Halogen Bonding in Perfluoroalkyl Adsorption.

Adsorption is a promising technology to remove perfluoroalkyl substances (PFAS), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), from contaminated water. Although a large number of materials have been evaluated for PFAS adsorption, guidelines that can facilitate the rational design and selection of adsorbents have not been established due to the lack of a mechanistic understanding on the molecular level. Using a novel interpretation of the Freundlich isotherm, this study identifies halogen bonding as the main mechanism controlling perfluoroalkyl adsorption by using a materiomic approach that compares the electrostatic polarities of a variety of carbon, polymer, and mineral-based materials reported in the literature.

Size-Controlled Capacity and Isocapacity Concentration in Freundlich Adsorption.

The Freundlich isotherm is a classic model widely used to analyze the equilibrium of solution-phase adsorption. Further analysis of the adsorption mechanism has, however, been hindered by the empirical nature of the Freundlich isotherm. By deriving the Freundlich isotherm from the Gibbs equation, this study presents a novel interpretation of the classic model with theoretical definitions for model parameters.

An X-ray absorption fine structure spectroscopy study of metal sorption to graphene oxide.

Remediation and prevention of environmental contamination by toxic metals is an ongoing issue. Additionally, improving water filtration systems is necessary to prevent toxic metals from circulating through the water supply. Graphene oxide (GO) is a highly sorptive material for a variety of heavy metals under different ionic strength conditions over a wide pH range, making it a promising candidate for use in metal adsorption from contaminated sites or in filtration systems.

Chemical Bath Deposition of Aluminum Oxide Buffer on Curved Surfaces for Growing Aligned Carbon Nanotube Arrays.

Direct growth of vertically aligned carbon nanotube (CNT) arrays on substrates requires the deposition of an aluminum oxide buffer (AOB) layer to prevent the diffusion and coalescence of catalyst nanoparticles. Although AOB layers can be readily created on flat substrates using a variety of physical and chemical methods, the preparation of AOB layers on substrates with highly curved surfaces remains challenging. Here, we report a new solution-based method for preparing uniform layers of AOB on highly curved surfaces by the chemical bath deposition of basic aluminum sulfate and annealing.

Infrared Signature of the Cation-π Interaction between Calcite and Aromatic Hydrocarbons.

The cation-π interaction is proposed as an important mechanism for the adsorption of aromatic hydrocarbons having non-zero quadrupole moments by mineral surfaces. Direct evidence supporting such a mechanism is, however, limited. Using the model mineral calcite, we probe the cation-π interaction with adsorbed benzene, toluene, and ethylbenzene (BTE) molecules using attenuated total reflectance Fourier transform infrared spectroscopy.

Opposing effects of humidity on rhodochrosite surface oxidation.

Rhodochrosite (MnCO3) is a model mineral representing carbonate aerosol particles containing redox-active elements that can influence particle surface reconstruction in humid air, thereby affecting the heterogeneous transformation of important atmospheric constituents such as nitric oxides, sulfur dioxides, and organic acids. Using in situ atomic force microscopy, we show that the surface reconstruction of rhodochrosite in humid oxygen leads to the formation and growth of oxide nanostructures. The oxidative reconstruction consists of two consecutive processes with distinctive time scales, including a long waiting period corresponding to slow nucleation and a rapid expansion phase corresponding to fast growth.

Multi-body coalescence in Pickering emulsions.

Particle-stabilized Pickering emulsions have shown unusual behaviours such as the formation of non-spherical droplets and the sudden halt of coalescence between individual droplets. Here we report another unusual behaviour of Pickering emulsions-the simultaneous coalescence of multiple droplets in a single event. Using latex particles, silica particles and carbon nanotubes as model stabilizers, we show that multi-body coalescence can occur in both water-in-oil and oil-in-water emulsions.

Binder-free carbon nanotube electrode for electrochemical removal of chromium.

Electrochemical treatment of chromium-containing wastewater has the advantage of simultaneously reducing hexavalent chromium (CrVI) and reversibly adsorbing the trivalent product (CrIII), thereby minimizing the generation of waste for disposal and providing an opportunity for resource reuse. The application of electrochemical treatment of chromium is often limited by the available electrochemical surface area (ESA) of conventional electrodes with flat surfaces. Here, we report the preparation and evaluation of carbon nanotube (CNT) electrodes consisting of vertically aligned CNT arrays directly grown on stainless steel mesh (SSM).

Multifunctional and recollectable carbon nanotube ponytails for water purification.

Carbon nanotubes (CNTs) are promising nanomaterials that have the potential to revolutionize water treatment practices in the future. The direct use of unbounded CNTs, however, poses health risks to humans and ecosystems because they are difficult to separate from treated water. Here, we report the design and synthesis of carbon nanotube ponytails (CNPs) by integrating CNTs into micrometer-sized colloidal particles, which greatly improves the effectiveness of post-treatment separation using gravitational sedimentation, magnetic attraction, and membrane filtration.

Removal of oil droplets from contaminated water using magnetic carbon nanotubes.

Water contaminated by oil and gas production poses challenges to the management of America's water resources. Here we report the design, fabrication, and laboratory evaluation of multi-walled carbon nanotubes decorated with superparamagnetic iron-oxide nanoparticles (SPIONs) for oil-water separation. As revealed by confocal laser-scanning fluorescence microscopy, the magnetic carbon nanotubes (MCNTs) remove oil droplets through a two-step mechanism, in which MCNTs are first dispersed at the oil-water interface and then drag the droplets with them out of water by a magnet.

Methylation of glycosylated sphingolipid modulates membrane lipid topography and pathogenicity of Cryptococcus neoformans.

In previous studies we showed that the replication of Cryptococcus neoformans in the lung environment is controlled by the glucosylceramide (GlcCer) synthase gene (GCS1), which synthesizes the membrane sphingolipid GlcCer from the C9-methyl ceramide. Here, we studied the effect of the mutation of the sphingolipid C9 methyltransferase gene (SMT1), which adds a methyl group to position 9 of the sphingosine backbone of ceramide. The C.

Membrane sphingolipids as essential molecular signals for Bacteroides survival in the intestine.

As predominant intestinal symbiotic bacteria, Bacteroides are essential in maintaining the health of the normal mammalian host; in return, the host provides a niche with plentiful nutrients for the symbionts. However, the intestinal environment is replete with chemical, physical, and biological challenges that require mechanisms for prompt and adept sensing of and responses to stress if the bacteria are to survive. Herein we propose that to persist in the intestine Bacteroides take advantage of their unusual bacterial sphingolipids to mediate signaling pathways previously known to be available only to higher organisms.

Copper doping improves hydroxyapatite sorption for arsenate in simulated groundwaters.

Hydroxyapatite (HAP) has been widely used to immobilize many cationic heavy metals in water and soils. Compared with its strong sorption for metal cations, the abilities of HAP to sorb metal anions, such as arsenic, are less significant. Improving HAP sorption for anionic arsenic species is important for expanding its application potential because the presence of arsenic in the environment has raised serious health concerns and there is need for cost-effective remediation methods.

Growth of manganese oxide nanostructures alters the layout of adhesion on a carbonate substrate.

Nanostructures grown under natural conditions can modify the layout of adhesion on mineral surfaces. Using force-volume microscopy and a silicon-nitride probe, we measure changes in adhesion when a patchy overgrowth of manganese oxide nanostructures forms on the surface of rhodochrosite. For the most part, the observations show that the adhesive force to the nanostructures is dominated by van-der-Waals attraction.

Interfacial forces are modified by the growth of surface nanostructures.

Nanostructures formed by chemical reaction can modify the interfacial forces present in aqueous solution near a surface. This study uses force-volume microscopyto explore this phenomenon for the growth of manganese oxide nanostructures on rhodochrosite. The interfacial forces above the oxide nanostructures are dominated by electrostatic repulsion for probe-surface separations greater than ca.

Electrical properties of mineral surfaces for increasing water sorption.

Thin films of nanostructures alter the electrical properties of mineral surfaces and thereby affect reactions with charged species such as metal ions and biological cells. In this study, electric-force microscopy is used to probe the electrical properties of a heterogeneous layout of manganese oxide nanostructures grown as a film on a MnCO3 substrate. The role of water sorption is examined by carrying out experiments for increasing relative humidity (RH).

Surface-potential heterogeneity of reacted calcite and rhodochrosite.

Nanostructures can form on mineral surfaces through reactions with H2O or O2 in the natural environment. In this study, nanostructures on the (1014) surfaces of calcite and rhodochrosite are characterized by their surface potentials using Kelvin probe force microscopy. Water-induced nanostructures on calcite have a topographic height of 1.

Relative reactivity of amino acids with chlorine in mixtures.

The relative reactivity of chlorine with amino acids is an important determinant of the resulting chlorination products in systems where chlorine is the limiting reagent, for example, in the human gastrointestinal tract after consumption of chlorine-containing water, or during food preparation with chlorinated water. Since few direct determinations of the initial reactivity of chlorine with amino acids have been made, 17 amino acids were compared in this study using competitive kinetic principles. The experimental results showed that (1) most amino acids have similar initial reactivities at neutral pH; (2) amino acids with thiol groups such as methionine and cysteine are exceptionally reactive and produce sulfoxides; (3) amino acids without thiol groups primarily undergo monochlorination of the amino nitrogen; and (4) glycine and proline are the least reactive.

Cyanogen chloride precursor analysis in chlorinated river water.

Amino acids have been cited as potential precursors of the disinfection byproduct cyanogen chloride in chlorinated drinking water. Screening experiments with 17 amino acids were performed in this study to comprehensively identify important CNCl precursors. Among this set, only glycine was found to yield detectable CNCl (i.

Mechanism and kinetics of cyanogen chloride formation from the chlorination of glycine.

Glycine is an important precursor of cyanogen chloride (CNCl)--a disinfection byproduct (DBP) found in chlorinated drinking water. To model CNCl formation from glycine during chlorination, the mechanism and kinetics of the reaction between glycine and free chlorine were investigated. Kinetic experiments indicated that CNCI formation was limited by either the decay rates of N,N-dichloroglycine or a proposed intermediate, N-chloroiminocarboxylate, CIN=CHCO2-.

Stability of cyanogen chloride in the presence of free chlorine and monochloramine.

Cyanogen chloride (CNCl) is a disinfection byproduct found in chlorinated and chloraminated drinking water. Although there is an apparent greater association of CNCI with chloraminated water relative to chlorination systems, it was not clear whether these phenomenological observations are explained by differences in the stability or formation potentials of CNCI between the two disinfectants. In this study, the stability of CNCl was examined in the presence of free chlorine and monochloramine using membrane introduction mass spectrometry.