Towards implementing hierarchical porous zeolitic imidazolate frameworks in dye-sensitized solar cells.
ABSTRACT: A one-pot method for encapsulation of dye, which can be applied for dye-sensitized solar cells (DSSCs), and synthesis of hierarchical porous zeolitic imidazolate frameworks (ZIF-8), is reported. The size of the encapsulated dye tunes the mesoporosity and surface area of ZIF-8. The mesopore size, Langmuir surface area and pore volume are 15 nm, 960-1500 m2 · g-1 and 0.36-0.61 cm3 · g-1, respectively. After encapsulation into ZIF-8, the dyes show longer emission lifetimes (greater than 4-8-fold) as compared to the corresponding non-encapsulated dyes, due to suppression of aggregation, and torsional motions.
Project description:Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m(2)/g), high thermal stability (up to 550 degrees C), and remarkable chemical resistance to boiling alkaline water and organic solvents.
Project description:A water stable and hybrid nonporous adsorbent, cubic zeolitic imidazolate framework-8 (ZIF-8), was synthesized for Acid orange 7 (AO7) removal from aqueous solutions in batch mode. Central composite design was utilized to explore the individual and interaction effects of pH, AO7 concentration, ZIF-8 dosage and contact time on dye adsorption. A second order polynomial equation (R2 = 0.9852, LOF = 0.1419) developed for prediction of the AO7 removal. Sorption model revealed that the adsorbent dosage and the dye concentration are major factors that controlled the AO7 removal efficiency. AO7 removal increased from 55 to 80% by increasing ZIF-8 dosage from 0.2 to 1 g/L. The dye removal, on the other hand, decreased from 84 to 70% with increasing AO7 concentration from 10 to 100 mg/L and increased from 60% to 80% by decreasing pH from 12 to 4. The dye removal followed the pseudo second order kinetic and the Langmuir isotherm model. The maximum monolayer adsorption capacity of 80.47 mg dye/g of ZIF-8 was obtained according to the Langmuir model.
Project description:We investigate the pressure-dependent mechanical behaviour of the zeolitic imidazolate framework ZIF-4 (M(im)2; M2+ = Co2+ or Zn2+, im- = imidazolate) with high pressure, synchrotron powder X-ray diffraction and mercury intrusion measurements. A displacive phase transition from a highly compressible open pore (op) phase with continuous porosity (space group Pbca, bulk modulus ?1.4 GPa) to a closed pore (cp) phase with inaccessible porosity (space group P21/c, bulk modulus ?3.3-4.9 GPa) is triggered by the application of mechanical pressure. Over the course of the transitions, both ZIF-4 materials contract by about 20% in volume. However, the threshold pressure, the reversibility and the immediate repeatability of the phase transition depend on the metal cation. ZIF-4(Zn) undergoes the op-cp phase transition at a hydrostatic mechanical pressure of only 28 MPa, while ZIF-4(Co) requires about 50 MPa to initiate the transition. Interestingly, ZIF-4(Co) fully returns to the op phase after decompression, whereas ZIF-4(Zn) remains in the cp phase after pressure release and requires subsequent heating to switch back to the op phase. These variations in high pressure behaviour can be rationalised on the basis of the different electron configurations of the respective M2+ ions (3d10 for Zn2+ and 3d7 for Co2+). Our results present the first examples of op-cp phase transitions (i.e. breathing transitions) of ZIFs driven by mechanical pressure and suggest potential applications of these functional materials as shock absorbers, nanodampers, or in mechanocalorics.
Project description:Zeolitic imidazolate framework-8 (ZIF-8) has received wide attention in recent years as a potential drug vehicle for the treatment of cancer due to its acid-responsiveness and moderate biocompatibility. However, its congenital deficiency of intrinsic imaging capability limits its wider applications; therefore, a postsynthetic exchange approach was utilized to introduce paramagnetic manganese(II) ions into the ZIF-8 matrix. As a result, bimetallic zeolitic imidazolate frameworks (Mn-Zn-ZIF) were thus fabricated and exhibited pH-responsive T1-weighted magnetic resonance imaging (MRI) contrast effect. Remarkably, we also found its own fluorescence derived from 2-methylimidazole, which is the first report of the intrinsic two-photon fluorescence imaging of ZIFs to our knowledge. Mn-Zn-ZIF still preserves the original properties of ZIF-8 of high surface areas, microporosity, and acid sensitivity. After further PEGylation of Mn-Zn-ZIF, the nanoparticles showed no obvious toxicity and its MRI contrast effect has also been enhanced. Our work highlights the promise of modified zeolitic imidazolate frameworks as potential cancer theranostic platforms.
Project description:Formic acid (FA; HCOOH) is one of the most promising candidates for the storage of hydrogen (H2). Herein, we report a H2 storage/production system based on the hydrogenation of CO2 and dehydrogenation of FA, using a nanostructured heterogeneous catalyst. Pd1Ag2 nanoparticles with an average size of 2.8 nm were encapsulated within a zeolitic imidazolate framework (ZIF-8) having a core-shell structure (ZIF-8@Pd1Ag2@ZIF-8). This composite displayed high activity and stability during both the hydrogenation of CO2 to produce FA and the dehydrogenation of FA into H2 and CO2. This improved performance is attributed to the use of ultrafine Pd1Ag2 nanoparticles as well as the spatial regulation of the nanoparticles within the reaction field. This study suggests a new strategy for controlling the spatial distribution of metal nanoparticles within MOFs so as to fine-tune the catalytic activity and selectivity of ZIF-8@metal nanoparticles@ZIF-8 catalysts.
Project description:Core-shell ZIF-8@ZIF-67- and ZIF-67@ZIF-8-based zeolitic imidazolate frameworks (ZIFs) were synthesized solvothermally using a seed-mediated methodology. Transmission electron microscopy-energy-dispersive X-ray spectrometry, line scan, elemental mapping, X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic emission spectroscopy analyses were performed to confirm the formation of a core-shell structure with the controlled Co/Zn elemental composition of ?0.50 for both the core-shell ZIFs. The synthesized core-shell ZIF-8@ZIF-67 and ZIF-67@ZIF-8 frameworks conferred enhanced H<sub>2</sub> (2.03 and 1.69 wt %) storage properties at 77 K and 1 bar, which are ca. 41 and 18%, respectively, higher than that of the parent ZIF-8. Notably, the distinctly remarkable H<sub>2</sub> storage properties shown by both the core-shell ZIFs over the bimetallic Co/Zn-ZIF and the physical mixture of ZIF-8 and ZIF-67 clearly evidenced their unique structural properties (confinement of porosity) and elemental heterogeneity due to the core-shell morphology of the outperforming core-shell ZIFs. Moreover, H<sub>2</sub> adsorption isotherm data of these frameworks are best fitted with the Langmuir model (<i>R</i> <sup>2</sup> ? 0.9999). Along with the remarkably enhanced H<sub>2</sub> storage capacities, the core-shell ZIFs also displayed an improved CO<sub>2</sub> capture behavior. Hence, we demonstrated here that the controlled structural features endorsed by the rationally designed porous materials may find high potential in H<sub>2</sub> storage applications.
Project description:The preparation and characterization of composite polybenzimidazole (PBI) membranes containing zeolitic imidazolate framework 8 (ZIF-8) and zeolitic imidazolate framework 67 (ZIF-67) is reported. The phosphoric acid doped composite membranes display proton conductivity values that increase with increasing temperatures, maintaining their conductivity under anhydrous conditions. The addition of ZIF to the polymeric matrix enhances proton transport relative to the values observed for PBI and ZIFs alone. For example, the proton conductivity of PBI@ZIF-8 reaches 3.1 × 10-3 S·cm-1 at 200 °C and higher values were obtained for PBI@ZIF-67 membranes, with proton conductivities of up to 4.1 × 10-2 S·cm-1. Interestingly, a composite membrane containing a 5 wt.% binary mixture of ZIF-8 and ZIF-67 yielded a proton conductivity of 9.2 × 10-2 S·cm-1, showing a synergistic effect on the proton conductivity.
Project description:We have synthesized hollow mesoporous silica (HMS) at a zeolitic imidazolate framework (ZIF) capsule that can be used as a drug delivery system for gentamicin (GM). The GM is first loaded into HMS. Then, the outer surface of the GM/HMS is coated with uniformed ZIF nanoparticles (denoted as GM/HMS@ZIF). The GM/HMS@ZIF has been successfully prepared and acts as a capsule for GM. The GM/HMS@ZIF shows a good biocompatibility and a good cellular uptake in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells. The GM is released slowly within 10?h under acidic conditions, which is used to simulate the pH of the endosome and lysosome compartments. The in vivo assay shows that the signal from fluorescein isothiocyanate (FITC) can be observed after 15 days, when the mice were injected with FITC/HMS@ZIF. This opens new opportunities to construct a delivery system for GM via one controlled low dose and sustained release for the therapy of Ménière's disease.
Project description:Metal organic frameworks (MOFs) exhibit unique features of finely tunable pore structures, excellent chemical stability and flexible surface structural functionality, making them advantageous for a wide range of applications including energy storage, compound separation, catalysis, and drug delivery. The present work enlightens a novel approach of single step fabrication of CCM-ZIF-8 as a drug carrier and its application as stimuli responsive drug delivery systems via external stimuli involving change in pH and in presence of biomimetic cell membrane like environment using liposomes and SDS micelles. The methodology is devoid of any post synthesis drug loading steps. The synthesized curcumin encapsulated ZIF-8 frameworks demonstrate ultrahigh drug encapsulation efficiency (ca. 83.33%) and good chemical stability. In vitro drug release of curcumin was three times higher in acidic medium than in physiological pH. Cytotoxicity results demonstrated enhanced therapeutic effect of CCM-ZIF-8 than free curcumin. Confocal microscopy results confirmed the easy cellular internalization of CCM-ZIF-8 in HeLa cells. Intracellular distribution studies at various incubation times confirmed the clathrin-mediated endocytosis to lysosomal pathway of CCM-ZIF-8, but without mitochondria being an intracellular fate. The results signify that CCM-ZIF-8 is an efficient drug carrier for passive tumor therapy in future for cancer treatments.
Project description:Zinc (Zn) holds great promise as a desirable anode material for next-generation rechargeable batteries. However, the uncontrollable dendrite growth and low coulombic efficiency of the Zn plating/stripping process severely impede further practical applications of Zn-based batteries. Here, these roadblocks are removed by using in situ grown zeolitic imidazolate framework-8 (ZIF-8) as the ion modulation layer to tune the diffusion behavior of Zn2+ ions on Zn anodes. The well-ordered nanochannels and N species of ZIF-8 can effectively homogenize Zn2+ flux distribution and modulate the plating/stripping rate, ensuring uniform Zn deposition without dendrite growth. The Zn corrosion and hydrogen evolution are also alleviated by the insulating nature of ZIF-8, resulting in high coulombic efficiency. Therefore, the Zn@ZIF anode shows highly reversible, dendrite-free Zn plating/stripping behavior under a broad range of current densities, and a symmetric cell using this anode can work correctly up to 1200 h with a low polarization at 2 mA cm-2. Moreover, this ultrastable Zn@ZIF anode also enables a full Zn ion battery with outstanding cyclic stability (10 000 cycles).