Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and microdevices and circuits. By means of optical forces, it enables the direct ...assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print identical NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and subsequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer on a sapphire substrate, we demonstrate for the first time the optical printing of AuAu NP dimers. Modeling the experiments considering optical, thermophoretic, and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the optical printing fabrication of complex nano structures and circuits based on connected colloidal NPs.
This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand place-exchange approach and the two-phase method, first developed for ...Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV–visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.
Co‐ and Ni‐based layered hydroxides constitute a unique class of two‐dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as ...supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α‐NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co−O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so‐called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational–experimental investigation of the electronic and structural details of α‐NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.
Layered hydroxides: This study demonstrates how an advanced synthetic method, as the Epoxide Route, allows for the production of well‐defined 2D materials in which the tunable oxidation state of the transition metal cations can be designed and understood on a rational basis, in order to enhance the electrochemical performance of these layered materials.
Iron-based nanoparticles were synthesized by a rapid method at room temperature using yerba mate (YM) extracts with FeCl3 in different proportions. Materials prepared from green tea (GT) extracts ...were also synthesized for comparison. These materials were thoroughly characterized by chemical analyses, XRD, magnetization, SEM-EDS, TEM-SAED, FTIR, UV–Vis, Raman, Mössbauer and XANES spectroscopies, and BET area analysis. It was concluded that the products are nonmagnetic iron complexes of the components of the extracts. The applicability of the materials for Cr(VI) (300 μM) removal from aqueous solutions at pH 3 using two Cr(VI):Fe molar ratios (MR), 1:3 and 1:0.5, has been tested. At Cr(VI):Fe MR = 1:3, the best YM materials gave complete Cr(VI) removal after two minutes of contact, similar to that obtained with commercial nanoscale zerovalent iron (N25), with dissolved Fe(II), and with a likewise prepared GT material. At a lower Cr(VI):Fe MR (1:0.5), although Cr(VI) removal was not complete after 20 min of reaction, the YM nanoparticles were more efficient than N25, GT nanoparticles and Fe(II) in solution. The results suggest that an optimal Cr(VI):Fe MR ratio could be reached when using the new YM nanoparticles, able to achieve a complete Cr(VI) reduction, and leaving very low Cr and Fe concentrations in the treated solutions. The rapid preparation of the nanoparticles would allow their use in removal of pollutants in soils and groundwater by direct injection of the mixture of precursors.
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•Synthesis of iron-based nanoparticles from yerba mate (YM) extract.•Iron-based nanoparticles from YM were completely characterized.•YM nanoparticles are nonmagnetic iron complexes of the extract components.•Cr(VI) removal higher than with commercial nZVI or green tea nanoparticles.
Sub‐nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and ...susceptibility to oxidation. In situ X‐ray Absorption spectroscopy and Near Ambient Pressure X‐ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion‐corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude “breathing” motions. A chemical phase diagram for Cu oxidation states of the Cu5‐oxygen system is presented, clearly different from the already known bulk and nano‐structured chemistry of Cu.
A combined XANES and NAP XPS study shows that Cu5 clusters are resistant to irreversible oxidation up to 773 K in the presence of oxygen. A theoretical model reveals that adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer and large amplitude “breathing” motions. A chemical phase diagram for Cu oxidation state of the Cu5‐O2 system is presented.
Low atomicity clusters present properties dependent on the size, due to the quantum confinement, with well‐defined electronic structures and high stability. Here it is shown that Ag5 clusters ...catalyze the complete oxidation of sulfur to S+6. Ag5 catalytic activity increases with different oxidant species in the order O2 ≪ H2O2 < OH•. Selective oxidation of thiols on the cysteine residues of glutathione and thioredoxin is the primary mechanism human cells have to maintain redox homeostasis. Contingent upon oxidant concentration, Ag5 catalyzes the irreversible oxidation of glutathione and thioredoxin, triggering apoptosis. Modification of the intracellular environment to a more oxidized state to mimic conditions within cancer cells through the expression of an activated oncogene (HRASG12V) or through ARID1A mutation, sensitizes cells to Ag5 mediated apoptosis. While cancers evolve to evade treatments designed to target pathways or genetic mutations that drive them, they cannot evade a treatment that takes advantage of aberrant redox homeostasis, which is essential for tumor progression and metastasis. Ag5 has antitumor activity in mice with orthotopic lung tumors reducing primary tumor size, and the burden of affected lymphatic nodes. The findings suggest the unique intracellular redox chemistry of Ag5 may lead to new redox‐based approaches to cancer therapy.
Ag5 clusters show unique catalytic activities to oxidize thiols. They catalyze the complete oxidation of thiols present in cysteine, glutathione, and thioredoxin. This oxidation is tunable by relevant biological oxidants species (hydrogen peroxide and hydroxyl radical), allowing Ag5 to inhibit the thiol‐based antioxidants leading to the selective death of tumor proliferating cells.
Sub-nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and ...susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu
clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O
molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation states of the Cu
-oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.
Compositional changes taking place during the synthesis of alloyed CdSeZnS nanocrystals (NCs) allow shifting of the optical features to higher energy as the NCs grow. Under certain synthetic ...conditions, the effect of those changes on the surface/interface chemistry competes with and dominates over the conventional quantum confinement effect in growing NCs. These changes, identified by means of complementary advanced spectroscopic techniques such as XPS (X-ray photoelectron spectroscopy) and XAS (X-ray absorption spectroscopy), are understood in the frame of an ion migration and exchange mechanism taking place during the synthesis. Control over the synthetic routes during NC growth represents an alternative tool to tune the optical properties of colloidal quantum dots, broadening the versatility of the wet chemical methods.
Graphene oxide has been widely deployed in electrical sensors for monitoring physical, chemical, and biological processes. The presence of abundant oxygen functional groups makes it an ideal ...substrate for integrating biological functional units to assemblies. However, the introduction of this type of defects on the surface of graphene has a deleterious effect on its electrical properties. Therefore, adjusting the surface chemistry of graphene oxide is of utmost relevance for addressing the immobilization of biomolecules, while preserving its electrochemical integrity. Herein, we describe the direct immobilization of glucose oxidase onto graphene oxide-based electrodes prepared by Langmuir–Blodgett assembly. Electrochemical reduction of graphene oxide allowed to control its surface chemistry and, by this, regulate the nature and density of binding sites for the enzyme and the overall responsiveness of the Langmuir–Blodgett biofilm. X-ray photoelectron spectroscopy, surface plasmon resonance, and electrochemical measurements were used to characterize the compositional and functional features of these biointerfaces. Covalent binding between amine groups on glucose oxidase and epoxy and carbonyl groups on the surface of graphene oxide was successfully used to build up stable and active enzymatic assemblies. This approach constitutes a simple, quick, and efficient route to locally address functional proteins at interfaces without the need for additives or complex modifiers to direct the adsorption process.
We report the synthesis, for the first time, of small, highly monodisperse Cu5 clusters in water without any surfactant or protective agent. For this purpose, we used a new approach based on the ...kinetic control of the reaction, which is achieved with an electrochemical method and using a solution with almost no conductivity (i.e., without added electrolytes commonly used in electrochemical methods). This allows the application of extremely small current densities needed to focus the reaction to synthesize only one selected cluster size. Clusters were characterized by ultraviolet–visible (UV–vis) and fluorescence spectroscopies, atomic force microscopy, electrospray ionization time-of-flight mass spectrometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and X-ray absorption near-edge spectroscopy, showing the presence of only Cu clusters with five atoms. Contrary to what should be expected, such clusters are very stable and remain unaltered in solution, for at least one year, because of their huge band gap (4.07 eV). Moreover, such Cu5 clusters are extremely stable to UV irradiation, temperature, and pH.
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