Natural Organic Macromolecules Research Articles

TiO2 (Core)/Crumpled Graphene Oxide (Shell) Nanocomposites Show Enhanced Photodegradation of Carbamazepine.

The presence of pharmaceuticals and personal care products (PPCPs) in aquatic systems is a serious threat to human and ecological health. The photocatalytic degradation of PPCPs via titanium oxide (TiO2) is a well-researched potential solution, but its efficacy is limited by a variety of environmental conditions, such as the presence of natural organic macromolecules (NOM). In this study, we investigate the synthesis and performance of a novel photoreactive composite: a three-dimensional (3D) core (TiO2)-shell (crumpled graphene oxide) composite (TiGC) used as a powerful tool for PPCP removal and degradation in complex aqueous environments. TiGC exhibited a high adsorption capacity (maximum capacity 11.2 mg/g, 100 times larger than bare TiO2) and a 30% enhancement of photodegradation (compared to bare TiO2) in experiments with a persistent PPCP model, carbamazepine (CBZ). Furthermore, the TiGC performance was tested under various conditions of NOM concentration, light intensity, CBZ initial concentration, and multiple cycles of CBZ addition, in order to illustrate that TiGC performance is stable over a range of field conditions (including NOM). The enhanced and stable performance of TiCG to adsorb and degrade CBZ in water extends from its core-shell composite nanostructure: the crumpled graphene oxide shell provides an adsorptive surface that favors CBZ sorption over NOM, and optical and electronic interactions between TiO2 and graphene oxide result in higher hydroxyl radical (•OH) yields than bare TiO2.

Crumpled graphene balls adsorb micropollutants from water selectively and rapidly

Thousands of anthropogenic materials (e.g., micropollutants, MPs) are discharged to surface and groundwaters daily and their wide distribution potentially threatens ecological and human health. Granular activated carbon (GAC) is a widely used adsorbent to remove MPs, but with several deficiencies such as slow adsorption kinetics and hindered performance by natural organic macromolecules (NOM). Here, we detail the synthesis of a novel adsorbent, three-dimensional (3D), stacking-resistant, crumpled graphene oxide balls (CGBs) and their adsorbent properties by using eight persistent MPs under relevant environmental conditions. CGBs displayed 4–8 times greater adsorption capacity than GAC for seven of the eight MPs on a surface area equivalent basis. Kinetic experiments show that seven of eight MPs in a mixture reach >90 % removal efficiency after 15 min contact time (compared to 5–10 % removal of GAC). CGB adsorption performance was also tested as a function of varying NOM concentration, with other realistic environmental conditions of pH, ionic strength, water hardness, and alkalinity, to demonstrate that CGB adsorption of MPs is not adversely affected by NOM even at high concentrations and is stable over a range of field conditions. These findings demonstrate that CGBs are potentially a powerful adsorbent for micropollutant removal in complex aqueous environments.

Nanofiltration scaling influenced by coexisting pollutants considering the interaction between ferric coagulant and natural organic macromolecules

The aim of present study was to evaluate the effects of the interaction between ferric coagulant and natural organic macromolecules (NOMs) on gypsum scaling during nanofiltration. Both crystallization process and membrane flux behavior were taken into consideration. Although bulk crystallization could be enhanced by ferric coagulant and humic acid (HA), it was hindered by the mixture of these coexisting pollutants due to their interaction in aqueous solution. According to the variation in zeta potential and the prediction with the NICA-Donnan model, Fe3+ could compete with Ca2+ for binding to HA, while the interaction between coagulant and HA reduced the concentration of active ingredients in the coagulant which could enhance scaling development. FTIR-ATR spectra showed that ferric coagulant and NOMs could promote the attachment of each other on membranes. Unlike bulk crystallization, surface crystallization could be enhanced by the combination of HA and ferric coagulant on nanofiltration membranes. Therefore, both ferric coagulant and HA could increase scaling layer resistance, and there were synergistic effects on aggravating the flux decline between them. Moreover, the effects of salt saturation and system pressure on coagulant-influenced gypsum scaling in nanofiltration were also investigated. Modified Hermia’s models were applied to theoretically verify the membrane fouling mechanisms. In addition, ferric coagulant was found to decrease the retention efficiency of ions and atrazine by nanofiltration membranes by weakening the steric hindrance.

A Comparison between the Oil Removal Capacity of Polymer-Coated Magnetic Nanoparticles in Natural and Synthetic Environmental Samples.

Oil spills can have dramatic impacts on the environment. The limitations of current oil remediation techniques have inspired researchers to study the application of nanotechnology for oil cleanup. Previously, we reported essentially 100% removal of a reference MC252 oil using polyvinylpyrrolidone (PVP)-coated iron oxide nanoparticles (NPs) from oil-water mixtures under a wide range of environmentally relevant conditions. Our previous results showed that in the synthetic water samples, the concentration of cations and natural organic macromolecules (NOM) can significantly affect the oil removal efficiency of NPs. Here, we studied the application of these NPs for oil removal from natural freshwater samples and compared the results with the synthetic water samples with the same concentrations of major ions and NOM. For both natural and synthetic samples, concentrations of NOM, calcium, and magnesium were positively correlated with oil removal ( p-value <0.05). NPs show an average of 30% higher oil removal efficiency from natural samples compared to the synthetic samples. Using up to 50 ppm of NP, essentially 100% oil removal was observed under most conditions specially hardwater samples (initial 0.15 g L-1 oil concentration). Results show that these NPs are a facile and reliable technique for removing oil under realistic conditions.

A High Resolution Study of Dynamic Changes of Ce2O3 and CeO2 Nanoparticles in Complex Environmental Media.

Ceria nanoparticles (NPs) rapidly and easily cycle between Ce(III) and Ce(IV) oxidation states, making them prime candidates for commercial and other applications. Increased commercial use has resulted in increased discharge to the environment and increased associated risk. Once in complex media such as environmental waters or toxicology exposure media, the same redox transformations can occur, causing altered behavior and effects compared to the pristine NPs. This study used high resolution scanning transmission electron microscopy and electron energy loss spectroscopy to investigate changes in structure and oxidation state of small, polymer-coated ceria suspensions in complex media. NPs initially in either the III or IV oxidation states, but otherwise identical, were used. Ce(IV) NPs were changed to mixed (III, IV) NPs at high ionic strengths, while the presence of natural organic macromolecules (NOM) stabilized the oxidation state and increased crystallinity. The Ce(III) NPs remained as Ce(III) at high ionic strengths, but were modified by the presence of NOM, causing reduced crystallinity and degradation of the NPs. Subtle changes to NP properties upon addition to environmental or ecotoxicology media suggest that there may be small but important effects on fate and effects of NPs compared to their pristine form.

Evaluation of polymer-coated magnetic nanoparticles for oil separation under environmentally relevant conditions: effect of ionic strength and natural organic macromolecules

Fluorescence spectra for oil–water mixtures before and after oil removal using PVP-coated magnetic nanoparticles under different environmentally relevant conditions.

Foreword to the Research Front on ‘Nano 2014'

This Research Front is dedicated to cutting-edge research on nanoparticles (NPs) and is based on research presented at the 9th International Conference on Environmental Effects of Nanoparticles andNanomaterials (ICEENN) held in Columbia, South Carolina, USA, in September 2014. The conference was attended by nearly 150 people from 17 countries, with a series of excellent invited and other oral presentations and poster presentations. In addition to a high-level academic conference, a panel discussion was organised considering the future environmental and health implications of ‘next generation’ nanoparticles, with a focus on nanohybrids. Nanohybrids are a key development in nanotechnology, which have also been discussed within the pages of this journal. Finally, a highly successful training course and a public day, attended by over 100 people from the public and local schools were organised. The papers presented here originated from the conference but went through the usual stringent peer-review process and represent some of the best work on environmental nanoscience and the ecotoxicology of nanoparticles available. The Research Front starts with Cross et al. who give a detailed review of the fate, behaviour and impacts of inorganic nanoparticles in sediments, concludingwith a discussion of the current state of the art and a priority list for much needed future research. The issue continues with methodological development and data for metal NP concentrations in earthworms, allowing bioaccumulation to be quantified. Khan et al. further present a study of the critical effects on aggregation of carbon nanotube (CNT) chirality, an important physical property of CNTs. The paper illustrates the significance of NP physico-chemistry on environmental fate and toxicology. This collection concludes with two papers considering and quantifying bioaccumulation and bioavailability. Kalman et al. investigated biouptake rates of Ag NPs with different coatings through aqueous and dietary exposures, showing food was the primary pathway for uptake in Daphnia magna. Goodhead et al. investigated the bioavailability of ceria NPs in fish, showing that experimental conditions played a significant role in biouptake, with natural organic macromolecules enhancing uptake to gill tissue in particular. I thank the authors for their excellent contributions to the Research Front. I also thank the members of the ICEENN series organising committee (Greg Goss, Richard Handy, Frank von der Kammer, Steve Klaine, Jamie Lead, Richard Owen and Eva Valsami-Jones) and the local organising committee (Mohammed Baalousha, Alan Decho, Lee Ferguson, Ann Johnson, Srikanth Nadadur, Omowunmi Sadik and Tara Sabo-Attwood). Thanks are also due to the members of the Center for Environmental Nanoscience and Risk for on-site organisation.

Synthesis of NOM-Capped Silver Nanoparticles: Size, Morphology, Stability, and NOM Binding Characteristics

Silver nanoparticle synthesis produced by green chemistry methods shows potential in areas such as medical applications and biosensing. Here, we show that natural organic macromolecules (NOM) can be used to synthesize and stabilize silver nanoparticles (AgNPs). Silver nitrate was mixed with one of four NOM types that formed NPs by chemical reduction with either ascorbic acid or sodium borohydride. Resulting NP suspensions were characterized by size, morphology, and stability. A range of particle sizes were obtained, but no clear trends were observed for chemical type or NOM concentration. One reaction (10 mg L–1 HA, Ag +, and Na BH4) produced monodisperse and stable (after three months storage) AgNPs of 10–20 nm, while others such as succinoglycan could be relevant to application in other fields, e.g., medical research. This method indicates the potential to produce relatively stable AgNPs coated with a number of ligands from sustainable sources that are nontoxic and biocompatible, suitable for environmen...

Chitosan-Coated Octadecyl-Functionalized Magnetite Nanoparticles: Preparation and Application in Extraction of Trace Pollutants from Environmental Water Samples

In the present study, chitosan-coated octadecyl-functionalized magnetite nanoparticles (Fe(3)O(4)-C(18)-chitosan MNPs) are synthesized and used as an adsorbent to extract trace analytes from environmental water samples. The magnetic nanoparticles, 20 nm in diameter, are of uniform size and have a high magnetic saturation value of 52 emu g(-1), which endue the adsorbent with a large surface area and convenience of isolation. The anionic pollutants, perfluorinated compounds (PFCs), are trapped by the octadecyl group of the interior hydrophobic layer. The positively charged chitosan polymer coating also contributes to PFC enrichment. At the same time, the coating improves the dispersibility of MNPs in aqueous solution and enhances the anti-interference ability of the adsorbent to natural organic macromolecules in complex samples by size exclusion or electrostatic repulsion. A liquid chromatography-tandem mass spectrometry system is employed in the determination of PFCs after preconcentration with the MNP adsorbent. The predominant factors affecting preconcentration are investigated and optimized. Under the selected conditions, concentration factors of 1000 are achieved by extracting the analytes from 500 mL of several environmental water samples and concentrating the eluants to 0.5 mL with a nitrogen flow. The method detection limits obtained for perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), perluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), and perfluorotetradecanoic acid (PFTA) in Gaobeidian wastewater are 0.24, 0.093, 0.24, 0.14, 0.075, 0.24, and 0.17 ng L(-1), respectively. Recoveries of PFOA, PFOS, PFNA, PFDA, PFUnDA, PFDoDA, and PFTA are in the ranges of 88-108%, 63-112%, 79-109%, 56-107%, 66-106%, 56-106%, and 66-103% for four spiked water samples with low relative standard deviation (2-8%), which indicates good method precision. The advantages of this novel adsorbent are high extraction efficiency, anti-interference, and convenient operation.

Particle size distributions of silver nanoparticles at environmentally relevant conditions

Silver nanoparticles (Ag NPs) are becoming increasingly popular as antimicrobial agents in consumer goods with consequent risk to environmental health from discharges. Environmentally relevant fate and transport investigations are limited but essential to gain understanding towards bioavailability and toxicology. In this study, monodisperse 15 nm citrate-stabilised Ag NPs were synthesised, characterised and then fractionated by flow field-flow fractionation (FlFFF) at environmentally relevant conditions (pH 5 or 8, presence of natural organic macromolecules (NOM) and presence of sodium or calcium). At low ionic strength, Ag NPs particle size increased as pH increased from 5 to 8. However, changing the ionic strength from 10 −3 to 10 −2 M Na increased instability of the Ag NPs, and loss of peak at pH 5 but in the presence of humic substance (HS), a reduction in NP size was seen, most likely due to a reduction in the diffuse layer. The presence of Ca 2+ ions, at the higher ionic strengths caused complete loss of the solution Ag NPs with or without HS, most likely due to aggregation. At the lower Ca 2+ ionic strength the Ag NPs were still unstable, but again, in the presence of HS the NPs were largely dispersed. The presence of HS improved stability of Ag NPs under these conditions by forming a surface coating resulting in both steric and charge stabilisation. This work implies that Ag NPs could have long residence times in aquatic systems in the presence of HS potentially resulting in increased bioavailability.

Influence of Humic Acids on the Growth of the Microorganisms Utilizing Toxic Compounds (Comparison between Yeast and Bacteria)

Humic acids, a heterogenic group of natural organic macromolecules with a complex polymeric structure, form a significant part of the soil and water environment. They have a high surface activity, thus they are able to interact with other components in the environment (mineral and microbial cell surfaces, organic and inorganic compounds). This work is focused on humic acid effects on the growth of microorganisms utilizing phenolic compounds as the sole carbon and energy source. For this purpose a bacterial population Rhodococcus erythropolis and a yeast strain Candida maltosa were used. Both microorganisms had been adapted to the degradation of phenol and phenolic compounds for many years. However, a toxic effect of these compounds still occurs. The addition of humic acids into the cultivation medium extended toleration of the bacteria to higher concentrations of phenolic compounds and increased the growth of this microbial population as well. In the case of the yeast, humic acids inhibited the growth. Humic acids easily form an additive layer on the surface of the investigated microorganisms. The generated humic acid layer can probably serve as a transport barrier and thus influence the growth of microbial populations.

Characterization of humic acids fractionated by ultrafiltration

Humic acid (HA) is a mixture of natural organic macromolecules having a range of physicochemical properties and exhibiting different reactivities in environmental systems. The objective of this study was to characterize chemical and molecular heterogeneity of HA by fractionating a bulk HA (BHA) into a series of subsamples, each having relatively homogeneous properties. The BHA was base extracted from Pahokee peat and was fractionated into eight fractions using an ultrafiltration apparatus with membranes having seven molecular cut-offs. The eight HA fractions obtained have apparent molecular sizes of <1, 1–3, 3–5, 5–10, 10–30, 30–100, 100–300 and >300 kDa, respectively, and their molecular size distributions were further calibrated using high performance size exclusion chromatography (HPSEC). The chemical and structural properties of the eight HA fractions were characterized systematically using elemental analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), Fourier transform infrared (FTIR), ultraviolet–visible (UV–vis), and solid state 13C-nuclear magnetic resonance ( 13C-NMR) spectroscopy. The results show that each HA fraction has a relatively narrow distribution of molecular sizes on HPLC chromatographs, suggesting that ultrafiltration technique is effective for fractionating broadly heterogeneous humic macromolecules into relatively homogeneous fractions. UV–vis spectroscopy and Py-GC-MS analyses indicate that the fractions with lower molecular weights have more heterogeneous functional groups, greater O/C atomic ratios, and higher contents of oxygen and lignin-derived aromatic structural units. Conversely, the HA fractions with higher molecular weights have lower contents of oxygen and aromatic structural units that correspond to greater H/C and lower O/C atomic ratios. This study suggests that HAs formed under the same biogeochemical conditions may consist of macromolecules with a range of chemical, structural and molecular properties.

Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites

An electron paramagnetic resonance (EPR) investigation was performed on the insoluble organic matter from the Orgueil and Murchison meteorites and on terrestrial coals with similar elemental composition. A complementary electron nuclear double resonance (ENDOR) study was also carried out. The measured g-factors of the observed paramagnetic radicals in the meteoritic organic matter exhibit a similar correlation with the chemical composition as for the type III (i.e., hydrogen-poor) terrestrial coals. The main result, obtained from EPR saturation and 1H ENDOR enhancement measurements, showed that the effective local concentration in radicals of about 3 to 4 × 10 19 spin.g −1 in the meteoritic organic matter is much higher than the average concentration, hence the occurrence of radical-rich regions accounting for 5% and 20% of the total volume for Murchison and Orgueil, respectively. This heterogeneity of concentration seems to be unique among natural organic macromolecules. It is proposed that these radical-rich regions correspond to pristine parts of the organic matter synthesized in conditions close to those prevailing in the interstellar medium, and which have survived the hydrothermal process on the parent body.

Characterization of NOM-colloid aggregates in surface waters: Coupling transmission electron microscopy staining techniques and mathematical modelling

The role of inorganic colloids and natural organic macromolecules in aquatic and soil systems is essential for our understanding of contaminant and nutrient transport. The submicron organic fraction, although important in terms of total surface area, is poorly electron-dense and thus not susceptible to observation by transmission electron microscopy. Several staining techniques were therefore developed to enable the observation of the submicron aggregate fraction in natural waters. Lead and silver based stains were especially successful in increasing the contrast of previously unobservable organic macromolecules. Computer simulations were developed for the interpretation of observed aggregate structures in natural waters. Based on the TEM observations, modelling was employed to examine the formation kinetics and structural characteristics of aggregates under different physicochemical conditions. The modelling results offered insight into the underlying mechanisms and important factors influencing the aggregation processes.

Particle—particle interactions in aquatic systems

The significance of particles in the transport and fate of substances in aquatic environments is illustrated and present knowledge of the speciation and structure of interfaces in these environments is assessed. The importance of particle deposition and aggregation in ground water aquifers and in lakes is illustrated. Attention is focussed on the adsorption of natural organic macromolecules and polyelectrolytes at interfaces in natural systems and the impacts of these substances on colloidal stability and deposition in natural systems. Finally, the status of present understandings in this area is assessed and directions for future study are proposed.