Entity

Time filter

Source Type


Gutierrez L.,Curtin University Australia | Gutierrez L.,University of the Pacific of Ecuador | Aubry C.,Masdar Institute of Science and Technology | Cornejo M.,ESPOL Polytechnic University | And 2 more authors.
Langmuir | Year: 2015

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, Ca2+ 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. Ca2+ 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. Ca2+ 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. © 2015 American Chemical Society. Source


Niu X.-Z.,King Abdullah University of Science and Technology | Liu C.,King Abdullah University of Science and Technology | Gutierrez L.,King Abdullah University of Science and Technology | Gutierrez L.,University of the Pacific of Ecuador | Croue J.-P.,King Abdullah University of Science and Technology
Water Research | Year: 2014

Photosensitizing properties of different dissolved organic matter (DOM) were investigated according to their performance in singlet oxygen (1O2), triplet state of DOM (3DOM*), and hydroxyl radical (·OH) productions. The photobleaching of DOM solutions after irradiation was characterized by fluorescence excitation-emission matrix and UV-Vis spectroscopy. The photosensitizing properties of pre-irradiated DOM solutions were changed in a sunlight simulator. The performance of DOMs in photosensitized degradation of several contaminants was investigated. For a 20h exposure, the observed degradation rate constant (kobs) of some contaminants decreased as a function of exposure time, and highly depended on the properties of both DOM and contaminant. Degradation of contaminants with lower kobs was more susceptible to DOM photobleaching-induced decrease in kobs. Under the current experimental conditions, the photobleaching-induced decrease of DOM photo-reactivity in contaminant degradation was mainly attributed to indirect phototransformation of DOM caused by the interactions between photo-inductive DOM moieties and photochemically-produced reactive species. Reactive contaminants can inhibit DOM indirect photobleaching by scavenging reactive species, photosensitized degradation of these contaminants exhibited a stable kobs as a result. This is the first study to report DOM photobleaching-induced changes in the simultaneous DOM photosensitized degradation of contaminants and the inhibitory effect of reactive contaminants on DOM photobleaching. © 2014 Elsevier Ltd. Source


Gutierrez L.,Curtin University Australia | Gutierrez L.,University of the Pacific of Ecuador | Aubry C.,Masdar Institute of Science and Technology | Dramas L.,King Abdullah University of Science and Technology | And 3 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

In the current investigation, a rigorous characterization of the high molecular weight (HMW) compounds of Skeletonema costatum (SKC) intracellular organic matter (IOM), including nanomechanical properties, was conducted. HMW SKC-IOM was characterized as a mixture of polysaccharides, proteins, and lipids. Atomic force microscopy (AFM) provided crucial information of this isolate at a nanoscale resolution. HMW SKC-IOM showed highly responsive to solution chemistry: fully extended chains at low ionic strength, and compressing structures with increasing electrolyte concentration in solution. Interestingly, two regions of different nanomechanical properties were observed: (a) Region #1: located farther from the substrate and showing extended polymeric chains, and (b) Region #2: located <10 nm above the substrate and presenting compressed structures. The polymer length, polymer grafting density, and compressibility of these two regions were highly influenced by solution conditions. Results suggest that steric interactions originating from HMW SKC-IOM polymeric structure would be a dominant interacting mechanism with surfaces. The current investigation has successfully applied models of polymer physics to describe the complex HMW SKC-IOM structural conformation at different solution conditions. The detailed methodology presented provides a tool to characterize and understand biopolymers interactions with surfaces, including filtration membranes, and can be extended to other environmentally relevant organic compounds. © 2016 Elsevier B.V. Source


Pei Y.,Curtin University Australia | Jarrett K.,Curtin University Australia | Garces L.G.,Curtin University Australia | Garces L.G.,University of the Pacific of Ecuador | And 6 more authors.
RSC Advances | Year: 2016

The synthesis and characterisation of soft matter nanoparticles based on AB diblock copolymers of oligo(ethylene glycol)methyl ether methacrylate (OEGMA) with 3-phenylpropyl methacrylate (PPMA) is described. Reversible addition-fragmentation chain transfer dispersion polymerization formulations that result in polymerization-induced self-assembly (RAFTDP-PISA) in methanol were utilized to access a range of poly(OEGMA-b-PPMA) (p(OEGMA-b-PPMA)) nanoparticles with the sphere-to-worm-to-vesicle order-order transitions being readily observed with increasing average degree of polymerization (Xn) of the pPPMA block for a fixed Xn of 28 for the pOEGMA block. Similarly the effect of total copolymer concentration on the resulting nanoparticle morphology is also demonstrated whereby we highlight how tuning of worm micelle diameters can be accomplished simply by varying the concentration of a formulation. The block copolymer nanoparticles were characterized by size exclusion chromatography (SEC), 1H NMR spectroscopy, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Additionally, we report the first examples utilizing 3D electron tomography and in situ atomic force microscopy (AFM) in methanol as convenient and powerful complementary techniques for the characterization of the resulting soft matter nano-objects with an emphasis on the direct visualization of worm nanoparticles. © 2016 The Royal Society of Chemistry. Source


Fernando F.,Museo de Ballenas | Fernando F.,University of the Pacific of Ecuador | Susana C.,PO Box 09 06 2370 | Susana C.,University of Los Andes, Colombia
Journal of Cetacean Research and Management | Year: 2012

Information on the genetic characterisation of humpback whales (Megaptera novaeangliae) wintering off Ecuador (Breeding Stock G) is presented. Mitochondrial DNA was extracted and sequenced from 230 skin samples collected between 2002 and 2008 to establish the genetic diversity of this population. From 182 usable samples, 41 different haplotypes were found, eight of which were new and unique. Haplotype diversity (h ± SD) was estimated to be 0.922 ±0.012 and the nucleotide diversity (π ± SD) 0.019 ± 0.009. A comparison with other areas within the Southeast Pacific (Colombia and Magellan Strait) and the Antarctic Peninsula suggested panmixia within Breeding Stock G, even though significant differentiation was found with Magellan Strait (p < 0.0001 in both FSTand ΦST). An additional analysis with the exact test of population differentiation showed significant differences in haplotype frequencies between breeding areas in Ecuador and southern Colombia (p <0.01), suggesting some level of stratification at breeding grounds as supported by photo-identification studies. The Ecuadorian dataset included haplotypes reported in all three Southern Hemisphere ocean basins indicating recent gene flow within the Southern Hemisphere. The population showed a male-biased sex ratio in adult animals of 2.16:1. Further research and a larger number of samples from breeding areas in the north (Panama and Costa Rica) are required to appropriately assess the extent of structure in this population. Source

Discover hidden collaborations