[en] Two 2-(1-imidazole)-1-hydroxyl-1,1'-ethylidenediphosphonato and oxalic acid bridged coordination polymers (H_2en)[Co_3(H_2zdn)_2(ox)(H_2O)_2] (1) and Cd_2(H_2zdn)(ox)_0_._5(H_2O) (2) (2-(1-imidazole)-1-hydroxyl-1,1'-ethylidenediphosphonic acid=H_5zdn; oxalic acid=H_2ox) were synthesized under hydrothermal conditions and characterized by the infrared (IR), thermogravimetric analyses (TGA), elemental analyses (EA) and X-ray diffraction (XRD). Compound 1 is bridged by phosphonate anions to 1D chain, and further linked by oxalate anions to 2D layer. Compound 2 is bridged by O–P–O units of H_5zdn to the layer, and then pillared by oxalate anions to generate 3D frameworks. Compound 1 shows anti-ferromagnetic behaviors analyzed with the temperature-dependent zero-field ac magnetic susceptibilities, while compound 2 exhibits an influence on the luminescent property. - Graphical abstract: Linked by oxalate, two zoledronate-based metal–organic frameworks are synthesized, which exhibits the different frameworks. Magnetism and luminescent properties have been studied. The weak antiferromagnetic coupling is conducted in 1. - Highlights: • Compound 1 and 2 are first linked by oxalate anion based on zoledronic acid. • Compound 1 generates a classic “dia Diamond” (6"6) topology. • Compound 2 exhibits a (4"4·6"2)(4"4·6"6) topology. • Magnetism and luminescent properties of 1 and 2 have been studied, respectively

[en] A new Bi(III) coordination polymer Bi_2(Hpdc)_2(pdc)_2·2H_2O (H_2pdc=pyridine-2,6-dicarboxylic acid) was synthesized by hydrothermal method. Solid state thermal decomposition of this complex under 500 °C for 1 h led to the foliated Bi_2O_3 nanoparticles, which were then characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Comparative study on their photocatalytic activity toward the degradation of rhodamine B (RhB), methylene blue (MB) and methyl orange (MO) in polluted water was explored, and the mechanism of these photocatalytic degradation was discussed. These results provided some interesting insights into their photocatalytic applications. - Graphical abstract: We regard Bi_2(Hpdc)_2(pdc)_2·2H_2O with 1D chain structures as the precursor, then calcinate the complex to prepare nano-powder α-Bi_2O_3. The photochemical experiment indicates that Bi_2(Hpdc)_2(pdc)_2·2H_2O can be used as an efficient photocatalyst for the degradation of RhB and MB. Interestingly, nano α-Bi_2O_3 shows higher activity than the commercial Bi_2O_3 for the degradation of RhB, MB or MO. Display Omitted - Highlights: • A novel dinuclear Bi(III) coordination polymer is hydrothermally synthesized. • Calcinating the precursor Bi-CP will result in the nano Bi_2O_3 with foliated morphology. • Nano Bi_2O_3 shows higher activity than the commercial Bi_2O_3 for the degradation of dyes.

[en] The Co₃O₄ anchored on the graphitic carbon nitride (g-C₃N₄) was fabricated via a facile co-precipitation method with MOFs/g-C₃N₄ as precursor. The as-prepared Co₃O₄/g-C₃N₄ composite delivers a high specific capacitance of 780 F g⁻¹ at the current density of 1.25 A g⁻¹ in 2 M KOH solution and the capacitance value retain 80% after 1000 cycles with the current density of 3 A g⁻¹. The capacitance of Co₃O₄/g-C₃N₄ composite is much greater than the bare Co₃O₄ with 419 F g⁻¹ at the current density 1.25 A g⁻¹. The investigation suggests that the excellent performance of capacitance may be assigned to as-prepared Co₃O₄/g-C₃N₄ composite, which could be a potential and outstanding electrode material in electrochemical energy storage devices.

[en] Manganese oxides have been received increasing interest due to their potential application in supercapacitor electrode material. In this paper, a new metal–organic framework Mn₃(MA)(H₂O)₂(ipa)₃ (1) (H₂ipa = isophthalic acid; MA = melamine) was synthesized via hydrothermal reaction; it presents a 3D network structure which can be simplified as an unusual non-interpenetrated pseudo-primitive 6-connected cubic topology. The Mn-MOF was regarded as a precursor to prepare variety of manganese oxides via calcination in different environments. Cyclic voltammetry and galvanostatic charge–discharge measurements were employed to characterize the electrochemical performance of MnO_X materials in Na₂SO₄ electrolyte. The results show that the MnO_X materials reveal excellent long-term cycling stability with enhanced capacitance after charge–discharge cycles. The optimum specific capacitance can be 150 F g⁻¹ with a current density of 1.0 A g⁻¹.

[en] We have successfully synthesized MnO/C nanorod arrays which is the first report of MnO/C nanoarrays derived from Mn-MOFs nanoarrays as precursor, and the contents of C are dependent on the temperature of calcinations of MOFs. The MnO/C-350 nanorod array electrode materials exhibit excellent electrocatalytic performances for oxygen evolution reaction; only a small over-potential of 329 mV versus RHE is needed for a current density of 20 mA cm⁻² with a Tafel slope of 70.02 mV dec⁻¹, and the material of MnO/C nanoarrays are superior to all reported MnO catalysts.

[en] It is a great challenge to develop Co₃O₄-based electrocatalysts of excellent performance for oxygen evolution reaction, because of its poor electrical conductivity. In this paper, we have prepared pristine Co₃O₄ (P-Co₃O₄) and Co₃O₄-C polyhedrons via two different calcination strategies. Then we have also displayed a simple and green reduction method to synthesize reduced Co₃O₄ (R-Co₃O₄) polyhedron with abundant surface oxygen vacancies. Oxygen vacancies and the doping of carbon species can enhance conductivity of electrocatalysts, thus, improving their electrocatalytic activities obviously. R-Co₃O₄ and Co₃O₄-C polyhedrons show lower overpotentials of 380 and 420 mV, respectively, compared to P-Co₃O₄ polyhedron (520 mV) at the current density of 10 mA cm⁻² in 1 M KOH solution (pH 13.7). And they also have smaller Tafel slopes of 86 and 78 mV dec⁻¹ than that of P-Co₃O₄ polyhedron (93 mV dec⁻¹), respectively. The integrated strategy reported here provides the way to design high-performance electrocatalysts for water oxidation.

[en] Transition metal oxides with hierarchical structures that grow on conductive substrates directly, which have been considered as promising catalysts for electrochemical catalysis. In this study, we used a stepwise synthesis method to prepare CuO nanoflake @Co₃O₄ nanowire composite nano-arrays (denote as CuO/Co₃O₄ composite), which show an excellent electrochemical performance. In the oxygen evolution reaction (OER), the CuO/Co₃O₄ composite shows lower overpotential of 450 mV at the current density of 50 mA cm⁻² and a smaller Tafel slope of 42 mV dec⁻¹ in KOH solution (1 M, pH = 13.7). In the electrocatalytic CO₂ reduction reaction, the prepared CuO/Co₃O₄ composite showed better CO selectivity in KHCO₃ aqueous solution (0.1 M, CO₂ saturated), the corresponding Faradaic efficiency of CO product reached 35.4%, and the product ratio of H₂ to CO was controlled by changing the potential values. The synthesis strategy reported here opens a way for designing high-performance electrodes for electrochemical catalysis and also provides new ideas for the construction of overall reaction (CO₂ + H₂O → CO + O₂).

[en] Integration of water oxidation catalysts on conductive support without polymer binder is an appealing strategy to improve the catalytic activity for electrochemical oxygen evolution reaction. Herein, the hierarchical CuO dandelion-like materials assembled from numerous ultrathin nanosheets are directly grown on Cu foil to produce a 3D oxygen evolution anode (CuO NSDs/CF). As a result of its integrated configuration and high electrocatalytic active sites, the anode exhibits superior electrocatalytic water oxidation activity in 1.0 M NaOH solution, associated with a small overpotential of 370 mV at 10 mA cm⁻² and a low Tafel slope of 41 mV dec⁻¹. Furthermore, the anode can maintain a relatively stable current density at 1.65 V versus RHE for at least 24 h, and a high Faradaic efficiency of 98% is also achieved.

[en] Electrocatalytic reduction of CO₂ to useful fuels or chemicals is a promising path for carbon recycling. In this study, a novel mixed-metallic MOF [Ag₄Co₂(pyz)PDC₄][Ag₂Co(pyz)₂PDC₂] was synthesized, and it transformed into Ag doped Co₃O₄ catalyst, which exhibits excellent electro-catalytic performance for reduction of CO₂ in water to syngas (H₂ + CO). The as-prepared Ag/Co₃O₄ material exhibits a high selectivity of CO in 0.1 M KHCO₃ aqueous solution (CO₂ saturated) with the corresponding faradaic efficiency up to 55.6%. Compared with the Ag/Co₃O₄ electrode, the maximum faradaic efficiency (FE) of CO of pure Co₃O₄ is 21.3% at − 1.8 V vs. SCE. The results show that the presence of Ag can improve the efficiency of CO significantly, thereby inhibiting the production of H₂. The stability of the samples can be maintained for more than 10 h at − 1.8 V vs. SCE. The ratio of production between H₂ and CO can be controlled by varying the potential values.

[en] Three new pyridine-2,3,5,6-tetracarboxylato (H₄pdtc) complexes K₂[Mn(H₂O)(pdtc)]·3H₂O 1, Na₂[M₃(H₂O)₆(pdtc)₂]·6H₂O (M=Mn 2, Co 3) were obtained and characterized by single-crystal X-ray diffraction methods and magnetic measurements. The characteristic building blocks of 1–3 are the pdtc bridged stair-like chains ∞¹([M(H₂O)](pdtc)_3/3)^2–, which results from the six-coordinated transition metal atoms bridged by pdtc⁴⁻ ligands. The infinite chains in 1 are assembled by hydrogen bonds into 2D supramolecular networks, which are held together by (4·8²) topological K⁺–H₂O networks to complete 3D architecture. While the stair-like chains in 2 and 3 are interconnected by trans-[M(H₂O)₄]²⁺ moieties to 2D polymeric layers, which are bridged by dimeric [Na₂(μ-H₂O)₂(H₂O)₂]²⁺ moieties to build up 3D framework. The magnetic properties of 1–3 were analyzed on the basis of (i) linear trinuclear M₃ models and (ii) the free Mn²⁺ and Co²⁺ ions with the zero-field splitting effect and spin–orbit coupling effect, respectively. - Graphic abstract: Synopsis. The characteristic building blocks and magnetic model of K₂[Mn(H₂O)(pdtc)]·3H₂O 1 and Na₂[M₃(H₂O)₆(pdtc)₂]·6H₂O (M=Mn 2, Co 3). Highlights: ► The characteristic building blocks of 1–3 are the pdtc bridged stair-like chains. ► The compound 2 and 3 are interlinked by trans-[M(H₂O)₄]²⁺ moieties to 2D layers. ► The magnetic behavior of 1 was analyzed with zero-field splitting effects. ► The magnetic behaviors were modulated with linear trinuclear model for 2 and 3