Latest ArticlesReverse water gas shift (RWGS) reaction is a crucial process in CO2 utilization. Herein, Ni- and NiCe-containing hexagonal mesoporous silica (Ni-HMS and NiCe-HMS) catalysts were synthesized using an in-situ one-pot method and applied for RWGS reaction. At certain reaction temperatures 500-750 ℃, Ni-HMS samples displayed a higher selectivity to the preferable CO than that of conventionally impregnated Ni/HMS catalyst. This could be originated from the smaller NiO nanoparticles over Ni-HMS catalyst. NiCe-HMS exhibited higher activity compared to Ni-HMS. The catalysts were characterized by means of TEM, XPS, XRD, H2-TPR, CO2-TPD, EPR and N2 adsorption-desortion technology. It was found that introduction of Ce created high concentration of oxygen vacancies, served as the active site for activating CO2. Also, this work analyzed the effect of the H2/CO2 molar ratio on the best NiCe-HMS. When reaction gas H2/CO2 molar ratio was 4 significantly decreased the selectivity to CO at low temperature, but triggered a higher CO2 conversion which is close to the equilibrium.
We predicted two stable two-dimensional materials of carbon and bismuth elements, namely BiC and Bi2C monolayers. The stabilities of two monolayers were examined by cohesive energy, Born criteria, first-principle MD simulations and phonon spectra, respectively. By including the spin-orbit coupling effects, the BiC monolayer is a metal and the Bi2C monolayer possesses a narrow direct (indirect) band gap of 0.403 (0.126) eV under the HSE06 (GGA-PBE) functional. For the adsorption of CO2 molecules, the BiC and Bi2C monolayers have three stable adsorption sites C2, T3 and T4 with the adsorption energies as -0.57, -0.51 and -0.81 eV, and the activation ability on the adsorption as T4 > T3 > C2. These consequences make the BiC and Bi2C monolayers to be promising adsorbents to capture CO2 gas, the Bi2C monolayer to be well photovoltaics and optoelectronics material, and the BiC monolayer to be ideal battery and electronics materials, respectively.
As a two-dimensional carbon based semiconductor, C3N acts as a promising material in many application areas. However, the basic physical properties such as Raman spectrum properties of C3N is still not clear. In this paper, we clarify the Raman spectrum properties of multilayer C3N. Moreover, the stacking driven Raman spectra change of multilayer C3N is also discussed.
Three imidazole-modified Ag-polyoxovanadates frameworks (APFs) with a controllable molar ratio of Ag+ to polyoxovanadates (POVs) [Ag(IM)2]2V4O12·2Ag(IM)2 (APF-1), [Ag2(1-eIM)4]2[Ag(1-eIM)2]3·2Ag(1-eIM)2·3(1-HeIM)[V10O28]2 (APF-2) and [Ag(1-pIM)2]3[HV10O28]·2Ag(1-pIM)2·2H2O (APF-3) (IM = imidazole; 1-eIM = 1-ethylimidazole and 1-pIM = 1-propylimidazole) have been successfully achieved by self-assembly of POVs, Ag+ cations, and three different imidazole derivatives. Interestingly, the molar ratios of Ag+ to POVs vary from 4:1, 4.5:1 to 5:1 by changing the vanadium resources and imidazole derivatives. Notably, the coordination environment of Ag+ cations and the structure of POVs in the APFs are also different. Specifically, for APF-1, the four Ag atoms adopt three-coordinated and four-coordinated geometries, respectively, and Ag-imidazole complexes and [V4O12]4− cluster form the one-dimensional polymeric chains. While Ag atoms in APF-2 and APF-3 exhibit two-, four- and five-coordinated geometries for APF-2, four-, five- and six-coordinated geometries for APF-3, respectively. These Ag+ cations and decavanadate clusters are assembled into the 2D supramolecular structure through the Ag-O bonds and Ag…Ag argentophilic interaction. Remarkably, thus-obtained APF-2 can serve as powerful efficient heterogeneous catalyst for construction of CN bond and detoxification of simulant sulfur mustard (yields up to 99%), which enable successful recycling for three cycles with remained catalytic activities and structure stability.
The properties of two-dimensional (2D) materials are highly dependent on their phase and thickness. Various phases exist in tin disulfide (SnS2), resulting in promising electronic and optical properties. Hence, accurately identifying the phase and thickness of SnS2 nanosheets is prior to their optoelectronic applications. Herein, layered 2H-SnS2 and 4H-SnS2 crystals were grown by chemical vapor transportation and the crystalline phase of SnS2 was characterized by X-ray diffraction, ultralow frequency (ULF) Raman spectroscopy and high-resolution transmission electron microscope. As-grown crystals were mechanically exfoliated to single- and few-layer nanosheets, which were investigated by optical microscopy, atomic force microscopy and ULF Raman spectroscopy. Although the 2H-SnS2 and 4H-SnS2 nanosheets have similar optical contrast on SiO2/Si substrates, their ULF Raman spectra obviously show different shear and breathing modes, which are highly dependent on their phases and thicknesses. Interestingly, the SnS2 nanosheets have shown phase-dependent electrical properties. The 4H-SnS2 nanosheet shows a current on/off ratio of 2.58 × 105 and excellent photosensitivity, which are much higher than those of the 2H-SnS2 nanosheet. Our work not only offers an accurate method for identifying single- and few-layer SnS2 nanosheets with different phases, but also paves the way for the application of SnS2 nanosheets in high-performance optoelectronic devices.
Molybdenum trioxide (MoO3) can be employed as an excellent host for intercalation due to its 2D layered structure that connected by van der Waals interactions. Herein, a series of polyoxometalate-based MoO3 composites (Al13@MoO3) were successfully prepared by interpolating the Keggin-type polycationic AlO4Al12(OH)24(H2O)127+ (Al13) into MoO3 gallery. These composites can be applied to rapidly adsorb the anionic dye methyl orange (MO) through strong electrostatic interactions lead to compact and stable gathering in the surrounding of the numerous charged Al13. Adsorption behaviors of composites with the different amount of Al13 were determined, these results revealed that Al13-3.34%@MoO3 exhibited the most remarkable adsorption capacity. More importantly, the composite maintains superior adsorption capacity for five consecutive adsorption/desorption cycles, suggesting that Al13@MoO3 can be an efficient and durable adsorbent.
Though Olefin-linked covalent organic frameworks (oCOFs) possess excellent π-electron delocalization, the barely reversible olefin linkage brings challenges for oCOFs' synthesis and functionalization. Here, we synthesize new oCOFs with tertiary amine knots which have twisted configuration and electron-donating nature. Investigation into the structural variation and photoelectric performance shows that the twisted configuration of oCOF-TFPA could favor to the intramolecular charge transfer process and reduce the possibility of aggregation-caused quenching. Photoelectrical measurements and electric band structure calculation both verify the superiority of this oCOFs' structure in photoelectric sensing.
By combining 5, 10, 15, 20-tetra(4-chlorine)phenylporphyrin (TClPP) and α-Keggin polyoxometalate H5PV2Mo10O40 (H5PVMo) via a simple ion-exchange method, an organic-inorganic hybrid material [C44H28N4Cl4]1.5[H2PMo10V2O40]·2C2H6O (H2TClPP-H2PVMo) was prepared and thoroughly characterized by a variety of techniques. The homogeneous photocatalytic degradation of 2-chloroethyl ethyl sulfide (CEES) (5 µL) by H2TClPP-H2PVMo (1 × 10−6 mol/L) was studied in methanol and methanol-water mixed solvent (v/v = 1:1), in which the degradation rate of CEES reached 99.52% and 99.14%, respectively. The reaction followed first-order reaction kinetics, and the half-life and kinetic constant in methanol and the mixed solvent were respectively 33.0 min, −0.021 min−1 and 15.7 min, −0.043 min−1. Mechanism analysis indicated that under visible light irradiation in the air, CEES was degraded via oxidation and alcoholysis/hydrolysis in methanol and the mixed solvent. O2·− and 1O2 generated by H2TClPP-H2PVMo selectively oxidized CEES into a nontoxic sulfoxide. Singlet oxygen capture experiments showed that H2TClPP-H2PVMo (ϕ = 0.73) had a higher quantum yield of singlet oxygen than TClPP (ϕ = 0.35) under an air atmosphere and visible light irradiation.
An organic-inorganic hybrid FeIII–PrIII-included 2-germano-20-tungstate [Pr(H2O)8]2H2[Fe4(H2O)4 (pca)4Ge2W20O72]•34H2O (Hpca = 2-pyridinecarboxylic acid) (1) was hydrothermally prepared. Its polyoxoanion comprises one tetra-FeIII incorporated [Fe4(H2O)4(pca)4Ge2W20O72]8- hybrid entity and two [Pr(H2O)8]3+ ornamental cations. The [Fe4(H2O)4(pca)4Ge2W20O72]8- 2-germano-20-tungstate entity can be regarded as an infrequent S-type [Ge2W20O72]16- cluster pocketed by four [Fe(H2O)(pca)]2+ cations. The S-type [Ge2W20O72]16- cluster could be imagined as condensation of two divacant Keggin [α-GeW10O37]10- segments by sharing two atoms. It is of interest is that carboxyl O and pyridine N atoms on pca ligands concurrently bind with Fe3+ cations in a five-membered heterocyclic fashion to increase the stability of the whole structure. Furthermore, the electrochemical biosensing properties of 1 as the modified electrode material have been investigated for detecting norepinephrine (NPP), showing a low detection limit of 3.25 µmol/L. This work not only enriches structures of heterometallic germanotungstates (GTs), but also expands applications of polyoxometalates (POMs) in the electrochemical biosensing field.
Stimuli-responsive hydrogels hold an irreplaceable statue in intelligent actuation materials because of their reversible stretchability and excellent biocompatibility. However, the poor mechanical performance and complicated fabrication process of anisotropic structures severely limit their further applications. Herein, we report a high-strength thermoresponsive wood-PNIPAM composite hydrogel actuator with complex deformations, through a simple in-situ polymerization. In this composite hydrogel actuator, the anisotropic wood and the thermoresponsive PNIPAM hydrogel hydroel can work together to provide bending and even other complex deformations. Owing to strong interfacial interaction, this actuator perfectly realized the combination of good mechanical properties (~1.1 MPa) and fast actuation speed (~0.9 s). In addition, by adjusting the orientation direction of wood, this actuator can achieve various complex deformations. Such composite hydrogel actuator could be a good candidate for intelligent applications, such as intelligent actuators, smart valves, manipulators and even soft robots.
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