simple and direct method to generate multifunctional coatings by altering their surface properties. This works best if the composition of the monolayers can be controlled. Mussel-inspired, noninnocent catecholates stand out from other ligands like carboxylates and amines because they are redox-active and allow for highly efficient surface binding and enhanced electron transfer to the surface. However, a comprehensive understanding of their surface chemistry, including surface coverage and displacement of the native ligand, is still lacking. Here, we unravel the displacement of oleate (OA) ligands on hydrophobic, OA-stabilized TiO₂ NPs by catecholate ligands using a combination of one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques. Conclusive pictures of the ligand shells before and after surface modification with catecholate were obtained by ¹H and ¹³C NMR spectroscopy (the ¹³C chemical shift being more sensitive and with a broader range). The data could be explained using a Langmuir-type approach. Gradual formation of a mixed ligand shell was observed, and the surface processes of catecholate adsorption and OA desorption were quantified. Contrary to the prevailing view, catecholate displaces only a minor fraction (∼20%) of the native OA ligand shell. At the same time, the total ligand density more than doubled from 2.3 nm^-2 at native oleate coverage to 4.8 nm^-2 at maximum catecholate loading. We conclude that the catecholate ligand adsorbs preferably to unoccupied Ti surface sites rather than replacing native OA ligands. This unexpected behavior, reminiscent of the Vroman effect for protein corona formation, appears to be a fundamental feature in the widely used surface modification of hydrophobic metal oxide NPs with catecholate ligands. Moreover, our findings show that ligand displacement on OA-capped TiO₂ NPs is not suited for a full ligand shell refunctionalization because it produces only mixed ligand shells. Therefore, our results contribute to a better understanding and performance of photocatalytic applications based on catecholate ligand-sensitized TiO₂ NPs.

Surface Modification of Pseudoboehmite-Coated Aluminum Plates with Squaramic Acid Amphiphiles

The functionalization of interfaces has become very important for the protection or modification of metal (metal oxides) surfaces. The functionalization of aluminum is particularly interesting because of its relevance in fabricating components for electronic devices. In this work, the utilization of squaramic acids for the functionalization of aluminum substrates is reported for the first time. The physicochemical properties of the interfaces rendered by n-alkyl squaramic acids on aluminum metal substrates coated with pseudoboehmite [Al(O)x(OH)y] layers are characterized by contact angle, grazing-angle Fourier-transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and matrix-assisted laser desorption ionization time-of-flight. Moreover, we could confirm the squaramic functionalization of the substrates by diffuse reflectance UV-vis spectroscopy, which cannot be used for the characterization of UV-vis-inactive substrates such as carboxylates and phosphonates, commonly used for coating metallic surfaces. Remarkably, the results of sorption experiments indicate that long-chain alkyl squaramic acid desorbs from activated-aluminum substrates at a reduced rate compared to palmitic acid, a carboxylic acid frequently used for the functionalization of metal oxide surfaces. Theoretical calculations indicate that the improved anchoring properties of squaramic acids over carboxylates are probably due to the formation of additional hydrogen bonding interactions on the interface. Accordingly, we propose N-alkyl squaramic acids as new moieties for efficient functionalization of metal oxides.

Electronic Communication in Confined Space Coronas of Shell-by-Shell Structured Al2 O3 Nanoparticle Hybrids Containing Two Layers of Functional Organic Ligands

A first series of examples for confined space interactions of electron-rich and electron-poor molecules organized in an internal corona of shell-by-shell (SbS)-structured Al₂ O₃ nanoparticle (NP) hybrids is reported. The assembly concept of the corresponding hierarchical architectures relies on both covalent grafting of phosphonic acids on the NPs surface (SAMs formation; SAM=self-assembled monolayer) and exohedral interdigitation of orthogonal amphiphiles as the second ligand layer driven by solvophobic interactions. The electronic communication between the chromophores of different electron demand, such as pyrenes, perylenediimides (PDIs; with and without pyridinium bromide headgroups) and fullerenes was promoted at the layer interface. In this work, it is demonstrated that the efficient construction principle of the bilayer hybrids assembled around the electronically "innocent" Al₂ O₃ core is robust enough to achieve control over electronic communication between electron-donors and -acceptors in the interlayer region. The electronic interactions between the electron-accepting and electron-donating moieties approaching each other at the layer interface were monitored by fluorescence measurements.

Rational design of nanosystems for simultaneous drug delivery and photodynamic therapy by quantum mechanical modeling

Drug delivery systems are based on reversible interactions between carriers and drugs. Spacers are often introduced to tailor the type of interaction and to keep drugs intact. Here, we model a drug delivery system based on a functionalized curved TiO₂ nanoparticle of realistic size (700 atoms - 2.2 nm) by the neurotransmitter dopamine to carry the anticancer chemotherapeutic agent doxorubicin (DOX). The multiscale quantum chemical study aims at unraveling the nature and mechanism of the interactions between the components and the electronic properties of the composite system. We simulate the temperature effect through molecular dynamics runs of thermal annealing. Dopamine binds preferentially to low coordinated Ti sites on the nanoparticle through dissociated bidentate and chelate modes involving the diol groups. DOX is tethered by H-bonds, π-π stacking, dipole-dipole interactions and dispersion forces. Comparing different coverage densities of the spacer on the nanoparticle surface, we assess the best conditions for an effective drug transport and release: only at full coverage, DOX does not slip among the dopamine molecules to reach the nanoparticle surface, which is crucial to avoid the formation of stable coordinative bonds with under-coordinated Ti atoms. Finally, given the strong absorption properties and fluorescence of DOX and of the TiO₂ photocatalyst, we model the effect of light irradiation through excited state calculations to localize excitons and to follow the charge carrier's life path. This fundamental study on the nature and mechanism of drug/carrier interaction provides a solid ground for the rational design of new experimental protocols for a more efficient drug transport and release and its combination with photodynamic therapy.

Multidentate Anchors for Surface Functionalization

The bottom-up functionalization of solid surfaces shows increasing importance for a wide range of interdisciplinary applications. Multidentate anchors with more than two contact points can bind to solid surfaces with strong chemisorption, well-defined upright configuration, and tailored functionality. The surface functionalization using multidentate anchors with three (tripodal), four (quadripodal), or more binding points is summarized herein, with a focus on those beyond classical tripodal anchors. In particular, the molecular design on how to achieve multisite interaction between anchor and substrate and the introduction of functional groups to thin films are discussed.

Corrosion inhibition of iron surfaces with phosphatidic acid

Preventing the corrosion of iron in inaccessible structures requires a coating method that reaches all surface areas and creates a uniform protective layer. An ages old practice to protect iron artefacts is to coat them with animal fat, that is, a mixture of lipids. This “method” is accidentally ingenious: some natural phospholipids found in animal fat have the potential to form a tightly packed self-assembled monolayer on metal oxide surfaces, similar to the surfactant monolayers that have attracted increasing attention lately. Thus, the most primitive corrosion prevention method may point at a way to coat complex iron structures in an industrial environment. Here the ability of phosphatidic acid, a natural lipid, to coat and protect iron surfaces was examined. Iron coated quartz crystal microbalance (QCM) sensors were used for the experiments, to monitor the deposition of the lipid as well as the acidic corrosion (dissolution) of iron in situ, in real time. The sensors were coated by self-assembled monolayers of di-myristoyl phosphatidic acid using the liposome deposition method. In this process, 50-100 nm vesicles formed by the lipid are delivered in an aqueous solution and spontaneously coat the iron surfaces upon contact. QCM and ellipsometry measurements confirmed that continuous bilayer and monolayer surface coatings can be achieved by this method. QCM measurements also confirmed that the layers were corrosion resistant in 0.01M acetic acid solution that would dissolve the thin iron layer in minutes in the absence of the protective coating. XPS results suggested a chemisorption-based mechanism of phosphatidic acid attachment to the iron surface. Hence, liposome deposition of phosphatidic acid offers a suitable solution to coat iron surfaces in inaccessible structures in situ.

Oxidized Titanium Tungsten Surface Functionalization by Silane-, Phosphonic Acid-, or Ortho-dihydroxyaryl-Based Organolayers

Titanium tungsten (TiW) films (200 nm thick) were cleaned by oxygen plasma, and the resulting oxidized surfaces were functionalized by 3-aminopropylphosphonic acid (APPA), 3-ethoxydimethylsilylpropylamine (APDMES), or dopamine (DA) to form three different organolayers. The three resulting organolayers were characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and Fourier transform infrared spectroscopy analyses. The stability of each organolayer was investigated. Our results suggested that the Si-O-Ti or Si-O-W bonds formed by the reactions of APDMES with surface-oxidized TiW were rather labile, whereas the catechol layer was less labile. The APPA layer was the most stable of all tested surface modifications.

Smooth and Transparent Films Showing Paradoxical Surface Properties: The Lower the Static Contact Angle, the Better the Water Sliding Performance

Smooth and transparent hydrophilic films showing excellent water sliding properties were prepared by using a sol-gel solution of 2-[methoxy (ethyleneoxy)₁₀ propyl]trimethoxysilane and tetraethoxysilane. The resulting hybrid films were statically hydrophilic (static water contact angles (CAs) were in the range of 30-45°), but water droplets (50 μL) could move smoothly on an inclined surface (minimum sliding angle was 6°) without pinning or tailing because of low CA hysteresis (5 ± 1°). Thanks to this hybrid film formation on aluminum (Al) substrate, drainage performance during condensation and frosting/defrosting markedly improved compared to that on hydrophilic, bare Al, or hydrophobic monolayer-covered Al substrates.

Crossing the bridge from molecular catalysis to a heterogenous electrode in electrocatalytic water oxidation

Significant progress has been made in designing single-site molecular Ru(II)-polypyridyl-aqua catalysts for homogenous catalytic water oxidation. Surface binding and transfer of the catalytic reactivity onto conductive substrates provides a basis for heterogeneous applications in electrolytic cells and dye-sensitized photoelectrosynthesis cells (DSPECs). Earlier efforts have focused on phosphonic acid (-PO₃H₂) or carboxylic acid (-CO₂H) bindings on oxide surfaces. However, issues remain with limited surface stabilities, especially in aqueous solutions at higher pH under conditions that favor water oxidation by reducing the thermodynamic barrier and accelerating the catalytic rate using atom-proton transfer (APT) pathways. Here, we address the problem by combining silane surface functionalization and surface reductive electropolymerization on mesoporous, nanofilms of indium tin oxide (ITO) on fluorine-doped tin oxide (FTO) substrates (FTO|nanoITO). FTO|nanoITO electrodes were functionalized with vinyltrimethoxysilane (VTMS) to introduce vinyl groups on the electrode surfaces by silane attachment, followed by surface electropolymerization of the vinyl-derivatized complex, [Ru^II(Mebimpy)(dvbpy)(OH₂)]²⁺ (1²⁺; Mebimpy: 2,6-bis(1-methyl-1H-benzo[d]imidazol-2-yl)pyridine; dvbpy: 5,5'-divinyl-2,2'-bipyridine), in a mechanism dominated by a grafting-through method. The surface coverage of catalyst 1²⁺ was controlled by the number of electropolymerization cycles. The combined silane attachment/cross-linked polymer network stabilized 1²⁺ on the electrode surface under a variety of conditions especially at pH > ∼6. Surface-grafted poly1²⁺ was stable toward redox cycling at pH ∼ 7.5 over an ∼4-h period. Sustained heterogeneous electrocatalytic water oxidation by the electrode gave steady-state currents for at least ∼6 h with a Faradaic efficiency of ∼68% for O₂ production.

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting

Photoelectrochemical water splitting is a promising carbon-free approach to produce hydrogen from water. A photoelectrochemical cell consists of a semiconductor photoelectrode in contact with an aqueous electrolyte. Its performance is sensitive to properties of the photoelectrode/electrolyte interface, which may be tuned through functionalization of the photoelectrode surface with organic molecules. This can lead to improvements in the photoelectrode's properties. This Minireview summarizes key computational investigations on using molecular functionalization to modify photoelectrode stability, barrier height, and catalytic activity. It is discussed how first-principles density functional theory, first-principles molecular dynamics, and device modeling simulations can provide predictive insights and complement experimental investigations of functionalized photoelectrodes. Challenges and future directions in the computational modeling of functionalized photoelectrode/electrolyte interfaces within the context of experimental studies are also highlighted.

Artificial photosynthesis with metal and covalent organic frameworks (MOFs and COFs): challenges and prospects in fuel-forming electrocatalysis

Mimicking photosynthesis in generating chemical fuels from sunlight is a promising strategy to alleviate society's demand for fossil fuels. However, this approach involves a number of challenges that must be overcome before this concept can emerge as a viable solution to society's energy demand. Particularly in artificial photosynthesis, the catalytic chemistry that converts energy in the form of electricity into carbon-based fuels and chemicals has yet to be developed. Here, we describe the foundational work and future prospects of an emerging and promising class of materials: metal- and covalent-organic frameworks (MOFs and COFs). Within this context, these porous and tuneable framework materials have achieved initial success in converting abundant feedstocks (H₂ O and CO₂ ) into chemicals and fuels. In this review, we first highlight key achievements in this direction. We then follow with a perspective on precisely how MOFs and COFs can perform in ways not possible with conventional molecular or heterogeneous catalysts. We conclude with a view on how spectroscopically probing MOF and COF catalysis can be used to elucidate reaction mechanisms and material dynamics throughout the course of reaction.

Carboxylate Anchors Act as Exciton Reporters in 1.3 nm Indium Phosphide Nanoclusters

Developing interfacial probes of ligand-nanocluster interactions is crucial for understanding and tailoring the optoelectronic properties of these emerging nanomaterials. Using transient IR spectroscopy, we demonstrate that ligand vibrational modes of oleate-capped 1.3 nm InP nanoclusters report on the photogenerated exciton. The exciton induces an intensity change in the asymmetric carboxylate stretching mode by 57% while generating no appreciable shift in frequency. Thus, the observed difference signal is attributed to an exciton-induced change in the dipole magnitude of the asymmetric carboxylate stretching mode. Additionally, the transient IR data reveal that the infrared dipole change is dependent on the geometry of the ligand bound to the nanocluster. The experimental results are interpreted using TDDFT calculations, which identify how the spatial dependence of an exciton-induced electron density shift affects the vibrational motion of the carboxylate anchors. More broadly, this work demonstrates transient IR spectroscopy as a useful method for characterizing ligand-nanocluster coupling interactions.

Mechanistic and energetic studies of superparamagnetic iron oxide nanoparticles as a cyclophosphamide anticancer drug nanocarrier: A quantum mechanical approach

Using Fe6(OH)18(H2O)6 as a ring cluster model for superparamagnetic iron oxide nanoparticles, noncovalent configurations and three mechanisms of covalent functionalization of superparamagnetic iron oxide nanoparticles with cyclophosphamide an anticancer drug were studied. Quantum molecular descriptors, solvation, and binding energies of noncovalent interactions were investigated the in gas and solution phases at the B3LYP and M06-2X density functional levels. In the vicinity of superparamagnetic iron oxide nanoparticles, the reactivity of the drug increases, showing cyclophosphamide can probably bind to superparamagnetic iron oxide nanoparticles through Cl ( k1 mechanism), P=O ( k2 mechanism), and NH in a six-membered ring ( k3 mechanism) groups. The activation parameters of all pathways were calculated, indicating the high barriers related to the k1 and k2 mechanisms are higher the barrier related to the k3 mechanism. The k3 mechanism is also spontaneous and exothermic and is therefore the preferred mechanism for covalent functionalization.

Clickable and Photo-Erasable Surface Functionalities by Using Vapor-Deposited Polymer Coatings

A prospective design for interface properties is enabled to perform precise functionalization, erasure capability for existing properties, reactivation of surface functionality to a second divergent property. A vapor-deposited, 2-nitro-5-(prop-2-yn-1-yloxy)methylbenzyl carbamate-functionalized poly-para-xylylene coating is synthesized in this study to realize such tasks by offering the accessibility of the azide/alkyne click reaction, an integrated photochemical decomposition/cleavage moiety, and the reactivation sites of amines behind the cleavage that allow the installation of a second surface function. With the benefits from the mild processing conditions used for the coatings and the rapid response of the photochemical reaction, the creation of sophisticated interface properties and localized chemical compositions was elegantly demonstrated with a hybrid functionality including a confined hydrophlic/hydrophobic wetting property and/or a cell adherent/repellent platform on such a coating surface.

Hetero-difunctional Reagent with Superior Flotation Performance to Chalcopyrite and the Associated Surface Interaction Mechanism

Surface modification by chemical reagents is of profound importance to modulate the surface characteristic and functionality of materials, which has attracted tremendous interest in many research fields and industrial applications, such as froth flotation of minerals. In this work, a new reagent S-[(2-hydroxyamino)-2-oxoethyl]- O-octyl-dithiocarbonate ester (HAOODE) with heterodifunctional ligands was designed and synthesized to improve the flotability of chalcopyrite (CuFeS₂). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed the co-adsorption of heterodifunctional ligands (i.e., dithiocarbonate and hydroxamate groups) of HAOODE on chalcopyrite via Cu(I)-S and Cu(II)-O covalent bonds. The bubble probe atomic force microscopy (AFM) technique was employed to quantitatively measure the air bubble-chalcopyrite interactions with and without the reagent adsorption. AFM force results revealed that the bubble could be more readily attached to flat chalcopyrite after HAOODE treatment under different hydrodynamic conditions because of the enhanced hydrophobic interaction, with the decay length D₀ increasing from 0.65 to 1.20 nm. The calculated bubble-particle interaction forces also demonstrated the critical influence of HAOODE treatment, hydrodynamic conditions, and bubble size on the interaction behavior and thin-film drainage process in flotation. In froth flotation, HAOODE exhibited superior recovery for chalcopyrite over pH 3-12 and excellent selectivity for chalcopyrite against pyrite (FeS₂) above pH 10.5, as compared to the conventional reagent sodium isobutyl xanthate. This work provides a useful approach to develop effective reagents that could selectively adsorb on desired mineral surfaces through heterodifunctional ligands and to quantitatively evaluate the role of reagent adsorption in the interactions between air bubbles and mineral surfaces at the nano- and microscale. Our results show implications on developing molecular design principles of novel reagents for surface modifications of materials in a wide range of engineering and biological applications.

Introducing the concept of pulsed vapor phase copper-free surface click-chemistry using the ALD technique

We report for the first time on a pulsed vapor phase copper-free azide-alkyne click reaction on ZnO by using the atomic layer deposition (ALD) process technology. This reproducible and fast method is based on an in situ two-step reaction consisting of sequential exposures of ZnO to propiolic acid and benzyl azide.

A robust ALD-protected silicon-based hybrid photoelectrode for hydrogen evolution under aqueous conditions

Hybrid systems combining molecular catalysts with inorganic materials is a promising solution towards cheap yet efficient and stable photoelectrochemical hydrogen production.

Hydrogen production through direct sunlight-driven water splitting in photo-electrochemical cells (PECs) is a promising solution for energy sourcing. PECs need to fulfill three criteria: sustainability, cost-effectiveness and stability. Here we report an efficient and stable photocathode platform for H₂ evolution based on Earth-abundant elements. A p-type silicon surface was protected by atomic layer deposition (ALD) with a 15 nm TiO₂ layer, on top of which a 300 nm mesoporous TiO₂ layer was spin-coated. The cobalt diimine–dioxime molecular catalyst was covalently grafted onto TiO₂ through phosphonate anchors and an additional 0.2 nm ALD-TiO₂ layer was applied for stabilization. This assembly catalyzes water reduction into H₂ in phosphate buffer (pH 7) with an onset potential of +0.47 V vs. RHE. The resulting current density is –1.3 ± 0.1 mA cm^–2 at 0 V vs. RHE under AM 1.5 solar irradiation, corresponding to a turnover number of 260 per hour of operation and a turnover frequency of 0.071 s^–1.

Halide Perovskites: Is It All about the Interfaces?

Design and modification of interfaces, always a critical issue for semiconductor devices, has become a primary tool to harness the full potential of halide perovskite (HaP)-based optoelectronics, including photovoltaics and light-emitting diodes. In particular, the outstanding improvements in HaP solar cell performance and stability can be primarily ascribed to a careful choice of the interfacial layout in the layer stack. In this review, we describe the unique challenges and opportunities of these approaches (section 1). For this purpose, we first elucidate the basic physical and chemical properties of the exposed HaP thin film and crystal surfaces, including topics such as surface termination, surface reactivity, and electronic structure (section 2). This is followed by discussing experimental results on the energetic alignment processes at the interfaces between the HaP and transport and buffer layers. This section includes understandings reached as well as commonly proposed and applied models, especially the often-questionable validity of vacuum level alignment, the importance of interface dipoles, and band bending as the result of interface formation (section 3). We follow this by elaborating on the impact of the interface formation on device performance, considering effects such as chemical reactions and surface passivation on interface energetics and stability. On the basis of these concepts, we propose a roadmap for the next steps in interfacial design for HaP semiconductors (section 4), emphasizing the importance of achieving control over the interface energetics and chemistry (i.e., reactivity) to allow predictive power for tailored interface optimization.

Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes

The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule-material hybrid systems are organized as "dark" cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends the scope of this review to prospects and challenges in targeting catalysis beyond "classical" H2 evolution and CO2 reduction to C1 products, by summarizing cases for higher-value products from N2 reduction, C x>1 products from CO2 utilization, and other reductive organic transformations.

Interactions between the Aryldiazonium Cations and Graphene Oxide: A DFT Study

Understanding the grafting behavior of the aryldiazonium cations is of fundamental and also of practical importance for the vast number of applications that involve the use of modified graphene oxide (from simple adsorption process to electronic and photovoltaic applications). In this work, the mechanism of the adsorption and grafting of diazonium cations on the graphene oxide surface was investigated by the use of density functional theory. Two types of aryldiazonium cations, one bearing only phenyl ring and the other nitrophenyl, were selected as adsorbates/grafted moiety. By evaluating the adsorption energies at 7 different positions onto the graphene oxide both in the gaseous and solvent phase (using COSMO approach), the most probable adsorption sites were found. Moreover, the most stable adsorption sites were used to calculate and plot NCI (noncovalent interactions). The obtained results are important as they not only give molecular insights regarding the nature of the interaction and its dependence on the adsorption site of the graphene oxide surface but also on the activation energy for such a grafting reaction to take place, providing a mechanistic aspect to understand these grafting reactions.

Functionalization of Commercial Sand Core Funnels as Hydrophobic Materials with Novel Physicochemical Properties

A solid surface morphology is of great importance for the fundamental research in the field of hydrophobic materials. Commercial sand core funnels (SCs) are embedded with multilevel pore size and surface roughness, which are excellent models to study the mechanism of surface wettability. This article described a simple, green, and facile method to fabricate hydrophobic surfaces on SCs via reacting with perfluorooctyltriethoxysilane (PFTS) vapor. Systematic analyses on the reaction, properties, and applications of the PFTS-modified SCs were conducted, which involved the reaction time and temperature, water resistance, mechanical durability, self-cleaning test, surface adhesion, and underoil superhydrophobicity. The water contact angle of the modified SCs increased with a decrease of the pore size and an increase of the surface roughness of the sand core particles. The wettability of the modified SCs agrees well with the intermediate states between Wenzel and Cassie-Baxter. The PFTS-modified SCs retained excellent chemical stability in rigid conditions and good mechanical properties. The hydrophobic SCs showed oil/water separation performance with excellent efficiency, reusability, and high flux. Especially for the PFTS-modified SCs with small pore sizes, water-in-oil emulsion separation was successfully realized. The easily accessible, relatively cheap raw materials and facile process in this work are very desirable to obtain a specific wetting surface, which will offer promising applications in various fields.

Straightforward Immobilization of Phosphonic Acids and Phosphoric Acid Esters on Mesoporous Silica and Their Application in an Asymmetric Aldol Reaction

The combined benefits of moisture-stable phosphonic acids and mesoporous silica materials (SBA-15 and MCM-41) as large-surface-area solid supports offer new opportunities for several applications, such as catalysis or drug delivery. We present a comprehensive study of a straightforward synthesis method via direct immobilization of several phosphonic acids and phosphoric acid esters on various mesoporous silicas in a Dean–Stark apparatus with toluene as the solvent. Due to the utilization of azeotropic distillation, there was no need to dry phosphonic acids, phosphoric acid esters, solvents, or silicas prior to synthesis. In addition to modeling phosphonic acids, immobilization of the important biomolecule adenosine monophosphate (AMP) on the porous supports was also investigated. Due to the high surface area of the mesoporous silicas, a possible catalytic application based on immobilization of an organocatalyst for an asymmetric aldol reaction is discussed.

Surface-bound quadruple H-bonded dimers: formation and exchange kinetics

While the mechanistic details of the dimerization of the self-complementary 2-ureido-4(1H)-pyrimidinone (UPy) motif are well studied in solution, no such investigation is available on a surface. Here we report an extensive study of hydrogen binding kinetics for quadruply H-bonded UPy arrays on aluminum surfaces and explore the ON/OFF capability of such arrays under externally controllable conditions. Also, we investigate the dynamic nature of this system whereby the interfacially H-bonded UPy is displaced by another UPy derivative in solution, and reveal the kinetics of the exchange process.