ß-Cyclodextrin/Quaternary Ammonium Salt as an Efficient Catalyst System for Chemical Fixation of CO2.

The environmental friendly biomaterial ß-cyclodextrin (ß-CD) was used for the synthesis of cyclic carbonates from CO2 with epoxides in the presence of quaternary ammonium salts as co-catalyst. The factors affecting the activity of this binary catalyst system, such as reaction temperature, time, CO2 pressure and the mole ratio of reactants, were investigated systematically. The excellent yield of cyclic carbonate (100%) was obtained at 130 °C, 3 MPa after 5 h with the catalyst system of ß-CD/tetrabutylammonium bromine (TBABr). The catalyst system of ß-CD/TBABr can also be applied to a wide substrates of epoxides with good to excellent yield and high selectivity (>99%). Recyclable ability of ß-CD/TBABr can also be detected and there was no significant decline in activity after five recycles. Finally, reaction mechanism was proposed based on the reaction results and literatures.

Solvent-Free Coupling Reaction of Carbon Dioxide and Epoxides Catalyzed by Quaternary Ammonium Functionalized Schiff Base Metal Complexes under Mild Conditions.

A series of bifunctional Schiff base metal catalysts (Zn-NPClR, Zn-NPXH, and M-NPClH) with two quaternary ammonium groups were prepared for carbon dioxide (CO2) and epoxide coupling reactions. The effects of the reaction variables on the catalytic activity were systematically investigated, and the optimal reaction conditions (120 °C, 1 MPa CO2, 3 h) were screened. The performances of different metal-centered catalysts were evaluated, and Co-NPClH showed excellent activity. This kind of bifunctional catalyst has a wide range of substrate applicability, excellent stability, and can be reused for more than five runs. A relatively high TOF could reach up to 1416 h-1 with Zn-NPClH as catalyst by adjusting reaction factors. In addition, the kinetic study of the coupling reaction catalyzed by three catalysts (Zn, Co, and Ni) was carried out to obtain the activation energy (Ea) for the formation of cyclic carbonates. Finally, a possible mechanism for this cyclization reaction was proposed.

Solvent- and Co-Catalyst-Free Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by Recyclable Bifunctional Niobium Complexes.

CO2, as a cheap and abundant renewable C1 resource, can be used to synthesize high value-added chemicals. In this paper, a series of bifunctional metallic niobium complexes were synthesized and their structures were characterized by IR, NMR and elemental analysis. All of these complexes have been proved to be efficient catalysts for the coupling reaction of CO2 and epoxides to obtain cyclic carbonates under solvent- and co-catalyst-free conditions. By using CO2 and propylene oxide as a model reaction, the optimal reaction conditions were systematically screened as: 100 °C, 1 MPa, 2 h, ratio of catalyst to alkylene oxide 1:100. Under the optimal reaction conditions, the bifunctional niobium catalysts can efficiently catalyze the coupling reaction with high yield and excellent selectivity (maximum yield of >99% at high pressure and 96.8% at atmospheric pressure). Moreover, this series of catalysts can also catalyze the coupling reaction at atmospheric pressure and most of them showed high conversion of epoxide. The catalysts have good substrate suitability and are also applicable to a variety of epoxides including diepoxides and good catalytic performances were achieved for producing the corresponding cyclic carbonates in most cases. Furthermore, the catalysts can be easily recovered by simple filtration and reused for at least five times without obvious loss of catalytic activity and selectivity. Kinetic studies were carried out preliminarily for the bifunctional niobium complexes with different halogen ions (3a(Cl-), 3b(Br-), 3c(I-)) and the formation activation energies (Ea) of cyclic carbonates were obtained. The order of apparent activation energy Ea is 3a (96.2 kJ/mol) > 3b (68.2 kJ/mol) > 3c (37.4 kJ/mol). Finally, a possible reaction mechanism is proposed.

Functionalized ß-Cyclodextrins Catalyzed Environment-Friendly Cycloaddition of Carbon Dioxide and Epoxides.

Ammonium, imidazole, or pyridinium functionalized ß-cyclodextrins (ß-CDs) were used as efficient one-component bifunctional catalysts for the coupling reaction of carbon dioxide (CO2) and epoxide without the addition of solvent and metal. The influence of different catalysts and reaction parameters on the catalytic performance were examined in detail. Under optimal conditions, Im-CD1-I catalysts functionalized with imidazole groups were able to convert various epoxides into target products with high selectivity and good conversion rates. The one-component bifunctional catalysts can also be recovered easily by filtration and reused at least for five times with only slight decrease in catalytic performance. Finally, a possible process for hydroxyl group-assisted ring-opening of epoxide and functionalized group- induced activation of CO2 was presented.

Self-assembly of carbon nanotubes on a hollow carbon polyhedron to enhance the potassium storage cycling stability of metal organic framework-derived metallic selenide anodes.

Potassium-ion batteries (PIBs) is increasingly studied because of their suitable redox potential and high natural abundance. However, potential anode materials with long-term cycling stability are still in high demand because of the large radius of K+. Herein, an MOF-derived hierarchical carbon structure and the self-assembly of CNTs on hollow carbon polyhedrons are used as carbon matrices to disperse and stabilize metal selenides(Co-Se@CNNCP). When the hybrid is utilized in PIBs, it displays a specific capacity of 410 mA h g-1 at 0.1 A g-1 after 80 cycles and 253 mA h g-1 at 0.5 A g-1 after 200 cycles with a capacity retention of 100%, while the metal selenides dispersed on hollow carbon polyhedrons without CNTs (Zn-Co-Se@NCP) lose 86% of their capacity after 200 cycles. The superior cycling stability of the hybrid is mainly attributed to the large amounts of CNTs suppressing the agglomeration of the metal selenide nanoparticles on the surface, and the hollow carbon polyhedrons cause a high structural integrity during the repreated K+ insertion and extraction process. This work offers a feasible route to design a hierarchical carbon matrix for use as the anode materials of PIBs with long-term cycling stability.

Rational design of MoSe2 nanosheet-coated MOF-derived N-doped porous carbon polyhedron for potassium storage.

For potassium-ion battery (PIB), it remains a huge challenge to develop an appropriate anode material to compensate the large radius of K+. MoSe2 shows great potential for efficient K+ insertion/extraction due to its unique lamellar structures with an interlayer spacing of 6.46 Å. However, pure MoSe2 has low electronic conductivity and agglomerates during long-term cycling. In the present work, MoSe2 nanosheets were fabricated on the N-doped porous carbon polyhedron (NPCP). The obtained product was designated as NPCP@MoSe2 and functioned as anode materials for PIBs. NPCP@MoSe2 displayed a promising reversible capacity (325 mAh/g at 100 mA/g after 80 cycles), long-term cycling performance (128 mAh/g at 500 mA/g after 800 cycles), and superior rate property at 5000 mA/g. The enhanced electrochemical performance of NPCP@MoSe2 could be attributed to the rational design of hybrid structures. Notably, the hollow NPCP provide a large contact area for the interactions among the electrolytes and electro-active materials as well as partly buffer the volume expansion. The synergistic effects between MoSe2 and NPCP could mitigate the agglomeration of MoSe2 nanosheets. Besides, the uniformly doping N elements enhanced the conductivity of the carbon matrix, and the N-group also provided potential binding active sites for K-ion accommodation. This work paves the ideas for the design of novel anode materials with high specific capacity, good cycling stability and outstanding rate capability for PIBs.

Hierarchical Ni-Co-O-C-P hollow tetragonal microtubes grown on Ni foam for efficient overall water splitting in alkaline media.

Exploring low-cost and highly efficient non-noble bifunctional electrocatalysts with high performances for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for large-scale sustainable energy systems. Herein, the Ni-Co-O-C-P hollow tetragonal microtubes grown on 3D Ni foam (Ni-Co-O-C-P/NF) was synthesized via a one-step solvothermal method and followed by a simple carbon coating and in situ phosphorization treatment. Benefiting from the unique open and hierarchical nano-architectures, the as prepared Ni-Co-O-C-P/NF presents a high activity and durability for both the HER and OER in alkaline media. The overall-water-splitting reaction requires a low cell voltage (1.54 V @ 10 mA cm-2) in 1 M KOH when Ni-Co-O-C-P/NF is used as both the anode and cathode. The highly flexible structure can provide a large amount of exposed active sites and shorten the mass transport distance. Furthermore, bimetallic phosphides also favor the electrocatalysis due to the higher electronic conductivity and the synergetic effect. This work demonstrated a promising bifunctional electrocatalyst for water electrolysis in alkaline media with potential in future applications.

Metal ion extraction using newly-synthesized bipyridine derivative as a chelating reagent in supercritical CO(2).

4,4'-Bis(dihexylaminocarbonyl)-2,2'-bipyridine (BDC-Bipy) was synthesized and studied systematically as a chelating reagent for metal ions extraction in supercritical CO(2). The compound showed high extraction efficiency for Co(2+) (100%), Cu(2+) (100%), Cd(2+) (98.2%), and Zn(2+) (100%) ions and good extraction efficiency for Sr(2+) (79.4%) and Pb(2+) (89.8%) when the extraction was performed in supercritical CO(2) at 313 K and 25 MPa with the system of BDC-Bipy, deionized water and perfluoro-1-octanesulfonic acid tetraethylammonium salt. The recoveries of mixed metal ions were also measured; unfortunately, the system of extraction has no selectivity for the metal ions.

Solvothermal synthesis of uniform bismuth nanospheres using poly(N-vinyl-2-pyrrolidone) as a reducing agent.

Uniform bismuth nanospheres were successfully prepared from bismuth nitrate in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) by solvothermal process. The product was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray. PVP plays a critical role both as a reducing agent and a capping agent in the formation of bismuth nanospheres. Shape and size of bismuth nanospheres could be tuned by changing the employed PVP/bismuth salt ratio. It was also found the solvent had an effect on the morphologies of bismuth nanomaterials. The possible formation and growth mechanism of bismuth nanospheres were also discussed and proposed to explain the reduction step.