The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Lars Wesemann - One of the best experts on this subject based on the ideXlab platform.
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low valent Lead Hydride chemistry hydroplumbylation of phenylacetylene and 1 1 dimethylallene
Chemical Communications, 2019Co-Authors: Sebastian Weis, Hartmut Schubert, Lars WesemannAbstract:Hydroplumbylation reactions of the low valent organoLead Hydride [(Ar*PbH)2] with phenylacetylene and 1,1-dimethylallene are presented. A vinyl plumbylene was isolated in the case of the alkyne reaction exhibiting a down field NMR signal for the CH unit attached to the low valent heavy atom. 1,1-Dimethylallene affords formation of an allyl plumbylene.
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low valent Lead Hydride and its extreme low field 1h nmr chemical shift
Journal of the American Chemical Society, 2017Co-Authors: Julia Schneider, Hartmut Schubert, Christian P. Sindlinger, Klaus Eichele, Lars WesemannAbstract:Although Hydrides of the group 14 elements are well-known as versatile starting materials in many chemical transformations, a Hydride of Lead in oxidation state II is so far unknown. In this work, we finally complete the jigsaw puzzle by reporting the isolation of the first low valent organoLead Hydride. The thermolabile dimeric organoLead Hydride was synthesized at low temperature and features a Hydride 1H NMR signal (in solution 35.61 ppm; in the solid state 31.1 ppm) at the lowest field observed so far for a diamagnetic compound in agreement with quantum chemical predictions.
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Low-Valent Lead Hydride and Its Extreme Low-Field 1H NMR Chemical Shift
2017Co-Authors: Julia Schneider, Hartmut Schubert, Christian P. Sindlinger, Klaus Eichele, Lars WesemannAbstract:Although Hydrides of the group 14 elements are well-known as versatile starting materials in many chemical transformations, a Hydride of Lead in oxidation state II is so far unknown. In this work, we finally complete the jigsaw puzzle by reporting the isolation of the first low valent organoLead Hydride. The thermolabile dimeric organoLead Hydride was synthesized at low temperature and features a Hydride 1H NMR signal (in solution 35.61 ppm; in the solid state 31.1 ppm) at the lowest field observed so far for a diamagnetic compound in agreement with quantum chemical predictions
Carmen Cámara - One of the best experts on this subject based on the ideXlab platform.
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evaluation of flow injection in Lead Hydride generation atomic absorption spectrometry
Mikrochimica Acta, 1995Co-Authors: Yolanda Madrid, Dipankar Chakraborti, Carmen CámaraAbstract:The present study explores the attractiveness of combining flow-injection (FI) with Lead Hydride generation atomic absorption spectrometry (AAS) to improve the selectivity and sensitivity of analysis. Lead Hydride was generated in three acid-oxidant media: HNO3-(NH4)2S2O8, lactic acid-K2Cr2O7 and HNO3-H2O2. The effect of chemical parameters (acid-oxidant concentration and NaBH4 concentration) was investigated and the performance of each generation medium in terms of interferences, sensitivity and detection limits was compared with that obtained in batch mode. In all cases improved sensitivity (HNO3-H2O2, 0.8 ng Pb; lactic acid-K2Cr2O7, 0.2 ng Pb; (NH4)2S2O8-HNO3, 4ng Pb) was obtained, most notably in HNO3-H2O2, which provided 12 times higher sensitivity than in batch mode and sharper absorption peaks. Furthermore, interference by Cu and Ni was lower in the proposed FI-HG system. Compared with the batch mode, about 10 to 100 times higher concentrations of interferent are tolerated in the sample. The use of FI also allows work at a lower NaBH4 concentration. The method was applied to the determination of Lead in water samples with a sampling frequency of 180 samples per hour. In terms of both sensitivity and freedom from interferences, lactic acid-K2Cr2O7 was the best of the generation media tested.
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Lead Hydride generation atomic absorption spectrometry: an alternative to electrothermal atomic absorption spectrometry. A review
Analyst, 1994Co-Authors: Yolanda Madrid, Carmen CámaraAbstract:Historical, theoretical and practical aspects of Lead Hydride generation and its application to spectrochemical analysis, especially atomic absorption spectrometry, are reviewed. Lead Hydride generation conditions (particularly the need to use oxidizing agents), possible generation and atomization mechanisms and interferences are described and discussed in detail. The main applications of Lead Hydride generation atomic absorption spectrometry to the determination of Lead in a wide variety of matrices and its advantages over graphite furnace atomic absorption spectrometry in the determination of low levels of Lead are addressed.
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determination of Lead in wine other beverages and fruit slurries by flow injection Hydride generation atomic absorption spectrometry with on line microwave digestion
Journal of Analytical Atomic Spectrometry, 1994Co-Authors: Carmen Cabrera, Yolanda Madrid, Carmen CámaraAbstract:A simple and rapid flow injection-Lead Hydride generation atomic absorption spectrometry (Fl-HG-AAS) method was optimized for the determination of Lead in wine, other beverages and fruit. Lead Hydride was generated in HNO3–H2O2 medium using NaBH4 as reducing agent. To determine Lead in beer, juice and fruit, a microwave over was coupled on-line to the Fl-HG-AAS system. For fruit, the Lead Hydride was generated from slurries of the fresh sample. No matrix effect was found in the determination of Lead. The method enabled the direct determination of Lead in untreated samples with use of an aqueous calibration graph. The detection limit was 10 µg l–1 in wine and other beverage samples, and 1.0 ng in fruit.
Julian F Tyson - One of the best experts on this subject based on the ideXlab platform.
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determination of Lead by Hydride generation atom trapping flame atomic absorption spectrometry
Journal of Analytical Atomic Spectrometry, 2008Co-Authors: Nusret Ertas, Zikri Arslan, Julian F TysonAbstract:An atom trapping approach is described for the determination of Lead by Hydride generation flame atomic absorption spectrometry. Lead Hydride (PbH4), generated on-line by reacting Lead in hydrochloric acid–potassium ferricyanide medium with sodium boroHydride (NaBH4), was trapped on the interior walls of a slotted T-tube under highly oxidizing flame conditions. Atomization was achieved by aspirating 50 µL of methyl isobutyl ketone (MIBK) to the flame. Optimization of the experimental parameters for the generation and collection of Lead Hydride was described to achieve the highest peak height sensitivity. The detection limits were 0.075, 0.047 and 0.028 µg L−1 for 2.6, 5.2 and 7.8 mL of blank solution (n = 13), respectively. Calibration was linear up to 3.0 µg L−1 for a 30-s trapping period. The relative standard deviation was between 2 and 4%. The method was successfully applied to the determination of Pb in NIST certified reference materials, San Joaquin Soil (SRM 2709) and Apple Leaves (SRM 1515).
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determination of Lead by flow injection Hydride generation atomic absorption spectrometry with tetrahydroborate immobilized on an anion exchange resin
Journal of Analytical Atomic Spectrometry, 2005Co-Authors: Wipharat Chuachuad, Julian F TysonAbstract:The efficiencies of four types of strongly basic anion-exchange resins in the tetrahydroborate form for the generation of Lead Hydride, used in the determination of Lead by quartz tube (QT) atomization AAS, were investigated. Amberlyst A-26 gave the highest peak-height and peak-area sensitivities. The effects of column dimensions, tetrahydroborate concentration, loading time, loading direction, carrier reagent flow rate, carrier gas flow rate, sample acidity, and stripping coil length were studied. Without the argon carrier gas, the sensitivity was improved almost five times, though the precision was dependent on carrier agent and waste flow rate. Three procedures for the purification of potassium hexacyanoferrate(III) were investigated; a batch procedure, based on plumbane generation, was found to be the most effective. The concentration of acid was critical. Interferences from coexisting cations and anions were investigated. Hydride forming elements and phosphate interfered, but less suppression than for conventional HG-AAS was observed for some species. The limit of detection (3s) in 3% K3Fe(CN)6 and 0.10 mol l−1 HNO3 was 0.25 μg l−1, with a sampling frequency of 20–40 h−1. The precision, expressed as RSD, was 6.4% and 3.5% (n = 5) at concentrations of 3.0 and 5.0 μg l−1, respectively. The method was applied to the analysis of different types of biological matrices including natural waters, wine, human saliva and human urine. The detection limits (3s) were 0.20–0.85 μg l−1 for natural waters and 3.1–5.2 μg l−1 for the wine, human saliva and human urine. Recoveries for spiked samples were 86–110%. The results of the analyses of NIST standard reference materials, freeze-dried urine (SRM 2670), and apple leaves (SRM 1515) were in agreement with the certified values and the results for San Joaquin soil (SRM 2709) agreed with the leaching recovery values.
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flow injection Hydride generation electrothermal atomic absorption spectrometry with in atomizer trapping for the determination of Lead in calcium supplements
Talanta, 2000Co-Authors: Julian F Tyson, Robert I Ellis, G R Carnrick, F FernandezAbstract:Abstract Lead Hydride was generated from acid solution, containing potassium ferricyanide as an oxidizing agent, by the reaction with alkaline boroHydride solution. The effects of reaction conditions (hydrochloric acid, ferricyanide and boroHydride concentrations), and the lengths of reaction and stripping coils were studied. The effects of trapping temperature and argon flow rate were also investigated. Under the conditions giving the best peak area sensitivity, the detection limit (concentration giving a signal equal to three S.D. of the blank signal) was 0.12 μg l−1 for a 1000 μl injection volume. The detection limit was improved to 0.03 μg l−1 when the ferricyanide was purified by passage through a cation-exchange resin. Two calcium supplement materials were analyzed by the flow injection (FI)-Hydride generation (HG)-electrothermal atomization atomic absorption spectrometry (ETAAS) method, giving values of 0.55 and 0.66 μg g−1, in agreement with results obtained by previously validated methods. For a 500-mg sample the limits of detection and quantification were 0.006 and 0.02 μg g−1, respectively.
Lu Wang - One of the best experts on this subject based on the ideXlab platform.
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in silico optimization of organic inorganic hybrid perovskites for photocatalytic hydrogen evolution reaction in acidic solution
Journal of Physical Chemistry C, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, William A Goddard, Youyong LiAbstract:We previously reported the atomistic reaction mechanism for the photocatalytic hydrogen evolution reaction (HER) on the CH_3NH_3PbI_3 organic–inorganic hybrid perovskites based on quantum mechanics calculations of the transition-state barriers, including several layers of explicit acidic solvent. Here, we extend these studies using in silico optimization to discover additional promising photocatalysts. We consider replacing (i) Pb with Sn, (ii) I with Br, and (iii) CH_3NH_3 cation with several organic cations, including NH_2(CH)NH_2 cation as the photocatalyst for HER. We compared the activation barriers and reaction energies for each case. In our previous studies, we found that both H atoms of the H_2 product are extracted from surface organic cations with protons from the solution migrating along Grotthuss water chains to replace the H of the organic cations. This two-step reaction mechanism involves formation of an intermediate Lead Hydride bond, with the Lead atoms and the surface organic cations both playing essential roles. Among the perovskites investigated here, we predict that NH_2(CH)NH_2PbI_3 exhibits the best HER performance with a predicted 10-fold improvement in the reaction rate compared to CH_3NH_3PbI_3. We also suggest that the Lead-free tin iodide perovskites might exhibit a rate comparable to that of Lead iodide perovskites with the same organic cations. However, replacing iodine by bromine significantly increases the activation barrier. We find for these Lead iodide perovskites, the increased proton affinity of the surface organic cations enhances the photocatalytic efficiency, with NH2(CH)NH2 the best case examined.
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pb activated amine assisted photocatalytic hydrogen evolution reaction on organic inorganic perovskites
Journal of the American Chemical Society, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, Youyong Li, William A GoddardAbstract:We report here the reaction mechanism for explicit aqueous solvent quantum mechanics (QM) studies determining the energetics and reaction barriers for the photocatalytic hydrogen evolution reaction (HER) on CH3NH3PbI3 surface. We find that both the Lead (Pb) atoms and the surface organic molecules play essential roles, Leading to a two-step Pb-activated amine-assisted (PbAAA) reaction mechanism involving an intermediate Lead Hydride state. Both H of H2 product are extracted from surface organic molecules, while two protons from the solution migrate along water chains via the Grotthuss mechanism to replace the H in organic molecule. We obtain a reaction barrier of 1.08 eV for photochemical generation of H2 on CH3NH3PbI3 compared to 2.61 eV for the dark reaction. We expect this HER mechanism can also apply to the other organic perovskites, but the energy barriers and reaction rates may depend on the basicity of electrolyte and intrinsic structures of perovskites.
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in silico optimization of organic inorganic hybrid perovskites for photocatalytic hydrogen evolution reaction in acidic solution c
The Journal of Physical Chemistry, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, William A Goddard, Youyong LiAbstract:We previously reported the atomistic reaction mechanism for the photocatalytic hydrogen evolution reaction (HER) on the CH₃NH₃PbI₃ organic–inorganic hybrid perovskites based on quantum mechanics calculations of the transition-state barriers, including several layers of explicit acidic solvent. Here, we extend these studies using in silico optimization to discover additional promising photocatalysts. We consider replacing (i) Pb with Sn, (ii) I with Br, and (iii) CH₃NH₃ cation with several organic cations, including NH₂(CH)NH₂ cation as the photocatalyst for HER. We compared the activation barriers and reaction energies for each case. In our previous studies, we found that both H atoms of the H₂ product are extracted from surface organic cations with protons from the solution migrating along Grotthuss water chains to replace the H of the organic cations. This two-step reaction mechanism involves formation of an intermediate Lead Hydride bond, with the Lead atoms and the surface organic cations both playing essential roles. Among the perovskites investigated here, we predict that NH₂(CH)NH₂PbI₃ exhibits the best HER performance with a predicted 10-fold improvement in the reaction rate compared to CH₃NH₃PbI₃. We also suggest that the Lead-free tin iodide perovskites might exhibit a rate comparable to that of Lead iodide perovskites with the same organic cations. However, replacing iodine by bromine significantly increases the activation barrier. We find for these Lead iodide perovskites, the increased proton affinity of the surface organic cations enhances the photocatalytic efficiency, with NH₂(CH)NH₂ the best case examined.
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In Silico Optimization of Organic–Inorganic Hybrid Perovskites for Photocatalytic Hydrogen Evolution Reaction in Acidic Solution
2018Co-Authors: Lu Wang, Tao Cheng, William A Goddard, Hai XiaoAbstract:We previously reported the atomistic reaction mechanism for the photocatalytic hydrogen evolution reaction (HER) on the CH3NH3PbI3 organic–inorganic hybrid perovskites based on quantum mechanics calculations of the transition-state barriers, including several layers of explicit acidic solvent. Here, we extend these studies using in silico optimization to discover additional promising photocatalysts. We consider replacing (i) Pb with Sn, (ii) I with Br, and (iii) CH3NH3 cation with several organic cations, including NH2(CH)NH2 cation as the photocatalyst for HER. We compared the activation barriers and reaction energies for each case. In our previous studies, we found that both H atoms of the H2 product are extracted from surface organic cations with protons from the solution migrating along Grotthuss water chains to replace the H of the organic cations. This two-step reaction mechanism involves formation of an intermediate Lead Hydride bond, with the Lead atoms and the surface organic cations both playing essential roles. Among the perovskites investigated here, we predict that NH2(CH)NH2PbI3 exhibits the best HER performance with a predicted 10-fold improvement in the reaction rate compared to CH3NH3PbI3. We also suggest that the Lead-free tin iodide perovskites might exhibit a rate comparable to that of Lead iodide perovskites with the same organic cations. However, replacing iodine by bromine significantly increases the activation barrier. We find for these Lead iodide perovskites, the increased proton affinity of the surface organic cations enhances the photocatalytic efficiency, with NH2(CH)NH2 the best case examined
Youyong Li - One of the best experts on this subject based on the ideXlab platform.
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in silico optimization of organic inorganic hybrid perovskites for photocatalytic hydrogen evolution reaction in acidic solution
Journal of Physical Chemistry C, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, William A Goddard, Youyong LiAbstract:We previously reported the atomistic reaction mechanism for the photocatalytic hydrogen evolution reaction (HER) on the CH_3NH_3PbI_3 organic–inorganic hybrid perovskites based on quantum mechanics calculations of the transition-state barriers, including several layers of explicit acidic solvent. Here, we extend these studies using in silico optimization to discover additional promising photocatalysts. We consider replacing (i) Pb with Sn, (ii) I with Br, and (iii) CH_3NH_3 cation with several organic cations, including NH_2(CH)NH_2 cation as the photocatalyst for HER. We compared the activation barriers and reaction energies for each case. In our previous studies, we found that both H atoms of the H_2 product are extracted from surface organic cations with protons from the solution migrating along Grotthuss water chains to replace the H of the organic cations. This two-step reaction mechanism involves formation of an intermediate Lead Hydride bond, with the Lead atoms and the surface organic cations both playing essential roles. Among the perovskites investigated here, we predict that NH_2(CH)NH_2PbI_3 exhibits the best HER performance with a predicted 10-fold improvement in the reaction rate compared to CH_3NH_3PbI_3. We also suggest that the Lead-free tin iodide perovskites might exhibit a rate comparable to that of Lead iodide perovskites with the same organic cations. However, replacing iodine by bromine significantly increases the activation barrier. We find for these Lead iodide perovskites, the increased proton affinity of the surface organic cations enhances the photocatalytic efficiency, with NH2(CH)NH2 the best case examined.
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pb activated amine assisted photocatalytic hydrogen evolution reaction on organic inorganic perovskites
Journal of the American Chemical Society, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, Youyong Li, William A GoddardAbstract:We report here the reaction mechanism for explicit aqueous solvent quantum mechanics (QM) studies determining the energetics and reaction barriers for the photocatalytic hydrogen evolution reaction (HER) on CH3NH3PbI3 surface. We find that both the Lead (Pb) atoms and the surface organic molecules play essential roles, Leading to a two-step Pb-activated amine-assisted (PbAAA) reaction mechanism involving an intermediate Lead Hydride state. Both H of H2 product are extracted from surface organic molecules, while two protons from the solution migrate along water chains via the Grotthuss mechanism to replace the H in organic molecule. We obtain a reaction barrier of 1.08 eV for photochemical generation of H2 on CH3NH3PbI3 compared to 2.61 eV for the dark reaction. We expect this HER mechanism can also apply to the other organic perovskites, but the energy barriers and reaction rates may depend on the basicity of electrolyte and intrinsic structures of perovskites.
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in silico optimization of organic inorganic hybrid perovskites for photocatalytic hydrogen evolution reaction in acidic solution c
The Journal of Physical Chemistry, 2018Co-Authors: Lu Wang, Hai Xiao, Tao Cheng, William A Goddard, Youyong LiAbstract:We previously reported the atomistic reaction mechanism for the photocatalytic hydrogen evolution reaction (HER) on the CH₃NH₃PbI₃ organic–inorganic hybrid perovskites based on quantum mechanics calculations of the transition-state barriers, including several layers of explicit acidic solvent. Here, we extend these studies using in silico optimization to discover additional promising photocatalysts. We consider replacing (i) Pb with Sn, (ii) I with Br, and (iii) CH₃NH₃ cation with several organic cations, including NH₂(CH)NH₂ cation as the photocatalyst for HER. We compared the activation barriers and reaction energies for each case. In our previous studies, we found that both H atoms of the H₂ product are extracted from surface organic cations with protons from the solution migrating along Grotthuss water chains to replace the H of the organic cations. This two-step reaction mechanism involves formation of an intermediate Lead Hydride bond, with the Lead atoms and the surface organic cations both playing essential roles. Among the perovskites investigated here, we predict that NH₂(CH)NH₂PbI₃ exhibits the best HER performance with a predicted 10-fold improvement in the reaction rate compared to CH₃NH₃PbI₃. We also suggest that the Lead-free tin iodide perovskites might exhibit a rate comparable to that of Lead iodide perovskites with the same organic cations. However, replacing iodine by bromine significantly increases the activation barrier. We find for these Lead iodide perovskites, the increased proton affinity of the surface organic cations enhances the photocatalytic efficiency, with NH₂(CH)NH₂ the best case examined.