Constructing stable palladium(II)-based metal–organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability ...is limited by synthetic challenges due to the inertness of the Pd–ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.
In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. ...Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g
at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H
BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C
H
@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.
Molten salt is an excellent medium for chemical reaction, energy transfer, and storage. Molten salt innovative technologies should be developed to recover metals from secondary resources and reserve ...metals from primary natural sources. Among these technologies, molten salt electrolysis is an economic and environment-friendly method to extract metals from waste materials. From the perspective of molten salt characteristics, the application of molten salts in chemistry, electrochemistry, energy, and thermal storage should be comprehensively elaborated. This review discusses further directions for the research and development of molten salt electrolysis and their use for metal recovery from various metal wastes, such as magnet scrap, nuclear waste, and cemented carbide scrap. Attention is placed on the development of various electrolysis methods for different metal containing wastes, overcoming some problems in electrolytes, electrodes, and electrolytic cells. Special focus is given to future development directions for current associated processing obstacles.
The effect of various retrogression and re-aging (RRA) treatments on mechanical properties and corrosion behavior of a new type Al–Zn–Mg–Cu–Er–Zr alloy was investigated by microhardness testing, ...tensile testing, intergranular corrosion (IGC) and exfoliation corrosion (EXCO) testing. The results show that the RRA treatment can effectively improve the IGC and EXCO resistance with less strength sacrificing because the grain interior precipitates and the grain boundary precipitates are similar to that of T6 temper and T73 temper. Meanwhile, as the microhardness of the retrogressed alloy reaches the peak value during the retrogression at 170 °C, the corresponding RRA-treated alloy possesses the better strength, but the corrosion resistance is poor in comparison with that of the retrogression at 190 °C. The optimal combination of strength, IGC and EXCO resistance is obtained after retrogression at 180 °C for 60 min. Moreover, for different heat treatment tempers, the corresponding microstructural evolution of the precipitates including Al
3
(Er, Zr) particles was also discussed in detail.
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•A soft-hard template cooperative organization approach for simultaneous introduction of mesoporous and nitrogen defects into g-C3N4.•The method greatly increases the specific surface ...area of g-C3N4 through mesopore connectivity.•The combination of soft and hard template creates a large number of nitrogen defects.•This material has excellent adsorption and catalytic properties.
The mesoporous graphitic carbon nitride (g-C3N4) was prepared by a facile soft-hard template cooperative organization approach to creating pores, with the melamine used as the precursor, and the mixture of silica sol and F127 was employed as mesoporous templates. Nitrogen-deficient mesoporous g-C3N4 samples were obtained by modifying the addition of F127. In addition, samples prepared with combined templates (FMCN-x) were compared with those using only soft (FCN) and hard (MCN) templates, and the results showed there was a significant increase in specific surface area and photocatalytic performance. Among them, sample FMCN-4 exhibited the maximum specific surface area of 104.18 m2/g and pore volume of 0.346 cm3/g. The presence of F127 enhances the pore formation effect of the silica sol, resulting in even higher specific surfaces with even smaller additions of silica sol. This situation reduces the amount of template etchant used subsequently and produces it in a more environmentally friendly cooperative organization. On the other hand, the soft-hard template cooperative organization approach introduced nitrogen defects in the g-C3N4 material, and the C/N ratio increased to 1.09 for FMCN-4, which improved the photocatalytic performance. FMCN-4 exhibited 95.71 % degradation efficiency to methyl orange in 90 min under simulated visible light irradiation. FMCN-4 also exhibits excellent visible light photocatalytic properties and good cycling stability.
The molten salt electrochemical method is an efficient one-step process to extract tungsten from tungsten carbide (WC). Owing to the limitation of molten salt electrochemical experiments and the ...number of data points, determining the optimal process conditions is challenging. In addition, the mechanism that affects the current efficiency is difficult to obtain intuitively. In this study, simulations of tungsten carbide anode electrolysis were obtained using the COMSOL Multiphysics 5.3, and the results were compared to the dissolution experiment of tungsten carbide with varying content of sodium tungstate (Fig.
1
). The experimental data fitted well with the theoretical current efficiency of 75%. At concentrations below 0.5 wt% of sodium tungstate, the anode dissolution showed a linear relationship against the concentration of sodium tungstate. At a constant concentration of sodium tungstate, the anodic dissolution decreased with increasing immersion depth, consistent with the variation of cell voltage difference before and after electrolysis. The optimal immersion depth and effective area of the anode estimated by simulations were 2.5 mm and 0.465 mm
2
, respectively (Fig. 2
).
Under the optimum electrolysis conditions simulated by COMSOL, the nano tungsten powder was obtained.
Graphic abstract
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•Electrochemical behaviors of tungsten ion reduction were elucidated.•Increasing the contents of F− could reduce the reduction step of tungsten ion.•Reduction process of tungsten ions ...was explained by simulation calculation.•Low-valence dissolution of W from WC was realized with appropriate Cl−/F− ratio.•One-step preparation of tungsten were conducted by changing coordination form.
The main obstacles to the production of metals such as tungsten are the multi-step reaction processes and disproportionation reactions. Tungsten has more metastable valence states in molten salt and is more likely to undergo side reactions. To implement the low-valence reduction of tungsten, the composition of the molten salt system was changed. The influence of fluoride ions on the valence states of tungsten ions was determined by experiments and simulation analysis. The preliminary results suggested that a one-step direct reduction to metallic tungsten could be achieved by selecting a proper Cl−/F− ratio. This change of the valence state, which is the primary issue for tungsten reduction, was overcome by understanding the interactions between the ions and the coordination form. More specific details related to the variation of the reaction process and coordination form were provided by simulations. The simulation results showed that low-valence tungsten ions were dissolved from tungsten carbide at appropriate Cl−/F− ratios, and the change of the coordination form of the tungsten ions affected the reduction process of these ions with various valence states.
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•The fundamental thermodynamic and dynamic properties of tungsten ions were determined.•Coordination form of tungsten ions from the electrolysis of WC was simple ions.•A method to ...confirm the standard electrode potential of unknown concentration ions.•Simulation calculation was used to verify the coordination form of tungsten ions.
The results of the coordination form of low-concentration ions in molten salt have great reference significance for exploring the electrolysis reaction mechanism. Given the low concentration of tungsten ions after the electrochemical dissolution of tungsten carbide, this can be difficult to judge the coordination form of tungsten ions through spectral characterization. This paper will struggle to tackle the problem by comparing the electrochemical behaviors of tungsten ions from the electrochemical dissolution of tungsten carbide and NaCl–KCl–2 wt% Na2WO4 melt. The electrochemical method had been investigated as a mean to understand the fundamental thermodynamic and mass transport properties of tungsten ions. The apparent standard potentials of oxidation and reduction couple at several temperatures were calculated by using a proposed new method. The diffusion coefficients of tungsten ions were determined. It can be concluded that the tungsten ions in the molten salt after tungsten carbide electrolysis were simple ions without coordinating anions by comparing the dynamics and thermodynamic calculation results of the two systems. The developed simulation boxes can serve as a verification for further theoretical investigations of the coordination form of tungsten ion groups at molecular scale. The results of this work provide necessary knowledge for the development methods to determine the dynamics and thermodynamic properties and coordination forms of metal ions.
The W–La
2
O
3
–Y
2
O
3
–ZrO
2
materials were prepared by vacuum hot pressing sintering process. The microstructure was characterized by scanning electron microscopy (SEM). The effects of sintering ...temperature, sintering pressure, holding time and heating rate on relative density, hardness and microstructure were studied. The sintering activation energy of the powder was calculated. Based on the result, the best sintering parameters by vacuum hot pressing sintering are as follows: sintering temperature of 1600 °C, sintering pressure of 60 MPa and holding time of 60 min. The heating rate is 10 °C·min
−1
from room temperature to 1000 °C and 4 °C·min
−1
from 1000 to 1600 °C. Using this process, the grain size is about 3 μm in diameter with relative density at 99.7%, and the hardness is HV 528.5. The sintering characteristic index (
n
) of the specimen is 4, and the sintering mechanism mainly depends on the diffusion from the surface to the intragranular in the volume diffusion. The sintering activation energy of W–La
2
O
3
–Y
2
O
3
–ZrO
2
material is 286.2 kJ·mol
−1
, which indicates that the powder has higher activity in sintering process.
Graphic abstract
The controlled preparation of hexagonal tungsten trioxide (h-WO
3
) nanostructures was achieved by adjusting the pH of the precursor solution. The effect of the pH on the morphology, elemental ...composition, and photocatalytic performance of the samples was characterized via X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Ultraviolet–visible (UV–Vis) spectra were used to evaluate the absorbance and the photocatalytic performance of methylene blue. Photoluminescence (PL), electrochemical impedance spectroscopy, photocurrent response and Brunauer–Emmett–Teller (BET) were used to study the optical properties, electrical performance, and specific surface area of the WO
3-
nanostructures, respectively. The results indicate that the WO
3
nanorods prepared at pH = 1.0 exhibit the highest photocatalytic performance (87.4% in 1 h), whereas the WO
3
nanoblocks prepared at pH = 3.0 show the lowest. The photocatalytic performance of the one dimensional (1D)-nanorods can be attributed to their high specific surface area and charge transfer ability. The h-WO
3
nanostructures were synthesized via a simple method and without a capping agent. They show an excellent photocatalytic performance, which is promising for their application in environment purification.
