[en] Three new metal–organic complexes Cu[Hbpdc]_2 (1), [Ni(bpdc)(H_2O)]·H_2O (2) and [Ni(H_2bpdc)(H_2O)_2]SO_4 (3) (H_2bpdc=2,2′-bipyridyl-5,5′-dicarboxylic acid) have been hydrothermally prepared and structurally characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. 1 is a 3-D supramolecular architecture formed by hydrogen bonding interactions between carboxyl O atoms and strong face-to-face π⋯π stacking interactions between bipyridyl rings of Hbpdc"− ligands, 2 exhibits an intriguing 2-D sheet constructed from [Ni(bpdc)(H_2O)] units and 3 displays an infinite 1-D chain built by ([Ni(H_2bpdc)(H_2O)_2]"2"+) fragments through SO_4"2"−. Moreover, thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of 3 have been conducted and the TG curve shows two-stage weight loss between 300 and 950 K and the corresponding apparent activation energies are calculated by Ozawa–Flynn–Wall (OFW) method and Friedman method. The most probable kinetic model function of the dehydration reaction of 3 has been estimated by Coats–Redfern integral method and Achar–Bridly–Sharp differential method. - Graphical abstract: Three metal–organic complexes containing 2,2′-dipyridyl-5,5′-dicarboxylate ligands were synthesized and the thermal decomposition kinetics were investigated. - Highlights: • Metal–organic complexes containing 2,2′-dipyridyl-5,5′-dicarboxylate ligands. • 3-D supramolecular architecture. • Thermal decomposition kinetics

[en] According to the published literature, there are three types of laser-clad over-enriched alloy formulations on the surface of aluminum alloys, AlCrFeCoNi, AlCrMnFeCoSi, AlMnFeZnSi. AlCrFeCoNi coating was prepared on the surface of aluminum alloy by the University of Texas in the United States in 2015. It is pointed out in the paper that this component is the best quality formula among many high-entropy alloys. The process experiment is characterized by water-soluble organic The suspension was made into a suspension and then spread on the surface of the aluminum alloy using an air-spart technique and cladding with a YAG laser. This paper mainly studies the powder experimental scheme of noble alloy layer on aluminum alloy surface. (paper)

[en] The Ti_xCrFeCoNiCu(x:molar ratio, $\mathrm{x}=0,0.2,0.5,0.8,\mathrm{o}\mathrm{r}1.0$) coating was depositd on aluminum by laser cladding. The phase structure, microstructure, hardness, wear resistance and corrosion resistance were studied. The results show that with the increase of Ti content, the phase structure of the Ti_xCrFeCoNiCu coating changes from single FCC to FCC + B2, and FCC + Laves phase. When Ti is increased to 1.0, cracks appear in the coating. The hardness of the Ti_xCrFeCoNiCu coating is enhanced with the increase of Ti content, and ranges from 215HV_0.2 to 585HV_0.2, which is about 3 to 7 times that of the substrate. The strengthening mechanism of Ti_0.2CrFeCoNiCu is solid solution strengthening, and when the Ti content is greater than 2, the strengthening mechanism of Ti_xCrFeCoNiCu coating is precipitation strengthening. The influence of Ti on the wear resistance exhibits the same trend as with hardness. When Ti increased from 0 to 0.8, the wear rate of the Ti_xCrFeCoNiCu coating changed from $2.26\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->4}{\mathrm{m}\mathrm{m}}^3{\mathrm{N}\mathrm{m}}^{-<!--\; ???\; -->1}$ to $9.92\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->7}{\mathrm{m}\mathrm{m}}^3{\mathrm{N}\mathrm{m}}^{-<!--\; ???\; -->1}:$ smaller than the substrate. The addition of Ti increases the current corrosion density of Ti_xCrFeCoNiCu coating, but both coatings still exhibits superior corrosion resistance relative to the substrate. (paper)

[en] Coatings with excellent mechanical properties are difficult to prepare on the aluminum alloy surfaces by laser surface engineering because of the low melting point and active chemical properties of aluminum (Al). Based on the unique entropy effect of a high-entropy alloy, we suppress the cracks in the cladding layer caused by the dilution ratio of the substrate, obtaining coatings exhibiting excellent wear resistance. The Al_0.8CrFeCoNiCu_0.5B_x coating exhibited a BCC1 + BCC2 + FCC phase when the x ≤ 0.1. When x ≥ 0.2, boride was formed in the Al_0.8CrFeCoNiCu_0.5B_x coatings, and it became the main phase of the Al_0.8CrFeCoNiCu_0.5B_0.3 and Al_0.8CrFeCoNiCuB_0.4 coatings; however, no Al-rich intermetallic compound with a complex phase structure was formed. When 0 ≤ x ≤ 0.3, the bonding strengths of the Al_0.8CrFeCoNiCu_0.5B_x coatings were 70.6–176.2 MPa. An increase in the boron content increased the hardness of all the coatings, except the Al_0.8CrFeCoNiCu_0.5B_0.3 coating. The hardness was 479–705 HV (6–9 times that of the substrate). The wear rate of the coating ranged from 1.50 × 10⁻⁷ to 1.19 × 10⁻⁵ mm³/Nm, which was only 0.01%–5.43% that of the substrate. The Al_0.8CrFeCoNiCu_0.5B_0.2 coating exhibited the highest resistance to wearing, and its wear mechanism was identified as abrasive wear. (paper)

[en] Preparing a coating with excellent mechanical properties on aluminum substrates by laser cladding has always been challenging because of the low melting point and high chemical activity of Al. In this study, we designed Al_0.8FeCoNiCrCu_0.5Si_x (x = 0, 0.2, 0.3, 0.4, and 0.5) high-entropy alloys (HEAs) as cladding materials. The proposed study aims to exploit the unique high-entropy effect of HEAs to restrict the the formation of hard and brittle intermetallic compounds via the reaction between Al in the substrate and added powders, thereby enhancing the quality of the formed coatings and ultimately improving the surface properties of the Al alloy. Results show that with an increase in the Si content, the structure of the Al_0.8CrFeCoNiCu_0.5Si_x coating changes from FCC + BCC1 + BCC2 to BCC1 + BCC2. The hardness of the Al_0.8FeCoNiCrCu_0.5Si_x coating first increases and then decreases with an increase in the Si content. The coatings with the highest and lowest hardness were those with compositions of Al_0.8FeCoNiCrCu_0.5Si_0.4 (592HV_0.2) and Al_0.8FeCoNiCrCu_0.5 (412HV_0.2), respectively, which is approximately seven and five times greater than that of the substrate, respectively. The effect of Si content on the wear resistance of the coating is the same as its effect on the hardness. The wear rates of coatings with different Si contents range from 1.19 × 10⁻⁶ mm³ Nm⁻¹ to 8.99 × 10⁻⁷ mm³ Nm⁻¹ and are only 0.34% to 0.25% of the substrate. Obvious, the Al_0.8FeCoNiCrCu_0.5Si_x HEAs can be used as coating materials to improve the mechanical properties of an Al alloy surface. (paper)

[en] The corrosion behavior of Al_0.8CrFeCoNiCu_0.5Si_x (x=0, 0.2, 0.3) high-entropy alloy laser cladding coatings in a 3.5% NaCl solution was investigated using polarization tests, impedance spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. As the Si content increased, the over-passivation potential and the width of the passivation zone for the Al_0.8CrFeCoNiCu_0.5Six coating expanded, while the corrosion current density tended to decrease, enhancing the stability of the passivation film and the corrosion resistance of the coating. The Al_0.8CrFeCoNiCu_0.5 coating underwent selective corrosion, with some pitting corrosion distribution showing no apparent regularity. The Al_0.8CrFeCoNiCu_0.5Si_0.2 coating exhibited a distinct grain profile with a tendency towards intergranular corrosion. The aggregation of Cu-rich and Al-Ni intergranular phases in the eutectic structure led to preferential erosion at the grain boundaries by corrosion ions in the Al_0.8CrFeCoNiCu_0.5Si_0.2 coating. The Al_0.8CrFeCoNiCu_0.5Si_0.3 coating presented corrosion pits, although their distribution did not display apparent regularity. The Al_0.8CrFeCoNiCu_0.5Si_x high-entropy alloy coating demonstrates superior corrosion resistance in solution compared to 5083 aluminum alloy. (author)

[en] In this paper, the synchronization of Chaotic Lur’e systems subject to aperiodic sampling is investigated. It is shown that sampling interval is bounded and nonuniform. A modified free-matrix-based (MFMB) time-dependent Lyapunov functional is developed to capture the information on sampling pattern, which is sufficiently used to analyze stability of Chaotic Lur’e systems. For a special case that the sampled-data controller suffers constant input delay, a discontinuous Lyapunov functional is presented based on the vector extension of Wirtinger’s inequality. The obtained stability condition leads to a less computational complexity than some of existing works. A longer value on the calculation of sampling interval is achieved. Two illustrative examples demonstrate the effectiveness of designed methods and less conservatism of the obtained results.

[en] Carbon quantum dots co-doped with iron and nitrogen (Fe@NCDs) were synthesized by using Passiflora edulis Sims (P. edulis) as a precursor. The Fe@NCDs exhibit outstanding peroxidase-mimetic activity owing to successful doping with iron resulting in a behavior similar to that of iron porphyrins. In the presence of H₂O₂, the Fe@NCDs catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) with a color change from colorless to blue. The blue oxidation product has a characteristic absorption peaking at 652 nm. A colorimetric assay was worked out for uric acid (UA) that measures the hydrogen peroxide produced during oxidation of UA by uricase. Response is linear in the 2–150 μM UA concentration range, and the limit of detection is 0.64 μM. The method was applied to the determination of UA in (spiked) urine, and recoveries ranged from 92.0 to 103.4%.

[en] Three organic–inorganic hybrid TM–Ln heterometallic phosphotungstates [Cu(dap)₂(H₂O)][Cu(dap)₂]_3.5[La(α-HPW₁₁O₃₉)₂]·6H₂O (1) [Cu(dap)₂(H₂O)]_0.5[Cu(dap)₂]₄[Nd(α-HPW₁₁O₃₉)₂]·4H₂O (2) and [Cu(dap)₂(H₂O)]₂[Cu(dap)₂]_3.5[Eu(α-PW₁₁O₃₉)₂]·6H₂O (3) (dap=1,2-diaminopropane) have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectra, optical diffuse reflectance spectra, powder X-ray diffraction (PXRD), thermogravimetric (TG) analyses and single-crystal X-ray diffraction. Their common features are that 1–3 all consist of asymmetric sandwich-type subunits [Ln(α-PW₁₁O₃₉)₂]¹¹⁻ and [Cu(dap)₂]²⁺ bridges. Both 1 and 2 display the 2-D (4,4)-topological sheets whereas 3 exhibits the 3-D 5-connected (4⁶·6⁴) topological framework. The magnetic properties of 2 and 3 and the luminescence performance of 3 have been measured. - Graphical Abstract: Three TM–Ln heterometallic phosphotungstates 1–3 have been synthesized and characterized by elemental analyses, IR spectra, optical diffuse reflectance spectra, X-ray diffraction, thermogravimetric analyses magnetic susceptibility and luminescent properties. Highlights: ► Cu^II–Ln^III heterometallic polyoxometalates. ► 2-D and 3-D organic–inorganic hybrid phosphotungstates. ► 2-D and 3-D structures consisting of Cu^II–Ln^III heterometals.

[en] An inorganic–organic hybrid hexa-copper-substituted germanotungstate Na₂[Cu(dap)₂]₂[Cu(dap)₂] ([Cu₆(H₂O)₂(dap)₂][B-α-GeW₉O₃₄]₂)·4H₂O (1) (dap=1,2-diaminopropane) has been hydrothermally prepared and characterized by elemental analyses, inductively coupled plasma atomic emission spectrometry (ICP–AES) analyses, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. 1 displays the six-connected 3D network with the long topological (O′Keefe) vertex symbol is 4·4·6₄·4·4·4·4·6₄·4·4·4·6₄·4·4·4 and the short vertex (Schläfli) symbol of 4¹²6³. Magnetic measurements indicate that there are the overall ferromagnetic exchange interactions in the belt-like hexa-Cu^II cluster in 1. Furthermore, the electrochemical behavior and electrocatalysis of 1 modified carbon paste electrode (1-CPE) have been studied. The reductions of nitrite, bromate and hydrogen peroxide are principally mediated by the W^VI-based wave. - Graphical abstract: A hexa-Cu^II sandwiched germanotungstate has been synthesized and structurally characterized. The magnetic, solid-state electrochemical and electrocatalytic properties have been investigated. Display Omitted - Highlights: • Transition-metal substituted polyoxometalates. • Hexa-copper-substituted germanotungstate. • Six-connected 3D network. • Electrocatalytic reduction of nitrite, bromate and hydrogen peroxide