1,720,988 research outputs found
Reactions of graphene oxide and buckminsterfullerene in the aquatic environment
Full text linkDue to unique physical and chemical properties, carbon-based nanomaterials, including C60 and graphene oxide, now being used in an increasing number of applications. Considering their widespread use, nanoparticles will inevitably find their way to the natural environment. However, their environmental fate and transport have not been intensively explored, resulting in a general lack of knowledge regarding their risk assessment and life cycle exposure concentrations. To this end, this study has investigated: (i) the photo mineralization of aqu/nC60 clusters under photo irradiation, and (ii) environmental transformation of graphene oxide in the aquatic environment. This study shows that CO2 was produced from aqu/nC60 when exposed to lamp light within the solar spectrum (300-410 nm), suggesting mineralization was indeed occurring to some extent. In addition, the ultraviolet-visible (UV-vis) spectrum and liquid chromatographic separation of photo-irradiated samples indicated that decomposition of C60 occurred. Aqueous graphene oxide suspensions produced reactive oxygen species (ROS), including superoxide anion (O2˙–)and hydrogen peroxide (H 2O2) when exposed to the same lamp light, under oxic conditions. The color of the GO suspension progressed from pale to dark brown during the photoreaction process, consistent with changes in the UV-vis spectrum. Raman spectra showed that the ratio of the ID/IG bands increased as irradiation proceeded, suggesting an increased number of defects (e.g., functional groups and vacancies) on the graphene oxide sheets. These defects may be the sites for ROS production. In dark environments, GO was able to accept electrons from a well know reducing agent and electron donor (NADH), oxidizing NADH to NAD+, and transferring these electrons to molecular oxygen in water, producing the reactive oxygen species (ROS) superoxide anion (O2˙–)and hydrogen peroxide (H 2O2). DNA cleavage was observed in air-satured GO suspensions that contained NADH, suggesting that ROS production could be a mechanism for DNA damage by GO within biological cells. Indirect photochemical reactions involving GO were shown to occur in an experiment in which hydroxyl radicals were generated by the photodecay of hydrogen peroxide. GO was oxidized by ˙OH within a 48 hr irradiation period, as measured by changes in the UV-Vis absorbance spectra over the wavelengths from 300 to 800 nm. Spectral changes were consistent with visible color changes (i.e., fading) from 0 to 48 hours. Hence, both direct and indirect photochemical reactions might greatly affect the lifetime and stability of GO in surface waters
Modeling of the surfactant adsorption to the water-oil interfaces
No full textA model that describes the adsorption of an ionic surfactant to an oil-water interface in the presence of an aqueous electrolyte that shares a common cation with the surfactant was developed, solved numerically, and evaluated with experimental interfacial tension data. The model includes algorithms for three processes: (i) the distribution of surfactant molecules between the interfacial and aqueous phases, (ii) the association of counter-ions with the charged interface, and (iii) the equation of state for the interface that defines the relationship between interfacial composition and interfacial tension. In defining distribution of surfactant between the aqueous and interfacial phases, both the chemical and electrical energies of phase transfer were considered. Calculation of the electrical energy of transfer requires calculating the electrical potential at the interface. In this study, the potential was calculated with both a double layer model (i.e., Gouy-Chapman model) and a triple layer model (i.e., Stern layer model) for ion distribution at and near the interface. The chemical energy of transfer is a measure of the non-ideal chemical interactions at the interfacial and in the aqueous phases and is equal to the ratio of surfactant activity coefficients in both phases. The relationship between the interfacial composition and interfacial tension was defined by the Gibbs equation assuming that only the activity of surfactant at the interface changes with composition at the interface. The overall model was solved numerically and related ionic strength and surfactant dose to interfacial tension, and interfacial surfactant concentration. The model was trained with laboratory and literature data, using a minimum number of adjustable parameters. The data collected in the laboratory consists of measured oil-water interfacial tension for a number of surfactants (all linear alkyl sulfates) at defined ionic strengths regulated with NaCl, with trichloroethylene (TCE) as the representative oil. A major part of this study was characterizing the ratio of surfactant activity coefficients for the interfacial and aqueous phases (i.e., the chemical energy of transfer). Two unique algorithms to describe this ratio were invoked and evaluated. The first algorithm was a simple exponential two-parameter empirical equation. The second was derived based on the Redlich-Kister expansion for describing excess energy. The calculated trend in the chemical energy of transfer was consistent with the trends predicted by both algorithms
Real-time monitoring and automated sampling of Purdue\u27s agricultural fields
No full textCurrently, sampling regimes rely on predetermined time or flow-weighted intervals at which to collect samples. During periods of high flow, such as storm events, automated samplers may run out of sample bottles before the end of the hydrograph, resulting in the loss of data and inaccurate load calculations. In this research, real-time monitoring sensor networks with automated samplers were used to monitor the flowrate in agricultural tile-drains and ditches. By characterizing site specific hydrographs, a model was developed that enabled the datalogger to create storm-specific sampling regimes, resulting in approximately 20 samples for each storm event that resulted in a significant hydrograph. The model uses a power-law relationship for defining each hydrograph’s recession curve and spaces sampling events at flow-weighted intervals over the expected recession. The model’s performance was found to be satisfactory when either average or best-fit values of the two model parameters were used to predict the recession curves. The average error in the cumulative flow represented by each recession sample in the six hydrographs analyzed was less than 10%. The use of this model to create a storm-specific sampling regime eliminated the uncertainty in determining the flow-weighted sampling interval and led to the optimal usage of the sample bottles available in the automated sampler
Evaluation of an in-situ permeable sand cap for remediation of coal tar impacted river sediment
No full textSediment within the Grand Calumet River in Northwest Indiana, adjacent to a former Manufactured Gas plant (MGP) site contains significant amounts of coal tar, consisting largely of mono- and poly-cyclic aromatic hydrocarbons (MAHs and PAHs). A proposed remediation strategy for the impacted reach of the river is to remove the top portion of the sediment and to replace this material with a permeable sand layer (i.e., cap), in an attempt to prevent further contamination of the benthic zone and the river. In this study, the compressibility of the sediment was examined in the laboratory with a drained consolidation test (DCT). In addition, eight sand cap test cells, each with a diameter of 76 cm, were installed in the sediment of the river to evaluate capping as a remediation method. Piezometers were installed within and outside each cell, and water flow through each cell was periodically monitored with a seepage meter. Pore water samples were collected through sampling tubes installed in each cell, and the concentrations of 18 MAHs and PAHs were monitored over time with depth. The compressibility tests demonstrated that consolidation of the sediment increased almost linearly at lower pressures (\u3c 13.8 kPa); however, as higher pressures were imposed (≤ 41.4 kPa), the ratio of consolidation per applied pressure decreased. In the field, the seepage meter measurements generally indicated groundwater discharge, as the sediment pore water generally flowed in the upward direction with Darcy fluxes ranging from -0.9 to 3.2 cm/day. Sand cap pore water concentrations of MAHs and PAHs, monitored over a four month period after test cell installation, were significantly lower near the sand-water interface (i.e., in the new benthic zone) compared to concentrations at the same location in the original sediment
Anionic and nonionic surfactant phase distribution processes in environmentally relevant matrices
No full textThe purpose of this research was to further characterize phase distribution processes of anionic and nonionic surfactants under conditions applicable to soil and groundwater remediation precesses. The interactions of: (1) sorption of a specific nonionic surfactant mixture to soil matrices, (2) precipitation of an anionic surfactant with calcium, (3) counterion binding to micelles, and (4) mixed micelle formation were investigated. Chemical speciation models were developed that calculate counterion binding in pure anionic and mixed anionic/nonionic surfactant systems. In addition, the mixed surfactant model allows for the calculation of precipitation boundaries, as well as the mixed cmc. Sorption of a nonionic surfactant mixture, polyoxyethylene 23 lauryl ether (Brij 35), was investigated with five well characterized soils. The results show that preferential sorption of homologues with long ethylene oxide (EO) chains occurs, likely due to hydrogen bonding between the EO groups and soil matrices. Additionally, adsorption isotherms for all soils revealed a plateau in the isotherm at aqueous phase surfactant concentration equal to the cmc. The association reactions involving counterions and micelles composed of the anionic surfactant, dodecylsulfate, were investigated using ultrafiltration experiments. To access this data, a model was developed while considers specific counterion binding within a Stern layer, with binding constant dependent upon the electrical potential as derived by Poisson-Boltzmann equation. The experimental and model results both show that magnitude of counterion binding is approximately the same for Ca\sp{2+} and Mg\sp{2+} and decreases for the monovalent species, Na\sp{2+}. However, high concentration of Na\sp+ compete for surface area diminishing the ability of the DS\sp- to bind either divalent species. Nevertheless, the change in ionic strength at high concentration of Na\sp+ is enough to lower the cmc such that the hardness tolerance actually increases. Based on the anionic surfactant model, a modified mixed surfactant model was developed which included two additional processes of nonideal mixing in the mixed micelles and precipitation of a divalent counterion with the anionic surfactant. The solubility product relationship and regular solution theory are employed to describe these two processes. The predictions for those mixed systems investigated (i.e., precipitation boundary and mixed cmc) show good agreement between the experimental data and model calculations
A triple-layer, planar coordinate model for describing counter -ion association to micelles
No full textA planar triple layer model describing ion association to micelles composed of the anionic surfactant dodecylsulfate (DS–) was developed and evaluated. The governing Poisson-Boltzmann equation was solved ( i) analytically, and (ii) with a numerical shooting method. The second solution was developed to confirm the accuracy of the first, and because the analytical solution is only valid for symmetrical electrolytes. The latter solution is applicable also to multiple valence counter-ion systems. Because the absolute value of the electrical potential at the micelle surface is so large, the classical Debye-Hückle approximation is invalid and was not made. To evaluate the resulting algorithms, they were incorporated into an overall speciation model that describes surfactant and metal ion equilibria in aqueous solutions, and includes an equation that describes DS– micelle-monomer phase distribution: [special characters omitted] where [DS–]w is the DS– surfactant monomer concentration in the aqueous phase, and also equal to the critical micelle concentration (cmc), e is the elementary charge (1.602 × 10–19 C), Ψs is the Stern layer potential, and k T is the product of Boltzmann\u27s constant and absolute temperature. The Stem layer thickness (λ s), and the Y-intercept of the cmc-electrical potential relationship (K1) were calculated by minimizing residuals between experimental and calculated cmc values over a range of experimental aqueous Na+ concentrations. For sodium dodecylsulfate in NaCl solutions, the analytical model and numerical model provided essentially the same result, the same optimum λ s, and K1 values, and accurate cmc predictions. For this system, λs = 1 Å, and K1 = –4.51. For sodium dodecylsulfate in MgCl2, NaCl electrolyte solutions, the numerical model provided increasing trend of optimum λs for increasing [Mg+2], (λs increases as 10.0, 11.0, 12.0 Å for [Mg+2]w increasing as 0.2, 0.5, 1.0 mM) with optimum K1 as –4.29, –4.22, –4.16 respectively. For sodium dodecylsulfate in AlCl 3, NaCl electrolyte solutions, the numerical model gave similar trend as that in MgCl2, NaCl solutions, while the optimum λ s is 11.0 Å, and optimum K1 is –4. 1. The average errors between the experimental cmc data and the optimal model results are 5.78 %, 3.56 %, 3.11 %, 4.14 %, and 4.62 % for pure NaCl, 0.2 mM, 0.5 mM, 1.0 mM MgCl2 - NaCl and 0.2 mM AlCl 3 - NaCl electrolyte systems solutions, respectively
Modeling soil -water phase transfer processes of aromatic amines
No full textAbiotic loss of aromatic amines from the aqueous phase to soils occurs with an initial rapid loss due to reversible chemical processes, followed by a slow loss due to irreversible reactions. A distributed parameter model (DP model) was developed to account for the short term reversible interactions considered: (a) acid dissociation of the protonated organic base (BH +); (b) partitioning of the nonionic species of aniline (B aq) to soil organic carbon; and (c) ion-exchange on the soil between BH+ and inorganic divalent cations (D2+ = Ca 2+ + Mg2+). This model expresses ion-exchange as separated association reactions for each cation to unoccupied cation exchange sites, with constants KBH and KD. A Gaussian distribution on log KBH values was employed. Aniline and 1-aminonaphthalene 24hr-isotherms measured on three Indiana soils at different pH and added calcium concentration were employed to evaluate this model. Model predictions were compared against the general form of the speciation model in which a singular value of KBH was employed (TS Model). Besides capturing the magnitude and sorption trends observed, the DP model also captures the nonlinearity of 1-aminonaphthalene measured isotherms. A reaction of Baq with irreversible sites (Cir) on the soil was added to the TS model to describe the long-term irreversible reactions of aniline. A kinetic rate constant, kir, and the total concentration of irreversible sites, CT, were employed as adjustable model parameters. A good fit was obtained with a single value of kir for all soils, pH values, and soil-water ratios evaluated. Competition among aromatic amines for ion-exchange sites was modeled by adding a correlation coefficient (ρ) to the DP model. This coefficient relates ion-exchange association constants (KBH) among amines. This model was evaluated by employing 24hr-isotherms constructed at different aniline to 1-aminonaphthalene solute ratios (MR). Results indicate that: (i) competition has a greater effect at low pH values where ion-exchange is the predominant process, and (ii) an inverse correlation between KBH values for aniline and 1-aminonaphthalene exists when these compounds are competing for ion exchange sites
Revisiting the Decay of Monochloramine
Full text linkAn aqueous solution containing predominantly monochloramine can be very complex chemically, as once it is formed, monochloramine can undergo a number of reactions. The loss of monochloramine primarily occurs through monochloramine hydrolysis or through a disproportionation reaction. However, there are only a few research papers that have investigated the kinetics of these two reactions. Some of the findings of these previous studies show inconsistencies with respect to the rate constant values of the reactions. Hence, both of these reactions were studied in depth in this work. In the case of the disproportionation reaction, previous studies have indicated that the presence of a buffer enhances the reaction rate, thought to occur through a general acid catalysed pathway. In this study, the assumption that the reaction proceeds through a general acid catalysed mechanism was re-evaluated, as it can be shown that this mechanism, in some cases, is mathematically identical to a specific acid (H+), general base catalysed mechanism. To test these mechanisms, the rate of the reaction was measured in different buffer systems (carbonate, acetate, phosphate) over a range of pH values from 3 to 5. The change of monochloramine concentration was monitored by measuring the change in light absorbance at wavelengths in the ultraviolet region where monochloramine and dichloramine have absorbance maxima. Whereas the presence of phosphate and acetate buffers increased the reaction rate, there was no rate enhancement in the presence of carbonate buffer. The results of the study showed that the reaction rate is dependent on the total concentration of the buffer, rather than the concentration of either the acid or base form alone. The results also suggest that the reaction may proceed between protonated and neutral monochloramine molecules, consistent with the specific acid catalysed mechanism. The buffer likely catalyses the reaction either by participating in the initial protonation process of monochloramine, or by assisting in the abstraction of a proton, allowing for the transfer of the chlorine atom to the monochloramine from which the proton is abstracted, forming dichloramine. In the case of the hydrolysis reaction, no previous study has been performed in which this reaction has been satisfactorily isolated from all other interfering reactions. To this end, a suitable hypochlorous acid (HOCl) scavenger was identified that allowed the hydrolysis reaction to be isolated from all competing reactions. Indeed, cyanide (the scavenger) reactions with (HOCl) at a rate much faster than HOCl reacts with ammonia (NH3). Hence, in a series of experiments, cyanide was added to monochloramine solutions to quench HOCl, formed during the hydrolysis reaction, preventing the rapid reverse reaction of monochloramine reformation from occurring. The result of this study showed that without interference from the back reaction, monochloramine decayed quite rapidly with a first order rate constant of k obs = 2.156 × 10-5 s-1 at a room temperature. A significant increase in the reaction rate was observed when the experiments were conducted at higher temperature. In addition to investigating these two reactions, a critical review of the experimental methods used to measure chlorine in water is provided
Assessment of Water Use and Indirect Water Reuse in a Large Scale Watershed: The Wabash River
No full textIn the context of climate change, increasing demands for freshwater make it necessary to manage our water resources in a sustainable way and find innovative ways to extend their life. An integrated water management approach needs to consider anthropogenic water use and reuse which represent major components of the current water cycle. In particular, unplanned, or de facto, indirect water reuse occurs in most of the U.S. river systems, however, there is little real-time documentation of it. Despite the fact that there are national and state agencies that systematically collect data on water withdrawals and wastewater discharges, their databases are organized and managed in a way that limits the ability to combine reported water data to perform large scale analysis about water use and indirect reuse. To better document these issues and to demonstrate the utility of such an analysis, I studied the Wabash River Watershed located in the U.S. Midwest. Existing data for freshwater extraction, use, discharge, and river streamflow were collected, curated and reorganized in order to characterize the water use and reuse within the basin. Indirect water reuse was estimated by comparing treated wastewater discharges with stream flows at selected points within the watershed. Results show that during the low flow months of JulyOctober 2007, wastewater discharges into the Wabash River basin contributed 82 to 121% of the stream flow, demonstrating that the level of water use and unplanned reuse is significant. These results suggest that intentional water reuse for consumptive purposes such as landscape or agricultural irrigation could have substantial ecological impacts by diminishing stream flow during vulnerable low flow periods. This research also completed a time series watershed-scale analysis of water use and unplanned indirect reuse for the Wabash River Watershed from 2009 to 2017. Results document the occurrence of indirect water reuse over time, ranging from 3% to 134% in a water-rich area of the U.S. The time series analysis shows that reported data effectively describe the water use trends through nine years, clearly reflecting both anthropogenic and natural events in the watershed, such as the retirement of thermoelectric power plants, and the occurrence of an extreme drought in 2012. Results demonstrate the feasibility and significance of using available water datasets to perform large scale water use analysis, describe limitations encountered in the process, and highlight areas for improvement in water data management
Photochemistry of single-walled carbon nanotubes in the aquatic environment, and their extraction from soils
Full text linkCarbon nanotubes (CNTs) are a class of engineered nanoparticles, composed of an array of sp2 carbon atoms arranged as fused benzene rings. Due to their exceptional electrical, mechanical, and physical properties, CNTs find applications in construction, aerospace, and medical industries. In the United States, CNTs already had an annual production of 2,000 tons in 2011. This rate of annual production indicates that CNTs will find their way into the environment, which will result in certain environmental exposure. Yet, there have not been sufficient and definitive studies on the health and environment effects of CNTs. For example, additional information regarding environmental transformation pathways is required to better evaluate the environmental and health consequences of these materials. Because photochemical transformation is a potentially important transformation pathway of both unfunctionalized single-walled carbon nanotubes (SWCNTs) and carboxylated SWCNTs (CSWCNTs), this process was investigated in this study. Results show that unfunctionalized SWCNTs can undergo indirect photo-transformation through reactions with hydroxyl radicals (produced from hydrogen peroxide), even in the absence of surfactants, which are often added to disperse the unfunctionalized tubes in water. Evidence for transformation includes UV-VIS and Near Infrared Fluorescence (NIRF) fading, and an increase in defects (sp 3 carbon), as observed through Raman analysis. While more rapid fading occurred under light, changes in the fluorescence of the SWCNTs also occurred in dark samples, suggested some metal-catalyzed Fenton\u27s reaction was occurring in the absence of light. Although direct photochemical transformation of unfunctionalized SWCNTs is very slow, direct photochemical transformation of aqueous suspensions of CSWCNTs occurs. Headspace analysis on lamp-light irradiated CSWCNT suspensions showed 2.69% of the carbon was mineralized within 30 days. The stable isotope composition of the SWCNTs and of the headspace CO2 shows that the CO2 originated from the SWCNTs. XPS analysis, coupled with chemical derivatization of specific oxygen containing functional groups, showed an increase in oxygen content after 60 days under sunlight exposure. Additionally, the wavelength dependency of reactive oxygen species (ROS) generation by CSWCNT was examined under 400- and 280-nm wavelength cutoff filters in sunlight. The aqueous colloidal dispersions of CSWCNTs generated ROS, including: Singlet oxygen (1O2), superoxide anion (O2· -), and hydroxyl radicals (·OH) under the 280-nm cutoff filter, whereas there was a much slower rate of formation of singlet oxygen ( 1O2) and superoxide anion (O2· -) under the 400-nm filter, with no measurable hydroxyl radicals (·OH) produced. To be able to investigate the fate and transport of CNTs in the environment, it is necessary to develop methods for carbon nanotube isolation (i.e., extraction), characterization, and possibly quantification from environmental samples. To this end, the potential to use solvent extraction for removing SWCNTs from sand (50+70 mesh) and three types of soil with different characteristics (e.g., Tracy, Drummer, and Clermont) was investigated. Extraction with 1,2-dichlorobenzene (DCB) under high power sonication was shown to have an accumulative extraction efficiency of more than 90% after four sequential extractions. To purify the SWCNTs from the co-extracted humic material, density gradient ultracentrifugation (DGU) was tested using two different commercially available unfunctionalized SWCNTs
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