Aluminosilicate Mineralogy and the Sorption of Organic Cations: Interplay between Electrostatic Barriers and Compound Structural Features.

Current predictive models of organic cation sorption assume that sorbates interact with all sites on aluminosilicate minerals in the same manner. To examine whether differences in aluminosilicate structure and the resultant changes in electrostatic potential influence the sorption of organic cations, seven smectites were chosen with different proportions of isomorphic substitutions (origin of clay charge) located in octahedral versus tetrahedral layers and with the presence or absence of aluminosilicate interlayers. Sorption coefficients for 14 benzylamine derivatives with systematic differences in compound structures were collected to understand the possible influence of aluminosilicate mineralogy.

Predicting Organic Cation Sorption Coefficients: Accounting for Competition from Sorbed Inorganic Cations Using a Simple Probe Molecule.

With the increasing number of emerging contaminants that are cationic at environmentally relevant pH values, there is a need for robust predictive models of organic cation sorption coefficients (K). Current predictive models fail to account for the differences in the identity, abundance, and affinity of surface-associated inorganic exchange ions naturally present at negatively charged receptor sites on environmental solids. To better understand how organic cation sorption is influenced by surface-associated inorganic exchange ions, sorption coefficients of 10 organic cations (including eight pharmaceuticals and two simple probe organic amines) were determined for six homoionic forms of the aluminosilicate mineral, montmorillonite.

Column Chromatography To Obtain Organic Cation Sorption Isotherms.

Column chromatography was evaluated as a method to obtain organic cation sorption isotherms for environmental solids while using the peak skewness to identify the linear range of the sorption isotherm. Custom packed HPLC columns and standard batch sorption techniques were used to intercompare sorption isotherms and solid-water sorption coefficients (Kd) for four organic cations (benzylamine, 2,4-dichlorobenzylamine, phenyltrimethylammonium, oxytetracycline) with two aluminosilicate clay minerals and one soil. A comparison of Freundlich isotherm parameters revealed isotherm linearity or nonlinearity was not significantly different between column chromatography and traditional batch experiments.

Nonlinearity of cationic aromatic amine sorption to aluminosilicates and soils: role of intermolecular cation-π interactions.

Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-π, π-π, and van der Waals interactions can increase aromatic cationic amine sorption to Na/Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3-2.

Polyfunctional ionogenic compound sorption: challenges and new approaches to advance predictive models.

Polyfunctional ionogenic compounds are unique in that they sorb to environmental solids at multiple receptor sites via multiple interaction mechanisms. However, existing sorption models fail to accommodate: (i) sorption via a single mechanism (e.g.

Trends in soil sorption coefficients within common antimicrobial families.

Sorption coefficients (K(d)) of fluoroquinolone, tetracycline, and sulfonamide antimicrobial compounds were measured for seven soils between pH 4.5 and 8.5 using batch sorption techniques.

Hydroxynaphthoic acid isomer sorption onto goethite.

This study used batch and attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) flow-through techniques, along with computational chemistry, to probe the sorption of hydroxynaphthoic acid (HNA) isomers at the goethite-water interface. The HNA isomers employed in this study, 1-hydroxy-2-naphthoic acid and 2-hydroxy-3-naphthoic acid, possessed an intramolecular hydrogen bond (IHB) between their carboxyl and hydroxyl groups, which resulted in coupled vibrational modes. Complimentary information from batch and ATR-FTIR studies suggested surface complexation via a bidentate structure, involving both the carboxylate and phenolate groups, as the dominant mode of sorption.

Improved speciation of dissolved organic nitrogen in natural waters: amide hydrolysis with fluorescence derivatization.

The objective of this study was to improve primary-amine nitrogen (1 degree-N) quantification in dissolved organic matter (DOM) originating from natural waters where inorganic forms of N, which may cause analytical interference, are commonly encountered. Efforts were targeted at elucidating organic-N structural criteria influencing the response of organic amines to known colorimetric and fluorescent reagents and exploring the use of divalent metal-assisted amide hydrolysis in combination with fluorescence analyses. We found that reaction of o-phthaldialdehyde (OPA) with primary amines is significantly influenced by steric factors, whereas fluorescamine (FLU) lacks sensitivity to steric factors and allows for the detection of a larger suite of organic amines, including di- and tri-peptides and sterically hindered 1degree-N.

Sorption of ciprofloxacin and oxytetracycline zwitterions to soils and soil minerals: influence of compound structure.

Oxytetracycline (OTC) zwitterions sorbed to a greater extent than ciprofloxacin (CIP) zwitterions onto goethite and soils with moderate-to-low effective cation exchange capacities (ECEC < 10 cmol(c)/kg) because adjacent pairs of hydroxyl groups on the OTC molecule (absent in CIP) facilitated greater surface complexation to soil metal oxides and aluminosilicate edge sites. CIP sorbed to a higher extentthan OTC onto aluminosilicates and onto soils with "high" ECEC values (>10 cmol(c)/kg). The sorption of heterocyclic compounds structurally similar to CIP indicated that both positive charge localization on the cationic amine and the extent of charge delocalization to the heterocyclic ring influenced molecular orientation within the montmorillonite interlayers, van der Waals interactions, and the potential for sorption.

Spectroscopic investigation of ciprofloxacin speciation at the goethite-water interface.

We investigated ciprofloxacin (a fluoroquinolone antibiotic) speciation as a function of pH in aqueous solution and in the presence of dissolved ferric ions and goethite using ATR-FTIR and UV-vis spectroscopy. The presence of dissolved and surface bound ferric species induced the deprotonation of the ciprofloxacin carboxylic acid group at pH < pKa1. The resultant ciprofloxacin zwitterions appeared to interact via both carboxylate oxygens to form bidentate chelate and bridging bidentate complexes within colloidal iron oxide-ciprofloxacin precipitates and bidentate chelates on the goethite surface.

Factors influencing the sorption of oxytetracycline to soils.

Veterinary antibiotics such as oxytetracycline (OTC) increasingly are found in the environment and often come into direct contact with soils via the release of animal wastes. Oxytetracycline is known to sorb strongly to soils by interaction with soil organic matter, clay minerals, and metal oxides. However, current knowledge of the influence of soil properties on OTC sorption is limited, as is our ability to predict OTC sorption to soils.

2,4-D sorption in iron oxide-rich soils: role of soil phosphate and exchangeable Al.

This study examined herbicide retention in iron oxide-rich variable charge soils (Ultisols) under no cultivation (forest), agriculture (farm), and turf maintenance (golf course) to explore the following hypothesis: inorganic phosphate accumulation from soil fertilization and liming to decrease exchangeable aluminum (Al) content will influence carboxylic acid herbicide sorption onto soils and leaching into groundwater. A suite of soil properties, including mineralogy (particularly soil iron and aluminum oxide content), exchangeable Al content, and soil phosphate content, influenced sorption of the anionic, 2,4-D. In general, 2,4-D sorption was lower in the presence of phosphate, possibly due to competition between phosphate and 2,4-D for surface sites or increase in surface negative charge resulting from phosphate sorption.

Fluoride sorption and associated aluminum release in variable charge soils.

Fluoride sorption and related aluminum (Al) release are evaluated in two iron-oxide-rich soils as a function of soil depth, composition, and physical-chemical properties and potential mechanisms of fluoride-surface interaction are suggested. Measured Al concentrations at equilibrium fluoride sorption, reflective of the net balance between Al dissolution and sequestration of the released Al by the solid phase, suggest net fluoride-assisted dissolution of Al-bearing amorphous and crystalline soil minerals. Strikingly, soils of similar depth and horizonation from the same soil order but of distinct soil series exhibited markedly different susceptibility to Al loss in the presence of fluoride, possibly a combined result of differences in the mechanism of fluoride sorption, soil mineralogy, reactivity of the surficial Al and Fe, and soil solution chemistry.

Sorption-desorption of ionogenic compounds at the mineral-water interface: study of metal oxide-rich soils and pure-phase minerals.

Sorption of the ionic compounds 2,4-D and quinmerac onto iron oxide-rich, variable charged soils was strongly influenced by mineralogy, particularly soil iron and aluminum oxides, whereas sorption of the neutral norflurazon was only related to total soil C. An appreciable fraction of the mass sorbed in stirred-flow studies was easily desorbed by deionized water, and desorption of ionic compounds was initially more rapid than sorption. This sorption-desorption behavior, although contrary to desorption hysteresis commonly observed in batch studies, suggests that the reversibly sorbed fraction is weakly bound to the soil surface.