Pristine ZIF-8 Research Articles

Enhancing CO2/CH4 and CO2/N2 separation performances of ZIF-8 by post-synthesis modification with [BMIM][SCN

Ionic liquid (IL)-incorporated metal organic frameworks (MOFs) are promising materials for gas adsorption and separation processes. In this work, 1-n-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) was incorporated in a zeolitic imidazolate framework (ZIF-8) to examine the adsorption and separation of different gases. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results confirmed that ZIF-8 retains its structural integrity in the IL-incorporated sample. The Brunauer–Emmett–Teller (BET) surface area and pore volume of the IL-incorporated sample decreased significantly indicating the IL confinement into the MOF. Results of thermogravimetric analysis (TGA) demonstrate changes in the decomposition temperatures of both bulk IL and pristine ZIF-8 when the IL was incorporated into the MOF pores. Fourier transform infrared (FTIR) spectroscopy was performed to confirm the presence of interactions and successful incorporation of IL into MOF. Gas adsorption isotherms of CO2, CH4, and N2 were measured for pristine ZIF-8 and IL-incorporated ZIF-8. The uptake amounts for each gas decreased as compared to their values on pristine ZIF-8, however, the decrease in the CO2 uptake was less compared to CH4 and N2. The IL-incorporated sample exhibited approximately 2.6-times higher ideal selectivity for CO2/CH4 and four-times higher ideal selectivity for CO2/N2 at 1 mbar than their corresponding values for pristine ZIF-8. These results indicate that IL-MOF combinations offer a huge potential for gas separations.

Recovery of Au(III) from leach solutions using thiourea functionalized zeolitic imidazolate frameworks (TU*ZIF-8)

Metal organic frameworks (MOFs) have diverse applications in adsorption/separation fields. However, little is known about MOFs as adsorbents for the adsorption of Au(III) from aqueous solutions. In this work, a highly porous MOFs, ZIF-8, was modified by thiourea (TU) via coordination-based post-synthetic modification strategy. Compared with pristine ZIF-8, the TU functionalized ZIF-8, TU*ZIF-8, exhibited a remarkable Au(III) adsorption ability with a saturation adsorption capacity of 4262.8 mg/g although its surface area and pore volume decreased with TU loading. Interestingly, the adsorption efficiency of Au(III) was >99% with a broad Au(III) concentration range of 50–400 mg/L using only 20 mg TU*ZIF-8. Meanwhile, TU*ZIF-8 showed an encouraging selectivity for Au(III) in the presence of some metal ions such as Cu(II), Cr(VI), Pb(II), Cd(II), Mn(II), Mg(II), and Co(II). The improved adsorption of Au(III) on TU*ZIF-8 is explained by the synergistic effect of electrostatic interaction and coordination interaction. Particularly, the coordination interaction between Au(III) and TU of TU*ZIF-8 plays a major role in the Au(III) adsorption process of TU*ZIF-8. This work suggests a potential application of functionalized MOFs for the efficient recovery of gold from aqueous solutions.

Facile synthesis of PEI-GO@ZIF-8 hybrid material for CO2 capture

Pristine graphene oxide (GO) sheets were pretreated with polyethyleneimine (PEI) to prepare PEI-modified GO (PEI-GO), which was further inserted with ZIF-8 crystals to form a novel PEI-GO@ZIF-8 nanocomposite for CO2 capture. The good dispersion of PEI and interlayer growth of ZIF-8 within the GO sheets is helpful for high CO2 adsorption. Therefore, the PEI-GO@ZIF-8 nanocomposite show high surface area and enhanced CO2 adsorption capacity. The adsorption capacity of the PEI-GO@ZIF-8 nanocomposite was six times higher than that of the pristine GO and ZIF-8. The CO2/N2 adsorption selectivity was significantly improved due to amine groups loading which provide more sites for CO2 adsorption. The preferential adsorption of CO2 over N2 makes PEI-GO@ZIF-8 nanocomposite be a promising candidate in the field of CO2 capture.

Design of ZIF-8/ion copolymer hierarchically porous material: Coordination effect on the adsorption and diffusion for carbon dioxide

The novel CO2 adsorbent (ZPMAC) was constructed by a facile in-situ growth of ZIF-8 onto the surface of a mesoporous amino-functionalized ion copolymer (PMAC). The existence of coordination effect between Zn2+ from ZIF-8 and nitrogen atom from the amino-alkyl chain in PMAC changed the pore structure of substrate for enhancing the amount of CO2 capture and accelerated the rate of CO2 adsorption. The ion copolymer PMAC, pristine ZIF-8 and hierarchically porous hybrid material ZPMAC were characterized by SEM, TEM, TGA, N2 adsorption-desorption, FT-IR, XRD, UV, and XPS techniques. It was observed that ZIF-8 loaded on the surface of PMAC uniformly and tightly. In the growth process of ZIF-8 nanoparticles, zinc ions were firstly coordinated with nitrogen atoms of the amino-alkyl chain in PMAC sample, and subsequently reacted with 2-methylimizadole to generate ZIF-8 nanoparticles. Obviously, the surface areas of ZPMAC increased and smaller peak value of micropore distribution was generated by the strong coordination interaction between ZIF-8 and PMAC after ZIF-8 modified. Meanwhile, the appearance of hierarchically porous structure was conducive to the transportation and adsorption of CO2 molecules, thus enhancing the amount of CO2 capture and the rate of adsorption effectively. This study was intended to design a new kind of hybrid materials by the means of in-situ growth of MOF materials onto the IL-type polymers and further study the influences of the structure and properties of ionic-type hybrid materials on the absorption capacity to meet the requirements of various applications.

Incorporation of acetate-based ionic liquids into a zeolitic imidazolate framework (ZIF-8) as efficient sorbents for carbon dioxide capture

Tuning the interior pores of solid sorbents to improve their adsorption characteristics is considered an effective approach to enhance gas separation performance. Herein, we examine the improvement of carbon dioxide (CO2) capture performance of a ZIF-8 impregnated with ionic liquid 1-Butyl-3-methylimidazolium Acetate [Bmim][Ac] and 1-Ethyl-3-methylimidazolium Acetate [Emim][Ac]. The synthesis and detailed characterizations of the developed composite materials are reported, and the impact of ionic liquid (IL) loading is studied. Fourier transform infrared (FTIR) spectroscopy was used to confirm the impregnation of the ILs into the pores of ZIF-8 and thermogravimetric analysis (TGA) was carried out to study the thermal stability of the composite materials. The powder X-ray diffraction (XRD) pattern of the ILs@ZIF-8 samples revealed that the crystal structure of ZIF-8 remained intact after the impregnation process. The Brunatuer–Emmett–Teller (BET) surface area and pore volumes have significantly decreased up to 80% for [Bmim][Ac]@ZIF-8 with 30 wt% IL loading confirming the presence of ILs inside the internal pores of ZIF-8. CO2 and N2 adsorption isotherms of the ILs@ZIF-8 composites were evaluated gravimetrically at (303, 313, and 323) K. The impregnated samples exhibited substantially higher CO2 uptake and CO2/N2 selectivity at all studied temperatures of up to 7 times higher the CO2 capacity at 0.2 bar and 303 K for [Bmim][Ac]@ZIF-30 as compared to the pristine ZIF-8. Findings from this work provide insights into the synthesis, structure, and sorption capacity of these novel composite materials, which could be utilized for the design of sorbents with outstanding properties to meet the environmental challenges.

Recovery of Acid-Gas-Degraded Zeolitic Imidazolate Frameworks by Solvent-Assisted Crystal Redemption (SACRed).

The acid stability of zeolitic imidazolate frameworks (ZIFs) is an important issue hindering their application. Acid-gas damage of ZIFs has been considered irreversible. However, we demonstrate a methodology called solvent-assisted crystal redemption (SACRed) to reverse acid-gas damage to ZIFs with a high degree of structural and functional recovery. For example, post-SACRed ZIF-8 is shown to be structurally and chemically near-identical with the original pristine ZIF-8 that suffered a large loss of surface area, porosity, and crystallinity during acid-gas exposure. We also provide mechanistic insight into the recovery process using deuterium-labeled linkers and 2H NMR spectroscopy. SACRed treatments could allow large extensions in the lifetime of ZIF-based membranes and adsorbents that degrade over time.

Inorganic Nanoparticles/Metal Organic Framework Hybrid Membrane Reactors for Efficient Photocatalytic Conversion of CO2.

Photocatalytic conversion of carbon dioxide (CO2) to useful products has potential to address the adverse environmental impact of global warming. However, most photocatalysts used to date exhibit limited catalytic performance, due to poor CO2 adsorption capacity, inability to efficiently generate photoexcited electrons, and/or poor transfer of the photogenerated electrons to CO2 molecules adsorbed on the catalyst surface. The integration of inorganic semiconductor nanoparticles across metal organic framework (MOF) materials has potential to yield new hybrid materials, combining the high CO2 adsorption capacity of MOF and the ability of the semiconductor nanoparticles to generate photoexcited electrons. Herein, controlled encapsulation of TiO2 and Cu-TiO2 nanoparticles within zeolitic imidazolate framework (ZIF-8) membranes was successfully accomplished, using rapid thermal deposition (RTD), and their photocatalytic efficiency toward CO2 conversion was investigated under UV irradiation. Methanol and carbon monoxide (CO) were found to be the only products of the CO2 reduction, with yields strongly dependent upon the content and composition of the dopant semiconductor particles. CuTiO2 nanoparticle doped membranes exhibited the best photocatalytic performance, with 7 μg of the semiconductor nanoparticle enhancing CO yield of the pristine ZIF-8 membrane by 233%, and methanol yield by 70%. This work opens new routes for the fabrication of hybrid membranes containing inorganic nanoparticles and MOFs, with potential application not only in catalysis but also in electrochemical, separation, and sensing applications.

Agar Aerogel Containing Small-Sized Zeolitic Imidazolate Framework Loaded Carbon Nitride: A Solar-Triggered Regenerable Decontaminant for Convenient and Enhanced Water Purification

Although ZIF-based adsorbents are promising for environmental remediation, their performance is limited by their large crystal size, intrinsic fragility, and poor processability and reusability. To this end, in this work, highly dispersed and small sized (14.95 nm) metal–organic frameworks (MOFs), via the restriction of overgrowth and agglomeration on carbon nitride (C3N4) nanosheets, are integrated into agar aerogel, forming a flexible and efficient aerogel absorbent with photocatalytic activity. This separation-free hybrid aerogel mantaining the crystal structure of zeolitic imidazolate framework (ZIF-8) with smaller size exhibits a 1.44 times greater adsorption capacity for dye than that of pristine bulk ZIF-8. Most importantly, the introduction of C3N4 nanosheets not only regulates the growth of ZIF-8 crystals but also enables the hybdrid aerogel with stable reusability throughout five consecutive adsorption–degradation cycles, obtained via solar irradiation. This ecofriendly, regeneration technology ...

In Situ Growth of Self-Assembled ZIF-8-Aminoclay Nanocomposites with Enhanced Surface Area and CO2 Uptake.

Self-assembly of metal-organic framework (MOF) nanoparticles (NPs) with a functional material can result in MOF nanocomposites having new and advanced properties along with the fabrication of new nanoscopic structures. However, such assembly of MOFs has not been realized to date. Here we report self-assembled nanocomposites of the zeolitic imidazolate framework (ZIF-8) and layered aminoclay (AC) for the first time, and the ZIF-8@AC composites exhibit significantly enhanced adsorption properties in comparison to those of pristine ZIF-8 nanoparticles. Four different composites denoted as ZIF-8@AC-1, ZIF-8@AC-2, ZIF-8@AC-3, and ZIF-8@AC-4 were synthesized by varying the clay content, and their AC contents were found to be 12.1, 18.3, 22.2, and 27.2 wt %, respectively. The composites were thoroughly characterized by PXRD, FTIR, Raman, and various microscopic techniques (FESEM, TEM, and STEM). The formation of the composites is driven by the specific interaction between unsaturated Zn(II) sites of ZIF-8 nanoparticles and NH2 groups of the aminoclay, which was validated from ζ potential and Raman spectroscopic measurements. The adsorption studies of the desolvated composites were also carried out in detail. The best performance is achieved with one of the composites, which exhibits a 42% increase in BET surface area while CO2 uptake at 298 K is doubled in comparison to the ZIF-8 nanoparticles.

ZIF-8 Films Prepared by Femtosecond Pulsed-Laser Deposition

As metal–organic frameworks (MOFs) are coming of age, processing strategies and morphology engineering have gained considerable importance, given the need of thin film geometries for many applications. Using the femtosecond pulsed-laser deposition (femto-PLD) technique, we have fabricated films of the zeolitic imidazolate framework (ZIF) zinc 2-methylimidazolate (ZIF-8) for the first time, thus extending the available film fabrication techniques for MOFs to physical vapor deposition. While deposition of pristine ZIF-8 turned out to be unsuccessful, we demonstrate that hybrid ZIF-8 impregnated with polyethylene glycol 400 as a “vehicle” ablate under ultrahigh vacuum conditions to form films with approximate composition Zn(C3N2H2–CH3)2·1/6PEG-400. By washing the films with ethanol, the polyethylene glycol (PEG) additive can be removed, leading to pure ZIF-8 films on sapphire substrates. The target films and powders were comprehensively characterized by diffraction, spectroscopic and microscopic techniques as well as thermogravimetry and Ar physisorption measurements.

Improving Gas Separation Performance of ZIF-8 by [BMIM][BF4] Incorporation: Interactions and Their Consequences on Performance

Gas separation performance of the zeolitic imidazolate framework (ZIF-8) was improved by incorporating an ionic liquid (IL), 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). Detailed characterization based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed that the morphology of ZIF-8 remains intact upon IL incorporation up to 28 wt %. Thermogravimetric analysis indicated the presence of direct interactions between the IL and metal organic framework (MOF). FTIR spectroscopy illustrated that the anion of the IL was shared between the imidazolate framework and [BMIM]+ cation. Adsorption isotherms of CO2, CH4, and N2 measured for pristine ZIF-8 and IL-loaded ZIF-8 samples, complemented by grand canonical Monte Carlo (GCMC) simulations, showed that these interactions influence the gas uptake performance of ZIF-8. CH4 and N2 uptakes decreased in the whole pressure range, while CO2 uptake first increased by approximately 9% at 0.1 bar in 20 wt % IL-loaded sample and then d...

Nickel-Platinum Nanoparticles Supported on Zeolitic Imidazolate Framework/Graphene Oxide as High-Performance Adsorbents for Ambient-Temperature Hydrogen Storage

A facile liquid impregnation method followed by a reduction treatment was applied for loading transition metals nickel, nickel-platinum, and platinum into zeolitic imidazolate framework (ZIF-8)/graphene oxide (GO) as potential adsorbents for ambient-temperature hydrogen storage. These materials have been characterized by powder X-ray diffraction, infrared spectra, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma-emission spectroscopy, and gas adsorption apparatus for their physical and chemical properties. The metal-doped ZIF-8/GO composites maintained the morphology of pristine ZIF-8, although their specific surface areas significantly decreased. The metal nanoparticles in the corresponding composites have average diameters of 4.2–5.1 nm, and uniformly located on the external surface and edges of ZIF-8/GO network. Hydrogen adsorption amounts on metal-doped samples were enhanced by factors of 2.3–3.8 times over ZIF-8 at 298 K due to the spillover effect. Notably, the Pt-doped ZIF-8/GO sample seems to be the best adsorbent for hydrogen storage because of the higher catalytic reactivity of platinum than nickel.

Novel amine modification of ZIF-8 for improving simultaneous removal of cationic dyes from aqueous solutions using supported liquid membrane

Effect of amine modification of ZIF-8 on pertraction of mixed Rhodamine B (RhB) and Methylene blue (MB) cationic dye in aqueous solution was studied using flat sheet supported liquid membrane (SLM). Mixtures of mono-(2-etylhexyl) ester of phosphoric acid (M2EHPA), bis-(2-etylhexyl) ester of phosphoric acid (D2EHPA) and nanoparticles were used as carrier and Sesame oil as diluent. Microporous hydrophobic PTFE membrane was used as support for liquid membrane, and strip phase was acetic acid. It was found that loading of amine modified ZIF-8 nanoparticles in carrier, increases the dyes pertraction efficiency more than the pristine ZIF-8 nanoparticles and the optimum loading was obtained as 2000mgL−1.Response surface methodology (RSM) based on Box-Benken design (BBD) with optimum amine modified ZIF-8 nanoparticles loading was used to design the experiments and analyze the effects of three major operating parameters including feed concentration, carrier concentration and initial feed phase pH. The optimum pertraction efficiency for MB and RhB were found as 88.3 and 99.1% respectively and obtained after 10h in feed concentration of 100mgL−1, carrier concentration of 35 vol.% and initial feed phase pH of 6.

Surfactant-assisted synthesis of ZIF-8 nanocrystals for phthalic acid adsorption

Phthalic acid (H2-PA) is the main degradation product of phthalic acid esters, which have been classified as priority pollutants in wastewater. The separation of H2-PA from waste water is thus of urgent importance for environmental protection. Here, zeolitic imidazole framework (ZIF-8) nanoparticles with different pore structures were prepared by a surfactant mediated method in aqueous solution and the effects of their pore structures on H2-PA removal were studied. The results showed that the ZIF-8 samples with high mesoporosity exhibited much faster adsorption rate than the pristine ZIF-8. The adsorption equilibrium data were well described by Freundlich isotherm model and the kinetics followed a pseudo-second-order kinetic equation/mechanism.

Beneficial cooperative effect between Pd nanoparticles and ZIF-8 material for hydrogen storage

One of the most interesting strategies for improving hydrogen storage capacity at room temperature in porous solids is the inclusion of catalytically-active metal nanoparticles to provide the spillover effect in MOF materials. However, there is a great controversy in the adsorption literature about this topic due to the low reproducibility of results and the lack of knowledge about this mechanism. In the present work, 5–9 nm Pd nanoparticles were homogeneously dispersed in a ZIF-8 material by a simultaneous liquid impregnation and chemical reduction with hydrazine. After verifying the structural and textural properties, the so obtained Pd/ZIF-8 material was tested in H2 and D2 adsorption–desorption analysis in order to determine its final hydrogen adsorption properties as well as to understand the involved mechanism in the hydrogen retention over the sample. Pd/ZIF-8 material showed a completely reversible hydrogen storage capacity at room temperature 30% higher than that of the pristine ZIF-8, being only 3% related to PdH0.18 formation. These results provide a better knowledge of the hydrogen retention mechanism by spillover in Pd-doped MOF materials, being useful in the designing of new materials for hydrogen storage at room temperature.

Effect of catalyst loading on hydrogen storage capacity of ZIF-8/graphene oxide doped with Pt or Pd via spillover

In this work, a series of zeolitic imidazolate framework (ZIF-8)/graphene oxide (GO) supported Pt or Pd nanoparticles (NPs) with different loading amounts were obtained via a simple liquid impregnation of ZIF-8/GO with metal salt solution followed by a reduction treatment. Powder X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma-emission spectroscopy, and nitrogen adsorption-desorption measurements were employed to investigate the physical and chemical properties of as-prepared samples. The Pt and Pd particles in the corresponding composites have average diameters of about 4.5 and 4.6 nm, respectively. All metal-doped ZIF-8/GO composites maintained the host framework of pure ZIF-8, although their specific surface areas were significantly reduced. The introduction of metal catalysts into the ZIF-8/GO matrix does not favor the hydrogen adsorption performance at 77 K due to the physisorption mechanism. In contrast, the adsorption isotherms at 298 exhibited dramatically improved storage capacities, by factors of 3.8–11.8 (Pt-doped ZIF-8/GO) and 7.9–12.6 (Pd-doped ZIF-8/GO) times over pristine ZIF-8 at the hydrogen pressure of 860 mmHg. This enhancement is mainly attributed to the spillover mechanism by metal catalysts into the ZIF-8/GO support. More importantly, the effect of catalysts dispersion and content on the level of hydrogen storage was also explored, which showed that the composites with the most homogeneous metal distribution and moderate loading amount would display the highest hydrogen adsorption performance.

Anglo American Platinum invests in US FCEV value chain

One of the most interesting strategies for improving hydrogen storage capacity at room temperature in porous solids is the inclusion of catalytically-active metal nanoparticles to provide the spillover effect in MOF materials. However, there is a great controversy in the adsorption literature about this topic due to the low reproducibility of results and the lack of knowledge about this mechanism. In the present work, 5–9 nm Pd nanoparticles were homogeneously dispersed in a ZIF-8 material by a simultaneous liquid impregnation and chemical reduction with hydrazine. After verifying the structural and textural properties, the so obtained Pd/ZIF-8 material was tested in H2 and D2 adsorption–desorption analysis in order to determine its final hydrogen adsorption properties as well as to understand the involved mechanism in the hydrogen retention over the sample. Pd/ZIF-8 material showed a completely reversible hydrogen storage capacity at room temperature 30% higher than that of the pristine ZIF-8, being only 3% related to PdH0.18 formation. These results provide a better knowledge of the hydrogen retention mechanism by spillover in Pd-doped MOF materials, being useful in the designing of new materials for hydrogen storage at room temperature.

Stabilization of graphene quantum dots (GQDs) by encapsulation inside zeolitic imidazolate framework nanocrystals for photoluminescence tuning

Luminescent graphene quantum dots (GQDs) are encapsulated and stabilized in Zeolitic Imidazolate Framework (ZIF-8) nanocrystals. The GQDs are well confined due to the adsorption on the growing face of the ZIF-8 nanocrystals and have a profound effect on the shape of the nanocrystals from rhombic dodecahedron to spherical. Stabilizing GQDs inside the ZIF-8 nanocrystals results in tailoring of the photoluminescence emission (ca. 32 nm, bathochromic shift) of the GQD@ZIF-8 nanocrystal composite even after 3 months of aging under normal laboratory conditions. Also the water adsorption (at STP) capacity increased for the GQD@ZIF-8 composite as compared to the pristine ZIF-8.