Graphene oxide fibers by microfluidics assembly: a strategy for structural and dimensional control.

Graphene oxide (GO) microfibers with controlled and homogeneous shapes and tunable diameters were fabricated using the 3 dimensional (3D) hydrodynamic focusing concept on a microfluidic device. Thermal and microwave treatments are used to obtain reduced graphene oxide (rGO) microfibers with outstanding electrical properties, thus enabling the development of ionic liquid-gate field-effect transistors (FET) based on graphene derivative microfibers.

Spontaneous chemical functionalization via coordination of Au single atoms on monolayer MoS2.

Surface functionalization of metallic and semiconducting 2D transition metal dichalcogenides (TMDs) have mostly relied on physi- and chemi-sorption at defect sites, which can diminish the potential applications of the decorated 2D materials, as structural defects can have substantial drawbacks on the electronic and optoelectronic characteristics. Here, we demonstrate a spontaneous defect-free functionalization method consisting of attaching Au single atoms to monolayers of semiconducting MoS2(1H) via S-Au-Cl coordination complexes. This strategy offers an effective and controllable approach for tuning the Fermi level and excitation spectra of MoS2 via p-type doping and enhancing the thermal boundary conductance of monolayer MoS2, thus promoting heat dissipation. The coordination-based method offers an effective and damage-free route of functionalizing TMDs and can be applied to other metals and used in single-atom catalysis, quantum information devices, optoelectronics, and enhanced sensing.

Ultrasmall (<2 nm) Au@Pt Nanostructures: Tuning the Surface Electronic States for Electrocatalysis.

The ability to tune the electronic properties of nanomaterials has played a major role in the development of sustainable energy technologies. Metallic nanocatalysts are at the forefront of these advances. Their unique properties become even more interesting when we can control the distribution of the electronic states in the nanostructure. Here, we provide a comprehensive evaluation of the electronic surface states in ultrasmall metallic nanostructures by combining experimental and theoretical methods. The developed strategy allows the controlled synthesis of bimetallic nanostructures in the core-shell configuration, dispensing of the use of any surfactant or stabilizing agents, which usually inactivate important surface phenomena. The synthesized ultrasmall Au@Pt nanoarchitecture (∼1.8 nm) presents an enhanced performance catalyzing the hydrogen evolution reaction. First-principles calculations of projected and space-resolved local density of states of Au55@Pt92 (core-shell), Au55Pt92 (alloy), and Pt147 nanoparticles show a prominent increase in the surface electronic states for the core-shell bimetallic nanomaterial. It arises from a more-effective charge transfer from gold to the surface platinum atoms in the core-shell configuration. In pure Pt147 or Au55Pt92 alloy nanoparticles, a great part of the electronic states near the Fermi level is buried in the core atoms, disabling these states for catalytic applications. The proposed experimental-theoretical approach may be useful for the design of other systems composed of metallic nanoparticles supported on distinct substrates, such as two-dimensional materials and porous matrices. These nanomaterials find several applications not only in heterogeneous catalysis but also in sensing and optoelectronic devices.

Engineering two-dimensional gold nanostructures using graphene oxide nanosheets as a template.

The rich plasmon resonance modes and local field enhancements of two-dimensional (2D) noble metal nanostructures have boosted their application in distinct areas like catalysis, photonics, medicine and sensing. Here, we develop a unique strategy for the controlled growth of asymmetric 2D gold nanostructures in aqueous media using graphene oxide as a template. By performing mild reduction of gold ions on the surface of Au seeds (∼2 nm) attached to graphene oxide nanosheets, the anisotropic growth of 2D gold nanostructures can be carried out through a simple procedure with a tunable control of the final size, shape and thickness, and consequently on their optical properties, without using surfactants.

Highly-controlled grafting of mono and dicationic 4,4'-bipyridine derivatives on SBA-15 for potential application as adsorbent of CuCl2 from ethanol solution.

This work describes a highly controlled post-grafting of mono and dicationic 4,4'-bipyridine alkoxysilane derivatives (Bipy(+) and Bipy(2+)) onto the surface of an ordered mesoporous silica, SBA-15. The materials obtained are designated as SBA-15/Bipy(+)Cl(-) and SBA-15/Bipy(2+)Cl(2)(-), both possessing chloride as counter ion. The regular arrangement of uniform pores of this inorganic matrix is likely to ensure good accessibility to the active centers (electron acceptors) attached to the surface. The materials are excellent adsorbents due to the ability of the functional groups to retain copper chlorides on their surfaces as anionic complexes (CuCl(2+n)(n-)) in ethanol. From the adsorption, results it was possible to probe the functional surface monolayer of the materials, which present a highly homogenous distribution of functional groups inside the ordered SBA-15 channels, with an exchange efficiency of 93% for SBA-15/Bipy(+)Cl(-) and 94% for SBA-15/Bipy(2+)Cl(2)(-). Both adsorbent materials are potentially useful in the pre-concentration and further analysis of Cu(II) present in trace amounts in ethanol, extensively used as an automotive fuel in Brazil.

Ion-exchange properties of imidazolium-grafted SBA-15 toward AuCl4(-) anions and their conversion into supported gold nanoparticles.

Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion-exchange properties of the functionalized porous solid (SBA-15/R(+)Cl(-)) toward AuCl(4)(-) anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log ß = 4.47) and the effective ion-exchange capacity (t(Q) = 0.79 mmol g(-1)) indicate that the AuCl(4)(-) species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl(4)(-) ions were submitted to a chemical reduction process with NaBH(4), converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane derivative: study of CuCl2 adsorption from ethanol solution.

This work describes the preparation and characterization of postfunctionalized ordered (SBA-15) and nonordered (SMD) mesoporous silicas with n-propyl-1,4-diazoniabicycle[2.2.2]octane chloride (DbCl) moiety. The main interest is based on the fact that these materials are excellent adsorbents due to the ability of functional groups to retain copper chlorides on their surfaces as anionic complexes CuCl(2+n)(n-). The specific surface areas (S(BET)) and average pore diameters (d(pore)) for SBA-15 and SMD are SBA-15, S(BET)=944 m(2) g(-1), d(pore)=9.0 nm; SMD, S(BET)=710 m(2) g(-1), d(pore)=11 nm. On functionalization with DbCl, reductions in the specific surface areas of the resulting materials (SBA-15/DbCl and SMD/DbCl) are observed and the following functionalization degrees (ϕ) were determined: SBA-15/DbCl, S(BET)=247 m(2) g(-1), ϕ=0.95 mmol g(-1); SMD/DbCl, S(BET)=83 m(2) g(-1), ϕ=1.2 mmol g(-1). The adsorption equilibria of CuCl(2) in ethanol were characterized, and the heterogeneous stability constants, ß(1) and ß(2), corresponding to formation of CuCl(4)(2-) and CuCl(3)(-) anionic species adsorbed on the surface were found. Also, the effective sorption capacities (t(Q)) were determined: SBA-15/DbCl, log ß(1)=4.46, log ß(2)=7.10, t(Q)=0.80 mmol g(-1); SMD/DbCl, log ß(1)=4.95, log ß(2)=7.52, t(Q)=0.75 mmol g(-1). Regeneration of the adsorbents requires a very simple procedure consisting of their immersion in aqueous solution followed by immediate release to the solution phase of the Cu(OH(2))(n)(2+) species, followed by chloride anions as the counterions.

Evaluations of the BET, I-point, and α-plot procedures for the routine determination of external specific surface areas of highly dispersed and porous silicas.

Nitrogen adsorption isotherms of silicas and other oxidic materials are distorted by the presence of micropore adsorption and capillary condensation. This distortion affects the determination of the specific area of the material, depending on the chosen calculation procedure. Correction of the initial (total) isotherm for micropore capacity decreases or eliminates this source of error to give a useful estimate of the external surface area. In the present work, 26 silica-based adsorbent materials were studied to obtain total and external specific surface areas by the Brunauer-Emmett-Teller (BET), I-point, and α-plot procedures, using the micropore capacities from the α-plots to obtain the corrected (external) isotherms. Errors in the specific surface areas due to the presence of micropores are given by the equation ΔsA = 3.267 (m(2)/cm(3) STP) sV(mic), where sA is the specific surface area in m(2)/g and sV(mic) is the micropore capacity in cm(3) STP/g. A consistent set of conversion factors was obtained by which the external specific surface area obtained using one of these procedures can be converted, with part-per-thousand precision, to either of the others. Although the I-point procedure presents the advantage of not requiring a defined p/p(0) range, the α-plot procedure is recommended for routine determinations of external specific areas of silicas and other oxidic materials, except for cases in which the shapes of the adsorption isotherms of the sample and the reference differ significantly from one another in the p/p(0) range used for the determination.