Metal-organic framework (MOF) nanoparticles, also called porous coordination polymers, are a major part of nanomaterials science, and their role in catalysis is becoming central. The extraordinary variability and richness of their structures afford engineering synergies between the metal nodes, functional linkers, encapsulated substrates, or nanoparticles for multiple and selective heterogeneous interactions and activations in these MOF-based nanocatalysts. Pyrolysis of MOF-nanoparticle composites forms highly porous N- or P-doped graphitized MOF-derived nanomaterials that are increasingly used as efficient catalysts especially in electro- and photocatalysis. This review first briefly summarizes this background of MOF nanoparticle catalysis and then comprehensively reviews the fast-growing literature reported during the last years. The major parts are catalysis of organic and molecular reactions, electrocatalysis, photocatalysis, and views of prospects. Major challenges of our society are addressed using these well-defined heterogeneous catalysts in the fields of synthesis, energy, and environment. In spite of the many achievements, enormous progress is still necessary to improve our understanding of the processes involved beyond the proof-of-concept, particularly for selective methane oxidation, hydrogen production, water splitting, CO2 reduction to methanol, nitrogen fixation, and water depollution.

State of the Art and Prospects in Metal-Organic Framework (MOF)-Based and MOF-Derived Nanocatalysis.

Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called "white" graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.

"White graphenes": boron nitride nanoribbons via boron nitride nanotube unwrapping

Nanoporous carbon (NPC) materials with high specific surface area have attracted considerable attention for electrochemical energy storage applications. In the present work, we have designed novel symmetric supercapacitors based on NPC by direct carbonization of Zn-based metal-organic frameworks (MOFs) without using an additional precursor. By controlling the reaction conditions in the present study, we synthesized NPC with two different particle sizes. The effects of particle size and mass loadings on supercapacitor performance have been carefully evaluated. Our NPC materials exhibit excellent electrochemical performance with a maximum specific capacitance of 251 F g-1 in 1 M H2SO4 electrolyte. The symmetric supercapacitor studies show that these efficient electrodes have good capacitance, high stability, and good rate capability.

Fabrication of symmetric supercapacitors based on MOF-derived nanoporous carbons

In this paper, an ultrathin 2D/2D Ti3C2/g-C3N4 heterojunction was synthesized by direct calcination the mixture of bulk Ti3C2 and urea, where urea not only acts as the gas template to exfoliate Ti3C2 into nanosheets, but also as the precursor of g-C3N4 to craft Ti3C2/g-C3N4 heterojunction. CO2 photoreduction activity tests reveal that pure g-C3N4 (UCN) exhibits very weak photoactivity. However, when Ti3C2 was coupled with g-C3N4, the photocatalytic performance is soaringly enhanced. The optimal sample (10TC) shows the yields of 5.19 and 0.044 μmol h−1 g−1 for CO and CH4, respectively, and the total CO2 conversion is 8.1 times higher than that of UCN. The enhanced CO2 photoreduction activity is mainly attributed to the combined effects of (1) improved CO2 adsorption and activation, and (2) the construction of ultrathin 2D/2D Ti3C2/g-C3N4 heterojunction, where the intimate contact stimulates an efficient spatial separation of photo-excited charge carriers.

2D/2D Ti3C2 MXene/g-C3N4 nanosheets heterojunction for high efficient CO2 reduction photocatalyst: Dual effects of urea

Inside-and-Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

Enhanced charge transfer for efficient photocatalytic H2 evolution over UiO-66-NH2 with annealed Ti3C2Tx MXenes

g-C3N4 foam/Cu2O QDs with excellent CO2 adsorption and synergistic catalytic effect for photocatalytic CO2 reduction.

3D porous Cu-NPs/g-C3N4 foam with excellent CO2 adsorption and Schottky junction effect for photocatalytic CO2 reduction

The porous and water-stable polyoxometalates-based Zr-MOFs PW12@UiO-NH2 was proposed for photocatalytic H2 evolution and degradation pollutants via adopting Keggin-type polyoxometalates (POMs) into UiO-66-NH2 through a facile one-step solvothermal method. Systematically characterizations were carried out to confirm the encapsulation of Keggin-type PW12 within the cavities of porous UiO-66-NH2 without modifying its fundamental framework. Benifiting from the integration of Keggin-type PW12 units with redox activity and porous UiO-66-NH2, the results showed that enhanced photocatalytic H2 evolution performance and RhB degradation activity for PW12@UiO-NH2 were realized compared with pristine UiO-66-NH2 under visible-light irradiation. The significant improvement of photocurrent density under a monochromatic light irradiation implied the faciliated separation procedure of photo-generated charge carriers with the incorporation of Keggin-type PW12 units. Hence, our findings reveal a novel topology POM-based MOFs which paves a way for environmental and energy applications.

Wei Fang

Papers

Enhanced charge transfer for efficient photocatalytic H2 evolution over UiO-66-NH2 with annealed Ti3C2Tx MXenes

g-C3N4 foam/Cu2O QDs with excellent CO2 adsorption and synergistic catalytic effect for photocatalytic CO2 reduction.

3D porous Cu-NPs/g-C3N4 foam with excellent CO2 adsorption and Schottky junction effect for photocatalytic CO2 reduction

Zr-MOFs based on Keggin-type polyoxometalates for photocatalytic hydrogen production

Carbonized rice husk foam constructed by surfactant foaming method for solar steam generation