Correction: A study of the depth and size of concave cube Au nanoparticles as highly sensitive SERS probes.

Correction for 'A study of the depth and size of concave cube Au nanoparticles as highly sensitive SERS probes' by J. M. Romo-Herrera et al., Nanoscale, 2016, 8, 7326-7333.

A study of the depth and size of concave cube Au nanoparticles as highly sensitive SERS probes.

High and uniform near fields are localized at the eight similar sharp corners of cubic gold nanoparticles. Moreover, by introducing concavity in the particle lateral planes, such field intensities can be further increased and tuned in the near infrared region without altering the overall size of the nanoparticles. Herein, we perform a thorough investigation of the morphological, crystallographic and plasmonic properties of concave gold nanocubes (GNCs) in the sub-70 nm size range, for their potential application as highly efficient SERS substrates in size-limiting cases. Theoretical calculations indicate that the highest increment of the near-field is located at the eight sharp tips and, interestingly, a medium near-field increment is also activated over the volume next to the concave surface. Remarkably, the plasmonic response of the concave cubic morphology showed great sensitivity to the concavity degree. Experimental SERS analysis nicely matches the outcome of the theoretical model, confirming that medium-sized concave GNCs (35 nm side length) possess the highest SERS activity upon excitation with a 633 nm laser, whereas larger 61 nm side concave GNCs dominate the optical response at 785 nm. Due to their size-intensity trade off, we envision that such small concave gold nanocubes can provide a highly active and efficient SERS platform for size-limiting applications, especially when near infrared excitations are required.

Insulating Carbon Nanotubes by Atomic Layer Deposition for Electrical Wiring Purposes.

Carbon Nanotubes (CNTs) are coated by an insulator (Al2O3) shell using the atomic layer deposition (ALD) technique. This is achieved in large quantities (tens of milligrams per batch) for electrical wiring purposes. Here we present a transmission electron microscopy (TEM) characterization together with a detailed high resolution elemental analysis by in-column energy dispersive X-ray spectroscopy (EDXS). An excellent conformality of the insulator around the CNTs is obtained. Moreover, the elemental maps show the composition of the shell while the line scan analyses demonstrate an abrupt shell-CNT interface achieved by our ALD approach.

Molecular assembly of multi-wall carbon nanotubes with amino crown ether: synthesis and characterization.

Synthetic methodology and physicochemical characterization of multi-wall carbon nanotubes (MWCNTs) functionalized with a crown ether molecule is reported. The MWCNTs were synthesized by spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. The nanotubes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxidation of MWCNTs was carried out by 8 h of sonication in a mixture of sulfuric and nitric acid (3:1). The MWCNT-COOH was amidated with 4-aminobenzo-15-crown-5 under mild reaction conditions using N,N'-dicyclohexylcarbodiimide and dimethylaminopyridine as catalyst and dimethylformamide as solvent, at room temperature for 24 h. The amidation product was characterized by scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a mass spectrometry study to determine the fragmentation pattern being m/z 309, 177 and 149 the most important ions.

Growth of hydroxyapatite nanoparticles on silica gels.

Synthetic, hydroxyapatite nanoparticles were grown on the surface of silica gels. The synthesis of those nanoparticles was obtained by immersing silica gels in a simulated body fluid (SBF) at 37 degrees C. The SBF was replaced every week to keep constant the Ca and P ion concentration and subsequent growth of hydroxyapatite was evaluated after 1-6 weeks of total soaking time in SBF. Hydroxyapatite nanoparticles were observed by scanning electron microscopy (SEM) on the surface of silica gel samples and confirmed by energy dispersive X-ray spectroscopy (EDS), Fourier Transform Infra Red Spectroscopy (FTIR) and powder X-ray Diffractometry (XRD) analysis. These particles show a regular shape and uniform size every week, keeping within the nanoscale always. Both the size and morphology of hydroxyapatite nanoparticles obtained are the result of the use of different chemical additives in the synthesis of silica gels, since they affect the liquid-to-solid interface, and the growth could correspond to a diffusion limited aggregation (DLA) process. A more detailed analysis, with higher magnifications, showed that hydroxyapatite nanoparticles are not solid spheres, showing a branched texture and their size depends on the scale and resolution of the measure instrument.

Synthesis and structural characterization of Mo-Ni-W oxide nanostructures.

In this work, we report the synthesis and characterization of Mo-Ni-W oxides. The precursor was prepared from an aqueous solution of ammonium heptamolibdate, ammonium metatungstate, and nickel nitrate with an atomic ratio of 1:1:1 (Mo:W:Ni). The solution was then transferred to a Teflon-lined stainless steel autoclave and heated to 200 degrees C and left at this temperature for 48 h. The resulting material was then washed and dried. The morphology and elemental composition were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The porosity was studied by the Brunauer, Emmett, and Teller method. The materials synthesized at 200 degrees C remained amorphous and had a specific surface area of 114 m2/g with pore size of 34 A. The average length was 1 microm and the average diameter was 60 nm. The crystalline phase of synthesized material corresponded to W0.4Mo0.6O3 and WO3. After annealing at 550 degrees C for two hours, the material was polycrystalline with a segregated structure of MoO3, WO3; NiMoO4 was observed. The sublimation of the molybdenum oxide was evident when annealed at 900 degrees C for two hours and finally two crystalline phases of material remained; roundish WO3 and elongated particles of NiWO4.

Synthesis of Ni-Mo-W sulfide nanorods as catalyst for hydrodesulfurization of dibenzothiophene.

Two trimetallic sulfurs, MoWNiS and MoWSNi, were synthesized to be used as a catalyst in hydrodesulfurization reactions. The mixed oxide mesoporous nanostructured MoO3 -WO3 with an Mo:W atomic ratio of 1:1 was used as the precursor. The first catalyst was prepared by impregnating nickel in the oxide precursor and then subsequent sulfiding with an H2S/H2 mix at 400 degrees C for 2 hours. The second catalyst was prepared by sulfiding the precursor and then impregnating the nickel, and finally reducing the material with a H2/N2 at 350 degrees C. In both catalysts the Mo:W:Ni atomic ratio was maintained at 1:1:0.5. The materials obtained were characterized by physical adsorption of nitrogen, X-ray diffraction, scanning electron microscopy, transmission electron microscopy. Furthermore, the materials obtained were evaluated by a dibenzothiophene hydrodesulfuration reaction. The diffraction patterns show that both materials are polycrystalline and mainly of MoS2 and WS2 phases.

Synthesis and characterization of porous Mo-W oxide nanostructures.

The present study reports the synthesis method, microstructure characterization, and thermal stability of nanostructured porous mixed oxide (MoO3-WO3) at 550 and 900 degrees C of annealing. The material was synthesized using a hydrothermal method. The precursor was prepared by aqueous solution using ammonium heptamolibdate and ammonium metatungstate, with an atomic ratio of Mo/W = 1. The pH was adjusted to 5, and then the solution was transferred to a teflon-lined stainless steel autoclave and heated at 200 degrees C for 48 h. The resultant material was washed using deionized water. The specific surface area, morphology, composition, and microstructure before and after annealing were studied by N2 physisorption, scanning electron microscopy (SEM), analytical transmission electron microscopy (TEM), and X-Ray diffraction (XRD). The initial synthesized materials showed low crystallinity and high specific surface area around (141 m2/g). After thermal annealing the material showed higher crystallinity and diminished its specific surface area drastically.

Co(Ni)/MoS2 nanostructured catalysts for the hydrodesulphurization of dibenzothiophene.

In this study Co(Ni)/MoS2 unsupported nanocatalysts (nanorods and nanoribbons) were synthesized with Co(Ni)/(Co(Ni) + Mo) = 0.3, 0.5 molar ratios for Co and Ni respectively. First the alpha-MoO3 nanostructures were impregnated with an aqueous solution of Co(Ni)Cl2 x 6H2O or Co(Ni)(NO3)2 x 6H2O, then were treated for 2 h at 473 K, and finally the precursors were activated under a H2S/H2 mixture (15% v/v H2S) by ramping the temperature from room temperature to 773 K and keeping it at that value for 2 h. The resulting materials were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, specific surface area and X-ray photoelectron spectroscopy, and tested as catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). It was found that these materials presented specific surface areas below 25 m2/g. The catalytic test showed that only when Co is added a promoter effect is observed compared with MoS2 unpromoted catalysts. Among the materials prepared, the Co/MoS2 catalyst made from cobalt chloride presented the highest catalytic activity (6.95 mol s(-1) g(-1)catalyst) for the HDS of DBT. The selectivity for the latter indicated a clear preference for the direct desulphurization over the hydrogenating pathway.

Simplified route to multi-walled carbon nanotube synthesis by aerosol assisted chemical vapor deposition.

Uniform multi-walled carbon nanotubes (MWCNTs) were obtained decomposing toluene inside of fused silica tubing previously covered with Co oxide thin film. The two-step process, ruled successively in the same aerosol assisted chemical vapor deposition (AACVD) set up, constitutes a simplified route to the synthesis of MWCNTs. First, Co oxide thin film was deposited inside of fused silica tubing at 723 K, using a precursor solution of Co acetate in absolute methanol. After Co oxide deposition, the covered tubing was heated up to 1173 K under Ar flow, then a mist of toluene was injected inside the tubing, using also Ar as carrier gas, consequently MWCNTs were obtained in the internal wall of the tubing. The Co oxide film and the MWCNTs were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Uniform and very long MWCNTs (several tens of microm) with diameters around 20 to 100 nm were observed, with the advantage that the content of Co particles inside the nanotube was very low.

Synthesis of multi-walled carbon nanotubes by spray-pyrolysis using a new iron organometallic complex as catalytic agent.

An organometallic catalytic agent ([(Hexyl)4N]3FeCl3Br3) has been synthesized through the reaction of tetrahexylammonium bromide ((Hexyl)4NBr) and iron chloride (FeCl3) aqueous solutions. Multi-walled carbon nanotubes (MWCNTs) were obtained by spray pyrolysis of toluene (carbon source) using the new organometallic compound as catalyst. The synthesized catalytic agent was characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TA) techniques. Spectroscopic results indicated that the new iron organometallic compound has suitable characteristics to grow MWCNTs by spray pyrolysis. The MWCNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The MWCNTs grow in a disordered way without orientation with diameters ranging from 20 to 50 nanometers. XRD patterns exhibit the 2-H graphite characteristics peaks of the MWCNTs.

Growth of multi-walled carbon nanotubes by nebulized spray pyrolysis of a natural precursor: alpha-pinene.

Multi-wall carbon nanotubes (MWCNT) were prepared by spray-pyrolysis of alpha-pinene, a botanical hydrocarbon, and ferrocene as catalyst at 900 degrees C. The MWCNT were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The microscopy studies show the formation of carbon nanotubes with diameters between 20 and 30 nm and length greater than one hundred microns. Nanoparticles were detected outside and inside the nanotubes and were identify as metallic iron and iron carbide, respectively. Raman spectroscopy reveals that the alpha-pinene grown carbon nanotubes are graphitized showing both the D and G bands at 1335 cm(-1) and 1585 cm(-1) respectively.

Optimization of the synthesis of alpha-MoO3 nanoribbons and hydrodesulfurization (HDS) catalyst test.

An optimized process for synthesis of alpha-MoO3 nanoribbons characterized by uniform morphology and composition was carried out. The optimized process turned out to be the aging of a precursor of an aqueous solution of ammonium heptamolybdate for a week under constant stirring at 333 K; followed by hydrothermal treatment for 36 h up to 48 h at 473 K. The dimensions of the nanoribbons were between 5 and 10 microm in length and a width between 100 and 600 nm. The thickness was between 60 and 200 nm. This material was tested for hydrodesulfurization (HDS) of dibenzothiophene (DBT) by in situ activation and showed its catalytic activities to be similar to those of unsupported MoS2 catalysts. The structure and morphology of these materials was characterized by analytical transmission electron microscopy, scanning electron microscopy, and X-ray diffraction using the Rietveld method to determine the quantitative crystallographic phases. A chemical semiquantitative analysis was carried out by energy dispersive spectroscopy and a qualitative analysis was carried out by electron energy loss spectroscopy.

Synthesis of MoS(2) nanorods and their catalytic test in the HDS of dibenzothiophene.

Partially sulfided nanostructures were synthesized by direct sulfurization of alpha-MoO(3) nanorods using a mixture of H(2)S/H(2), 15 vol%, at several temperatures (400, 500, 600, 700, and 800 degrees C). These materials were tested as catalysts in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and characterized by specific surface areas using the expression developed by Brunauer, Emmett, and Teller (BET equation), x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM images show a gradual evolution from a smooth surface to a rough material, presenting some type of holes all over the particles, but keeping their rod-like structure throughout sulfidation. The results of evaluating the catalysts in the HDS of DBT showed that the best temperature for sulfidation is 500 degrees C. In all samples, a higher selectivity for hydrogenation over sulfur removal was observed.