Intermolecular spin–spin coupling constants between P atoms

This paper reports the study by NMR spectroscopy and ab initio methods of the structure of 3,4-dimethyl-1-cyanophosphole and its dimer. The dimer presents a P···P interaction of the pnictogen type due to the presence of σ-holes. NMR of the monomer was recorded in CDCl₃ solution while NMR of the dimer corresponds to the solid state (CPMAS) experiments. The ^2pJ_PP spin–spin coupling constant has not been measured, but calculated at the B3LYP level. AIM, NBO and ELF methodologies have been used to describe the electronic structure of the dimer.     

Chemical Regulation of Carbon Quantum Dots from Synthesis to Photocatalytic Activity

Carbon quantum dots (CQDs) were synthesized by heating various carbon sources in HNO₃ solution at reflux, and the effects of HNO₃ concentration on the size of the CQDs were investigated. Furthermore, the oxygen‐containing surface groups of as‐prepared CQDs were selectively reduced by NaBH₄, leading to new surface states. The experimental results show that the sizes of CQDs can be tuned by HNO₃ concentration and then influence their photoluminescent behaviors; the photoluminescent properties are related to both the size and surface state of the CQDs, but the photocatalytic activities are determined by surface states alone. The different oxygen‐containing groups on the surface of the CQDs can induce different degrees of the band bending upward, which determine the separation and combination of the electron–hole pairs. The high upward band bending, which is induced by C?O and COOH groups, facilitates separation of the electron–hole pairs and then enhances high photocatalytic activity. In contrast, the low upward band bending induced by C? OH groups hardly prevents the electron–hole pairs from surface recombination and then exhibits strong photoluminescence. Therefore, both the photocatalytic activities and optical properties of CQDs can be tuned by their surface states.     

Stabilization of the Triphosphallyl Ligand η3‐P3{P(O)H} at Iridium via Alkaline Activation of P4

The selective functionalization of the polyphosphorus moiety Ph₂PCH₂PPh₂PPPP present as a tetrahapto‐ligand in complex [Ir(dppm)(Ph₂PCH₂PPh₂PPPP)]⁺ ( 1 , dppm=Ph₂PCH₂PPh₂) was obtained by reaction of 1 with water under basic conditions at room temperature. The formation of the new triphosphaallyl moiety η³‐P₃{P(O)H} was determined in solution by NMR spectroscopy, and confirmed in the solid state by a single‐crystal X‐ray structure of the stable product [Ir(κ²‐dppm)(κ¹‐dppm)(η³‐P₃{P(O)H})] ( 2 ). In solution, 2 has a fluxional behavior attributable to the four P atoms belonging to the tetraphosphorus moiety in 1 and exhibits a chemical exchange process involving the two PPh₂ moieties of the same bidentate ligand, as determined by 1D and 2D NMR spectroscopy experiments carried out at variable temperature. The mechanism of the reaction was investigated at the DFT level, which suggested a selective attack of an in‐situ generated OH^? anion on one of the non‐coordinated phosphorus atoms of the P₄ moiety. The reaction then evolves through an acid‐assisted tautomerization, which leads to the final compound 2 . Bonding analysis pointed out that the new unsubstituted P₃‐unit in the η³‐P₃{P(O)H} moiety behaves as a triphosphallyl ligand.     

Ligand Functionalization and Its Effect on CO2 Adsorption in Microporous Metal–Organic Frameworks

We report two new 3D structures, [Zn₃(bpdc)₃(2,2′‐dmbpy)] (DMF)_x(H₂O)_y ( 1 ) and [Zn₃(bpdc)₃(3,3′‐dmbpy)]?(DMF)₄(H₂O)_0.5 ( 2 ), by methyl functionalization of the pillar ligand in [Zn₃(bpdc)₃(bpy)] (DMF)₄?(H₂O) ( 3 ) (bpdc=biphenyl‐4,4′‐dicarboxylic acid; z,z′‐dmbpy=z,z′‐dimethyl‐4,4′‐bipyridine; bpy=4,4′‐bipyridine). Single‐crystal X‐ray diffraction analysis indicates that 2 is isostructural to 3 , and the power X‐ray diffraction (PXRD) study shows a very similar framework of 1 to 2 and 3 . Both 1 and 2 are 3D porous structures made of Zn₃(COO)₆ secondary building units (SBUs) and 2,2′‐ or 3,3′‐dmbpy as pillar ligand. Thermogravimetric analysis (TGA) and PXRD studies reveal high thermal and water stability for both compounds. Gas‐adsorption studies show that the reduction of surface area and pore volume by introducing a methyl group to the bpy ligand leads to a decrease in H₂ uptake for both compounds. However, CO₂ adsorption experiments with 1′ (guest‐free 1 ) indicate significant enhancement in CO₂ uptake, whereas for 2′ (guest‐free 2 ) the adsorbed amount is decreased. These results suggest that there are two opposing and competitive effects brought on by methyl functionalization: the enhancement due to increased isosteric heats of CO₂ adsorption (Q_st), and the detraction due to the reduction of surface area and pore volume. For 1′ , the enhancement effect dominates, which leads to a significantly higher uptake of CO₂ than its parent compound 3′ (guest‐free 3 ). For 2′ , the detraction effect predominates, thereby resulting in reduced CO₂ uptake relative to its parent structure 3′ . IR and Raman spectroscopic studies also present evidence for strong interaction between CO₂ and methyl‐functionalized π moieties. Furthermore, all compounds exhibit high separation capability for CO₂ over other small gases including CH₄, CO, N₂, and O₂.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

Highly selective synthesis of single-walled carbon nanotubes from methane in a coupled Downer-turbulent fluidized-bed reactor

For the synthesis of single-walled carbon nanotubes (SWCNTs) from CH₄ over a Fe/MgO catalyst, we proposed a coupled Downer-turbulent fluidized-bed (TFB) reactor to enhance the selectivity and yield (or production rate) of SWCNTs. By controlling a very short catalyst residence time (1–3 s) in the Downer, only part of Fe oxides can be reduced to form Fe nano particles (NPs) available for the growth of SWCNTs. The percentage of unreduced Fe oxides increased and the yield of SWCNTs decreased accordingly with the increase of catalyst feeding rate in Downer. SWCNTs were preferentially grown on the catalyst surface and inhibited the sintering of the Fe crystallites which would be formed thereafter in the downstream TFB, evidenced by TEM, Raman and TGA. The coupled Downer-turbulent fluidized-bed reactor technology allowed higher selectivity and higher production rate of SWCNTs as compared to TFB alone.     

Sulfonated carbon catalyzed oxidation of aldehydes to carboxylic acids by hydrogen peroxide

Sulfonated carbon as a strong and stable solid acid catalyst exhibited excellent catalytic performance in various acid-catalyzed reactions. Here, sulfonated carbon, as catalyst for oxidation reaction, was prepared via the carbonization of starch followed by sulfonation with concentrated sulfuric acid. N₂ physisorption, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray fluorescence and acid-base titration were used to characterize the obtained materials. The catalytic activity of sulfonated carbon was studied in the oxidation of aldehydes to carboxylic acids using 30 wt% H₂O₂ as oxidant. This oxidation protocol works well for various aldehydes including aromatic and aliphatic aldehydes. The sulfonated carbon can be recycled for three times without obvious loss of activity.     

Porous V2O5-SnO2/CNTs composites as high performance cathode materials for lithium-ion batteries

Vanadium pentoxide (V₂O₅) exhibits high theoretical capacities when used as a cathode in lithium ion batteries (LIBs), but its application is limited by its structural instability as well as its low lithium and electronic conductivities. A porous composite of V₂O₅-SnO₂/carbon nanotubes (CNTs) was prepared by a hydrothermal method and followed by thermal treatment. The small particles of V₂O₅, their porous structure and the coexistence of SnO₂ and CNTs can all facilitate the diffusion rates of the electrons and lithium ions. Electrochemical impedance spectra indicated higher ionic and electric conductivities, as compared to commercial V₂O₅. The V₂O₅-SnO₂/CNTs composite gave a reversible discharge capacity of 198 mAh·g^?1 at the voltage range of 2.05–4.0 V, measured at a current rate of 200 mA·g^?1, while that of the commercial V₂O₅ was only 88 mAh·g^?1, demonstrating that the porous V₂O₅-SnO₂/CNTs composite is a promising candidate for high-performance lithium secondary batteries.     

Purified oxygen- and nitrogen-modified multi-walled carbon nanotubes as metal-free catalysts for selective olefin hydrogenation

Oxygen- and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) were applied as metal-free catalysts in selective olefin hydrogenation. A series of NCNTs was synthesized by NH₃ post-treatment of OCNTs. Temperature-programmed desorption, N₂ physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygen- and nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 °C led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis.     

Nano composite system based on coumarin derivative–titanium dioxide nanoparticles and ionic liquid: Determination of levodopa and carbidopa in human serum and pharmaceutical formulations

The combination of coumarin derivative (7-(1,3-dithiolan-2-yl)-9,10-dihydroxy-6H-benzofuro[3,2-c]chromen-6-on), (DC)–titanium dioxide nanoparticles (TiO₂) and ionic liquid (IL) yields nanostructured electrochemical sensor, formed a novel kind of structurally uniform and electrocatalytic activity material. This new ionic liquid–TiO₂ nanoparticles modified carbon paste electrode (IL–CTP) due to its enhanced conductivity presented very large current response from electroactive substrates. The modified electrode was characterized by different methods including a scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and voltammetry. A pair of well-defined quasi reversible redox peaks of coumarin derivative was obtained at the modified carbon paste electrode (DC/IL–CTP) by direct electron transfer between the coumarin derivative and the CP electrode. Dramatically enhanced electrocatalytic activity was exemplified at the DC/IL–CTP electrode, as an electrochemical sensor to study the electro oxidation of levodopa (LD) and carbidopa (CD). Based on differential pulse voltammetry (DPV), the oxidation of LD and CD exhibited the dynamic range between 0.10– 900.0 μM and 20.0–900.0 μM respectively, and the detection limit (3σ) for LD and CD were 41 nM and 0.38 μM, respectively. DPV was used for simultaneous determination of LD and CD at the DC/IL–CTP electrode, and quantitation of LD and CD in some real samples (such as tablets of Parkin-C Fort and Madopar, Sinemet, water, urine, and human blood serum) by the standard addition method.