Formation of Gold Nanoclusters from Goldcarbonyl Chloride inside the Metal-Organic Framework HKUST-1

Gas-phase infiltration of the carbonylchloridogold(I), Au(CO)Cl precursor into the pores of HKUST-1 ([Cu3(BTC)2(H2O)2], Cu-BTC) SURMOFs (surface-mounted metal-organic frameworks; BTC = benzene-1,3,5-tricarboxylate) leads to Au(CO)Cl decomposition within the MOF through hydrolysis with the aqua ligands on Cu. Small Aux clusters with an average atom number of x ≈ 5 are formed in the medium-sized pores of the HKUST-1 matrix. These gold nanoclusters are homogeneously distributed and crystallographically ordered, which was supported by simulations of the powder X-ray diffractometric characterization. Aux@HKUST-1 was further characterized by scanning electron microscopy (SEM) and infrared reflection absorption (IRRA) as well as Raman spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

Dual-Function HKUST-1: Templating and Catalyzing Formation of Graphitic Carbon Nitride Quantum Dots Under Mild Conditions

Graphitic carbon nitride quantum dots (g-CNQDs) are highly promising photoresponsive materials. However, synthesis of monodispersed g-CNQDs remains challenging. Here we report the dual function of MOF [Cu3 BTC2 ] (HKUST-1) as a catalyst and template simultaneously to prepare g-CNQDs under mild conditions. Cyanamide (CA), a graphitic carbon nitride precursor, catalytically dimerized inside the larger MOF cavities at 90 °C and condensed into g-CNQDs at 120 °C in a controlled fashion. The HKUST-1 template was stable under the reaction conditions, leading to uniform g-CNQDs with a particle size of 2.22±0.68 nm. The as prepared g-CNQDs showed photoluminescence emission with a quantum yield of 3.1 %. This concept (MOF dual functionality) for catalyzing CA polycondensation (open metal sites (OMSs) effect) and controlling the produced particle size (pore-templating effect), together with the tunable MOF porosity, is expected to produce unique g-CNQDs with controllable size, morphology, and surface functionality.

Surface-coordinated metal-organic framework thin films (SURMOFs) for electrocatalytic applications

The design and development of highly efficient electrocatalysts are very important in energy storage and conversion. As a kind of inorganic organic hybrid material, metal-organic frameworks (MOFs) have been used as electrocatalysts in electrocatalytic reactions due to their structural diversities and fascinating functionalities. Particularly, MOF thin films are coordinated on substrate surfaces by a liquid phase epitaxial (LPE) layer by layer (LBL) growth method (called surface-coordinated MOF thin films, SURMOFs), and recently have been studied in various applications due to their precisely controlled thickness, preferred growth orientation and homogeneous surface. In this review, we will summarize the preparation and electrocatalysis of SURMOFs and their derived thin films (SURMOF-D). The SURMOF based thin films possess diverse topological structures and flexible properties, providing abundant catalytically active sites and fast charge transfer for efficient electrocatalytic performance in the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CRR), supercapacitors, tandem electrocatalysis and so on. The research challenges and problems of SURMOFs for electrocatalytic applications are also discussed at the end of the review.

l-Histidine Crystals as Efficient Vehicles to Deliver Hydrophobic Molecules

l-Histidine (l-His) molecules can form highly ordered fluorescent crystals with tunable size and geometry. The polymorph A crystal of l-His contains hydrophobic domains within the structure's interior. Here, we demonstrate that these hydrophobic domains can serve as vehicles for highly efficient entrapment and transport of hydrophobic small molecules. This strategy shows the ability of l-His crystals to mask the hydrophobicity of various small molecules, helping to address issues related to their poor solubility and low bioavailability. Furthermore, we demonstrate that we can modify the surface of these crystals to define their function, suggesting the significance of l-His crystals in designing site-specific and bioresponsive platforms. As a demonstration, we use l-His crystals with loaded doxorubicin, featuring hyaluronic acid covalently bonded on the crystal surface, controlling its release in response to hyaluronidase. This strategy for entrapment of hydrophobic small molecules suggests the potential of l-His crystals for targeted drug-delivery applications.

MOF-templated synthesis of 3D Bi2O3 supracrystals with bcc packing

We describe a non-conventional, MOF-based approach with modified linkers to fabricate 3D Bi2O3 supracrystals. The nanoparticle (NP) assembly exhibits bcc-packing, which is difficult to achieve with other methods. The NPs possess a very narrow size distribution. The individual NPs were synthesized inside the pores of a surface-mounted metal-organic framework (SURMOF) template via a photo-decomposition procedure. The supracrystals were thoroughly characterized using X-ray diffraction (XRD), infrared (IR) and Raman spectroscopy as well as high-resolution transmission electron microscopy (HR-TEM) and SAED (Selected Area Electron Diffraction). In order to achieve sharp size distributions of the NPs, the pores within the SURMOF were functionalized with amino (-NH2) functional groups acting as nucleation centers. MOFs lacking such additional functionalities, Cu3(BTC)2, yielded much broader size distributions. These findings provide a unique molecular design tool for creating nanometer-sized reaction compartments for the synthesis of supracrystals with packing types not accessible via self-assembly.

Improving the Loading Capacity of Metal-Organic Framework Thin Films Using Optimized Linkers

The large surface area of metal-organic frameworks (MOFs) sparks great interest for their use in storage applications. While the bulk of MOF applications focuses on incorporation of gases, we demonstrate that these highly porous frameworks are also well-suited for metal ion storage. For well-defined, highly oriented surface-anchored MOF thin films grown on modified gold surfaces using liquid-phase epitaxy (LPE), also referred to as SURMOFs, we determined the loading of two different types of MOF materials with a total of seven types of metal ions (Zn(2+), Ag(+), Pd(2+), Fe(3+), Cd(2+), Ni(2+), and Co(2+)). Measurements using a quartz crystal microbalance (QCM) allowed determination of loading capacities as well as diffusion constants in a quantitative fashion. The adsorption capacities were observed to be highly ion specific; the largest uptake was for Fe(3+) and Pd(2+) ions with six and four metal ions per MOF pore, respectively. By comparing results for SURMOFs fabricated from different types of linkers, we demonstrate that S-containing functionalities in particular drastically improve the storage capacity of MOFs for metal ions.

Bi₂O₃ nanoparticles encapsulated in surface mounted metal-organic framework thin films

We describe a novel procedure to fabricate a recyclable hybrid-photocatalyst based on Bi2O3@HKUST-1 MOF porous thin films. Bi2O3 nanoparticles (NPs) were synthesized within HKUST-1 (or Cu3(BTC)2) surface-mounted metal-organic frame-works (SURMOFs) and characterized using X-ray diffraction (XRD), a quartz crystal microbalance (QCM) and transmission electron microscopy (TEM). The Bi2O3 semiconductor NPs (diameter 1-3 nm)/SURMOF heterostructures exhibit superior photo-efficiencies compared to NPs synthesized using conventional routes, as demonstrated via the photodegradation of the nuclear fast red (NFR) dye.

Chiral Porous Metacrystals: Employing Liquid-Phase Epitaxy to Assemble Enantiopure Metal-Organic Nanoclusters into Molecular Framework Pores

We describe the fabrication of hybrid yet well-ordered porous nanoparticle (NP) arrays with full three-dimensional periodicity by embedding nanometer-sized metal-organic clusters (MOCs) into metal-organic frameworks (MOFs). Although conventional NP@MOF encapsulation procedures failed for these fairly large (1.66 nm diameter) NPs, we achieved maximum loading efficiency (one NP per pore) by using a modified liquid phase epitaxy (LPE) layer-by-layer approach to grow and load the MOF. The preformed NPs, homochiral Ti4(OH)4(R/S-BINOL)6 clusters (Ti-MOC, BINOL = 1,1'-bi-2-naphthol), formed a regular lattice inside the pores of an achiral HKUST-1 (or Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate) MOF thin film. Exposure to the different enantiomers of methyl lactate revealed that the NP@MOF metacrystal is quite efficient regarding enantiomer recognition and separation. The approach presented here is also suited for other MOF types and expected to provide a substantial stimulus for the fabrication of metacrystals, crystalline solids made from nanoparticles instead of atoms.

Controlling embedment and surface chemistry of nanoclusters in metal–organic frameworks

A combined theoretical and experimental approach demonstrates that nanocluster embedment into the pores of metal–organic frameworks (MOF) may be influenced by the chemical functionalisation of the MOF.

Liquid-Phase Epitaxy Effective Encapsulation of Lanthanide Coordination Compounds into MOF Film with Homogeneous and Tunable White-Light Emission

As a new family of hybrid inorganic-organic materials with large porosity, metal-organic frameworks (MOFs) have received attractive attention recently on encapsulating functional guest species. Although the encapsulation of luminescent guest into bulk MOFs can tune the luminescent property, the powder composite materials are limited to the application in optical sensors and devices. In the present work, we use a modified liquid-phase epitaxial (LPE) pump method for the fabrication of lanthanide coordination compounds (LCCs)-encapsulated MOF thin film on substrate with high encapsulation efficiency. The resultant composite film reveals an oriented and homogeneous composite film, in which a white light emission by tuning the LCCs of red, blue and green emission can be obtained. This strategy may open new perspectives for developing high-encapsulation-efficiency, oriented, and homogeneous solid-state lighting composite films in the application of optical sensors and devices.

Planar-chiral building blocks for metal–organic frameworks

The first example of a planar-chiral building block being used for chiral metal–organic frameworks (MOFs) is presented.