Engineering the electronic structure of sub-nanometric Ru clusters via Pt single-atom modification for highly efficient electrocatalytic hydrogen evolution.

Developing electrocatalysts with high activity toward the hydrogen evolution reaction (HER) is a prerequisite for hydrogen fuel generation and sustainable development, but current Pt-based catalysts usually suffer from high cost and unsatisfactory performance in non-acidic media. In this work, we report an environmentally friendly and pyrolysis-free synthesis strategy to prepare an efficient catalyst, CNT-NPA-PtRu, with Pt single-atom engineered sub-nanometric Ru clusters anchored at phytic acid-modified carbon nanotubes for electrochemical HER at all pH conditions. The electronic structure of active sub-nanometric Ru clusters was optimized, which further enhanced the HER activity. The synthesized CNT-NPA-PtRu catalyst presents superior performance, reaching the current density of 10 mA cm-2 with only 18.3, 18.7 and 15 mV overpotential in alkaline, acidic and neutral electrolyte, respectively. Experimental results and theoretical calculations reveal that the single Pt atom on the sub-nanometric Ru cluster surface could modulate the electronic structure of Ru and subsequently optimize the adsorption of reaction intermediates, thus promoting HER performance. These findings underscore the importance of engineering the electronic structure of sub-nanometric clusters and offer an effective approach for the generation of high-performance electrocatalysts for HER.

A carbonyl-rich covalent organic framework as a high-performance cathode material for aqueous rechargeable zinc-ion batteries.

Aqueous rechargeable zinc-ion batteries (ZIBs) provide high theoretical capacity, operational safety, low-cost and environmental friendliness for large-scale energy storage and wearable electronic devices, but their future development is plagued by low capacity and poor cycle life due to the lack of suitable cathode materials. In this work, a covalent organic framework (Tp-PTO-COF) with multiple carbonyl active sites is synthesized and successfully introduced in aqueous rechargeable ZIBs for the first time. Tp-PTO-COF delivers high specific capacities of 301.4 and 192.8 mA h g-1 at current densities of 0.2 and 5 A g-1, respectively, along with long-term durability and flat charge-discharge plateaus. The remarkable electrochemical performance is attributed to the abundance of nucleophilic carbonyl active sites, well defined porous structure and inherent chemical stability of Tp-PTO-COF. Moreover, the structural evolution and Zn2+ ion intercalation mechanism are discussed and revealed by the experimental analysis and density functional theory calculations. These results highlight a new avenue to develop organic cathode materials for high performance and sustainable aqueous rechargeable ZIBs.

Evaluation of an Ionic Porous Organic Polymer for Water Remediation.

The targeted synthesis of a novel ionic porous organic polymer (iPOP) was reported. The compound (denoted as QUST-iPOP-1) was built up through a quaternization reaction of tris(4-imidazolylphenyl)amine and cyanuric chloride, and then benzyl bromide was added to complete the quaternization of the total imidazolyl units. It featured a special exchangeable Cl-/Br--rich structure with high permanent porosity and wide pore size distribution, enabling it to rapidly and effectively remove environmentally toxic oxo-anions including Cr2O72-, MnO4-, and ReO4- and anionic organic dyes with different sizes including methyl blue, Congo red, and methyl orange from water. Notably, QUST-iPOP-1 showed ultra-high capacity values for radioactive TcO4- surrogate anions (MnO4- and ReO4-), Cr2O72-, methyl blue, and Congo red, and these were comparable to some reported compounds of exhaustive research. Furthermore, the relative removal rate was high even when other concurrent anions existed.

Tuning Surface Energy of Zn Anodes via Sn Heteroatom Doping Enabled by a Codeposition for Ultralong Life Span Dendrite-Free Aqueous Zn-Ion Batteries.

Aqueous Zn-ion batteries (AZBs) have been considered as one of the most promising large-scale energy storage systems, owing to the advantages of raw material abundance, low cost, and eco-friendliness. However, the severe growth of Zn dendrites leads to poor stability and low Coulombic efficiency of AZBs. Herein, to effectively inhibit the growth of Zn dendrites, a new strategy has been proposed, i.e., tuning the surface energy of the Zn anode. This strategy can be achieved by in situ doping of Sn heteroatoms in the lattice of metallic Zn via codeposition of Sn and Zn with a small amount of the SnCl2 electrolyte additive. Density functional theory calculations have suggested that Sn heteroatom doping can sharply decrease the surface free energy of the Zn anode. As a consequence, driven by the locally strong electric field, metallic Sn tends to deposit at the tips of the Zn anode, thus decreases the surface energy and growth of Zn at the tips, resulting in a dendrite-free Zn anode. The positive effect of the SnCl2 additive has been demonstrated in both the Zn∥Zn symmetric battery and the Zn/LFP and Zn/HATN full cell. This novel strategy can light a new way to suppress Zn dendrites for long life span Zn-ion batteries.

A tri-functional metal-organic framework heterogeneous catalyst for efficient conversion of CO2 under mild and co-catalyst free conditions.

Herein, we developed a tri-functional MOF heterogeneous catalyst, MIL-IMAc-Br-, by a post-synthesis modification method for the first time. Due to the synergistic role of three functional sites, including Lewis acid sites, Brønsted acid sites and Br- anion sites, MIL-IMAc-Br- displayed an efficient catalytic performance for the cycloaddition reaction of CO2 and epoxides to form cyclic carbonates under mild and co-catalyst free conditions.

Capture of organic iodides from nuclear waste by metal-organic framework-based molecular traps.

Effective capture of radioactive organic iodides from nuclear waste remains a significant challenge due to the drawbacks of current adsorbents such as low uptake capacity, high cost, and non-recyclability. We report here a general approach to overcome this challenge by creating radioactive organic iodide molecular traps through functionalization of metal-organic framework materials with tertiary amine-binding sites. The molecular trap exhibits a high CH3I saturation uptake capacity of 71 wt% at 150 °C, which is more than 340% higher than the industrial adsorbent Ag0@MOR under identical conditions. These functionalized metal-organic frameworks also serve as good adsorbents at low temperatures. Furthermore, the resulting adsorbent can be recycled multiple times without loss of capacity, making recyclability a reality. In combination with its chemical and thermal stability, high capture efficiency and low cost, the adsorbent demonstrates promise for industrial radioactive organic iodides capture from nuclear waste. The capture mechanism was investigated by experimental and theoretical methods.Capturing radioactive organic iodides from nuclear waste is important for safe nuclear energy usage, but remains a significant challenge. Here, Li and co-workers fabricate a stable metal-organic framework functionalized with tertiary amine groups that exhibits high capacities for radioactive organic iodides uptake.

Functionalized metal organic frameworks for effective capture of radioactive organic iodides.

Highly efficient capture of radioactive organic iodides (ROIs) from off-gas mixtures remains a substantial challenge for nuclear waste treatment. Current materials utilized for ROI sequestration suffer from low capacity, high cost (e.g. use of noble metals), and poor recyclability. Recently, we have developed a new strategy to tackle this challenge by functionalizing MOF materials with tertiary amines to create molecular traps for the effective capture and removal of ROIs (e.g. radioactive methyl iodide) from nuclear wastes. To further enhance the uptake capacity and performance of CH3I capture by ROI molecular traps, herein, we carry out a systematic study to investigate the effect of different amine molecules on ROI capture. The results demonstrate a record-high CH3I saturation uptake capacity of 80% for MIL-101-Cr-DMEDA at 150 °C, which is 5.3 times that of Ag0@MOR (15 wt%), a leading adsorbent material for capturing ROIs during nuclear fuel reprocessing. Furthermore, the CH3I decontamination factors (DFs) for MIL-101-Cr-DMEDA are as high as 5000 under simulated reprocessing conditions, largely exceeding that of facility regulatory requirements (DF = 3000). In addition, MIL-101-Cr-DMEDA can be recycled without loss of capacity, illustrating yet another advantage compared to known industrial adsorbents, which are typically of a "single-use" nature. Our analysis also shows that both physisorption and chemisorption of CH3I occur at the three amine-grafted MOFs. While chemisorption takes place at the amine functionalized sites, the amount of physisorption correlates with the MOF porosity. A possible binding site of amine-CH3I interaction has been identified via an in situ IR spectroscopic study. The results suggest that CH3I interacts strongly and directly with the tertiary nitrogen of the amine molecules. The CH3I uptake amount decreases as the amine chain length increases, in trend with the decreasing pore space of the corresponding framework. The strategy to build MOF-based molecular traps developed in this work not only leads to a new record-high performance for ROI capture, but also offers an effective way of systematically tuning the porosity by varying the length of functionalized amine molecules. This study also demonstrates that MOFs represent a promising new platform for selective capture and removal of radioactive nuclear waste.

Multifunctional Luminescent Porous Organic Polymer for Selectively Detecting Iron Ions and 1,4-Dioxane via Luminescent Turn-off and Turn-on Sensing.

The first case of selective Fe(3+) ions and 1,4-dioxane luminescent sensor based on a porous organic polymer, POP-HT, was synthesized by reaction of tetra(p-aminophenyl)methane and chromophoric 2,5,8-trichloro-s-heptazine. POP-HT displayed prominent fluorescence quenching or enhancement in the presence of Fe(3+) ion or 1,4-dioxane. Moreover, an excellent linear relationship was established between luminescent intensity and the corresponding Fe(3+) ion or 1,4-dioxane concentration. The mechanisms of luminescence quenching and enhancement were also studied by both experiment and theoretical calculation. The results of this study suggest that POP-HT can work as an effective luminescent indicator for qualitative and quantitative detection of Fe(3+) ions and 1,4-dioxane in aqueous solution over other metal ions and organic solvents.

3d-4f Metal-Organic Framework with Dual Luminescent Centers That Efficiently Discriminates the Isomer and Homologues of Small Organic Molecules.

A 3d-4f luminescent metal-organic framework (MOF), [Tb2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (4), and three analogues {[La2(Cu8I8)(C12H8NO2)6(C4H8O2)2(H2O)2]·3C4H8O2·2H2O (1), [Ce2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (2), and [Eu2(Cu8I8)(C12H8NO2)6(H2O)4]·5C4H8O2 (3)}, were self-assembled from copper(I) halide clusters and lanthanide metal ions with an organic linker [3-(pyridin-4-yl)benzoic acid] under solvothermal conditions. Compound 4 with high quantum yield (Φ = 68%) exhibits reversible luminescence behavior, accompanying the removal and recovery of guest molecules (1,4-dioxane). Because of the unique porous structure and dual luminescent centers of compound 4, it can efficiently differentiate benzene series with different sizes and provide readouts in corresponding optical signals. Furthermore, it also can unambiguously discriminate the isomers, homologues, and other small molecules with similar structural motifs from one another. The luminescent color of the MOF sensor in different guest solvents has obvious changes that can be clearly distinguished by the naked eye. This multicolor luminescence originates from emissions of the dual luminescent centers, and the emissions have shifted, enhanced, weakened, or quenched to different degrees.

Creation of a new type of ion exchange material for rapid, high-capacity, reversible and selective ion exchange without swelling and entrainment.

Ion-exchange materials, currently dominated by resins, are widely used in a plethora of areas. However, the drawbacks of conventional resins necessitate the creation of a new model of ion exchange materials that feature controllable swelling, easily accessible ion exchange sites, high ion exchange capacity, fast ion exchange kinetics, and high chemical stability as illustrated herein in the context of functionalizing a porous organic polymer (POP) with ion exchange groups. The advantages of POP-based ion exchange materials in comparison with conventional resins and other types of ion exchange materials have been highlighted through an evaluation of their performances in scavenging precious metals at trace concentrations, removal of nuclear waste model ions, and size-selective ion capture. Our work thereby provides a new perspective to develop ion functionalized POPs as a versatile type of ion exchange materials for various applications.

Creating extra pores in microporous carbon via a template strategy for a remarkable enhancement of ambient-pressure CO2 uptake.

In this work, we illustrate a template strategy to create extra pores in microporous carbon for enhancing ambient-pressure CO2 uptake, as exemplified in the context of carbonizing the silicon-containing POP, PPN-4, followed by removal of the silicon template. The resultant PPN-4/C600 demonstrates a remarkable enhancement of CO2 uptake capacity at 295 K and 1 bar by a factor of 2.3 compared to the parent PPN-4.

Metal-organic framework based upon the synergy of a Brønsted acid framework and Lewis acid centers as a highly efficient heterogeneous catalyst for fixed-bed reactions.

We report a strategy of combining a Brønsted acid metal-organic framework (MOF) with Lewis acid centers to afford a Lewis acid@Brønsted acid MOF with high catalytic activity, as exemplified in the context of MIL-101-Cr-SO3H·Al(III). Because of the synergy between the Brønsted acid framework and the Al(III) Lewis acid centers, MIL-101-Cr-SO3H·Al(III) demonstrates excellent catalytic performance in a series of fixed-bed reactions, outperforming two benchmark zeolite catalysts (H-Beta and HMOR). Our work therefore not only provides a new approach to achieve high catalytic activity in MOFs but also paves a way to develop MOFs as a new type of highly efficient heterogeneous catalysts for fixed-bed reactions.

Highly selective adsorption of ethylene over ethane in a MOF featuring the combination of open metal site and π-complexation.

The introduction of the combination of open metal site (OMS) and π-complexation into MOF has led to very high ethylene-ethane adsorption selectivity at 318 K, as illustrated in the context of MIL-101-Cr-SO3Ag. The interactions with ethylene from both OMS and π-complexation in MIL-101-Cr-SO3Ag have been investigated by in situ IR spectroscopic studies and computational calculations, which suggest that π-complexation contributes dominantly to the high ethylene-ethane adsorption selectivity.

Mercury nano-trap for effective and efficient removal of mercury(II) from aqueous solution.

Highly effective and highly efficient decontamination of mercury from aqueous media remains a serious task for public health and ecosystem protection. Here we report that this task can be addressed by creating a mercury 'nano-trap' as illustrated by functionalizing a high surface area and robust porous organic polymer with a high density of strong mercury chelating groups. The resultant porous organic polymer-based mercury 'nano-trap' exhibits a record-high saturation mercury uptake capacity of over 1,000 mg g(-1), and can effectively reduce the mercury(II) concentration from 10 p.p.m. to the extremely low level of smaller than 0.4 p.p.b. well below the acceptable limits in drinking water standards (2 p.p.b.), and can also efficiently remove >99.9% mercury(II) within a few minutes. Our work therefore presents a new benchmark for mercury adsorbent materials and provides a new perspective for removing mercury(II) and also other heavy metal ions from contaminated water for environmental remediation.

Introduction of π-complexation into porous aromatic framework for highly selective adsorption of ethylene over ethane.

In this work, we demonstrate for the first time the introduction of π-complexation into a porous aromatic framework (PAF), affording significant increase in ethylene uptake capacity, as illustrated in the context of Ag(I) ion functionalized PAF-1, PAF-1-SO3Ag. IAST calculations using single-component-isotherm data and an equimolar ethylene/ethane ratio at 296 K reveal that PAF-1-SO3Ag shows exceptionally high ethylene/ethane adsorption selectivity (Sads: 27 to 125), far surpassing benchmark zeolite and any other MOF reported in literature. The formation of π-complexation between ethylene molecules and Ag(I) ions in PAF-1-SO3Ag has been evidenced by the high isosteric heats of adsorption of C2H4 and also proved by in situ IR spectroscopy studies. Transient breakthrough experiments, supported by simulations, indicate the feasibility of PAF-1-SO3Ag for producing 99.95%+ pure C2H4 in a Pressure Swing Adsorption operation. Our work herein thus suggests a new perspective to functionalizing PAFs and other types of advanced porous materials for highly selective adsorption of ethylene over ethane.

Metal-cation-directed de novo assembly of a functionalized guest molecule in the nanospace of a metal-organic framework.

In this work, a new strategy is developed to encapsulate a metal-functionalized guest molecule into a metal-organic framework (MOF) via metal-cation-directed de novo assembly from the component fragments of the guest molecule. This strategy, as illustrated in proof-of-principle studies on the de novo assembly of metal(II) phthalocyanine molecules into bio-MOF-1, can circumvent some drawbacks of existing approaches for encapsulating guest molecules into MOFs, such as inaccessibility for larger guest molecules due to limitations of the MOF window size and disruption of the MOF framework structure by functionalized guest molecules. Overall, this work provides a general yet versatile approach for encapsulating a broader range of metal-functionalized guest molecules into MOFs for various applications.

A dual functional MOF as a luminescent sensor for quantitatively detecting the concentration of nitrobenzene and temperature.

We report here a luminescent metal-organic framework [Zn3(TDPAT)(H2O)3] [TDPAT = 2,4,6-tris(3,5-dicarboxyl phenylamino)-1,3,5-triazine] exhibiting strong luminescence at room temperature, which can serve as the first case of a dual functional luminescent sensor for quantitatively detecting the concentration of nitrobenzene and temperature.

Reversible switching of slow magnetic relaxation in a classic lanthanide metal-organic framework system.

The reversible sorption-desorption of terminal coordinated water molecules and the guest molecules can switch slow magnetic relaxation in a classic lanthanide metal-organic framework system, Dy(BTC)(H2O)·DMF and Dy(BTC).

A strategy toward constructing a bifunctionalized MOF catalyst: post-synthetic modification of MOFs on organic ligands and coordinatively unsaturated metal sites.

A new strategy toward constructing bifunctionalized MOFs has been developed based on post-synthetic modification of MOFs on organic ligands and coordinatively unsaturated metal sites, respectively. Based on this strategy, an organo-bifunctionalized MOF catalyst has been synthesized for the first time and successfully applied in one-pot tandem reaction.