Browsing by Subject "adsorption"

Now showing 1 - 18 of 18
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    Adsorption and desorption of atrazine on a melamine-based soil amendment
    (Texas A&M University, 2004-09-30) Neitsch, Susan Lynn
    Adsorption kinetics and adsorption-desorption of atrazine on organoclay composites prepared with the surfactant 6-piperazin-1-yl-N,N'-bis-(1,1,3,3-tetramethyl-butyl)-(1,3,5)triazine-2,4-diamine and Houston Black clay were studied using the indirect batch equilibration procedure. The organoclay composites sorbed significantly more atrazine than the Houston Black clay. Adsorption equilibrium was reached after 72 h for the organoclay composites. Atrazine adsorption isotherms were described by linear partitioning. The Koc values ranged from 605 to 5271 L kg-1 for the organoclay composites compared to a value of 41 L kg-1 for the Houston Black clay. The organoclay composite containing 20% surfactant on a total weight basis provided the most efficient adsorption of atrazine, although organoclay composites containing much lower amounts of surfactant also adsorbed significant amounts of atrazine. An average of 11% of sorbed atrazine was released during desorption. Characterization of desorption products showed only atrazine molecules being released from the organoclay composites.
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    Adsorption of As(V), As(III) and methyl arsenic by calcite and the impact of some groundwater species
    (2009-05-15) Jones, Robert Garret
    The objective of this research was to investigate the retention of arsenate (iAsV), arsenite (iAsIII), monomethyl arsenate (MMAsV) and dimethyl arsenate (DMAsV) by calcite and assess the impact of dissolved Ca2+, Mg2+, phosphate and sulfate on arsenic solubility, adsorption and precipitation phenomena. Adsorption kinetics of iAsV, evaluated at a low and high concentration, was a relatively rapid process, with a fast initial reaction rate within the first few minutes and a subsequent slower reaction rate as equilibrium was approached. The relative adsorption of arsenicals decreased in the following order: iAsV > iAsIII > DMAV > MMAV. In no case was a clear adsorption maximum observed with increasing dissolved arsenic concentration. Dissolved 0.01 M Ca2+ resulted in an increase in iAsV adsorption; however, in the presence of 0.1 M Ca2+ adsorption of iAsV was decreased. The presence of Mg2+ as 0.01 M Mg(NO3)2 resulted in decreased iAsV adsorption probably the result of a lower iAsV affinity for adsorbed Mg2+ as compared to Ca2+. Phosphate and sulfate were highly competitive with iAsV in adsorption to calcite and both resulted in decreased iAsV adsorption. The total prevention of iAsV adsorption at initial equimolar arsenic/phosphate concentrations > 88 ?M each could be from the consumption of available calcite surface sites by the specific adsorption of phosphate. Equilibrium modeling, using the geochemical and mineral speciation of equilibrium model (MINTEQA2), indicated that at low concentrations of arsenate or phosphate solid-phase precipitation was not likely and adsorption processes likely controlled solubility. At high concentrations of arsenate Ca3(AsO4)2 ? 3 2/3 H2O and Ca3(AsO4)2 ? 4 1/4 H2O solid phases could be controlling arsenate solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased adsorption, suggesting that processes which could affect the speciation of arsenic in the environment, could increase arsenic mobility in environmental systems where calcite and dissolved aqueous calcium play a predominant role in controlling arsenic solubility. Dissolved aqueous concentrations of magnesium, phosphate and sulfate generally reduced the ability of arsenic to be adsorbed to calcite.
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    Adsorption, desorption, and stabilization of arsenic on aluminum substituted ferrihydrite
    (Texas A&M University, 2006-04-12) Masue, Yoko
    Because of As toxicity, the complexity of its chemistry, and the recent lowering of the maximum contaminant level of As in municipal drinking water, there has been considerable interest for improved methods to remove As from water. Although Al and Fe hydroxides have been extensively studied as adsorbents for As removal during water treatment, coprecipitated Al:Fe hydroxides have received only minimal attention. The theoretical and experimental feasibility of coprecipitated Al:Fe hydroxide systems were evaluated by studying their mineralogy, stability, and As adsorption and desorption behavior. The broad XRD peaks revealed that Al was substituted into the ferrihydrite structure and that this was the only major product up to about a 2:8 Al:Fe molar ratio. Gibbsite and bayerite were identified when Al content was higher. The rate of recrystallization of ferrihydrite into goethite and hematite was significantly reduced as Al substitution was increased. In general, adsorption capacity of both AsV and AsIII decreased with increase in Al:Fe molar ratio; however, similar AsV adsorption capacities were observed with Fe and Al:Fe hydroxides with Al:(Al+Fe) molar ratios < 0.20. Both AsIII and AsV adsorption isotherms were effectively described by Langmuir and Freundlich equations. Adsorption maxima of AsV on Fe and Al:Fe hydroxides were observed at pH 3 to 7, and that of AsV on Al hydroxide was observed at pH 5.2, with significant decreases in adsorption with increase and decrease in pH. Adsorption maxima of AsIII decreased by approximately 4 % for each 10 % increase in Al substitution up to 5:5 Al:Fe molar ratio. Adsorption maxima of AsIII on Fe and Al:Fe hydroxides were observed at pH 8 to 9. AsIII adsorption on Al hydroxide was negligible. Counterion Ca2+, compared to Na+, enhanced the retention of AsV, especially at pH > 7. Counterion concentration did not significantly affect AsV adsorption. Though phosphate desorbed both AsV and AsIII from all Al:Fe hydroxides, quantitative desorption was never observed. The results of this study indicate the possible utility of coprecipitated Al:Fe hydroxide in wastewater treatment. Based on adsorption/desorption behavior and stability of the Al:Fe hydroxide product, the preferred Al:Fe molar ratio was 2:8.
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    Characterization and Safety of Clays as Potential Dietary Supplements to Prevent Aflatoxicosis
    (2011-05-10) Marroquin-Cardona, Alicia 1979-
    Aflatoxins are toxic metabolites produced by Aspergillus flavus and A. parasiticus fungi. Aflatoxin B1 (AFB1) is the most toxic and is a potent carcinogen with antinutritional and immunosuppressive effects. Several natural outbreaks of poisoning have been reported in both animals and humans, with fatal consequences in some of the cases. Inclusion of clay minerals in the diet is a promising strategy to reduce the bioavailability of aflatoxins from contaminated foods. Several clay-based products are currently sold as ?mycotoxin binders? for addition in feeds, many of them lacking of detailed efficacy and safety data. Similarly, clays intended for human consumption in different countries also lack of safety studies, and for most of them the mineral composition is unknown. Earlier studies in our laboratory have shown that NovaSil clay (NS), a Ca-bentonite, is able to reduce the adverse effects associated with aflatoxin exposure in different animal species and recent human trials have confirmed its efficacy and safety. Most clays are derived from naturally-occurring deposits and batch-to-batch variations in composition, particle size, non-framework trace metal content and dioxin levels are expected. Therefore, objectives in this research were to determine the mineral composition, aflatoxin binding capacity and potential safety of ?mycotoxin binders? and edible clays for humans, and to investigate the mineral characteristics and safety of two potential aflatoxin adsorbents, a refined clay with more uniform particle size (UPSN) and a sodium bentonite (Na-BENT). Both clays have low dioxin/furans and heavy metals levels. According to mineralogical analysis, most of the ?binders? contained montmorillonite but the sorption capacities for AF varied. Most of the edible clays for humans contained kaolinite, mica and quartz, and they had low sorption capacities for aflatoxin. UPSN and Na-BENT had similar mineral characteristics and high sorption capacities for aflatoxin. After a 3-month rodent study using Sprague Dawley rats, no overall toxicity was observed for either clay. No changes were observed for most of the blood and serum biochemical parameters. Important findings included the increased serum Na, Ca, vitamin E and Na/K ratio and the reduction of serum K and Zn (in males) due to ingestion of the bentonites. Nonetheless, all parameters fell within the normal ranges reported for rats less than 6 months old and no trends of dose dependency were observed. We conclude that ingestion of low levels of bentonites does not present a health risk.
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    Design and performance of an ammonia measurement system
    (Texas A&M University, 2007-04-25) Boriack, Cale Nolan
    Ammonia emissions from animal feeding operations (AFOs) have recently come under increased scrutiny. The US Environmental Protection Agency (EPA) has come under increased pressure from special interest groups to regulate ammonia. Regulation of ammonia is very difficult because every facility has different manure management practices. Different management practices lead to different emissions for every facility. Researchers have been tasked by industry to find best management practices to reduce emissions. The task cannot be completed without equipment that can efficiently and accurately compare emissions. To complete this task, a measurement system was developed and performance tested to measure ammonia. Performance tests included uncertainty analysis, system response, and adsorption kinetics. A measurement system was designed for measurement of gaseous emissions from ground level area sources (GLAS) in order to sample multiple receptors with a single sensor. This multiplexer may be used in both local and remote measurement systems to increase the sampling rate of gaseous emissions. The increased data collection capacity with the multiplexer allows for nearly three times as many samples to be taken in the same amount of time while using the same protocol for sampling. System response analysis was performed on an ammonia analyzer, a hydrogen sulfide analyzer, and tubing used with flux chamber measurement. System responses were measured and evaluated using transfer functions. The system responses for the analyzers were found to be first order with delay in auto mode. The tubing response was found to be a first order response with delay. Uncertainty analysis was performed on an ammonia sampling and analyzing system. The system included an analyzer, mass flow controllers, calibration gases, and analog outputs. The standard uncertainty was found to be 443 ppb when measuring a 16 ppm ammonia stream with a 20 ppm span. A laboratory study dealing with the adsorption kinetics of ammonia on a flux chamber was performed to determine if adsorption onto the chamber walls was significant. The study found that the adsorption would not significantly change the concentration of the output flow 30 minutes after a clean chamber was exposed to ammonia concentrations for concentrations above 2.5 ppm.
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    Development of an ammonia emission protocol and preliminary emission factor for a central Texas dairy
    (Texas A&M University, 2004-09-30) Rose, Adam Joseph
    A protocol was developed to measure ammonia emission concentrations from dairies using an isolation flux chamber. A hybrid dairy in Comanche county, Texas, was measured for one week each during August 2002 and January 2003. Sixty total ammonia samples were taken from the free stall barn, open lot, mixing tank, separated solids, compost, and two lagoons using the developed protocol. The ammonia concentration measurements were made using a chemiluminescence analyzer located inside a mobile laboratory. From the emission concentrations recorded, it was estimated that 9.68 metric tons of ammonia were produced from this dairy per year. An emission factor of 13.34 ? 28.80 kilograms per day per thousand head of cattle (kg/day/1000 head) was estimated for this dairy (?95% confidence intervals) during summer conditions. For winter conditions the emission factor was 12.05 ? 12.89 kg/day/1000 head. The 11% difference of the emission factors from summer to winter conditions was predominantly from the change in ambient and control volume temperatures (a mean difference of approximately 25 degrees Celsius), differences in source temperatures, and seasonal variability in husbandry. The adsorption of ammonia onto different polymer tubing used in pollutant stream conveyance was researched for possible systematic losses. Teflon and low density polyethylene (LDPE) were tested for ammonia losses with treatments of: temperature, length, and inlet concentration. Inlet concentration and temperature were significant factors used to describe ammonia adsorption for Teflon, whereas LDPE was also affected by tubing length. These factors were used to create a model to correct the summer dairy measurements for ammonia losses, resulting in an emission factor increase of 8.3% over the original value obtained from the flux chamber. A nitrogen mass balance was performed to estimate the amount of nitrogen available for ammonia formation as excreted - 177.5 kilograms per year per animal (wet basis). The amount of ammonia excreted per year was also estimated to be 26.63 kilograms per year. The measured ammonia emitted from the dairy was five times less than the ammonia excreted and thirty-six times less than the total nitrogen excreted.
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    Diphosphine Dioxide Cages and Hydrogen Peroxide Adducts of Phosphine Oxides: Syntheses and Applications in Surface Science
    (2013-12-09) Hilliard, Casie Renee
    Understanding the adsorption of phosphine oxides on silica surfaces has a threefold incentive. (a) Efficiently removing phosphine oxides from reaction mixtures is crucial after many synthetic procedures, for example the Wittig reaction. (b) Using the P=O group for probing the surface acidity of oxides. (c) Most importantly, getting more insight regarding the nature of the P=O/surface interaction. Hereby, the mobility of the adsorbed species is of fundamental interest. In the classical 31P MAS and in HRMAS NMR spectra the reduction of the originally large CSA, the residual halfwidth, as well as the downfield shift of the signals when adsorbing phosphine oxides on silica surfaces are most indicative. This research provides new insights regarding the strength of the phosphine oxide adsorption on various silica surfaces and the diverse modes of mobility. Furthermore, an oxidation procedure for the synthesis of a variety of phosphine oxides, including the model compounds used for the adsorption studies, has been developed. It yields the well-defined H2O2 adducts as key intermediates, which have been fully characterized and methods for their controlled and efficient decomposition are described. For adsorbed phosphine oxides, the changes of the 31P solid-state NMR signals as compared to the polycrystalline materials can stem from both the translational mobility of the compound across the silica surface and the interaction of the P=O group with the silanol groups of the silica. Molecules containing two phosphine oxide groups, one of them being sterically prevented from interacting with the surface, are target compounds for the adsorption studies. Since the P nuclei are bound within the same molecule, both experience the same translational mobility, but only one P=O group can undergo quaternization by contact with the surface. Therefore, the contribution of each factor to the CSA reduction upon adsorption can be determined. The diphosphine cages and their dioxides can serve as such probe molecules and their adsorption on silica has been examined. Since none of these small cages, containing five to twelve methylene groups in each alkyl chain, are presently known in the literature, a new synthetic route to access the diphosphine cage derivatives, namely the dioxide cages, had to be explored. Employing Fe gyroscopes as starting materials and releasing the phosphine oxides from the metal center to form the dioxide cage molecules is most effective and will be highlighted. Having synthesized the diphosphine dioxide cages, their 31P MAS NMR characteristics in the polycrystalline and surface-adsorbed states will be discussed in detail. In summary, the two largest diphosphine dioxide cages adsorbed on silica only show one signal in the 31P solid-state NMR spectra, indicating both sides of each cage are interacting with the support. On the other hand, the smallest cage, containing 10 methylene groups in each alkyl chain, when adsorbed results in two distinct signals in the 31P solid-state NMR spectra, meaning one P=O group is adsorbed on the support while the other is pointing away from the surface, as desired. Examining the different CSA values of the two signals proves that both the translational mobility and partial quaternization effect play a role in the overall CSA reduction for the adsorbed species.
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    Imazethapyr: red rice control and resistance, and environmental fate
    (Texas A&M University, 2005-11-01) Avila, Luis Antonio de
    Imazethapyr was recently approved for use in rice, but limited information is available regarding its efficacy, environmental fate or potential red rice resistance. Therefore, experiments were conducted to 1) determine the effect of flooding time, and stage of imazethapyr application in red rice control, 2) assess the acetolactate synthase resistance to imazethapyr on red rice ecotypes, 3) determine the relative photolysis of imazethapyr, and 4) determine the effect of soil and moisture on imazethapyr adsorption and availability. When imazethapyr was applied in sequential application of PRE followed by a POST application, to achieve >95% red rice control, flood needed to be established within 14 DAT when imazethapyr was applied EPOST, and 7 DAT when imazethapyr was applied LPOST. Delaying the flood up to 21 DAT reduced rice grain yield for both EPOST and LPOST application timings. Based on enzymatic activity, the mean I50 values were 1.5, 1.1, 1.5, 1.6, 20.8, and 590.6 mM of imazethapyr, respectively, for LA 5, MS 5, TX 4, ??Cypress??, ??CL-121??, and ??CL-161??. CL-161 was 32 times more resistant than CL-121, and at least 420 times more resistant than the average of the red rice ecotypes and ??Cypress??. Results from the ALS assay showed that red rice ecotypes and Cypress had high susceptibility to imazethapyr when compared with the tolerant CL-121 and the resistant CL-161. Measurable enzymatic tolerance to ALS-inhibiting herbicides has not yet developed in these red rice ecotypes. Imazethapyr quantum yield (fI ) was 0.023 ?? 0.002 while the hydroxyl radical rate constant ( I OH k?? ) was 2.8 ?? 0.44 x 1013 M-1 h-1. These results show that imazethapyr is susceptible to both direct and indirect photolysis. The results also show that imazethapyr photolysis in paddy water will be affected by turbidity due to its impact on the availability of sunlight to drive direct and indirect photolysis reactions. Imazethapyr was more available and more concentrated in sandy soil. With higher amounts of water in soil there was greater amount of imazethapyr in soil solution and a lower concentration of herbicide due to dilution. The double centrifuge method provided a better estimate of plant available herbicide.
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    Management of produced water in oil and gas operations
    (Texas A&M University, 2005-02-17) Patel, Chirag V.
    Produced water handling has been an issue of concern for oil and gas producers as it is one of the major factors that cause abandonment of the producing well. The development of effective produced water management strategies poses a big challenge to the oil and gas industry today. The conversion of produced water into irrigation or fresh water provides a cost effective tool to handle excessive amounts of the produced water. In this research we proposed on-site produced water treatment units configured to achieve maximum processing throughput. We studied various advanced separation techniques to remove oil and dissolved solids from the produced water. We selected adsorption as the oil removing technique and Reverse Osmosis (RO) as the dissolved solids removing technique as being the best for our purpose. We performed experiments to evaluate operating parameters for both adsorption and RO units to accomplish maximum removal of oil and dissolved solids from the produced water. We compared the best models fitting the experimental data for both the processes, then analyzed and simulated the performance of integrated produced water treatment which involves adsorption columns and RO units. The experimental results show that the adsorption columns remove more than 90% of the oil and RO units remove more than 95% of total dissolved solids from the produced water. The simulation results show that the proper integration and configuration of adsorption and RO units can provide up to 80% efficiency for a processing throughput of 6-8 gallons per minute of produced water. From an oil and gas producer?s viewpoint output from the produced water treatment system is a revenue generating source. The system is flexible and can be modified for the applications such as rangeland restoration, reservoir recharge and agricultural use.
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    Methyl arsenic adsorption and desorption behavior on iron oxides
    (Texas A&M University, 2005-08-29) Lafferty, Brandon James
    Arsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.
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    Modeling H2 adsorption in carbon-based structures
    (2009-05-15) Lamonte, Kevin Anthony
    Hydrogen storage has been identified as a primary bottleneck in the large-scale implementation of a hydrogen-based economy. Many research efforts are underway to both improve the capacity of existing hydrogen storage systems and develop new systems. One promising area of research is hydrogen physi-sorbed into carbonbased structures such as nanotubes and graphene. Two novel systems consisting of a phthalocyanine salt with a large cation were studied. Ab initio, density functional theory, and molecular dynamics simulations of tetramethylammonium lithium phthalocyanine (TMA-LiPc) and trimethyl-(2-trimethylazaniumylethyl) azanium phthalocyanine (TMA2-Pc) were undertaken to estimate the H2 gas-solid adsorption uptake (wt/wt) as a function of pressure and temperature. For TMA-LiPc, the maximum H2 binding energy was approximately 0.9 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.49 ? ranged from 2.1% to 6.0% (wt/wt) at 300 K, 2.5% to 6.5% at 273K, 3.3% to 7.2% at 236K, 5.2% to 8.6% at 177K, and 10.4% to 11.7% at 77K. At ILD 10 ? H2 adsorption was about 1.5% (wt/wt) higher at all points. For TMA2-Pc, the maximum H2 binding energy was approximately 1.3 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.12 ? ranged from 0.5% to 2.6% (wt/wt) at 300 K, 0.6% to 2.8% at 273K, 0.8% to 3.2% at 236K, 1.4% to 3.9% at 177K, and 4.5% to 6.0% at 77K. At ILD 10 ? H2 adsorption ranged from about 0.1% (wt/wt) at 40 bar to 0.5% higher at 250 bar. The behavior of H2 adsorption for both TMA-LiPc and TMA2-Pc were compared. The adsorbed H2 probability density was compared to pair correlation function data and surfaces of constant binding energy. Regions of relatively high H2 density appear to correlate well with the binding energy, but the total adsorption does not, indicating that the adsorption is driven by factors other than binding energetics. Lithium ion transport in TMA2-Pc was also investigated for suitability as an electrolyte medium for use in lithium ion battery systems.
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    Plant-Soil Interactions, Weed Control, and Rice Tolerance as Affected by Saflufenacil
    (2012-10-19) Camargo, Edinalvo
    Saflufenacil is a new herbicide for broadleaf weed control. Limited information is available for crop tolerance, weed control and herbicide behavior in the rice environment. Studies were designed to 1 and 2) evaluate rice tolerance and weed control to saflufenacil in combination with clomazone and imazethapyr; 3) evaluate the absorption and translocation of imazethapyr and saflufenacil in weed species 4) assess saflufenacil degradation and persistence in soils; and 5) investigate the use of reference compounds during the determination of pesticide adsorption (Kd). None or minimal rice injury was observed from preemergence (PRE) application of saflufenacil. Intense injury (68%) was noted with combinations of clomazone (505 g ha-1) applied PRE and saflufenacil (50 g ha-1) applied postemergence (POST). Similarly, rice injury up to 83% was observed in earlier evaluations when saflufenacil was applied POST with imazethapyr. However, subsequent evaluations indicated rice recovery from herbicide treatments. Combination of saflufenacil with imazethapyr resulted in hemp sesbania control ? 88% and red rice control of 100%. Rice yield was not adversely altered by the herbicide treatments used in the clomazone and imazethapyr weed control programs. Imazethapyr plus saflufenacil provided a greater uptake (30%) and translocation (35%) of 14C-imazethapyr than imazethapyr alone in the TX4 red rice. Absorption of 14C-saflufenacil ranged from approximately 40 to 60% in hemp sesbania plants. At 12 and 24 hours after treatment a greater percentage of the absorbed saflufenacil was quantified above the treated leaf at the two lower light intensities. Similar trends were observed for basipetal movement of saflufenacil. An accelerated solvent extraction method was developed to extract saflufenacil from soil. Half-life averaged among soils was 59 and 33 days for saturated and field capacity, respectively. Saflufenacil persistence in the environment was 2 to 3 times longer under flooded conditions for most of the studied soils. Adsorption values were affected by soil to solution ratios, particularly when the soil-pesticide interaction resulted in Kd values > than 2 mL g-1. The use of reference compounds during Kd estimation allowed for calculation of a conceptual adsorption window generating a more comprehensive set of data with alternatives for comparison of soils and methods.
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    Regeneration of Carbon Aerogel Exhausted in Water Purification
    (2012-02-14) Tewari, Sanjay
    Carbon has been used electrochemically in various forms for water treatment and the carbon aerogel is one of them. Carbon Aerogels (CA) are used as electrodes due to their high surface capacity and high electrical conductivity. They are also known as Carbon Nanofoams (CNF). CA electrodes attract oppositely charged ions that are nearby. This concept is known as Capacitive De-Ionization (CDI). The use of CA in CDI for water purification is well documented, but not much work has been done on regeneration of CA electrodes. Once saturated, these electrodes lose their ability to adsorb additional ions and it must be restored by regeneration. If they cannot be regenerated, they would need to be replaced, which would greatly increase the cost of the treatment they are expensive. The goal of this study is to obtain data to define optimal regeneration conditions and to develop predictive capability by examining desorption behavior of adsorbed ions on CA electrodes. This study focuses on desorption of adsorbed ions and regeneration of CA. Various experiments were conducted to explore the effects on regeneration of CA of shorting of electrodes, change of polarity of electrodes, flow speed of water over CA electrodes, and temperature of regeneration water. The optimal combination of experimental variables was identified and was used for remaining experiments that tested the effect of size, charge and mass of adsorbed ions on regeneration of CA. Also, the effect of thickness of CA and its pore size on regeneration of CA was studied. Results indicated that application of reverse potential for the first few minutes of the total regeneration time provided the greatest regeneration. Longer application of reverse potential did not result in higher regeneration. The regeneration behavior when no potential applied with and without shorting was as expected. Application of reverse potential with variable temperature or variable flow speed of water over CA surfaces provided results that were different from the ones that were obtained with no potential being applied with or without shorting of electrodes.
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    Rock-Fluid Chemistry Impacts on Shale Hydraulic Fracture and Microfracture Growth
    (2012-07-16) Aderibigbe, Aderonke
    The role of surface chemical effects in hydraulic fracturing of shale is studied using the results of unconfined compression tests and Brazilian tests on Mancos shale- cored at depths of 20-60 ft. The rock mineralogy, total organic carbon and cation exchange capacity were determined in order to characterize the shale. Adsorption tests to study the interaction of the shale and aqueous fluid mixture were also carried out using surface tension measurements. The uniaxial compressive strengths and tensile strengths of individual shale samples after four hours exposure to water, 2.85 x 10^-3 M cationic surfactant (dodecyltrimethylammonium bromide-DTAB) and 2.81 x 10^-3 M anionic surfactant (sodium dodecylbenzenesulfonate-SDBS) were analyzed using ANOVA and Bonferroni tests. These mechanical strengths were largely reduced on exposure to the aqueous environments studied, despite the relatively low clay and low swelling clay content of the Mancos shale. Further comparison of the uniaxial compressive strengths and tensile strengths of the shale on exposure to water, to the strengths when exposed to the surfactant solutions showed that their difference was not statistically significant indicating that exposure to water had the greatest effect on strength loss. The surface tension measurement of 2.85 x 10^-4 M DTAB and 2.81 x 10^-4 M SDBS solutions before and after equilibration with shale showed about 80% increase in surface tension in the DTAB solution and 10% increase in surface tension in the SDBS solution. The probable sorption mechanism is electrostatic attraction with negatively charged sites of the shale as shown by significant loss of the cationic surfactant (DTAB) to the shale surface, and the relatively minor adsorption capacity of the anionic surfactant (SDBS). Although these adsorption tests indicate interaction between the shale and surfactant solutions, within the number of tests carried out and the surfactant concentration used, the interaction does not translate into a significant statistical difference for impacts of surfactants on mechanical strength of this shale compared to the impact of water alone. The relevance of this work is to facilitate the understanding of how the strength of rock can be reduced by the composition of hydraulic fracturing fluids, to achieve improved fracture performance and higher recovery of natural gas from shale reservoirs.
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    Study of Adsorption of Methanol in an Activated Carbon and Carbon Nanotube Matrix for Use in a Solar Based Refrigeration Cycle
    (2012-07-16) Sambath, Srivaths
    This thesis seeks to investigate the adsorption capabilities of activated carbon and carbon nanotubes. The adsorption of methanol on both of these substances was tested for their application in a solar based refrigeration cycle. Research on carbon nanotubes and their growth has been carried out for applications in the semiconductor industry. Enough focus has not been given to the use of nanotubes for refrigeration purposes. Adsorption refrigerators have been designed with the energy source being solar energy. Various adsorbent/adsorbate pairs have been tested in literature. The present work focuses on carbon nanotubes because theoretically, nanotubes should be able to adsorb better than activated carbon due to their high surface to volume ratios and hence a higher number of adsorption sites available for methanol to adsorb. The amount of adsorption of methanol on nanotubes depends on whether the end caps of the nanotubes are open or closed and also on the hydrophilic nature of the nanotubes. Nanotubes with ends closed are supposed to adsorb less than the nanotubes with their ends opened. The ends of carbon nanotubes can be blocked because of iron and other impurities. In this project, nanotubes are annealed under high vacuum to open the end caps. The hydrophobic nature of the nanotubes is corrected by treating them with concentrated nitric acid. The hydrophobic nature of the nanotubes is corrected by treating them with concentrated nitric acid. The acid treated nanotubes are used to obtain adsorption data at different temperatures. The adsorption of methanol on activated carbon, pristine and treated carbon nanotubes is measured at different temperatures. Electron microscopy is used to validate that annealing the nanotubes at high temperature under vacuum opens the end caps of the nanotubes. Finally, a matrix of nanotubes and carbon powder is prepared with different concentrations. The mixture is tested for adsorption of methanol. It is observed that the carbon nanotubes, pristine or treated, do not perform better than activated carbon. However, performance seems to increase when mixtures of activated carbon and carbon nanotubes are used as adsorbent. Also, it is found that mixtures containing annealed nanotubes perform better than mixtures with pristine nanotubes. Kinetics of the adsorption process is calculated for the different adsorbents used, which is used to explain the increase in the amount of methanol adsorbed for the activated carbon-carbon nanotube mixture.
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    Texas Bentonites as Amendments of Aflatoxin-Contaminated Poultry Feed
    (2012-07-16) Barrientos Velazquez, Ana Luisa
    Aflatoxins are toxic organic compounds produced by fungi in grains. Moderately contaminated grains that cannot be used as food are often directed to animal feed. Economically-feasible detoxification measures for contaminated feeds are needed. The objectives of this research were to identify effective bentonites as aflatoxin adsorbents and to evaluate the performance of the clays as aflatoxin amendments in feed for broiler chickens. Five bentonite samples from Gonzales, Texas, USA were collected and analyzed against the published selection criteria for aflatoxin adsorbents: aflatoxin adsorption capacity, pH, cation exchange capacity (CEC), organic carbon, particle size distribution, and mineralogical and structural compositions. Two bentonites were identified as potentially good aflatoxin adsorbents based on the analyses. These two bentonites were selected for an in vivo poultry experiment where chickens were fed with aflatoxin-contaminated corn (1400 ppb) to test the detoxification efficacy of the clays. Detailed mineralogy analyses were conducted on these two samples (4TX and 1TX) after size fractionation. Clay 4TX and 1TX contained 87 percent and 65 percent clay, respectively. Smectite was the dominant mineral phase in both clay fractions. Quartz and feldspars were also present in both samples. These minerals are unlikely to cause harmful effects on the chickens. The presence of pyrite and heavy metals in 1TX raised concerns about its use in animal feed. The clays were introduced into feed by mixing the dry bentonite powder with the feed for twelve minutes in a mechanical mixer. The body weight was increased by 21 percent with clay 4TX and 14 percent with clay 1TX in the aflatoxin diet. The concentration of total aflatoxins in liver was reduced by 36 percent with the addition of clays. Liver visual appearance was also improved from pale red to a more reddish color resembling the healthy red liver. All chickens fed clean feed had significantly higher body weights than those fed with highly contaminated feed, suggesting that the clays did not completely eliminate aflatoxin toxicity. The published aflatoxin binder selection criteria were useful for screening bentonites as aflatoxin amendments. The selected bentonites based on the criteria could effectively sequester aflatoxins in vivo. Yet direct mixing of bentonite as dry powder to highly contaminated poultry feed could not eliminate the toxicity of aflatoxins.
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    Thermodynamic and transport properties of self-assembled monolayers from molecular simulations
    (Texas A&M University, 2006-04-12) Aydogmus, Turkan
    The purpose of the work is to employ molecular simulation to further extend the understanding of Self-Assembled Monolayers (SAMs), especially as it relates to three particular applications: organic-inorganic composite membranes, surface treatments in Micro-Electro-Mechanical Systems (MEMS) and organic-surface-modified Ordered Mesoporous Materials (OMMs). The first focus area for the work is the use of SAMS in organic-inorganic composite membranes for gas separations. These composite membranes, recently proposed in the literature, are based on the chemical derivatization of porous inorganic surfaces with organic oligomers. Our simulations achieve good qualitative agreement with experiment in several respects, including the improvement in the overall selectivity of the membrane and decrease in the permeance when increasing the chain length. The best improvement in the overall solubility selectivity is reached when the chains span throughout the pore. The second application focus is on the use of SAMs as coatings in MEMS devices. The work focuses on the modeling of adhesion issues for SAM coatings at the molecular level. It is shown that as the chain length is increased from 4 to 18 carbon atoms, the adhesion forces between two monolayers at the same separations decreases. The third application focus is on the use of SAMs for tailoring surface and structural properties of OMMs, in particular, porous silicas. A molecular study of structural and surface properties of a silica material with a 5 nm pore size, modified via chemical bonding of organosilanes with a range of sizes (C4, C8 and C18) is presented. Grand canonical MC simulations are employed to obtain nitrogen adsorption isotherms for unmodified and modified MCM-41 material models. Furthermore, the density profiles of alkyl chains and nitrogen molecules are analyzed to clarify the differences in the adsorption mechanisms in unmodified and modified materials. The position of the capillary condensation steps gradually shifted to lower pressure values with the increase in size of the bonded ligands, and this shift was accompanied by a gradual disappearance of the hysteresis loop. As the length of the bonded ligands is increased, a systematic decrease in the pore diameter is observed and the multi-layer adsorption mechanism in modified model materials diminishes.
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    Transports of Polymer Nanomedicine in the Environment
    (2013-11-14) Zhang, Ming
    With increasing production and commercial use of polymer nanomedicine and a lack of regulation to govern their disposal, polymer nanomedicine may enter into soils and ultimately into ground water system. In this dissertation, adsorption of polymeric nanoparticulate drug delivery system (PNDDS) in the environmental surface as well as uptake of nanomedicine into plants was investigated. Cellulose surface and silica surface were chosen as environmental surfaces and ryegrass was chosen as a plant. The adsorption of PNDDS onto cellulose and silica surface was studied by quartz crystal microbalance with dissipation (QCM) and atomic force microscopy (AFM). Uptake of PNDDS into ryegrass was investigated by spectrofluorometry (SFM), confocal microscopy, scanning electron microscopy (SEM) and cross sectional transmission electron microscopy (TEM). It is found that PNDDS can partially irreversibly adsorb on cellulose and silica surface. After adsorption, PNDDS may deform, disintegrate, or keep the same size depended on properties of PNDDS and PNDDS/surface interaction. Uptake of PNDDS into ryegrass was observed and PNDDS was found both in root cell and intercellular space. PNDDS could transport up to stem of ryegrass but not leaf. Adsorption onto root surface is the rate-determined step of the uptake process. This dissertation represents an important step in understanding environmental impact of polymer nanomedicine. This is very important considering that PNDDS on and in the plants may later be consumed by animals and bacteria and accumulate in their bodies, and can adversely influence environmental health. Also silica/cellulose surface and plants may also be used to treat waste water with PNDDS. Transport behavior and kinetics of PNDDS onto environmental surface studied in this dissertation also could guide to study transport behavior of the same type or other types of polymer nanomedicine in similar or other environmental systems.