Carbon Coupling Research Articles

Heterogeneous palladium (II)‐complexed dendronized polymer: A rare palladium catalyst for the one‐pot synthesis of 2‐arylbenzoxazoles

The palladium complex of dendronized amine polymer (EG–Gn–Pd, n = 0, 1 and 2) having ethylene glycol‐initiated polyepichlorohydrin as core was synthesized on a Merrifield resin support and was well characterized. Generally, palladium catalysts are known for carbon–carbon coupling reactions. Here, a developed catalyst was found to be good for benzoxazole synthesis. Higher generation dendronized polymer (EG–G2–Pd) was found to be better catalyst over lower generation dendronized polymers. Moreover, dendronized polymers were found to be a better catalyst over dendrigraft polymers. The catalyst reusability was checked and good yield was obtained for five cycles.

Pure-Blue Fluorescence Molecule for Nondoped Electroluminescence with External Quantum Efficiency Approaching 13%

A pure-blue light-emitting material is one of the key components in the preparation of organic light-emitting diode (OLED) displays. Although high-efficiency blue OLEDs have been realized in therma...

Soil element coupling is driven by ecological context and atomic mass

AbstractThe biogeochemical cycling of multiple soil elements is fundamental for life on Earth. Here, we conducted a global field survey across 16 chronosequences from contrasting biomes with soil ages ranging from centuries to millions of years. For this, we collected and analysed 435 topsoil samples (0–10 cm) from 87 locations. We showed that high levels of topsoil element coupling, defined as the average correlation among nineteen soil elements, are maintained over geological timescales globally. Cross‐biome changes in plant biodiversity, soil microbial structure, weathering, soil pH and texture, and mineral‐free unprotected organic matter content largely controlled multi‐element coupling. Moreover, elements with heavier atomic mass were naturally more decoupled and unpredictable in space than those with lighter mass. Only the coupling of carbon, nitrogen and phosphorus, which are essential to life on Earth, deviated from this predictable pattern, suggesting that this anomaly may be an undeniable fingerprint of life in terrestrial soils.

Responses of forest carbon and water coupling to thinning treatments from leaf to stand scales in a young montane pine forest

BackgroundWater-use efficiency (WUE) represents the coupling of forest carbon and water. Little is known about the responses of WUE to thinning at multiple spatial scales. The objective of this research was to use field measurements to understand short-term effects of two thinning treatments (T1: 4500 stems ha−1; and T2: 1100 stems ha−1) and the control (NT: 27,000 stems ha−1) on WUE at the three spatial scales (leaf level: the ratio of leaf photosynthesis to leaf transpiration; tree-level: tree growth to tree transpiration; and stand level: net primary production (NPP) to stand transpiration) and intrinsic WUEi (the ratio of leaf photosynthesis to stomatal conductance at leaf-level; and NPP to canopy conductance at stand-level) in a 16-year old natural lodgepole pine forest. Leaf-level measurements were conducted in 2017, while tree- and stand-level measurements were conducted in both 2016 (the normal precipitation year) and 2017 (the drought year).ResultsThe thinning treatments did not significantly affect the tree- and stand-level WUE in the normal year of 2016. However, the thinning significantly affected WUE in the drought year of 2017: T2 exhibited significantly higher tree-level WUE (0.49 mm2 kg−1) than NT (0.08 mm2 kg−1), and compared to NT, the stand-level WUE values in the thinned stands (T1 and T2) were significantly higher, with means of 0.31, 0.56 and 0.70 kg m−3, respectively. However, the leaf-level and stand-level WUEi in the thinned stands in the drought year were significantly lower than those in the unthinned stands. No significant differences in the leaf-level WUE were found among the treatments in 2017. In addition, the thinning did not significantly change the WUE-VPD relationships at any studied spatial scale.ConclusionsThe thinning treatments did not cause significant changes in all studied WUE metrics in a normal year. However, their effects were significantly promoted under the drought conditions probably due to the decrease in soil water availability, demonstrating that thinning can improve WUE and consequently support forests to cope with the drought effects. The inconsistent results on the effects of the thinning on forest carbon and water coupling at the spatial scales and the lack of the consistent WUE metrics constraint across-scale comparison and transferring of WUE.

A model for estimating transpiration from remotely sensed solar-induced chlorophyll fluorescence

Terrestrial evapotranspiration (ET) is an important flux that links global cycles of carbon, water and energy and is largely driven by transpiration (T) through leaf stomata in vegetated areas during the growing season. ET, however, remains one of the most uncertain hydrological variables at the global scale. In this study, we proposed a semi-mechanistic model for estimating terrestrial T by deriving an analytical solution between solar-induced chlorophyll fluorescence (SIF) and stomatal conductance (gc) as well as vapor pressure deficit (VPD), combining theories on the photosynthetic pathway and optimal stomatal behavior. The relationships of SIF-ETR and ETR-gc·VPD0.5 was calibrated by the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) model. This model was validated by hourly canopy SIF and concurrent eddy covariance flux observations at both forest and cropland ecosystems. Results showed that the SIF combined with VPD can better predict gc than using SIF alone with a more consistent seasonal trends found in both SIF and gc·VPD0.5. The correlation between gc·VPD0.5 and SIF was stronger than those between gc and SIF and between gc and VIs. Canopy T was accurately predicted from SIF at both hourly (R2 > 0.65) and daily (R2 > 0.76) scales and was also successfully estimated using SIF observations from the TROPOspheric Monitoring Instrument (TROPOMI) at cropland ecosystems. In comparison with empirical relationships of directly linking gc with SIF or VIs, the proposed model produced latent heat flux (λE) estimation in best agreement with measured values at all three sites. Our model could be a step forward in understanding the coupling of carbon and water cycles and may be used in ecosystem models for improving ET estimation over large areas.

Organic carbon coupling with sulfur reducer boosts sulfur based denitrification by Thiobacillus denitrificans

Sulfur autotrophic denitrification utilizes elemental sulfur as the electron donor for nitrate removal from aquatic environments. Organic carbon could stimulate the conversion of sulfur and facilitates the S0-based denitrification process in the mix-trophic. In this study, the co-cultured system of sulfur reducer (Geobacter sulfurreducens) and Thiobacillus denitrificans was used to investigate that how organic carbon could boost the S0-based denitrification. The results showed that the rate of S0-based denitrification was improved with C/N ratio of 0.13 and this improvement continued even after the acetate was exhausted. Sulfur probe test and Raman analysis suggested that reduced sulfur species (Sx2−) were formed with the addition of organic carbon. The Sx2− could recombine with element sulfur and the bioavailability of S0 would be improved, as a result, the rate of S0-based denitrification increased as well. Nitrate reduction rate could further increase with the C/N ratio of 0.88, but it would decrease significantly when the C/N ratio increased to 1.50 as the high concentration of generated S2−. Our results provided explanations that why organic carbon addition would improve the bioavailability of S0 which could further promote the S0-dominant denitrification process.

Heat and carbon coupling reveals ocean warming due to circulation changes.

Anthropogenic global surface warming is proportional to cumulative carbon emissions1-3; this relationship is partly determined by the uptake and storage of heat and carbon by the ocean4. The rates and patterns of ocean heat and carbon storage are influenced by ocean transport, such as mixing and large-scale circulation5-10. However, existing climate models do not accurately capture the observed patterns of ocean warming, with a large spread in their projections of ocean circulation and ocean heat uptake8,11. Additionally, assessing the influence of ocean circulation changes (specifically, the redistribution of heat by resolved advection) on patterns of observed and simulated ocean warming remains a challenge. Here we establish a linear relationship between the heat and carbon uptake of theocean in response to anthropogenic emissions. This relationship is determined mainly by intrinsic parameters of the Earth system-namely, the ocean carbon buffer capacity, the radiative forcing of carbon dioxide and the carbon inventory of the ocean. We use this relationship to reveal the effect of changes in ocean circulation from carbon dioxide forcing on patterns of ocean warming in both observations and global Earth system models from the Fifth Coupled Model Intercomparison Project (CMIP5). We show that historical patterns of ocean warming are shaped by ocean heat redistribution, which CMIP5 models simulate poorly. However, we find that projected patterns of heat storage are primarily dictated by thepre-industrial ocean circulation (and smallchanges in unresolved ocean processes)-that is, by the patterns of added heat owing toocean uptake of excess atmospheric heat rather than ocean warming by circulation changes. Climate models show more skill in simulating ocean heat storage by the pre-industrial circulationcompared to heat redistribution, indicating that warming patterns of the ocean may become more predictable as the climate warms.

Cu-Ag Tandem Catalysts for High-Rate CO2 Electrolysis toward Multicarbons

Summary Tandem electrocatalysis decouples individual steps within a chemically complicated pathway via multicomponent catalyst design. Such a concept is attractive for CO2 electro-conversion to multicarbons (C2+), especially at high rates. Here, we show that a Cu-Ag tandem catalyst on a gas diffusion electrode (GDE) can enhance the C2+ production rate from CO2 through CO2 reduction to CO on Ag and subsequent carbon coupling on Cu. With added Ag, the C2+ partial current over a Cu surface increases from 37 to 160 mA/cm2 at −0.70 V versus reversible hydrogen electrode (RHE) in 1 M KOH with no mutual interference between the two metals. Moreover, the intrinsic C2H4 and C2H5OH activity in the tandem platform is significantly higher than Cu alone under either pure CO2 or CO atmosphere. Our results indicate that the CO-enriched local environment generated by Ag can enhance C2+ formation on Cu beyond CO2 or CO feeding, suggesting new mechanisms in a tandem three-phase environment.

Patterns and driving factors of water and nitrogen use efficiency in Robinia pseudoacacia L. on the Loess Plateau in China

Water use efficiency (WUE) and nitrogen use efficiency (NUE) demonstrates the competitive strategies of plants with limited resources, which is important in mediating survival productivity and fitness of plants. Previous studies have found that there is a trade-off relationship between WUE and NUE and that they are affected by many factors, such as climate variables, geographical variables and soil properties. However, the patterns of WUE and NUE in Robinia pseudoacacia on the Loess Plateau are unclear and their driving factors need to be investigated to advance our knowledge of these key parameters to understand the coupling of carbon, nitrogen and water cycle. In this study, we calculated the WUE and NUE in Robinia pseudoacacia along a precipitation transect on the Loess Plateau and examined the effects of influencing factors on WUE and NUE. Our results showed that WUE varied from 64.03 to 103.08 μmol mmol−1, and NUE varied from 11.26 to 18.19 gC g−1N. Latitude played a substantial role in WUE, and soil nitrogen (ammonium nitrogen and total nitrogen) played a substantial role in NUE. In addition, NUE in Robinia pseudoacacia was lower than the average value of whole plants on the Loess Plateau, and the growth of Robinia pseudoacacia was mainly restricted by phosphorus. By dividing into three zones, zone 3 had higher WUE in where with higher latitude and lower precipitation, and NUE was not significant among the three zones. These results highlight the importance of location variables and soil chemical properties to WUE and NUE and provide useful information for understanding the coupling of carbon, nitrogen and water cycle of plants in ecosystems.

Deciphering Structure–Functionality Relationship of Polycarbonate-Based Polyelectrolytes by AIE Technology

Conjugated polyelectrolytes prepared from carbon–carbon coupling polymerization have difficulties in controlling the precision molecular weight (Mn), so that the effect of Mn on their performance r...

Promotion function of forest vegetation on the water & carbon coupling cycle in karst critical zone: Insights from karst groundwater systems in south China

The earth is gradually turning green due to afforestation, especially in China. Because the carbon cycle is driven by the groundwater cycle in karstification, the process of water & carbon coupling cycle (PWCC) in karst forest area can not only promote vegetation growth but also enhance chemical weathering processes of carbonate rocks to absorb more CO2. Therefore, carbon sequestration can occur during the process of ecological restoration in karst areas. However, forest respiration also increases with the vegetation growth which can produce extra CO2 back to atmosphere. To study the promotion function of forest vegetation during different succession stages on the PWCC in karst critical zone, three karst groundwater systems with different vegetation coverages (a native forest, a secondary forest during reforestation and a crop area in rural land) are chosen in southwest China. Their long-term monitoring of indicators, including precipitation (P), partial pressure of air CO2 (PCO2), groundwater discharge (Q), hydrochemical and isotope components, was conducted. The results indicated that part of CO2 produced by forest respiration diffuses into the atmosphere as a carbon source, and the remaining dissolves into the groundwater, thereby increasing corrodibility. The carbon sequestration mechanism differs at different vegetation succession stages. The secondary forest development stage displays an obvious carbon sequestration effect during the process of rocky desertification control. When the succession stage approaches the top-level ecosystem, the carbon sequestration effect descend sharply until the net carbon sequestration can be ignored.

Crystal structure of {μ2-1,2-bis-[(4-methyl-phenyl-sulfan-yl]-3-oxoprop-1-ene-1,3-di-yl-1:2κ2 C 3:C 1}dicarbon-yl-1κ2 C-[μ2-methyl-enebis(di-phenyl-phos-phane)-1:2κ2 P:P'](tri-phenyl-phosphane-2κP)iron-platinum(Fe-Pt), [(OC)2Fe(μ-dppm){μ-C(=O)C(4-MeC6H4SCH2)=CCH2SC6H4Me-4}Pt(PPh3)

The title compound, [FePt(C19H18OS2)(C18H15P)(C25H22P2)(CO)2], 1, [(OC)2Fe(μ-dppm)(μ-C(=O)C(CH2SC6H4Me-4)=CCH2SC6H4Me-4)Pt(PPh3)], represents the first example of a diphosphane-bridged heterobimetallic Fe-Pt dimetalla-cyclo-pentenone complex resulting from a bimetallic activation of metal-coordinated carbonyl ligand with an inter-nal alkyne, namely 1,4-bis-(p-tolyl-thio)-but-2-yne. The bridging μ2-C(=O)C(CH2SC6H4Me-4)=CCH2SC6H4Me-4 unit (stemming from a carbon-carbon coupling reaction between CO and the triple bond of the alkyne di-thio-ether) forms a five-membered dimetalla-cyclo-pentenone ring, in which the C=C bond is π-coordinated to the Fe center. The latter is connected to the Pt center through a short metal-metal bond of 2.5697 (6) Å.

Organic electrosynthesis using a fluoride ion mediator

Abstract Recent studies on fluoride ion-mediated anodic methoxylation of fluoroalkyl sulfides and sulfur-containing five-membered heterocyclic compounds together with its synthetic applications are summarized in this review. The first example of anodic methoxylation of 2-acyloxy-3,3,3-trifluoropropyl sulfides accompanying with [1,2]-rearrangement of acyloxy group is described. Fluoride ion-mediated anodic intramolecular cyclization of 3,3,3-trifluoropropyl sulfides bearing OH and t-BuCOO groups provides CF3-containing 1,3-oxathiolane and ethylene carbonate derivatives, respectively. Fluoride ion mediator can be also applied to anodic intramolecular carbon–carbon coupling to form oxindole and 3-oxotetrahydroisoquinoline derivatives.

Nonlinear Coupling of Carbon and Nitrogen Release During Litter Decomposition and its Responses to Nitrogen Addition

AbstractDuring decomposition of plant litter, it remains unclear whether carbon (C) and nitrogen (N) are released at similar proportional rates, which hinders our prediction of soil C and N dynamics under the context of global changes. Here, we investigated the relationships between C and N release and their responses to N addition (5 g N m−2 yr−1) to better understand this question. Litter gross N release and immobilization were differentiated by the 15N‐labeling technique. Results showed that the linear relationship between gross N release and C release followed the 1:1 line during the first year but then deviated above the 1:1 line for three types of the four studied litters. Nitrogen addition did not change this relationship, showing an inhibition effect on both C and N releases from the N‐rich foliar litter at the later stage. The inhibition effect of N addition was not found in the N‐poor twig litter, indicating that initial litter N interacted with deposited N to affect litter N release. We propose a novel conceptual model to describe that under N addition, the decrease in gross N release caused a decline in net N release from N‐rich litter, while a decline in net N release from N‐poor litter was due to the increase in gross N immobilization. These findings point to the importance of differentiating the gross N release and immobilization processes for understanding the response of litter N cycling to increasing N deposition and the relationships between C and N release during different stages of litter decomposition.

Atomically dispersed palladium catalyses Suzuki\u2013Miyaura reactions under phosphine-free conditions

Single-atom catalysts have emerged as a new frontier in catalysis science. However, their applications are still limited to small molecule activations in the gas phase, the classic organic transformations catalyzed by single-atom catalysts are still rare. Here, we report the use of a single-atom Pd catalyst for the classic Suzuki–Miyaura carbon–carbon coupling reaction under phosphine-free and open-air conditions at room temperature. The single-atom Pd catalyst is prepared through anchoring Pd on bimetal oxides (Pd-ZnO-ZrO2). The significant synergetic effect of ZnO and ZrO2 is observed. The catalyst exhibits high activity and tolerance of a wide scope of substrates. Characterization demonstrates that Pd single atoms are coordinated with two oxygen atoms in Pd-ZnO-ZrO2 catalyst. The catalyst can be fabricated on a multi-gram scale using a simple in situ co-precipitation method, which endows this catalytic system with great potential in practical applications.

Polyvinylpyridine-Supported Palladium Nanoparticles: An Efficient Catalyst for Suzuki–Miyaura Coupling Reactions

Palladium nanoparticles (Pd NPs) synthesized by the metal vapor synthesis technique were supported on poly(4-vinylpyridine) 2% cross-linked with divinylbenzene (Pd/PVPy). Transmission electron microscopy revealed the presence of small metal nanoparticles (dm = 2.9 nm) highly dispersed on the PVPy. The Pd/PVPy system showed high catalytic efficiency in Suzuki-Miyaura carbon–carbon coupling reactions of both non-activated and deactivated aromatic iodides and bromides with aryl boronic acids, carried out under an air atmosphere. The high turnover of the catalyst and the ability of the PVPy resin to retain active Pd species are highlighted. By comparing the catalytic performances of Pd/PVPy with those observed by using commercially available Pd-based supported catalysts, the reported system showed higher selectivity and lower Pd leaching.

Evidence of Arithmetical Uncertainty in Estimation of Light and Water Use Efficiency

It was demonstrated that conventional resource use efficiency (RUE) estimation methodology is largely subject to arithmetic weakness. Extensive field research data on aboveground biomass (AGB), absorbed photosynthetically active radiation (APAR), and crop evapotranspiration (ETc) in maize, soybean, sorghum, and winter wheat confirmed this methodological bias for light use efficiency (LUE) and water use efficiency (WUE) estimation. LUE and WUE were derived using cumulated (data aggregates across samplings) and independent (data increments across samplings) approaches. Use of cumulated data yielded strong-but-false correlation between AGB and APAR or ETc, being a statistical artefact. RUE values from an independent approach were substantially lower than that from a cumulated approach with greater standard errors. Overall, a cumulated approach tends to oversimplify the complex interactions among carbon and resource coupling in agroecosystems, which is accurately represented when employing an independent approach instead.

Dry reforming of methane over the cobalt catalyst: Theoretical insights into the reaction kinetics and mechanism for catalyst deactivation

Cobalt shows high catalytic activity for the important dry reforming of methane (DRM) reaction. However, it is prone to deactivation and the corresponding mechanism remains controversial. In this work, we combined density functional theory calculations and microkinetic modeling to study the active site and reaction mechanism of Co catalyzed DRM reaction, employing face centered cubic Co(111) and Co(211) as models. It was found that the step site over Co(211) is the active site for the reaction, and on Co(111), the C + O and CH + O paths are the preferred reaction pathways, while the C + O path is dominant on Co(211). The dissociation of CH4 is the rate-controlling step of DRM over both Co(111) and Co(211). We found that Co(111) is mainly deactivated due to carbon deposition whilst Co(211) undergoes surface oxidization. In addition, Co(111) tends to follow the surface carbon coupling mechanism, and surface carbon clusters formed will lead to catalyst deactivation.

Carbon‐Based Material‐Supported Palladium Nanocatalysts in Coupling Reactions: Discussion on their Stability and Heterogeneity

Scientific interest in carbon‐based materials (CBMs) has grown dramatically over the past few decades. Due to a variety of atomic orbital hybrid forms (sp, sp2 and sp3 hybridization), carbon can form a variety of materials with diverse structures and characteristics. CBMs used as efficient catalyst supports show extensive promise in organic reactions, which is attributed to their structural similarity with organics, large specific surface area, chemical stability, and photocatalytic properties. This review presents the synthesis of CBM‐supported palladium nanocatalysts based on impregnation, template methods, etc. The CBMs include activated carbon (AC), graphene, carbon nanotubes (CNTs), and their functionalized products, as supports for improving the activity and recyclability of simple Pd nanocatalysts. After surveying the literature where these catalysts have been utilized for carbon–carbon coupling reactions, there is a particular emphasis on Suzuki, Heck, and Sonogashira reactions. The catalytic mechanism of these Pd nanocatalysts (surface heterogeneous catalysis or homogeneous catalysis caused by Pd leaching) is discussed in detail, especially the effect of Pd leaching on the stability of the catalyst.

In-situ embedding cobalt-doped copper sulfide within ultrathin carbon nanosheets for superior lithium storage performance

Construction of well-defined hybrid composites consisting of transition metal sulfides and two-dimensional (2D) carbon nanosheets as high-performance anodes for lithium-ion batteries (LIBs) is of great significance but remains challenging. Herein, we have developed a novel strategy to in-situ fabricate a nanohybrid composites consisting of cobalt-doped copper sulfides nanoparticles embedded in 2D carbon nanosheets (2D Co-Cu2S@C) through a one-pot sulfurization of 2D nanosheet-like Co-doped copper-based metal-organic frameworks (MOFs) precursors. When applied as LIBs anodes, the as-prepared 2D Co-Cu2S@C composites could deliver a specific capacity of 780 mAh g−1 at 0.5 A g−1 after 300 cycles and a high-rate capability with 209 mAh g−1 at 5 A g−1, superior to most reported copper sulfide-based anodes. The exceptional performance could be attributed to the synergism of ultrathin structure (~4 nm), appropriate cobalt doping and strong carbon coupling, resulting in the shortened paths for Li+ transportation, enlarged exposing surface for Li+ adsorption, enhanced electric conductivity for charge transfer as well as robust mechanical property against volume expansion.