Recent advancements in supercapacitor technology

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201901316

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Metal–organic frameworks (MOFs) have emerged as particularly exciting inorganic–organic hybrid porous materials which can be simply self-assembled from their corresponding inorganic metal ions/clusters with organic linkers. MOFs can combine the inherent physical and chemical properties of both inorganic and organic photonic units due to their inorganic–organic hybrid nature. Furthermore, the pores within MOFs can also be utilized to encapsulate a large number of guest species as photonic units. The vast combination possibilities, synergistic effects, as well as controllable and ordered arrangements of multiple photonic units (MPUs) have distinguished MOFs from other inorganic and organic photonic materials and enabled them to be a promising platform to realize novel photonic functional applications. In this review, we summarize the recent and important progress in the design and construction of photonic MOFs, as well as their various applications in luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, data storage, and biomedicine. In addition, we highlight the construction strategy and the synergistic effects of MOFs towards achieving high performance and novel photonic functions. Finally, we also outline the challenges in these fields and put forward the prospects and directions for future development.

Photonic functional metal-organic frameworks.

Metal-organic frameworks (MOFs) can contain open metal sites (OMS) or coordinatively unsaturated sites (CUS) or open coordination sites (OCS) when vacant Lewis acid sites on the metal ions or cluster nodes have been generated. This review combines for the first time all aspects of OMS in MOFs, starting from different preparation strategies over theoretical studies on the effects of OMS with host-guest interactions up to distinct OMS-MOF applications. In the experimental part the focus of this review is on MOFs with proven OMS formation which are not only invoked but are clearly verified by analytical methods.

Coordinatively unsaturated metal sites (open metal sites) in metal–organic frameworks: design and applications

The oxygen evolution reaction (OER) is a critical electrochemical reaction in water splitting and rechargeable metal–air batteries. It plays a pivotal role in achieving high-efficiency clean-energy production and energy storage in these devices. Transition metal-based bimetallic MOFs (TMB MOFs) with two different metal ions possess specific synergistic effects, which could exhibit OER performance and stability superior to those of the corresponding monometallic MOFs for water oxidation. Benefiting from the diversity of chemical composition and structural type, TMB MOFs can also serve as precursors and templates to obtain alloy-particle-decorated carbon materials with high surface area, or metal compounds such as bimetallic sulfides, phosphides, and hydroxides with atomic-level mixing of heterometallic elements. These materials with high-density active sites exhibit much improved catalytic activity in the water oxidation reaction. This article aims to review the recent progress with TMB MOFs and their derivatives in relation to applications as electrocatalysts in OER, including analysis of the mechanism of the OER process with the assistance of DFT calculations and in situ or operando techniques.

Transition metal-based bimetallic MOFs and MOF-derived catalysts for electrochemical oxygen evolution reaction

Arrays of ultrasmall and uniform carbon nanodots (CDs) are of pronounced interest for applications in optical devices. Herein, we describe a low-temperature calcination approach with rather inexpensive reactants. After glucose molecules had been loaded into the pores of metal–organic frameworks (MOFs), well-defined CD arrays were produced by heating to 200 °C. The size and spacing of the CDs could be controlled by the choice of templating MOF: HKUST-1, ZIF-8, or MIL-101. The sizes of the obtained CDs were approximately 1.5, 2.0, and 3.2 nm, which are close to the corresponding MOF pores sizes. The CD arrays exhibited interesting photophysical properties, including photoluminescence with tunable emission and pronounced nonlinear optical (NLO) effects. The NLO properties of the obtained CD arrays were significantly different from those of a CD suspension, thus indicating the existence of collective phenomena.

MOF-Templated Synthesis of Ultrasmall Photoluminescent Carbon-Nanodot Arrays for Optical Applications

Developing efficient and inexpensive oxygen evolution reaction (OER) catalysts is one of the critical issues in energy storage and conversion technology. Herein, an oriented thin film of 3-D MOF Co/Ni(BDC)2TED (BDC = 1,4-benzenedicarboxylate; TED = triethylenediamine) nanosheet arrays is first obtained on Cu foam by a liquid-phase epitaxial layer-by-layer growth approach. The obtained thin film of bimetallic MOF nanosheet arrays has preferred growth with [001]-orientation and strong adhesion on the substrates without the use of binder materials, which provides more accessible active sites for electrocatalytic performance. The OER activity of such surface-mounted MOF nanosheet arrays can be optimized effectively via tuning the thicknesses and Co/Ni ratios. The Co/Ni(BDC)2TED grown on Cu foam with 40 cycles at a Co/Ni ratio of 1/1 shows superior OER activity with required overpotentials of 260 and 287 mV to achieve current densities of 10 and 50 mA cm−2 and excellent stability. The experiments and theoretical calculations reveal that the synergistic effect of Co/Ni and rich metal sites dominated by nanosheet interfaces improve the electrocatalytic activity. This work provides more insight into the OER activity of the MOF thin film as an electrode material and presents a new strategy for developing promising highly efficient electrocatalysts in practical applications.

A surface-mounted MOF thin film with oriented nanosheet arrays for enhancing the oxygen evolution reaction

Metal–organic frameworks (MOFs) with third-order nonlinear optical (NLO) properties are still in their infancy but are very important. In this work, we first develop a layer by layer autoarm immersion method for preparing porphyrin-based MOF (PIZA-1) thin films with third-order NLO properties. By precisely controlling the thickness, the nonlinear absorption of PIZA-1 thin films can be switched continuously between reverse saturable absorption (RSA) and saturable absorption (SA) by using the Z-scan technique. In addition, the optical limiting effect could be further optimized by loading C60 in the pores of the PIZA-1 thin film. These findings not only open a new route for the exploitation of third-order NLO thin film materials, but also offer an insightful understanding of porphyrin-based MOF thin films for future broad practical applications.

/pdf/auto-controlled-fabrication-of-a-metal-porphyrin-framework-18ck7nyhk3.pdf

Auto-controlled fabrication of a metal-porphyrin framework thin film with tunable optical limiting effects.

Many metal-organic cages (MOCs) and a few hydrogen-bonded organic cages (HOCs) have been investigated, but little is reported about cooperative self-assembly of MOCs and HOCs. Herein, we describe an unprecedented MOC&HOC co-crystal composed of tetrahedral Ti4 L6 (L=embonate) cages and in-situ-generated [(NH3 )4 (TIPA)4 ] (TIPA=tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine) cages. Chiral transfer is observed from the enantiopure Ti4 L6 cage to enantiopure [(NH3 )4 (TIPA)4 ] cage. Two homochiral supramolecular frameworks with opposite handedness (PTC-235(Δ) and PTC-235(Λ)) are formed. Such MOC&HOC co-crystal features high stability in water and other solvents, affording single-crystal-to-single-crystal transformation to trap CH3 CN molecules and identify disordered NH4 + cations. A tablet pressing method is developed to test the third-order nonlinear optical property of KBr-based PTC-235 thin film. Such a thin film exhibits an excellent optical limiting effect.

Combining a Titanium-Organic Cage and a Hydrogen-Bonded Organic Cage for Highly Effective Third-Order Nonlinear Optics.

This study reports an oriented and homogenous cobalt-metalloporphyrin network (PIZA-1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C60) into the PIZA-1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA-1 thin film with [110]-orientation presents much higher selectivity of benzene over toluene and p-xylene than that of the PIZA-1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin-based metal-organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.

De-Jing Li

Papers

MOF-Templated Synthesis of Ultrasmall Photoluminescent Carbon-Nanodot Arrays for Optical Applications

A surface-mounted MOF thin film with oriented nanosheet arrays for enhancing the oxygen evolution reaction

Auto-controlled fabrication of a metal-porphyrin framework thin film with tunable optical limiting effects.

Combining a Titanium-Organic Cage and a Hydrogen-Bonded Organic Cage for Highly Effective Third-Order Nonlinear Optics.

Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds.