Core-Shell ZIF-8@ZIF-67-Derived Cobalt Nanoparticle-Embedded Nanocage Electrocatalyst with Excellent Oxygen Reduction Performance for Zn-Air Batteries

Metal-nitrogen-carbon (M-N-C) catalysts obtained from zeolitic imidazolate frameworks (ZIFs) have great potential in the oxygen reduction reaction (ORR). Herein, based on the same three-dimensional (3D) topological structure of ZIF-67 and ZIF-8, ZIF-67 is grown on the ZIF-8 surface by the epitaxial growth method, and ZIF-8 is used as a sacrificial template to obtain a Co-embedded layered porous carbon nanocage (CoPCN) electrocatalyst. Meanwhile, the self-sacrificing template effectively improves the specific surface area of the porous structure and reduces the depletion of active sites. The CoPCN shows a high half-wave potential of 0.885 V and superior stability as well as excellent methanol resistance. Theoretical calculations demonstrate that the Co-N1-C2 sites of CoPCN effectively reduce the energy barrier of ORR. In addition, a zinc-air battery (ZAB) based on the CoPCN exhibits excellent peak power density (90 mW cm-2) and superior cycle performance. This work presents a novel idea in the design of ZIF precursor systems to synthesize efficient ORR catalysts.

Encapsulation and thermal properties of composite phase change materials based on cobalt/nitrogen double-doped ZIF-67 derived carbon

To solve the problems of easy leakage and weak thermal conductivity of single-phase change material, in this experiment, cobalt/nitrogen-doped ZIF-67 derived carbon (CoN-ZIF-Cx) was constructed as the carrier material, and paraffin was used as the phase change core material to construct thermally enhanced shaped composite phase change materials (P0.6@CoN-ZIF-Cx). The composite PCMs were characterized using scanning electron microscopy, isothermal nitrogen adsorption-desorption, X-ray diffraction, and Fourier infrared spectroscopy, and their performance was evaluated using transient planar heat source techniques, differential scanning calorimetry, and thermal cycling tests. The results indicated that the impurities of the acid-washed porous carbon material were reduced and the loading of the paraffin was 60%, and the prepared P0.6@CoN-ZIF-Cx had an excellent thermal performance. Among them, P0.6@CoN-ZIF-C3 has the melting and crystallization enthalpy of 71.03 J g-1 and 68.81 J g-1. The thermal conductivity is 0.4127 W m-1 K-1, a 46.19% thermal conductivity improvement compared with pure paraffin. It still has favourable thermal storage capacity after 50 cycles without paraffin leakage during the phase transition.

Metal-organic framework derived inverse opal type 3D graphitic carbon for highly stable lithium-ion batteries

Graphitic carbon-based anodes for lithium-ion batteries have seen remarkable development and commercial acceptance during the past three decades. Still, the performance of these materials is limited due to the low surface area, stacking of layers, poor porosity, and meager conductivity. To overcome these limitations, we propose using polystyrene as a core and small-sized zeolitic imidazolate framework-67 (ZIF-67) particles as decorators to develop a highly porous three-dimensional graphitic carbon material. The developed material is optimized with the carbonization temperature for the best anodic performance of LIBs. The pyridinic nitrogen content in the material carbonized at 700 °C makes it high performing and more stable than the samples treated at 600, 800, and 900 °C. The packed coin cell exhibited an initial discharge capacity of 775 mA h g-1 at a current density of 50 mA g-1, which increases to 806 mA h g-1 after testing the material at different current densities for 55 cycles. The packed half-cell exhibited a highly stable performance of about 96% even after testing for 2000 cycles at 1 A g-1.

Influence of ZIF-9 and ZIF-12 structure on the formation of a series of new Co/N-doped porous carbon composites as anode electrodes for high-performance lithium-ion batteries

A series of new Co/N-doped porous carbon composites, denoted as Co/CZIF-9 and Co/CZIF-12, containing Co nanoparticles encapsulated in nitrogen-doped carbon matrices were prepared by annealing Co-based zeolite imidazolate framework materials, ZIF-9 and ZIF-12, as the efficient precursors at different temperatures. The structural features of the as-synthesized composites at 900 °C were determined by analytical methods with high reliability. Consequently, Co/CZIF-12_900 exhibits a high first specific discharge capacity of 971.0 mA h g^-1 at a current density of 0.1 A g^-1. Notably, the specific discharge/charge capacity of Co/CZIF-12_900 reaches about 508.8 mA h g^-1 at 0.1 A g^-1 after 100 cycles. The outstanding behaviors can be accounted for by the efficient incorporation of hetero-nitrogen doping and the Co nanoparticles within the layered structure of porous carbon, enhancing electrical conductivity and structural stability and limiting volume change during the intercalation/deintercalation of Li⁺ ions. These findings suggest that the Co/CZIF-12_900 material could be employed as a promising anode electrode for energy storage products.

Novel ZIF-67-derived Co@CNTs nanocomposites as effective adsorbents for removal of tetracycline and sulfadiazine antibiotics

Tetracycline (TCC) and sulfadiazine (SDZ) are two of the most consumed antibiotics for human therapies and bacterial infection treatments in aquafarming fields, but their accumulative residues can result in negative effects on water and aquatic microorganisms. Removal techniques are therefore required to purify water before use. Herein, we concentrate on adsorptive removal of TCC and SDZ using cobalt@carbon nanotubes (Co@CNTs) derived from Co-ZIF-67. The presence of CNTs on the edge of nanocomposites was observed. Taguchi orthogonal array was designed with four variables including initial concentration (5-20 mg L^-1), dosage (0.05-0.2 g L^-1), time (60-240 min), and pH (2-10). Concentration and pH were found to be main contributors to adsorption of tetracycline and sulfadiazine, respectively. The optimum condition was found at concentration 5 mg L^-1, dosage 0.2 g L^-1, contact time 240 min, and pH 7 for both TCC and SDZ removals. Confirmation tests showed that Co@CNTs-700 removed 99.6% of TCC and 97.3% of SDZ with small errors (3-5.5%). Moreover, the kinetic and isotherm were studied, which kinetic and isotherm data were best fitted with pseudo second-order model and Langmuir. Maximum adsorption capacity values for TCC and SDZ were determined at 118.4-174.1 mg g^-1 for 180 min. We also proposed the main role of interactions such as hydrogen bonding, π-π stacking, and electrostatic attraction in the adsorption of antibiotics. With high adsorption performance, Co@CNTs-700 is expected to remove antibiotics efficiently from wastewater.

Highly efficient utilization of sodium storage sites for MOF-derived carbon by rapid carbonization

Rapid carbonization within only 10 min achieves the balance of sodium storage sites and electronic conductivity for MOF-derived carbon, delivering excellent sodium storage properties. This work supplies a novel and environment-friendly method to treat MOF-derived materials in the field of electrochemistry.

Promoted Sb removal with hydrogen production in microbial electrolysis cell by ZIF-67-derived modified sulfate-reducing bacteria bio-cathode

Bio-cathode Microbial electrolysis cell (MEC) has been widely discovered for heavy metals removal and hydrogen production. However, low electron transfer efficiency and heavy metal toxicity limit MEC treatment efficiency. In this study, ZIF-67 was introduced to modify Sulfate-reducing bacteria (SRB) bio-cathode to enhance the bioreduction of sulfate and Antimony (Sb) with hydrogen production in the MEC. ZIF-67 modified bio-cathode was developed from a bio-anode microbial fuel cell (MFC) by operating with an applied voltage of 0.8 V to reverse the polarity. Cyclic voltammetry, linear sweep voltammetry and electrochemical impedance were done to confirm the performance of the ZIF-67 modified SRB bio-cathode. The synergy reduction of sulfate and Sb was accomplished by sulfide metal precipitation reaction from SRB itself. Maximum sulfate reduction rate approached 93.37 % and Sb removal efficiency could reach 92 %, which relies on the amount of sulfide concentration generated by sulfate reduction reaction, with 0.923 ± 0.04 m³ H₂/m³ of hydrogen before adding Sb and 0.857 m³ H₂/m³ of hydrogen after adding Sb. The hydrogen was mainly produced in this system and the result of gas chromatography (GC) indicated that 73.27 % of hydrogen was produced. Meanwhile the precipitates were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy to confirm Sb₂S₃ was generated from Sb (V).

Highly Sensitive and Reliable Piezoresistive Strain Sensor Based on Cobalt Nanoporous Carbon-Incorporated Laser-Induced Graphene for Smart Healthcare Wearables

The development of highly sensitive, reliable, and cost-effective strain sensors is a big challenge for wearable smart electronics and healthcare applications, such as soft robotics, point-of-care systems, and electronic skins. In this study, we newly fabricated a highly sensitive and reliable piezoresistive strain sensor based on polyhedral cobalt nanoporous carbon (Co-NPC)-incorporated laser-induced graphene (LIG) for wearable smart healthcare applications. The synergistic integration of Co-NPC and LIG enables the performance improvement of the strain sensor by providing an additional conductive pathway and robust mechanical properties with a high surface area of Co-NPC nanoparticles. The proposed porous graphene nanosheets exploited with Co-NPC nanoparticles demonstrated an outstanding sensitivity of 1,177 up to a strain of 18%, which increased to 39,548 beyond 18%. Additionally, the fabricated sensor exhibited an ultralow limit of detection (0.02%) and excellent stability over 20,000 cycles even under high strain conditions (10%). Finally, we successfully demonstrated and evaluated the sensor performance for practical use in healthcare wearables by monitoring wrist pulse, neck pulse, and joint flexion movement. Owing to the outstanding performance of the sensor, the fabricated sensor has great potential in electronic skins, human-machine interactions, and soft robotics applications.

Rapid adsorption of triclosan and p-chloro-m-xylenol by nitrogen-doped magnetic porous carbon

Contamination of water resources with organic substances like phenolic fungicides is undesirable due to the improvement of living standards, the huge production of chemicals, the heavy consumption of daily chemical products, and the growth of the population. In this study, Co-based zeolitic imidazole framework-67 (ZIF-67(Co)) was synthesized using the "one-pot method," and the best Co-based N-doped magnetic porous carbon (Co-NPC) was prepared by ZIF-67(Co) carbonization in an atmosphere of N₂. The materials were tested using an X-ray diffractometer (XRD), scanning electron microscope (SEM), infrared spectroscopy (IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption, and magnetization analysis. These characterizations indicated that the Co-NPC was successfully prepared. With the original morphology of ZIF-67(Co) crystals, the Co-NPC also has good porosity, magnetic properties, and a large specific surface area. In water, Co-NPC-800 has a good adsorption capacity for triclosan (TCS) and p-chloro-m-xylenol (PCMX), which are kinds of aromatic fungicides. The adsorption of Co-NPC-800 on both reached equilibrium within 3 min, which is in accordance with the quasi-second-order kinetic model. At 298 K, the maximum adsorption capacity of Co-NPC-800 for TCS and PCMX was 163 and 39 mg·g^-1, respectively. The adsorption of TCS and PCMX by Co-NPC-800 is a spontaneous endothermic process with reduced entropy. The combination of Co-NPC-800 and phenols come from multiple actions of electrostatic, π-π, and hydrogen bond effects. Moreover, Co-NPC-800 can be regenerated through simple washing and can be reused at least three times by a magnet. The Co-NPC-800 has good porosity, large specific surface area, comparable adsorption capacity, rapid adsorption time, so it could be broadly used in sewage treatments and other environmental fields.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO₂ and electrochemical synthesis of H₂ O₂ are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

Porous carbon nanoarchitectonics for the environment: detection and adsorption

As a post-nanotechnology concept, nanoarchitectonics has emerged from the 20th century to the 21st century. This review summarizes the recent progress in the field of metal-free porous carbon nanoarchitectonics.

Zeolitic imidazolate framework-derived porous carbon enhances methanogenesis by facilitating interspecies electron transfer: Understanding fluorimetric and electrochemical responses of multi-layered extracellular polymeric substances

Modulating microbial electron transfer during anaerobic digestion can significantly improve syntrophic interactions for enhanced biogas production. As a carbonaceous conductive material, zeolite imidazolate framework-67 (ZIF-67)-derived porous carbon (PC) was hypothesized to act as a microbial electron transfer highway and assessed with respect to understanding the fluorimetric and electrochemical responses of multilayered extracellular polymeric substances (EPS). The highest biomethane yield (614.0 mL/g) from ethanol was achieved in the presence of 100 mg/L PC prepared at a carbonization temperature of 800 °C (PC-800), which was 28.2% higher than that without PC addition. Electrochemical analysis revealed that both the redox peak currents and conductivity of the methanogenic sludge increased, while the free charge transfer resistance decreased with PC-800 addition. The conductive PC-800 potentially functioned as an abiotic electron conduit to promote direct interspecies electron transfer, thereby resulting in decreased expression of functional genes associated with electrically conductive pili (e-pili) and hemeproteins. Additionally, PC-800 stimulated the secretion of redox-active humic substances (HSs), and excitation emission matrix spectra analysis indicated that the largest increase in percent fluorescence response of HSs occurred in the tightly bound EPS (TB-EPS) with addition of PC-800. This was attributed to the strong complexation ability of PC-800 particles to hydroxyl/carboxylic/phenolic moieties of HSs contained in the TB-EPS. Microbial analysis revealed that syntrophic/exoelectrogenic bacteria such as Pelotomaculum and Syntrophomonas, as well as hydrogenotrophic/electrotrophic methanogens such as Methanoculleus and Methanobacterium, were enriched in methanogenic sludge with adding PC-800. This study provided comprehensive insights for understanding the interactions among ZIF-derived PC, methanogenic microorganisms and their multilayered EPS.

In situ formation of Co3O4 nanoparticles embedded N-doped porous carbon nanocomposite: a robust material for electrocatalytic detection of anticancer drug flutamide and supercapacitor application

The one-step synthesis of heteroatom-doped porous carbons is reported with the in situ formation of cobalt oxide nanoparticles for dual electrochemical applications (i.e., electrochemical sensor and supercapacitor). A single molecular template of zeolitic imidazole framework-67 (ZIF-67) was utilized for the solid-state synthesis of cobalt oxide nanoparticle-decorated nitrogen-doped porous carbon (Co₃O₄@NPC) nanocomposite through a facile calcination treatment. For the first time, Co₃O₄@NPC nanocomposite derived from ZIF-67 has been applied as an electrode material for the efficient electrochemical detection of anticancer drug flutamide (FLU). The cyclic voltammetry studies were performed in the operating potential from 0.15 to - 0.65 V (vs. Ag/AgCl). Interestingly, the fabricated drug sensor exhibited a very low reduction potential (- 0.42 V) compared to other  reported sensors. The fabricated sensor exhibited good analytical performance in terms of low detection limit (12 nM), wide linear range (0.5 to 400 μM), and appreciable recovery results (~ 98%, RSD 1.7% (n = 3)) in a human urine sample. Hereafter, we also examined the supercapacitor performance of the Co₃O₄@NPC-modified Ni foam in a 1M KOH electrolyte, and noticeable a specific capacitance of 525 F g^-1 at 1.5 A g^-1 was attained, with long-term cycling stability. The Co₃O₄@NPC nanocomposite supercapacitor experiments outperform the associated MOF-derived carbons and the Co₃O₄-based nanostructure-modified electrodes.

Cobalt and nitrogen co-doped porous carbon/carbon nanotube hybrids anchored with nickel nanoparticles as high-performance electrocatalysts for oxygen reduction reactions

Non-precious metal-nitrogen-carbon (MNC) materials have been recognized as alternatives to noble-metal catalysts, such as Au/C, Pt/C and Ru/C. As the precursors of MNC catalysts, carbonized zeolite imidazole frameworks (ZIFs) have been widely studied due to their porosity and the composition of ligands, including carbon and nitrogen. Herein, we successfully synthesize a non-precious metal-based ORR catalyst with nickel nanoparticles anchored on cobalt and nitrogen co-doped porous carbon/carbon nanotubes (Ni/Co-NC), employing ZIF-67 metal-organic frameworks as precursors. The Ni/Co-NC catalyst shows an excellent onset potential of 0.984 V and a half-wave potential of 0.869 V in 0.1 M KOH, comparable to those of commercial Pt/C. The excellent ORR performance of Ni/Co-NC was attributed to the synergistic coexistence of the atomically dispersed metal species coordinated with nitrogen (metal-N sites) and carbon-encapsulated nickel nanoparticles as well as the hierarchical porous structure in the catalyst. In addition, the Ni/Co-NC catalyst possesses outstanding anti-poisoning capacity and long-term duration against methanol crossover in an alkaline environment. The obtained results enable the Ni/Co-NC catalyst to explore potential applications in energy conversion and storage systems.

Enhancing Cr(VI) reduction and immobilization by magnetic core-shell structured NZVI@MOF derivative hybrids

Hexavalent chromium (Cr(VI)) has significantly threatened the environmental health because of its distinct toxicity. A novel magnetic core-shell structured NZVI@ZD composite was designed for simultaneous adsorption and reduction of Cr(VI). NZVI@ZD was synthesized by carbonization of the as-prepared core-shell structure NZVI@zeolitic imidazole framework-67 (ZIF-67). After carbonization, the original ZIF-67 shell shape was preserved well with marginal parts developing to graphitized carbon. Both cobalt (Co) and NZVI nanoparticles were finely dispersed in the porous ZIF-67 derivative (ZD). NZVI@ZD exhibited excellent removal performance for Cr(VI), owing to its high specific surface area and large pore size favorable for Cr(VI) adsorption and diffusion. The maximum adsorption capacity of NZVI@ZD for Cr(VI) was surprisingly as high as 226.5 mg g^-1, surpassing the pristine ZIF-67 (29.35 mg g^-1) and NZVI@ZIF-67 (36.53 mg g^-1). Zeta potential and X-ray photoelectron spectroscopy (XPS) spectra revealed that electrostatic attraction, reduction and precipitation might be involved in the Cr(VI) removal process by NZVI@ZD, resulting in the conversion of the adsorbed Cr(VI) to Cr(III) of lower toxicity and an eventual immobilization on the NZVI@ZD. The magnetic core-shell structured NZVI@ZD possessed superior adsorptive reactivity for Cr(VI) to most other traditional or newly reported materials, thus should be deemed highly efficient for Cr(VI)-contaminated wastewater treatment.

From metal-organic frameworks to porous carbon materials: recent progress and prospects from energy and environmental perspectives

Metal-organic frameworks (MOFs) have emerged as promising materials in the areas of gas storage, magnetism, luminescence, and catalysis owing to their superior property of having highly crystalline structures. However, MOF stability toward heat or humidity is considerably less as compared to carbons because they are constructed from the assembly of ligands with metal ions or clusters via coordination bonds. Transforming MOFs into carbons is bringing the novel potential for MOFs to achieve industrialization, and carbons with controlled pore sizes and surface doping are one of the most important porous materials. By selecting MOFs as a precursor or template, carbons with heteroatom doping and well-developed pores can be achieved. In this review, we discussed the state-of-art study progress made in the new development of MOF-derived metal-free porous carbons. In particular, the potential use of metal-free carbons from environmental and energy perspectives, such as adsorption, supercapacitors, and catalysts, were analyzed in detail. Moreover, an outlook for the sustainable development of MOF-derived porous carbons in the future was also presented.

MIL-100(Fe) and its derivatives: from synthesis to application for wastewater decontamination

MIL-100(Fe), an environmental-friendly and water-stable metal-organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications. Graphical abstract.

ZIF-67-Derived N-Doped Co/C Nanocubes as High-Performance Anode Materials for Lithium-Ion Batteries

Co nanoparticles embedded in nitrogen-doped carbon nanocubes (Co/NCs) for applications as anode materials in rechargeable lithium-ion batteries were synthesized by calcining Co-based metal-organic framework. Sizes of Co nanoparticles were ∼15 nm according to X-ray diffraction (XRD) and transmission electron microscopy. Electrochemical performances of the as-prepared anode nanocube composite at 700 °C showed a high initial capacity of 1375.1 mAh g^-1 in the voltage range of 0.01-3.0 V at the current rate of 0.1 A g^-1. After 100 cycles, capacity remained at 688.6 mAh g^-1. Thereinto, the role of Co nanoparticles in electrochemical reaction was also elucidated by in situ XRD experiment. Capacity increase of Co/NCs at the high currents was observed, which are potentially caused by the activation of electrode and pseudocapacitance during cycling. High surface area and abundant mesopores contributed to the improved electrochemical performances of the anode, providing numerous pathways and sites for Li⁺ transfer and storage and accordingly contributing to pseudocapacitance capacity.