Adsorption from aqueous solutions on opened carbon nanotubes: organic compounds speed up delivery of water from inside

We report the results of first systematic studies of organic adsorption from aqueous solutions onto relatively long single walled carbon nanotubes (four tubes, in initial and oxidised forms). Using molecular dynamics simulations (GROMACS package) we discuss the behaviour of tube-water as well as tube-adsorbate systems, for three different adsorbates (benzene, phenol and paracetamol).

Testing isotherm models and recovering empirical relationships for adsorption in microporous carbons using virtual carbon models and grand canonical Monte Carlo simulations

Using the plausible model of activated carbon proposed by Harris and co-workers and grand canonical Monte Carlo simulations, we study the applicability of standard methods for describing adsorption data on microporous carbons widely used in adsorption science. Two carbon structures are studied, one with a small distribution of micropores in the range up to 1 nm, and the other with micropores covering a wide range of porosity. For both structures, adsorption isotherms of noble gases (from Ne to Xe), carbon tetrachloride and benzene are simulated. The data obtained are considered in terms of Dubinin-Radushkevich plots. Moreover, for benzene and carbon tetrachloride the temperature invariance of the characteristic curve is also studied. We show that using simulated data some empirical relationships obtained from experiment can be successfully recovered. Next we test the applicability of Dubinin's related models including the Dubinin-Izotova, Dubinin-Radushkevich-Stoeckli, and Jaroniec-Choma equations. The results obtained demonstrate the limits and applications of the models studied in the field of carbon porosity characterization.

Hyper-parallel tempering Monte Carlo simulations of Ar adsorption in new models of microporous non-graphitizing activated carbon: effect of microporosity

The adsorption of gases on microporous carbons is still poorly understood, partly because the structure of these carbons is not well known. Here, a model of microporous carbons based on fullerene- like fragments is used as the basis for a theoretical study of Ar adsorption on carbon. First, a simulation box was constructed, containing a plausible arrangement of carbon fragments. Next, using a new Monte Carlo simulation algorithm, two types of carbon fragments were gradually placed into the initial structure to increase its microporosity. Thirty six different microporous carbon structures were generated in this way. Using the method proposed recently by Bhattacharya and Gubbins ( BG), the micropore size distributions of the obtained carbon models and the average micropore diameters were calculated. For ten chosen structures, Ar adsorption isotherms ( 87 K) were simulated via the hyper- parallel tempering Monte Carlo simulation method. The isotherms obtained in this way were described by widely applied methods of microporous carbon characterisation, i. e. Nguyen and Do, Horvath - Kawazoe, high- resolution alpha(a)s plots, adsorption potential distributions and the Dubinin - Astakhov ( DA) equation. From simulated isotherms described by the DA equation, the average micropore diameters were calculated using empirical relationships proposed by different authors and they were compared with those from the BG method.

The study of chiral adsorption systems using synchrotron- based structural and spectroscopic techniques: stereospecific adsorption of serine on Au-modified chiral Cu{531} surfaces

We apply modern synchrotron-based structural techniques to the study of serine adsorbed on the pure andAumodified intrinsically chiral Cu{531} surface. XPS and NEXAFS data in combination with DFT show that on the pure surface both enantiomers adsorb in l4 geometries (with de-protonated b-OH groups) at low coverage and in l3 geometries at saturation coverage. Significantly larger enantiomeric differences are seen for the l4 geometries, which involve substrate bonds of three side groups of the chiral center, i.e. a three-point interaction. The l3 adsorption geometry, where only the carboxylate and amino groups form substrate bonds, leads to smaller but still significant enantiomeric differences, both in geometry and the decomposition behavior. When Cu{531} is modified by the deposition of 1 and 2ML Au the orientations of serine at saturation coverage are significantly different from those on the clean surface. In all cases, however, a l3 bond coordination is found at saturation involving different numbers of Au atoms, which leads to relatively small enantiomeric differences.

Colloidal gas aphrons (CGA): dispersion and structural features

Colloidal gas aphrons (CGA) have previously been defined as surfactant stabilized gas microbubbles and characterized for a number of surfactants in terms of stability, gas holdup and bubble size even though there is no conclusive evidence of their structure (that is, orientation of surfactant molecules at the gas–liquid interface, thickness of gas–liquid interface, and/or number of surfactant layers). Knowledge of the structure would enable us to use these dispersions more efficiently for their diverse applications (such as for removal of dyes, recovery of proteins, and enhancement of mass transfer in bioreactors). This study investigates dispersion and structural features of CGA utilizing a range of novel predictive (for prediction of aphron size and drainage rate) and experimental (electron microscopy and X-ray diffraction) methods. Results indicate structural differences between foams and CGA, which may have been caused by a multilayer structure of the latter as suggested by the electron and X-ray diffraction analysis.

Interactions of surfactants (edge activators) and skin penetration enhancers with liposomes

Incorporating edge activators (surfactants) into liposomes was shown previously to improve estradiol vesicular skin delivery; this phenomenon was concentration dependent with low or high concentrations being less effective. Replacing surfactants with limonene produced similar behaviour, but oleic acid effects were linear with concentration up to 16% (w/w), beyond which it was incompatible with the phospholipid. This present study thus employed high sensitivity differential scanning calorimetry to probe interactions of additives with ipalmitoylphosphatidylcholine (DPPC) membranes to explain such results. Cholesterol was included as an example of a membrane stabiliser that removed the DPPC pre-transition and produced vesicles with a higher transition temperature (Tm). Surfactants also removed the lipid pre-transition but reduced Tm and co-operativity of the main peak. At higher concentrations, surfactants also formed new species, possibly mixed micelles with a lower Tm. The formation of mixed micelles may explain reduced skin delivery from liposomes containing high concentrations of surfactants. Limonene did not remove the pre-transition but reduced Tm and co-operativity of the main peak, apparently forming new species at high concentrations, again correlating with vesicular delivery of estradiol. Oleic acid obliterated the pre-transition. The Tm and the co-operativity of the main peak were reduced with oleic acid concentrations up to 33.2 mol%, above which there was no further change. At higher concentrations, phase separation was evident, confirming previous skin transport findings.

The importance of attractive three-point interaction in enantioselective surface chemistry: stereospecific adsorption of serine on the intrinsically chiral Cu{531} surface

Both enantiomers of serine adsorb on the intrinsically chiral Cu{531} surface in two different adsorption geometries, depending on the coverage. At saturation, substrate bonds are formed through the two oxygen atoms of the carboxylate group and the amino group (μ3 coordination), whereas at lower coverage, an additional bond is formed through the deprotonated β−OH group (μ4 coordination). The latter adsorption geometry involves substrate bonds through three side groups of the chiral center, respectively, which leads to significantly larger enantiomeric differences in adsorption geometries and energies compared to the μ3 coordination, which involves only two side groups. This relatively simple model system demonstrates, in direct comparison, that attractive interactions of three side groups with the substrate are much more effective in inducing strong enantiomeric differences in heterogeneous chiral catalyst systems than hydrogen bonds or repulsive interactions.

Applicability of molecular simulations for modelling the adsorption of the greenhouse gas CF4 on carbons

Tetrafluoromethane, CF4, is powerful greenhouse gas, and the possibility of storing it in microporous carbon has been widely studied. In this paper we show, for the first time, that the results of molecular simulations can be very helpful in the study of CF4 adsorption. Moreover, experimental data fit to the results collected from simulations. We explain the meaning of the empirical parameters of the supercritical Dubinin–Astakhov model proposed by Ozawa and finally the meaning of the parameter k of the empirical relation proposed by Amankwah and Schwarz.

Estimating root–soil contact from 3D X-ray microtomographs

Adequate contact with the soil is essential for water and nutrient adsorption by plant roots, but the determination of root–soil contact is a challenging task because it is difficult to visualize roots in situ and quantify their interactions with the soil at the scale of micrometres. A method to determine root–soil contact using X-ray microtomography was developed. Contact areas were determined from 3D volumetric images using segmentation and iso-surface determination tools. The accuracy of the method was tested with physical model systems of contact between two objects (phantoms). Volumes, surface areas and contact areas calculated from the measured phantoms were compared with those estimated from image analysis. The volume was accurate to within 0.3%, the surface area to within 2–4%, and the contact area to within 2.5%. Maize and lupin roots were grown in soil (<2 mm) and vermiculite at matric potentials of −0.03 and −1.6 MPa and in aggregate fractions of 4–2, 2–1, 1–0.5 and < 0.5 mm at a matric potential of −0.03 MPa. The contact of the roots with their growth medium was determined from 3D volumetric images. Macroporosity (>70 µm) of the soil sieved to different aggregate fractions was calculated from binarized data. Root-soil contact was greater in soil than in vermiculite and increased with decreasing aggregate or particle size. The differences in root–soil contact could not be explained solely by the decrease in porosity with decreasing aggregate size but may also result from changes in particle and aggregate packing around the root.

Transient climate change simulations with a coupled atmosphere–ocean GCM including the tropospheric sulfur cycle

The time-dependent climate response to changing concentrations of greenhouse gases and sulfate aerosols is studied using a coupled general circulation model of the atmosphere and the ocean (ECHAM4/OPYC3). The concentrations of the well-mixed greenhouse gases like CO2, CH4, N2O, and CFCs are prescribed for the past (1860–1990) and projected into the future according to International Panel on Climate Change (IPCC) scenario IS92a. In addition, the space–time distribution of tropospheric ozone is prescribed, and the tropospheric sulfur cycle is calculated within the coupled model using sulfur emissions of the past and projected into the future (IS92a). The radiative impact of the aerosols is considered via both the direct and the indirect (i.e., through cloud albedo) effect. It is shown that the simulated trend in sulfate deposition since the end of the last century is broadly consistent with ice core measurements, and the calculated radiative forcings from preindustrial to present time are within the uncertainty range estimated by IPCC. Three climate perturbation experiments are performed, applying different forcing mechanisms, and the results are compared with those obtained from a 300-yr unforced control experiment. As in previous experiments, the climate response is similar, but weaker, if aerosol effects are included in addition to greenhouse gases. One notable difference to previous experiments is that the strength of the Indian summer monsoon is not fundamentally affected by the inclusion of aerosol effects. Although the monsoon is damped compared to a greenhouse gas only experiment, it is still more vigorous than in the control experiment. This different behavior, compared to previous studies, is the result of the different land–sea distribution of aerosol forcing. Somewhat unexpected, the intensity of the global hydrological cycle becomes weaker in a warmer climate if both direct and indirect aerosol effects are included in addition to the greenhouse gases. This can be related to anomalous net radiative cooling of the earth’s surface through aerosols, which is balanced by reduced turbulent transfer of both sensible and latent heat from the surface to the atmosphere.

Influence of earthworm Eisenia fetida on removal efficiency of N and P in vertical flow constructed wetland.

This study investigates biomass, density, photosynthetic activity, and accumulation of nitrogen (N) and phosphorus (P) in three wetland plants (Canna indica, Typha augustifolia, and Phragmites austrail) in response to the introduction of the earthworm Eisenia fetida into a constructed wetland. The removal efficiency of N and P in constructed wetlands were also investigated. Results showed that the photosynthetic rate (P n), transpiration rate (T r), and stomatal conductance (S cond) of C. indica and P. austrail were (p < 0.05) significantly higher when earthworms were present. The addition of E. fetida increased the N uptake value by above-ground of C. indica, T. augustifolia, and P. australis by 185, 216, and 108 %, respectively; and its P uptake value increased by 300, 355, and 211 %, respectively. Earthworms could enhance photosynthetic activity, density, and biomass of wetland plants in constructed wetland, resulting in the higher N and P uptake. The addition of E. fetida into constructed wetland increased the removal efficiency of TN and TP by 10 and 7 %, respectively. The addition of earthworms into vertical flow constructed wetland increased the removal efficiency of TN and TP, which was related to higher photosynthetic activity and N and P uptake. The addition of earthworms into vertical flow constructed wetland and plant harvests could be the significantly sustainable N and P removal strategy

Effects of nitrogen and sulfur fertilization on free amino acids, sugars, and acrylamide-forming potential in potato

Nitrogen (N) fertilizer is used routinely in potato (Solanum tuberosum) cultivation to maximize yield. However, it also affects sugar and free amino acid concentrations in potato tubers, and this has potential implications for food quality and safety because free amino acids and reducing sugars participate in the Maillard reaction during high-temperature cooking and processing. This results in the formation of color, aroma, and flavor compounds, but also some undesirable contaminants, including acrylamide, which forms when the amino acid that participates in the final stages of the reaction is asparagine. Another mineral, sulfur (S), also has profound effects on tuber composition. In this study, 13 varieties of potato were grown in a field trial in 2010 and treated with different combinations of N and S. Potatoes were analyzed immediately after harvest to show the effect of N and S fertilization on concentrations of free asparagine, other free amino acids, sugars, and acrylamide-forming potential. The study showed that N application can affect acrylamide-forming potential in potatoes but that the effect is type- (French fry, chipping, and boiling) and variety-dependent, with most varieties showing an increase in acrylamide formation in response to increased N but two showing a decrease. S application reduced glucose concentrations and mitigated the effect of high N application on the acrylamide-forming potential of some of the French fry-type potatoes.

Bounding the role of black carbon in the climate system: a scientific assessment

Black carbon aerosol plays a unique and important role in Earth’s climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr�-1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m�-2 with 90% uncertainty bounds of (+0.08, +1.27)Wm�-2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m�-2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m�-2 with 90% uncertainty bounds of +0.17 to +2.1 W m�-2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m�-2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (�-0.50 to +1.08) W m-�2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (�-0.06 W m�-2 with 90% uncertainty bounds of �-1.45 to +1.29 W m�-2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

Lithium and oxygen adsorption at the b-MnO2 (110) surface

The adsorption and co-adsorption of lithium and oxygen at the surface of rutile-like manganese dioxide(b-MnO2), which are important in the context of Li–air batteries, are investigated using density functional theory. In the absence of lithium, the most stable surface of b-MnO2, the (110), adsorbs oxygen in the form of peroxo groups bridging between two manganese cations. Conversely, in the absence of excess oxygen, lithium atoms adsorb on the (110) surface at two different sites, which are both tricoordinated to surface oxygen anions, and the adsorption always involves the transfer of one electron from the adatom to one of the five-coordinated manganese cations at the surface, creating (formally) Li+ and Mn3+ species. The co-adsorption of lithium and oxygen leads to the formation of a surface oxide, involving the dissociation of the O2 molecule, where the O adatoms saturate the coordination of surface Mn cations and also bind to the Li adatoms. This process is energetically more favourable than the formation of gas-phase lithium peroxide (Li2O2) monomers, but less favourable than the formation of Li2O2 bulk. These results suggest that the presence of b-MnO2 in the cathode of a nonaqueous Li–O2 battery lowers the energy for the initial reduction of oxygen during cell discharge.

Fluorinated ionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a)

The factors influencing the formation of water-in-134a-propellant microemulsions using the fluorinated ionic surfactants ammonium perfluorooctanoate, ammonium perfluoroheptanoate, and sodium perfluorooctanoate has been determined. None of the fluorinated ionic surfactants could be used to prepare clear, one-phase systems when used as sole surfactant, but they could be when combined with a short-chain fluoro- or hydrocarbon alcohol in surfactant:cosurfactant weight-mixing ratios (K(m)) in the range 1:2 to 2:1. When hydrocarbon alcohols were used this clear region extended over a wide range of compositions and was confirmed by means of photon correlation spectroscopy (PCS) to contain microemulsion droplets in the propellant-rich part of the phase diagram. PCS studies performed in the presence of the water-soluble drug terbutaline sulfate showed that it was possible to solubilize the drug within water-in-propellant microemulsion droplets. These studies confirm for the first time that it is possible to prepare water-in-propellant 134a microemulsions using fluorinated ionic surfactants and to solubilize water-soluble drugs within these systems.