A bilayer coating as an oxygen-transfer cascade for the electrochemical ambient conversion of methane to oxygenates

Oxidation of methane at ambient conditions to useful oxygenates at a bilayer-coated electrode is demonstrated. The composition of the coating, a Mn porphyrin mediator layer on top of a N(OH)₂/NiOOH one, allows a cascade of oxygen transfer events upon applying a potential. It is shown, using (spectro)electrochemical techniques, density functional theory computations and product analytical methods, that formate and methanol accompanied by CO₂ suppression can be observed at a certain potential range. This can lead to further development of similar oxygen/electron transfer cascades for possible use in devices for energy conversion and fuel/product generation.

DFT and Empirical Considerations on Electrocatalytic Water/Carbon Dioxide Reduction by CoTMPyP in Neutral Aqueous Solutions*

A combined experimental and density functional theory (DFT) investigation was employed in order to examine the mechanism of electrochemical CO₂ reduction and H₂ formation from water reduction in neutral aqueous solutions. A water soluble cobalt porphyrin, cobalt [5,10,15,20-(tetra-N-methyl-4-pyridyl)porphyrin], (CoTMPyP), was used as catalyst. The possible attachment of different axial ligands as well as their effect on the electrocatalytic cycles were examined. A cobalt porphyrin hydride is a key intermediate which is generated after the initial reduction of the catalyst. The hydride is involved in the formation of H₂ and formate and acts as an indirect proton source for the formation of CO in these H⁺ -starving conditions. The experimental results are in agreement with the computations and give new insights into electrocatalytic mechanisms involving water soluble metalloporphyrins. We conclude that in addition to the porphyrin's structure and metal ion center, the electrolyte surroundings play a key role in dictating the products of CO₂ /H₂ O reduction.

Enhancement of photoelectrochemical organics degradation and power generation by electrodeposited coatings of g-C3N4 and graphene on TiO2 nanotube arrays

New g-C₃N₄ coatings obtained via electropolymerization (EP) of melamine followed by a heat treatment and graphene oxide (GO) coatings based on combining GO sheets via EP of GO phenolic groups are used to improve the performance of photoanodes composed of TiO₂ nanotube arrays towards the photoelectrochemical (PEC) oxidation of methanol. This process, as examined in Na₂CO₃ solution (pH 11.4) for the two types of coatings and serving as a model for the degradation of an organic pollutant, demonstrates enhanced PEC performance as compared to that obtained using electrochemically reduced GO coatings. PEC oxidation currents obtained with 1 M methanol reach saturation at potentials as low as ∼-0.4 V vs. Ag/AgCl, with the highest saturation current density of ∼2.6 mA cm^-2 and photon-to-current efficiency of 52% as observed for the new TiO₂NTs/g-C₃N₄ photoanodes. Electrochemical impedance spectroscopy measurements for these photoanodes show a charge transfer resistance one order of magnitude lower than that obtained by the other types of coatings. This indicates an enhanced charge separation ability for the photogenerated electron-hole pairs and faster interfacial charge transfer between the electron donor (methanol) and acceptor (holes). It is also demonstrated that the process of organics degradation can be achieved not only via an applied potential but also in a galvanic photofuelcell with methanol and oxygen serving as the fuel and oxidant, respectively. The power densities achieved with the electrochemically prepared g-C₃N₄ photoanodes (∼0.5 mW cm^-2) are at least one order of magnitude higher than those reported for other TiO₂-based systems.

Graphene Oxide Sheets Combine into Conductive Coatings by Direct Oxidative Electropolymerization

New coatings are obtained when graphene oxide is further oxidized at moderate anodic potentials (≤~1.3 V vs. Ag/AgCl). Based on a variety of spectroscopic and electrochemical observations, the coatings are attributed to the direct electropolymerization of graphene oxide sheets via oxidation of the phenol edge groups on graphene. Depending on the applied potential, ether or carboxylic groups are formed. The coatings obtained via further oxidation are characterized by a lower O/C ratio due to decarboxylation and a higher content of C=C bonds. These bonds extend aromatic conjugation into the combined graphene oxide sheets and are responsible for the highly conductive nature of these coatings.

Electropolymerization as a new route to g-C3N4 coatings on TiO2 nanotubes for solar applications

A simple procedure comprising of electropolymerization followed by heat treatment allows conductive 3D structures, such TiO₂ nanotubes, to be coated with thin and uniformly distributed g-C₃N₄ films.

Tautomerism in N-confused porphyrins as the basis of a novel fiber-optic humidity sensor

It is shown that N -confused porphyrins exhibit tautomerism not only in organic solvents, as already reported, but also after incorporation in dry/humid Nafion films. This allows the development of a new fiber-optic humidity sensor which exhibits long-term stability and a linear response over the humidity range 0 to at least 4000 ppm.

Interaction of Fe(III) tetrakis(4-N-methylpyridinium)porphyrin with sodium dodecyl sulfate at submicellar concentrations

Interaction of water soluble Fe(III) tetrakis(4- N-methylpyridinium)porphyrin (Fe(III)TMPyP) with sodium dodecyl sulfate (SDS) in submicellar concentrations has been studied by surface tension, optical absorption, resonance light scattering (RLS), zeta-potential, and energy dispersive X-ray spectroscopy (EDS) measurements. Measurements were conducted for a fixed concentration of Fe(III)TMPyP (6 x 10 (-5) M) and SDS in various concentrations ranging between 6 x 10 (-6) and 6 x 10 (-2) M. Two macroscopic phase transitions, precipitation and redissolution, were observed as function of SDS concentration. The presence of a new surface active porphyrin-surfactant complex was detected. Furthermore, the presence of two oppositely charged Fe(III)TMPyP-SDS bulk moieties has been demonstrated. Possible structures for the different moieties are suggested, and the phase transitions are discussed.

Effect of drying on the biological activities of a red microalgal polysaccharide

The red microalga Porphyridium sp. produces a polysaccharide exhibiting a variety of biological activities with potential for medical and cosmetic uses. For this reason, it is important that the drying process, which is the end point of production, should not destroy the natural characteristics of the material. The objective of this study was to evaluate the effect of drying at temperatures ranging from 40 to 140 degrees C on the bioactivities of the polysaccharide. Drying the polysaccharide at temperatures above 90 degrees C caused a significant decline in its biological activities (antiviral and anti-cell proliferation) and reduced elasticity, viscosity, and intrinsic viscosity relative to lyophilized polysaccharide and to the starting product. The relationship between molecular weight and intrinsic viscosity indicated that the polysaccharide takes a rigid coil conformation, which stiffens as a result of drying. FTIR analysis revealed that drying caused both significant conformational alterations in the polymer chains and changes in the interaction between the polysaccharide and the glycoprotein to which it is noncovalently associated. Differential scanning calorimetry analysis of the water adsorbed on the charged groups of the polysaccharide showed that drying at higher temperatures increased the bound water content due to dissociation of the polymer chains. Thus, it is recommended that the polysaccharide be dried in a two-step process in which free water is removed by convection and bound freezing water is removed by lyphophilization.

Selective separation of cis-trans geometrical isomers of beta-carotene via CO2 supercritical fluid extraction

We investigated a novel method for the selective separation of beta-carotene isomers from a freeze-dried powder of the algae Dunaliella bardawil using supercritical fluid extraction. The separation method relies on the different dissolution rate of the 9Z and all-E isomers of beta-carotene in SC-CO(2). At first, the equilibrium solubility of the two isomers in SC-CO(2) was determined at the extraction conditions of 44.8 MPa and 40 degrees C. The solubility of the 9Z isomer was found to be nearly 4 times higher than that of the all-E isomer (1.92 x 10(-5) g all-E isomer/g CO(2) compared to 7.64 x 10(-5) g 9Z isomer/g CO(2)). When supercritical fluid extraction was applied to a carotenoid concentrate from the algae (29 wt% beta-carotene) or a freeze-dried powder of the algae (3.1% beta-carotene), a selective separation of the 9Z/all-E isomers of beta-carotene was obtained. Thirty-nine percent recovery of beta-carotene with 80% purity of 9Z isomer was achieved at the initial stages of extraction (40 mL CO(2)). The extraction rate of beta-carotene from the freeze-dried algae powder was slower than that from the carotenoid concentrate, resulting in a reduction in the recovery and purity of the 9Z isomer. This indicates that even at the initial stage of the extraction the internal mass resistance is significant. Isomer purity and recovery could be enhanced upon grinding of the algae powder.

Graduate primary care training: a collaborative alternative for family practice, internal medicine, and pediatrics

The Residency Program in Social Medicine at Montefiore Medical Center is a collaborative, integrated training program for primary care pediatricians, internists, and family physicians within one interdisciplinary organization. Since 1970 we have trained more than 200 physicians, prepared them for board certification in their specialty, emphasized the psychosocial aspects and social determinants of health and illness, and shared a faculty, curriculum, and commitment to provide medical care for inner-city, underserved populations. We discuss the program's history and curriculum, administrative and academic structure, shared "cross-track" faculty units (psychosocial; social medicine; and research, education, and evaluation), and graduates' practice outcomes. The interdisciplinary character of the Residency Program in Social Medicine helps physicians successfully serve the underserved and exemplifies that interdisciplinary medical education succeeds when interdisciplinary health care teams are organized for optimal patient care. Only the federal government has the perspective and power to foster more interdisciplinary collaboration and strengthen primary care education in a period of shrinking resources.