Edgar Mosquera

ZnO/Ag/CdO nanocomposite for visible light-induced photocatalytic degradation of industrial textile effluents.

A ternary ZnO/Ag/CdO nanocomposite was synthesized using thermal decomposition method. The resulting nanocomposite was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, and X-ray photoelectron spectroscopy. The ZnO/Ag/CdO nanocomposite exhibited enhanced photocatalytic activity under visible light irradiation for the degradation of methyl orange and methylene blue compared with binary ZnO/Ag and ZnO/CdO nanocomposites. The ZnO/Ag/CdO nanocomposite was also used for the degradation of the industrial textile effluent (real sample analysis) and degraded more than 90% in 210 min under visible light irradiation. The small size, high surface area and synergistic effect in the ZnO/Ag/CdO nanocomposite is responsible for high photocatalytic activity. These results also showed that the Ag nanoparticles induced visible light activity and facilitated efficient charge separation in the ZnO/Ag/CdO nanocomposite, thereby improving the photocatalytic performance.

ZnO/Ag/Mn2O3 nanocomposite for visible light-induced industrial textile effluent degradation, uric acid and ascorbic acid sensing and antimicrobial activity

A facile and inexpensive route has been developed to synthesize a ternary ZnO/Ag/Mn2O3 nanocomposite having nanorod structures based on the thermal decomposition method. The as-synthesized ternary ZnO/Ag/Mn2O3 nanocomposite was characterized and used for visible light-induced photocatalytic, sensing and antimicrobial studies. The ternary ZnO/Ag/Mn2O3 nanocomposite exhibited excellent and enhanced visible light-induced photocatalytic degradation of industrial textile effluent (real sample analysis) compared to pure ZnO. Sensing studies showed that the ternary ZnO/Ag/Mn2O3 nanocomposite exhibited outstanding and improved detection of uric acid (UA) and ascorbic acid (AA). It also showed effective and efficient bactericidal activities against Staphylococcus aureus and Escherichia coli. These results suggest that the small size, high surface area and synergistic effect among ZnO, AgNPs and Mn2O3 induced visible light photocatalytic activity by decreasing the recombination of photogenerated electrons and holes, and extending the response of pure ZnO to visible light, enhanced sensing of UA and AA and antimicrobial activity. Overall, the ternary ZnO/Ag/Mn2O3 nanocomposite is a valuable material that can be used for a range of applications, such as visible light-induced photocatalysis, sensing and antimicrobial activity. Therefore, ternary nanocomposites could have important applications in environmental science, sensing, and biological fields.

Influence of oleic acid on the nucleation and growth of 4-N,N-dimethylamino-4-N-methyl-stilbazoliumtosylate (DAST) crystals

A simple method to control the nucleation and morphology of (4-N,N-dimethylamino-4-N-methyl-stilbazoliumtosylate) DAST crystals is explored. At equal concentrations of oleic acid and DAST in methanol, pure DAST crystals with an irregular hexagonal shape are obtained by a solvent evaporation method. The influence of oleic acid on facilitating the growth in specific faces is investigated. The purity of the grown crystal is investigated by powder XRD, NMR and Raman spectroscopy analyses. As a major improvement, we present a method where a preference for the growth of one of the desired faces (010) in the final morphology of the DAST crystal is possible which would be attractive for terahertz generation and detection studies.

The shell effect on the room temperature photoluminescence from ZnO/MgO core/shell nanowires: exciton–phonon coupling and strain

The room temperature photoluminescence from ZnO/MgO core/shell nanowires (NWs) grown by a simple two-step vapor transport method was studied for various MgO shell widths (w). Two distinct effects induced by the MgO shell were clearly identified. The first one, related to the ZnO/MgO interface formation, is evidenced by strong enhancements of the zero-phonon and first phonon replica of the excitonic emission, which are accompanied by a total suppression of its second phonon replica. This effect can be explained by the reduction of the band bending within the ZnO NW core that follows the removal of atmospheric adsorbates and associated surface traps during the MgO growth process on one hand, and a reduced exciton-phonon coupling as a result of the mechanical stabilization of the outermost ZnO NW monolayers by the MgO shell on the other hand. The second effect is the gradual increase of the excitonic emission and decrease in the defect related emission by up to two and one orders of magnitude, respectively, when w is increased in the ∼3-17 nm range. Uniaxial strain build-up within the ZnO NW core with increasing w, as detected by x-ray diffraction measurements, and photocarrier tunneling escape from the ZnO core through the MgO shell enabled by defect-states are proposed as possible mechanisms involved in this effect. These findings are expected to be of key significance for the efficient design and fabrication of ZnO/MgO NW heterostructures and devices.

Influence of TiO2 nanostructures on anti-adhesion and photoinduced bactericidal properties of thin film composite membranes

This work investigates the influence of TiO2 nanostructures on the anti-adhesion and photoinduced bactericidal properties of thin film composite (TFC) membranes. TiO2 nanostructures with different morphologies, nanoparticle size, and crystalline phase contents were incorporated within the membrane structure during the interfacial polymerization process. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and contact angle measurements. Bacterial anti-adhesion tests were performed using Escherichia coli. Bacteria suspensions were incubated in the presence of the modified membranes under three different conditions (dark, UV, and visible light) with the aim to induce photoactivation of the TiO2 nanostructures. The anti-adhesion properties of the membranes were confirmed by fluorescence microscopy using a live/dead bacterial viability kit. XRD, SEM, and EDX analyses confirmed that the TiO2 nanostructures were incorporated into the membrane. This incorporation resulted in TFC membranes exhibiting excellent bacterial anti-adhesion properties, as well as marked bactericidal activity. The anti-adhesion effect can be attributed to the physicochemical properties of the modified membrane surface (mainly hydrophilicity) and the bactericidal effect on the membrane surface was attributed to the photoactivation of TiO2 nanostructures upon irradiation, mainly by UV light. The influence of the morphology and the dispersion capacities of the TiO2 nanostructures on anti-adhesion and photoinduced bactericidal properties of TFC membranes were evidenced. The incorporation of a mixture of nanoparticles and nanorods into the TFC membrane reached higher hydrophilicity, lower roughness and uniform dispersion on the surface membrane improving the anti-adhesion capability and the bacterial degradation performance upon irradiation.

Sol–gel synthesis, structural, optical and magnetic characterization of Ag3(2+x)PrxNb4−xO11+δ (0.0 ≤ x ≤ 1.0) nanoparticles

In this work we have studied the optical and magnetic properties of sol–gel synthesized nanocrystalline Ag3(2+x)PrxNb4−xO11+δ (x = 0.0, 0.50 and 1.0; S1–S3) samples. The structural, morphological, optical and magnetic properties of the nanoparticle were investigated using X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray profile, optical absorbance spectroscopy, vibrating sample magnetometer and electron paramagnetic resonance spectroscopy. The X-ray diffraction results reveal the formation of single-phase monoclinic lattice structure with P2/m in all the samples. The optical absorption spectra indicates charge transfer from O2− to Nb5+ of niobium and 3H4 to 1D2, 3P0, 3P1 and 3P2 of praseodymium (4f2) ions. Magnetic studies reveal that the samples exhibit ferromagnetism at room temperature. EPR lineshapes of the nanoparticles S1–S3 at 77 and 300 K show a broad unresolved isotropic lineshapes due to the relaxation process.

Non-isothermal Characterization of the Precipitation Hardening of a Cu-11Ni-19Zn-1Sn Alloy

The precipitation hardening of a Cu-11Ni-19Zn-1Sn alloy has been studied by means of Differential Scanning Calorimetry (DSC), High-Resolution Transmission Electron Microscopy (HRTEM), and hardness measurements. The calorimetric curves, in the range of temperatures analyzed, show the presence of one exothermic reaction followed by an endothermic one. The exothermic DSC peak is due to the segregation of Cu2NiZn precipitates and it is associated to a noticeable improvement of the mechanical properties of the alloy. The endothermic effect is associated to the dissolution of the Cu2NiZn precipitates into the copper matrix for restoring the starting Cu-11Ni-19Zn-1Sn homogeneous solid solution. The reaction mechanisms of these processes have been proposed from the kinetic analysis of the exothermic and endothermic DSC signals. The results obtained point out that tin plays a decisive role on the precipitation hardening of the alloy, because age hardening is not observed in the case of a Cu-Ni-Zn ternary alloy of similar composition.

Estudio exploratorio II: Identificación de nanopartículas en procesos industriales de soldadura y de minería

espanolSe realizo un estudio exploratorio sobre la exposicion laboral a nanoparticulas en procesos de empresas del sector minero, fundicion y soldadura. Para evaluar la exposicion se utilizo un metodo cualitativo simplificado y un metodo semi-cuantitativo basado en las tecnicas tradicionales de higiene ocupacional y de espectroscopia y microscopia electronica para caracterizar las nanoparticulas en cuanto a composicion elemental, morfologia y tamanos. Se evaluo cualitativamente el riesgo de exposicion a nanoparticulas de silice y hierro, encontrandose una mayor criticidad en los procesos de preparacion de muestras de minerales y de vaciado de colada en moldes de fundicion. El analisis de muestras personales y ambientales evidencio la exposicion de trabajadores a nanoparticulas de silice, hierro, magnesio, aluminio, manganeso, entre otras. La toxicidad de estas depende de la morfologia y via de ingreso (la principal via es por inhalacion). Se identificaron morfologias esfericas e irregulares, asi como nanoalambres, aglomerados, estructuras cristalinas y amorfas, con tamanos bajo 100 nm. El trabajo realizado entrega la composicion elemental y morfologica de las nanoparticulas a los cuales se exponen los trabajadores en los procesos evaluados, junto con el alcance de los metodos de evaluacion y la necesidad futura de realizar estudios cuantitativos para determinar niveles de exposicion y concentraciones. EnglishAn exploratory study on occupational exposure to nanoparticles in processes of mining companies, casting and welding was performed. To assess exposure it was used a simplified qualitative and semiquantitative method based on traditional techniques of occupational hygiene and spectroscopy and electron microscopy to characterize nanoparticles in terms of elemental composition, morphology and size. The risk of exposure to silica nanoparticles and iron was qualitatively assessed, finding a bigger criticality in the process of sample preparation and emptying mineral casting molds. Analysis of personal and environmental samples showed workers exposure to nanoparticles of silica, iron, magnesium, aluminum, manganese, among others. The toxicity of these depends on the morphology and route of entry (the main way is by inhalation). Spherical and irregular morphologies were identified, as well as nanowires, crystalline and amorphous structures with sizes below 100 nm. The work performed gives the elemental composition and morphology of nanoparticles to which workers are exposed in the processes evaluated, along with the scope of the evaluation methods and the future need for quantitative studies to determine exposure levels and concentrations.