Mauricio Cornejo

Citrate-Coated Silver Nanoparticles Interactions with Effluent Organic Matter: Influence of Capping Agent and Solution Conditions

Fate and transport studies of silver nanoparticles (AgNPs) discharged from urban wastewaters containing effluent organic matter (EfOM) into natural waters represent a key knowledge gap. In this study, EfOM interfacial interactions with AgNPs, and their aggregation kinetics were investigated by atomic force microscopy (AFM) and time-resolved dynamic light scattering (TR-DLS), respectively. Two well-characterized EfOM isolates, i.e., wastewater humic (WW humic) and wastewater colloids (WW colloids, a complex mixture of polysaccharides-proteins-lipids), and a River humic isolate of different characteristics were selected. Citrate-coated AgNPs were selected as representative capped-AgNPs. Citrate-coated AgNPs showed a considerable stability in Na(+) solutions. However, Ca(2+) ions induced aggregation by cation bridging between carboxyl groups on citrate. Although the presence of River humic increased the stability of citrate-coated AgNPs in Na(+) solutions due to electrosteric effects, they aggregated in WW humic-containing solutions, indicating the importance of humics characteristics during interactions. Ca(2+) ions increased citrate-coated AgNPs aggregation rates in both humic solutions, suggesting cation bridging between carboxyl groups on their structures as a dominant interacting mechanism. Aggregation of citrate-coated AgNPs in WW colloids solutions was significantly faster than those in both humic solutions. Control experiments in urea solution indicated hydrogen bonding as the main interacting mechanism. During AFM experiments, citrate-coated AgNPs showed higher adhesion to WW humic than to River humic, evidencing a consistency between TR-DLS and AFM results. Ca(2+) ions increased citrate-coated AgNPs adhesion to both humic isolates. Interestingly, strong WW colloids interactions with citrate caused AFM probe contamination (nanoparticles adsorption) even at low Na(+) concentrations, indicating the impact of hydrogen bonding on adhesion. These results suggest the importance of solution conditions and capping agents on the stability of AgNPs in solution. However, the characteristics of organics would play a crucial role in the fate and transport of these nano contaminants in urban wastewaters and natural water systems.

Synthesis, characterization and experimental, theoretical, electrochemical, antioxidant and antibacterial study of a new Schiff base and its complexes

A new Schiff base ligand was synthesized by reaction of salicylaldehyde with 1,6-bis(4-chloro-2-aminophenoxy)hexane. Then the Schiff base complexes were synthesized by metal salts and the Schiff base. The metal to ligand ratio of metal complexes was found to be 1:1. The Cu(II) complex is proposed to be square planar and the Co(II), Ni(II), Mn(II) and Zn(II) complexes are proposed to be tetrahedral geometry. The Ti(III) and V(III) complexes are proposed to be a capped octahedron in which a seventh ligand has been added to triangular face. The complexes are non-electrolytes as shown by their molar conductivities (ΛM). The structure of metal complexes is proposed from elemental analysis, FT-IR, UV-vis, magnetic susceptibility measurements, molar conductivity measurements, Mass Spectra and thermal gravimetric analysis. In addition antimicrobial and antioxidant studies, cyclic voltammetry of the complexes, theoretical 1H NMR and HOMO-LUMO energy calculations of the new di-functional ligand were done.

Hydration and strength evolution of air-cured zeolite-rich tuffs and siltstone blended cement pastes at low water-to-binder ratio

Abstract This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ~45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.

Hydration process of zeolite-rich tuffs and siltstone-blended cement pastes at low W/B ratio, under wet curing condition

An extensive study in blended cement pastes that comprised two different experimental settings was carried out so as to analyse the hydration process and compressive strength evolution up to 91 days. The aim of this study was to understand the hydration process using zeolite-rich tuffs and siltstone as supplementary cementitious materials at low water-to-binder ratio (W/B = .3) under wet curing condition. It was observed that there were two competing reactions, i.e. pozzolanic reaction and carbonation, during the hydration process, thus leading to a decrease in the content of calcium hydroxide (CH); however, carbonation played a more important role than the pozzolanic reaction in consuming it at the given W/B ratio. The total amount of CH consumed by pozzolanic reaction was likely around 8%, while carbonation transformed around 19% of the total amount of CH at 91 days. Although fully hydrated cement paste incorporates .23 g of water per g of cement, only 60% of this value was used at such a W/B ratio. In addition, the amount of normalised water in hydrates increased as the dosage increased by factor of .158% per 1% of dosage. Finally, the optimal dosages at which Zeo1, Zeo2 and Limo showed the highest compressive strength were in the ranges of 12.5–15%, 17.5–20% and 10–12.5%, respectively .

Phase Transformation of Amorphous Rice Husk Silica

This work aims at assessing the crystallization process of amorphous silica from rice husk (RH) by in situ X-ray diffraction, upon heating up to 1450 °C in a high-temperature chamber. The study includes microstructural characterization by transmission electron microscopy. The work was conducted on rice husk ash (RHA), obtained by combustion of RH at 650 °C with and without leaching in 1 N HCl solution, obtaining samples with variable impurity content. The results showed that crystallization of RHA amorphous silica upon continuous heating occurred at higher temperatures compared to the isothermal one, considering the sample purity. The type of polymorph silica identified in the samples during continuous heating consisted of cristobalite or a combination of cristobalite and tridymite depending on the impurity levels in the samples. The study revealed silica crystallites with spherical shape nucleated by a dominant homogeneous mechanism. The size of crystallites ranges from around 2 nm to 20 nm. Larger particles nucleated on impurities and constituted by combinations of P, Ca, K, Mg, and Na were also observed.

Non-Born–Oppenheimer electron, nuclear and nuclear–electron second-order density matrices for exactly solvable four-particle model system

AbstractProperties of the non-Born–Oppenheimer two-matrix are examined for four-particle systems of the Coulomb–Hooke and Moshinsky types. We obtain for both these models explicit closed-form analytic expressions for the electron and nuclear 2-RDM. An explicit expression is also obtained for the electron–nuclear 2-RDM in the Moshinsky case, which shows coupling between the electron and nuclear coordinates.

Análisis del Ciclo de Vida de la Producción de Cemento a Base de Zeolitas a Escala de Laboratorio

Resumen–. Este estudio busca servir de base para el desarrollo sostenible en la industria del cemento y la construccion, ambas implican impactos al medio ambiente como consecuencia de la creciente demanda de sus servicios y productos. La preocupacion por estos efectos adversos al desarrollo sostenible, lleva a desarrollar tecnologias mas eficientes en la industria cementera, pero aun hay muchos problemas y consecuencias latentes; en busca de soluciones, se propone la produccion de cemento desde fuentes alternativas de materia prima, en este caso de zeolitas, y medir el impacto que esto conlleva al medio ambiente. Para realizar esta cuantificacion se utilizo la metodologia de analisis de ciclo de vida (ACV). Se observa que la carga ambiental de este procedimiento es mayor que la del cemento Portland ordinario (CPO), pero esto se debe a la escala en que se realizo el estudio, y esta podria verse menguada cuando el procedimiento se realice a escala industrial. Palabras clave-zeolitas, sostenible, LCA, cemento, construccion.