Complex Surface Structures Research Articles

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

AbstractCarbon dioxide (CO2) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2O remains under debate because of the complex surface structure of Cu2O under reducing conditions, leading to limited guidance in designing improved Cu2O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu2O(111) for the CO2 reduction reaction (CO2RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (CuCUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO2RR. Moreover, the CO2RR was evaluated over Cu2O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2RR and suppress the HER.

Visual Simulation of Multiple Fluids in Computer Graphics: A State-of-the-Art Report

Realistic animation of various interactions between multiple fluids, possibly undergoing phase change, is a challenging task in computer graphics. The visual scope of multi-phase multi-fluid phenomena covers complex tangled surface structures and rich color variations, which can greatly enhance visual effect in graphics applications. Describing such phenomena requires more complex models to handle challenges involving the calculation of interactions, dynamics and spatial distribution of multiple phases, which are often involved and hard to obtain real-time performance. Recently, a diverse set of algorithms have been introduced to implement the complex multi-fluid phenomena based on the governing physical laws and novel discretization methods to accelerate the overall computation while ensuring numerical stability. By sorting through the target phenomena of recent research in the broad subject of multiple fluids, this state-of-the-art report summarizes recent advances on multi-fluid simulation in computer graphics.

Occurrence state of co-existing arsenate and nickel ions at the ferrihydrite-water interface: Mechanisms of surface complexation and surface precipitation via ATR-IR spectroscopy

Arsenic and nickel are common contaminants that usually co-exist in many contaminated natural and mining environments. More research on the interaction of these two contaminants is needed such as their coordination structure and occurrence state at mineral-water interfaces. In this study, we investigated the structure of surface complexes and surface precipitates formed by co-existing As(V) and Ni(II) ions at the ferrihydrite-water interface by varying the order of adsorption processes, pH, aging time and Ni(II) concentration using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). ATR-FTIR analysis revealed the presence of complexed AsONi bonds which produced ternary surface complexes. These ternary AsONi surface complexes formed through a layer by layer alternative coordination on top of the binary AsOFe surface site complexes of ferrihydrite. Such multilayer surface complexes formed as initial surface precipitates which were found to refine their surface structure from amorphous to crystalline phases and were a function of incubation time, coverage of multilayer surface complexes, Ni(II) concentration and pH. Our results presented here can well explain the formation process of surface precipitates on the molecular scale and are of use to forecast the fate and mobility of commonly As(V) and Ni(II) species at the ferrihydrite-water interface commonly found in natural or mine tailings water-soil environments.

Regimes of Flow over Complex Structures of Endothelial Glycocalyx: A Molecular Dynamics Simulation Study

Flow patterns on surfaces grafted with complex structures play a pivotal role in many engineering and biomedical applications. In this research, large-scale molecular dynamics (MD) simulations are conducted to study the flow over complex surface structures of an endothelial glycocalyx layer. A detailed structure of glycocalyx has been adopted and the flow/glycocalyx system comprises about 5,800,000 atoms. Four cases involving varying external forces and modified glycocalyx configurations are constructed to reveal intricate fluid behaviour. Flow profiles including temporal evolutions and spatial distributions of velocity are illustrated. Moreover, streamline length and vorticity distributions under the four scenarios are compared and discussed to elucidate the effects of external forces and glycocalyx configurations on flow patterns. Results show that sugar chain configurations affect streamline length distributions but their impact on vorticity distributions is statistically insignificant, whilst the influence of the external forces on both streamline length and vorticity distributions are trivial. Finally, a regime diagram for flow over complex surface structures is proposed to categorise flow patterns.

In Ukrainian

Quercetin and rutin have potent antioxidant and metal ion chelating capacity, possess various biological, biochemical and therapeutic activity, but their application is limited because of low solubility. Anticeptic cationic gemini surfactant ethonium (2-ethylene-bis-(N-dimethylcarbdecyloximethyl) ammonium dichloride) was considered to be a promising solubilizer for flavonoids. The supramolecular interactions of quercetin and rutin with ethonium have been studied spectrophotometrically. The bathochromic shift of quercetin and rutin spectra in pre-micellar ethonium solutions testifies an increase in their polarity. Indeed, the calculated values of quercetin and rutin apparent dissociation constants in ethonium solutions are lower than that in water. In micellar solutions the flavonoid spectral characteristics and protolytic properties remain unchanged, whereas the solubility of quercetin and rutin raises 250 and 5 times, respectively. The binding constants of quercetin (lgK b = 3.71) and rutin (lgK b = 2.52) with ethonium are determined from the solubility data. The formation of supramolecular complexes also causes the essential increase of quercetin and rutin adsorption on silica surface at рН > 5 both in pre-micellar and micellar ethonium solutions in similar ways. This allows us to assume that the structures of surface complexes formed by pre-micellar associates or micelles have no principal differences. The shape of the obtained pH-dependences of quercetin and rutin adsorption suggests that flavonoids as a part of ethonium supramolecular complexes adsorb on silica mainly through the ionic interactions between the positively charged nitrogen atoms and dissociated silanol groups. The results of physico-chemical study may be a base for the development a composition of new medicinal remedies.

Electrochemical machining of a convex strips structure on a revolving part by using site directed power interruption

Revolving parts with complex surface structures are widely used in machinery and mechanical equipment. The ECM process provides its adequacy to cut hard materials with different shapes, and its applications are widely increased, due to its outstanding advantages. In this paper, a new method for machining a convex strips structure on a cylinder by using site directed power interruption (SDPI) in the ECM process is presented. A variable correction value of the power-off time was defined and optimized to obtain the ideal interval for better machining accuracy and stability. The electric field distribution and the simulated convex profiles show that the stray current density can be reduced effectively by using the proposed method. The correction value has an important influence on the machining accuracy. A suitable correction value in the range of 0.6–1.2 s can effectively improve the machining accuracy of the convex strips structure. Experiments were also conducted to verify the proposed method. Results have confirmed that the stray corrosion on the convex strips surface is significantly reduced and the machining accuracy of convex strips structure is remarkably improved by using the proposed method with a suitable correction value in the ECM process. Finally, a convex strip with a height of 2 mm on a thin-wall revolving part was also produced successfully using a correction value of 0.9.

Accounting for the Complex Surface Structure in Ellipsometric Studies of the Effects of Magnetron Sputtering Modes on the Growth and Optical Properties of In2O3 Films

The efficiency of invoking additional information on optical transmission in solving the inverse problem of ellipsometry by a minimization method is demonstrated in practice for In2O3 fi doped and nondoped with Sn on Al2O3 (012) substrates. This approach allows the thickness and refractive index of thin films with rough surfaces to be uniquely determined. Solutions of the inverse problem in the framework of one-, two-, and multilayer models are compared. The last provides the best description of the experimental data and the correct parameters of the samples. The dependences of the investigated properties of films produced with different magnetron sputtering modes are found using the above methods and models and do not contradict general concepts about the film formation by this material.

Revealing Catalytically Relevant Surface Species by Kinetic Isotope Effect Spectroscopy: H-Bonding to Ester Carbonyl of trans-Ethyl Pyruvate Controls Enantioselectivity on a Cinchona-Modified Pt Catalyst.

Monitoring active surface species on an operating technical catalyst is a challenging task due to the presence of multiple different adsorption sites and the abundance of bulk species. In this work, kinetic isotope effect (KIE) spectroscopy is introduced to capture the signals of catalytically relevant hydrogenation species from the IR spectroscopic detection in attenuated total reflection mode. The catalytic interface formed between a cinchona-modified Pt/Al2O3 catalyst and the solvent toluene is sensitively probed directly at the rate limiting step(s) during the asymmetric hydrogenation of ethyl pyruvate by measuring the effects of substituting H2 by D2 kinetically and spectroscopically in the same operando experiment. The application of KIE spectroscopy provides unprecedented molecular level insight into the structure of the diastereomeric intermediate surface complex and the phenomenon rate enhancement, which revolutionizes our understanding of chirally modified metal catalysts.

Links between nanoscale and macroscale surface properties of natural root mucilage studied by atomic force microscopy and contact angle

Soil water repellency originating from organic coatings plays a crucial role for soil hydraulics and plant water uptake. Focussing on hydrophobicity in the rhizosphere induced by root-mucilage, this study aims to explore the link between macroscopic wettability and nano-microscopic surface properties. The existing knowledge of the nanostructures of organic soil compounds and its effect on wettability is limited by the lack of a method capable to assess the natural spatial heterogeneity of physical and chemical properties.In this contribution, this task is tackled by a geostatistical approach via variogram analysis of topography and adhesion force data acquired by atomic force microscopy and macroscopic sessile drop measurements on dried films of mucilage. The results are discussed following the wetting models given by Wenzel and Cassie-Baxter.Undiluted mucilage formed homogeneous films on the substrate with contact angles >90°. For diluted samples contact angles were smaller and incomplete mucilage surface coverage with hole-like structures frequently exhibited increased adhesion forces. Break-free distances of force curves indicated enhanced capillary forces due to adsorbed water films at atmospheric RH (35 ± 2%) that promote wettability. Variogram analysis enabled a description of complex surface structures exceeding the capability of comparative visual inspection.

Structure and reactivity of oxalate surface complexes on lepidocrocite derived from infrared spectroscopy, DFT-calculations, adsorption, dissolution and photochemical experiments

Oxalate, together with other ligands, plays an important role in the dissolution of iron(hdyr)oxides and the bio-availability of iron. The formation and properties of oxalate surface complexes on lepidocrocite were studied with a combination of infrared spectroscopy (IR), density functional theory (DFT) calculations, dissolution, and photochemical experiments. IR spectra measured as a function of time, concentration, and pH (50–200 µM oxalate, pH 3–7) showed that several surface complexes are formed at different rates and in different proportions. Measured spectra could be separated into three contributions described by Gaussian line shapes, with frequencies that agreed well with the theoretical frequencies of three different surface complexes: an outer-sphere complex (OS), an inner-sphere monodentate mononuclear complex (MM), and a bidentate mononuclear complex (BM) involving one O atom from each carboxylate group. At pH 6, OS was formed at the highest rate. The contribution of BM increased with decreasing pH. In dissolution experiments, lepidocrocite was dissolved at rates proportional to the surface concentration of BM, rather than to the total adsorbed concentration. Under UV-light (365 nm), BM was photolyzed at a higher rate than MM and OS. Although the comparison of measured spectra with calculated frequencies cannot exclude additional possible structures, the combined results allowed the assignment of three main structures with different reactivities consistent with experiments. The results illustrate the importance of the surface speciation of adsorbed ligands in dissolution and photochemical reactions.

Multimorphology Mesoporous Silica Nanoparticles for Dye Adsorption and Multicolor Luminescence Applications

A series of mesoporous SiO2 nanoparticles (MSNs) have been synthesized by a modified sol–gel process. The morphology could be manipulated from flower-like nanospheres to flower-like nanodisks, circular nanodisks and sunken nanovesicles by simply adjusting the amount of ammonia. Among the various morphologies, the flower-like nanospheres (N1) with a large specific surface area of 1037.16 m2 g–1 exhibited the highest and fastest adsorption capacity for dye-RhB because of the most complex surface structure (234.61 mg g–1, approximately 90% in the first 5 min). The RhB adsorption processes on different MSNs were explained by Langmuir, Freundlich and Temkin isotherm models, and a transition from multilayer adsorption to homogeneous adsorption was achieved. The adsorption kinetics was in accord with the pseudo-second-order model, suggesting the rate-limiting step of RhB on MSNs was mainly chemical process. The luminescence properties of different samples revealed that the nanovesicles structure (N5) exhibited t...

Beyond Simple Cartoons: Challenges in Characterizing Electrochemical Biosensor Interfaces.

Design and development of surface-based biosensors is challenging given the multidisciplinary nature of this enterprise, which is certainly the case for electrochemical biosensors. Self-assembly approaches are used to modify the surface with capture probes along with electrochemical methods for detection. Complex surface structures are created to improve the probe-target interaction. These multicomponent surface structures are usually idealized in schematic representations. Many rely on the analytical performance of the sensor surface as an indication of the quality of the surface modification strategy. While directly linked to the eventual device, arguments for pursuing a more extensive characterization of the molecular environments at the surface are presented as a path to understanding how to make electrochemical sensors that are more robust, reliable with improved sensitivity. This is a complex task that is most often accomplished using methods that only report the average characteristics of the surface. Less often applied are methods that are sensitive to the probe (or adsorbate) present in nonideal configurations (e.g., aggregates, clusters, nonspecifically adsorbed). Though these structures may compose a small fraction of the overall modified surface, they have an uncertain impact on sensor performance and reliability. Addressing this issue requires application of imaging methods over a variety of length scales (e.g., optical microscopy and/or scanning probe microscopy) that provide valuable insight into the diversity of surface structures and molecular environments present at the sensing interface. Furthermore, using in situ analytical methods, while complex, can be more relevant to the sensing environment. Reliable measurements of the nature and extent of these features are required to assess the impact of these nonideal configurations on the sensing process. The development and use of methods that can characterize complex surface based biosensors is arguably required, highlighting the need for a multidisciplinary approach toward the preparation and analysis of the biosensor surface. In many ways, representing the surface without reliance on overly simplified cartoons will highlight these important considerations for improving sensor characteristics.

Adaptive feed control of operating tool in Robot machine

Adaptive ornate milling technology involves variation of milling operational parameters (particularly, cutter feed speed) based on wood surface texture at the processing spot. It is appropriate to use wood fiber orientation optical recognition method for adaptive ornate milling.
 Adaptive milling method is very efficient for ornate milling, when cutter moves along a complex trajectory in space, and feed direction and fibers alignment substantially alters along the trajectory. Moreover, at sharp trajectory sections, adaptive choice of operational parameters permits to materially reduce the chance of wood damaging. Adaptive milling method is most effective for poor value wood that has low stress-strain properties and complex surface structure, so is very prone to damage.
 System for programmed PID controller adjustment involves computer with software for certain operating system, input/output hardware and connector cables. Communication with facilities is typically performed by use of ОРС server. While adjusting, an object is included in the control loop. The system adjusts and PID controller is registering obtained parameters. Obtained in such way controller parameters will be near optimal due to intuitive user interface, high computer capability and limitless system identification algorithms.
 The format in the search shows schematic structure of automated control system of tool feed in adaptive milling, which uses CNC-controlled 3D vertical milling machine, control computer and camera for wood fiber orientation optical recognition, its signal being transferred to milling parameters optimization application.
 It should be noted that at such milling with control of supply rate along the complex trajectory of supply of the milling tool, it would be possible to significantly reduce the percentage of shatters. This would allow to significantly reduce economic expenditures for additional operations concerning the surface recovery.

Insights into the selective catalytic reduction of NO by NH3 over Mn3O4(110): a DFT study coupled with microkinetic analysis

Nitric oxide (NO x ), as one of the main pollutants, can contribute to a series of environmental problems, and to date the selective catalytic reduction (SCR) of NO x with NH3 in the presence of excess of O2 over the catalysts has served as one of the most effective methods, in which Mn-based catalysts have been widely studied owing to their excellent low-temperature activity toward NH3-SCR. However, the related structure-activity relation was not satisfactorily explored at the atomic level. By virtue of DFT+U calculations together with microkinetic analysis, we systemically investigate the selective catalytic reduction process of NO with NH3 over Mn3O4(110), and identify the crucial thermodynamic and kinetic factors that limit the catalytic activity and selectivity. It is found that NH3 prefers to adsorb on the Lewis acid site and then dehydrogenates into NH2* assisted by either the two- or three-fold lattice oxygen; NH2* would then react with the gaseous NO to form an important intermediate NH2NO that prefers to convert into N2O rather than N2 after the sequential dehydrogenation, while the residual H atoms interact with O2 and left the surface in the form of H2O. The rate-determining step is proposed to be the coupling reaction between NH2* and gaseous NO. Regarding the complex surface structure of Mn3O4(110), the main active sites are quantitatively revealed to be O3c and Mn4c.

Mimicking bug-like surface structures and their fluid transport produced by ultrashort laser pulse irradiation of steel

Ultrashort laser pulses with durations in the fs-to-ps range were used for large area surface processing of steel aimed at mimicking the morphology and extraordinary wetting behaviour of bark bugs (Aradidae) found in nature. The processing was performed by scanning the laser beam over the surface of polished flat sample surfaces. A systematic variation of the laser processing parameters (peak fluence and effective number of pulses per spot diameter) allowed the identification of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, i.e., LIPSS, grooves, spikes, etc.). Moreover, different laser processing strategies, varying laser wavelength, pulse duration, angle of incidence, irradiation atmosphere, and repetition rates, allowed to achieve a range of morphologies that resemble specific structures found on bark bugs. For identifying the ideal combination of parameters for mimicking bug-like structures, the surfaces were inspected by scanning electron microscopy. In particular, tilted micrometre-sized spikes are the best match for the structure found on bark bugs. Complementary to the morphology study, the wetting behaviour of the surface structures for water and oil was examined in terms of philic/phobic nature and fluid transport. These results point out a route towards reproducing complex surface structures inspired by nature and their functional response in technologically relevant materials.

3D printing of responsive hydrogels for drug-delivery systems

3D printing technology has enabled unprecedented flexibility in the design and manufacturing of complex objects, which can be utilized in personalized and programmable medicine. The aim of this study is to evaluate the potential of 3D printing by digital light processing to fabricate drug-loaded systems with special designs and unique drug-release characteristics, which otherwise are not possible to fabricate by conventional pharmaceutical manufacturing methods. Oral dosage forms of pH responsive hydrogels were 3D printed using acrylic acid monomer, cross-linker (polyethylene glycol diacrylate) and photoinitiator (2,4,6-trimethylbenzoyl-diphenylphosphine oxide [TPO] nanoparticles). Sulforhodamine B, a pH independent fluorescent dye, was used to model a small molecule hydrophilic drug. The printed structures exhibited pH responsive swelling and the effect of pH and tablets’ surface area were studied on drug release. The tablets showed higher swelling and faster drug release at higher pH, making them a promising system for enhancing drug absorption in the intestine. Structures with large surface area and complex structures showed enhanced swelling and faster drug release and vice versa.

In Ukrainian

A review of recent literature data on appearance of spontaneous oscillations in electrochemical systems of practical relevance is presented. They include electrocatalytic reactions of electrooxidation of hydrogen and small organic molecules on noble metals, oscillatory processes during preparation of different nanostructured materials such as nanotubes and multilayered structures, electrochemical systems with electrodissolution – passivation -electrodeposition of metals and alloys. Many of these systems belong to N-NDR or HN-NDR type of oscillator. They are investigated by different experimental techniques including electrochemical impedance spectroscopy, differential electrochemical mass spectroscopy, surface-enhanced infrared absorption spectroscopy, electrochemical quartz crystal microbalance/nanobalance, Auger electron analysis etc. It has been shown that electrochemical oscillations and more complex spatio-temporal surface structures in these systems are very sensitive to variation of experimental parameters such as applied potential, current density, solution concentration, structure and composition of electrode/electrolyte interface etc. The influence of these parameters on non-linear behavior of a model N-NDR electrochemical system was presented based on the theory of electrochemical impedance spectroscopy. An electrochemical reaction in the chosen model is related to the potential-dependent adsorption/desorption of electroactive particles on a planar, cylindrical or spherical interface and a preceding chemical reaction in the Nernst diffusion layer under potentiostatic conditions. The obtained results indicate that the range of Hopf instability giving rise to spontaneous oscillations in the system can be regulated by variation of electrode form and radius, thickness of the Nernst diffusion layer, diffusion coefficient of electroactive species, ohmic loses, bulk concentration of electroactive species. The role of mass transfer function in appearance of dynamic instabilities in the non-equilibrium system was determined.

Generation of continuously rotating polarization by combining cross-polarizations and its application in surface structuring.

In this study, we develop a simple but highly effective technique that generates a continuously varying polarization within a laser beam. This is achieved by having orthogonal linear polarizations on each side of the beam. By simply focusing such a laser beam, we can attain a gradually and continuously changing polarization within the entire Rayleigh range due to diffraction. To demonstrate this polarization distribution, we apply this laser beam onto a metal surface and create a continuously rotating laser induced periodic surface structure pattern. This technique provides a very effective way to produce complex surface structures that may potentially find applications, such as polarization modulators and metasurfaces.

Retrieving Aerial Scene Images with Learned Deep Image-Sketch Features

This paper investigates the problem of retrieving aerial scene images by using semantic sketches, since the state-of-the-art retrieval systems turn out to be invalid when there is no exemplar query aerial image available. However, due to the complex surface structures and huge variations of resolutions of aerial images, it is very challenging to retrieve aerial images with sketches and few studies have been devoted to this task. In this article, for the first time to our knowledge, we propose a framework to bridge the gap between sketches and aerial images. First, an aerial sketch-image database is collected, and the images and sketches it contains are augmented to various levels of details. We then train a multi-scale deep model by the new dataset. The fully-connected layers of the network in each scale are finally connected and used as cross-domain features, and the Euclidean distance is used to measure the cross-domain similarity between aerial images and sketches. Experiments on several commonly used aerial image datasets demonstrate the superiority of the proposed method compared with the traditional approaches.

Centrifuge modelling of building response to tunnel excavation

Understanding the building response to tunnelling-induced settlements is an important aspect of urban tunnelling in soft ground. Previous centrifuge modelling research demonstrated significant potential to study this tunnel–soil–structure interaction problem. However, these recent studies were limited by simplified building models, which might result in uncertainties when interpreting the building performance to tunnelling subsidence. This paper presents an experimental modelling procedure and the results of a series of centrifuge tests, involving relatively complex surface structures subjected to tunnelling in sand. Powder-based three-dimensional (3D) printing was adopted to fabricate building models with realistic layouts, facade openings and foundations. The 3D printed material had a Young's modulus and a brittle response similar to historic masonry. Modelling effects and boundary conditions are quantified. The good agreement between the experimentally obtained results and previous research demonstrates that the soil–structure interaction during tunnel excavation is well replicated. The experimental procedure provides a framework to quantify how building features affect the response of buildings to tunnelling subsidence.