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Excellent-quality graphene sheets produced via the direct liquid phase exfoliation of highly crystalline graphite (avoiding any oxidative treatment), were employed for the first time as 2D scaffolds for the in-situ synthesis of zeolitic-imidazolate-framework (ZIF-8) material. Our synthetic approach involved the efficient, urea-assisted exfoliation of natural graphite (without using any acids), and the subsequent selective, mild functionalization of the resulting high-quality graphene sheets with benzoic acid functional groups. The graphene derivatives were next decorated via the in-situ development of ultrasmall (approx. 30 nm) ZIF-8 nanocrystals. We discuss the critical role of the functionalized graphene to the selective nucleation and crystal growth of ZIF-8 nanocrystals exclusively at their surface. In-depth gas sorption studies of different gases revealed that the novel ZIF-8@Graph nano-composites exhibited improved porosity (in terms of surface area and pore volume) compared to analogous Graphene Oxide/ZIF-8 hybrids. In addition, the gate effect of the ZIF-8 nanocrystals anchored onto the high-quality graphene, was found very different compared to bulk ZIF-8, a behavior that is attributed mainly to the significantly smaller crystal size and the perfect 2D confinement of ZIF-8 along graphene. Finally, preliminary CO2 adsorption properties of the synthesized novel nano-composites are reported, at near ambient temperature.

Multi-layer silica, zirconia and alumina tubular nanofiltration membranes were modified using alginic acid, a natural organic polymer. Polymers of two different molecular weights (MW) were used. The hybrid membranes exhibited a drop of the permeability value of about three and one orders of magnitude for the membranes modified by high ‘MW’ and low ‘MW’, respectively, whereas the improvement of Cd 2+ retention efficiency was about one order of magnitude in both cases. The modified silica membranes exhibited higher retention factors R %, which was more than 99% for 200 ml yield of clean water from a feeding solution of 100 ppm in Cd 2+ . The metal binding capacity of both deposited alginic acid co-polymers was proportional to the binding capacity of the alginate beads produced by the same batch of alginic acid. Mercury intrusion measurements revealed that the high MW alginates had deposited mainly into larger pores of the α-alumina support (2.5–3 μm), while the low MW alginate could penetrate into all the succeeding intermediate layers. EDAX analysis revealed the existence of significant carbon content in both succeeding γ-alumina layers, probably because of the wide MW distribution of the high MW alginate. The retention efficiency of the membrane decreased only by 8% after the first regeneration run and remained constant for 100 ml of cleaned water effluent.

Tubular, composite asymmetric carbon membranes, consisting of a macroporous substrate and a microporous thin layer, have been prepared from commercial phenolic based resin precursors and were studied using static (adsorption) and dynamic (permeability/selectivity) techniques. Based on sorption measurements, it was concluded that asymmetric activation occurs mainly due to the pre-formulated rigid shape of the composite membrane. In the case of skin samples, the observed low-pressure hysteresis was attributed to the existence of constrictions, which hinder the access of gas molecules to certain micropores. On the other hand the similarity of pore size distributions of all samples, pointed out that the pore microstructure, derived from similar phenol–formaldehyde resins, is not affected by the powder size of the precursor. According to high temperature ( T = 308 K) CO 2 adsorption isotherms, enhanced adsorption capacity was observed, even at supercritical conditions. Integral permeability experiments performed on the developed membranes revealed defect free behaviour with molecular sieving properties. The gas flux followed the activated diffusion mechanism and activation energies were calculated. The membranes exhibited high CO 2 selectivity (about 15) for equimolar mixture of CO 2 /N 2 . This property, which can be attributed to micropore blocking caused by the preferential adsorption of CO 2 , enables the use of the produced membranes in numerous industrial processes involving CO 2 separation. Furthermore, both single gas and gas mixture permeation techniques revealed that the separation mechanism is a combination of molecular sieving and selective adsorption mechanisms.

Two types of composite nanofiltration (NF) membranes were examined for their ultra thin separation layer integrity by initially applying gas permeability measurements. The examined materials were sol–gel derived γ-alumina and silica membranes, supported on macroporous α-alumina tubes. Relative permeability measurements of the system He/H 2 O indicated the existence of defects with size greater than 25 nm, as Helium permeation was not completely blocked even at high water relative pressures. The existence of defects was also confirmed by application of a recently developed mercury intrusion technique, which additionally enabled the accurate definition of the defects size. Furthermore segments of the defect bearing membranes were modified by chemical vapor deposition of SiO 2 under several reaction conditions, to examine the possibility of simultaneously reducing the NF pores size and mending the defects. The similarity of water vapor differential permeability results before and after modification constitutes a proof that NF pores remained unaffected under the specific CVD conditions applied. However significant plugging of the defects has been observed with the novel mercury intrusion technique and a good agreement with the outcome of relative permeability measurements was noted, mainly in the estimation of the largest pores size. SEM micrographs of the CVD treated membranes revealed that differential pressure across the reactor sides leads to the formation of an extra silica deposit on either the thin layer or the support surface of the membrane. This was especially the case in the presence of large pores (defects) and was further verified by the novel mercury intrusion method.