Graphene oxide membranes for gas separation

Recently, the carbon based materials1 attracted attention of the scientific community for applications in membrane gas separation. Tremendous number of carbon based materials such as carbon nanotubes, chemically modified graphene, graphene oxide (GO) or graphite (nano)particles in mixed matrix membrane (MMM) composites was tested within past decade2. It was found that even small loading of graphene and (GO) additives, i.e. 0.05 to 1 wt.%3, led to considerable changes of composite materials properties (elastic modulus, tensile strength, electrical conductivity, and thermal stability) compared to neat polymers. Please click Additional Files below to see the full abstract

Aging of polymers of intrinsic microporosity studied by sorption and permeation

Polymers of intrinsic microporosity (PIMs)1 seem to be effective materials for gas and vapor separations.2 However, gas separation efficiency of PIMs can be strongly influenced by the material aging process connected with the changes of PIMs inner structure.3 With respect to potential industrial applications, the investigation of such changes and their effect on gas and vapor transport is necessary. In this work, we present a detailed study of i) CO2 sorption in PIM-1 via momentary measurements during four years and ii) methanol permeation in PIM-11 and EA-TB-PIM2 via continuous and momentary experiments. Sorption experiments were performed gravimetrically using a self-developed apparatus equipped with McBain’s spiral balances. In this case, PIM-1 membranes were pre-treated (soaking in ethanol with consequent drying at different temperatures) in order to study the influence of temperature on PIM-1 aging. Methanol permeation experiments were performed using a differential flow permeameter with H2 and He as carrier gases. Permeation experiment were performed with PIM-1 and PIM-EA-TB methanol treated membranes. CO2 sorption measurements revealed that, assuming the validity of the solution-diffusion model, the decrease of permeability during aging can be attributed directly to the decrease of diffusivity, whereas solubility is time independent in the studied period of four years. Although higher preparation temperature led to the initial drop of diffusivity, this process stabilized separation performance of PIMs over time (Figure 1). MeOH permeation experiments confirmed previous findings from CO2 tests, that the permeability decrease during the aging is a diffusivity controlled process. Moreover, it was found that the momentary permeation data can be mathematically transferred to continuous data, which are more relevant for applications but more difficult to measure. The nature of aging process was studied by infrared spectroscopy. We have found that aging of PIMs does not influence their chemical structure and; therefore, they undergo only the so called physical-aging. Please click Additional Files below to see the full abstract

A novel time lag method for the analysis of mixed gas diffusion in polymeric membranes by on-line mass spectrometry: Method development and validation

European Union's Seventh Framework Program (FP7/2007-2013) under Grant agreement no. 608490. project M4CO2. CNR/FCT Italian/Portuguese Bilateral Project 2015-2016 "Advanced studies of the transport properties and gas separation by polymers of intrinsic microporosity (PIMs) and Ionic Liquid Gel Membranes via novel methods" and the CNR-CAS Bilateral Agreement 2016-2018 "Innovative polymeric membranes for pervaporation and advanced gas and vapour separations".A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax® and glassy Hyflon® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements.publishersversionpublishe

Operating Systems' Resource Access Control Models

The thesis deals with models used in access control to operating systems' resources. The thesis' goals are the theoretical description of these models and their comparison, the description of their implementations in selected operating systems and the description of their utilization in securing typified servers. In the first chapter, the reader is introduced to basic terms and principles of computer security and access control. In the second, also theoretical part, selected access control models are described from different viewpoints, for example their factual specialization, basic rules, principles and evolution. At the end of the chapter, the models are compared to each other according to specified criteria. The third, more practically oriented chapter, continues from the initial, both general and concrete introduction with operating systems, to description of access control model implementations in selected operating systems. At the end of the chapter, these implementations too are compared according to specified criteria. The fourth, final part, is dedicated to the description of the actual securing of a web and file server using operating system level access control means. The end of the chapter is dedicated to the possibilities of using these means to secure web applications. The contribution of this thesis from the theoretical point of view is a well-arranged and compact access control model comparison, and also the merger of the theoretical base with practical use of the described model implementations. The thesis is recommended to people interested in the computer security issues in general and people interested in access control from both theoretical and practical sides, e.g. system administrators or system designers

Foundation pit and foundation structures of the new buildind of Vyšehrad station

katedra geotechnik