A new approach for ultra-high adsorption of cationic methylene blue in a Zr-sulfonic-based metal–organic framework

A series of Zr-sulfonic-based metal–organic frameworks have been synthesized by the solvothermal method, namely VNU-17 and VNU-23. Particularly, VNU-17 and VNU-23 adopt the sulfonate group (SO₃⁻) moieties densely packed within their structure, which can efficiently uptake MB⁺ from wastewater. The maximum adsorption capacity for MB⁺ onto VNU-23 is up to 1992 mg g⁻¹ at pH = 7, which is more than five times that of activated carbon and possesses the highest value among all the reported MOF materials. In addition, VNU-23 retains the adsorption uptake of MB for at least five cycles. The adsorption isotherms and kinetic studies reveal that MB⁺ dye adsorption onto VNU-23 fits a Langmuir isotherm and the pseudo second order kinetic model. Furthermore, the ultra-high adsorption capacity of VNU-23 for MB dye can be accounted for by the suitable pore/channel size together with electrostatic attraction and π–π interactions. These results indicate that VNU-23 can be utilized as a promising candidate for removing MB⁺ from an aqueous medium.

A series of Zr-sulfonic-based metal–organic frameworks have been synthesized by the solvothermal method, namely VNU-17 and VNU-23.     

Synthesis of bimetallic–organic framework Cu/Co-BTC and the improved performance of thiophene adsorption

A bimetallic–organic porous material (Cu/Co-BTC) with a paddle-wheel structure has been successfully synthesized by a solvothermal approach. The as-synthesized materials were characterized by XRD, SEM, ICP-AES, UV-Vis, TGA and N₂ adsorption at 77 K. The prepared Cu/Co-BTC samples were investigated in thiophene (TP) adsorption from model gasolines by the fixed bed adsorption method at 298 K. The results showed that only a small amount of Co could be successfully introduced into the framework of HKUST-1, and the introduction of Co had little effect on the crystalline structure, morphology, porosity, and thermal stability. The bimetallic Cu/Co-BTC with a Cu/Co ratio of 174 displayed significantly improved adsorption desulfurization performance, showing an increase in breakthrough volume by 30% compared with HKUST-1, implying that the central metal in the MOF plays an important role in adsorption desulfurization. The addition of toluene or cyclohexene (3.20–3.30 vol%) as a competitor in the model gasoline led to a decline in desulfurization performance, especially when cyclohexene was added. The bimetallic Cu/Co-BTC showed a slight loss in breakthrough volume by only 5% after regenerating 7 times, displaying an excellent regeneration property.

The adsorbent Cu/Co-BTC-174 exhibited the largest breakthrough sulfur capacity, with an improvement by 30% in comparison to HKUST-1.     

Enhancement of photocatalytic hydrogen evolution with catalysts based on carbonized MOF-5 and g-C3N4

The study presents enhancement of photocatalytic hydrogen generation after metal–organic framework (MOF5) carbonization at 700 °C and its utilization as a co-catalyst of graphitic carbon nitride (gCN). Thermal treatment of MOF5 affected the formation of ZnO nanoparticles which played the role of co-catalyst for H₂ evolution. Moreover, significant band-gap narrowing of MOF5 was observed, which also affected the narrowing of the hybrid band gap. The appropriate conduction band position of the carbonized MOF allowed photogenerated electron transfer from gCN to the carbonized MOF, hence, improving the separation of the charge carriers and reducing the overpotential for H₂ generation. The mechanism of the photocatalytic process was also discussed.

The study presents enhancement of photocatalytic hydrogen generation after metal–organic framework (MOF5) carbonization at 700 °C and its utilization as a co-catalyst of graphitic carbon nitride (gCN).     

A multifunctional microporous metal–organic framework: efficient adsorption of iodine and column-chromatographic dye separation

In this work, a multifunctional microporous metal–organic framework (MOF), [Cd(ABTC)(H₂O)₂(DMA)]·4DMA (JLNU-4; JLNU = Jilin Normal University; H₄ABTC = 3,3′,5,5′-azobenzenetetracarboxylic acid), has been synthesized based on the ligand H₄ABTC under solvothermal conditions. JLNU-4 shows excellent uptake of iodine both in solution and in the vapor phase, owing to the existence of a microporous structure in JLNU-4. The adsorption kinetics during the process of iodine adsorption were analyzed via a series of qualitative and quantitative analyses, such as the Langmuir and Freündlich adsorption isotherms. In addition, according to UV/vis spectroscopy analysis and the colour variance of JLNU-4, the relatively small sized dye methylene blue (MB) could be efficiently adsorbed by JLNU-4, through size-exclusion effects. Particularly, JLNU-4 can serve as a column-chromatographic filler for the separation of dye molecules. Therefore, JLNU-4 is a multifunctional microporous MOF for iodine adsorption and column-chromatographic dye separation.

JLNU-4 shows excellent uptake of iodine and could selectively adsorb dyes; therefore it can be used for column-chromatographic dye separation.     

One-pot synthesis of cup-like ZSM-5 zeolite and its excellent oxidative desulfurization performance

A one-step method to synthesize small size cup-like hollow ZSM-5 single crystals is reported in this paper. Characterization methods show that the product has a typical ZSM-5 structure and most crystals are uniform, mono dispersed crystal shells with distinct hollow structure. The average size of a single crystal is about 350 nm. Every cup-like hollow ZSM-5 crystal can act as a microreactor in the reaction, and the ZSM-5 based catalyst POM-MOF-ZSM-5 (polyoxometalates (POM), metal–organic frameworks (MOF)) shows excellent oxidative desulfurization performance of DBT (dibenzothiophene).

One-pot synthesis of small size cup-like hollow ZSM-5 single crystals and their oxidative desulfurization performance.     

Active control of broadband plasmon-induced transparency in a terahertz hybrid metal–graphene metamaterial

A hybrid metal–graphene metamaterial (MM) is reported to achieve active control of broadband plasmon-induced transparency (PIT) in the THz region. The unit cell consists of one cut wire (CW), four U-shaped resonators (USRs) and monolayer graphene sheets under the USRs. Via near-field coupling, broadband PIT can be produced through the interference between different modes. Based on different arrangements of graphene positions, not only can we achieve electrical switching of the amplitude of broadband PIT, but can also realize modulation of the bandwidth of the transparent window. Simultaneously, both the capability and region of slow light can be dynamically tunable. This work provides schemes to manipulate PIT with more degrees of freedom, which will find significant applications in multifunctional THz modulation.

A hybrid metal–graphene metamaterial (MM) is reported to achieve active control of broadband plasmon-induced transparency (PIT) in the THz region.     

Formation of nickel–cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties

Here, nickel–cobalt sulphide particles embedded in graphene layers (porous Ni–Co–S@G), were successfully prepared by one-step annealing of metallocene/metal–organic framework (MOF) hybrids involving simultaneous carbonization and sulfidation. Benefiting from the porous structure, highly conductive graphene layers and large loading of super-capacitive Ni–Co–S, the obtained Ni–Co–S@G composites exhibited excellent electrochemical performance with a specific capacitance of 1463 F g⁻¹ at a current density of 1 A g⁻¹. A flexible solid-state asymmetric supercapacitor (ASC), assembled with Ni–Co–S@G and active carbon, demonstrated a high energy density of 51.0 W h kg⁻¹ at a power density of 650.3 W kg⁻¹. It is noteworthy that the ASC offered robust flexibility and excellent performance that was maintained when the devices were bent at various angles. The results indicate that the as-prepared materials could potentially be applied in high-performance electrochemical capacitors.

Ni–Co–S@graphene composites, derived from a metallocene/MOF precursor, presents high energy density and excellent cycling stability.     

Facile stabilization of a cyclodextrin metal–organic framework under humid environment via hydrogen sulfide treatment

Increasing resistance to humid environments is a major challenge for the application of γ-CD-K-MOF (a green MOF) in real-world utilisation. γ-CD-K-MOF–H₂S with enhanced moisture tolerance was obtained by simply treating MOF with H₂S gas. XPS, Raman and TGA characterizations indicated that the H₂S molecules coordinated with the metal centers in the framework. H₂S acting as a newly available water adsorption potential well near the potassium centers protects the metal–ligand coordination bond from attack by water molecules and thus improves the moisture stability of MOF. After 7 days exposure in 60% relative humidity, γ-CD-K-MOF–H₂S retained its crystal structure and morphology, while γ-CD-K-MOF had nearly collapsed. In addition, the formaldehyde uptake tests indicated that γ-CD-K-MOF retain their permanent porosity after interaction with H₂S. This simple and facile one-step strategy would open a new avenue for preparation of moisture stable MOFs for practical applications.

The moisture stable γ-CD-K-MOF was obtained by simply treating MOF with H₂S gas. H₂S acting as new water adsorption sites protected the metal–ligand bonds from water attack and thus enhanced the moisture resistance of γ-CD-K-MOF.     

In situ deposition of MOF199 onto hierarchical structures of bamboo and wood and their antibacterial properties

Tremendous efforts have been dedicated to developing functionalized cellulose materials by synthesis with copper-based metal–organic frameworks (MOF199), also known as HKUST-1. However, few studies have explored the deposition of MOFs on woody materials due to the complex chemical compositions of these materials (cellulose, hemicellulose, lignin) and their difficulty of bonding with MOF crystals. In this article, for the first time, MOF199 was successfully synthesized onto two different woody materials, moso bamboo and balsa wood, via in situ deposition at room temperature. The results show that the diverse surface roughness and the hierarchical structures of woody materials have significant effects on the size of MOF199 crystal. Additionally, bamboo and wood coated with MOF199 exhibited better antibacterial activities against Staphylococcus aureus (S. aureus) than Escherichia coli (E. coli); they could minimize S. aureus colony levels to 2.08 from 8.98 CFU cm⁻². This study provides a facile method for the functionalization of woody materials with MOFs for antibacterial applications.

MOF199 is deposited on moso bamboo and balsa wood under mild conditions. A uniform and dense MOF199 layer with perfect crystal morphology was successfully obtained on the hierarchical surface of both bamboo and wood.     

Adsorption of tetracycline antibiotics from an aqueous solution onto graphene oxide/calcium alginate composite fibers

In this study, we report the preparation of a novel environmentally friendly and highly efficient adsorbent, graphene oxide/calcium alginate (GO/CA) composite fibers, via a freeze-drying method using calcium chloride as a cross-linking reagent between graphene oxide and sodium alginate. The maximum tetracycline adsorption capacity of the GO/CA composite fibers predicted by the Langmuir model reached 131.6 mg g⁻¹. The adsorption properties of tetracycline onto the fibers were investigated through several parameters including the solution pH, the adsorbent dose, the initial concentration of tetracycline, and the agitation time. The Langmuir and Freundlich adsorption isotherms were used to investigate the adsorption equilibrium. The kinetics of the adsorption process was predicted using the pseudo-first-order and pseudo-second-order kinetic equations. Furthermore, the mechanism of adsorption was investigated, and it was found that the hydrogen bonding and π–π interaction should serve as predominant contributions to the significantly enhanced adsorption capability.

In this study, we report the preparation of a novel environmentally friendly and highly efficient adsorbent, graphene oxide/calcium alginate (GO/CA) composite fibers, via a freeze-drying method using calcium chloride as a cross-linking reagent between graphene oxide and sodium alginate.     

Early stages of phase selection in MOF formation observed in molecular Monte Carlo simulations

Metal–organic frameworks (MOF) comprising metal nodes bridged by organic linkers show great promise because of their guest-specific gas sorption, separation, drug-delivery, and catalytic properties. The selection of metal node, organic linker, and synthesis conditions in principle offers engineered control over both structure and function. For MOFs to realise their potential and to become more than just promising materials, a degree of predictability in the synthesis and a better understanding of the self-assembly or initial growth processes is of paramount importance. Using cobalt succinate, a MOF that exhibits a variety of phases depending on synthesis temperature and ligand to metal ratio, as proof of concept, we present a molecular Monte Carlo approach that allows us to simulate the early stage of MOF assembly. We introduce a new Contact Cluster Monte Carlo (CCMC) algorithm which uses a system of overlapping “virtual sites” to represent the coordination environment of the cobalt and both metal–metal and metal–ligand associations. Our simulations capture the experimentally observed synthesis phase distinction in cobalt succinate at 348 K. To the best of our knowledge this is the first case in which the formation of different MOF phases as a function of composition is captured by unbiased molecular simulations. The CCMC algorithm is equally applicable to any system in which short-range attractive interactions are a dominant feature, including hydrogen-bonding networks, metal–ligand coordination networks, or the assembly of particles with “sticky” patches, such as colloidal systems or the formation of protein complexes.

Clusters produced in simulations of MOF assembly at metal : ligand ratios of (a) 5 : 1 and (b) 1 : 1 with identical interaction potentials.     

Adsorption of aniline from aqueous solution using graphene oxide-modified attapulgite composites

Adsorption is an efficient treatment method for aniline removal in water treatment. In this work, the composites of graphene oxide-modified attapulgite were prepared and used firstly to remove aniline from wastewater. The composites were characterized by Fourier transformed infrared, Brunauer–Emmett–Teller, scanning electron microscopy and X-ray diffraction analysis. The effects of initial concentration, time, temperature and pH value on adsorption of aniline on graphene oxide-modified attapulgite are investigated. pH and temperature are found to have a significant influence on the adsorption amount. The experimental results showed that graphene oxide-modified attapulgite possesses strong adsorption ability for aniline with hydrogen bond interaction. The saturated adsorption amount could reach up to 90 mg g⁻¹ at pH = 2–4. The Langmuir isotherm is found to describe well the equilibrium adsorption data. Finally, graphene oxide-modified attapulgite is also observed to possess excellent reusability.

Adsorption is an efficient treatment method for aniline removal in water treatment.     

Europium ion post-functionalized zirconium metal–organic frameworks as luminescent probes for effectively sensing hydrazine hydrate

We describe a highly sensitive chemical sensor for the detection of the hydrazine hydrate. The chemical sensor was synthesized by simply doping a UiO-66 type metal–organic framework (MOF) with Eu³⁺ through a well-known post-synthetic modification method. The Eu³⁺@MOF was characterized by powder X-ray diffraction (PXRD), nitrogen gas adsorption isotherm measurements, FTIR, and ICP-MS. This luminescent probe exhibits strong emission intensity, and more significantly, displays various merits, such as high selectivity with notable photoluminescence quenching effect, rapid response time, and remarkable sensitivity with low detection of limit for hydrazine recognition. Under the optimal experimental conditions, hydrazine hydrate can be detected by this method in concentrations as low as 0.18 μM, which is much lower than the threshold limit value (10 ppb, ≈0.3 μM) of hydrazine exposure recommended by the U.S. Environmental Protection Agency (EPA). More interestingly, a portable film sensing device derived from this MOF display quick response to hydrazine hydrate within 90 s. A possible luminescent quenching mechanism for hydrazine hydrate was also investigated.

A luminescent metal–organic framework have been realized for efficiently sensing hydrazine hydrate.     

A 2D metal–organic framework/reduced graphene oxide heterostructure for supercapacitor application

Metal organic frameworks (MOFs) with two dimensional (2D) nanosheets have attracted special attention for supercapacitor application due to their exceptional large surface area and high surface-to-volume atom ratios. However, their electrochemical performance is greatly hindered by their poor electrical conductivity. Herein, we report a 2D nanosheet nickel cobalt based MOF (NiCo-MOF)/reduced graphene oxide heterostructure as an electrode material for supercapacitors. The NiCo-MOF 2D nanosheets are in situ grown on rGO surfaces by simple room temperature precipitation. In such hybrid structure the MOF ultrathin nanosheets provide large surface area with abundant channels for fast mass transport of ions while the rGO conductive and physical support provides rapid electron transport. Thus, using the synergistic advantage of rGO and NiCo-MOF nanosheets an excellent specific capacitance of 1553 F g⁻¹ at a current density of 1 A g⁻¹ is obtained. Additionally, the as synthesized hybrid material showed excellent cycling capacity of 83.6% after 5000 cycles of charge–discharge. Interestingly, the assembled asymmetric device showed an excellent energy density of 44 W h kg⁻¹ at a power density of 3168 W kg⁻¹. The electrochemical performance obtained in this report illustrates hybridization of MOF nanosheets with carbon materials is promising for next generation supercapacitors.

In this 2D NiCo-MOF/rGO hybrid, the MOF nanosheets provide abundant active sites while the conductive rGO provide rapid electron transport.     

Effect of thiophene S on the enhanced ORR electrocatalytic performance of sulfur-doped graphene quantum dot/reduced graphene oxide nanocomposites

In this study, a novel and simple hydrothermal method was developed to synthesize sulfur-doped graphene quantum dots (S-GQDs) with a diameter of 1–6 nm and S-GQD/reduced graphene oxide hybrids. The results indicated that an increase in the sulfur content led to superior ORR electrocatalytic activity. Moreover, it is found that thiophene S plays a significant role in the electrocatalytic activity. In addition, the average electron transfer number depends on the content of thiophene S. It is believed that the proposed synthesis strategy is a general and effective method for designing high-performance metal-free electrocatalytic materials.

Thiophene S of sulfur-doped graphene quantum dots play an important role in electrocatalysis by increasing the electron transfer numbers.     

Novel porous iron phthalocyanine based metal–organic framework electrochemical sensor for sensitive vanillin detection

Vanillin is widely used as a flavor enhancer and is known to have numerous other interesting properties, including antidepressant, anticancer, anti-inflammatory, and antioxidant effects. However, as excess vanillin consumption can affect liver and kidney function, simple and rapid detection methods for vanillin are required. Herein, a novel electrochemical sensor for the sensitive determination of vanillin was fabricated using an iron phthalocyanine (FePc)-based metal–organic framework (MOF). Scanning electron microscopy and transmission electron microscopy showed that the FePc MOF has a hollow porous structure and a large surface area, which impart this material with high adsorption performance. A glassy carbon electrode modified with the FePc MOF exhibited good electrocatalytic performance for the detection of vanillin. In particular, this vanillin sensor had a wide linear range of 0.22–29.14 μM with a low detection limit of 0.05 μM (S/N = 3). Moreover, the proposed sensor was successfully applied to the determination of vanillin in real samples such as vanillin tablets and human serum.

A novel electrochemical sensor based on an iron phthalocyanine (FePc) MOF for the sensitive detection of vanillin.     

Electrochemical characterization of and theoretical insight into a series of 2D MOFs, [M(bipy)(C4O4)(H2O)2]·3H2O (M = Mn (1), Fe (2), Co (3) and Zn (4)), for chemical sensing applications

The electrochemical sensing applications of a series of water-stable 2D metal–organic framework (MOF)-modified screen-printed carbon electrodes (SPCEs) are reported. The MOF materials in this study are [M(bipy)(C₄O₄)(H₂O)₂]·3H₂O, in which bipy = 4,4′-bipyridine and M = Mn, Fe, Co and Zn. The MOF materials are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing that the MOFs have a layer-by-layer rod structure with a smooth surface. We use the nitrofurazone molecule as a probe to investigate the influence of the metal ions of MOFs on electrochemical sensing ability. Cyclic voltammetry demonstrated that the Mn-MOF electrode of interest delivered stronger signals than that of other electrodes. Through first-principles calculations, we also revealed that the change in the spin polarization of divalent metal ions passing from the free ion state to the MOF environment appeared to be significantly correlated with the enhancement in the peak response current. The theoretical and experimental results consistently indicate that Mn-MOF has the smallest bandgap and good sensitivity among these MOF materials. Accordingly, we proposed a simple model to illustrate this observation and disclosed the importance of the electron configuration of the transition metal constructing the MOF materials used in improving electrochemical sensing applications.

Framework-to-metal charge transfer of the MOF materials results in enhancing electrochemical sensing ability to nitrofurazone.     

Superhydrophobic and superoleophilic graphene aerogel for adsorption of oil pollutants from water

Three-dimensional graphene based materials with superhydrophobic/superoleophilic attributes are highly desirable for water treatment. The graphene aerogel (GA) was prepared by hydrothermal reaction of the graphene oxide (GO) solution in the presence of dopamine followed by freeze-drying. The subsequent surface modification of GA using fluoroalkylsilane occurred by a vapor–liquid deposition process. The superhydrophobic graphene aerogel (SGA) fabricated from GA exhibits superhydrophobicity and superoleophilicity with the water contact angle of 156.5° and the oil contact angle of 0°. With this property, SGA could selectively adsorb various types of oils/organic solvents from the oil–water mixture. Moreover, the SGA possesses excellent low bulk density (9.6 mg cm⁻³), high absorption capacity (110–230 fold weight gain), and superior adsorption recyclability. With all these desirable features, the SGA is a promising candidate for oil-polluted water remediation.

SGA with superhydrophobic and oleophilic properties was prepared from a PDA functionalized graphene aerogel via a hydrothermal method and subsequent hydrophobic modification using fluoroalkylsilane through vapor–liquid deposition.     

Ultrathin 2D metal–organic framework nanosheets prepared via sonication exfoliation of membranes from interfacial growth and exhibition of enhanced catalytic activity by their gold nanocomposites

Ultrathin two-dimensional (2D) metal–organic framework (MOF) nanosheets were prepared by a facile sonication exfoliation of MOF membranes from interfacial growth. The stacked form of nanosheets constituting the MOF membranes was significantly different to that of its layered MOF counterparts. This led to decreased interaction between nanosheets, so they could exfoliate readily from the MOF membranes. Moreover, Au nanoparticles were introduced to form nanocomposites. Enhanced catalytic activity and long-term stability of these nanocomposites were observed by a model reaction of the reduction of 4-nitrophenol to 4-aminophenol. This preparation method could be extended to other 2D MOF nanosheets and their nanocomposites.

Cu-MOF nanosheets were prepared by sonication exfoliation and the Au/Cu-MOF nanocomposites exhibited higher catalytic activity than pure Au NPs.     

Polyvinylpyrrolidone-assisted synthesis of highly water-stable cadmium-based metal–organic framework nanosheets for the detection of metronidazole

Recently, much effort has been dedicated to ultra-thin two-dimensional metal–organic framework (2D MOF) nanosheets due to their outstanding properties, such as ultra-thin morphology, large specific surface area, abundant modifiable active sites, etc. However, the preparation of high-quality 2D MOF nanosheets in good yields still remains a huge challenge. Herein, we report 2D cadmium-based metal–organic framework (Cd-MOF) nanosheets prepared in a one-pot polyvinylpyrrolidone (PVP)-assisted synthesis method with high yield. The Cd-MOF nanosheets were characterized with good stability and dispersion in aqueous systems, and were highly selective and sensitive to the antibiotic metronidazole (MNZ) with low limit of detection (LOD: 0.10 μM), thus providing a new and promising fluorescent sensor for rapid detection of MNZ in aqueous solution.

Except PVP was added for Cd-MOF nanosheets, the preparation process of bulk and Cd-MOF nanosheets was similar.