Surface Chemical Transformations Research Articles

Effect of different galvanic coupling methods on the surface chemical transformation of TC4 titanium alloy

In clinical applications, titanium and its alloy implants often suffer from corrosion, wear and tear, and poor biological activity. Surface modification is critical for improving the stability and bioactivity of titanium and its alloys. Zinc phosphate chemical conversion has received increasing attention as a promising technique for biomedical applications. However, the presence of a passive oxide layer on the TC4 (Ti6Al4V) surface poses challenges for conventional chemical conversion methods. In this study, the principle of galvanic coupling was utilized to facilitate the surface chemical transformation of TC4 titanium alloy, referred to as galvanic coupling phosphate chemical conversion (GCPCC). The effects of two types of galvanic coupling and different plastic deformations on the surface chemical transformation of TC4 titanium alloy at different temperatures were mainly investigated. The results indicate that the Ti/Fe multipoint coupling formed by magnetron sputtering during chemical transformation at 70 °C significantly enhances the nucleation sites of hopeite (Zn3(PO4)2·4H2O) and accelerates the nucleation rate. Compared with line-coupled conversion coatings, multipoint coupling GCPCC coatings exhibit superior uniformity and finer microstructure, and the thickness of the laths is significantly reduced from 5 to 10 μm to less than 1 μm. Moreover, the temperature exerts a substantial influence on the formation of conversion coatings. At 70 °C, the GCPCC coating primarily comprises hopeite, while the coating resulting from chemical conversion treatment consists of both hopeite and an amorphous ZnP-like granular coating at 50 °C.

Imaging and Quantifying the Chemical Communication between Single Particles in Metal Alloys.

The communication within particle agglomerates in industrial alloys can have a significant impact on the macroscopic reactivity, putting a high demand on the adaptation of wide-field methodologies to clarify this phenomenon. In this work, we report the application of correlated optical microscopies probing operando both local pH and local surface chemical transformation correlated with identical location scanning electron microscopy to quantify in situ the structure reactivity of particle agglomerates of foreign elements in the Al alloy. The optical operando analyses allow us (i) to reveal and quantify the local production of OH- from proton and oxygen reduction at individual Si- or Fe-rich microparticles and (ii) to quantify (and model) the chemical communication between these active sites, within a few micrometer range, on the local chemical transformation of the material. Wide-field image analysis highlights the statistical importance of chemical communication that may introduce a new conceptual framework for the understanding of the mechanisms in related fields of charge transfer, electrocatalysis, and corrosion.

Sulfide modifies physicochemical properties and mercury adsorption of microplastics

Microplastics (MPs) tend to accumulate and undergo a sulfur weathering process that leads to significant surface changes in sulfur-rich anaerobic environments, such as sewage and wastewater treatment plants. Aged MPs can have a profound impact on environmental behaviors of various toxic pollutants, especially heavy metals. Although previous studies have investigated the adsorption characteristics of metal ions on MPs that are aged in aerobic environments, the sorptive interactions of sulfur-aged MPs in anaerobic environments with mercury, i.e., Hg(II), are largely unknown. In this study, laboratory investigations were conducted to study the sorptive behaviors of Hg(II) by six common MPs treated anaerobically in the presence of sulfide. Adsorption isotherms show that the sulfur aging process greatly enhances the MP sorption capacity of Hg(II). The mechanisms including changes in the specific surface area, electrostatic interactions, surface precipitation, and surface functional groups are responsible for the enhanced adsorption capacities of sulfur-aged MPs. The thiol group that forms on the MP surface plays a dominant role in enhancing the MP adsorption capacity of Hg(II), which is determined by the formation of unsaturated bonds in the molecular chains of MPs. Furthermore, the pathways of surface chemical transformation of MPs during sulfur aging have been proposed. This study promotes our understanding of the potential hazard of MPs as well as the fate and transport of heavy metals in the presence of aged MPs.

Real-Space Imaging of a Single-Molecule Monoradical Reaction.

Organic radicals consisting of light elements exhibit a low spin-orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Here, we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications.

Rational Method of Monitoring Molecular Transformations on Metal-Oxide Nanowire Surfaces.

Metal-oxide nanowires have demonstrated excellent capability in the electrical detection of various molecules based on their material robustness in liquid and air environments. Although the surface structure of the nanowires essentially determines their interaction with adsorbed molecules, understanding the correlation between an oxide nanowire surface and an adsorbed molecule is still a major challenge. Herein, we propose a rational methodology to obtain this information for low-density molecules adsorbed on metal oxide nanowire surfaces by employing infrared p-polarized multiple-angle incidence resolution spectroscopy and temperature-programmed desorption/gas chromatography-mass spectrometry. As a model system, we studied the surface chemical transformation of an aldehyde (nonanal, a cancer biomarker in breath) on single-crystalline ZnO nanowires. We found that a slight surface reconstruction, induced by the thermal pretreatment, determines the surface chemical reactivity of nonanal. The present results show that the observed surface reaction trend can be interpreted in terms of the density of Zn ions exposed on the nanowire surface and of their corresponding spatial arrangement on the surface, which promotes the reaction between neighboring adsorbed molecules. The proposed methodology will support a better understanding of complex molecular transformations on various nanostructured metal-oxide surfaces.

Ammonium deficiency caused by heterogeneous reactions during a super Asian dust episode

AbstractMineral dust particles exert profound impacts on air quality, visibility, and ocean biogeochemistry. Interactions between dust particles and other anthropogenic pollutants modify not only the size spectrum and morphology but also physicochemical properties of dust particles, thereby affecting their radiative properties and ability to act as cloud condensation nuclei and in turn their impact on climate. Here we report field observations on the surface chemical transformations in a super Asian dust plume captured in coastal areas of China and the adjacent marginal seas. The dust plume showed enhanced concentrations of sulfate, nitrate, and calcium along with a decrease in ammonium. The percentages of total Ca in water‐soluble form increased from an intrinsic value of ~5% to 25–40% at four stations along the path of the dust plume. From these increases, we estimated the extent to which carbonate was modified by heterogeneous reactions and calculated that the enhanced sulfate and nitrate could account for 40–60% of the observed concentrations. Our observation suggests that the formation of ammonium sulfate via the H2SO4‐NH3‐H2O ternary system was impeded by heterogeneous reactions in the marine boundary layer when dust loads exceeded a certain threshold. A conceptual model is proposed to elucidate the heterogeneous reactions during the super Asian dust event and their impacts on atmospheric chemistry.

Numerical Analysis of Multicomponent Suspension Droplets in High-Velocity Flame Spray Process

The liquid feedstock or suspension as a different mixture of liquid fuel ethanol and water is numerically studied in high-velocity suspension flame spray (HVSFS) process, and the results are compared for homogenous liquid feedstock of ethanol and water. The effects of mixture on droplet aerodynamic breakup, evaporation, combustion, and gas dynamics of HVSFS process are thoroughly investigated. The exact location where the particle heating is initiated (above the carrier liquid boiling point) can be controlled by increasing the water content in the mixture. In this way, the particle inflight time in the high-temperature gas regions can be adjusted avoiding adverse effects from surface chemical transformations. The mixture is modeled as a multicomponent droplet, and a convection/diffusion model, which takes into account the convective flow of evaporating material from droplet surface, is used to simulate the suspension evaporation. The model consists of several sub-models that include premixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling of multicomponent droplet breakup and evaporation, as well as heat and mass transfer between liquid droplets and gas phase.

Stabilization of the (1 1 0) tetragonal zirconia surface by hydroxyl chemical transformation

Different hydroxyl coverages on the (1 1 0) and (1 0 1) surfaces of tetragonal zirconia have been studied with periodic density functional theory. The tetragonal zirconia (1 1 0) surface is polar and intrinsically unstable. It is however very efficiently stabilized by hydroxyl formation which decreases the effective charge of surface oxygen atoms and hence avoids the electrostatic instability. The hydroxylation induces a strong stabilization of the (1 1 0) surface with respect to the non-polar (1 0 1) termination, and explains why the (1 1 0) surface of ZrO 2 can be found in some catalytic preparations. Surface chemical transformation appears to be a more efficient way to stabilize the (1 1 0) surface in comparison with the surface reconstruction processes.

Inverted Microcontact Printing on Polystyrene-block-Poly(tert-butyl acrylate) Films: A Versatile Approach to Fabricate Structured Biointerfaces Across the Length Scales

The combination of the recently introduced soft lithographic technique of inverted microcontact printing (i-muCP) and spin-coated films of polystyrene- block-poly( tert-butyl acrylate) (PS 690- b-P tBA 1210) as a reactive platform is shown to yield a versatile approach for the facile fabrication of topographically structured and chemically patterned biointerfaces with characteristic spacings and distances that cross many orders of magnitude. The shortcomings of conventional muCP in printing of small features with large spacings, due to the collapse of small or high aspect ratio stamp structures, are circumvented in i-muCP by printing reactants using a featureless elastomeric stamp onto a topographically structured reactive polymer film. Prior to molecular transfer, the substrate-supported PS 690- b-P tBA 1210 films were structured by imprint lithography resulting in lateral and vertical feature sizes between >50 microm-150 nm and >1.0 microm-18 nm, respectively. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and water contact angle measurements provided evidence for the absence of surface chemical transformations during the imprinting step. Following the previously established hydrolysis and activation protocol with trifluoroacetic acid and N-hydroxysuccinimide, amino end-functionalized poly(ethylene glycol) (PEG-NH 2), as well as bovine serum albumin and fibronectin as model proteins, were successfully transferred by i-muCP and coupled covalently. As shown, i-muCP yields increased PEG coverages and thus improved performance in suppressing nonspecific adsorption of proteins by exploiting the high local concentrations in the micro- and nanocontacts during molecular transfer. The i-muCP strategy provides access to versatile biointerface platforms patterned across the length scales, as shown for guided cancer cell adhesion, which opens the pathway for systematic cell-surface interaction studies.

Scanning near-field photolithography—surface photochemistry with nanoscale spatial resolution

This tutorial review describes recent advances that have challenged the traditional view that the Rayleigh limit, of approximately lambda/2, represents the ultimate resolution accessible using optical methods. Near-field optical methods offer a powerful capability for optical measurement and manipulation of materials. Using a scanning near-field optical microscope coupled to a UV laser it is possible to create photopatterned molecular structures with dimensions nearly 15 times smaller than the Rayleigh limit. Near-field methods offer the possibility for selective initiation of surface chemical transformations with exquisite spatial resolution, bringing the prospect of unifying top-down and bottom-up nanofabrication into view.

An investigation on pulse discharge effect on the surface chemical transformation of fly ash

Non-thermal plasma has been widely investigated to apply to environmental protection. The effectiveness of electrical discharge technology on decomposition and transformation of toxic gases has been widely studied, while its influence on the toxic substances in fly ash is not clear. In this paper, the surface chemical transformation of fly ash from electrostatic precipitators has been studied by surface pulse discharge. A surface mechanical change and a destruction of powder particles were visible after discharging. This indicates that the pulse discharge causes an effective destruction of the fly ash powder and its particles. The composition analysis showed that volatile organic compound (VOC) content in samples decreases after discharging. A positive pulse discharge showed a higher decrease in VOC content than that of a negative one did. We concluded that by using the surface pulse discharge, especially in the case of positive pulse discharge, the non-thermal plasma is also effective on decomposition and transformation of toxic substances in fly ash, which reaches a 51% VOC decomposition effectiveness.

Observing surface chemical transformations by atomic-resolution scanning tunneling microscopy: sulfide electrooxidation on gold(111)

Abstract : The prospects of utilizing atomic-resolution scanning tunneling microscopy (STM) as a real-space in-situ probe of molecular transformations on electrochemical surfaces are illustrated for the specific case of sulfide electrooxidation on Au(111) in aqueous solution. At relatively low electrode potentials, sulfide adsorption yields ordered ( 3 x 3)R30 deg layers. The onset of sulfide electrooxidation produces marked changes in the adsorbate structure, arrays of rectangular close-packed structures being formed which consist predominantly of S8 rings. The ring dimensions, including the S-S bond distances, differ significantly from bulk-phase polysulfur, being affected apparently by the gold substrate structure. Further reaction yields multilayer Sx structures exhibiting greater disorder. The likely scope of reactive surface electrochemistry amenable to STM is noted.

Thermal and ion-beam-induced etching of InP with chlorine

Surface spectroscopic techniques have been used to investigate adsorption and thermal and ion-induced processes at the InP(100)-Cl2 interface. Two adsorption states are identified and etching reactions are interpreted in terms of surface chemical transformations and desorption processes involving these states.