One of the distinguishing features of metal-organic frameworks and other non-traditional porous materials, such as interlocked cage molecules, is their ability to respond flexibly to changes in their environment by changing their structures. There are a variety of mechanisms for this, including the relative displacement of two rigid networks and the repositioning of a linker with respect to an inorganic building unit. We have concentrated on rotations about single bonds in organic linkers as a route to change structures that has some similarities with the restructuring mechanisms adopted by biological molecules. This presentation will both review progress and cover recent results that include a new system that adopts multiple distinct crystal structures by this single bond rotation mechanism.(1)
Reticular chemistry is concerned with linking of molecular building blocks with strong bonds into extended structures. This has resulted in metal-organic frameworks and covalent organic frameworks. The chemistry of these frameworks and their application to harvesting water from desert air among other applications will be presented.
Metal-organic frameworks (MOFs) have been at the forefront of research activity for almost two decades now. In the present work, we developed various MOFs that can carry out many energy-intensive separations either by a periodic arrangement of requisite functionalities in the channels for optimal host-guest interactions or by tuning the aperture size of the channel window to afford size-selective separations. We were able to achieve many industrially important separations like CO2 capture, olefin/paraffin separation, branched/linear paraffin separation and natural gas upgrading. Molecular-level Insight was obtained for a better understanding of the separation processes. In collaboration with industrial partners, some of the MOFs with exceptional performance will be investigated in a real like conditions at demonstration scale for taking them to the next level. Economical and rapid scale-up methods for these materials are being developed and we have successfully produced these materials in kg quantities.
Membrane-based separation is a promising alternative to conventional processes such as cryogenic distillation and/or adsorption based separation. Among the existing membranes for gas separation, polymeric membranes and inorganic membranes have been immensely studied, but each type has its own pros and cons. Therefore, current situation demands the development of mixed matrix membranes (MMMs) by incorporating molecular sieve fillers into the polymer matrix, which provides a decent strategy to combine the merits of each material and fabricate novel hybrid membranes with superior gas separation performance. Metal-organic frameworks (MOFs) have been proposed as novel molecular sieve fillers owing to their unique pore structure and chemical variability. MMMs fabricated using MOFs fillers was supposed to outperform other porous fillers, but due to the limitation in separation performance of the filler within and challenges concerning the compatibility between MOF filler and polymer interface structure, only a small fraction of the works reported both improved permeability and selectivity simultaneously. In this presentation, we will show our research focused on enhancing the compatibility of the MOF filler and polymer matrix by judiciously modifying the MOF’s surface chemistry, and exploring how morphology, particle size and particle distribution drastically influence gas separation performance.
Using examples from our recent work, I will present two approaches used by our group to develop porous materials to be applied in a variety of separation applications. The first one is a curiosity-driven approach, which we employ either for new separation challenges for which benchmark and/or performance targets are ill-defined or in the context of emerging adsorbent materials. I will illustrate this aspect through our recent findings on porous boron nitride. Our second approach, based on molecular engineering, accelerates materials development for well-defined applications. Such approach links molecular modelling, experiments and process modelling to quickly identify the best adsorbent(s) for a given separation. In this context, I will present our work on the use of metal organic frameworks for industrially relevant gas separations.
Two-dimensional materials have risen in popularity as a desired material for membrane in the last decade. Nanoporous single-layer graphene, prepared by incorporating subnanometer vacancy defects in the graphene lattice, is highly promising for high flux gas separation because the resistance to diffuse is controlled by a single transition state at the nanopore [1–3]. Molecular sieving resolution (MSR), defined as the difference in the kinetic diameters of molecules to be separated, of a fraction of an angstrom has been predicted, allowing separation of industrially-relevant mixtures such as CO2/N2, CO2/CH4, O2/N2, etc, allowing graphene-based membranes to compete with those from zeolites and carbon molecular sieves. However, the realization of single-layer graphene membranes for gas separation has been hampered because of the difficulty in controlling the nucleation and growth of vacancy defects in graphene.
Modification of membrane surfaces by grafting polymer brushes from the surface has been shown to impart unique surface properties. Here we focus on magnetically responsive membranes where magnetically responsive polymer chains are grown from the membrane surface. We have developed a range of microfiltration1, ultrafiltration2 and nanofiltration3 membranes by grafting magnetically responsive polymer brushes from the membrane surface. Atom transfer radical polymerization (ATRP) has been used to graft poly-hydroxyethyl methacrylate (polyHEMA) from the surface of the membrane. Superparamagnetic nanoparticles have been attached to the chain ends. In an oscillating magnetic field, movement of the magnetically responsive nanobrushes leads to suppression of concentration polarization resulting in higher permeate fluxes and better rejection. We have also grafted poly(N-isopropylacrylamide) a thermo-responsive polymer that exhibits a lower critical solution temperature, using ATRP, from the surface of the membrane4. By carefully choosing the frequency of the oscillating magnetic field, movement of the polymer chains can induce mixing. Using much higher frequencies, around 1,000 Hz, heating will lead to collapse of poly(N-isopropylacrylamide) layer as the temperature of the grafted polymer layer increase above the lower critical solution temperature of the grafted poly(N-isopropylacrylamide).
Unlike nanofiltration and microfiltration membranes where the majority the polymer chains are grafted from the barrier layer or the inside pore surface respectively, in the case of ultrafiltration membranes significant grafting can occur from both the barrier layer and the internal pore surface. In addition, given the smaller pore sizes compared to microfiltration membranes, pore plugging by the grafted polymer chains must be avoided. We have developed a novel technique to selectively graft from the external barrier layer and not the internal membrane pore surface. We show that the magnetically responsive polymer brushes can have a significantly different effect on rejection and flux of model feed streams consisting of proteins such as bovine serum albumin, depending on their location on the membrane barrier layer or in the pores. Our work highlights the importance of being able to control not only the three-dimensional structure of the grafted polymers but also their location; from the membrane barrier layer or from the inside pore surface.
References 1. H. H. Himstedt, Q. Yang, X. Qian, S. R. Wickramasinghe, M. Ulbricht (2012), Toward remote-controlled valve functions via magnetically responsive capillary pore membranes’, J Membr. Sci., 423, 257-266. 2. B. M. Carter, A. Sengupta, X. Qian, M. Ulbricht, S. R. Wickramasinghe (2018), Controlling external versus internal pore modification of ultrafiltration membranes using surface-initiated AGET-ATRP, J Membr. Sci, 554, 109-116. 3. Q. Yang, Q., H. H. Himstedt, M. Ulbricht, X. Qian, X., S. R. Wickramasinghe, Designing magnetic field responsive nanofiltration membranes, J Membr. Sc., 430 (2013) 70-78. 4. X. Qian, Yang, Q., Vu, A. T., Wickramasinghe, S. R. (2016), ‘Localized Heat generation from Magnetically Responsive Membranes’, Industrial & Engineering Research, 55 (33), 9015-9027.
Seaside atrium of University Library
Auditorium between building 4 and 5
With the Industrial Revolution in the 19th century, humans began to create technologies that consumed huge amounts of energy. Initially, people used coal (solid) as an energy resource, but the 20th century ushered in the era of petroleum (liquid). In the 21th century, where the depletion of petroleum has become a concern, gases (e.g., natural gas and biogas) should play important roles. Hence, the trend has been shifting from solid to liquid to gas. In the future, an “era of gas” should be realized [1.2]. The recent advent of porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) as new functional microporous materials, have attracted the attention of chemists and physicists due to highly efficient capacity of storage, separation and conversion of gaseous substances. Among them, soft porous properties  of PCPs are essential for low-energy separation of gas resources, flue gases, air, pollutant gases and other industrial materials[4,5]. We could also develop several approaches to utilize PCPs for catalysts for CO” fixation .
REFERENCES  S. Kitagawa, Acc. Chem. Res., 2017, 50, 514–516. Commentary  S. Kitagawa, Angew.Chem.Int.Ed.,2015,54,10686-10687. Editorial  S.Horike, et al., Nature Chem. 2009,1,695. (Reviews) H.Sato, et al., Science. 2014,343,167.  C.Gu, et al., Science. 2014,363,387. S.Horike et al., Acc.Chem.Res.2013,46,2376.  P.Wu, et al., Nat.Commun.2019,10,4362.
The selective recognition of anions has numerous applications in areas as diverse as the environment and medicine. Most of these applications require anion recognition to occur in a competitive aqueous environment, but the design of receptors capable of selective binding to anions in water is difficult, predominantly as a result of the high hydration energy of anionic species. In natural systems, highly efficient and selective anion recognition is achieved through the construction of large peptides/proteins that take advantage of the numerous H-bonding interactions available from various amino acids with additional contributions from NH groups along the protein backbone. This has inspired research into the development of synthetic anion receptors that combine both natural and non-natural binding motifs. We present here novel anion receptors based on macrocyclic and linear peptidic and peptidomimetic scaffolds, that are capable of selective anion recognition, sensing, extraction or transport.
While recent OSN research efforts mostly focused on the synthesis and fabrication of solvent resistant membranes, fundamental understanding of chemical-physical aspects that govern solvent and solute transport in OSN membranes remains entirely unexplored. In spite of this, development of competitive membranes processes relies on the solid molecular-level understanding of transport mechanism in the membrane material. In this talk we critically discuss the hypothesis of membrane compaction, which has been invoked to explain solvent flux vs. p non-linearity in OSN experiments. Although physically sound, occurrence of membrane compaction under pressure does not have an experimental support. To demonstrate that the molecular origin of flux non-linearity is purely thermodynamic, we propose a thermodynamic-diffusion framework which describes solvent transport in OSN membranes in terms of the concentration gradient produced by the applied pressure across the membrane. Solvent diffusion coefficient in the membrane increases with increasing p, which further confirms that flux decline is not related to membrane compaction. This study demonstrates that the solution-diffusion model, if properly corrected for frame of reference (i.e., convection) and non-ideal effects, provides a satisfactory description of small molecule transport in OSN membranes, without the need to resort to pore-flow or more complicated transport models. In this talk we critically discuss the hypothesis of membrane compaction, which has been invoked to explain solvent flux vs. Dp non-linearity in OSN experiments. Although physically sound, occurrence of membrane compaction under pressure does not have an experimental support. To demonstrate that the molecular origin of flux non-linearity is purely thermodynamic, we propose a thermodynamic-diffusion framework which describes solvent transport in OSN membranes in terms of the concentration gradient produced by the applied pressure across the membrane. Solvent diffusion coefficient in the membrane increases with increasing Dp, which further confirms that flux decline is not related to membrane compaction. The developed framework allows to quantify both frame of reference and non-ideal thermodynamic effects on solvent diffusion coefficients in OSN membranes. This study demonstrates that the solution-diffusion model, if properly corrected for frame of reference (i.e., convection) and non-ideal effects, provides a satisfactory description of small molecule transport in OSN membranes, without the need to resort to pore-flow or more complicated transport models. Advancing fundamental understanding of OSN will lay the foundation for a more mature use of this process, and allow the most effective operative conditions to be set to maximize its productivity and efficiency.
Membrane-based gas separation is a rapidly emerging technology that has been well established for the purification hydrogen streams, nitrogen production from air and is showing an increasingly larger roles in natural gas sweetening and vapor/gas separations. One actively pursued strategy to generate new polymeric membrane materials with combinations of high permeability and high selectivity is the introduction of a bimodal distribution of microporosity (pores < 20 Å) and ultramicroporosity (pores < 7 Å) in the polymer matrix. It has been shown that rigid ladder-type chains comprising fused rings joined by sites of contortion pack inefficiently in the solid state to produce polymers of intrinsic microporosity (PIMs). Furthermore, the successful integration of monomers contorted by spirobisindane, ethanoanthracene, Tröger’s base and triptycene moieties into polyimide structures has generated highly permeable intrinsically microporous polyimides (PIM-PIs). Some of these PIMs and PIM-PIs exhibited significantly enhanced performance for O2/N2, H2/N2, H2/CH4 and CO2/CH4 separations with properties located on the most recent permeability/selectivity upper bounds.1,2 Several series of PIM-PIs will be presented based on rigid and bicyclic moieties, which are solution processable to form mechanically robust films with high internal surface areas (up to 1000 m2 g-1). Gas permeation and physisorption data indicate the development of ultramicroporous structures that are tunable for different gas separation applications. Specific emphasis will be placed on the potential use of hydroxyl- and carboxyl-functionalized PIM-PIs for energy demanding applications for natural gas treatment and olefin/paraffin separation. PIM-PIs with highly polar functional groups define the recently proposed 2018 mixed-gas polymer upper bound for CO2/CH4 separation.3 The potential use of PIM-PIs as matrix materials for hybrid polymer/MOF and microporous carbons will be demonstrated. References 1. Swaidan, R., Ghanem, B., Pinnau, I., ACS Macro Lett. 2: 947-951, 2015. 2. Comesaña-Gándara, B., Chen, J., Grazia Bezzu, C., Carta, M., Rose, I., Ferrari, M.-C., Esposito, E., Fuoco, A., Jansen, J.C., McKeown, N.B., Energy. Environ. Sci. 12: 2733-2740, 2019. 3. Wang, Y., Ma, X., Ghanem, B.S., Alghunaimi, F., Pinnau, I., Han, Y., Mater. Today Nano 3: 69-95, 2018.