MOF-Derived Zn/N-Doped Porous Carbon Film on a Carbon Nanotube for High-Performance Supercapacitors

Designing high-performance binder-free electrochemical electrodes is crucially important toward supercapacitors. In this paper, a Zn/N-doped porous carbon film coating on flexible carbon nanotubes (ZIF-8@CT-800) derived from the epitaxial Zn-MOF film growth on cotton textile was successfully fabricated via a combination of the liquid-phase epitaxial (LPE) method and calcination treatments. The ZIF-8@CT-800 serves directly as a self-supported electrode for supercapacitors and exhibits a high areal capacitance of 930 mF·cm-2 at a current density of 1 mA·cm-2 and a good recyclability of 86% after 2000 cycles. The excellent supercapacitor property is ascribed to the unique structural design of ZIF-8@CT-800, which provides appropriate channels for enhanced electronic and ionic transport as well as increased surface area for accessing more electrolyte ions. This work will provide significant guidance for designing MOF-derived porous carbon to construct flexible binder-free electrode materials with high electrochemical performance.

Defect-engineered chiral metal-organic frameworks

Chirality has an important impact on chemical and biological research, as most active substances are chiral. In recent decades, metal-organic frameworks (MOFs), which are assembled from metal ions or clusters and organic linkers via metal-ligand bonding, have attracted considerable scientific interest due to their high crystallinity, exceptional porosity and tunable pore sizes, high modularity, and diverse functionalities. Since the discovery of the first functional chiral metal-organic frameworks (CMOFs), CMOFs have been involved in a variety of disciplines such as chemistry, physics, optics, medicine, and pharmacology. The introduction of defect engineering theory into CMOFs allows the construction of a class of defective CMOFs with high hydrothermal stability and multi-stage pore structure. The introduction of defects not only increases the active sites but also enlarges the pore sizes of the materials, which improves chiral recognition, separation, and catalytic reactions, and has been widely investigated in various fields. This review describes the design and synthesis of various defective CMOFs, their characterization, and applications. Finally, the development of the materials is summarized, and an outlook is given. This review should provide researchers with an insight into the design and study of complex defective CMOFs.

Chemical catalytic upgrading of polyethylene terephthalate plastic waste into value-added materials, fuels and chemicals

The substantial production of polyethylene terephthalate (PET) products, coupled with high abandonment rates, results in significant environmental pollution and resource wastage. This has prompted global attention to the development of rational strategies for PET waste treatment. In the context of renewability and sustainability, catalytic chemical technology provides an effective means to recycle and upcycle PET waste into valuable resources. In this review, we initially provide an overview of strategies employed in the thermocatalytic process to recycle PET waste into valuable carbon materials, fuels and typical refined chemicals. The effect of catalysts on the quality and quantity of specific products is highlighted. Next, we introduce the development of renewable-energy-driven electrocatalytic and photocatalytic systems for sustainable PET waste upcycling, focusing on rational catalysts, innovative catalytic system design, and corresponding underlying catalytic mechanisms. Moreover, we discuss advantages and disadvantages of three chemical catalytic strategies. Finally, existing limitations and outlook toward controllable selectivity and yield enhancement of value-added products and PET upvaluing technology for scale-up applications are proposed. This review aims to inspire the exploration of waste-to-treasure technologies for renewable-energy-driven waste management toward a circular economy.

Acidified Nitrogen Self-Doped Porous Carbon with Superprotonic Conduction for Applications in Solid-State Proton Battery

Solid proton electrolytes play a crucial role in various electrochemical energy storage and conversion devices. However, the development of fast proton conducting solid proton electrolytes at ambient conditions remains a significant challenge. In this study, a novel acidified nitrogen self-doped porous carbon material is presented that demonstrates exceptional superprotonic conduction for applications in solid-state proton battery. The material, designated as MSA@ZIF-8-C, is synthesized through the acidification of nitrogen-doped porous carbon, specifically by integrating methanesulfonic acid (MSA) into zeolitic imidazolate framework-derived nitrogen self-doped porous carbons (ZIF-8-C). This study reveals that MSA@ZIF-8-C achieves a record-high proton conductivity beyond 10-2  S cm-1 at ambient condition, along with good long-term stability, positioning it as a cutting-edge alternative solid proton electrolyte to the default aqueous H2 SO4 electrolyte in proton batteries.

Tailoring C─N Containing Compounds into Carbon Nanomaterials with Tunable Morphologies for Electrocatalytic Applications

Carbon materials with unique sp2 -hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient "bottom-up" strategy by pyrolysis of graphitic carbon nitride (g-C3 N4 ) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3 N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses.

Arrayed Pt Single Atoms via Phosphotungstic Acids Intercalated in Silicate Nanochannels for Efficient Hydrogen Evolution Reactions

Single-atom catalysts, known for their high activity, have garnered significant interest. Currently, single-atom catalysts were prepared mainly on 2D substrates with random distribution. Here, we report a strategy for preparing arrayed single Pt (Pt1) atoms, which are templated through coordination with phosphotungstic acids (PTA) intercalated inside hexagonally packed silicate nanochannels for a high single Pt-atom loading of ca. 3.0 wt %. X-ray absorption spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy, in conjunction with the density-functional theory calculation, collectively indicate that the Pt single atoms are stabilized via a four-oxygen coordination on the PTA within the nanochannels' inner walls. The critical reduction in the Pt-adsorption energy to nearly the cohesive energy of Pt clustering is attributed to the interaction between PTA and the silicate substrate. Consequently, the transition from single-atom dispersion to clustering of Pt atoms can be controlled by adjusting the number density of PTA intercalated within the silicate nanochannels, specifically when the number ratio of Pt atoms to PTA changes from 3.7 to 18. The 3D organized Pt1-PTA pairs, facilitated by the arrayed silicate nanochannels, demonstrate high and stable efficiency with a hydrogen production rate of ca. 300 mmol/h/gPt─approximately twice that of the best-reported Pt efficiency in polyoxometalate-based photocatalytic systems.

Hierarchical Hollow Carbon Particles with Encapsulation of Carbon Nanotubes for High Performance Supercapacitors

A novel and sustainable carbon-based material, referred to as hollow porous carbon particles encapsulating multi-wall carbon nanotubes (MWCNTs) (CNTs@HPC), is synthesized for use in supercapacitors. The synthesis process involves utilizing LTA zeolite as a rigid template and dopamine hydrochloride (DA) as the carbon source, along with catalytic decomposition of methane (CDM) to simultaneously produce MWCNTs and COx -free H2 . The findings reveal a distinctive hierarchical porous structure, comprising macropores, mesopores, and micropores, resulting in a total specific surface area (SSA) of 913 m2  g-1 . The optimal CNTs@HPC demonstrates a specific capacitance of 306 F g-1 at a current density of 1 A g-1 . Moreover, this material demonstrates an electric double-layer capacitor (EDLC) that surpasses conventional capabilities by exhibiting additional pseudocapacitance characteristics. These properties are attributed to redox reactions facilitated by the increased charge density resulting from the attraction of ions to nickel oxides, which is made possible by the material's enhanced hydrophilicity. The heightened hydrophilicity can be attributed to the presence of residual silicon-aluminum elements in CNTs@HPC, a direct outcome of the unique synthesis approach involving nickel phyllosilicate in CDM. As a result of this synthesis strategy, the material possesses excellent conductivity, enabling rapid transportation of electrolyte ions and delivering outstanding capacitive performance.

Surface-structure tailoring of Dendritic PtCo nanowires for efficient oxygen reduction reaction

Platinum-based alloy nanowire catalysts demonstrates great promise as electrocatalysts to facilitate the cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs). However, it is still challenge to further improve the Pt atom utilization of Pt based nanowires featuring inherent structural stability. Herein, a new structure of PtCo nanowire with nanodendrites was developed using CO-assistance solvent thermal method. The dendrite structure with an average length of about 7 nm are characterized by a Pt-rich surface and the high-index facets of {533}, {331} and {311}, and grows from the ultra-fine wire structure with an average diameter of about 3 nm. PtCo nanowires with nanodendrites developed in this work shows outstanding performance for ORR, in which its mass activity of 1.036 A/mgPt is 5.76 times, 1.74 times higher than that of commercial Pt/C (0.180 A/mgPt) and PtCo nanowires without nanodendrites (0.595 A/mgPt), and its mass activity loss is only 18% under the accelerated durability tests (ADTs) for 5k cycles. The significant improvement is attributed to high exposure of active sites induced by the dendrite structure with Pt-rich surface with the high-index facets and Pt-rich surface. This structure may provide a new idea for developing novel 1D Pt based electrocatalysts.

Ultrafast Response and High Selectivity of Diethylamine Gas Sensors at Room Temperature Using MOF-Derived 1D CuO Nano-Ellipsoids

Environmental and health monitoring requires low-cost, high-performance diethylamine (DEA) sensors. Materials based on metal-organic frameworks (MOFs) can detect hazardous gases due to their large specific surface area, many metal sites, unsaturated sites, functional connectivity, and easy calcination to remove the scaffold. However, developing facile materials with high sensitivity and selectivity in harsh environments for accurate DEA detection at a low detection limit (LOD) at room temperature (RT) is challenging. In this study, p-type semiconducting porous CuOx sensing materials were synthesized using a simple solvothermal process and annealed in an argon atmosphere at three different temperatures (x = 400, 600, and 800 °C). Significant variations in particle size, specific area, crystallite size, and shape were noticed when the annealing temperature was elevated. Cu-MIL-53 annealed at 400 °C (CuO-400) has a typical nanoellipsoid (NEs) shape with a length of 61.5 nm and a diameter of 33.2 nm. Surprisingly, CuO-400 NEs showed an excellent response to DEA with an ultra-LOD (Rg/Ra = 7.3 @ 100 ppb, 55% relative humidity), excellent selectivity and sensitivity (Rg/Ra = 236 @ 15 ppm), exceptional long-term stability and repeatability, and a fast response/recovery period at RT, outperforming most previously reported materials. CuO-400 NEs have outstanding gas-sensing characteristics due to their high porosity, 1D nanostructure, unsaturated Cu sites (Cu+ and Cu2+), large specific surface area, and numerous oxygen vacancies. This study presents a generic approach to produce future CuO derived from Cu-MOFs-sensitive materials, revealing new insights into the design of effective sensors for environmental monitoring at RT.

Direct Synthesis of Mixed-Metal Paddle-Wheel Metal-Organic Frameworks with Controlled Metal Ratios under Ambient Conditions

Currently, synthesizing mixed-metal metal-organic frameworks (MM-MOFs) in a single step remains a challenge due to the varying reactivities of different metal cations. This often results in the formation of mixtures of monometallic MOFs or MM-MOFs with nonstoichiometric metal ratios. A promising approach to overcoming this issue is the controlled precursor method, which uses prebuilt polynuclear complexes with structures similar to the secondary building units (SBUs) of the desired MOFs. In this study, we report that metal acetates can serve as natural prebuilt SBUs, enabling the controlled synthesis of MBDs ([M2(BDC)2DABCO]n, M = metal, BDC = 1,4-benzenedicarboxylic acid, DABCO = 1,4-diazabicyclo[2,2,2]octane) under ambient conditions. By exploiting the fact that metal acetates readily form soluble paddle-wheel dimers similar to the SBUs of MBDs, we achieve the direct synthesis of mixed-metal MBDs at room temperature. The metal ratios (Zn, Co, and Ni) in the resulting MBDs are controllable, and the production yields exceed 90%. The use of metal acetates facilitates the fast and uniform nucleation of MBDs, regardless of the metal cations involved. This similarity in nucleation rates leads to the formation of bimetallic and trimetallic MBDs with predefined metal ratios and homogeneous metal distribution while maintaining the quality of the MOFs. Importantly, this strategy offers an efficient pathway for synthesizing mixed metal MBDs using stoichiometric amounts of metal salts without toxic additives, high energy consumption, and complex synthesis steps.

Disclosing gate-opening/closing events inside a flexible metal-organic framework loaded with CO2 by reactive and essential dynamics

We have combined reactive molecular dynamics simulations with principal component analysis to provide a clearer view of the interactions and motion of the CO2 molecules inside a metal-organic framework and the movements of the MOF components that regulate storage, adsorption, and diffusion of the guest species. The tens-of-nanometer size of the simulated model, the capability of the reactive force field tuned to reproduce the inorganic-organic material confidently, and the unconventional use of essential dynamics have effectively disclosed the gate-opening/closing phenomenon, possible coordinations of CO2 at the metal centers, all the diffusion steps inside the MOF channels, the primary motions of the linkers, and the effects of their concerted rearrangements on local CO2 relocations.

Adenosine/β-Cyclodextrin-Based Metal-Organic Frameworks as a Potential Material for Cancer Therapy

Recently, researchers have employed metal-organic frameworks (MOFs) for loading pharmaceutically important substances. MOFs are a novel class of porous class of materials formed by the self-assembly of organic ligands and metal ions, creating a network structure. The current investigation effectively achieves the loading of adenosine (ADN) into a metal-organic framework based on cyclodextrin (CD) using a solvent diffusion method. The composite material, referred to as ADN:β-CD-K MOFs, is created by loading ADN into beta-cyclodextrin (β-CD) with the addition of K⁺ salts. This study delves into the detailed examination of the interaction between ADN and β-CD in the form of MOFs. The focus is primarily on investigating the hydrogen bonding interaction and energy parameters through the aid of semi-empirical quantum mechanical computations. The analysis of peaks that are associated with the ADN-loaded ICs (inclusion complexes) within the MOFs indicates that ADN becomes incorporated into a partially amorphous state. Observations from SEM images reveal well-defined crystalline structures within the MOFs. Interestingly, when ADN is absent from the MOFs, smaller and irregularly shaped crystals are formed. This could potentially be attributed to the MOF manufacturing process. Furthermore, this study explores the additional cross-linking of β-CD with K through the coupling of -OH on the β-CD-K MOFs. The findings corroborate the results obtained from FT-IR analysis, suggesting that β-CD plays a crucial role as a seed in the creation of β-CD-K MOFs. Furthermore, the cytotoxicity of the MOFs is assessed in vitro using MDA-MB-231 cells (human breast cancer cells).

Rational Fabrication of Ionic Covalent Organic Frameworks for Chemical Analysis Applications

The rapid development of advanced material science boosts novel chemical analytical technologies for effective pretreatment and sensitive sensing applications in the fields of environmental monitoring, food security, biomedicines, and human health. Ionic covalent organic frameworks (iCOFs) emerge as a class of covalent organic frameworks (COFs) with electrically charged frames or pores as well as predesigned molecular and topological structures, large specific surface area, high crystallinity, and good stability. Benefiting from the pore size interception effect, electrostatic interaction, ion exchange, and recognizing group load, iCOFs exhibit the promising ability to extract specific analytes and enrich trace substances from samples for accurate analysis. On the other hand, the stimuli response of iCOFs and their composites to electrochemical, electric, or photo-irradiating sources endows them as potential transducers for biosensing, environmental analysis, surroundings monitoring, etc. In this review, we summarized the typical construction of iCOFs and focused on their rational structure design for analytical extraction/enrichment and sensing applications in recent years. The important role of iCOFs in the chemical analysis was fully highlighted. Finally, the opportunities and challenges of iCOF-based analytical technologies were also discussed, which may be beneficial to provide a solid foundation for further design and application of iCOFs.

Niobium- and cobalt-modified dual-source-derived porous carbon with a honeycomb-like stable structure for supercapacitor and hydrogen evolution reaction

Designing porous carbon materials with tailored architecture and appropriate compositions is essential for supercapacitor (SC) and hydrogen evolution reaction (HER). Herein, Nb/Co-modified dual-source porous carbon (Nb/Co-DSPC) with a honeycomb structure was obtained by introducing a secondary carbon source (Co/Zn-ZIF) and transition metal Nb into activated Typha carbon (ATC). The addition of a secondary carbon source and Nb resulted in superior specific surface area (1272.38 m²/g), excellent hydrophilicity (34.73°) and abundant bimetallic active sites (Nb/Co-N_x) in Nb/Co-DSPC, providing excellent charge storage capacity and electrocatalytic activity. The Nb/Co-DSPC electrode displayed an outstanding capacitance of 337 F/g at 0.5 A/g and showed excellent stability after 15,000 charge-discharge cycles. In addition, Nb/Co-DSPC shows an overpotential of 114 mV at 10 mA cm^-2, better than those of Co-DSPC (139 mV) and ATC (162 mV) alone. This study offers a reliable strategy for advanced multifunctional porous carbon electrode materials preparations.

Nanostructured biosensing platforms for the detection of food- and water-borne pathogenic Escherichia coli

Pathogenic bacterial infection is one of the principal causes affecting human health and ecosystems. The accurate identification of bacteria in food and water samples is of significant interests to maintain safety and health for humans. Culture-based tests are practically tedious and may produce false-positive results, while viable but non-culturable microorganisms (NCMs) cannot be retrieved. Thus, it requires fast, reliable, and low-cost detection strategies for on-field analysis and point-of-care (POC) monitoring. The standard detection methods such as nucleic acid analysis (RT-PCR) and enzyme-linked immunosorbent assays (ELISA) are still challenging in POC practice due to their time-consuming (several hours to days) and expensive laboratory operations. The optical (surface plasmon resonance (SPR), fluorescence, and surface-enhanced Raman scattering (SERS)) and electrochemical-based detection of microbes (early stage of infective diseases) have been considered as alternative routes in the emerging world of nanostructured biosensing since they can attain a faster and concurrent screening of several pathogens in real samples. Moreover, optical and electrochemical detection strategies are opening a new route for the ability of detecting pathogens through the integration of cellphones, which is well fitted for POC analysis. This review article covers the current state of sensitive mechanistic approaches for the screening and detection of Escherichia coli O157:H7 (E. coli) pathogens in food and water samples, which can be potentially applied in clinical and environmental monitoring.

Morphology-Engineering Construction of Anti-Aggregated Co/N-Doped Hollow Carbon from Metal-Organic Frameworks for Efficient Biomass Upgrading

The controlled pyrolysis of metal/carbon-containing precursors is commonly used for fabricating multifunctional metal/carbon-based catalysts, nevertheless, the inevitable agglomeration of these precursors in pyrolysis is extremely negative for efficient catalysis. This study reports the first example of suppressing the interfacial fusion and agglomeration of metal/carbon-based catalyst in its pyrolysis-involved fabrication process by developing a facile morphology-engineering strategy. Metal-organic framework precursors are chosen as a proof of concept and five Co/N-doped hollow carbons with different morphologies (rhombic dodecahedron, cube, plate, interpenetration twin, and rod) are synthesized via the pyrolysis of their corresponding core-shell ZIF-8@ZIF-67 precursors. It is demonstrated that the interpenetration twin precursor shows the minimum interfacial contact of interparticles due to its partly-concave morphology with abundant facets, which endows it with the best resistibility from interfacial fusion and thus aggregation of interparticles during pyrolysis. Benefiting from its unique anti-aggregated structure with high specific surface area, abundant fully-exposed active sites, and good dispersibility, the resultant 36-facet Co/N-doped hollow carbon exhibit remarkably improved catalytic property for biomass upgrading as compared with its aggregated counterparts. This study highlights the crucial role of engineering morphology to prevent metal/carbon-containing precursors from detrimental agglomeration during pyrolysis, demonstrating a new approach to constructing anti-aggregated metal/carbon-based catalysts.

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection

Guiding metal organic framework (MOF) morphology, especially without the need for chemical additives, still remains a challenge. For the first time, we report a unique surface guiding approach in controlling the crystal morphology formation of zeolitic imidazole framework-8 (ZIF-8) and HKUST-1 MOFs on disrupted alkanethiol self-assembled monolayer (SAM)-covered Au substrates. Selective molecule removal is applied to generate diverse SAM matrices rich in artificial molecular defects in a monolayer to direct the dynamic crystal growth process. When a 11-mercaptoundecanol alkanethiol monolayer is ruptured, the hydroxyl tail groups of surface residue molecules act as nucleating sites by coordination with precursor metal ions. Meanwhile, the exposed alkane chain backbones stabilize a particular facet of MOF nuclei in the dynamic growth by slowing down their crystal growth rates along a specific direction. The competitive formation between the [110] and [100] planes of ZIF-8 ultimately regulates the crystal shapes from rhombic dodecahedron, truncated rhombic dodecahedron, and truncated cube to cube. Similarly, changeable morphologies of HKUST-1 crystals are also achieved from cube and tetrakaidekahedron to octahedron, originating from the competitive selection between the [100] and [111] planes. In addition to the artificial matrix preferred orientation of initial nucleation, parameters such as temperature also play a crucial role in the resulting crystal morphology. Standing on the additive-free MOF crystal morphology growth control, porous architectures prepared in this approach can act as templates for ligand-free metal (Au, Ag, and Cu) nanocluster synthesis. The nanocluster-embedded MOF structures represent distinct crystal morphology-dependent optical properties, and interestingly, their fluorescence emission can be highly enhanced by facet-induced nanocluster packing alignments. These findings not only provide a unique thought on MOF crystal morphology guidance but also pave a new route for the accompanied property investigation and further application.

Self-catalyzed Co, N-doped carbon nanotubes-grafted hollow carbon polyhedrons as efficient trifunctional electrocatalysts for zinc-air batteries and self-powered overall water splitting

It is still essential and challenging to explore inexpensive and versatile electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), for the development of rechargeable zinc-air batteries (ZABs) and overall water splitting. Herein, a rambutan-like trifunctional electrocatalyst is fabricated by re-growth of secondary zeolitic imidazole frameworks (ZIFs) on ZIF-8-derived ZnO and the following carbonization treatment. Co nanoparticles (NPs) are encapsulated into N-doped carbon nanotubes (NCNT) grafted N-enriched hollow carbon (NHC) polyhedrons to form the Co-NCNT@NHC catalyst. The strong synergy between the N-doped carbon matrix and Co NPs endows Co-NCNT@NHC with trifunctional catalytic activity. The Co-NCNT@NHC displays a half-wave potential of 0.88 V versus RHE for ORR in alkaline electrolyte, an overpotential of 300 mV at 20 mA cm^-2 for OER, and an overpotential of 180 mV at 10 mA cm^-2 for HER. Impressively, a water electrolyzer is successfully powered by two rechargeable ZABs in series, with Co-NCNT@NHC as the 'all-in-one' electrocatalyst. These findings are inspiring for the rational fabrication of high-performance and multifunctional electrocatalysts intended for the practical application of integrated energy-related systems.

Multifunctional TiO2 Nanotube-Matrix Composites with Enhanced Photocatalysis and Lithium-Ion Storage Performances

As a multifunctional material, TiO₂ shows excellent performance in catalytic degradation and lithium-ion storage. However, high electron-hole pair recombination, poor conductivity, and low theoretical capacity severely limit the practical application of TiO₂. Herein, TiO₂ nanotube (TiO₂ NT) with a novel double-layer honeycomb structure were prepared by two-step electrochemical anodization. Honeycombed TiO₂ NT arrays possess clean top surfaces and a long-range ordering, which greatly facilitates the preparation of high-performance binary and ternary materials. A binary TiO₂ nanotube@Au nanoparticle (TiO₂ NT@Au NP) composite accompanied by appropriately concentrated and uniformly distributed gold particles was prepared in this work. Interestingly, the TiO₂ nanotube@Au nanoparticle (TiO₂ NT@Au NP) composites not only showed the excellent catalytic degradation effect of methylene blue, but also demonstrated large lithium-ion storage capacity (310.6 μAh cm^-2, 1.6 times of pristine TiO₂ NT). Based on the realization of the controllable fabrication of binary TiO₂ nanotube@MoS₂ nanosheet (TiO₂ NT@MoS₂ NS) composite, ternary TiO₂ nanotube@MoS₂ nanosheet@Au nanoparticle (TiO₂ NT@MoS₂ NS@Au NP) composite with abundant defects and highly ordered structure was also innovatively designed and fabricated. As expected, the TiO₂ NT@MoS₂ NS@Au NP anode exhibits extremely high initial discharge specific capacity (487.4 μAh cm^-2, 2.6 times of pristine TiO₂ NT) and excellent capacity retention (81.0%).

A resonant energy transfer electrochemiluminescence immunosensor based on low trigger potential of Zn-metal organic framework and CoOOH nanosheets for 5-fluorouracil detection

The organic luminophores have inspired widespread interest in electrochemiluminescence (ECL). Herein, a novel rod-like metal-organic framework was formed by chelating Zn ion with 9,10-di(p-carboxyphenyl)-anthracene (DPA), defined as Zn-MOF for simplicity. In this proposal, the prepared Zn-MOF was first used as a powerful organic luminophore with low trigger potential, thus developing a competitive ECL immunoassay for ultrasensitive detection of 5-fluorouracil (5-FU) with 1,4-diazabicyclo[2.2.2]octane (D-H₂) as the coreactant. The absorption spectrum of cobalt oxyhydroxide (CoOOH) nanosheets and the ECL emission spectrum of Zn-MOF could be highly matched, which ensured the occurrence of resonance energy transfer (RET). For that, ECL-RET was applied in the assembly strategy of the ECL biosensor, and Zn-MOF was used as the energy donor and CoOOH nanosheets as the acceptor. Taking advantage of the luminophore and ECL-RET, the immunoassay can be used for ultra-sensitive quantitative detection of 5-fluorouracil. The proposed ECL-RET immunosensor showed satisfactory sensitivity and accuracy with a wider linear range from 0.001 to 1000 ng/mL, and a lower detection limit (0.52 pg/mL). Hence, it is worth believing that this strategy can pave a bright research direction for the detection of 5-FU or other biological small molecules.

Single-atom nanozymes Co-N-C as an electrochemical sensor for detection of bioactive molecules

A properly designed sensing interface is crucial for the accurate and sensitive detection of biologically active molecules. Single-atom nanozymes from transition metal and nitrogen-doped carbon materials (M-N-C) have caught attention owing to their large surface area and strong bionic enzyme activity. Herein, a three-dimensional layered electrochemical electrode consisting of a Co-N-C nanoenzyme embedded in a reduced graphene oxide aerogel was prepared for the detection of hydrogen peroxide (H₂O₂), dopamine (DA) and uric acid (UA). Due to its unique three-dimensional layered structure, rGA has excellent electrical conductivity and high material loading and is used to enhance the electrocatalytic performance of Co-N-C. The combination of single-atom nanozymes and electrochemical detection shows unique advantages in catalytic activity and selectivity. The limit of detection and detection range are 0.74 μM and 3-2991 μM respectively for H₂O_2. Furthermore, it has been successfully implemented for the in-situ detection of H₂O₂ in living cells. In addition, their simultaneous detection is also realized by the sensors for DA and UA. And it can accurately capture the signal of UA and DA in the urine. Meanwhile, the electrode displays satisfactory stability and repeatability. Therefore, this paper provides a new detection strategy for a variety of bioactive molecules, showing great potential in cell biology, pathophysiology and diagnostics.

Hydrothermal Synthesis of ZnO Superstructures with Controlled Morphology via Temperature and pH Optimization

Zinc oxide, as a widely used material in optics, electronics, and medicine, requires a complete overview of different conditions for facile and easily reproducible syntheses. Two types of optimization of ZnO hydrothermal preparation from zinc acetate and sodium hydroxide solution are presented, which allowed for obtaining miscellaneous morphologies of materials. The first was a temperature-controlled synthesis from 100 to 200 °C, using citric acid as a capping agent. The formation of hexagonal rods at the lowest temperature was evidenced, which agglomerated to flower-like structures at 110 and 120 °C. It was followed by transformation to flake-like roses at 160 °C, up to disordered structures composed of nanosized plates (>180 °C). The transformations were generated through a temperature change, which had an impact on the diffusion effect of hydroxide and citrate complexes. The second optimization was the hydrothermal synthesis free of organic additives and it included only a pH variation from 7.5 to 13.5. It was found that by utilizing a slow-dropping process and varying amounts of NaOH solutions, it is possible to obtain well-formed hexagonal pellets at pH 8.0-8.5. Strongly basic conditions of pH 11.0 and 13.5 impeded superstructure formations, giving small elongated particles of ZnO. All samples were characterized by high phase purity and crystallinity, with a specific surface area of 18-37 m²/g, whereas particle size distribution indicated a predominance of small particles (<1 μm).

Mechanistic investigation of cellulose regulating the morphology and photocatalytic activity of Al-doped ZnO

The morphology of metal oxide is a crucial factor for improving of catalysis properties. As a renewable and environmentally friendly biomass material, cellulose has been widely used to induce the morphology of semiconductors. The contributions of cellulose hydroxyl groups and spatial hindrance in tailoring Al doped ZnO (AZO) morphologies were investigated. The morphology of AZO could be gradually induced from flake-like to flower-like with the increase of cellulose hydroxyl content per unit volume. At the same time, the changes in spatial hindrance had no apparent effect on the morphology of AZO. So the cellulose hydroxyl groups that act to induce the in situ growth of AZO nanoparticles on cellulose substrates. The results further confirmed the strong interaction between cellulose hydroxyl groups and Zn²⁺. In addition, the photocatalytic activities of Al-doped ZnO/cellulose nanocomposites (AZOC) with different morphologies were evaluated by the degradation of bisphenol A (BPA). The high hydroxyl contents of cellulose substrates contributed to the growth of flower-like AZO with high light utilization and photocatalytic activity. This work proposed cleaner strategies to modify semiconductor morphologies for photocatalysis by regulating the content of cellulose hydroxyl contents.

Removal of pharmaceutical and personal care products (PPCPs) by MOF-derived carbons: A review

Nowadays, the increasing demand for pharmaceuticals and personal care products (PPCPs) has resulted in the uncontrolled release of large amounts of PPCPs into the environment, which poses a great challenge to the existing wastewater treatment technologies. Therefore, novel materials for efficient treatment of PPCPs need to be developed urgently. MOF-derived carbons (MDCs), have many advantages such as high mechanical strength, excellent water stability, large specific surface area, excellent electron transfer capability, and environmental friendliness. These advantages give MDCs an excellent ability to remove PPCPs. In this review, the effects of different substances on the properties and functions of MDCs are discussed. In addition, representative applications of MDCs and composites for the removal of PPCPs in the field of adsorption and catalysis are summarized. Finally, the future challenges of MDCs and composites are foreseen.

A Metal-Organic Frameworks Derived 1T-MoS2 with Expanded Layer Spacing for Enhanced Electrocatalytic Hydrogen Evolution

Metal phase molybdenum disulfide (1T-MoS₂ ) is considered a promising electrocatalyst for hydrogen evolution reaction (HER) due to its activated basal and superior electrical conductivity. Here, a one-step solvothermal route is developed to prepare 1T-MoS₂ with expanded layer spacing through the derivatization of a Mo-based organic framework (Mo-MOFs). Benefiting from N,N-dimethylformamide oxide as external stress, the interplanar spacing of (002) of the MoS₂ catalyst is extended to 10.87 Å, which represents the largest one for the 1T-MoS₂ catalyst prepared by the bottom-up approach. Theoretical calculations reveal that the expanded crystal planes alter the electronic structure of 1T-MoS₂ , lower the adsorption-desorption potentials of protons, and thus, trigger efficient catalytic activity for HER. The optimal 1T-MoS₂ catalyst exhibits an overpotential of 98 mV at 10 mA cm^-2 for HER, corresponding to a Tafel slope of 52 mV dec^-1 . This Mo-MOFs-derived strategy provides a potential way to design high-performance catalysts by adjusting the layer spacing of 2D materials.

Development of novel MOF-mixed matrix three-dimensional membrane capsules for eradicating potentially toxic metals from water and real electroplating wastewater

The stability and applicability of UiO-66-(NH₂)₂ metal-organic framework (MOF) nanoparticles (NPs) were successfully improved in this study by incorporating them into alginate biopolymer during the manifestation of crosslinking agents-calcium chloride and glutaraldehyde-via a simple, environment-friendly, and facile approach to eradicate potentially toxic metals (PTMs) such as Cr⁶⁺, Cr³⁺, Cu²⁺, and Cd²⁺ from water and real electroplating wastewater. Hydrophilic functional groups (i.e., -OH, -COOH, and -NH₂) are imperative in the smooth loading of UiO-66-(NH₂)₂ MOF- NPs into three-dimensional (3-D) membrane capsules (MCs). The X-ray photoelectron spectroscopy (XPS) results suggested that UiO-66-(NH₂)₂ MOF was effectively bonded in/on the capsule via electrostatic crosslinking between -H₃N⁺ and -COO^-. Scanning electron microscopy results revealed a porous honeycomb configuration of the 3-D SGMMCs (S: sodium alginate, G: glutaraldehyde, M: MOF NPs, and MCs: membrane capsules). The maximum monolayer absorption capacities for Cr⁶⁺, Cr³⁺, Cu²⁺, and Cd²⁺ were 495, 975, 1295, and 1350 mg/g, respectively. The results of Fourier transform infrared spectroscopy and XPS analyses showed that electrostatic attraction and ion exchange were the main processes for PTM removal used by the as-developed 3-D SGMMCs. The as-developed 3-D SGMMCs exhibited outstanding selectivity for removing the targeted PTMs under the specified pH/conditions and maintained >80% removal efficiency for up to six consecutive treatment cycles. Notably, > 60% removal efficiencies for Cr⁶⁺ and Cu²⁺ were observed when treating real electroplating wastewater. Therefore, the as-developed 3-D SGMMCs can be used as an exceptional multifunctional sorbent to remove and recover PTMs from real electroplating wastewater.

Saiz P, Reizabal A, Wuttke S, Celaya-Azcoaga L, Valverde A, Fernández de Luis R. A State-of-the-Art of Metal-Organic Frameworks for Chromium Photoreduction vs. Photocatalytic Water Remediation

Hexavalent chromium (Cr(VI)) is a highly mobile cancerogenic and teratogenic heavy metal ion. Among the varied technologies applied today to address chromium water pollution, photocatalysis offers a rapid reduction of Cr(VI) to the less toxic Cr(III). In contrast to classic photocatalysts, Metal-Organic frameworks (MOFs) are porous semiconductors that can couple the Cr(VI) to Cr(III) photoreduction to the chromium species immobilization. In this minireview, we wish to discuss and analyze the state-of-the-art of MOFs for Cr(VI) detoxification and contextualizing it to the most recent advances and strategies of MOFs for photocatalysis purposes. The minireview has been structured in three sections: (i) a detailed discussion of the specific experimental techniques employed to characterize MOF photocatalysts, (ii) a description and identification of the key characteristics of MOFs for Cr(VI) photoreduction, and (iii) an outlook and perspective section in order to identify future trends.

PdS Quantum Dots as a Hole Attractor Encapsulated into the MOF@Cd0.5Zn0.5S Heterostructure for Boosting Photocatalytic Hydrogen Evolution under Visible Light

Herein, a new photocatalyst PdS@UiOS@CZS is successfully synthesized, where thiol-functionalized UiO-66 (UiOS), a metal-organic framework (MOF) material, is used as a host to encapsulate PdS quantum dots (QDs) in its cages, and Cd_0.5Zn_0.5S (CZS) solid solution nanoparticles (NPs) are anchored on its outer surface. The resultant PdS@UiOS@CZS with an optimal ratio between components displays an excellent photocatalytic H₂ evolution rate of 46.1 mmol h^-1 g^-1 under visible light irradiation (420∼780 nm), which is 512.0, 9.2, and 5.9 times that of pure UiOS, CZS, and UiOS@CZS, respectively. The reason for the significantly enhanced performance is that the encapsulated PdS QDs strongly attract the photogenerated holes into the pores of UiOS, while the photogenerated electrons are effectively migrated to CZS due to the heterojunction effect, thereby effectively suppressing the recombination of charge carriers for further high-efficiency hydrogen production. This work provides an idea for developing efficient photocatalysts induced by hole attraction.

Mechanically interlocked molecules in metal-organic frameworks

Mechanically interlocked molecules (MIMs) have great potential in the development of molecular machinery due to their intercomponent dynamics. The incorporation of these molecules in a condensed phase makes it possible to take advantage of the control of the motion of the components at the macroscopic level. Metal-organic frameworks (MOFs) are postulated as ideal supports for intertwined molecules. This review covers the chemistry of the mechanical bond incorporated into metal-organic frameworks from the seminal studies to the latest published advances. We first describe some fundamental concepts of MIMs and MOFs. Next, we summarize the advances in the incorporation of rotaxanes and catenanes inside MOF matrices. Finally, we conclude by showing the study of the rotaxane dynamics in MOFs and the operation of some stimuli-responsive MIMs within MOFs. In addition to emphasising some selected examples, we offer a critical opinion on the state of the art of this research field, remarking the key points on which the future of these systems should be focused.

Two-dimensional assembly made up of ZIF-8 particles for the high-efficient capture of the iodine and dyes

The removal of the pollutants from the environment is the need of the environmental protection. ZIF-8 is promising adsorbents, and the construction of ZIF-8 assembly is essential to boost its performance. Here, we showed the easy synthesis of two-dimensional (2D) assembly built by ZIF-8 particles (2D A-ZIF-8) for the high-efficient capture of the iodine (I₂) and dyes. The assembly was synthesized by the controllable reaction of 2-methylimidazole (2-MIM) with 2D Zn-glycerol (Zn-GL) precursor. Time-dependent experiments showed the predominant replacement of GL at outer boundary and then basic plane of the precursor by 2-MIM. The assembly can be synthesized with high output and combined the advantage of large accessible surface of 2D sheets, the plentiful pores of ZIF-8 and enhanced stability of assembly, endowing the large potential as adsorbent. The high adsorption capacity of I₂ (200 wt%) was achieved on A-ZIF-8, while it is about 128 wt% on traditional dodecahedronal ZIF-8. The assembly also showed the excellent adsorption capacity for methyl orange (MO) (46.3 mg g^-1) and methylene blue (MB) (46.5 mg g^-1) at a concentration of 50 mg L^-1. It can be easily separated for reuse benefited from the large size and enhanced stability of assembly.

Highly efficient C(CO)-C(alkyl) bond cleavage in ketones to access esters over ultrathin N-doped carbon nanosheets

Selective oxidative cleavage of the C(CO)–C bond in ketones to access esters is a highly attractive strategy for upgrading ketones. However, it remains a great challenge to realize this important transformation over heterogeneous metal-free catalysts. Herein, we designed a series of porous and ultrathin N-doped carbon nanosheets (denoted as CN-X, where X represents the pyrolysis temperature) as heterogeneous metal-free catalysts. It was observed that the fabricated CN-800 could efficiently catalyze the oxidative cleavage of the C(CO)–C bond in various ketones to generate the corresponding methyl esters at 130 °C without using any additional base. Detailed investigations revealed that the higher content and electron density of the graphitic-N species contributed to the excellent performance of CN-800. Besides, the high surface area, affording active sites that are more easily accessed, could also enhance the catalytic activity. Notably, the catalysts have great potential for practical applications because of some obvious advantages, such as low cost, neutral reaction conditions, heterogeneous nature, high efficiency, and broad ketone scope. To the best of our knowledge, this is the first work on efficient synthesis of methyl esters via oxidative esterification of ketones over heterogeneous metal-free catalysts.

Ultrathin and metal-free N-doped carbon nanosheets showed high activity and selectivity for oxidative esterification of ketones via C(CO)–C bond cleavage to access methyl esters.

Functionalized MOF-Derived Nanoporous Carbon as Compatible Nanofiller to Fabricate Defect-Free PDMS-Based Mixed Matrix Pervaporation Membranes

Metal-organic framework (MOF)-based polydimethylsiloxane mixed matrix membranes applied for alcohol recovery with high permeability and selectivity are drawing more and more attention. However, the design and fabrication of high-quality and stable MOF-based mixed matrix membrane for pervaporation are still a big challenge. Herein, PDMS functionalized MOF-derived nanoporous carbon (P-ZNC) was first explored as compatible nanofiller to mutually blend with polydimethylsiloxane on PVDF substrate to fabricate defect-free mixed matrix membranes via dip-coating and thermal cross-linkng. Induced by UV illumination, hydrophobic modification of MOF-derived nanoporous carbon was successfully realized under mild conditions within one step, simplifying the operation step. By using this facile strategy, we can not only solve the existing problem of agglomeration, but also covalently cross-link MOF derivative with polymeric matrix and effectively eliminate the interface defect between polymer and nanoparticles without any extra steps. The method also gives a good level of generality for the synthesis of versatile stable nanoporous MOF-derived carbon-based mixed matrix membranes on various supports. The prepared PDMS/P-ZNC with commendable structures possessed excellent separation performance in low concentration n-butanol recovery and had a good balance between permeance, selectivity, and stability.

In Situ Construction of ZIF-67-Derived Hybrid Tricobalt Tetraoxide@Carbon for Supercapacitor

The Co3O4 electrode is a very promising material owing to its ultrahigh capacitance. Nevertheless, the electrochemical performance of Co3O4-based supercapacitors is practically confined by the limited active sites and poor conductivity of Co3O4. Herein, we provide a facile synthetic strategy of tightly anchoring Co3O4 nanosheets to a carbon fiber conductive cloth (Co3O4@C) using the zeolitic imidazolate framework-67 (ZIF-67) sacrificial template via in situ impregnation and the pyrolysis method. Benefiting from the enhancement of conductivity and the increase in active sites, the binder-free porous Co3O4@C supercapacitor electrodes possess typical pseudocapacitance characteristics, with an acceptable specific capacitance of ~251 F/g at 1 A/g and long-term cycling stability (90% after cycling 5000 times at 3 A/g). Moreover, the asymmetric and flexible supercapacitor composed of Co3O4@C and activated carbon is further assembled, and it can drive the red LED for 6 min.

Reticular Nanoscience: Bottom-Up Assembly Nanotechnology

The chemistry of metal-organic and covalent organic frameworks (MOFs and COFs) is perhaps the most diverse and inclusive among the chemical sciences, and yet it can be radically expanded by blending it with nanotechnology. The result is reticular nanoscience, an area of reticular chemistry that has an immense potential in virtually any technological field. In this perspective, we explore the extension of such an interdisciplinary reach by surveying the explored and unexplored possibilities that framework nanoparticles can offer. We localize these unique nanosized reticular materials at the juncture between the molecular and the macroscopic worlds, and describe the resulting synthetic and analytical chemistry, which is fundamentally different from conventional frameworks. Such differences are mirrored in the properties that reticular nanoparticles exhibit, which we described while referring to the present state-of-the-art and future promising applications in medicine, catalysis, energy-related applications, and sensors. Finally, the bottom-up approach of reticular nanoscience, inspired by nature, is brought to its full extension by introducing the concept of augmented reticular chemistry. Its approach departs from a single-particle scale to reach higher mesoscopic and even macroscopic dimensions, where framework nanoparticles become building units themselves and the resulting supermaterials approach new levels of sophistication of structures and properties.

Highly porous nitrogen-doped carbon superstructures derived from the intramolecular cyclization-induced crystallization-driven self-assembly of poly(amic acid)

Hierarchically porous carbon nanomaterials have shown significant potential in electrochemical energy storage due to the promoted charge and mass transfer. Herein, a facile template-free method is proposed to prepare nitrogen-doped carbon superstructures (N-CSs) with multi-level pores by pyrolysis of polymeric precursors derived from the intramolecular cyclization-induced crystallization-driven self-assembly (ICI-CDSA) of poly(amic acid) (PAA). The excellent thermal stability of PAA enables the N-CSs to inherit the hierarchical structure of the precursors during pyrolysis, which facilitates the formation of meso- and macropores while the decomposition of the precursors promotes the creation of micropores. Electrochemical tests demonstrate the ultrahigh surface-area-normalized capacitance (76.5 μF cm-2) of the N-CSs facilitated by the hierarchically porous structure, promoting the charge and mass transfer, as well as the high utilization of pyridinic and pyrrolic nitrogen (12.9%) to provide significant pseudocapacitance contribution up to 40.6%. Considering the diversity of monomers of PAA, this ICI-CDSA strategy could be extended to prepare carbon nanomaterials with various morphologies, pore structures and chemical compositions.