The oxygen evolution reaction (OER) in water splitting plays a critical role in some clean energy production systems. Transition-metal oxides as one of the most common OER electrocatalysts have been widely explored; however, their activity is limited by low electrical conductivity, slow mass transfer, and inadequate active sites. Herein, we develop a feasible strategy in which layered twodimensional metal−organic frameworks (2D MOFs) act as templates to construct metal oxide/carbon (MO x /C, M = Co, Ni, and Cu) nanosheet arrays for the OER. Because of improved conductivity and more exposed active sites afforded by their 2D structures with rich hierarchical pores and the incorporation with porous carbon, these 2D MOF-derived MO x /C arrays present high electrocatalytic activities and good durability. Particularly, Co 3 O 4 /C BDC , NiO/C BDC , and Cu 2 O/ S−C TDC exhibit low overpotentials of 208, 285, and 313 mV at the current density of 10 mA cm −2 , respectively, outperforming all previously reported corresponding metal oxide-based catalysts.

However, only limited MOFs were explored for electrocatalytic water splitting, mainly due to the poor structure stability of most MOFs in water system, especially under acidic/alkaline conditions. [11-13] Most importantly, metal nodes in most MOFs are coordinately saturated with ligand/ solvent molecules, [14,15] which are inert in electrocatalysis, even if these metal sites are highly exposed by rich pores. [16] For instance, Zhang and co-workers reported a new metal azolate framework [Co 2 (µ-Cl) 2 (bbta)], [12] but showing poor OER activity. The metal sites became active only on the functionalization by hydroxide ligands, and then exhibited efficient electrocatalysis performance. In addition, the low electrical conductivity for most MOFs also affects the electrocatalytic activity. [17] The principal reason is that the larger inner impedance of most organic ligands and rigid pore structures are not conducive to long-range charge transport. [18,19] Despite few of efforts including synthesis of ultrathin 2D layers or introduction of conductive materials in channels for exposing more active sites or improving their conductivity, the electrocatalytic activity enhancement is still not prominent. [20,21] Thus, it is desired to rationally design or optimize the structure and composition of MOFs to improve water spitting activity. Herein, we propose that the construction of defects into MOFs could be a feasible strategy to create highly active sites and improve conductivity for optimizing electrocatalytic properties. As a proof of concept, a Ni(II)-based MOF [Ni 2 (OH) 2 (BDC); BDC = 1,4-benzenedicarboxylate] with intrinsic 2D metal-oxide layers connected by BDC ligands [22] was selected and its defectrich nanosheet array (as D-Ni-MOF NSA) was prepared via a simply alkali-etched strategy (Figure 1). The intrusion of KOH leads to partial breaking of NiO bonds in the MOF, accompanied with the generation of open unsaturated Ni sites and the introduction of extra-framework K cations. Subsequently, the unsaturated Ni sites were attacked by the OH − ions, leading to the exposed active site NiO(OH), while the original framework topology is still well maintained. Theoretical/experimental results reveal that the above features could endow the D-Ni-MOF with richer active sites and largely improved conductivity, compared with pristine Ni-MOF. Finally, the assembled D-Ni-MOF||D-Ni-MOF electrolyte cell could achieve comparable electrocatalytic performance with that of the noble metal-based benchmark catalysts, demonstrating a promising bifunctional electrocatalyst for overall water splitting. The exploration of efficient electrocatalysts is the central issue for boosting the overall efficiency of water splitting. Herein, pertinently creating active sites and improving conductivity for metal-organic frameworks (MOFs) is proposed to tailor electrocatalytic properties for overall water splitting. An Ni(II)-MOF nanosheet array is presented as an ideal material model and a facile alkali-etched strategy is developed to break its NiO b...

Two stable Al(iii)-MOFs were designed and synthesized for the selective detection of two organic arsenic compounds in aqueous medium.

A sulfonic acid functionalized metal−organic framework (MOF) Cr 3 (μ 3 -O)(H 2 O) 3 (NDC(SO 3 H 5/6 ) 2 ) 3 (BUT-8(Cr)-SO 3 H, NDC(SO 3 H) 2 2− = 4,8-disulfonaphthalene-2,6-dicarboxylatlate) with high chemical and thermal stability is used for the catalytic esterification, showing excellent performance in various esterification reactions of monoacids, diacids, and acid anhydrides. In the structure of this MOF, uniformly distributed catalytic active sites of Brønsted acidic −SO 3 H with high density are decorated on its onedimensional channels, which leads to improved catalytic activity. The reaction conversion and corresponding yield of esters can achieve >99% and >90%, respectively. BUT-8(Cr)-SO 3 H also represents good size-selectivity in the catalytic esterification owning to the steric or impeded diffusion effects of reactants in its pore structure. In addition, its robust structure also guarantees good reusability. On the basis of the above advantages and excellent catalytic performance, this acid group functionalized MOF could be a promising candidate for the sustainable chemical catalysis.

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In this study, a MIL-53(Al)-packed column was successfully prepared and firstly applied to separate phthalate acid esters (butyl benzyl phthalate, di-n-butyl phthalate, diethyl phthalate, bis(2-ethylhexyl) phthalate, and dimethyl phthalate). Their baseline separation could be achieved within 12 min with a mobile phase of methanol/H2 O ratio at 92:8, and the temperature and flow rate was 40°C and 0.6 mL/min, respectively. The stacking effect and electrostatic force were the key factors in the separation. Moreover, there was a substantial linear relation between the peak height, peak area, and the analyte mass, and the relative standard deviations of retention time, peak height, peak area, and half peak width for five replicate separations of the analytes were within the ranges 0.31-0.88%, 0.72-1.52%, 1.33-1.53%, and 0.46-0.95%, respectively. The results of the calculation of the thermodynamics parameters showed that the separation of phthalate acid esters was controlled by both enthalpy change (ΔH) and entropy change (ΔS).

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