Martin P. Attfield

Nanoporous Organic Polymer/Cage Composite Membranes

Organic?organic composite membranes are prepared by in?situ crystallization of cage molecules in a polymer of intrinsic microporosity. This allows a direct one-step route to mixed-matrix membranes, starting with a homogeneous molecular solution. Extremely high gas permeabilities are achieved, even after ageing for more than a year, coupled with good selectivity for applications such as CO2 recovery.

Crystal Growth of the Nanoporous Metal–Organic Framework HKUST-1 Revealed by In Situ Atomic Force Microscopy†

Shoaee, Maryiam Anderson, Michael W. Attfield, Martin R. 32 WILEY-V C H VERLAG GMBH WEINHEIM 368LN

Sustainable wastewater treatment and recycling in membrane manufacturing

It is widely accepted that membrane technology is a green and sustainable process; however, it is not well known that the membrane fabrication process itself is quite far from green, with more than 50 billion liters of wastewater being generated every year contaminated with toxic solvents such as DMF and NMP. This urgent challenge is often overlooked and recent attempts to improve the sustainability of membrane fabrication have been limited to the replacement of toxic solvents with greener alternatives. Our recent survey from membrane industries indicates that such wastewater contributes to more than 95% of the total waste generated during the membrane fabrication process, and their disposal is considered cumbersome. Hence, recycling wastewater in the membrane industry is a pressing challenge to be resolved to augment the rapidly growing membrane market. In this work, a continuous wastewater treatment process is proposed and the quality of the recycled water was validated through membrane fabrication and performance tests. Seven different classes of adsorbents—graphene, polymers with intrinsic microporosity, imprinted polymers, zeolites, metal organic frameworks, activated carbon, and resins—were evaluated. The isotherm and kinetic behaviors of the best adsorbents have been fully characterized and the adsorbent regenerability without any performance loss has been confirmed for up to 10 wastewater treatment cycles. It has been demonstrated that over 99% of the organic impurities in the wastewater can be successfully removed and the recycled water can be reused without adverse effects on the final membrane performance. The proposed wastewater treatment technique can reduce the process mass intensity (PMI) of membrane fabrication by 99.9% per m2 of the membrane produced. The required energy duty for different regeneration methods and wastewater treatment methods revealed that the adsorption technology is the most effective method, with the lowest energy requirement of about 1200 kJ per m2 of the membrane produced.

Revelation of the molecular assembly of the nanoporous metal organic framework ZIF-8.

Crystalline nanoporous materials are one of the most important families of complex functional material. Many questions pertaining to the molecular assembly mechanism of the framework of these materials remain unanswered. Only recently has it become possible to answer definitively some of these questions by observation of growing nanoscopic surface features on metal organic frameworks (MOFs) through use of in situ atomic force microscopy (AFM). Here we reveal that a growth process of a MOF, zeolitic imidazolate framework ZIF-8, occurs through the nucleation and spreading of successive metastable unenclosed substeps to eventually form stable surface steps of the enclosed framework structure and that this process is reliant on the presence of nonframework species to bridge the developing pores during growth. The experiments also enable identification of some of the fundamental units in the growth process and the stable crystal surface plane. The former findings will be applicable to numerous nanoporous materials and support efforts to synthesize and design new frameworks and to control the crystal properties of these materials.

Crystal growth mechanisms and morphological control of the prototypical metal-organic framework MOF-5 revealed by atomic force microscopy

Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H(2)bdc ratio producing square terraces with steps parallel to the <100> direction or rhombus-shaped terraces with steps parallel to the <110> direction when the Zn/H(2)bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications.

Crystal growth of nanoporous metal organic frameworks

Nanoporous metal organic frameworks (MOFs) form one of the newest families of crystalline nanoporous material that is receiving worldwide attention. Successful use of MOFs for application requires not only development of new materials but also a need to control their crystal properties such as size, morphology, and defect concentration. An understanding of the crystal growth processes is necessary in order to aid development of routes to control such properties of the crystallites. In this Perspective article we aim to provide a short overview of the current work and understanding concerning the nucleation and growth processes of nanoporous MOFs and how this work may be expanded upon to further our comprehension of this subject. We also focus heavily on in situ studies that provide real time information on the developing materials and generally provide the most conclusive findings on the processes under investigation.

Strong negative thermal expansion in siliceous faujasite

Strong isotropic negative thermal expansion (α = –4.2 × 10–6 K–1) found for siliceous faujasite over a temperature range of 25 to 573 K is attributed to transverse vibrations of the bridging oxygen atoms, a model supported by structural refinements of X-ray diffraction data as a function of temperature.

Growth Mechanism of Microporous Zincophosphate Sodalite Revealed by In Situ Atomic Force Microscopy

Microporous zincophosphate sodalite crystal growth has been studied in situ by atomic force microscopy. This simple model system permits an in depth investigation of some of the axioms governing crystal growth of nanoporous framework solids in general. In particular, this work reveals the importance of considering the growth of a framework material as the growth of a dense phase material where the framework structure, nonframework cations, and hydrogen-bonded water must all be considered. The roles of the different components of the structure, including the role of strict framework ordering, are disentangled, and all of the growth features, both crystal habit and nanoscopic surface structure, are explained according to a simple set of rules. The work describes, for the first time, both ideal growth and growth leading to defect structures on all of the principal facets of the sodalite structure. Also, the discovery of the presence of anisotropic friction on a framework material is described.

Synthesis and structure of a novel microporous gallophosphate, Na3Ga5(PO4)4O2(OH)2·2H2O

The structure of the title compound, Na3Ga5(PO4)4O2(OH)2·2H2O, consists of GaO6 octahedra, GaO5 trigonal bipyramids and PO4 tetrahedra which, by sharing edges and corners, form an open structure containing channels (ca. 4 A diameter) running along the [001] direction; two water molecules per formula unit can be desorbed.

Crystal growth of MOF-5 using secondary building units studied by in situ atomic force microscopy

Crystal growth of the metal–organic framework, MOF-5, using basic zinc benzoate, [Zn4O(O2CC6H5)6], was studied in real time using atomic force microscopy. The two-dimensional nuclei involved in layer growth were found to form by a two-step process whereby 1,4-benzenedicarboxylate units first attach to the MOF-5 surface followed by addition of a layer of Zn species and connecting 1,4-benzenedicarboxylate units. No evidence of a growth mechanism involving nucleophilic substitution of a benzoate group from an intact [Zn4O(O2CC6H5)6] molecule by a surface attached 1,4-benzenedicarboxylate unit was found. This indicates that the [Zn4O(O2CC6H5)6] molecules undergo a degree of dissociation before incorporation into the MOF-5 framework. The [Zn4O(O2CC6H5)6]-containing growth solutions were found to influence the relative growth rates along different crystallographic directions and to lead to a faster nucleation rate under certain conditions when compared to growth solutions containing simpler zinc salts. This suggests a degree of remnant association of the zinc species derived from the [Zn4O(O2CC6H5)6] cluster during crystal growth under these conditions.