Synthesis of Robust MOFs@COFs Porous Hybrid Materials via an Aza‐Diels–Alder Reaction: Towards High‐Performance Supercapacitor Materials

Four octamolybdate compounds with properties of organic dye adsorption and photocatalytic reduction of Cr(VI)

Hydrothermal synthesis was used to create four different POM-based compounds, namely {[Co(Hptpm)2(β-Mo8O26)0.5(ξ-Mo8O26)0.5]}·H2O (1), [Co(Hptpm)2(δ-Mo8O26)]·H2O (2), [Co(Hptpm)2(β-Mo8O26)] (3) and [Zn(Hptpm)2(β-Mo8O26)] (4) (ptpm = 4-[3-(3-pyridine-2-yl-[1,2,4]triazol-4-yl)-propyl]-morpholine). 1-4 containing different octamolybdate isomers were characterized. Compounds 1-4 showed good electrochemical performance and can be utilized as bifunctional sensors for NO2-, H2O2, Cr(VI) and Fe(III). Taking compound 1 as an example, the detection limits are 0.081 μM for NO2-, 0.072 μM for H2O2, 0.054 μM for Cr(VI) and 0.063 μM for Fe(III), respectively. Compounds 1-4 have good capacitance. Moreover, compounds 1-4 also show good adsorption properties for organic cationic dyes. The cationic dyes include methylene blue (MB), crystal violet (CV) and neutral red (NR). In addition, 1-4 have excellent characteristics that can reduce Cr(VI) to Cr(III) by photocatalytic technology. Within 30 min, the reduction rates were 95.85% for 1, 93.99% for 2, 90.29% for 3 and 88.18% for 4.

Regulating the Synergistic Effect in Bimetallic Two-Dimensional Polymer Oxygen Evolution Reaction Catalysts by Adjusting the Coupling Strength Between Metal Centers

Bimetallic electrocatalysts with its superior performance has a broad application prospect in oxygen evolution reaction (OER), but the fundamental understanding of the mechanism of synergistic effect is still limited since there lacks a practical way to decouple the influence factors on the intrinsic activity of active sites from others. Herein, a series of bimetallic Co-Ni two-dimensional polymer (2DP) model OER catalysts with well-defined architecture, monolayer characteristic, were designed and synthesized to explore the influence of the coupling strength between metal centers on OER performance. The coupling strength was regulated by adjusting the spacing between metal centers or the conjugation degree of bridge skeleton. Among the examined 2DPs, CoTAPP-Ni-MF-2DP, which has the strongest coupling strength between metal centers exhibited the best OER performance. These model systems can help to explore the precise structure-performance relationships, which is important for the rational catalyst design at the atomic/molecular levels.

Sensitive photoelectrochemical detection of colitoxin DNA based on NCDs@CuO/ZnO heterostructured nanocomposites with efficient separation capacity of photo-induced carriers

A metal-organic framework (MOF) of Cu-TPA (terephthalic acid) microsphere was prepared, followed by calcinating the MOF precursor of Cu-TPA/ZIF-8 mixture to obtain the CuO/ZnO. N-doped carbon dots (NCDs) were employed to combine the CuO/ZnO composite to form a tripartite heterostructured architecture of NCDs@CuO/ZnO, which led to a fierce enlargement of the photocurrent response. This  was ascribed to the thinner-shell structure of the CuO microsphere and the fact that hollow ZnO particles could sharply promote the incidence intensity of visible light. The more porous defectiveness exposed on CuO/ZnO surface was in favor of rapidly infiltrating electrolyte ions. The p-n type CuO/ZnO composite with more contact interface could abridge the transfer distance of photo-induced electron (e^-1)/hole (h⁺) pairs and repress their recombination availably. NCDs not only could boost electron transfer rate on the electrode interface but also successfully sensitized the CuO/ZnO composite, which resulted in high conversion efficiency of photon-to-electron. The probe DNA (S1) was firmly assembled on the modified ITO electrode surface (S1/NCDs@CuO/ZnO) through an amidation reaction. Under optimal conditions, the prepared DNA biosensor displayed a wide linear range of 1.0 × 10^-6 ~ 7.5 × 10^-1 nM and a low limit of detection (LOD) of 1.81 × 10^-7 nM for colitoxin DNA (S2) measure, which exhibited a better photoelectrochemistry (PEC) analysis performance than that obtained by differential pulse voltammetry techniques. The relative standard deviation (RSD) of the sensing platform for target DNA detection of 5.0 × 10^-2 nM was 6.3%. This proposed DNA biosensor also showed good selectivity, stability, and reproducibility, demonstrating that the well-designed and synthesized photoactive materials of NCDs@CuO/ZnO are promising candidates for PEC analysis.

Enhancing Photocatalytic Hydrogen Production via the Construction of Robust Multivariate Ti-MOF/COF Composite

Titanium metal-organic frameworks (Ti-MOFs), as an appealing type of artificial photocatalysts, have shown great potentials in the field of solar energy conversion due to their well-studied photo-redox activity similar to TiO 2 and good optical responsiveness of linkers serving as the antenna to absorb visible-light. Although enormous efforts have been dedicated to developing Ti-MOFs with high photocatalytic activity, their solar energy conversion performances are still poor. Herein, a covalent-integrated strategy has been implemented to construct a series of multivariate Ti-MOF/COF hybrid materials, PdTCPP⸦PCN-415(NH 2 )/TpPa (composites 1, 2, and 3), featuring excellent visible-light utilization, suitable band gap, and high surface area for photocatalytic H 2 production. Notably, the resulting composites demonstrated remarkably enhanced visible-light-driven photocatalytic H 2 evolution performance, especially for the composite 2 with the maximum H 2 evolution rate of 13.98 mmol g -1 h -1 (turn-over frequency (TOF) = 227 h -1 ), which is much higher than the prototypical counterparts, PdTCPP⸦PCN-415(NH 2 ) (0.21 mmol g -1 h -1 ) and TpPa (6.51 mmol g -1 h -1 ). Our work thereby suggests a new approach to develop highly efficient photocatalysts for photocatalytic H 2 evolution reaction and beyond.

Covalently Aligned Molybdenum Disulfide-Carbon Nanotubes Heteroarchitecture for High-Performance Electrochemical Capacitors

Advanced two-dimensional nanosheets that promote the dynamic transportation and storage capacity of ions are significant for high-performance electrochemical capacitors (ECs). However, such materials often possess a low energy density. We have developed an ordered heteroarchitecture of molybdenum disulfide-carbon nanotubes (MoS₂ -CNTs) in which CNTs are vertically grafted within a MoS₂ framework by C-Mo covalent bonds. Benefiting from this in situ vertical bridge, high-speed interlaminar conductivity, unimpeded ion-diffusion channels and sufficient pseudocapacitive reactivity, the MoS₂ -CNTs presents ultralarge capacitance (5485 F g^-1 ) and good structural stability in potassium hydroxide electrolyte. Moreover, the all-unified solid-state flexible ECs obtained through direct-write printing construction deliver high energy density (226 mWh g^-1 ), good capacitance (723 F g^-1 ) and stable high/low-temperature operating ability, which can power a wearable health-monitoring device.

Chemical Conversion and Locking of the Imine Linkage: Enhancing the Functionality of Covalent Organic Frameworks

Imine-based covalent organic frameworks (COFs) are a widely studied class of functional, crystalline, and porous nanostructures which combine a relatively facile crystallization with tuneable compositions and porosities. However, the imine linkage constitutes an intrinsic limitation due to its reduced stability in harsh chemical conditions and its unsuitability for in-plane π-conjugation in COFs. Urgent solutions are therefore required in order to exploit the full potential of these materials, thereby enabling their technological application in electronics, sensing, and energy storage devices. In this context, the advent of a new generation of linkages derived from the chemical conversion and locking of the imine bond represents a cornerstone for the synthesis of new COFs. A marked increase in the framework robustness is in fact often combined with the incorporation of novel functionalities including, for some of these reactions, an extension of the in-plane π-conjugation. This Minireview describes the most enlightening examples of one-pot reactions and post-synthetic modifications towards the chemical locking of the imine bond in COFs.