Solid Metal-organic Framework Research Articles

Optical, thermal and semiempirical study of Samarium bi-tartrate trihydrate

In this comprehensive study, we investigated the structure, optical, and thermal aspects of [Sm(C4H5O6)(C4H4O6)][3H2O], a samarium based metal-organic framework. Testing and exploring advanced semiempirical quantum models, we provide some insights into ground-state molecular properties within the solid metal-organic framework. The single-excitation configuration interaction approach within the spectroscopic method INDO/S-CIS was utilized in the computation of UV spectra, singlet, and triplet excited states for the uncoordinated organic component. We also exploited the established Judd-Ofelt theory to elucidate the spectroscopic properties, allowing us to predict various attributes, including absorption and luminescence traits. The inclusion of thermogravimetric analysis exposes a multifaceted thermal decomposition process. Moreover, this analysis was explored in the determination of activation energies associated with distinct stages of decomposition.

Beyond Pristine Metal-Organic Frameworks: Preparation of Hollow MOFs and Their Composites for Catalysis, Sensing, and Adsorption Removal Applications.

Metal-organic frameworks (MOFs) have been broadly applied to numerous domains with a substantial surface area, tunable pore size, and multiple unsaturated metal sites. Recently, hollow MOFs have greatly attracted the scientific community due to their internal cavities and gradient pore structures. Hollow MOFs have a higher tunability, faster mass-transfer rates, and more accessible active sites when compared to traditional, solid MOFs. Hollow MOFs are also considered to be candidates for some functional material carriers. For example, composite materials such as hollow MOFs and metal nanoparticles, metal oxides, and enzymes have been prepared. These composite materials integrate the characteristics of hollow MOFs with functional materials and are broadly used in many aspects. This review describes the preparation strategies of hollow MOFs and their composites as well as their applications in organic catalysis, electrochemical sensing, and adsorption separation. Finally, we hope that this review provides meaningful knowledge about hollow-MOF composites and their derivatives and offers many valuable references to develop hollow-MOF-based applied materials.

Ultrasensitive Microfluidic Paper-Based Electrochemical/Visual Analytical Device via Signal Amplification of Pd@Hollow Zn/Co Core-Shell ZIF67/ZIF8 Nanoparticles for Prostate-Specific Antigen Detection.

An effective signal amplification strategy is essential to enhance the analytical performance of microfluidic paper-based analytical devices (μPADs) for tracing biomarkers. Here, a simple but efficient approach with superior electrocatalytic performance of Pd@hollow Zn/Co core-shell ZIF67/ZIF8 nanoparticles for regulating the efficacious signal amplification process was utilized to realize the detection of prostate-specific antigen (PSA). By rationally designing the core-shell structure of ZIF67/ZIF8 with hollow characteristics on the nanoscale and introducing the noble metal element Pd into the cavity, the diffusion limitation and porous confinement reduction of the obtained nanomaterials with uniform morphology and satisfactory chemical stability could be realized, which endowed it with better catalytic performance than solid metal-organic frameworks (MOFs) and ensured effective signal amplification of H2O2 reduction for achieving enhanced electrochemical signals. Moreover, with the assistance of signal probes, the remaining H2O2 could flow to the color area to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine to form a colored product by changing the spatial configuration of the μPAD, thus realizing the visual detection of PSA. On the basis of this novel analytical device, dual-mode ultrasensitive detection of PSA could be achieved with a lower limit of detection of 0.78 pg/mL (S/N = 3) and a wider linear range from 5 pg/mL to 50 ng/mL. This work provided the opportunity of introducing the noble metal element Pd into the cavity of the MOF hollow structure to improve its electrocatalytic efficiency and construct a high-performance μPAD for clinical detection of other biomarkers.

Multi-shelled hollow metal-organic frameworks for optimizing the adsorption performance of antibiotics

Antibiotics have been widely used in the prevention and treatment of diseases such as humans, poultry and aquaculture due to their remarkable antibacterial effects. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Therefore, the effective removal of trace antibiotic technology and materials in water has gradually attracted the attention of all parties in recent years. However, due to the difficulty in pore size, porosity, physical and chemical properties modification, the application of traditional porous materials, such as activated carbon, zeolites and silicates, are limited to some extent. As a new type of porous materials, metal-organic frameworks (MOFs) are considered as a promising platform for the adsorption applications. Inspired by the favorable structure and morphology of inorganic materials, hollow structures are promising materials for enhancing the adsorption performance. Herein, we fabricated multi-shelled hollow MOFs through step-by-step crystal growth and subsequent etched by acetic acid. The solid MOFs particles size about 200 nm, and the hollow cavity of single shell hollow MOFs (SSHM) about 100 nm. The diameters of double shell hollow MOFs (DSHM) inner cavity and outer shell were 50 and 50 nm, respectively. Triple shell hollow MOFs (TSHM) inner cavity and outer shell diameters were 20 and 70 nm, respectively. Powder X-ray diffraction (XRD) and N2 sorption confirmed the crystallographic structure and porosity of the resulting hollow MOFs. The hollow MOFs showed similar diffraction peaks position and intensity with pristine MOFs, which indicated that the high phase purity of the product MOFs. The BET surface of solid, single, double and triple shell MOFs were 2389.1, 2454.2, 2052.7 and 2396.2 m2/g, respectively. The hollow structured MOFs exhibited higher adsorption capacity than the solid MOFs, and the adsorption capacity increased with the number of layers. Particularly, the triple-shelled hollow MOFs (TSHM) for oxytetracycline and tetracyclines adsorption capacity is about 76 and 95 mg/g, respectively, which is three times higher than the solid MIL-101. The high adsorption capacity and removal efficiency may be attributed to the enhanced active site in each layer of multi hollow structure that can sorption more molecules. The recycling experiment showed that the adsorption efficiency of antibiotics in water by TSHM was relatively stable, and it still showed good crystallinity and morphological stability after reuses of up to 4 cycles. The enhanced adsorption capacity and excellent reusability obtained in this study demonstrated the potential of multi-shelled hollow MOFs structures as a novel adsorbent for the removal of organic molecules.

Paper-based microfluidic devices for glucose assays employing a metal-organic framework (MOF)

This paper describes the development of two microfluidic paper-based analytical devices (μPADs), one well-based and the other based on a lateral flow assay (LFA) configuration, to detect glucose via a colorimetric assay using the solid metal-organic framework (MOF) Zr-PCN-222(Fe), to encapsulate glucose oxidase (GOx). The well-based platform consisted of laminate sheets and multiple layers of wax-printed chromatography paper. Solutions of KI and glucose placed into the well flowed through the device and reacted with the GOx@MOF species sandwiched between the paper layers realizing a yellow-brown color. The LFA platform consisted of chromatography paper between parafilm and polyvinyl acetate (PVA) layers. GOx@MOFs spotted on the paper subjected to solutions of KI and glucose yielded a brown color. The devices were then dried, scanned, and analyzed yielding a correlation between average inverse yellow intensity and glucose concentrations. The development of these devices employing MOFs as biomimetic catalysts should further expand the applications of microfluidic technologies for sensors a variety of analytes.

Hollow Functional Materials Derived from Metal-Organic Frameworks: Synthetic Strategies, Conversion Mechanisms, and Electrochemical Applications.

Hollow materials derived from metal-organic frameworks (MOFs), by virtue of their controllable configuration, composition, porosity, and specific surface area, have shown fascinating physicochemical properties and widespread applications, especially in electrochemical energy storage and conversion. Here, the recent advances in the controllable synthesis are discussed, mainly focusing on the conversion mechanisms from MOFs to hollow-structured materials. The synthetic strategies of MOF-derived hollow-structured materials are broadly sorted into two categories: the controllable synthesis of hollow MOFs and subsequent pyrolysis into functional materials, and the controllable conversion of solid MOFs with predesigned composition and morphology into hollow structures. Based on the formation processes of hollow MOFs and the conversion processes of solid MOFs, the synthetic strategies are further conceptually grouped into six categories: template-mediated assembly, stepped dissolution-regrowth, selective chemical etching, interfacial ion exchange, heterogeneous contraction, and self-catalytic pyrolysis. By analyzing and discussing 14 types of reaction processes in detail, a systematic mechanism of conversion from MOFs to hollow-structured materials is exhibited. Afterward, the applications of these hollow structures as electrode materials for lithium-ion batteries, hybrid supercapacitors, and electrocatalysis are presented. Finally, an outlook on the emergent challenges and future developments in terms of their controllable fabrications and electrochemical applications is further discussed.

Metal-organic-framework template-derived hierarchical porous CoP arrays for energy-saving overall water splitting

Developing highly active and low-cost electrocatalysts with superior durability is attractive but challenging for energy-saving electrolytic hydrogen generation via water electrolysis. Herein, a novel metal-organic framework (MOF)-based growth-etching-phosphorization strategy is reported to construct hierarchical porous CoP nanostructure arrays on nickel foam substrate (HP-CoP NA/NF) for overall water splitting (OWP). Interconnected 2D cobalt-based MOF are fabricated via an aqueous solution reaction at room temperature, and then solid MOFs are uniformly converted into porous CoP arrays with hierarchical 3D configuration through a Co2+−etching process with subsequent phosphorization treatment. This unique array architecture is beneficial for providing highly exposed active sites, shortening ion diffusion path and promoting gas release during the electrochemical reactions. Resultantly, this MOFs-derived CoP catalyst exhibits an outstanding electrocatalytic activity in catalyzing not only hydrogen and oxygen evolution reactions with the low overpotentials of 70 and 258 mV at 10 mA cm−2, respectively, but also some other small molecules electro-oxidation reactions, especially for urea oxidation reaction. Furthermore, the two-electrode electrolyzer comprising bifunctional HP-CoP NA/NF electrode delivers a current density of 10 mA cm−2 at an ultralow cell voltage of 1.38 V in the presence of urea, which is 180 mV smaller than that of pure water splitting. This work introduces a reference for the development of MOF-derived hierarchical nanostructured catalysts for energy-saving water splitting.

A generic and facile strategy to fabricate metal-organic framework films on TiO2 substrates for photocatalysis.

We present a facile and compelling method for the synthesis of metal-organic framework (MOF) thin films on TiO2-coated conductive glass substrates. This generic deposition approach is extended to five representative MOF films (e.g. UiO, MIL, IRMOF, and NU series) with high crystallinity and excellent surface coverage, achieving a MOF/TiO2 heterostructure interface. The tunable thickness and functionality of MOF films as well as the preferred orientation of MOF microcrystallites are described. After the incorporation of [Ru(bpy)3]2+ functionality via postsynthetic ligand exchange, the resultant MOF films serve as a robust and efficient catalyst for photo-oxidation of thioanisole. Importantly, our deposition technique avoids the direct contact between solid MOF catalysts and magnetic stirring, thus overcoming the problem that the vast majority of MOF powder catalysts are subject to defragmentation or decomposition under the physical treatment methods.

Structure, ferroelectric ordering, and semiempirical quantum calculations of lanthanide based metal-organic framework: [Nd(C4H5O6)(C4H4O6)][3H2O

We investigate the structure and ferroelectric behavior of a lanthanide based metal-organic framework (MOF), [Nd(C4H5O6)(C4H4O6)][3H2O]. X-ray crystal structure analyses reveal that it crystallizes in the P41212 space group with Nd centres, coordinated by nine oxygen atoms, forming a distorted capped square antiprismatic geometry. The molecules, bridged by tartrate ligands, form a 2D chiral structure. The 2D sheets are further linked into a 3D porous framework via strong hydrogen-bonding scheme (O-H…O ≈ 2.113 Å). Dielectric studies reveal two anomalies at 295 K and 185 K. The former is a paraelectric-ferroelectric transition, and the later is attributed to the freezing down of the motion of the hydroxyl groups. The phase transition is of second order, and the spontaneous polarization in low temperature phase is attributed to the ordering of protons of hydroxyl groups. The dielectric nonlinearity parameters have been calculated using Landau– Devonshire phenomenological theory. In addition, the most recent semiempirical models, Sparkle/PM7, Sparkle/RM1, and Sparkle/AM1, are tested on the present system to assay the accuracy of semiempirical quantum approaches to predict the geometries of solid MOFs. Our results show that Sparkle/PM7 model is the most accurate to predict the unit cell structure and coordination polyhedron geometry. The semiempirical methods are also used to calculate different ground state molecular properties.

Rigidifying fluorescent linkers by metal-organic framework formation for fluorescence blue shift and quantum yield enhancement.

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

Metal−Organic Frameworks: Structural, Energetic, Electronic, and Mechanical Properties

The structural, energetic, electronic, and mechanical properties of a series of metal-organic framework (MOF) materials have been systematically studied with the density functional based tight-binding method. The cubic array of Zn(4)O(CO2)6 units (connectors) connected by different types of organic secondary building blocks (linkers) was considered. The results show that these materials are stable with bulk moduli ranging from 0.5 to 24 GPa with decreasing size of the linker. All MOFs are semiconductors or insulators with band gaps between 1.0 and 5.5 eV, mainly determined by highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of the linker molecules. The atomic charges are nearly the same for free building blocks and the solid MOFs.

Adsorção de corantes têxteis utilizando a estrutura metal-orgânica [Cu3(BTC)2(H2O)3]n obtida por síntese eletroquímica

Metal-Organic Framework (MOF) é uma rede de coordenação com ligantes orgânicos e estrutura porosa. O objetivo dessa pesquisa foi sintetizar por via eletroquímica a MOF [Cu3(BTC)2(H2O)3]n e aplicá-la como material adsorvente para a remoção de corantes de tecidos nos efluentes. A MOF foi síntizada eletroquimicamente e por via amperométrica, fixando-se o potencial em 12 V durante 17 min, resultando em 73% de rendimento de um sólido azul. O produto final foi usado na sua forma bruta e caracterizado por FTIR e voltametria cíclica. Essa MOF, quando em contato com uma mistura que simulou um efluente de indústria têxtil, permitiu sua descoloração, acompanhada da decantação de um sólido colorido. Essa despigmentação também foi observada através da análise do sobrenadante por espectroscopia UV-Vis. O espectro de FTIR do sólido decantado após a mistura da MOF com o corante, evidenciou a adsorção dos pigmentos da solução pela MOF. Esse resíduo sólido de MOF apresentou-se ambientalmente vantajoso, por ter sido facilmente separado do efluente tratado e por ser regenerável e reutilizável. Isso o diferencia do lodo gerado nos processos de coagulação/floculação tradicionais, que pode ser danoso ao meio ambiente.