Recently,the chain-walking ethylene polymerization strategy has garnered widespread attention as an efficient and straightforward method for preparing polyolefin elastomers.In this study,a series of 2,4,8-triarylnaphthyl iminopyridyl nickel catalysts were synthesized and used in ethylene polymerization.These catalysts demonstrated moderate catalytic activity(105 g mol^(−1) h^(−1)),producing high-molecular-weight(up to 145.5 kg/mol)polyethylene materials with high branching degrees(75−95/1000C)and correspondingly low melting points.Detailed analysis using 13C NMR spectroscopy revealed that the polyethylenes primarily featured methyl and long-chain branches.Mechanical testing of the polyethylene samples obtained from catalysts Ni1−Ni3 exhibited moderate stress at break(4.64−6.97 MPa)coupled with a very high strain at break(1650−3752%),indicating their very good ductility.Furthermore,these polyethylenes showcased great elastic recovery abilities,with strain recovery values ranging from 72%to 85%.In contrast,the polyethylene produced by Ni4 displayed notably inferior tensile strength(0.16 MPa)and tensile recovery(43%).To the best of our knowledge,this study represents the inaugural utilization of a nickel iminopyridyl catalyst in the preparation of a polyethylene thermoplastic elastomer.
Porous aromatic framework 1(PAF-1)is an extremely representative nanoporous organic framework owing to its high stability and exceptionally high surface area.Currently,the synthesis of PAF-1 is catalyzed by the Ni(COD)2/COD/bpy system,suffering from great instability and high cost.Herein,we developed an in situ reduction of the Ni(II)catalytic system to synthesize PAF-1 in low cost and high yield.The active Ni(0)species produced from the NiCl_(2)/bpy/NaI/Mg catalyst system can effectively catalyze homocoupling of tetrakis(4-bromophenyl)methane at the room temperature to form PAF-1 with high Brunauer-Emmett-Teller(BET)-specific surface area up to 4948 m^(2) g^(−1)(Langmuir surface area,6785 m2 g−1).The possible halogen exchange and dehalogenation coupling mechanisms for this new catalytic process in PAF's synthesis are discussed in detail.The efficiency and universality of this innovative catalyst system have also been demonstrated in other PAFs'synthesis.This work provides a cheap,facile,and efficient method for scalable synthesis of PAFs and explores their application for high-pressure storage of Xe and Kr.
Shanshan WangYue WuWenxiang ZhangHao RenGuangshan ZhuHeping Ma
We synthesized heterostructures by tethering Ni(II)-doped CdS(Ni:CdS)quantum dots(QDs)toβ-Pb_(0.33)V_(2)O_(5)nanowires(NWs)using L-cysteine as a molecular linker,and we evaluated the influence of doping on their redox photocatalytic reactivity.We initially hypothesized that incorporating Ni:CdS QDs into heterostructures could alter excited-state dynamics and mechanisms,and that the localization of excited electrons on Ni 3d states could promote redox photocatalytic mechanisms including reduction of CO_(2).Isolated Ni:CdS QDs were ferromagnetic,and they exhibited enhanced photocatalytic hydrogen evolution and photostability relative to undoped CdS QDs.Both Pb_(0.33)V_(2)O_(5)/CdS heterostructures(with undoped QDs)and Pb_(0.33)V_(2)O_(5)/Ni:CdS heterostructures(with Ni(II)-doped QDs)exhibited substantial energetic overlap between valence-band states of QDs and intercalative mid-gap states ofβ-Pb_(0.33)V_(2)O_(5)NWs.Within Pb_(0.33)V_(2)O_(5)/CdS heterostructures,photoexcitation of CdS QDs was followed by rapid(50-100 ps)transfer of both holes and electrons toβ-Pb_(0.33)V_(2)O_(5)NWs.In contrast,within Pb_(0.33)V_(2)O_(5)/Ni:CdS heterostructures,holes were transferred from Ni:CdS QDs toβ-Pb_(0.33)V_(2)O_(5)NWs within 100 ps,but electrons were transferred approximately 20-fold more slowly.This difference in electron-and hole-transfer kinetics promoted charge separation across the Pb_(0.33)V_(2)O_(5)/Ni:CdS interface and enabled the photocatalytic reduction of CO_(2)to CO,CH_(4),and HCO_(2)H with>99.9%selectivity relative to the reduction of H+to H2.These results highlight the opportunity to fine-tune dynamics and mechanisms of excitedstate charge-transfer,and mechanisms of subsequent redox half-reactions,by doping QDs within heterostructures.Moreover,they reveal the promise of heterostructures comprising QDs and MxVyO5 materials as CO_(2)-reduction photocatalysts.
