Aspects Of Surface Chemistry Research Articles

Trends in the Reactivity of Pentacyclic Ether Derivatives on Silicon and Germanium Surfaces Revealed by Energy Decomposition Analysis for Extended Systems

We analyze the adsorption and ring‐opening reaction of pentacyclic chalcogen alkyls with chalcogen atoms ranging from oxygen to tellurium using computational analysis. Thus extends our previous investigation of THF on silicon towards germanium surface and towards the heavier chalcogen homologues. We found an increasing dative bond strength of the precursor state with the period of the chalcogen atom on both surfaces. Using energy decomposition analysis for extended systems (pEDA), differences in the trends between silicon and germanium were revealed. Following the dative bound state, subsequent ring‐opening reactions were found to proceed via a nucleophilic back‐side attack, similar to a molecular SN2 reaction. Reaction energies and barrier heights show a maximum for the sulfur derivative. This trend was found to correlate with the position of the transition state in the reaction and agrees with the molecular reactivity. The uniquely low barrier of THF can be attributed to its ring strain. Our findings shed light on the fundamental aspects of surface chemistry and the benefits of using quantitative bonding analysis in this field. It also paves the way for future explorations into the functionalization of semiconductor surfaces using higher‐period ether derivatives.

Design and engineering of 3D plasmonic superstructure based on Pickering emulsion templates for surface-enhanced Raman spectroscopy applications in chemical and biomedical sensing

The integration of Pickering emulsion as a versatile template facilitates the assembly of nanoscale and microscale NPs, leading to the formation of intricate 3D superstructures. These superstructures exhibit collective properties, including optical, electric, and catalytic functionalities, surpassing individual building block. This review comprehensively explores the design and engineering principles behind the creation of these multifaceted superstructures. The exploration begins with the fundamental aspects of surface chemistry governing nanoparticles, a crucial factor in directing their assembly behavior at the curved liquid–liquid emulsion interface. Emphasis is placed on understanding emulsion stability, a pivotal element guiding the formation of stable 3D architectures. The discussion extends to unraveling the underlying mechanisms promoting the formation of these 3D superstructures. The focus lies in elucidating the optical functionalities of these superstructures, particularly in the context of surface-enhanced Raman spectroscopy application. The surveyed literature showcases diverse Pickering emulsion-based strategies employed in the assembly of plasmonic nanoparticles into intricate superstructures, offering controlled architectures and unlocking unique potentials for chemical and biochemical sensing.

Irreversible Structural Dynamics in Bimetallic Pt-Ni Alloy Catalyst Under Alternating Redox Environments

The better understanding on the structural dynamics of a bimetallic catalyst during its interaction with reactive environments is a prerequisite for the development of an efficient catalyst for proton exchange membrane fuel cells (PEMFCs). The main focus should be given to the outermost layers of catalytically active material which are directly involved in catalysis.Herein, we applied the synchrotron radiation photoelectron spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS) techniques to investigate surface chemistry aspects in a PtNi alloy catalyst under alternating oxidation (O2) and reduction (H2) atmospheres at different temperatures that simulate its behavior as a cathode catalyst in PEMFCs. The experimental results are substantiated by theoretical calculations on model PtNi nanoalloys.We showed that PtNi alloy does not maintain its chemical integrity and undergoes surface reconstruction during the switching between oxidizing and reducing conditions in terms of relative surface nickel enrichment. Along with compositional changes catalyst coarsening was observed by atomic force microscopy (AFM).The revealed behavior of the PtNi alloy provides valuable fundamental insights that help to gain advanced understanding of PtNi alloy catalytic activity in real conditions. Figure 1

Catalytic Mechanisms of Nanozymes and Their Applications in Biomedicine.

The research on nanozymes has increased dramatically in recent years and a new interdiscipline, nanozymology, has emerged. A variety of nanomaterials have been designed to mimic the characteristics of natural enzymes, which connects an important bridge between nanotechnology and biological science. Unlike natural enzymes, the nanoscale properties of nanozymes endow them with the potential to regulate their enzymatic-like activity from different perspectives. The mechanisms behind those methods are intriguing. In this Review, we introduce these mechanisms from the aspects of surface chemistry, surface modification, molecular imprinting, and hybridization and then focus attention on some specific catalytic mechanisms of several representative nanozymes. The applications of nanozymes ranging from bioassay, imaging, to disease therapy are also discussed in detail to prove the fact that the inherent physicochemical properties of nanomaterials not only make nanozymes the analogues of biological enzymes, but also endow them with incomparable advantages and broad prospects in biomedical fields. Finally, four characteristics and some challenges of nanozymes are summarized.

A Critical Review on Functionalization of Air‐Cathodes for Nonaqueous Li–O2 Batteries

AbstractThis review reports on the most updated technological aspects of Li–air battery cathode materials. It provides the reader with recent developments, alongside critical views. The requirements for air‐cathodes, as well as the classification and characterization of carbon‐based and carbon‐free air cathodes, are listed. The effects of two major substituent groups of materials, namely carbon and advanced materials (metals, metal‐oxides, metal‐carbides, and metal‐nitrides) aimed at replacing carbon, are discussed in terms of their chemical and electrochemical stability. The report covers aspects of surface chemistry and structure influence on the electrolyte and discharge products stability. The review also reports on the efforts to suppress side reactions and deterioration of the polymeric binders (if a composite electrode is being considered). This is recognized as a means to enhance Li–air battery performance. The report concludes with an outlook and perspective, providing the readers with some insight on other factors and their impact on the long road toward a viable air‐cathode suitable for Li–air battery operations.

Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy.

Atomic scale details of surface structure play a crucial role for solid-liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to dominate many aspects of surface chemistry and physics. Here, we use high resolution dynamic Atomic Force Microscopy (AFM) to visualize and characterize in ambient water the morphology and atomic scale structure of a variety of nanoparticles of common clay minerals adsorbed to flat solid surfaces. Atomically resolved images of the (001) basal planes are obtained on all materials investigated, namely gibbsite, kaolinite, illite, and Na-montmorillonite of both natural and synthetic origin. Next to regions of perfect crystallinity, we routinely observe extended regions of various types of defects on the surfaces, including vacancies of one or few atoms, vacancy islands, atomic steps, apparently disordered regions, as well as strongly adsorbed seemingly organic and inorganic species. While their exact nature is frequently difficult to identify, our observations clearly highlight the ubiquity of such defects and their relevance for the overall physical and chemical properties of clay nanoparticle-water interfaces.

Recent Advances on Nitrous Oxide (N2O) Decomposition over Non-Noble-Metal Oxide Catalysts: Catalytic Performance, Mechanistic Considerations, and Surface Chemistry Aspects

Nitrous oxide (N2O) is the largest stratospheric-ozone-depleting substance, being concomitantly the third most potent greenhouse gas. The direct catalytic decomposition of N2O (deN2O process) is one of the most promising remediation technologies for N2O emissions abatement. Although noble metals (NMs)-based catalysts demonstrate satisfactory deN2O performance, their high cost and sensitivity to various effluent stream components (e.g., water vapor, oxygen) limit their widespread industrial applications. Hence, the development of NMs-free catalysts of low cost and satisfactory deN2O performance is of paramount importance. This survey appraises the recent advances, which have been reported since 2000, on N2O decomposition over non-noble-metal oxidic catalysts. Initially, a brief overview of N2O sources, environmental consequences, and remediation technologies is provided. The literature related to the deN2O process over NMs-free metal oxides (MOs) is categorized and critically discussed, as follows: (i) bar...

Global transcriptomic analysis of model human cell lines exposed to surface-modified gold nanoparticles: the effect of surface chemistry.

Gold nanoparticles (Au NPs) are attractive for biomedical applications not only for their remarkable physical properties, but also for the ease of which their surface chemistry can be manipulated. Many applications involve functionalization of the Au NP surface in order to improve biocompatibility, attach targeting ligands or carry drugs. However, changes in cells exposed to Au NPs of different surface chemistries have been observed, and little is known about how Au NPs and their surface coatings may impact cellular gene expression. The gene expression of two model human cell lines, human dermal fibroblasts (HDF) and prostate cancer cells (PC3) was interrogated by microarray analysis of over 14,000 human genes. The cell lines were exposed to four differently functionalized Au NPs: citrate, poly(allylamine hydrochloride) (PAH), and lipid coatings combined with alkanethiols or PAH. Gene functional annotation categories and weighted gene correlation network analysis were used in order to connect gene expression changes to common cellular functions and to elucidate expression patterns between Au NP samples. Coated Au NPs affect genes implicated in proliferation, angiogenesis, and metabolism in HDF cells, and inflammation, angiogenesis, proliferation apoptosis regulation, survival and invasion in PC3 cells. Subtle changes in surface chemistry, such as the initial net charge, lability of the ligand, and underlying layers greatly influence the degree of expression change and the type of cellular pathway affected.

Surface chemistry aspects of bastnaesite flotation with octyl hydroxamate

Surface chemistry features of bastnaesite were investigated with respect to octyl hydroxamate adsorption and the wetting characteristics at different levels of hydroxamate adsorption. The wetting characteristics of bastnaesite in the absence of collector adsorption were examined using both contact angle measurements and MD simulations. As expected, it was found that bastnaesite is naturally hydrophilic. Surface chemistry studies included octyl hydroxamate adsorption by the solution depletion method. The surface state was described by sum-frequency vibrational spectroscopy (SFVS) and molecular dynamic simulations (MDS). The adsorption isotherm at low levels of hydroxamate adsorption was established and the hydrophobic surface state was described from contact angle measurements. The relationship between hydrophobicity and adsorption density was examined for the first time by MD simulations. The SFVS spectra indicate that a well-ordered monolayer was formed at a hydroxamate concentration of about 1×10−4M.

Lucio Isa

Lucio Isa

Toward residual-layer-free nanoimprint lithography in large-area fabrication

In the paper, residual-layer-free nanoimprint lithography for large-area fabrication is reviewed. In order to remove the residual layer during the imprint process, polymer resists and mold materials should be designed with the aspects of surface chemistry and mold geometries in mind. Various approaches for residual-layerfree nanoimprint lithography are discussed including incomplete filling by polymer mass, reverse imprint methods, self-removal techniques, and the employment of elastomeric mold deformation. In addition, issues that must be overcome to enable large-area roll-to-roll nanoimprinting without a residual layer are presented.

Characterization and Dispersion of Multiwalled Carbon Nanotubes (MWCNTs) in Aqueous Suspensions: Surface Chemistry Aspects

Dispersability of multiwalled carbon nanotubes (MWCNTs) in aqueous suspensions was investigated with gum arabic GA (anionic) and polydiallyldimethylammonium chloride (PDADMAC) cationic dispersants. The isoelectric point (iep) of MWCNTs was at pH 4.5. The surface charge of MWCNTs changed to highly negative and iep shifted to pH < 1.5 with GA, whereas with PDADMAC highly positive and iep is shifted to pH 10.2. The interaction energy of MWCNTs with GA and PDADMAC was 9.79 and 10.35 RT unit, respectively. The higher interaction energy with PDADMAC shows more favorable interaction with them. Stabilization mechanism with GA is attributed mainly by electrostatic repulsive forces, whereas with PDADMAC, electrostatic and steric effect.

Core–shell composite of SiCN and multiwalled carbon nanotubes from toluene dispersion

Carbon nanotubes are known to have high thermal conductivity, and in bulk form, a topology that could constitute the matrix of an inhomogeneous solid [1]. Among the promised applications of carbon nanotubes is a composite material that is practical for thermal management and suitable for commercial products that behave as thermal emitters, absorbers, and interfaces. However, carbon nanotubes are known to oxidize in the temperature range of 400 to 600 C, which limits the options for forming the composite and the applicability for high-temperature environments where such a composite is needed. A variety of polymer, metal, and ceramic composites bearing carbon nanotubes have been reviewed [2, 3]. More recently, Francis and Riedel [4] reported the use of polyureasilazane as a route to form a shell–core composite containing nanotubes. In their work, the SiCN shell is derived from polyureasilazane. However, the polyureasilazane is a viscous liquid in which nanotubes do not readily disperse. Francis and Riedel were able to report a multiple-step process that includes cross-linking (at 280 C), pressing, mixing, ball milling, and baking again at higher temperature. We have found an alternate route of forming a similar composite that is facilitated by dispersing the nanotubes in toluene and then mixing with polyureasilazane. A single episode of baking forms a core–shell structure of amorphous SiCN surrounding MWCNTs (abbreviated hereafter as SiCN/MWCNT). Our primary application is that of coating thermal detectors and other surfaces intended to absorb and thermalize laser radiation. The challenge is shared by other applications that demand heat dissipation without oxidation and melting. Before now, we have pursued nanotubes (single-walled and multi-walled) applied from a volatile suspension, grown vertically aligned, and bound in potassium silicate [5–7]. Here we report on the method of preparation and some aspects of surface chemistry that distinguish the shell–core composite from its constituents.

Surface chemistry aspects of coal flotation in bore water

Several theories have been proposed to explain enhancement of coal flotation in salt solutions. In this paper, surface chemistry aspects of coal flotation in bore (hypersaline) water were examined using bubble-particle attachment time experiments, zeta potential measurements, cyclic measurements of contact angle and Atomic Force Microscopy (AFM). The attachment time experiments showed that the bubble-particle attachment in deionized water was instantaneous and independent of the particle size. The attachment in bore water required longer time, which increased with increasing particle size. The cyclic measurements of contact angle on a flat coal surface showed that the coal hydrophobicity as measured by the advancing (maximum) and receding (minimum) contact angle did not change in the presence of salt ions. The zeta potential measurements show that both the coal particles and air bubbles were negatively charged in bore water. The AFM studies showed that bore water reduced repulsive surface forces between the coal particles and air bubbles but had little effect on the force of adhesion. The overall results suggest that enhancement of coal flotation in hypersaline water is not entirely attributed to the surface chemistry aspects as previously proposed.

A short review on surface chemical aspects of Li batteries: A key for a good performance

We review herein several important aspects of surface chemistry in Li-ion batteries, and discuss the use of ionic liquids (ILs) for rechargeable Li batteries. We explored the suitability of ILs for 5 V cathodes and Li-graphite anodes. Some advantages of the use of ILs to attenuate the thermal behavior of delithiated cathode materials are demonstrated. We also report briefly on a comparative study of the following cathode materials: LiNi 0.5Mn 0.5O 2; LiNi 0.33Mn 0.33Co 0.33O 2; LiNi 0.4Mn 0.4Co 0.2O 2; LiNi 0.8Co 0.15Al 0.05O 2 and LiMnPO 4, in standard electrolyte solutions based on mixtures of alkyl carbonates and LiPF 6. We also discuss aging, rate capability, cycle life and surface chemistry of these cathode materials. The techniques applied included electrochemical measurements, e.g., XRD, HRTEM, Raman spectroscopy, XPS and FTIR spectroscopy. We found that ILs based on cyclic quaternary alkyl ammonium cations may provide much better electrolyte solutions for 5 V cathodes than standard electrolyte solutions, while being quite suitable for Li-graphite electrodes. All the lithiated transition metal oxides studied (as mentioned above) develop unique surface chemistry during aging and cycling due to the acid-base and nucleophilic reactions of their surface oxygen anions. LiMn 0.33Ni 0.33Co 0.33O 2 has the highest rate capability compared to all the other above-mentioned cathode materials. Cathodes comprising nanometric size carbon-coated LiMnPO 4 produced by HPL demonstrate a better rate capability than LiNi 0.5Mn 0.5O 2 and LiNi 0.8Co 0.15Al 0.05O 2 cathodes. The former material seems to be the least surface reactive with alkyl carbonates/LiPF 6 solutions, among all the cathode materials explored herein.

Studies of fluorocarbon film deposition and its correlation with etched trench sidewall angle by employing a gap structure using C4F8∕Ar and CF4∕H2 based capacitively coupled plasmas

A high-aspect ratio, small gap structure that provides a sample surface region without direct ion bombardment has been used to study surface chemistry aspects of fluorocarbon (FC) film deposition and to simulate FC film deposition on trench sidewalls during plasma-based pattern transfer. As on the sidewalls of microscopic trenches being etched, thin FC layers form by arrival of reactive neutrals on the shadowed surface portions of the small gap structure. The deposition rates, composition, and chemical bonding of FC films formed in the small gap structure were determined by ellipsometry and x-ray photoemission spectroscopy as a function of process conditions for C4F8∕Ar and CF4∕H2 discharges produced in a dual frequency (40.68∕4MHz) capacitively coupled plasma reactor. Actual trench features were also produced using photoresist patterned organosilicate films for the same plasma processes. Scanning electron microscopy of the trenches shows a characteristic sidewall slope angle for different process conditions. We find that plasma process conditions producing lower FC film deposition rates on the shielded surface of the gap structure yield more vertical trench sidewalls. This relationship confirms the relevance of the small gap structure approach to the examination of trench sidewall chemistry. Since the present approach produces macroscopic samples of gap-deposited FC films, it enables direct surface chemical characterization of a material that is analogous to sidewall deposited films and allows to avoid the difficulties connected with direct measurements of microscopic samples. The lack of ion bombardment for the shielded deposition increases the retention of the chemical structure of the FC film precursors for the deposited films, which promises to be useful for obtaining mechanistic insights on film precursors.

Csaba Horváth – Scholar, Scientist, Mentor, Friend

At Farbwerke Hoechst, Csaba did research and development work on the surface chemistry of organic pigment dyes and learned about the practical aspects of surface chemistry. During his doctoral research, Csaba invented and developed porous-layer open tubular columns which offers remarkable advantages over wall-coated OTC, e.g., a higher loadability and the ability to use all retention mechanisms afforded by adsorption. He also prepared surface-treated beads, an approach that he used later in the context of HPLC. Working with S.R. Lipsky on the development of analytical methodologies for lunar samples, searching for trace compounds which could show the presence of life on the moon in a distant past, he imagined applying to LC the same principles that he had used earlier in GC, and built the first instrument for high pressure liquid chromatography. Very early, he understood the potential of this new separation method to revolutionize biochemistry and molecular biology. Working for Picker-Nuclear, Csaba developed the first commercial instrument for HPLC, which was also the first instrument to use microbore HPLC columns (for ion-exchange separations of biological compounds). From the beginning, Csaba focused his interests on the separation of samples of biological origin, becoming the pioneer of modern bioanalytical chemistry. Hemore » devoted considerable attention to the development of the theory and applications of reversed-phase liquid chromatography, the most widely applied chromatographic method of analysis, pioneered the use of displacement chromatography for preparative HPLC, and innumerable applications of HPLC to the separation of samples of biological origin. He developed the solvophobic theory of retention in RPLC, the use of entropy-enthalpy compensation in the study of retention mechanisms, and the fundamentals of electrochromatography. The importance of his spearheading HPLC, RPLC, and their applications in the life sciences, fields in which these new methods are leading to countless breakthroughs, is such that his contributions will remain among the major scientific achievemetns of the 20th century.« less

Studies of film deposition in fluorocarbon plasmas employing a small gap structure

A small gap structure was designed to examine surface chemistry aspects of film deposition for fluorocarbon (FC) plasmas produced using both inductively coupled plasma (ICP) and capacitively coupled plasma (CCP) systems. The small gap structure provides a completely shadowed region without direct ion bombardment. Neutrals diffuse into this region and form a fluorocarbon layer. The lack of ion bombardment increases the retention of the chemical structure of the FC film precursors. The surface chemistry of FC film deposited in this region is compared with film deposited in the region exposed to direct ion bombardment. For films deposited in the exposed region, x-ray photoelectron spectroscopy analysis shows that CF2 is the dominant chemical bond for pure C4F8 in both ICP and CCP systems. For C4F8∕Ar discharges, C–C bonding is dominant for the polymer formed in the ICP system, whereas CF2 species are dominant for films deposited in the CCP system. In the completely shadowed region, CF2 bonding is dominant fo...

General aspects of surface chemistry of metal β-diketonates

Chemical reactions of metal β-diketonates, which are conventional CVD precursors, on hot surface, have been considered. Extensive experimental data on thermal behaviour of metal β-diketonate vapours obtained by high-temperature mass spectrometry have been generalized. The influence of different gas reagents on thermal stability of the compounds has been discussed. The main mechanisms of the decomposition of compounds under investigation, leading to metal and oxide formation on hot surface, have been established. Application of mass spectrometric data to the optimization of CVD processes (precursor choice, temperature range of deposition) has been shown. A possibility to predict film composition using the data on gaseous decomposition products has been considered.

Interfacial studies on dissolved gas flotation of oil droplets for water purification

The removal of emulsified residual oil from water is an important issue due to the increasing concern with the environment. In the present paper various surface chemistry aspects of dissolved gas flotation were studied aiming at a better understanding of the mechanisms of the process. These studies included surface and interfacial tension measurements of a model system composed of n-dodecane in the presence and absence of nonyl-phenol. Critical micelle concentration and spreading coefficients determinations were undertaken at different NaCl concentrations. The spreading coefficient proved to be a critical parameter in oil droplets flotation. After bubble–drop contact and rupture of the water film, oil drops have a tendency to spread over the bubble surfaces. The spreading coefficient increased with increasing salt concentration. An experimental setup was designed to measure the induction contact time between single n-dodecane droplets and air bubbles. Induction time decreased with increasing salt concentration. In the presence of the nonyl-phenol aqueous solution, induction time decreased with time of stabilization. On the other hand, induction time increased with time of stabilization when nonyl-phenol was added to the organic phase. The mechanisms involved are discussed and some results obtained in a dissolved air flotation batch unit in which bubbles size was measured and controlled are also presented.