Control Of Surface Composition Research Articles

Insights into in situ surface reconstruction in cobalt perovskite oxides for enhanced catalytic activity

An depth understanding of the fundamental interactions between surface termination and catalytic activity is crucial to prompt the properties of functional perovskite materials. The elastic energy due to size mismatch and electrostatic attraction of the charged Sr dopant by positively charged oxygen vacancies induced inert A-site surface enrichment rearrangement for perovskites. Lower temperatures could reduce A-site enrichment, but it is difficult to form perovskite crystals. La0.8Sr0.2CoO3-δ (LSCO) as a model perovskite oxide was modified with additive urea to reduce the crystallization temperature, and suppress Sr segregation. The LSCO catalysts with 600 °C annealing temperature (LSCO-600) exhibited a 19.4-fold reaction reactivity of toluene oxidation than that with 800 °C annealing temperature (LSCO-800). Combined surface-sensitive and depth-resolved techniques for surface and sub-surface analysis, surface Sr enrichment was effectively suppressed due to decreased oxygen vacancy concentration and smaller electrostatic driving force. DFT calculations and in-situ DRIFTs spectra well revealed that tuning the surface composition/termination affected the intrinsic reactivity. The catalyst surface with lower Sr enrichment could easily adsorb toluene, cleave, and decompose benzene rings, thus contributing to toluene degradation to CO2. This work demonstrates a green and efficient way to control surface composition and termination at the atomic scale for higher catalytic activity.

Rational design of ICD-inducing nanoparticles for cancer immunotherapy.

Nanoparticle-based cancer immunotherapy has shown promising therapeutic potential in clinical settings. However, current research mainly uses nanoparticles as delivery vehicles but overlooks their potential to directly modulate immune responses. Inspired by the endogenous endoplasmic reticulum (ER) stress caused by unfolded/misfolded proteins, we present a rationally designed immunogenic cell death (ICD) inducer named NanoICD, which is a nanoparticle engineered for ER targeting and retention. By carefully controlling surface composition and properties, we have obtained NanoICD that can effectively accumulate in the ER, induce ER stress, and activate ICD-associated immune responses. In addition, NanoICD is generally applicable to various proteins and enzymes to further enhance the immunomodulatory capacity, exemplified by encapsulating catalase (CAT) to obtain NanoICD/CAT, effectively alleviated immunosuppressive tumor microenvironment and induced robust antitumor immune responses in 4T1-bearing mice. This work demonstrates engineered nanostructures' potential to autonomously regulate biological processes and provides insights into the development of advanced nanomedicines for cancer treatment.

Keplerate polyoxomolybdate nanoball mediated controllable preparation of metal-doped molybdenum disulfide for electrocatalytic hydrogen evolution in acidic and alkaline media

Rationally designed novel cost-effective hydrogen evolution reaction (HER) electrocatalysts with controlled surface composition and advanced structural superiority is extremely critical to optimize the HER performance. Polyoxometalates (POMs) with structural diversity and adjustable element compositions represent a promising precursor for rational design and preparation of HER electrocatalysts. Herein, a series of transition metal-doped MoS2 materials with different surface engineered structures (Fe, Cr, V doping and S vacancies) (M-MoS2/CC, M = Fe, Cr and V) were fabricated by a simple hydrothermal-vulcanization strategy using Keplerate polyoxomolybdate nanoball ({Mo72Fe30}, {Mo72Cr30}, {Mo72V30}, {Mo132}) as precursors. The enlarged interlayer spacing as well as the integration of homogeneous transition metal doping and abundant sulfur vacancies endows prepared M-MoS2/CC with superior HER electrocatalytic performance and excellent long-term working stability in both acidic and alkaline media. The optimized Fe-MoS2/CC afford current densities of 10 and 50 mA/cm2 at overpotentials of 188/272 mV and 194/394 mV in 0.5 mol/L H2SO4 and 1.0 mol/L KOH aqueous solution, respectively, outperforming most of reported typical transition metal sulfide-based catalysts. This work represents an important breakthrough for POMs-mediated highly efficient transition metal sulfide-based HER electrocatalysts with wide range pH activity and may provide new options for the rational design of promising HER electrocatalysts and beyond.

Constructing porous RuCu nanotubes with highly efficient alloy phase for water splitting in different pH conditions

Controlling surface composition is a direct approach to develop active electrocatalysts for water splitting. Here, porous RuCu nanotubes with Ru1Cu1 alloy phase are successfully constructed by a multi-step wet chemistry method, which illustrate excellent performance for water splitting in different pH conditions. Particularly, it only requires 11 and 229 mV to get 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction in 1 M KOH medium, respectively. Moreover, it just requires nearly 2.0 V to reach 300 mA cm−2 in flowing alkaline water electrolyzer device, which is much better than Pt/C // RuO2 system. Further mechanism studies reveal that Ru1Cu1 alloy phase acts as the main role in hydrogen evolution because it largely weakens the free energy of adsorption hydrogen and activates water molecules to facilitate the dissociation. Afterwards, Ru1Cu1 alloy also effectively reduces the free energy of rate-determining step during oxygen evolution reaction. Besides, the unique one dimensional and porous structure of nanotubes strengthens the transfer of electrons and the releasing of gas products, enhancing the reaction kinetics. This work emphasizes the importance of alloy composition for water splitting, which guides the rational regulation of electrocatalysts.

SAMs on Gold Derived from Adsorbates Having Phenyl and Cyclohexyl Tail Groups Mixed with Their Phase-Incompatible Fluorinated Analogues.

This article investigates two types of mixed self-assembled monolayers (SAMs) derived from adsorbates having cyclohexyl and phenyl tail groups mixed with their perfluorinated analogues. The mixed SAMs were characterized using ellipsometry, X-ray photoelectron spectroscopy (XPS), polarization-modulation infrared reflection absorption spectroscopy, and contact angle measurements. The XPS results show preferential adsorption of the nonfluorinated adsorbate in the perfluorocyclohexyl-terminated/cyclohexyl-terminated pair due to the steric bulk of the tail groups. On the other hand, mixed surfaces with a precisely controlled surface composition were achieved with the phenyl-terminated/perfluorophenyl-terminated mixed SAMs, exhibiting a linear relationship between the mole fraction on the surface and the mole fraction in solution. The results suggest that the relative solubility, steric bulk of the tail group moiety, and the interaction between two different adsorbates are the key factors driving the phase phenomena observed in the SAMs. More importantly, this study suggests that the interfacial properties can be controlled with a minimal loss of packing densities with the phenyl-terminated/perfluorophenyl-terminated mixed SAMs.

Control of surface composition and microstructure of nano super-hydrophilic TiO2-CuOy coatings through reactive sputtering to improve antibacterial ability, corrosion resistance, and biocompatibility

In this work, the TiO2-CuOy antibacterial superhydrophilic nano-coating succeeded to be prepared on titanium sheet via the reactive magnetron sputtering, influence of oxygen content on the surface morphology, phase composition and structure of TiO2-CuOy coatings were investigated, the bonding of TiO2-CuO system to O2 molecule in TiO2-CuO-O2 systems was simulated through molecular dynamics, and the corresponding antibacterial, biological and physical properties were also studied. Results showed that CuOy transformed from Cu to Cu2O to CuO as the oxygen increased from 0% to50%, TiO2-CuOy coatings consisted of nano-grains, the surface roughness showed a decline trend with decreased grain size, it was consistent with the simulation result in TiO2-CuO-O2 system. After being irradiated under UV, TiO2-CuOy coatings became super-hydrophilic, which obtained enhanced properties in anti-bacteria, cytocompatibility and corrosion resistance. Owing to smaller grain size and surface roughness, higher copper ions releasing amount, CuOy either in Cu2O or CuO type performed better compared to normal nano-copper, in which TiO2-Cu2O coating was nontoxic and significantly promoted MC3T3-E1 cells proliferation, especially its antibacterial rate reached 99.985% to S.aureus under 2 h direct contact, which was able to prevent the infections occurring at the operation site in the early implantation.

Facile electrochemical fabrication of Ag/Cu bi-metallic catalysts and the dependence of their selectivity for electrochemical CO2 reduction on the surface composition

Herein, bimetallic Ag/Cu nanowires (NWs) are prepared by electrochemical synthesis of Cu NWs and subsequent Ag galvanic displacement for the electrochemical reduction of CO2 to CO. The delicate execution of the displacement fabricates bimetallic NWs that possess controlled surface composition. The surface composition of NW is precisely controlled by varying the displacement time, and it is revealed by numerical and experimental methods that the catalytic activity is closely affected by the composition. The surface coverage of Ag measured based on under potential deposition according to the displacement time ranges from 70% to 94.3%. An increase in the Ag surface composition results in an improvement in the CO Faradaic efficiency from 29.8% to 39.6% and a significant increase in CO partial current density compared with Cu NWs and Ag foil. Namely, the catalytic activity of Ag/Cu NWs is dependent on the Ag coverage, and is governed by scaling relation.

Effects of Electrolyte on Laser-Induced Periodic Surface Structures with Picosecond Laser Pulses.

Short-pulsed laser-induced periodic surface structures (SPLIPSSs) have the possibility to control tribology, wettability and biocompatibility. Nevertheless, the optimal structure depends on each functionality, which has not been clarified. The hybrid process with a short-pulsed laser and electrochemical machining (SPLECM) is, then, proposed to fabricate micro/nano hybrid structures and to modify the surface composition for providing high functionalities with material surfaces. Electrochemical machining is a well-established micro-elution and deposition method with noncontact between a workpiece and a tool. In this study, the effects of electrolytes on SPLIPSSs were investigated experimentally by the picosecond laser irradiation on 304 stainless steel substrates in various electrolytes. The geometry of SPLIPSSs depended on the types and the concentration of electrolytes. In the case of copper nitrate solution and copper sulfate solution, LIPSSs and spheroidization of copper were obtained. This study demonstrated the possibility of SPLECM to fabricate micro/nano structures and to control surface composition.

Amphiphilic Marine Antifouling Coatings Based on a Hydrophilic Polyvinylpyrrolidone and Hydrophobic Fluorine-Silicon-Containing Block Copolymer.

The development of environmentally friendly and highly efficient antifouling coatings is vastly desirable in the marine industry. Herein, we prepared a novel amphiphilic block copolymer that combined hydrophilic polyvinylpyrrolidone (PVP) with hydrophobic poly(1-(1H,1H,2H,2H-perfluorodecyloxy)-3-(3,6,9-trioxadecyloxy)-propan-2-yl acrylate) (PFA) and polydimethylsiloxane (PDMS). The amphiphilic copolymer (PVP-PFA-PDMS) was blended into a cross-linked PDMS matrix to form a set of controlled surface composition and surface-renewal coatings with efficient antifouling and fouling-release properties. These coatings incorporated the biofouling settlement resistance ability attributed to the hydrophilic PVP segments and the reduced adhesion strength attributed to the low surface energy of fluorine-silicon-containing segments. As expected, the coatings showed an excellent antifouling performance against bacteria and marine unicellular Navicula parva diatoms (98.1 and 98.5% of reduction, respectively) and fouling-release performance against pseudobarnacle adhesion (84.3% of reduction) compared to the pristine PDMS coating. Moreover, a higher-content PVP-based coatings presented higher ability to resist biofouling adhesion. The nontoxic antifouling coating developed in this paper hold the potential to be applied in a variety of marine industrial facilities.

Lipid-mediated growth of SrCO3/CaCO3 hybrid films as bioactive coatings for Ti surfaces

SrCO3 is frequently used as Sr2+ source in ceramic cements, but its application as bioactive coating for metallic implants has not been explored yet. Aiming at rapid osteointegration and because of the well-known Sr2+ effects on bone metabolism, researchers have sought to design Sr2+-containing biomaterials. In this context, developing simple techniques to prepare Sr2+-based coatings is a must nowadays. Here, we describe the use of a bioinspired lipid-mediated approach to grow SrCO3 hybrid films on Ti surfaces at room temperature. To obtain these coatings, we applied the Langmuir-Blodgett technique to deposit phospholipid films with high degree of organization on Ti. In this way, we expected that controlled SrCO3 crystal growth could be templated by the array of nucleation points arising from electrostatic interaction between Sr2+ and the phospholipid polar heads. To control surface composition and the amount of Sr2+ released from the coatings, we also promoted CaCO3 co-precipitation in the hybrid films. We characterized the hybrid coatings in terms of morphology, chemical structure, wettability, and ability to release Sr2+ upon immersion in biological medium. In vitro osteoblast culture on mixed SrCO3/CaCO3 films revealed that the osteogenic response depended on surface composition, as indicated by alkaline phosphatase activity overexpression, which is an early indicator of osteoblast differentiation. Results showed that the mixed SrCO3/CaCO3 hybrid film created a synergic environment for osteoblasts, and that proper Sr2+ release associated with a Ca2+-rich environment might have optimized the Sr2+ anabolic effect. In conclusion, we have proposed a bioinspired and versatile technique to grow hybrid films that can control surface composition and Sr2+ release. Our results open an opportunity to explore the use of SrCO3-based coatings for rapid metallic implant osteointegration.

Designer liquid-liquid interfaces made from transient double emulsions

Current methods for generating liquid-liquid interfaces with either controlled composition or coverage often rely on adsorption equilibria which limits the freedom to design such multiphase materials, in particular when different components are used. Moreover, when interfaces become densely populated, slowing down of adsorption may impose additional constraints. Up to now, it is not possible to control surface coverage and composition of droplet interfaces at will. Here, we report a generic and versatile method to create designer liquid-liquid interfaces, using transient double emulsions. We demonstrate how the surface coverage in Pickering emulsions can be controlled at will, even for dense particulate layers going up to multilayers. Moreover, composite droplet interfaces with compositional control can be generated, even with particles which would have intrinsically different or even opposite adsorption characteristics. Given its simplicity, this method offers a general approach for control of composition of liquid-liquid interfaces in a variety of multiphase systems.

RAFT Emulsion Polymerization as a Platform to Generate Well‐Defined Biocompatible Latex Nanoparticles

Current approaches to generate core-shell nanoparticles for biomedical applications are limited by factors such as synthetic scalability and circulatory desorption of cytotoxic surfactants. Developments in controlled radical polymerization, particularly in dispersed states, represent a promising method of overcoming these challenges. In this work, well-defined PEGylated nanoparticles are synthesized using reversible addition fragmentation chain transfer emulsion polymerization to control particle size and surface composition and were further characterized with light scattering, electron microscopy, and size exclusion chromatography. Importantly, the nanoparticles are found to be tolerated both in vitro and in vivo, without the need for any purification after particle synthesis. Pharmacokinetic and biodistribution studies in mice, following intraperitoneal injection of the nanoparticles, reveal a long (>76 h) circulation time and accumulation in the liver.

Mesoporous Silica Nanoparticles for Targeted and Stimuli‐Responsive Delivery of Chemotherapeutics: A Review

AbstractMesoporous silica nanoparticles (MSNs) exhibit the typical characteristics of inorganic materials that make them promising drug delivery carriers for cancer therapy. Their structural properties allow the targeted delivery of chemotherapeutic drugs to enhance drug efficacy and reduce adverse effects. The functionalization of MSNs with targeting ligands to a specific tissue/cell and stimuli‐responsive capping materials to seal drugs inside the MSNs pores are widely studied for biomedical and pharmaceutical applications. Furthermore, multiple stimuli‐responsive MSN‐based drug delivery systems are developed to enhance the delivery of anticancer drugs to their specific target and thereby improve the release of the drugs at the intended site. In addition, several toxicity studies are conducted to evaluate the biosafety and biocompatibility of MSNs. Although MSNs present reduced toxicity compared to colloidal silica, they can induce cytotoxicity associated with oxidative stress by increased reactive oxygen species production and decreased glutathione levels that can ultimately lead to cell death. However, different modifications to control morphology and surface composition can be applied to overcome the biocompatibility concerns. In this review, a comprehensive overview of the controlled synthesis, functionalization, targeting and biocompatibility of MSNs, as well as their biomedical application as a chemotherapeutic delivery system is provided.

In vitro and in vivo evaluation of PEO-modified titanium for bone implant applications

This work investigated the capacity of plasma electrolytic oxidation coatings on titanium for biological regulation via controlled surface composition and morphology in order to improve osseointegration and implant fixation. PEO coatings with relatively high Ca/P ratios of ~2.0 and ~4.0 were designed, characterized and evaluated in vitro, focusing on murine osteoblast and osteoclast activities in order to reflect the equilibrium between bone synthesis and resorption. The coating with elevated anatase content and surface Ca/P ratio of ~2.0 disclosed a diminished osteoclast activity and adequate osteoblast differentiation, favoring an augmented bone matrix synthesis over resorption processes. The coating with Ca/P ratio of 4.0 and reduced pore population density enabled greater osteoclastic resorptive activity. Additionally, commercial mechanised dental implants were PEO-coated and placed in an adult pig for 8 weeks in order to test their biocompatibility and implant integration in a preliminary in vivo approach. Both coatings revealed positive behaviour, strong bone matrix deposition at the implant-tissue interface and higher mean BIC values than Ti CP, with no appreciable differences between the two coatings.

A Comprehensive Review on Controlling Surface Composition of Pt‐Based Bimetallic Electrocatalysts

AbstractWith increasing energy demands worldwide, significant efforts have been made to develop superior electrocatalysts for efficient energy conversion systems. Among all the electrocatalysts exploited, Pt‐based bimetallic nanomaterials stand out by virtue of their high catalytic activity and relatively low cost due to the introduction of a nonprecious metal component. It should be noted that electrocatalytic reactions only take place on the surface of catalysts, so investigations of the surface composition of Pt‐based bimetallic nanomaterials are necessary for practical electrocatalysts. In this review, recent studies on controlling the surface composition of Pt‐based bimetallic catalysts for the oxygen reduction reaction, formic acid electrooxidation, and ethanol electrooxidation are summarized. The controlling strategies, including the chemical method and the electrochemical method, are discussed. The impacts of surface composition compositions on the electrocatalytic performance are also discussed. Finally, the challenges and future directions for controlling the surface composition of Pt‐based bimetallic nanomaterials are addressed.

Early Stage Anodic Instability of Glassy Carbon Electrodes in Propylene Carbonate Solvent Containing Lithium Hexafluorophosphate.

Irreversible changes to the morphology of glassy carbon (GC) electrodes at potentials between 3.5 and 4.5 V vs Li/Li+ in propylene carbonate (PC) solvent containing lithium hexafluorophosphate (LiPF6) are reported. Analysis of cyclic voltammetry (CV) experiments in the range of 3.0 to 6.0 V shows that the capacitance of the electrochemical double-layer increased irreversibly beginning at potentials as low as 3.5 V. These changes resulted from nonfaradaic interactions, and were not due to oxidative electrochemical decomposition of the electrode and electrolyte, anion intercalation, nor caused by the presence of water, a common impurity in organic electrolyte solutions. Atomic force microscopy (AFM) images revealed that increasing the potential of a bare GC surface from 3.0 to 4.5 V resulted in a 6× increase in roughness, in good agreement with the changes in double-layer capacitance. Treating the GC surface via exposure to trichloromethylsilane vapors resulted in a stable double-layer capacitance between 3.0 and 4.5 V, and this treatment also correlated with less roughening. These results inform future efforts aimed at controlling surface composition and morphology of carbon electrodes.

Chemically controlled surface compositions of Ag–Pt octahedral catalysts

Abstract

Model Amphiphilic Block Copolymers with Tailored Molecular Weight and Composition in PDMS-Based Films to Limit Soft Biofouling.

A set of controlled surface composition films was produced utilizing amphiphilic block copolymers dispersed in a cross-linked poly(dimethylsiloxane) network. These block copolymers contained oligo(ethylene glycol) (PEGMA) and fluoroalkyl (AF6) side chains in selected ratios and molecular weights to control surface chemistry including antifouling and fouling-release performance. Such properties were assessed by carrying out assays using two algae, the green macroalga Ulva linza (favors attachment to polar surfaces) and the unicellular diatom Navicula incerta (favors attachment to nonpolar surfaces). All films performed well against U. linza and exhibited high removal of attached sporelings (young plants) under an applied shear stress, with the lower molecular weight block copolymers being the best performing in the set. The composition ratios from 50:50 to 60:40 of the AF6/PEGMA side groups were shown to be more effective, with several films exhibiting spontaneous removal of the sporelings. The cells of N. incerta were also removed from several coating compositions. All films were characterized by surface techniques including captive bubble contact angle, atomic force microscopy, and near edge X-ray absorption fine structure spectroscopy to correlate surface chemistry and morphology with biological performance.

The Trypanosome Exocyst: A Conserved Structure Revealing a New Role in Endocytosis.

Membrane transport is an essential component of pathogenesis for most infectious organisms. In African trypanosomes, transport to and from the plasma membrane is closely coupled to immune evasion and antigenic variation. In mammals and fungi an octameric exocyst complex mediates late steps in exocytosis, but comparative genomics suggested that trypanosomes retain only six canonical subunits, implying mechanistic divergence. We directly determined the composition of the Trypanosoma brucei exocyst by affinity isolation and demonstrate that the parasite complex is nonameric, retaining all eight canonical subunits (albeit highly divergent at the sequence level) plus a novel essential subunit, Exo99. Exo99 and Sec15 knockdowns have remarkably similar phenotypes in terms of viability and impact on morphology and trafficking pathways. Significantly, both Sec15 and Exo99 have a clear function in endocytosis, and global proteomic analysis indicates an important role in maintaining the surface proteome. Taken together these data indicate additional exocyst functions in trypanosomes, which likely include endocytosis, recycling and control of surface composition. Knockdowns in HeLa cells suggest that the role in endocytosis is shared with metazoan cells. We conclude that, whilst the trypanosome exocyst has novel components, overall functionality appears conserved, and suggest that the unique subunit may provide therapeutic opportunities.

Tuning Pt-Skin or M-Rich Surface on Bimetallic Nanoparticles (Pt3Ni, PtBi, Pt3Co) for Enhanced Electrocatalytic Activities

Controlling surface composition of bimetallic catalysts is of significance in energy conversion and storage. We synthesized a series of bimetallic catalysts of different surface composition on porous graphitic carbon (PtBi/PC, Pt3Ni/PC, Pt3Co/PC: figures A, C, E, G) with average diameter < 4 nm by controlled thermal treatment method. Formic acid oxidation on Pt/C is performed via the poisoning path (figure B), whereas oxidation of formic acid to form CO2 is done via the non-poisoning path on the PtBi/PC (figure D). The value of the peak current density is 4.6 times of that of the Pt/C catalysts. Pt3Ni catalyst with Pt-skin surface showed over 300% increase in mass activity compared with Pt/C for the oxygen reduction reaction (figure F). When we tuned the surface composition to Ni-rich, it showed 300% increasein mass activity when compared with Pt/C towards oxidizing of HCOOH. Ethanol oxidation on Pt3Co/PC with Pt-skin surface showed 2.5 times on mass activity than that of Pt/C. In addition, we proposed a new method to characterize Pt-skin or M-rich structure by using formic acid oxidation as probe reaction with the characterization of cyclic voltammetry and electrochemical in situFTIRs. Our approach to control surface composition can be used to design nanocatalysts for different reaction and enhance their catalytic performances. and The method is simple and clean that is effective and promotional to be industrialized. Figure 1