Calcite‐CO2 mixed into CO2‐free air: a new CO2‐in‐air stable isotope reference material for the VPDB scale

In order to generate a reliable and long‐lasting stable isotope ratio standard for CO₂ in samples of clean air, CO₂ is liberated from well‐characterized carbonate material and mixed with CO₂‐free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO₂ is generated by a conventional acid digestion of powdered carbonate. Evolved CO₂ gas is mixed and equilibrated with a prefabricated gas comprised of N₂, O₂, Ar, and N₂O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high‐precision air‐CO₂ work (about ±0.015‰ for δ¹³C and ±0.025‰ for δ¹⁸O). To establish a valid δ¹⁸O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 47°C has been determined with a high level of precision. Using identical procedures, CO₂‐in‐air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, δ¹³C = +1.95‰ and δ¹⁸O = ?2.2‰ exactly); (2) a local calcite similar in isotopic composition to NBS 19 (‘MAR‐J1’, δ¹³C = +1.97‰ and δ¹⁸O = ?2.02‰), and (3) a natural calcite with isotopic compositions closer to atmospheric values (‘OMC‐J1’, δ¹³C = ?4.24‰ and δ¹⁸O = ?8.71‰). To quantitatively control the extent of isotope‐scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L‐SVEC, IAEA‐CO‐1, IAEA‐CO‐8, CAL‐1 and CAL‐2) were also processed. As a further control pure CO₂ reference gases (Narcis I and II, NIST‐RM 8563, GS19 and GS20) were mixed with CO₂‐free synthetic air. Independently, the pure CO₂ gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB‐scale for CO₂‐in‐air (e.g. CG‐99, based on calibration of pure CO₂ gas) has been carefully established. The systematic high‐precision comparison of secondary carbonate and CO₂ reference materials covering a wide range in isotopic composition revealed that assigned δ‐values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross‐contamination errors for high‐precision isotope ratio measurements. As a result of the experiments, a new standard reference material (SRM), which consists of two 5‐L glass flasks containing air at 1.6 bar and the CO₂ evolved from two different carbonate materials, is available for distribution. These ‘J‐RAS’ SRM flasks (‘Jena‐Reference Air Set’) are designed to serve as a high‐precision link to VPDB for improving inter‐laboratory comparability. a Copyright © 2005 John Wiley & Sons, Ltd.     

A system for high‐quality CO2 isotope analyses of air samples collected by the CARIBIC Airbus A340‐600

In 2007, JRC‐IRMM began a series of atmospheric CO₂ isotope measurements, with the focus on understanding instrumental effects, corrections as well as metrological aspects. The calibration approach at JRC‐IRMM is based on use of a plain CO₂ sample (working reference CO₂) as a calibration carrier and CO₂‐air mixtures (in high‐pressure cylinders) to determine the method‐related correction under actual analytical conditions (another calibration carrier, in the same form as the samples). Although this approach differs from that in other laboratories, it does give a direct link to the primary reference NBS‐19‐CO₂. It also helps to investigate the magnitude and nature for each of the instrumental corrections and allows for the quantification of the uncertainty introduced. Critical tests were focused on the instrumental corrections. It was confirmed that the use of non‐symmetrical capillary crimping (an approach used here to deal with small samples) systematically modifies δ¹³C(CO₂) and δ¹⁸O(CO₂), with a clear dependence on the amount of extracted CO₂. However, the calibration of CO₂‐air mixtures required the use of the symmetrical dual‐inlet mode. As a proof of our approach, we found that δ¹³C(CO₂) on extracts from mixtures agreed (within 0.010‰) with values obtained from the ‘mother’ CO₂ used for the mixtures. It was further found that very low levels of hydrocarbons in the pumping systems and the isotope ratio mass spectrometry (IRMS) instrument itself were critical. The m/z 46 values (consequently the calculated δ¹⁸O(CO₂) values) are affected by several other effects with traces of air co‐trapped with frozen CO₂ being the most critical. A careful cryo‐distillation of the extracted CO₂ is recommended. After extensive testing, optimisation, and routine automated use, the system was found to give precise data on air samples that can be traced with confidence to the primary standards. The typical total combined uncertainty in δ¹³C(CO₂) and δ¹⁸O(CO₂) on the VPDB‐CO₂ scale, estimated on runs of CO₂‐air mixtures, is ±0.040‰ and 0.060‰ (2‐σ values). Inter‐comparison with MPI‐BGC resulted in a scale discrepancy of a similar magnitude. Although the reason(s) for this discrepancy still need to be understood, this basically confirms the approach of using specifically prepared CO₂‐air mixtures as a calibration carrier, in order to achieve scale unification among laboratories. As important practical application and as a critical test, JRC‐IRMM took part in the passenger aircraft‐based global monitoring project CARIBIC ( http://www.caribic‐atmospheric.com ). In this way, reliable CO₂ isotope data for the tropopause region and the free troposphere were obtained. From June 2007 to January 2009, approximately 500 CARIBIC air samples have been analysed. Some flights demonstrated a compact correlation of both δ¹³C(CO₂) and δ¹⁸O(CO₂) with respect to CO₂ concentration, demonstrating mixing of tropospheric and stratospheric air masses. These excellent correlations provide an independent, realistic data quality check. Copyright © 2009 John Wiley & Sons, Ltd.     

Repeat‐pulse 13CO2 labeling of canola and field pea: implications for soil organic matter studies

Both the quantity and quality of plant residues can impact soil properties and processes. Isotopic tracers can be used to trace plant residue decomposition if the tracer is homogeneously distributed throughout the plant. Continuous labeling will homogeneously label plants but is not widely accessible because elaborate equipment is needed. In order to determine if the more accessible repeat‐pulse labeling method could be used to trace plant residue decomposition, this labeling procedure was employed using ¹³CO₂ to enrich field pea and canola plants in a controlled environment. Plants were exposed weekly to pulses of 33 atom% ¹³CO₂ and grown to maturity. The distribution of the label throughout the plant parts (roots, stem, leaves, and pod) and biochemical fractions (ADF and ADL) was determined. The label was not homogeneously distributed throughout the plant; in particular, the pod fractions were less enriched than other fractions indicating the importance of continuing labeling well into plant maturity for pod‐producing plants. The ADL fraction was also less enriched than the ADF fraction. Because of the heterogeneity of the label throughout the plant, caution should be applied when using the repeat‐pulse method to trace the fate of ¹³C‐labeled residues in the soil. However, root contributions to below‐ground C were successfully determined from the repeat‐pulse labeled root material, as was ¹³C enrichment of soil within the top 15 cm. Canola contributed more above‐ and below‐ground residue C than field pea; however, canola was also higher in ADF and ADL fractions indicating a more recalcitrant residue. Copyright © 2010 John Wiley & Sons, Ltd.     

Short‐term dynamics of isotopic composition of leaf‐respired CO2 upon darkening: measurements and implications

Recent advances in understanding the metabolic origin and the temporal dynamics in δ¹³C of dark‐respired CO₂ (δ¹³C_res) have led to an increasing awareness of the importance of plant isotopic fractionation in respiratory processes. Pronounced dynamics in δ¹³C_res have been observed in a number of species and three main hypotheses have been proposed: first, diurnal changes in δ¹³C of respiratory substrates; second, post‐photosynthetic discrimination in respiratory pathways; and third, dynamic decarboxylation of enriched carbon pools during the post‐illumination respiration period. Since different functional groups exhibit distinct diurnal patterns in δ¹³C_res (ranging from 0 to 10‰ diurnal increase), we explored these hypotheses for different ecotypes and environmental (i.e. growth light) conditions. Mass balance calculations revealed that the effect of respiratory substrates on diurnal changes in δ¹³C_res was negligible in all investigated species. Further, rapid post‐illumination changes in δ¹³C_res (30 min), which increased from 2.6‰ to 5‰ over the course of the day, were examined by positional ¹³C‐labelling to quantify changes in pyruvate dehydrogenase (PDH) and Krebs cycle (KC) activity. We investigated the origin of these dynamics with Rayleigh mass balance calculations based on theoretical assumptions on fractionation processes. Neither the estimated changes of PDH and KC, nor decarboxylation of a malate pool entirely explained the observed pattern in δ¹³C_res. However, a Rayleigh fractionation of ¹²C‐discriminating enzymes and/or a rapid decline in the decarboxylation rate of an enriched substrate pool may explain the post‐illumination peak in δ¹³C_res. These results are highly relevant since δ¹³C_res is used in large‐scale carbon cycle studies. Copyright © 2009 John Wiley & Sons, Ltd.     

A Long‐Lived Mononuclear Cyclopentadienyl Ruthenium Complex Grafted onto Anatase TiO2 for Efficient CO2 Photoreduction

This work shows a novel artificial donor–catalyst–acceptor triad photosystem based on a mononuclear C₅H₅‐RuH complex oxo‐bridged TiO₂ hybrid for efficient CO₂ photoreduction. An impressive quantum efficiency of 0.56 % for CH₄ under visible‐light irradiation was achieved over the triad photocatalyst, in which TiO₂ and C₅H₅‐RuH serve as the electron collector and CO₂‐reduction site and the photon‐harvester and water‐oxidation site, respectively. The fast electron injection from the excited Ru²⁺ cation to TiO₂ in ca. 0.5 ps and the slow backward charge recombination in half‐life of ca. 9.8 μs result in a long‐lived D⁺–C–A^? charge‐separated state responsible for the solar‐fuel production.     

A method for 13C‐labeling of metabolic carbohydrates within French bean leaves (Phaseolus vulgaris L.) for decomposition studies in soils

The molecular composition of plant residues is suspected to largely govern the fate of their constitutive carbon (C) in soils. Labile compounds, such as metabolic carbohydrates, are affected differently from recalcitrant and structural compounds by soil‐C stabilisation mechanisms. Producing ¹³C‐enriched plant residues with specifically labeled fractions would help us to investigate the fate in soils of the constitutive C of these compounds. The objective of the present research was to test ¹³C pulse chase labeling as a method for specifically enriching the metabolic carbohydrate components of plant residues, i.e. soluble sugars and starch. Bean plants were exposed to a ¹³CO₂‐enriched atmosphere for 0.5, 1, 2, 3 and 21 h. The major soluble sugars were then determined on water‐soluble extracts, and starch on HCl‐hydrolysable extracts. The results show a quick differential labeling between water‐soluble and water‐insoluble compounds. For both groups, ¹³C‐labeling increased linearly with time. The difference in δ¹³C signature between water‐soluble and insoluble fractions was 7‰ after 0.5 h and 70‰ after 21 h. However, this clear isotopic contrast masked a substantial labeling variability within each fraction. By contrast, metabolic carbohydrates on the one hand (i.e. soluble sugars + starch) and other fractions (essentially cell wall components) on the other hand displayed quite homogeneous signatures within fractions, and a significant difference in labeling between fractions: δ¹³C = 414 ± 3.7‰ and 56 ± 5.5‰, respectively. Thus, the technique generates labeled plant residues displaying contrasting ¹³C‐isotopic signatures between metabolic carbohydrates and other compounds, with homogenous signatures within each group. Metabolic carbohydrates being labile compounds, our findings suggest that the technique is particularly appropriate for investigating the effect of compound lability on the long‐term storage of their constitutive C in soils. Copyright © 2009 John Wiley & Sons, Ltd.     

High CO2‐Capture Ability of a Porous Organic Polymer Bifunctionalized with Carboxy and Triazole Groups

A new porous organic polymer, SNU‐C1 , incorporating two different CO₂‐attracting groups, namely, carboxy and triazole groups, has been synthesized. By activating SNU‐C1 with two different methods, vacuum drying and supercritical‐CO₂ treatment, the guest‐free phases, SNU‐C1‐va and SNU‐C1‐sca , respectively, were obtained. Brunauer–Emmett–Teller (BET) surface areas of SNU‐C1‐va and SNU‐C1‐sca are 595 and 830 m²g^?1, respectively, as estimated by the N₂‐adsorption isotherms at 77 K. At 298 K and 1 atm, SNU‐C1‐va and SNU‐C1‐sca show high CO₂ uptakes, 2.31 mmol g^?1 and 3.14 mmol g^?1, respectively, the high level being due to the presence of abundant polar groups (carboxy and triazole) exposed on the pore surfaces. Five separation parameters for flue gas and landfill gas in vacuum‐swing adsorption were calculated from single‐component gas‐sorption isotherms by using the ideal adsorbed solution theory (IAST). The data reveal excellent CO₂‐separation abilities of SNU‐C1‐va and SNU‐C1‐sca , namely high CO₂‐uptake capacity, high selectivity, and high regenerability. The gas‐cycling experiments for the materials and the water‐treated samples, experiments that involved treating the samples with a CO₂‐N₂ gas mixture (15:85, v/v) followed by a pure N₂ purge, further verified the high regenerability and water stability. The results suggest that these materials have great potential applications in CO₂ separation.     

CO2 Fixation into Novel CO2 Storage Materials Composed of 1,2‐Ethanediamine and Ethylene Glycol Derivatives

A new CO₂ fixation process into solid CO₂‐storage materials (CO₂SMs) under mild conditions has been developed. The novel application of amine–glycol systems to the capture, storage, and utilization of CO₂ with readily available 1,2‐ethanediamine (EDA) and ethylene glycol derivatives (EGs) was demonstrated. Typically, the CO₂SMs were isolated in 28.9–47.5 % yields, followed by extensive characterization using ¹³C NMR, XRD, and FTIR. We found that especially the resulting poly‐ethylene‐glycol‐300‐based CO₂SM (PCO₂SM) product could be processed into stable tablets for CO₂ storage; the aqueous PCO₂SM solution exhibited remarkable CO₂ capturing and releasing capabilities after multiple cycles. Most importantly, the EDA and PEG 300 released from PCO₂SM were found to act as facilitative surfactants for the multiple preparation of CaCO₃ microparticles with nano‐layer structure.     

An Air‐ and Water‐Tolerant Zinc Hydride Cluster That Reacts Selectively With CO2

The reaction of [Zn₃Cl₃ L ], in which L ^3? is a tris(β‐diketiminate) cyclophane, with K(sBu)₃BH afforded [Zn₃(μ‐H)₃ L ] ( 2 ), as confirmed by NMR spectroscopy, NOESY, and X‐ray crystallography. The complex 2 was air‐stable and unreactive towards water, methanol, and other substrates (e.g., nitriles) at room temperature over 24 h but reacted with CO₂ (ca. 1 atm) to generate [Zn₃(μ‐H)₂(μ‐1,1‐O₂CH)] ( 3 ). In contrast, [Zn₃(OH)₃ L ] ( 4 ) was found to be unreactive toward CO₂ over the course of several days at 90 °C.     

High‐Performance K–CO2 Batteries Based on Metal‐Free Carbon Electrocatalysts

Metal–CO₂ batteries have attracted much attention owing to their high energy density and use of greenhouse CO₂ waste as the energy source. However, the increasing cost of lithium and the low discharge potential of Na–CO₂ batteries create obstacles for practical applications of Li/Na–CO₂ batteries. Recently, earth‐abundant potassium ions have attracted considerable interest as fast ionic charge carriers for electrochemical energy storage. Herein, we report the first K–CO₂ battery with a carbon‐based metal‐free electrocatalyst. The battery shows a higher theoretical discharge potential (E^?=2.48 V) than that of Na–CO₂ batteries (E^?=2.35 V) and can operate for more than 250 cycles (1500 h) with a cutoff capacity of 300 mA h g^?1. Combined DFT calculations and experimental observations revealed a reaction mechanism involving the reversible formation and decomposition of P12₁/c1‐type K₂CO₃ at the efficient carbon‐based catalyst.     

Ag@Au Core‐Shell Nanowires for Nearly 100 % CO2‐to‐CO Electroreduction

Electrochemical reduction of carbon dioxide (CO₂) to CO is regarded as an efficient method to utilize the greenhouse gas CO₂, because the CO product can be further converted into high value‐added chemicals via the Fisher–Tropsch process. Among all electrocatalysts used for CO₂‐to‐CO reduction, Au‐based catalysts have been demonstrated to possess high selectivity, but their precious price limits their future large‐scale applications. Thus, simultaneously achieving high selectivity and reasonable price is of great importance for the development of Au‐based catalysts. Here, we report Ag@Au core–shell nanowires as electrocatalyst for CO₂ reduction, in which a nanometer‐thick Au film is uniformly deposited on the core Ag nanowire. Importantly, the Ag@Au catalyst with a relative low Au content can drive CO generation with nearly 100 % Faraday efficiency in 0.1 m KCl electrolyte at an overpotential of ca. ?1.0 V. This high selectivity of CO₂ reduction could be attributed to a suitable adsorption strength for the key intermediate on Au film together with the synergistic effects between the Au shell and Ag core and the strong interaction between CO₂ and Cl^? ions in the electrolyte, which may further pave the way for the development of high‐efficiency electrocatalysts for CO₂ reduction.     

Pb2(OH)2[p‐O2C‐C6H4‐CO2]: Synthese und Kristallstruktur

Pb₂(OH)₂[p‐O₂C‐C₆H₄‐CO₂]: Synthesis and Crystal Structure Single crystals of Pb₂(OH)₂[p‐O₂C‐C₆H₄‐CO₂] ( 1 ) were obtained by hydrothermal reaction of terephthalic acid and PbCO₃ at 180 °C (10 days). 1 crystallizes in the monoclinic space group P2₁/c with Z = 2 (a = 1115.6(2) pm, b = 380.10(4) pm, c = 1141.3(2) pm, β = 93.39(1)°, V = 0.4831(1) nm³). The crystal structure is characterized by ladder‐type Pb(OH)_3/3 double chains, which are connected to a three‐dimensional framework by terephthalate dianions.     

13C/12C isotope labeling to study carbon partitioning and dark respiration in cereals subjected to water stress

Despite the relevance of carbon (C) loss through respiration processes (with its consequent effect on the lower C availability for grain filling), little attention has been given to this topic. Literature data concerning the role of respiration in cereals are scarce and these have been produced using indirect methods based on gas‐exchange estimations. We have developed a new method based on the capture of respired CO₂ samples and their analysis by gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). In order to analyse the main processes involved in the C balance during grain filling (photosynthesis, respiration, allocation and partitioning) the ambient isotopic ¹³C/¹²C composition (δ¹³C) of the growth chamber was modified during this period (δ¹³C ca. ?12.8 ± 0.3‰ to ca. ?20.0 ± 0.2‰). The physiological performance, together with the C allocation on total organic matter (TOM) and respiration of wheat (Triticum aestivum L., var. Califa sur) and two hybrids, tritordeum (X Tritordeum Asch. & Graebn line HT 621) and triticale (X Triticosecale Wittmack var. Imperioso), were compared during post‐anthesis water stress. In spite of the larger ear DM/total ratio, especially under drought conditions, the grain filling of triticale and wheat was mainly carried out with pre‐anthesis C, while the majority of C assimilated during post‐anthesis was invested in respiration processes. In the case of wheat and tritordeum, the C balance data suggested a reallocation during grain filling of photoassimilates stored prior to anthesis from shoot to ear. Furthermore, the lower percentage of labeled C on respired CO₂ of droughted tritordeum plants, together with the lower plant biomass, explained the fact that those plants had more C available for grain filling. Copyright © 2009 John Wiley & Sons, Ltd.     

A Cationic MOF with High Uptake and Selectivity for CO2 due to Multiple CO2‐Philic Sites

The reaction of N‐rich pyrazinyl triazolyl carboxyl ligand 3‐(4‐carboxylbenzene)‐5‐(2‐pyrazinyl)‐1H‐1,2,4‐triazole (H₂cbptz) with MnCl₂ afforded 3D cationic metal–organic framework (MOF) [Mn₂(Hcbptz)₂(Cl)(H₂O)]Cl ? DMF ? 0.5 CH₃CN ( 1 ), which has an unusual (3,4)‐connected 3,4T1 topology and 1D channels composed of cavities. MOF 1 has a very polar framework that contains exposed metal sites, uncoordinated N atoms, narrow channels, and Cl^? basic sites, which lead to not only high CO₂ uptake, but also remarkably selective adsorption of CO₂ over N₂ and CH₄ at 298–333 K. The multiple CO₂‐philic sites were identified by grand canonical Monte Carlo simulations. Moreover, 1 shows excellent stability in natural air environment. These advantages make 1 a very promising candidate in post‐combustion CO₂ capture, natural‐gas upgrading, and landfill gas‐purification processes.     

A dynamic soil chamber system coupled with a tunable diode laser for online measurements of δ13C, δ18O,and efflux rate of soil‐respired CO2

High frequency observations of the stable isotopic composition of CO₂ effluxes from soil have been sparse due in part to measurement challenges. We have developed an open‐system method that utilizes a flow‐through chamber coupled to a tunable diode laser (TDL) to quantify the rate of soil CO₂ efflux and its δ¹³C and δ¹⁸O values (δ¹³C_R and δ¹⁸O_R, respectively). We tested the method first in the laboratory using an artificial soil test column and then in a semi‐arid woodland. We found that the CO₂ efflux rates of 1.2 to 7.3 µmol m^?2 s^?1 measured by the chamber‐TDL system were similar to measurements made using the chamber and an infrared gas analyzer (IRGA) (R² = 0.99) and compared well with efflux rates generated from the soil test column (R² = 0.94). Measured δ¹³C and δ¹⁸O values of CO₂ efflux using the chamber‐TDL system at 2 min intervals were not significantly different from source air values across all efflux rates after accounting for diffusive enrichment. Field measurements during drought demonstrated a strong dependency of CO₂ efflux and isotopic composition on soil water content. Addition of water to the soil beneath the chamber resulted in average changes of +6.9 µmol m^?2 s^?1, ?5.0‰, and ?55.0‰ for soil CO₂ efflux, δ¹³C_R and δ¹⁸O_R, respectively. All three variables initiated responses within 2 min of water addition, with peak responses observed within 10 min for isotopes and 20 min for efflux. The observed δ¹⁸O_R was more enriched than predicted from temperature‐dependent H₂O‐CO₂ equilibration theory, similar to other recent observations of δ¹⁸O_R from dry soils (Wingate L, Seibt U, Maseyk K, Ogee J, Almeida P, Yakir D, Pereira JS, Mencuccini M. Global Change Biol. 2008; 14: 2178). The soil chamber coupled with the TDL was found to be an effective method for capturing soil CO₂ efflux and its stable isotope composition at high temporal frequency. Published in 2010 by John Wiley & Sons, Ltd.     

A Highly Active N‐Heterocyclic Carbene Manganese(I) Complex for Selective Electrocatalytic CO2 Reduction to CO

We report here the first purely organometallic fac‐[Mn^I(CO)₃(bis‐^MeNHC)Br] complex with unprecedented activity for the selective electrocatalytic reduction of CO₂ to CO, exceeding 100 turnovers with excellent faradaic yields (η_CO≈95 %) in anhydrous CH₃CN. Under the same conditions, a maximum turnover frequency (TOF_max) of 2100 s^?1 was measured by cyclic voltammetry, which clearly exceeds the values reported for other manganese‐based catalysts. Moreover, the addition of water leads to the highest TOF_max value (ca. 320 000 s^?1) ever reported for a manganese‐based catalyst. A Mn^I tetracarbonyl intermediate was detected under catalytic conditions for the first time.     

Dimension‐Matched Zinc Phthalocyanine/BiVO4 Ultrathin Nanocomposites for CO2 Reduction as Efficient Wide‐Visible‐Light‐Driven Photocatalysts via a Cascade Charge Transfer

Cascade charge transfer was realized by a H‐bond linked zinc phthalocyanine/BiVO₄ nanosheet (ZnPc/BVNS) composite, which subsequently works as an efficient wide‐visible‐light‐driven photocatalyst for converting CO₂ into CO and CH₄, as shown by product analysis and ¹³C isotopic measurement. The optimized ZnPc/BVNS nanocomposite exhibits a ca. 16‐fold enhancement in the quantum efficiency compared with the reported BiVO₄ nanoparticles at the excitation of 520 nm with an assistance of 660 nm photons. Experimental and theoretical results show the exceptional activities are attributed to the rapid charge separation by a cascade Z‐scheme charge transfer mechanism formed by the dimension‐matched ultrathin (ca. 8 nm) heterojunction nanostructure. The central Zn²⁺ in ZnPc could accept the excited electrons from the ligand and then provide a catalytic function for CO₂ reduction. This Z‐scheme is also feasible for other MPc, such as FePc and CoPc, together with BVNS.     

trans‐(Cl)‐[Ru(5,5′‐diamide‐2,2′‐bipyridine)(CO)2Cl2]: Synthesis,Structure, and Photocatalytic CO2 Reduction Activity

A series of trans‐(Cl)‐[Ru(L)(CO)₂Cl₂]‐type complexes, in which the ligands L are 2,2′‐bipyridyl derivatives with amide groups at the 5,5′‐positions, are synthesized. The C‐connected amide group bound to the bipyridyl ligand through the carbonyl carbon atom is twisted with respect to the bipyridyl plane, whereas the N‐connected amide group is in the plane. DFT calculations reveal that the twisted structure of the C‐connected amide group raises the level of the LUMO, which results in a negative shift of the first reduction potential (E_p) of the ruthenium complex. The catalytic abilities for CO₂ reduction are evaluated in photoreactions (λ>400 nm) with the ruthenium complexes (the catalyst), [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine; the photosensitizer), and 1‐benzyl‐1,4‐dihydronicotinamide (the electron donor) in CO₂‐saturated N,N‐dimethylacetamide/water. The logarithm of the turnover frequency increases by shifting E_p a negative value until it reaches the reduction potential of the photosensitizer.     

Adsorption of CO2 and Coadsorption of H and CO2 on Potassium‐Promoted Cu(115)

The influence of potassium, in the submonolayer regime, on the adsorption and coadsorption of CO₂ and H on a stepped copper surface, Cu(115), has been studied by photoelectron spectroscopy, temperature‐programmed desorption, and work‐function measurements. Based on the fast recording of C 1s and O 1s core‐level spectra, the uptake of CO₂ on K/Cu(115) surfaces at 120 K has been followed in real time, and the different reaction products have been identified. The K 2p_3/2 peak exhibits a chemical shift of ?0.4 eV with CO₂ saturation, the C 1s peaks of the CO₃ and the CO species show shifts of ?0.8 and ?0.5 eV, respectively, and the C 1s peak of the physisorbed CO₂ exhibits no shift. The effects of gradually heating the CO₂/K/Cu(115) surface include the desorption of physisorbed CO₂ at 143 K; the desorption of CO at 193 K; the ordering of the CO₃ species, and subsequently the dissociation of the carbonate with desorption at 520–700 K. Formate, HCOO^?, was synthesized by the coadsorption of H and CO₂ on the K/Cu(115) surface at 125 K. Formate formed exclusively for potassium coverages of less than 0.4 monolayer, whereas both formate and carbonate were formed at higher coverages. The desorption of formate‐derived CO₂ took place in the temperature range 410–425 K and carbonate‐derived CO₂ desorbed at 645–660 K, depending on the potassium coverage.     

Use of [13C]/[12C] ratios as an indicator of the role of microorganisms in protection of plants from the phytotoxic action of naphthalene

Using molecular and isotopic mass spectrometry, we investigated the toxic effect of naphthalene as a representative of polycyclic aromatic hydrocarbons (PAHs) on plants growing under sterile conditions and plants inoculated with microorganisms capable and incapable of naphthalene degradation. Tobacco plants of the Samsun variety were grown in a closed gas-nutrient system on a mineral medium with sucrose as a carbon source. Naphthalene used as a toxicant at a concentration of 5.2 × 10^?4% contained ¹³C isotope whose amount was characterized by the value δ¹³C = +281.4 ± 0.6‰ relative to the PDB standard and differed from that of sucrose, the main source of carbon (δ¹³C = ?12.0 ± 0.1‰). Degradation of naphthalene was determined by the inclusion of its carbon in metabolic CO₂ and plant tissues (the root, stem, leaves). The effect of naphthalene on plants was indicated by the rates of O₂ production and CO₂ uptake during the light period as compared with the dark period of exposure. A decrease of the toxic effect of naphthalene on plants was observed only at the inoculation of plants with Pseudomonas aureofaciens BS1393 rhizosphere bacteria bearing plasmid pBS216, which controls the naphthalene biodegradation ability. The occurrence of other heterotrophic microorganisms incapable of naphthalene degradation had no similar protective effect.