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The discharge of synthetic dyes from different industrial sources has become a global issue of concern. Enormous amounts are released into wastewater each year, causing concerns due to the high toxic consequences. Photocatalytic semiconductors appear as a green and sustainable form of remediation. Among them, graphitic carbon nitride (g-C3N4) has been widely studied due to its low cost and ease of fabrication. In this work, the synthesis, characterization, and photocatalytic study over methylene blue of undoped, B/S-doped, and exfoliated heterojunctions of g-C3N4 are presented. The evaluation of the photocatalytic performance showed that exfoliated undoped/S-doped heterojunctions with 25, 50, and 75 mass % of S-doped (g-C3N4) present enhanced activity with an apparent reaction rate constant (kapp) of 1.92 × 10-2 min-1 for the 75% sample. These results are supported by photoluminescence (PL) experiments showing that this heterojunction presents the less probable electron-hole recombination. UV-vis diffuse reflectance and valence band-X-ray photoelectron spectroscopy (VB-XPS) allowed the calculation of the band-gap and the valence band positions, suggesting a band structure diagram describing a type I heterojunction. The photocatalytic activities calculated demonstrate that this property is related to the surface area and porosity of the samples, the semiconductor nature of the g-C3N4 structure, and, in this case, the heterojunction that modifies the band structure. These results are of great importance considering that scarce reports are found concerning exfoliated B/S-doped heterojunctions.
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Zwitterionic molecules are known to resist nonspecific protein adsorption and have been proposed as an alternative to the widely used polyethylene glycol. Recently, zwitterionic-like nanoparticles were created from the coimmobilization of positive and negative ligands, resulting in surfaces that also prevent protein corona formation while keeping available sites for bioconjugation. However, it is unclear if they are able to keep their original properties when immersed in biological environments while retaining a toxicity-free profile, indispensable features before considering these structures for clinics. Herein, we obtained optimized zwitterionic-like silica nanoparticles from the functionalization with varying ratios of THPMP and DETAPTMS organosilanes and investigated their behavior in realistic biological milieu. The generated zwitterionic-like particle was able to resist single-protein adsorption, while the interaction with a myriad of serum proteins led to significant loss of colloidal stability. Moreover, the zwitterionic particles presented poor hemocompatibility, causing considerable disruption of red blood cells. Our findings suggest that the exposure of ionic groups allows these structures to directly engage with the environment and that electrostatic neutrality is not enough to grant low-fouling and stealth properties.
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Formic acid (FA) is a promising CO and hydrogen energy carrier, and currently its generation is mainly centered on the hydrogenation of CO2 . However, it can also be obtained by the hydrothermal conversion of CO with H2 O at very high pressures (>100â bar) and temperatures (>200 °C), which requires days to complete. Herein, it is demonstrated that by using a nano-Ru/Fe alloy embedded in an ionic liquid (IL)-hybrid silica in the presence of the appropriate IL in water, CO can be catalytically converted into free FA (0.73 m) under very mild reactions conditions (10â bar at 80 °C) with a turnover number of up to 1269. The catalyst was prepared by simple reduction/decomposition of Ru and Fe complexes in the IL, and it was then embedded into an IL-hybrid silica {1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic (acetate, SILP-OAc) and hydrophobic [bis((trifluoromethyl)sulfonyl)amide, SILP-NTf2 ] anions}. The location of the alloy nanoparticles on the support is strongly related to the nature of the anion, that is, in the case of hydrophilic SILP-OAc, RuFe nanoparticles are more exposed to the support surface than in the case of the hydrophobic SILP-NTf2 , as determined by Rutherford backscattering spectrometry. This catalytic membrane in the presence of H2 O/CO and an appropriate IL, namely, 1,2-dimethyl-3-n-butylimidazolium 2-methyl imidazolate (BMMImâ MeIm), is stable and recyclable for at least five runs, yielding a total of 4.34 m of free FA.
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Interacting superparamagnetic iron(II) oxide nanoparticles (NPs) with sizes of 5.3 ± 1.6 nm were prepared by simple decomposition of [Fe(COT)2] (COT = 1,3,5,7-cyclooctatetraene) with 5 bar of H2 in 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI·NTf2) ionic liquid (IL). The static and dynamic magnetic characterization revealed a superparamagnetic behavior with weak dipolar interactions of these NPs. In situ structural studies by X-ray absorption spectroscopy demonstrated that they consist of nanostructured FeO. This approach is an appropriate method to prepare and stabilize nanostructured FeO particles, where the presence of an IL proved to be fundamental to suppress the aggregation and usual overoxidation of the FeO NPs.
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In situ time-resolved X-ray absorption spectroscopy (XAS) measurements collected at the Pt L3-edge during the synthesis of Pt nanoparticles (NPs) in aqueous solution are reported. A specially designed dispenser-reactor apparatus allowed for monitoring changes in the XAS spectra from the earliest moments of Pt ions in solution until the formation of metallic nanoparticles with a mean diameter of 4.9 ± 1.1â nm. By monitoring the changes in the local chemical environment of the Pt atoms in real time, it was possible to observe that the NPs formation kinetics involved two stages: a reduction-nucleation burst followed by a slow growth and stabilization of NPs. Subsequently, the synthesized Pt NPs were supported on activated carbon and characterized by synchrotron-radiation-excited X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The supported Pt NPs remained in the metallic chemical state and with a reduced size, presenting slight lattice parameter contraction in comparison with the bulk Pt values.
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Unsupported bimetallic Co/Pt nanoparticles (NPs) of 4.4 ± 1.9 nm can be easily obtained by a simple reaction of [bis(cylopentadienyl)cobalt(ii)] and [tris(dibenzylideneacetone) bisplatinum(0)] complexes in 1-n-butyl-3-methylimidazolium hexafluorophosphate IL at 150 °C under hydrogen (10 bar) for 24 h. These bimetallic NPs display core-shell like structures in which mainly Pt composes the external shell and its concentration decreases in the inner-shells (CoPt3@Pt-like structure). XPS and EXAFS analyses show the restructuration of the metal composition at the NP surface when they are subjected to hydrogen and posterior H2S sulfidation, thus inducing the migration of Co atoms to the external shells of the bimetallic NPs. Furthermore, the isolated bimetallic NPs are active catalysts for the Fischer-Tropsch synthesis, with selectivity for naphtha products.
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This study investigated the synthesis of platinum nanoparticles (Pt NPs) in ethylene glycol using low cost and low toxicity chemicals as reducing (ascorbic acid) and stabilizing agents (polyvinylpyrrolidone and sodium citrate). By monitoring the changes in the local chemical environment of the Pt atoms in real time by in situ dispersive X-ray absorption spectroscopy, it is observed that the NP formation kinetics involved three different stages within 3 h 30 min of the reaction: a reduction-nucleation burst, followed by diffusion-limited Ostwald ripening growth and subsequent stabilization of the NPs. The resulting Pt NPs were analyzed by transmission electron microscopy and X-ray diffraction, revealing a monodisperse average size distribution of 2.7 ± 0.5 nm, characterized by highly crystalline and stable Pt clusters, showing no significant aging for at least nine months.
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The use of in situ time-resolved dispersive X-ray absorption spectroscopy (DXAS) to monitor the formation of Cu2(OH)3Cl particles in an aqueous solution is reported. The measurements were performed using a dedicated reaction cell, which enabled the evolution of the Cu K-edge X-ray absorption near-edge spectroscopy to be followed during mild chemical synthesis. The formed Cu2(OH)3Cl particles were also characterized by synchrotron-radiation-excited X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The influence of polyvinylpyrrolidone (PVP) on the electronic and structural properties of the formed particles was investigated. The results indicate clearly the formation of Cu2(OH)3Cl, with or without the use of PVP, which presents very similar crystalline structures in the long-range order. However, depending on the reaction, dramatic differences were observed by in situ DXAS in the vicinities of the Cu atoms.
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High-sensitivity low-energy ion scattering (HS-LEIS) analysis was used to elucidate the outermost layer of both functionalized and non-functionalized imidazolium ionic liquids (ILs). The IL outermost layer is composed of all atoms of both cations and anions. The HS-LEIS analyses also allow for quantitative measurement of the thickness of IL overlayers on Au nanoparticles prepared by sputter deposition, which was shown to be a monolayer of ions, as predicted by density functional theory calculations.
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Pd nanoparticles (NPs) were successfully obtained by the reduction of PdCl2 with L-ascorbic acid, whose morphology was revealed by HRTEM to be a worm-like system, formed by linked crystallite clusters with an average short-axis diameter of 5.42 nm. In situ UV-vis absorption measurements were used to monitor their formation, while XPS and XRD characterization confirmed the NPs' metallic state. A straightforward way to support the obtained Pd NPs on activated carbon (AC) was used to prepare a catalyst for NO decomposition reaction. The Pd/AC catalysts proved to be highly active in the temperature range of 323 to 673 K, and a redox mechanism is proposed, where the catalyst's active sites are oxidized by NO and reduced by carbon, emitting CO2 and enhancing their capacity to absorb and dissociate NO.