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Based on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension length of the welding wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved "mass-spring" model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. Through the dynamic model, the short-circuit transition frequency, welding current and voltage, contact droplet and residual droplet equivalent radius (including mean and statistical distribution) and the dynamic changes of droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results, they were in good agreement. The dynamic changes of droplet displacement, velocity, welding wire extension length and liquid bridge shape are discussed. The results show that the fluctuations of droplet displacement, velocity, and extension length of welding wire is the smallest at the optimal arc point, and the smaller the radius of curvature of the initial liquid bridge is, the better the stability of short-circuit transition is.

Tourism destination images in terms of the gaps between the projected and perceived images are of great significance in the development of destinations. Additionally, the use of big-data in tourism studies remains under-utilized despite the boom in big-data applications and the increasing number of electronic User Generated Contents (UGC). Aiming to take advantage of tourism UGC to fully understand the destination image gap between official promotion materials and tourist perception of Sanya City in China, this study innovatively employed a big-data analysis technique, Tourism Sentiment Evaluation (TSE) model and proposed a new analysis framework integrating the “cognitive-affective” model with the gap analysis of projected and perceived destination image to explore the destination image gap of Sanya. It is found that Sanya’s perceptive destination image is overall consistent with its official positioning; however, there also exist image gaps between the two groups in terms of the impact of festival events and tourists’ attitude towards core scenic spots amongst others. This study’s findings are discussed in light of their methodological, theoretical, and practical implications for destination positioning, marketing, and management.

Removal of CH4 and CO2 from C2H2 streams remains challenging in the chemical industry. Herein, a robust three-dimensional metal-organic framework, Cu-CPAH, was designed and synthesized through a hydrothermal method. Cu-CPAH exhibits highly selective C2H2 adsorption capacity with respect to both CH4 and CO2, which is ascribed to the enrichment of active sites in the framework. Dynamic breakthrough results reveal that Cu-CPAH serves as a solid adsorbent for high-efficiency purification of C2H2 from an equal proportion of C2H2/CO2 or C2H2/CO2/CH4 at room temperature. Discrete Fourier transform simulations confirm that various active sites preferentially interact with C2H2 other than CO2 and CH4, signifying for the first time that the imino functional groups in the cage contribute greatly to the preferential affinity to C2H2 over CO2 and CH4.

Covalent organic frameworks (COFs) have shown great potential for use in ion sensing; however, applications of existing COFs are limited to sensing either cations or anions. In this study, a three-dimensional COF, COF-TT, is constructed by reacting the bis(tetraoxacalix[2]arene[2]triazine) core with tetra(p-aminophenyl)methane to provide a luminescent sensor. COF-TT exhibits ultrahigh thermal stability and exceptional chemical stability in aqueous solutions over a broad pH range from 2 to 14, which signifies immense practical potential for sensing applications. Excellent selectivity and high sensitivity of COF-TT toward Fe3+ cations and CrO42−, Cr2O72−, and MnO4− anions are evident via luminescence quenching. COF-TT also exhibits excellent recyclability in terms of washing and re-exposure cycles. Both experimental data and theoretical calculations are employed to unveil the mechanisms of the quenching effect and sensing properties of COF-TT.

A composite was designed and synthesized based on MIL-101, MoS2, and an iron-substituted polyoxometalate. MoS2 and PW11O39Fe(H2O)4− (PW11Fe) were introduced on the surface of MIL-101 and encapsulated in the cages of MIL-101, respectively. First, a facile microwave synthesis method was developed for synthesizing the composite MIL-101/MoS2. Then, PW11Fe clusters were diffused into the pores of MIL-101/MoS2. The composite PW11Fe@MIL-101/MoS2 could rapidly adsorb rhodamine B (RhB). An adsorption capacity of 378 mg g−1 was achieved in the first 5 min. Moreover, PW11Fe@MIL-101/MoS2 could be potentially used for the separation of dyes. Its RhB adsorption capacity at equilibrium was about four times higher than that of MIL-101. In contrast, its methyl orange (MO) adsorption capacity was about three times lower than that of MIL-101.

Novel 2D graphene analogues with high conductivity are highly demanded as anode materials for lithium-ion batteries (LIBs). Here we report the preparation and characterization of a π-conjugated microporous polymer NGA-CMP with an experimental bandgap of 2.34 eV. Heated sample NGA-CMP400 is used for the first time as an anode material for LIBs. NGA-CMP400 achieves a high reversible capacity of 701 mA h g-1 at 1 A g-1 with extremely stable cycling performance over 500 cycles. The rational design of this kind of graphene-like 2D material with inherent porosity and enhanced electronic conductivity possesses important significance in carbon-based anode materials for LIBs.

Developing efficient noble-metal-free catalysts for the electrochemical N2 reduction reaction (NRR) under ambient conditions shows promise in fertilizer production and hydrogen storage. Here, as a proof-of-concept prototype, we design and implement an Fe–N/C–carbon nanotube (CNT) catalyst derived from a metal–organic framework and carbon-nanotube-based composite with built-in Fe–N3 active sites. This catalyst exhibits enhanced NRR activity with NH3 production (34.83 μg·h–1·mg–1cat.), faradaic efficiency (9.28% at −0.2 V vs RHE), selectivity, and stability in 0.1 M KOH aqueous media under mild conditions. Experimental and theoretical results both reveal that Fe–N3 species are the primary catalytically active centers for the NRR. This work provides insight into precise construction of more efficient and stable NRR electrocatalysts and further expands the possibilities of transition metal–nitrogen–carbon (M–N–C)-based nanomaterials in NRR fields.

The production of 1-butene by ethylene dimerization is an important chemical industrial process currently implemented using homogeneous catalysts. Here, we describe a highly active heterogeneous catalyst (Ni-ZIF-8) for ethylene dimerization, which consists of isolating Ni-active sites selectively located on the crystal surface of a zeolitic imidazolate framework. Ni-ZIF-8 can be easily prepared by a simple one-pot synthesis method in which site-specific anchoring of Ni is achieved spontaneously because of the incompatibility between the d8 electronic configuration of Ni2+ and the three-dimensional framework of ZIF-8. The full exposure and square-planar coordination of the Ni sites accounts for the high catalytic activity of Ni-ZIF-8. It exhibits an average ethylene turnover frequency greater than 1 000 000 h-1 (1-butene selectivity >85%) at 35 °C and 50 bar, far exceeding the activities of previously reported heterogeneous catalysts and many homogeneous catalysts under similar conditions. Moreover, compared to molecular Ni complexes used as homogeneous catalysts for ethylene dimerization, Ni-ZIF-8 has significantly higher stability and shows constant activity during 4 h of continuous reaction. Isotopic labeling experiments indicate that ethylene dimerization over Ni-ZIF-8 follows the Cossee-Arlman mechanism, and detailed characterizations combined with density functional theory calculations rationalize this observed high activity.

A novel microporous Cu-MOF [Cu3(L)2(DMF)]·(H3O)2·3DMF, 1, with dual functionalities of open metal sites (OMSs) and Lewis basic sites (LBSs) based on a V-shaped organic ligand 5,5'-azanediyldiisophthalate was synthesized by hydrothermal method. The framework contains two types of 1D channels with BET surface areas 419 m2 g−1 and pore volume 0.23 cm3 g−1. It shows moderately high adsorption selectivity for C2H2/CH4 and C2H2/N2 at room temperature, the selectivity is 122 and 7.8 (50% and 50%), 181 and 165.7 (5% and 95%).

A Cu metal-organic framework (MOF), [Cu4 (PMTD)2 (H2 O)3 ]⋅20 H2 O, 1, (where PMTD is 1,4-phenylenebis(5-methyl-4H-1,2,4-triazole-3,4-diyl)bis(5-carboxylato-3,1-phenylene)bis(hydroperoxymethanide)), with a rare chiral Oh -type cage, and dual functionalities of open metal sites and Lewis basic sites, based on a designed U-shaped ligand, was synthesized by hydrothermal methods. It exhibits high CO2 , C2 , and C3 hydrocarbon storage capacity under atmospheric pressure, as well as high H2 (1.96 wt.%) adsorption capacity at 77 K. Methane purification capacity was tested and verified step by step. Isosteric heats (Qst ) studies reveal that CH4 has the weakest van der Waals host-guest interactions among the seven gases at 298 K. Ideal adsorbed solution theory (IAST) calculation reveals that compound 1 is more selective toward CO2 , C2 H6 , and C3 H8 over CH4 in further calculating its separation capacity, as exemplified for CO2 /CH4 (50:50, 5:95), C2 H6 /CH4 (50:50, 5:95), or C3 H8 /CH4 (50:50, 5:95) binary gas mixtures. Breakthrough experiments show that 1 has a significantly higher adsorption capacity for CO2 , C2 H6 , and C3 H8 than CH4 . The selective adsorption properties of 1 make it a promising candidate for methane purification.

MnO x –CeO 2 catalysts were synthesized to investigate the active sites for NO oxidation by varying the calcination temperature. XRD and TEM results showed that cubic CeO 2 and amorphous MnO x existed in MnO x –CeO 2 catalysts. High temperature calcination caused the sintering of amorphous MnO x and transforming to bulk crystalline Mn 2 O 3 . H 2 -TPR and XPS results suggested the valence of Mn in MnO x –CeO 2 was higher than pure MnO x , and decreased with the increasing calcination temperature. The turnover frequency (TOF) was calculated based on the initial reducibility according to H 2 -TPR quantitation and kinetic study. The TOF results indicated that the initial reducibility of amorphous MnO x with high valence manganese ions was equivalent to the active sites for NO oxidation. It can be inferred that the amorphous MnO x plays a key role in low-temperature NO oxidation.

By using a triazol-functionalized tricarboxylate, three novel metal coordination polymers, namely, [Zn2L(OH)]·0.5H2O (1), [Co2L(OH)(H2O)]·5.5H2O (2), [Cu2(HL)] (3) L = ［5-(3-(4-carboxyphenyl)−5-methyl-4H-1,2,4-triazol-4-yl)isophthalate］ were synthesized under hydrothermal reactions. All the compounds were characterized by element analysis, IR spectroscopy, thermogravimetric analysis, power X-ray diffrcation and single-crystal X-ray diffrcation. Structural analysis reveals that compounds 1 and 2 have 3D networks with flu topologies where rigid trizaol-functionalized ligands as 4-connected nodes and Zn4(COO)6 or Co4(COO)6 clusters serves as 8-connected secondary building units. Compound 3 has 3D network with pcu topology where Cu4(COO)4 clusters serve as 6-connected secondary building units. Gas adsorption studies reveal that desolvated compoud 1 exhibits high H2 absorption capacity at 77 K and highly selective separation abilities of CO2 and C3H8 over CH4 at room temperature. The results suggest that 1 has potential application in gas storage and separation. In addition, the magnetic properties of compound 2 were also investigated.

The refractory VNbTa alloys with single body centered cubic (BCC) structure were prepared. The proceed alloy exhibited excellent combination of strength and plasticity. The underlying mechanism was related to the solid solution strengthening effect caused by large atomic size misfit of elements among Nb, Ta and V.

A porous NH2-MOF-76(Eu) (MOF 1) with unexpected non-luminescence was designed and synthesized. It exhibits selective fluorescence recovery for sensing dipicolinic acid (DPA), a biomarker of Bacillus anthracis. Moreover, a new europium-based MOF (MOF 2) with evident channel changes was obtained through a single-crystal to single-crystal phase transition.

Heteroatom-rich two-dimensional graphene-like structure polymers are highly demanded as high-performance anode materials for lithium ion batteries. Here, a new microporous poly-benzimidazole (MPBI) is accomplished by a condensation reaction between pyromellitic acid and 1,2,4,5-tetraaminobenzene in polyphosphoric acid medium. After heat-treatment at 550 °C, the integrated frame structure of the obtained MPBI-550 remains unchanged without the residual edge groups. Due to the holey pore framework, nitrogen-rich aromatic rings and two-dimensional graphene-like structure, MPBI-550 is suitable for lithium-ion battery anode. It exhibits a remarkable long cycling life, high reversible capacity of 700 mAh g−1 (at 1 A g−1) after 500 cycles and a good rate performance. Such a low-cost and high-performance material constitutes a step towards the design and manufacture of functional anode materials for next generation lithium-ion batteries.

To improve the yield of cellulolytic enzyme lignin (CEL) and to minimize the structural changes induced by isolation, the dissolution-regeneration of ball-milled soybean stem in a lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent was applied prior to enzymatic hydrolysis. The regenerated stem was enzymatically hydrolyzed for 72 h to remove the carbohydrates and then extracted with 1, 4-dioxane to obtain the cellulolytic enzyme lignin (named as DR-CEL). As expected, the yield of DR-CEL was much higher than that of CEL. With 2 h of ball-milling, the yield of DR-CEL was 40.1% (based on the total lignin in the raw stem). As the ball-milling time increased to 4 h, the yield of DR-CEL improved up to 82.4%, which was much higher than that of CEL with a yield of 26.0%. All the isolated lignin preparations were characterized using FT-IR, 1H NMR and 1H-13C HSQC NMR. The results showed that the main structural characteristics of these two kinds of lignin (CEL & DR-CEL) were similar, except for a slightly higher amount of carbohydrates in DR-CEL. As a result, the combination of the dissolution–regeneration and enzyme hydrolysis of ball-milled sample has a great potential in isolating lignin with higher yield and minimal structural changes.

A Cu metal-organic framework (MOF), [Cu

Reactions of divalent transition metal ions with the N,N′-sulfuryldiimidazole ligand (sdi) gave rise to eleven coordination polymers, namely, [Zn(sdi)(NO3)2(H2O)] (1), [Zn(sdi)2(NO3)2] (2), [Co(sdi)2(NO3)2] (3), [Cu(sdi)2(NO3)2]·2CO(CH3)2 (4), [Mn(sdi)2(H2O)2]·2NO3 (5), [Co(sdi)2(H2O)2]·2ClO4 (6), [Zn(sdi)(bdc)0.5(OCH3)(H2O)]·ClO4·H2O (7), [Cd(sdi)(N3)2] (8), [Mn(sdi)(N3)2] (9), [Ni(sdi)2(SO4)] (10) and [Cd(sdi)0.5(Hbtc)(OCH3)] (11) (H2bdc = 1,4-benzenedicarboxylic acid, H3btc = 1,3,5-benzenetricarboxylic acid). X-ray single-crystal analyses reveal that they have rich structural chemistry ranging from zero-dimensional (0D) (1), one-dimensional (1D) (2–7), two-dimensional (2D) (8) to three-dimensional (3D) (9–11) networks. Compound 1 displays a 0D structure which consists of [Zn(sdi)]2 dimers. Compounds 2–7 possess 1D chains with closed loops. Compound 8 shows a 2D (63) network. Compounds 9 and 10 exhibit 3D uninodal 6-connected pcu frameworks with (412·63) topology. Compound 11 displays a 3D uninodal 4-connected framework with a CdSO4-like net (65·8). The effects of metal ions and anions on the final motifs of the compounds have been discussed in detail. All the compounds are characterized using powder X-ray diffraction (PXRD), IR spectroscopy, thermal stability analysis and elemental analyses. Moreover, the photoluminescence properties of 1, 2, 7, 8 and 11 have been investigated. Magnetic investigation of 9 reveals spin canting antiferromagnetic interactions.