Surface Molecular Structure Research Articles

Synthesis, characterization and properties of Ni2+-doped ZnAl2O4-based spinel-type solid acid catalysts: SO42−/Zn1-xNixAl2O4

A novel series of SO42−/Zn1-xNixAl2O4 spinel-type solid acid catalysts were prepared simply by doping Ni2+ ions in the lattice of spinel ZnAl2O4 and applied in the synthesis of n-butyl acetate. The crystal structures, surface molecular structures, morphologies and acidic properties were characterized by the methods of XRD, Raman, FE-SEM, EDS and FT-IR (direct and NH3 adsorbed). The experimental results revealed that both Ni2+ content and the doping ion had a significant influences on the stability of spinel structure and the acidic properties of the catalysts. Doping Ni2+ played a significant role in stabling the spinel structure and consequently increasing the number of active acid centers. Compared with undoped SO42−/ZnAl2O4 and Cu2+-doped SO42−/Zn0.9Cu0.1Al2O4, Ni2+-doped SO42−/Zn0.9Ni0.1Al2O4 presented the higher catalytic activity with 92.0% conversion of acetic acid in the esterification of acetic acid with n-butanol. Moreover, Ni2+-doped SO42−/Zn0.9Ni0.1Al2O4 exhibited the better excellent reusability, which remained above 60% conversion of acetic acid even after being used six times in the esterification of acetic acid with n-butanol. Raman and FT-IR results proved that M-O bonds in tetrahedral (Td) and octahedral (Oh) sites were covalently linked with sulfate species to generate surface acid sites, which provided the main basis for the establishment of acid center formation model on AB2O4 spinel oxides. In addition, a possible Eley-Rideal model mechanism for the esterification of carboxylic acid with alcohol was proposed on this basis of both the characterization results and the results of the catalytic activities.

Hexagonal tungsten oxide-polyaniline hybrid electrodes for high-performance energy storage

Progress toward the development of advanced supercapacitor technologies is closely associated with the continuous evolution of nanostructured electrode materials. Herein, work is described in which an inner/outer layer nanostructured hexagonal tungsten oxide (h-WO3)-polyaniline (PANI) hybrid nanomaterial has been elaborately designed and synthesized by a hydrothermal-electrodeposition method. The surface morphology, molecular structure, crystal phase, and chemical composition of the hybrid nanomaterial were studied by FESEM (EDX), FTIR, XRD (SXRD), TEM, and XPS. The resulting WO3-PANI hybrid exhibits a significantly enhanced gravimetric specific capacitance (278 F/g at a current density of 1 A/g) with an outstanding areal specific capacitance of 979 mF/cm2, good rate performance (77.2% capacitance retention from 0.5 to 10 A/g), and stable cycling performance (91.9% capacitance retention over 1500 cycles). The outstanding electrochemical properties of the WO3-PANI electrode are ascribed to its ingenious nanostructure design and the synergistic effects of each component. The symmetric supercapacitors based on WO3-PANI electrodes show a high areal capacitance and remarkable flexibility, suggesting potential application in flexible energy storage devices. Based on analysis and study the band structure and the electrochemical properties of the PANI-coated WO3 hybrid electrode, a possible mechanism for the synergistic effects was proposed in a new perspective.

Focus on the Essential: Extracting the Decisive Energy Barrier of a Complex Process

AbstractMolecular processes at surfaces can be composed of a rather complex sequence of steps. The kinetics of even seemingly simple steps are demonstrated to depend on a multitude of factors, which prohibits applying a simple Arrhenius law. This complexity can make it challenging to experimentally determine the kinetic parameters of a single step. However, a molecular‐level understanding of molecular processes such as structural transitions requires elucidating the atomistic details of the individual steps. Here, a strategy is presented to extract the energy barrier of a decisive step in a very complex structural transition by systematically addressing all factors that impact the transition kinetics. Only by eliminating these factors in the measurement the experimental data will follow an Arrhenius law and the barrier can be extracted for the single step. Using the system of 2,5‐dihydroxybenzoic acid on calcite (10.4) as an example, the energy barrier is determined for the attachment‐assisted dissociation of molecular dimers in the structural transition from a striped to a dense molecular surface structure. This disentanglement approach is mandatory for a direct comparison with theoretical results and provides molecular‐level insights into the transition mechanism.

Enhanced electromechanical properties of natural rubber using highly efficient and cost-effective mussel-inspired modification of TiO2 nanoparticles

Recently, dopamine and its secondary function are being used as the intermediate to tailor the surface molecular structure of high-dielectric-constant nanoparticles, which improves interfacial interaction of dielectric elastomer (DE) composites, due to their versatile adhesion properties. However, the high-cost of dopamine limits the large-scale applications of DE. Herein, a mussel-inspired modification of TiO2 nanoparticles is presented to prepare high-performance natural rubber (NR) DE composites by replacing dopamine with cheaper poly(catechol/polyamine) (PCPA). First, the TiO2 nanoparticles were deposited with PCPA. Then, the PCPA-coated TiO2 nanoparticles were further grafted with γ-methacryloxypropyl trimethoxy silane (KH570), which contains double bonds and denoted as TiO2-PCPA-KH570. Owing to the presence of CC bonds, the TiO2-PCPA-KH570 nanoparticles participated in the vulcanization of NR and the TiO2-PCPA-KH570/NR composites exhibited enhanced filler dispersion and interfacial interaction, leading to the improved mechanical, dielectric, and electromechanical properties. Furthermore, the 10 phr TiO2-PCPA-KH570/NR composite resulted in the largest actuated strain of 12.3%, which is ~2 times higher than that of the largest actuated strain of pure NR (6.0%). The present study provides a high-efficient and cost-effective route to obtain DEAs with enhanced electromechanical properties.

The effect of sonication time on the surface morphology and dissolubility of naproxen sodium powders

The purpose of this study is to investigate the effect of ultrasound sonication time to the mean particle size, crystallite dimensions and specific surface area of naproxen sodium (NNa) active ingredient. The sonication time effect of ultrasound on the surface morphology, crystallinity, molecular structures and saturation solubility of NNa active ingredient have been examined using UV–vis spectroscopy, zeta potential, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements. It has been determined that different ultrasound sonication time duration has changed the surface morphology and crystal structure of the drug active substances. It has been observed that ultrasonic sonication time doesn't have a linear correlation with the increase on the surface area and decrease on the particle size. On the contrary, it has been detected that optimum sonication time has a great effect on decreasing the particle size of drug active substances and increasing the surface area, therefore increasing the saturation solubility. • The effect of ultrasound sonication time on the specific surface area of NNa active ingredient were investigated. • The different sonication time has changed the surface morphology and crystal structure of the drug active substances. • The optimum sonication time has a great effect on decreasing the particle size and increasing the surface area.

Templated Fabrication of Graphitic Carbon Nitride with Ordered Mesoporous Nanostructures for High-Efficient Photocatalytic Bacterial Inactivation under Visible Light Irradiation

Biohazards are widely present in water, and a variety of waterborne diseases can be aroused by contaminated water. Therefore, the effective removal of biological hazards from water is necessary for the protection of human health. In this study, graphitic carbon nitride (g-C3N4) with ordered mesoporous nanostructures was successfully synthesized by a template method using SBA-15 as a hard template. The morphology, crystal structure, specific surface area, molecular structure, and light absorption properties of the as-prepared sample were characterized by TEM, XRD, BET, FT-IR, and UV-Vis DRS, respectively. The photocatalytic performance of the ordered mesoporous g-C3N4 was evaluated by the inactivation of Escherichia coli K-12 in water under visible light irradiation. Results showed that the bacterial inactivation efficiency can reach as high as 99% within 2 h of VL irradiation, which is 4 times higher than that of bulk g-C3N4. Moreover, the photocatalytic bacterial inactivation mechanism was revealed by a scavenging study, and the main active species in the photocatalytic inactivation process was found to be a photogenerated hole. This work will provide useful information for the development of new efficient g-C3N4-based materials for enhanced water disinfection applications by introducing ordered mesoporous nanostructures in a photocatalyst design and fabrication.

Improved charging behaviors and flashover voltage of polypropylene film based on surface molecular structure modification

The elevated temperature in operating capacitors speeds up the transportation of charges and causes the flashover to occur easily. Direct fluorination was used to modify the polypropylene film applied as capacitor dielectric, and behaviors of surface charging and flashover voltage at different temperatures were investigated. The surface morphology, functional groups and elemental composition of polypropylene film before and after modification treatment were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray analysis (EDAX), respectively. The surface charging behaviors were analyzed by the surface potential decay (SPD) method at temperature varying from 293 to 353 K. The flashover voltage was analyzed by the view of surface charge and trap characteristics. A thin layer of fluorination which changed the surface state of polypropylene film was formed, which can effectively inhibit the surface charge injection and accumulation at different temperatures. Shallow traps were introduced by the surface molecular structure modification, which was confirmed by the simulation of three-dimensional (3D) electrostatic potential and density of states (DOS). The modification of surface molecular structure, which suppresses the accumulation of surface charge leading to the inhibited distortion of electric field, effectively increased the flashover voltage at different temperatures.

New sights into the electrochemical interface provided by in situ X-ray absorption fine structure and surface X-ray scattering

Abstract Various important processes, such as electron transfer reactions, adsorption/desorption, solvation/desolvation, and formation/cleavage of chemical bonds, take place at electrolyte/electrode interfaces during electrocatalytic reactions. Those processes have been understood on the basis of changes in the surface composition, atomic arrangement, and molecular and electronic structures of the interfaces by using various in situ analysis techniques. To date, in situ analysis and observation of those interfacial processes at an ideal single-crystal surface are indispensable not only for fundamental understanding of the reaction mechanism but also for rational design of the highly efficient and durable electrocatalytic materials. Here, historical and recent progress of in situ studies on electrocatalytic reactions is briefly reviewed with a focus on two major techniques, X-ray absorption fine structure and surface X-ray scattering.

Sum Frequency Generation Vibrational Spectroscopy Using Evanescent Waves-Toward Probing Irregular and Complex Surfaces of Mesoscopic-Scale Materials.

With the rapid development of materials science, on-demand techniques are highly needed with the capability to characterize materials in the micrometer and nanometer scales. In this work, we show that, by employing a prism geometry, total internal reflection sum frequency generation (SFG) vibrational spectroscopy allows for characterizing mesoscopic materials with irregular or complex surfaces. Four representative examples were presented. First, we reveal that mechanical grinding can subtly alter the surface molecular structures of original materials. Second, spin coating can substantially change the surface molecular structures of particle samples. Third, surface restructuring of carboxylated multiwalled carbon nanotubes can happen in response to the surrounding environment. Fourth, surface adsorption and desorption dynamics of toluene on activated charcoal can be traced. Such experiments demonstrate that there are still a broad range of research fields ahead SFG can be directed to, where materials in mesoscopic scales with irregular or complex surfaces can be studied.

INFLUENCE OF SURFACE POLISHING ON THE FRICTION BEHAVIORS OF NBR

An experimental study on the tribology behavior and mechanism of NBR-Steel pair has been carried out. Abrasive paper was used to polish the NBR surface. The influences of surface topography on the friction coefficient were investigated based on the block-on-ring tribometer. Results show that polishing with abrasive paper is an effective method to reduce the friction coefficient of NBR on steel. Superlubricity was also found in the test. A new method to explain the superlubricity based on the contact angle and surface molecular structure was put forward in this work. Abrasive paper polishing changes the surface asperities, so affects the contact angle, so as to influence the boundary limiting shearing strength, and then causes the superlubricity. During the friction process the microstructure obviously changed, along with mechanical breaking of the molecular chain.

Ag-LaFeO3 nanoparticles using molecular imprinting technique for selective detection of xylene

Xylene is a hazardous volatile organic compound, however, the selective detection of ppm-level xylene using oxide semiconductor gas sensor remains a challenging issue. In this study, Ag-LaFeO3 was modified with molecular imprinting technique, in which methacrylic acid and hydroxyethyl methylacrylate are used as functional monomers, respectively. Based on XRD, EDS, XPS, SEM, TEM, BET nitrogen adsorption observations, the structure and morphology of the samples are characterized. The as-prepared molecularly imprinted nanoparticles with methacrylic acid as functional monomer exhibit high selectivity and response to xylene gas, and the response is dependent on the type and content of the functional monomer. To 5 ppm xylene, the optimal response is 36.2 at the operating temperature of 99 °C. In addition, low cross-responses to the other test gases were observed. The remarkable enhancement in the gas-sensing properties of the samples is attributed to their high specific surface area and molecular imprinting structure.

Effect of Surface Passivation on Nanodiamond Crystallinity

Diamonds approaching the nanoscale have the potential for use as probe materials as their optical properties can be sensitive to optical/electric fields, mechanical stress/pressure, and the configuration of nuclear spins. The surface of nanodiamonds impacts their optical properties and sensing capabilities, and examining the nanodiamond surface through X-ray absorption can give insights into molecular surface structures. Here, quantum dot models with varying amounts of surface carbon passivation are prepared, optimized, and compared. The loss of the diamond sp3 lattice is examined by investigating the bond length and tetrahedral character of the carbons comprising nanodiamonds for the appearance of aromatic sp2 surface domains. Electronic transitions in the carbon K-edge region, using the energy-specific time-dependent density functional theory method, as well as vibrational spectra are computed from the optimized models. The surface reorganization is shown to affect the electronic characteristics of the ...

Groundwater Arsenic and Silicate Adsorption on TiO2 and the Regeneration of TiO2

Titanium dioxide (TiO2) was widely used to remove arsenic (As) from groundwater due to its excellent properties. Previous studies show that the coexisting silicate ions (Si) could occupy the available surface sites of TiO2 and further inhibit As adsorption and TiO2 regeneration. To investigate the effect of Si adsorption on the As molecular surface structure, an extended X-ray absorption fine structure (EXAFS) analysis was conducted in this work. The results indicated that the presence of Si exhibited no impact on the As adsorption configuration on TiO2. In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy results demonstrated that the polymerization of Si that formed on the TiO2 surface compete with As adsorption sites, increasing the difficulty for TiO2 regeneration. To effectively regenerate TiO2, the removal efficiency of Si polymers on TiO2 via sodium fluoride (NaF) was studied. The results showed that NaF could remove Si monomer and polymer from TiO2, and the regenerated TiO2 could be reused with a stable adsorption performance. In situ ATR-FTIR spectroscopy suggested that NaF desorbed the Si monomer and polymer effectively. When spent TiO2 was regenerated with NaOH and NaF in three treatment cycles, As and Si desorption rates were 86.8%-100.3% and 67.9%-82.0%, respectively. The present study provides a new insight into regenerating absorbents with coadsorbed As and Si in groundwater.

Chemical Reactive Anchoring Lipids with Different Performance for Cell Surface Re-engineering Application.

Introduction of selectively chemical reactive groups at the cell surface enables site-specific cell surface labeling and modification opportunity, thus facilitating the capability to study the cell surface molecular structure and function and the molecular mechanism it underlies. Further, it offers the opportunity to change or improve a cell’s functionality for interest of choice. In this study, two chemical reactive anchor lipids, phosphatidylethanolamine–poly(ethylene glycol)–dibenzocyclooctyne (DSPE–PEG2000–DBCO) and cholesterol–PEG–dibenzocyclooctyne (CHOL–PEG2000–DBCO) were synthesized and their potential application for cell surface re-engineering via lipid fusion were assessed with RAW 264.7 cells as a model cell. Briefly, RAW 264.7 cells were incubated with anchor lipids under various concentrations and at different incubation times. The successful incorporation of the chemical reactive anchor lipids was confirmed by biotinylation via copper-free click chemistry, followed by streptavidin-fluorescein isothiocyanate binding. In comparison, the cholesterol-based anchor lipid afforded a higher cell membrane incorporation efficiency with less internalization than the phospholipid-based anchor lipid. Low cytotoxicity of both anchor lipids upon incorporation into the RAW 264.7 cells was observed. Further, the cell membrane residence time of the cholesterol-based anchor lipid was evaluated with confocal microscopy. This study suggests the potential cell surface re-engineering applications of the chemical reactive anchor lipids.

Crystal growth in ice and snow

Surface molecular structure is the arbiter in the contest between energy and entropy that largely determines how ice and snow crystals develop.

Solvothermal Liquefaction of Corn Stalk: Physico-Chemical Properties of Bio-oil and Biochar

This study investigated the conversion of corn stalk to bio-oil by solvothermal liquefaction using ethanol as a solvent. Effect of reaction temperature, time and solvent to biomass ratio on the yield and the properties of bio-oil and biochar was studied. Analysis of corn stalk and bio-oil were done to determine the surface functional groups, existing bonds and molecular structure of specified compounds. Investigations were done to identify different compounds in bio-oil, the thermal stability, and weight loss kinetics of biochar. Study shows that percentage yield of bio-oil increases with increase in temperature and time, up to a specific level, and then starts declining. Further, the heating value, carbon content, and fixed carbon content of both bio-oil and biochar increased to 30.52, 22.8 MJ/kg, and 66.42 and 61.25%, 26.10 and 27.97% respectively from those (19.55 MJ/kg, 51.12 and 6.36%) of the corn stalk. This study suggests that the bio-oil contained mostly phenolic compounds and its derivatives. Two major DTG peaks were observed at 380 and 620 °C indicating the improvement in thermal stability of the biochar after solvolysis liquefaction process. Investigation results can be very useful in optimizing process parameters for solvothermal liquefaction.

Molecular dynamics simulation of temperature-dependent atrazine aqueous solution

The molecular dynamic simulations have been performed to investigate the atrazine aqueous solution at different temperature. Molecular structure, transport characteristics, hydrogen bonds dynamics and vibration power spectra were obtained by using the OPLS and TIP4P models. Simulation results show that the atrazine molecules do not have a significant effect in water and the tiny solubility of atrazine due to the molecular surface area and structure. As the temperature increases, the water's tetrahedral structure and the hydrated shells are weakened. The hydrogen bonding lifetimes of atrazine-water and water-water show a decrease with temperature. The self-diffusion coefficient of water increase linearly and the self-diffusion coefficient of atrazine shows an nonlinear increment. The vibration power spectrum of atrazine was calculated and compared with the existing infrared spectra.

A phospholipid polymer graft layer affords high resistance for wear and oxidation under load bearing conditions.

Manipulating the surface and substrate of cross-linked polyethylene (CLPE) is an essential approach for obtaining life-long orthopedic bearings. We therefore proposed a bearing material comprised of an antioxidative substrate generated by vitamin E blending (HD-CLPE[VE]) with a poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-grafted surface, and investigated its wear resistance and oxidative stability under accelerated aging and load bearing conditions. Neither the hydration nor friction kinetics of the molecular network structure of the PMPC-grafted surface or the HD-CLPE(VE) substrate were influenced by accelerated aging but rather exhibited high stability even under high oxidation conditions. The characteristics of the PMPC-grafted surface improved the wear and impact fatigue resistance of the HD-CLPE(VE) liner regardless of accelerated aging. Notably, the PMPC-grafted surface was found to affect the potential oxidative stability at the rim part of the acetabular liner. PMPC chains serve several important functions on the surface regardless of load bearing, such as high lubricity or low lipophilicity attributed to phosphorylcholine groups and/or surrounding water-fluid film, and suppression of lipid diffusion attributed to methacrylate main chains on the surface. Together, these results provide preliminary evidence that the PMPC graft layer and vitamin E-blended substrate might positively affect the extent of orthopedic implant durability.

Highly selective adsorption of dyes and arsenate from their aqueous mixtures using a silica-sand/cationized-starch composite

A novel composite adsorbent (ST-CTA-SS) composed of starch-3-chloro-2-hydroxypropyl triethyl ammonium chloride (ST-CTA) and micro silica-sand (SS) was prepared simply, with the characteristics of environmental-friendliness and low cost. A variety of techniques were used for characterizing the surface morphology, molecular structure, and settleability of this composite adsorbent. ST-CTA-SS was applied to the removal of arsenate [As(V)] and two anionic dyes, acid green 25 (AG25) and methyl orange (MO), from water in respective single and two metal-dye binary systems. ST-CTA-SS shows a marked improvement of the adsorption capacities for the aforementioned three pollutants, which is attributed to the prominent composited structure compared with ST-CTA without SS. The adsorption capacities of ST-CTA-SS for AG25, MO, and As(V) are up to approximately 912.6 ± 44.6, 458.7 ± 21.3, and 76.63 ± 3.53 mg g−1, respectively, and the adsorption saturations for those three pollutants are all achieved within 20 min. Moreover, this composite adsorbent always exhibited highly selective adsorption of dyes, either MO or AG25, over As(V) from their aqueous mixtures. After saturated adsorption, ST-CTA-SS could be rapidly settled and separated from water due to the imbedded SS, which could be easily regenerated by dilute NaOH solutions. This starch-based composite adsorbent thus owns significant application potentials in water treatment.

Surface molecular structure defects and laser-induced damage threshold of fused silica during a manufacturing process

Laser induced damage of fused silica is a serious problem for high power laser systems, and damage precursors are mainly induced by manufacturing processes. In this work, fused silica samples were prepared from a manufacturing process including grinding, polishing and etching procedures. The chemical disorder of the prepared samples was inspected by using fluorescence microscopy and ultra-violet fluorescence spectrometer. The physical disorder was characterized by using Infrared and Raman spectrometer. Laser induced damage thresholds (LIDTs) were measured in R-on-1 mode by 355 nm 6.4 ns laser pulse. Results showed that with the manufacturing processes transforming from grinding to etching, the magnitude of fluorescence point defects reduced while their types did not change, the Si-O-Si bonds of prepared samples were strained and the strained bonds were mitigated. The LIDTs increased with the reducing of fluorescence defects and strained Si-O-Si bonds. However, these structural defects can not be eliminated by the current manufacturing process. Improvements may be needed to eliminate the structural defects for a higher LIDT of fused silica.