Adaptive response by an electrolyte: resilience to electron losses in a dye-sensitized porous photoanode

Photovoltage and photocurrents below theoretical limits in dye-sensitized photoelectrochemical solar energy conversion systems are usually attributed to electron loss processes such as dye–electron and electrolyte–electron recombination reactions within the porous photoanode. Whether recombination is a major loss mechanism is examined here, using a multiscale reaction–diffusion computational model to evaluate system characteristics. The dye-sensitized solar cell with an I⁻/I₃⁻ redox couple is chosen as a simple, representative model system because of the extensive information available for it. Two photoanode architectures with dye excitation frequencies spanning 1–25 s⁻¹ are examined, assuming two distinct recombination mechanisms. The simulation results show that although electrolyte–electron reactions are very efficient, they do not significantly impact photoanode performance within the system as defined. This is because the solution-phase electrolyte chemistry plays a key role in mitigating electron losses through coupled reactions that produce I⁻ within the photoanode pores, thereby cycling the electrolyte species without requiring that all electrolyte reduction reactions take place at the more distantly located cathode. This is a functionally adaptive response of the chemistry that may be partly responsible for the great success of this redox couple for dye-sensitized solar cells. The simulation results provide predictions that can be tested experimentally.

Interfacial electrolyte reactions in the pores of a photoanode consume electrons. The losses are offset by compensating solution-phase reactions that generate I⁻ locally, and promote efficient dye cycling and photocurrent generation.     

A PRELIMINARY INVESTIGATION OF THE USE OF LIMONENE FOR DETECTING SINGLET OXYGEN AS A COMPONENT OF POLLUTED AIR

Abstract— Exploratory experiments using simulated conditions indicate that the terpene, (+)-limonene can serve to detect O₂(¹Δ_g) in polluted atmospheres. ¹O₂ attack on limonene results in the formation of specific oxidation products in a specific distribution; quantitative identification of these products is a highly specific test for ¹O₂.     

Relationship Between Professional Development,Teachers' Instructional Practices,and the Achievement of Students in Science and Mathematics

The purpose of this study was to examine the relationship between different types of professional development, teachers' instructional practices, and the achievement of students in science and mathematics. The types of professional development studied included immersion, examining practice, curriculum implementation, curriculum development, and collaborative work. Data regarding teachers' instructional practices and the amount of professional development were collected using teacher surveys. Ninety‐four middle school science teachers and 104 middle school mathematics teachers participated in the study. Student achievement was measured using eighth grade state science and mathematics achievement test data. Regression analyses suggested that for both science and mathematics teachers, examining practice and curriculum development were significantly related to the use of standards‐based instructional practices. Only curriculum development for mathematics teachers was significantly related to student achievement. Implications of results for the professional development of science and mathematics teachers are discussed.     

A rapid,spatially dispersive frequency comb spectrograph aimed at gas phase chemical reaction kinetics

This New Views article will highlight some recent advances in high sensitivity gas detection using direct infrared absorption frequency comb laser spectroscopy, with a focus on frequency comb use in chemical reaction kinetics and our own contribution to this field. Our recently implemented detection technique uses a combination of a 12.9?GHz free spectral range virtually imaged phased array and diffraction grating to spatially disperse the mid-infrared frequency comb onto a camera. Individual frequencies or ‘comb teeth’ of a 250?MHz repetition-rate frequency comb are able to be resolved. High molecular sensitivity is achieved by increasing the interaction path length using a Herriott multipass cell. High spectral resolution, broadband spectral coverage, and high molecular sensitivity are all achieved on an adjustable 1–50 µs timescale, making this frequency comb apparatus ideal for measuring chemical reaction kinetics where multiple absorbing species can be monitored simultaneously. This New Views article will also discuss some of the challenges and decisions that chemists might face in implementing this advanced physics technology in their own laboratory.

Spatially dispersed 250 MHz mid-infrared frequency comb laser, with absorption of some frequencies by a dilute sample of methane.     

A phase I, randomized study of combined IL-2 and therapeutic immunisation with antiretroviral therapy

Background  

Fully functional HIV-1-specific CD8 and CD4 effector T-cell responses are vital to the containment of viral activity and disease progression. These responses are lacking in HIV-1-infected patients with progressive disease. We attempted to augment fully functional HIV-1-specific CD8 and CD4 effector T-cell responses in patients with advanced chronic HIV-1 infection.     

Reaction of 3-Diazocamphor with Silver Ion - Formation of Tricyclanone

The usual method of formation of tricyclanone (1) involves thermolysis of an intimate mixture of 3-diazocamphor (3) and copper powder and is thought to involve ketocarbene (5).¹ Recently this method has been supplemented² by one which involves reaction of 3,3-dibromocamphor with diethylzinc in benzene where α-elimination to give ketocarbene (5) is mediated by 3-bromocamphor carbanion whose role is indicated by trapping as 3-bromocamphor; this material accounts for ca. 10% of product even after prolonged reaction times.     

Simultaneous determination of inulin and p-aminohippuric acid (PAH) in human plasma and urine by high-performance liquid chromatography

Inulin and p-aminohippuric acid (PAH) clearances are used for the estimation of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). A simple and rapid high-performance liquid chromatography (HPLC) method with UV detection is described for the simultaneous determination of inulin and PAH in the same chromatogram in the plasma and urine of humans. Plasma and urine samples were hydrolyzed with perchloric acid (0.7%) in boiling water. The mobile phase consisted of 0.01 M potassium dihydrogenphosphate with 0.02 M tetramethylammonium chloride and o-phosphoric acid (pH 3)-acetonitrile (94:6, v/v), pumped at a rate of 1.2 ml min-1 on a C8 reversed-phase column. Tannic acid was used as the internal standard and UV detection at 285 nm was employed. The calibration curves were linear over the concentration range of 12.5-100 mg l-1 for inulin and 6.25-50 mg l-1 for PAH with determination coefficients greater than 0.997. The method is accurate (bias < 13%) and reproducible (intra- and inter-day relative standard deviation less than 11%), with a limit of quantitation of 12.5 mg l-1 and 6.25 mg l-1 for inulin and PAH, respectively. Analytical recoveries from urine and plasma were ranged from 81 to 108% for both compounds. This fully validated method, which allows the simultaneous determination of inulin and PAH clearances, is simple, rapid (total run time < 10 min) and requires only a 200 microliters plasma or urine sample.     

The solubility of oxygen in aqueous fluorocarbon emulsions

The solubility of oxygen in aqueous fluorocarbon emulsions has been measured directly for several perfluorocarbons and monobromo or monoiodo-perfluorocarbons. The measured oxygen solubilities are consistent with results for the solubility of oxygen in neat liquid perfluorinated organic compounds.     

Molybdenum-phosphorus triple bond stabilization by ancillary alkoxide ligation: synthesis and structure of a terminal phosphide tris-1-methylcyclohexanoxide complex

Using alcoholysis, we converted terminal phosphide PMo(N[i-Pr]Ar)3 into a new, monomeric terminal phosphide PMo(OR)3, where R = 1-methylcyclohexyl or 1-adamantyl. Dimerization of the PMo unit was observed upon alcoholysis with 2,6-dimethylphenol, and the dimer [PMo(N[i-Pr]Ar)(O-2,6-C6H3Me2)2]2 was isolated and characterized by X-ray crystallography.