An official website of the United States government
Abstract Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications. MOF nanocrystals, and their assembled super-structures, can display unique properties and reactivities when compared with their bulk analogues. MOF nanostructures of 0-D, 2-D, and 3-D dimensions can be routinely obtained by controlling reaction conditions and ligand additives, while formation of 1-D MOF nanocrystals (nanowires and nanorods) and super-structures has been relatively rare. We report here a facile templated interfacial synthesis methodology for the preparation of a series of 1-D MOF nano- and micro-structures with precisely controlled shapes and sizes. Specifically, by applying track-etched polycarbonate (PCTE) membranes as the templates and at the oil/water interface, we rapidly and reproducibly synthesize zeolitic imidazolate framework-8 (ZIF-8) and ZIF-67 nano- and micro structures of sizes ranging from 10 nm to 20 μm. We also identify a size confinement effect on MOF crystal growth, which leads to single crystals under the most restricted conditions and inter-grown polycrystals at larger template pore sizes, as well as surface directing effects that influence the crystallographic preferred orientation. Our findings provide a potentially generalizable method for controlling the size, morphology, and crystal orientations of MOF nanomaterials, as well as offering fundamental understanding into MOF crystal growth mechanisms.
more »
« less
Metal-Organic Framework Nanoparticles
Due to their well-defined 3D architectures, permanent porosity, and diverse chemical functionalities, metal–organic framework nanoparticles (MOF NPs) are an emerging class of modular nanomaterials. Herein, recent developments in the synthesis and postsynthetic surface functionalization of MOF NPs that strengthen the fundamental understanding of how such structures form and grow are highlighted; the internal structure and external surface properties of these novel nanomaterials are highlighted as well. These fundamental advances have resulted in MOF NPs being used as components in chemical sensors, biological probes, and membrane separation materials, as well as building blocks for colloidal crystal engineering.
more »
« less
- Award ID(s):
- 1709888
- PAR ID:
- 10065615
- Date Published:
- Journal Name:
- Advanced Materials
- ISSN:
- 0935-9648
- Page Range / eLocation ID:
- 1800202
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Determination of the surface hydrophobicity or wettability of nanomaterials and nanoparticles (NPs) is often challenged by the heterogeneous properties of NPs that vary with particle size, shape, surface charge, aggregation states, and surface sorption or coating. This study first summarized inherent limitations of the water contact angle, octanol–water partition coefficient ( K ow ) and surface adsorption of probe molecules in probing nanomaterial hydrophobicity. Then, we demonstrated the principle of a scanning probe method based on atomic force microscopy (AFM) for the local surface hydrophobicity measurement. Specifically, we measured the adhesion forces between functionalized AFM tips and self-assembled monolayers (SAMs) to establish a linear relationship between the adhesion forces and water contact angles based on the continuum thermodynamic approach (CTA). This relationship was used to determine the local surface hydrophobicity of seven different NPs ( i.e. , TiO 2 , ZnO, SiO 2 , CuO, CeO 2 , α-Fe 2 O 3 , and Ag), which agreed well with bulk contact angles of these NPs. Some discrepancies were observed for Fe 2 O 3 , CeO 2 and SiO 2 NPs, probably because of surface hydration and roughness effects. Moreover, the solution pH and ionic strength had negligible effects on the adhesion forces between the AFM tip and MWCNTs or C 60 , indicating that the hydrophobicity of carbonaceous nanomaterials is not influenced by pH or ionic strength (IS). By contrast, natural organic matter (NOM) appreciably decreased the hydrophobicity of MWCNTs and C 60 due to surface coating of hydrophilic NOM. This scanning probe method has been proved to be reliable and robust toward the accurate measurement of the nanoscale hydrophobicity of individual NPs or nanomaterials in liquid environments.more » « less
-
Hybrid materials combining the optoelectronic absorption and tunability of quantum dots (QDs) with the high surface area, chemical functionality, and porosity of metal-organic frameworks (MOFs) are emerging as systems with unique optoelectronic properties relevant to applications in catalysis, sensing, and energy conversion and storage. A key component of the electronic interaction between QDs and MOFs is the transfer of charge between the two materials. This review examines the mechanisms driving charge transfer at the QD/MOF interfaces and the effects that both physical and chemical composition have on this process. We provide an overview of the key experimental approaches, including spectroscopic and electrochemical techniques, which have been used for probing charge transfer dynamics in this hybrid system. Challenges in controlling interfacial structure, distinguishing between charge and energy transfer, and optimizing stability are also discussed. This review highlights recent work on the preparation and characterization of QD/MOF hybrid materials, as well as fundamental studies advancing the understanding of charge transfer processes that occur in these systems.more » « less
-
Access to well-defined, model-like, non-noble metal intermetallic compound nanomaterials (<10 nm) with phase pure bulk, bulk-like 1st-atomic-layer surface composition, and unique electronic and surface chemical properties is critical for the fields of catalysis, electronics, and sensor development. Non-noble metal intermetallic compounds are compositionally ordered solid compounds composed of transition metals and semimetals or post-transition metals. Their synthesis as model-like high-surface-area supported nanoparticles is challenging due to the elevated reactivity of the constituent elements and their interaction with the support material. In this study, we have developed a systematic understanding of the fundamental phenomena that control the synthesis of these materials such that phase pure bulk nanoparticles (<10 nm) may be produced with bulk-like surface terminations. The effects of the precursor and support choice, chemical potential of H 2 , reduction temperature, and annealing procedures were investigated to understand the fundamental kinetics of particle formation and interactions that dictate phase purity and stability and 1st-atomic-layer surface composition. The understanding developed may serve as a foundation for further developing advanced synthesis procedures for well-defined nanoparticles with increasing compositional complexity.more » « less
-
Abstract Nanoparticles of zeolitic imidazole framework‐8 (ZIF‐8 NPs), which are the subclass of metal‐organic frameworks consisting of Zn ion and 2‐methylimidazole, have been identified as promising drug carriers since their large microporous structure is suited for encapsulating hydrophobic drug molecules. However, one of the limitations of ZIF‐8 NPs is their low stability in physiological solutions, especially in the presence of water and phosphate anions. These molecules can interact with the coordinatively unsaturated Zn sites at the external surface to induce the degradation of ZIF‐8 NPs. In this study, herein a facile approach is reported to enhance the chemical stability of ZIF‐8 NPs by surface coating with polyacrylic acid (PAA). The PAA‐coated ZIF‐8 (PAA‐ZIF‐8) NPs are prepared by mixing ZIF‐8 NPs and PAA in water. PAA coating inhibits the degradation of ZIF‐8 NPs in water as well as phosphate‐buffered saline over 6 days, which seems to be due to the coordination of carboxyl groups of PAA to the reactive Zn sites. Furthermore, the PAA‐ZIF‐8 NPs loaded with the anticancer drug doxorubicin (Dox) show cytotoxicity in human colon cancer cells. These results clearly show the feasibility of the PAA coating approach to improve the chemical stability of ZIF‐8 NPs without impairing their drug delivery capability.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adma.201800202
