Synthesis and molecular level characterisation of amorphous microporous networks

Conjugated microporous polymers (CMPs) are a class of materials that have advantageous properties, such as extended π-conjugation, tuneable micropore size and surface area, and the ability to swell. Owing to the limited solubility and the amorphous nature of CMPs, little information is known about their structure and characterisation is dominated by solid-state NMR spectroscopy. NMR is a technique which is sensitive to both molecular level structure and dynamics. An increase in understanding of these networks is required to give an overall picture of their physical properties and origins of flexibility, ultimately leading to the design of such materials for specific applications. In addition to the challenges with characterisation, a considerable disadvantage of CMPs is the cost of their synthesis. Many of the current routes to CMPs involve the use of heavy metal catalysts. Development of methodologies that use cheap monomers and do not require metal catalysts would increase the viability of CMPs for use in industrial applications. In this work advanced structural elucidation and investigations of network flexibility and porosity were achieved using two approaches. The first involves identification of a reaction mechanism for the formation of CMP-1 by examination of the products of reaction after incremental time periods. The second involves employing advanced solid-state NMR techniques, specifically deuterium NMR, to probe the molecular motions of deuterated versions of CMP-1 and CMP-2. Swelling experiments of CMP-1 and CMP-2 with benzene-d6 were also used to investigate changes in porosity for swollen and non-swollen networks. A new synthetic route to CMPs was also developed by exploiting the reaction between aldehydes and amines. In particular the formation of aminal linkages shall be explored, as this would allow preparation of branched networks from bi-functional monomers. Newly synthesised materials are to be fully characterised and their gas sorption properties will be analysed

Quid Pro Flow

How do you get into flow? We trained in flow chemistry during postdoctoral research and are now applying it in new areas: materials chemistry, crystallization, and supramolecular synthesis. Typically, when researchers think of "flow", they are considering predominantly liquid-based organic synthesis; application to other disciplines comes with its own challenges. In this Perspective, we highlight why we use and champion flow technologies in our fields, summarize some of the questions we encounter when discussing entry into flow research, and suggest steps to make the transition into the field, emphasizing that communication and collaboration between disciplines is key

Quid Pro Flow

How do you get into flow? We trained in flow chemistry during postdoctoral research and are now applying it in new areas: materials chemistry, crystallization, and supramolecular synthesis. Typically, when researchers think of “flow”, they are considering predominantly liquid-based organic synthesis; application to other disciplines comes with its own challenges. In this Perspective, we highlight why we use and champion flow technologies in our fields, summarize some of the questions we encounter when discussing entry into flow research, and suggest steps to make the transition into the field, emphasizing that communication and collaboration between disciplines is key

Size-controlled synthesis of spinel nickel ferrite nanorods by thermal decomposition of a bimetallic Fe/Ni-MOF

In this work, size-controlled synthesis of nickel ferrite nanoparticles was achieved by the calcination of a bimetallic (Fe/Ni) metal-organic framework (MOF). The bimetallic MOF (Fe2Ni-MIL-88B) itself was prepared by a two-step route. The first step involved synthesis of the secondary building unit (SBU) by reacting stoichiometric amounts of Ni and Fe precursors with acetic acid. A ligand substitution reaction (terephthalate replaces acetate) in the SBU leads to the formation of the MOF, which was characterized by PXRD, FTIR, SEM and TEM. Afterwards, the MOF was calcined under air atmosphere to obtain nickel ferrite nanorods. PXRD analysis confirmed the spinel structure of the nickel ferrites while electron microscopic analysis (SEM, TEM) revealed their nanorod-like morphology. By increasing the calcination temperature from 600 to 1000 °C, particle size increased from 16 to 32 nm. Oxidation of benzyl alcohol was used as a model test reaction to probe the applicability of spinel nickel ferrite nanorods for catalysis. Interestingly, the largest nanorods exhibited the highest activity (86% conversion), thus demonstrating the potential of spinel ferrites in catalyzing oxidation reactions

Combining continuous flow oscillatory baffled reactors and microwave heating: Process intensification and accelerated synthesis of metal-organic frameworks

We have constructed a continuous flow oscillatory baffled reactor (CF-OBR) equipped with a homogeneous and controllable microwave applicator in an entirely novel design. This affords a new route to chemical production incorporating many of the principles of process intensification and allows, for the first time, investigation of the synergistic benefits of microwave heating and CF-OBRs such as; faster and continuous processing; improved product properties and purity; improved control over the processing parameters; and reduced energy consumption. The process is demonstrated by the production of a metal-organic framework (MOF), HKUST-1, a highly porous crystalline material with potential applications in gas storage and separation, catalysis, and sensing. Our reactor enabled the production of HKUST-1 at the 97.42 g/h scale, with a space time yield (STY) of 6.32 × 105 kg/m3/day and surface area production rate (SAPR) of 1.12 × 1012 m2/m3/day. This represents the highest reported STY and fastest reported synthesis (2.2 seconds) for any MOF produced via any method to-date and is an improvement on the current SAPR for HKUST-1 by two orders of magnitude owing to the superior porosity exhibited by HKUST-1 produced using our rig (Langmuir surface area of 1772 compared to 600 m2/g)

Developing a sustainable route to environmentally relevant metal-organic frameworks: ultra-rapid synthesis of MFM-300(Al) using microwave heating

NO2, SO2 and CO2 are major air pollutants causing significant environmental and health problems. Metal-organic frameworks (MOFs), in particular [Al2(OH)2(C16O8H6)](H2O)6 (trivial names: NOTT-300/MFM-300(Al)), have shown great promise for capturing these gases. However MOF syntheses often involve toxic solvents and long durations which are inherently energy intensive, an environmental burden, and have serious safety risks. There is a pressing need to develop environmentally-friendly routes to MOFs that require less energy and implement safer solvents particularly when considering scale-up beyond the laboratory for industrial application. We report the rapid synthesis of MFM-300(Al) in aqueous conditions and 10 minutes using microwave heating. This is the fastest reported synthesis of MFM-300(Al) to date with a 99.77 % reduction in reaction time compared to the current reported 3-day conventional heated route. The microwave synthesized sub-micron crystalline material exhibits gas uptake capacities of 8.8 mmol g-1 at 273 K and 1.0 bar for CO2, 8.5 mmol g-1 at 298 K and 0.17 bar for SO2, and 1.9 mmol g-1 at 298 K and 0.01 bar for NO2. These are 26 %, 70 %, and 90 % greater for CO2, SO2, and NO2, respectively, when compared to previously reported MFM-300(Al) materials produced via a 3-day conventionally heated route demonstrating the production of high quality materials at a fraction of the time with enhanced gas properties. Crucially, this offers an opportunity to move from batch to continuous processing owing to reduced reaction times underpinned by targeted heating

Realising the environmental benefits of metal–organic frameworks: recent advances in microwave synthesis

Metal–organic frameworks (MOFs) are a broad class of porous crystalline materials that show great potential for a wide-range of applications in areas such as energy and environmental sustainability. MOFscan show significant advantages in gas selectivity and separation over traditional adsorbents such as zeolites and activated carbons since they are tuneable both in terms of porosity and chemical functionality. The ability to control the pore environment of the MOF is one of their remarkable advantages and affords control over the structure and properties required for specific applications. Despite these advantages, the industrial adoption of MOFs is slow owing to the paucity of scalable, environmentally sustainable manufacturing methods and higher costs compared to zeolites. Microwave (MW) technology is an extremely promising method of MOF production owing to significantly reduced reaction times and subsequently lower process energy consumption, control over MOF properties, and the ability to produce MOFs and MOF-hybrids otherwise difficult to isolate or unobtainable through other synthetic routes. However, the ability to produce the multiple kilogram or even tonne quantities of MOFs required by industry using MW technology is yet to be achieved owing to little or no understanding of the interaction(s) of reactants and MOFs with the electric field, and crucially, how this informs the design of the scale up processes. This review aims to bridge this gap in knowledge by (1) highlighting recent advances in understanding of MW–MOF interactions and areas for future focus; (2) providing an up-to-date and comprehensive summary of literature on MW synthesis of MOFs, focusing on examples where MW heating has facilitated novel and unique results in the laboratory; and (3) emphasising the advantages, challenges and current steps and methodologies required towards industrial-scale MW production of MOFs

Network formation mechanisms in conjugated microporous polymers

We discuss in detail the mechanism of formation of a highly microporous polymer, CMP-1, formed mainly via Sonogashira–Hagihara coupling. We demonstrate how the microporosity evolves with time, and discuss the importance of alkyne homo-coupling on the microporosity

Rapid synthesis of magnetic microspheres and the development of new macro–micro hierarchically porous magnetic framework composites †

Magnetic framework composites (MFCs) are a highly interesting group of materials that contain both metal–organic frameworks (MOFs) and magnetic materials. Combining the unique benefits of MOFs (tuneable natures, high surface areas) with the advantages of magnetism (ease of separation and detection, release of guests by induction heating), MFCs have become an attractive area of research with many promising applications. This work describes the rapid, scalable synthesis of highly porous magnetic microspheres via a flame-spheroidisation method, producing spheres with particle and pore diameters of 206 ± 38 μm and 12.4 ± 13.4 μm, respectively, with a very high intraparticle porosity of 95%. The MFCs produced contained three main iron/calcium oxide crystal phases and showed strong magnetisation (Ms: 25 emu g−1) and induction heating capabilities (≈80 °C rise over 30 s at 120 W). The microspheres were subsequently surface functionalised with molecular and polymeric coatings (0.7–1.2 wt% loading) to provide a platform for the growth of MOFs HKUST-1 and SIFSIX-3-Cu (10–11 wt% loading, 36–61 wt% surface coverage), producing macro–micro hierarchically porous MFCs (pores > 1 μm and <10 nm). To the best of our knowledge, these are the first example of MFCs using a single-material porous magnetic scaffold. The adaptability of our synthetic approach to novel MFCs is applicable to a variety of different MOFs, providing a route to a wide range of possible MOF–microsphere combinations with diverse properties and subsequent applications