Rationally designed novel cost-effective hydrogen evolution reaction(HER)electrocatalysts with controlled surface composition and advanced structural superiority is extremely critical to optimize the HER performance.Polyoxometalates(POMs)with structural diversity and adjustable element compositions represent a promising precursor for rational design and preparation of HER electrocatalysts.Herein,a series of transition metal-doped MoS_(2)materials with different surface engineered structures(Fe,Cr,V doping and S vacancies)(M-MoS_(2)/CC,M=Fe,Cr and V)were fabricated by a simple hydrothermalvulcanization strategy using Keplerate polyoxomolybdate nanoball({Mo_(72)Fe_(30)},{Mo_(72)Cr_(30)},{Mo_(72)V_(30)},{Mo_(132)})as precursors.The enlarged interlayer spacing as well as the integration of homogeneous transition metal doping and abundant sulfur vacancies endows prepared M-MoS_(2)/CC with superior HER electrocatalytic performance and excellent long-term working stability in both acidic and alkaline media.The optimized Fe-MoS_(2)/CC afford current densities of 10 and 50 mA/cm^(2)at overpotentials of 188/272 mV and 194/394 mV in 0.5 mol/L H_(2)SO_(4)and 1.0 mol/L KOH aqueous solution,respectively,outperforming most of reported typical transition metal sulfide-based catalysts.This work represents an important breakthrough for POMs-mediated highly efficient transition metal sulfide-based HER electrocatalysts with wide range pH activity and may provide new options for the rational design of promising HER electrocatalysts and beyond.
The development of CO_(2)separation membranes with high permeability and high selectivity,as well as ultra-thin selective layers,has always been challenging.Herein,a molecular-scaled co-assembly strategy is employed to fabricate the Pebax-Mo_(132)(Pebax=polyether-block-amide copolymer;Mo_(132)=(NH_(4))_(42)[Mo_(72)^(Ⅵ)Mo_(60)^(Ⅴ)O_(372)(CH_(3)COO)_(30)(H_(2)O)_(72)])membranes.The optimal selfstanding membrane,Pebax-Mo_(132)-5%,shows a CO_(2)permeability of~384 Barrer and an ultra-high ideal CO_(2)/N_(2)selectivity of~244,outperforming most membranes reported in the literature.The CO_(2)permeability and ideal CO_(2)/N_(2)selectivity are increased by 70%and 367%,respectively,compared with the pristine Pebax membrane.A thin-film composite membrane prepared by spin-coating technique on a support membrane with gutter layers also exhibits a CO_(2)permeance of 838 GPU and a CO_(2)/N_(2)selectivity of 136.Such excellent performance can be attributed to the following reasons:(1)strong hydrogen bonding interactions between{Mo_(132)}clusters and Pebax confer excellent interfacial compatibility to the mixed matrix membranes;(2)incorporation of hollow{Mo_(132)}clusters into the Pebax molecular chain decreases the crystallinity of Pebax,and thereby accelerates the chain dynamics and increases the free volume of the membrane;(3)in situ diffuse reflectance infrared Fouriertransform spectroscopy demonstrates that the{Mo_(132)}clusters can effectively catalyze the hydration reaction of CO_(2)and promote the transport of CO_(2);(4)furthermore,the 0.35 nm pores of the crown ether-type{Mo_(9)O_(9)}allow the accurate size sieving of CO_(2)(0.33 nm)and N_(2)(0.36 nm)molecules.
Wan-Lei ZhaoHongqiang LiRuoxuan ZhengYixin YangWei ChenYu-Fei Song
Abstract By reacting the unique Keplerate type molybdenum-oxide based polyoxometalate (NH4)42·[MoI320372·(CH3COO)30(H2O)y2]·ca.300H2·ca. 10CH3COONH4(1) with tetramethylammonium bromide, a new derivative (NH4)26[TMA]16{MoI32O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca.189H2O(2, TMA=tetramethylammonium) was prepared. Compound 2 was characterized by Fourier transform infrared spectroscopy(FTIR), UV-Vis, elemental and thermogravimetric analyses. By the well-established Z-scan technique, investigations on the nonlinear opti- cal(NLO) properties of the series of compounds derived from the Keplerate type molybdenum-oxide-based poly- oxometalate, namely, the newly prepared compound 2, the three previously reported compounds, included compound 1, (NH4hs(TBA)24{Mo132O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca. 173H2O(3, TBA=tetrabutylammonium) and (DODA)40(NH4)2[(H2O)nMo132O372(CH3COO)3o(H20)72](4, DODA=dimethyldioctadecylammonium), reveal that the third-order nonlinearity[x(3)] values of compounds 1, 2 and 3 in the DMF/H2O solution and compound 4 in chloro- form are almost the same, which indicates that the counter cations with different length of alkyl chains show ignora- ble impacts on the NLO susceptibility. In other words, the remarkable third-order nonlinearities[x(3)≈10 19 m2/V2] mainly come from the [MoI32O372(CH3COO)30(H2O)72]42 anions. This fact reveals that the applications of the NLO active polyoxometalates in various environments(such as hydrophilic, hydrophobic, polar, apolar, etc.) can be achieved by simply varying cations to meet the demands in the design of diverse devices. Keywords Keplerate type polyoxometalate; Nonlinear optical property; Z-Scan technique; Self-defocusing; Reverse saturable absorption
ZHOU Yunshan QU Ningning WANG Xuan ZHANG Lijuan SHI Zonghai HASSAN ul Sadaf
The Keplerate‐type giant nanoporous isopolyoxomolybdate (NH4)42[MoVI72MoV60O372‐(CH3COO)30(H2O)72], denoted {Mo132}, has been used as a catalyst for the synthesis of1,2,4,5‐tetrasubstituted imidazoles by the one‐pot, four‐component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent‐free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT‐IR, UV and X‐ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo132} exhibited high catalytic activity towards the synthesis of 1,2,4,5‐tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5‐tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work‐up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.