No abstract

2D metal-organic framework (2D MOF) nanosheets and their derived nanocomposites have been widely studied in recent years due to their ultrathin atomic-level thickness, large surface area and adjustable structure. This review is thus aimed at summarizing the recent studies on synthesis methods and the photocatalytic mechanism of 2D MOF nanosheets. The synthesis methods can be concretely divided into top-down and bottom-up methods, including physical and chemical exfoliation, interfacial synthesis, three-layer synthesis and surfactant-assisted synthesis. The photocatalytic mechanisms can also be categorized into three classes: photo-absorption, photo-generated carrier separation and transport, and surface redox reaction. Moreover, the applications of 2D MOF nanosheets in the field of photocatalysis, including photocatalytic hydrogen evolution, photocatalytic CO2 reduction, photocatalytic degradation and organic chemical photosynthesis, were also briefly discussed. Finally, some challenges and expectations with regard to 2D MOF nanosheets in photocatalysis will be addressed.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low‐cost anode catalysts. Many pre‐catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre‐catalyst, thiospinel CoFe2S4, and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2S4 gives a mixture with both Fe–S component and active oxyhydroxide (Co(Fe)OxHy) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe–S component in a major form of Fe3S4. The interface spin channel is demonstrated in the reconstructed CoFe2S4, which optimizes the energetics of OER steps on Co(Fe)OxHy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O–O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers.

For the advancement of laser technologies and optical engineering, various types of new inorganic and organic materials are emerging. Metal−organic frameworks (MOFs) reveal a promising use in nonlinear optics, given the presence of organic linkers, metal cluster nodes, and possible delocalization of π-electron systems. These properties can be further enhanced by the inclusion of solely inorganic materials such as polyoxometalates as prospective low-cost electron-acceptor species. In this study, a novel hybrid nanocomposite, namely, SiW 12 @NU-1000 composed of SiW 12 (H 4 SiW 12 O 40 ) and Zrbased MOF (NU-1000), was assembled, completely characterized, and thoroughly investigated in terms of its nonlinear optical (NLO) performance. The third-order NLO behavior of the developed system was assessed by Z-scan measurements using a 532 nm laser. The effect of two-photon absorption and self-focusing was significant in both NU-1000 and SiW 12 @NU-1000. Experimental studies suggested a much superior NLO performance of SiW 12 @NU-1000 if compared to that of NU-1000, which can be assigned to the charge-energy transfer between SiW 12 and NU-1000. Negligible light scattering, good stability, and facile postsynthetic fabrication method can promote the applicability of the SiW 12 @NU-1000 nanocomposite for various optoelectronic purposes. This research may thus open new horizons to improve and enhance the NLO performance of MOF-based materials through π-electron delocalization and compositing metal−organic networks with inorganic molecules as electron acceptors, paving the way for the generation of novel types of hybrid materials for prospective NLO applications.

Oxygen evolution reaction (OER) represents a highly important electrochemical transformation in energy storage and conversion technologies. Considering the low rate of this four-electron half-reaction, there is a demand for efficient, stable, and noble-metal-free electrocatalysts to improve the kinetic and economical parameters. In this work, a new pillared-MOF@NiV-LDH nanocomposite based on a Co II metal−organic framework (pillared-MOF) and heterometallic Ni/ V-layered double hydroxide (NiV-LDH) was assembled via a simple protocol, characterized, and explored as an electrocatalyst in OER. A remarkable electrocatalytic efficiency of pillared-MOF@NiV-LDH in 1 M KOH is evidenced by a low overpotential (238 mV at 10 mA cm −2 current density) and a small value of the Tafel slope (62 mV dec −1 ). These parameters are very close to those of the reference IrO 2 electrocatalyst and are superior to the majority of the LDH-and MOF-based systems previously applied for OER. Excellent stability of pillared-MOF@NiV-LDH was confirmed by the chronopotentiometry tests for 70 h and linear-sweep voltammetry after 7000 cycles. Features such as rich electroactive sites, porous structure, high surface area, and synergic effect between pillared-MOF and NiV-LDH are likely responsible for the remarkable electrocatalytic efficiency of this electrocatalyst in OER. Despite prior reports on the application of NiV-LDH in OER, the present study describes the first example where this type of LDH is blended with MOF to generate a nanocomposite material. The interface between the two components of the composite can improve the electronic structure and, in turn, the electrocatalytic behavior. The introduction of this composite paves the way toward the synthesis of other multicomponent materials with potential applications in different energy fields.