ZIF-8 Films Research Articles

Performance improvement photodetectors with high speed and detectivity using terbium-doped ZIF-8 and MOF-5 films

Crystal engineering is critical for improving the crystal quality and tuning the optoelectronic properties of metal-organic frameworks (MOFs) materials. Doping MOFs is one of the practical approaches to improve the optoelectronic properties of MOFs. Here, a simple and effective method is used to grow MOF nanoparticles as films on the surface of the material. MOF-5 and ZIF-8 nanoparticles can be uniformly grown as films on the Si substrates. The crystalline quality of MOF films is improved after doping with Tb. Meanwhile, two-dimensional conducting photodetectors and photodetector arrays were prepared with perovskite films. Meanwhile, planar conducting photodetector arrays were prepared with MOF films. The photoluminescence (PL) intensity of the Tb-ZIF-8 and Tb-MOF-5 films shows an improvement compared to both ZIF-8 and MOF-5 layers, which leads to improved charge carriers transfer. The maximum photocurrents were about 4 × 10−8 A and 3 × 10−8 A of exposed light at 525 and 425 nm, respectively, at a fixed bias of 10 V for Tb-ZIF-8. The highest photo response of approximately 2.4 × 10−7 and 1.2 × 10−7 A was measured under 525 and 450 nm for the Tb-MOF-5-based device, respectively. The photocurrent behavior is optimized in the visible range due to the increased number of photo-generated carriers at 525 nm. The Tb-MOF-5 based device is a more powerful photodetector than the Tb-ZIF-8 based device under the same conditions. In addition, the stability of Tb-MOF-5 and Tb-ZIF-8 based photodetectors was obtained 77 % and 30 %, respectively. The photodetectors of Tb-MOF-5 have higher stability and better performance than Tb-ZIF-8.

Reactive Extrusion Printing of Zeolitic Imidazolate Framework Films.

An outstanding challenge for the field of metal-organic frameworks (MOFs) is structuring to form forms with greater useability. Reactive extrusion printing (REP) is a technique for the direct formation of films from their molecular components on-demand and on-location. Here we apply REP for the first time to zeolitic imidazolate frameworks (ZIFs) and study the interplay of solvent and molarity ratio on the phase distribution between ZIF-8 and ZIF-L in reactive printed films. Our results show that REP controllably directs phase formation between ZIF-L and ZIF-8 and that REP also gives control over crystal size and that high-quality ZIF-8 films, in particular, are produced in low-dispersity interconnected nanoparticulate form. Importantly, we show that REP is responsive to established surface-functionalization techniques to control important printing parameters of line width and thickness. This work expands the repertoire of REP to the important class of ZIFs.

Surface plasmon resonance sensor of hollow microstructure fiber based on ZIF-8 thin film

An annular hollow microstructured fiber surface plasmon resonance (SPR) sensor based on ZIF-8 film is proposed for the measurement of CO2 concentration in air. Internal detection is adopted to enhance the spectral response to CO2 gas, and nano-gold pillars are embedded on both sides of the channel. The geometric parameters of the sensor are optimized to achieve an average sensitivity of 1.01 nm/% over the range of CO2 concentration from 0% to 100%. The results indicate that the sensor is a promising SPR gas sensor with great potential in CO2 detection applications.

Role of the Coordination of Metal Ions by Ammonia for the Anodic Electrosynthesis of MOF Films

Metal-organic frameworks (MOFs), consisting of inorganic nodes coordinated by organic ligands, have received tremendous attention in the past decades due to their high surface area, high porosity, designable pore-aperture shape/size, and tunable building units (including metal centers and functional ligands). For most of their applications, such as separation, catalysis, sensors, and energy storage/conversion devices, MOFs in the form of films/membranes are desired. Anodic electrodeposition is a promising and cost-effective method to in-situ prepare metal-organic framework (MOF) films on metal substrates. However, the anodic synthesis of continuous zeolitic imidazolate framework (ZIF) films, an important subclass of MOF materials, has been proved challenging. Here, we report a facile anodic deposition method that enables the ultra-fast preparation of uniform and continuous ZIF-8 films with tunable thickness from the aqueous solution at room temperature by using the ammonia hydroxide-assisted deprotonation strategy (AHADS). The growth rate of the MOF films is flexibly controlled by the applied current densities, the concentration of the linkers, and the amount of added ammonia hydroxide. The roll-to-roll deposition of the ZIF-8 films on the zinc foils shows the possibility of this method for large-scale industrial synthesis. The control experiments and theoretical calculations reveal that the formation of Zn(NH3)4 2+ complex by adding excessive ammonia hydroxide is crucial to promote the coordination of 2-Methylimidazole (Hmim) with Zn2+. Afterward, the Zn2+ cation attracts electrons of Hmim and thus weakens the N-H bond, which decreases the free energy for the deprotonation of Hmim. As a result, the ZIF-8 films can be aqueously deposited at low pH under room temperature. Various pure ZIF films (ZIF-4, ZIF-7, and ZIF-67) with different metal nodes or organic linkers were successfully deposited via this strategy. In addition, ZIF-8 films deposited on the zinc foil show ability to decrease the overpotential for the zinc plating and stripping, suggesting its possibility for use in reversible zinc metal batteries. This work broadens the applicability of anodic deposition and indicates the potential applications of metal-supported MOF films in energy storage and conversion fields

Preparation and Lithium-Ion Separation Property of ZIF-8 Membrane with Excellent Flexibility.

Metal-organic framework (MOF) membranes exhibit immense potential for separation applications due to their regular pore channels and scalable pore sizes. However, structuring a flexible and high-quality MOF membrane remains a challenge due to its brittleness, which severely restricts its practical application. This paper presents a simple and effective method in which continuous, uniform, defect-free ZIF-8 film layers of tunable thickness are constructed on the surface of inert microporous polypropylene membranes (MPPM). To provide heterogeneous nucleation sites for ZIF-8 growth, an extensive amount of hydroxyl and amine groups were introduced on the MPPM surface using the dopamine-assisted co-deposition technique. Subsequently, ZIF-8 crystals were grown in-situ on the MPPM surface using the solvothermal method. The resultant ZIF-8/MPPM exhibited a lithium-ion permeation flux of 0.151 mol m-2 h-1 and a high selectivity of Li+/Na+ = 1.93, Li+/Mg2+ = 11.50. Notably, ZIF-8/MPPM has good flexibility, and the lithium-ion permeation flux and selectivity remain unchanged at a bending curvature of 348 m-1. These excellent mechanical characteristics are crucial for the practical applications of MOF membranes.

Highly sensitive detection of thiram residues on fruit peel surfaces using a filter paper-based SERS sensor with AgNWs@ZIF-8

The widely used pesticide thiram is found in various environments and foodstuffs, posing a risk to human health and contaminating the environment. In this work, the novel SERS flexible sensor (FP/AgNWs@ZIF-8) consisting of silver nanowires and zeolite imidazole frameworks combined with filter paper was prepared for the sensitive and rapid detection of thiram on fruit peel surfaces. The effect that different coating cycles of ZIF-8 films exert on the Raman signal enhancement of the sensor was investigated. The results show that optimal Raman response to 4-Aminothiophenol (4-ATP) was demonstrated in the FP/AgNWs@ZIF-8(5) sensor, with a low LOD of 1.6 × 10−15 M due to a coating period of 5. Furthermore, a novel SERS FP/AgNWs@ZIF-8 sensor with a porous and flexible structure on low-cost and eco-friendly paper was obtained, as to be immersed in a solution of thiram or wiped on a nectarine skin surface, and the highly sensitive LODs of 1.4 × 10−12 M and 7.4 fg/cm2 were achieved, respectively. Therefore, this facile, rapid, and sensitive flexible sensor at low-cost has excellent potential for pesticide residue detection and environmental toxicity analysis.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid.

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF3) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF3 was shown to overpass MIL-101(Cr) in terms of AA/H2O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Development of mechanically robust and anticorrosion slippery PEO coating with metal–organic framework (MOF) of magnesium alloy

A novel anticorrosion and mechanically robust coating system was discovered via plasma electrolytic oxidation (PEO), in-situ MOFs growth strategy, and lubricant-infusion to produce slippery surface of AZ31 magnesium alloy. The PEO coating acts as a transition layer and provides a moderate corrosion barrier to Mg alloy. The homogenous and uniform ZIF-8 film on the PEO coating surface was successfully constructed by a practical and simple in-situ method. The incorporation of ZIF-8 particles plays a vital role to strengthen the corrosion resistance of PEO coating while increasing superhydrophobicity. Furthermore, the ZIF-8 film provides the anchoring site for storing infused lubricants to create a slippery surface. The prepared PEO-MOF-SLIPS showed six orders of magnitude lower icorr value than bare Mg alloy, indicating substantially improved corrosion resistance with an effective barrier performance. In addition, PEO-MOF-SLIPS demonstrates superior corrosion potential of −0.21 V/Ag/AgCl, after 2 days of immersion in 3.5 wt.% NaCl solution. The potentiodynamic polarization test (PDS) results proved that the slippery surface has superior water-repellence to other coatings, indicating higher endurance of SLIPS in 3.5 wt.% NaCl solution. Moreover, the PEO-MOF-SLIPS maintained its hydrophobicity for a longer time in 3.5 wt.% NaCl solution compared to PEO-MOF-SHS. EIS test results also proved that the PEO-MOF-SLIPS has a better resistance than that of PEO-MOF-SHS in prolonged immersion in a corrosive solution. According to the abrasion test, the PEO-MOF-SHS maintained its superhydrophobicity up to 100 cm under 100 g load and 80 cm under 200 g load. On the other hand, the PEO-MOF-SLIPS maintained its contact angle stable under both abrasion loadings. The as-prepared slippery surface showed durable water-repellent against the corrosive solution and higher mechanical robustness. The results demonstrate that the MOFs modified PEO coatings system provides a new pathway to the construction of the slippery surface of Mg alloy. It also proves that water-stable MOFs are efficient corrosion-resistant materials and can be used for various anticorrosion applications.

Hierarchical nanostructure investigation of Zeolitic Imidazolate Frameworks (ZIF-8 and ZIF-67) multilayers using depth dependent Doppler broadening spectroscopy

Zeolitic Imidazolate Frameworks (ZIFs) based gas separation is proposed to be an energy efficient process compared to conventional processes currently used in the industries. In order to achieve high gas separation factor, diffusion of gases through the size selective aperture of ZIFs has to be maximized suppressing the gas diffusion through the non-selective inter-crystal grain boundary structure. In this regard, a priori depth dependent experimental characterization of pore architecture of ZIF based multilayer membranes is quite essential. In the present study, depth dependent positron annihilation Doppler broadening spectroscopy has been used to investigate the pore interconnectivity and grain boundary structure for alternatively deposited bi- and tri-layers of ZIF-67 and ZIF-8 using fast current driven synthesis method (FCDS). The phase purity and chemical bonding of the films have been established using X-ray diffraction and Fourier transform infra red spectroscopy. The electron microscopy images of the films have shown uniform and densely packed film deposition using the present methodology. The S-E profiles of multilayers films measured using Doppler broadening spectroscopy confirm the modifications in pore interconnectivity and crystal packing as compared to seed films (ZIF-8 and ZIF-67). The S-E profiles of multilayers could not be modeled considering individual ZIF-8 and ZIF-67 films deposited over each other with distinct interface structure. The present study confirms that multilayer deposition of ZIF-8 and ZIF-67 using FCDS leads to modification in crystal packing throughout the bulk of the film. It is confirmed that grain boundary structure is significantly improved in case of multilayers as compared to pure ZIF-67 based film, which can be attributed to the better gas separation performance of multilayers compared to pure ZIF-67 observed in literature.

Synthesis of core-shell ZIF-8@α-Fe2O3 nanorods and improvement of selectivity for ammonia gas

Uniform and dense α-Fe2O3 nanorods were directly synthesized on the ceramic tube substrate by hydrothermal method, and then a layer of porous and dense ZIF-8 film was hydrothermally grown and coated on the surface of α-Fe2O3 nanorods after immersion in ligand solution and high-temperature treatment. Then the core-shell ZIF-8 @ α-Fe2O3 nanorods were obtained. The elements, composition, surface morphology, and crystal structure of the samples were analyzed by XPS, SEM, TEM, and XRD. These results indicate that the width of the rod-shaped α-Fe2O3 was between 20 and 40 nm while the rod-shaped α-Fe2O3 coated with a layer of dense porous ZIF-8 was between 50 and 80 nm. The gas sensing results reveal that compared with pure α-Fe2O3 nanorods, ZIF-8 @ α-Fe2O3 had a great improvement in gas selectivity (11.7), response value (136.9 for ammonia gas of 50 ppm at 280 ℃). The working process and gas sensing mechanism of the ZIF-8 @ α-Fe2O3 were discussed and it demonstrates that ZIF-8 not only plays a screen role in the gas-sensitive response process, but also increases the sensitivity by adsorbing oxygen molecules. It proved that the direct growth of ZIF-8 @ α-Fe2O3 on the ceramic tube provides a more effective way to improve the gas response and selectivity.

Continuous Film Based on Zeolitic Imidazole Framework-8 for an Enhanced Resistive Memory Property

Although metal-organic frameworks attract much attention in electronic devices, the discontinuity at and weak interfacial contact with the substrate are still challenging. In this paper, an $\mathrm{Ag}$/(polyethylene glycol + zeolitic imidazole framework-8) @ (polyvinyl alcohol + 2-methylimidazole)/fluorine-doped tin oxide [$\mathrm{Ag}$/(PEG + ZIF8) @ (PVA + 2MIM)/FTO] structured resistive memory is fabricated. The interfacial contact and active site are enhanced by modifying FTO with (PVA + 2MIM). The continuity of ZIF-8 film is enhanced by compositing PEG. The resistive memory exhibits a lower set voltage of 1.3 V, a higher endurance of more than 140 cycles, and a longer retention time of over 10 000 s, in comparison with control devices of $\mathrm{Ag}$/ZIF-8/FTO and $\mathrm{Ag}/$ZIF-8 @ (PVA + 2MIM)/FTO. The mechanism of the resistive switching behavior is analyzed by conduction models, and explained by redox reactions of the top active electrode to form and rupture conductive filaments under the electric field. This study suggests a facial and general technology for synthesizing a continuous film with strong contact with the substrate, benefiting electronic devices.

Impact of Chemical Primers on the Growth, Structure, and Functional Properties of ZIF-8 Films

Impact of Chemical Primers on the Growth, Structure, and Functional Properties of ZIF-8 Films

Facile In Situ Growth of Zif-8 Nanosheets with Enhanced Anti-Corrosion Performance for Carbon Steel in Seawater

Carbon steel is one of the most important and widely used structural materials, but preventing its corrosion remains a great challenge. Herein, a metal–organic framework film consisting of Zif-8 nanosheets array was prepared using a one-step in situ growth method. This coating film can effectively inhibit the corrosion behavior of low carbon steel in seawater, resulting in improved corrosion resistance (4010 Ω·cm−2) and low corrosion current density (23 μA·cm−2). After long-term immersion in seawater, no notable pitting corrosion was observed and the film integrity was well preserved, demonstrating the feasibility of Zif-8 film for anti-corrosion coating.

Electrochemical fabrication of long-range ordered macro-microporous metal–organic framework films

Centimeter-scale (4 × 3 cm2) 3DOM ZIF-8 film on substrate is developed by electrochemical cathodic deposition method. This controllable and facile method enabled to create 3DOM ZIF-8 films with varying uniform macropores sizes within a few minutes.

Sandwich-like QDs/MOFs films for selective sensing and multicolor emitting

A novel type sandwich-like composite films composed of ZIF-8 and CdTe QDs were successfully constructed through facile layer-by-layer assembly strategy and their potential applications were also explored. Based on the limitation effects of the aperture of ZIF-8, CdTe QDs/ZIF-8 fluorescent composite films exhibit obvious selective optical response toward hydrogen peroxide and folic acid. Furthermore, tunable colorful light emission composite films in the red-green region are obtained through incorporating two different sized QDs and ZIF-8 films into one composite films.

Synthesis of ZIF-8-coated Pt/SiO2 by vapor deposition for alkyne semi-hydrogenation

In this work, ZIF-8/Pt/SiO2 catalysts were prepared by combining atomic layer deposition (ALD) and vapor phase conversion methods. First, Pt metal nanoparticles were deposited on SiO2 nanowires by ALD. Then, ZnO was further deposited, also by ALD. Subsequently, the ZnO film was converted into ZIF-8 film by vapor phase crystallization to form a sandwich structure (ZIF-8/Pt/SiO2). The microstructures of the catalysts were characterized by XRD, TEM, BET, IC-MS, XPS, and CO-DRIFT. It was shown that the Pt particles were highly dispersed on the SiO2 nanowires before and after coating with ZIF-8, and the ZIF-8 film was coated continuously on the entire catalyst with high conformity. The performance of the catalyst was studied by using the semi-hydrogenation of 1-heptyne as a probe reaction. The ZIF-8 film induces an electron density increase in the Pt component, leading to an increase of the olefin selectivity from 14% to 70% in the 1-heptyne hydrogenation reaction. A reduced thickness of the ZIF-8 film increases the catalytic activity but does not affect the selectivity of 1-heptylene.

Transport Diffusion of Linear Alkanes (C5-C16) through Thin Films of ZIF-8 as Assessed by Quartz Crystal Microgravimetry.

We report uptake capacities and transport diffusivities, D, for each of eight linear alkanes (ranging from C5 to C16) in quartz crystal-supported films of solvent-evacuated ZIF-8. Analyses of the alkane uptake profiles revealed that the transport dynamics are governed by guest diffusion through metal-organic framework (MOF) (ZIF-8) crystallites rather than by rates of entry into films at the MOF/vapor interface. The obtained diffusivities range from just over 10-18 m2/s to just under 10-14 m2/s. Notably, minimum cross-sectional widths for all guests exceed the crystallographically measured width of ZIF-8's largest apertures and imply consistently with previous experimental and computational studies that apertures expand to accommodate guest uptake. On average, each additional carbon decreases the transport diffusivity of an alkane by twofold. Closer examination, however, reveals an odd-even effect such that linear alkanes having even numbers of carbons diffuse more rapidly than alkanes featuring one more or one less carbon atom. Thus, ZIF-8's differentiation of transport diffusivities for pairs of alkanes differing in length by only one carbon atom can be significantly greater than the aforementioned factor of 2. Elucidation of the microscopic basis for the odd-even behavior, however, awaits the outcome of molecular dynamics calculations that are beyond the scope of the present study. For compact, solvothermally prepared films, guest transport is dominated by 1D diffusion from the film/vapor interface and toward the underlying quartz crystal. For much lower density, electrophoretically deposited (EPD) films, crystallites behave nearly independently, and guest transport can be adequately modeled by assuming rapid permeation of macroscopic voids between crystallites, followed by entry and rate-limiting radial diffusion into isolated crystallites. One consequence is that EPD films can be much more rapidly infiltrated by molecular guests than can compact, solvothermally grown films. The combined results have potentially favorable implications for the development of kinetic separation schemes for closely related analytes.

ZnO@ZIF-8 Core-Shell Structure Gas Sensors with Excellent Selectivity to H2.

As the energy crisis becomes worse, hydrogen as a clean energy source is more and more widely used in industrial production and people’s daily life. However, there are hidden dangers in hydrogen storage and transportation, because of its flammable and explosive features. Gas detection is the key to solving this problem. High quality sensors with more practical and commercial value must be able to accurately detect target gases in the environment. Emerging porous metal-organic framework (MOF) materials can effectively improve the selectivity of sensors as a result of high surface area and coordinated pore structure. The application of MOFs for surface modification to improve the selectivity and sensitivity of metal oxides sensors to hydrogen has been widely investigated. However, the influence of MOF modified film thickness on the selectivity of hydrogen sensors is seldom studied. Moreover, the mechanism of the selectivity improvement of the sensors with MOF modified film is still unclear. In this paper, we prepared nano-sized ZnO particles by a homogeneous precipitation method. ZnO nanoparticle (NP) gas sensors were prepared by screen printing technology. Then a dense ZIF-8 film was grown on the surface of the gas sensor by hydrothermal synthesis. The morphology, the composition of the elements and the characters of the product were analyzed by X-ray diffraction analysis (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) and differential scanning calorimetry (DSC). It is found that the ZIF-8 film grown for 4 h cannot form a dense core-shell structure. The thickness of ZIF-8 reaches 130 nm at 20 h. Through the detection and analysis of hydrogen (1000 ppm), ethanol (100 ppm) and acetone (50 ppm) from 150 °C to 290 °C, it is found that the response of the ZnO@ZIF-8 sensors to hydrogen has been significantly improved, while the response to ethanol and acetone was decreased. By comparing the change of the response coefficient, when the thickness of ZIF-8 is 130 nm, the gas sensor has a significantly improved selectivity to hydrogen at 230 °C. The continuous increase of the thickness tends to inhibit selectivity. The mechanism of selectivity improvement of the sensors with different thickness of the ZIF-8 films is discussed.

Toward miniaturizing microelectronics using covalent organic framework dielectric

Toward miniaturizing microelectronics using covalent organic framework dielectric

Thin Films of Metal-Organic Framework Interfaces Obtained by Laser Evaporation.

Properties such as large surface area, high pore volume, high chemical and thermal stability, and structural flexibility render zeolitic imidazolate frameworks (ZIFs) well-suited materials for gas separation, chemical sensors, and optical and electrical devices. For such applications, film processing is a prerequisite. Herein, matrix-assisted pulsed laser evaporation (MAPLE) was successfully used as a single-step deposition process to fabricate ZIF-8 films. By correlating laser fluency and controlling the specific transfer of lab-synthesized ZIF-8, films with user-controlled physical and chemical properties were obtained. Films’ characteristics were evaluated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The analysis showed that frameworks of ZIF-8 can be deposited successfully and controllably to yield polycrystalline films. The deposited films maintained the integrity of the individual ZIF-8 framework, while undergoing minor crystalline and surface chemistry changes. No significant changes in particle size were observed. Our study demonstrated control over both the MAPLE deposition conditions and the outcome, as well as the suitability of the listed deposition method to create composite architectures that could potentially be used in applications ranging from selective membranes to gas sensors.