The formation of Fe oxides is influenced by pedogenic factors including ionic environments However, the surface chemistry of Fe oxides formed under different ionic conditions remains obscure Tins study reveals the impact of the structural chemistry of the Fe oxides formed under the influence of low-molecular-weight organic acids and inorganic ligands on their surface chemistry. The selected ligands at optimal ligand/Fe(II) molar ratios (MRs) promoted the crystallization of the Fe oxides formed and decreased their specific surface area through fundamental structural changes. At relatively high ligand/Fe(II) MRS, the ligands inhibited the crystallization of the Fe oxides formed, resulting in the development of micropores, the increase in their surface roughness and irregularity as revealed by atomic force microscopy, as well as the increase in their specific surface area. The net negative surface charge of the Fe oxides consistently increased as the ligand/Fe(II) MR increased. The ligands altering the surfaceproperties of the Fe oxides generally followed the order of the stability constants of the Fe-ligand complexes: silicic acid > citrate > tartrate > oxalate > sulfate > carbonate. The kinetics and mechanisms of adsorption/desorption of P and Ph on the Fe oxides formed at various citrate/Fe(II) MRs were investigated by conventional batch method, pressure-jump relaxation spectrometry and differential Fourier transform infrared spectroscopy. The apparent rate constants, intrinsic rate and equilibrium constants, activation energies, pre-exponential factor values of P and Ph adsorption by the Fe oxides formed and the coordination of P and Ph on the Fe oxide surfaces greatly varied with the amount of the citrate ligands coprecipitated with Fe and their surface properties. The mechanistic rate laws of P and Pb adsorption by the Fe oxides formed at the citrate/Fe(II) MRs of 0 and 0.001 were different. The P adsorption occurred in two sequential reactions whereas the Pb adsorption included two parallel reactions. The role of organic and inorganic ligands in influencing the surface properties of Fe oxides through their effect on crystallization is profound. The subsequent impact on the dynamics of nutrients and pollutants in terrestrial and aquatic environments merits close attention.

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The work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations.

Although the impacts of foreign species on aqueous transformations and arsenic adsorption by 2-line ferrihydrite (FH2) have been extensively studied, much less is known about the impact of transformation inhibitors on solid-state transformation of FH2 and arsenic adsorption. In this study, the influence of inhibitors (Si(IV), Mg(II), Al(III), Ti(IV), and Ci(citrate)), aging time, and heat treatment on FH2 transformation and arsenic adsorption was investigated. The FH2s were synthesized by mixing Fe(III) salts with an inhibitor at pH 7.5 and air drying for 2 d. With increases in Al/Fe molar ratio, FH2, poorly crystalline Al hydroxide, gibbsite, and bayerite were formed in the FH2-Al series, whereas FH2 was formed in the other FH2s. Heat treatment had a more considerable impact on the transformation, structure, and PZC of FH2 than aging at RT for 235 d. Upon heating the FH2s at 360 oC, most of the amorphous Fe oxide was transformed into hematite, whereas Si and Al had stronger retarding effects on transformation than the other inhibitors. Hematite and FH2 were identified with increases in Si/Fe molar ratio, whereas with increasing Al/Fe molar ratio, FH2 remained, gibbsite and bayerite were decomposed, and boehmite appeared as a trace component. However, the effect of Si was much more pronounced than that of Al in retarding the transformation. The adsorption density for As(III) on the FH2s (at pH 7) decreased in the order: FH2-Mg-2 > FH2 > FH2-Al-1, whereas As(V) followed the order: FH2-Al-1 > FH2-Mg-2 > FH2. Compared to aging at RT for 235 d, heat treatment at 360 oC resulted in significantly reduced arsenic adsorption. The heated FH2 showed a smaller adsorption capacity for arsenic compare to that of the other FH2s. In contrast, the heated FH2-Al and FH2-Si series showed much higher adsorption capacities for As(V) than any other FH2, whereas the heated FH2-Mg series exhibited the largest adsorption capacity of As(III) among the heated FH2s. It is concluded that the use of the FH2-Al, FH2-Mg, or FH2-Si series instead of pure FH2 as filter media in water treatment might achieve more efficient arsenic removal and enhance arsenic retention at waste-disposal sites.

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.

The work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations.

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