•Metal-organic frameworks (MOFs) are attractive materials for many industrial applications.•Limited cost-effective MOF production technologies account for the slow progress of MOF-based products.•This short review brings together scattered literature that addresses pilot-scale production of MOF materials.•Some technical aspects for accelerating the transition of MOFs from laboratory to real-world application are also presented.Metal-organic frameworks (MOFs) have been under development over the past 20 years. Similar to other technologies, research on MOFs in the upcoming 30 years will move towards the direction where MOF materials can deliver societal benefits by solving real-world problems. Taking technology from laboratory to applications is always a challenge. Analysis of the current MOFs research efforts indicates that the high cost, limited availability of MOF products and the knowledge gap for cost-effective production technologies account for the slow progression towards the development of envisioned MOF products at pilot-scale level. This short review brings together the scattered literature that addresses pilot-scale production of MOF materials. An additional aspect focuses on the progress on the development of pilot-scale synthetic strategies with green and sustainable features for MOF materials, which is an imperative to promote MOF-enabled products into the real world.Download high-res image (287KB)Download full-size image

•Research on MOF materials has expanded to various novel applications.•Knowledge needs to be available to aid the proper use of MOF structural defects.•This review covers MOF structural defects towards envisioned applications.•The latest advances on formation, detection and control of MOF defects are discussed.Research on metal–organic framework (MOF) materials has gathered increasing interest starting from the early excitement as porous materials for gas storage down to various novel applications as catalysts, heat energy storage materials, chemical sensors, drug delivery and electronic-related devices. Towards these envisioned applications, the specific properties of MOFs need to be tailored strategically to achieve the optimized performance. Since the structural defects in MOFs were recognized by MOF research community, the introduction of defects into MOF structures has been proposed as a way to alter their performance behaviours for the intended applications. For example, MOFs structural defects have been demonstrated to be beneficial in applications such as by leading to: (a) improved gas diffusion and mass transport caused by missing linker and metal vacancies, (b) enhanced catalytic performance caused by the open metal sites, (c) optimized operation of MOF-battery materials by grafted metal ions or counter-ions at defects and (d) other effects on electronic, magnetic or optical functionalities. This review starts with a discussion on the presence and formation of the structural defects in MOFs and thereafter highlights the latest advances in the detection techniques of MOF defects. Later, the discussion focusses on defects’ control towards practices of various interests and finally outlines possible future research directions for MOFs’ defects.

•Waste PET bottles were used as a direct source of BDC acid linker to synthesis Cr-MOF.•The obtained Cr-MOF materials are good for hydrogen storage applications.•It is of great economic value to produce PET-based MOF materials.It is of great economic value to produce high-value PET-based MOF materials by the veritable elimination of waste PET, and provide sufficient MOF materials for hydrogen storage applications. Consequently, this work demonstrates the use of waste PET bottles as direct source of BDC acid linker during the synthesis of Cr-MOF. The PET-derived Cr-MOF materials showed even better textural and hydrogen storage properties than that from commercial BDC (Sigma–Aldrich).

•Zr-/Cr-MOF nanocrystals as examples were incorporated into electrospun nanofibers.•The vacuum degassing was able to create visible porosity.•The MOF nanocrystals inside the polymeric nanofibers were fully accessible by H2 gas.•The composites can achieve over 50% H2 uptake of those of individual MOF nanocrystals.In this study, Zr-MOF and Cr-MOF were chosen as representatives of the developed MOFs in our laboratory and were incorporated into electrospun nanofibers. The obtained MOF nanofibers composites were evaluated as hydrogen storage media. The results showed that the incorporation of vacuum degassing was able to create visible porosity in and/or on the PAN nanofibers and the MOF nanocrystals inside the polymeric nanofibers were fully accessible by N2 and H2 gases. With 20 wt.% loading of MOF nanocrystals, the composites were able to achieve over 50% of the H2 uptake capacity of individual MOF nanocrystals. In addition, the composites also showed good thermal stabilities.

•Zr-fumarate MOFs were synthesized using water as solvent and HCOOH as modulator.•The resultant Zr-fum MOFs has high thermal and hydro stabilities.•The H2 uptake capacity is comparable to early reported MOF materials.•The easy production qualifies them as good candidate for H2 storage applications.In this work, we synthesized Zr-fumarate MOFs by applying water as solvent and formic acid as modulator. Highly crystalline Zr-fumarate MOF obtained from 120 °C, 24 h synthesis conditions showed high thermal and hydro stabilities. Compared to the early reported MOF materials, the lower cost, more environmentally friendly synthesis process and comparable hydrogen uptake capacity make Zr-fumarate MOFs a good candidate for hydrogen storage applications.

•Powder Zr-MOF material was shaped into pellets (0.5–15 mm) using sucrose as binder.•The diameter of pellets can be controlled by shaping time.•The Zr-MOF pellets can be produced in kilograms order within 30 min operation time.•Drop and tumbling tests were used to evaluate the mechanical strength of the pellets.•The process facilitates the transition of MOF powders from lab to applications.Shaping of Zr-MOF powder material into spherical pellets with diameters of 0.5–15 mm in the presence of 10 wt.% sucrose as a binder was successfully demonstrated using a granulator. Zr-MOF pellets were produced in a kilogram batch within 30 min operation time. This granulation approach is a more efficient way to shape MOF-type powder materials into application-specific configurations compared to the mechanical pressing method. The pellets could be conveniently packed in a small hydrogen storage tank. The physical degradation characteristics of the Zr-MOF pellets were studied by drop test and simulated tumbler drum test. The results showed zero breakage of the pellets after 70 consecutive drops at a height of 0.5 m and 5% breakage after 60 min of tumbling time at a speed of 25 rpm. Although the compromised value of the surface area led to a decreased hydrogen storage capacity, this shaping approach still holds promise given an appropriate choice of binder.

•Bipyramidal core–shell MIL-101@UiO-66 nanocrystals was prepared via a facile method.•It has high thermo-stability and good moisture tolerance.•It has enhanced H2 storage capacity over the individual MOF components.The fabrication of core–shell nanocrystals by incorporating microporous UiO-66 into mesoporous MIL-101 is reported. The growth of the core–shell MIL-101@UiO-66 nanocrystals was observed and supported by TEM and PXRD. The accessible pore volumes of the individual metal-organic framework (MOF) components and the core–shell hybrid crystals were also characterized. The hydrogen storage capacity exhibited by the resulting core–shell nanocrystals was 26% and 60% higher than those of pure phase MIL-101 and UiO-66, respectively. Finally, the fabricated core–shell MIL-101@UiO-66 structure exhibited a high degree of moisture tolerance.

•High crystalline Cr-MOF with well-defined shape was prepared via modulated synthesis.•High reproducibility can be expected at certain optimized synthesis conditions.•It has good structure-stability in 80 °C H2O and DMF solutions for 5 days.•It has enhanced H2 storage capacity against the reported results.Modulated synthesis of MIL-101(Cr) in high yield and with good reproducibility using formic acid as a modulator is reported. Higher molar ratio of formic acid/CrCl3 was found to form better shape-defined MIL-101(Cr) crystals with higher surface area, larger pore volume and better hydrogen uptake performance. The highly crystalline MIL-101(Cr), composed of crystals in the size range of 100–150 nm with multifaceted surface, could be obtained in an optimized molar regime of CrCl3·6H2O/H2BDC/100HCOOH/550H2O at 210 °C for 8 h. The MIL-101(Cr) obtained from the modulated synthesis also showed high thermal and moisture stabilities as well as enhanced hydrogen storage capacity, making this material particularly promising for practical hydrogen storage applications.

•High crystalline Zr-MOF with well-defined shape was prepared via modulated synthesis.•It has improved ease of handling during filtration process with micro-sized crystals.•It has higher thermo-stability and good stability in selected aqueous media.•It has enhanced H2 storage capacity against the reported results.A modulated synthesis of Zr-metal organic framework (Zr-MOF) with improved ease of handling and decreased reaction time is reported to yield highly crystalline Zr-MOF with well-defined octahedral shaped crystals for practical hydrogen storage applications. The Zr-MOF obtained from the modulated synthesis showed high thermal and moisture stabilities with enhanced hydrogen storage capacity. Further study suggests that the modulated synthesis of Zr-MOF may lead to the development of a flow-through synthesis process.

In this work, enrichment of para-hydrogen is performed by flowing ultra-purity hydrogen gas at low temperature (77K) in the presence of a developed catalyst anchored in a MOF hybrid material. This approach fits within the bigger scope of the development of a novel material-based controllable switch for uptake/release of hydrogen in a storage system. The effect of the tuned dielectric properties of the material was tested against the hydrogen storage capacities.

•In-situ IR monitoring technique was for the first time used to monitor the crystallization of Zr-fumarate MOF.•The participations of both modulator acid (HCOOH) and solvent (DMF) during the structural formation of Zr-fum MOF were abserved.•The results help to understand the formation of structural defects in MOFs.The in-situ IR technique was employed to monitor the crystallization process of Zr-fumarate (Zr-fum) MOF under real synthesis conditions. The results evidenced the participations of both modulator acid (HCOOH) and solvent (DMF) during the structural formation of Zr-fum MOF. This observation will contribute to the quest for understanding of the formation of structural defects in MOFs, which is a topic that is currently under intense investigation.