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In 1972 the Fluid - Mosaic Membrane Model of membrane structure was proposed based on thermodynamic principals of organization of membrane lipids and proteins and available evidence of asymmetry and lateral mobility within the mem...
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In 1972 the Fluid - Mosaic Membrane Model of membrane structure was proposed based on thermodynamic principals of organization of membrane lipids and proteins and available evidence of asymmetry and lateral mobility within the membrane matrix [S. J. Singer and G. L. Nicolson, Science 175 (1972) 720-731]. After over 40 years, this basic model of the cell membrane remains relevant for describing the basic nano-structures of a variety of intracellular and cellular membranes of plant and animal cells and lower forms of life. In the intervening years, however, new information has documented the importance and roles of specialized membrane domains, such as lipid rafts and protein/glycoprotein complexes, in describing the macrostructure, dynamics and functions of cellular membranes as well as the roles of membrane-associated cytoskeletal fences and extracellular matrix structures in limiting the lateral diffusion and range of motion of membrane components. These newer data build on the foundation of the original model and add new layers of complexity and hierarchy, but the concepts described in the original model are still applicable today. In updated versions of the model more emphasis has been placed on the mosaic nature of the macrostructure of cellular membranes where many protein and lipid components are limited in their rotational and lateral motilities in the membrane plane, especially in their natural states where lipid-lipid, protein-protein and lipid-protein interactions as well as cell-matrix, cell-cell and intracellular membrane-associated protein and cytoskeletal interactions are important in restraining the lateral motility and range of motion of particular membrane components. The formation of specialized membrane domains and the presence of tightly packed integral membrane protein complexes due to membrane-associated fences, fenceposts and other structures are considered very important in describing membrane dynamics and architecture. These structures along with membrane-associated cytoskeletal and extracellular structures maintain the long-range, non-random mosaic macro-organization of membranes, while smaller membrane nano- and submicro-sized domains, such as lipid rafts and protein complexes, are important in maintaining specialized membrane structures that are in cooperative dynamic flux in a crowded membrane plane. This Article is Part of a Special Issue Entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.
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A membrane can be defined broadly as a physical barrier, which allows the selective passage of species from one side to the other under a driving force, or which controls the rate of permeation. Across the spectrum of separations ...
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A membrane can be defined broadly as a physical barrier, which allows the selective passage of species from one side to the other under a driving force, or which controls the rate of permeation. Across the spectrum of separations or membrane processes, the species may be organic or aqueous liquids, solutes, vapors, gases, ions or electrons. An example of controlled transport of species is drug delivery. One of the advantages of a membrane process is the avoidance of a phase change, which may typically occur for conventional separation processes. Another advantage is the relatively small footprint of a membrane system, and its scalability and flexibility of onsite “at source” operation, for example, a small water treatment plant (Hoek and Tarabara, 2013; Baker, 2004).
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Membrane separation of various mixtures of organic and inorganic substances can be considered as one of the most energy-conserving separation methods. Continuing efforts in the development of new membranes with improved thermal, c...
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Membrane separation of various mixtures of organic and inorganic substances can be considered as one of the most energy-conserving separation methods. Continuing efforts in the development of new membranes with improved thermal, chemical, and enhanced transport properties have led to many new possible applications since the 1960s. Various types of membranes are employed extensively for desalination, drinking water production, wastewater reclamation, and reuse. Development of novel membranes and new operational approaches offered promising opportunities to industry (Singh, 2015).
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This paper is an overview about the development of inorganic filtration membranes by Fraunhofer IKTS/DE. It deals with the membrane materials, the properties of which are the main reason for the superior stability of the membranes...
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This paper is an overview about the development of inorganic filtration membranes by Fraunhofer IKTS/DE. It deals with the membrane materials, the properties of which are the main reason for the superior stability of the membranes. The membrane production is explained below, ranging from the shaping of ceramic supports to the coating of thin membrane layers. In the third part, current examples of the membrane application are shown.
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Filtration studies using 0.2-mu m titanium dioxide membranes fused on porous stainless-steel tubes is reported for solutions containing sodium nitrate alone and in the presence of commercial anionic, direct and acid dyes. Solution...
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Filtration studies using 0.2-mu m titanium dioxide membranes fused on porous stainless-steel tubes is reported for solutions containing sodium nitrate alone and in the presence of commercial anionic, direct and acid dyes. Solution pH was adjusted with dilute sodium hydroxide and nitric acid to maintain maximum solubility of all ions and simplify the system. Electrolyte rejections and color rejections were measured separately from pHvalues of 4-10. Tubes were supplied by Dupont Separation Systems (Seneca, SC, USA). Results show that the charge or ionic nature of the membrane surface was responsible for the ion rejections and decreased to near 0% as the salt concentration was raised to 5000 ppm. Dye rejection did not approach 0% at higher salt concentrations but remained above 20% for the acid dye, Acid Red 1, and 50% for the larger-molecular-weight direct dye, Direct Red 2. The results are interpreted in terms of existing theories for inorganic membranes. [References: 13]
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Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the m...
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Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.
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Water scarcity is a grand challenge that requires continuous exploration of new desalination technologies in order to augment the global supply of fresh water. In this context, membrane distillation (MD) is a promising technology ...
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Water scarcity is a grand challenge that requires continuous exploration of new desalination technologies in order to augment the global supply of fresh water. In this context, membrane distillation (MD) is a promising technology that operates based on a thermal gradient to transfer vapor molecules across a porous hydrophobic membrane. Lack of suitable membranes is one of the major challenges hindering commercialization of the MD process. As a result, MD membranes have attracted unprecedented research attention over the decades and significant progress has been witnessed in the design and fabrication of suitable MD membranes. This review represents a timely overview of the desired characteristics of MD membranes that have been developed. The state of the art of various developments and the recent research trends in MD membrane have been thoroughly discussed. An up-to-date review of the polymeric, inorganic, electrospun, dual-layer, triple-layer, and modified MD membranes is provided. Finally, the research gaps, challenges faced, and future research directions are highlighted.
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The elaboration of porous ceramic membranes using low-cost materials has attracted much interest. Indeed, the choice of suitable raw materials (including additives or binders) is critical to the membrane's performance. However, wi...
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The elaboration of porous ceramic membranes using low-cost materials has attracted much interest. Indeed, the choice of suitable raw materials (including additives or binders) is critical to the membrane's performance. However, with the growing need for more cost-effective resources with superior performance, many studies have been conducted for selecting suitable cheap raw materials for the intended use and then adjusting the overall characteristics, and therefore allowing the ceramic membranes to be tailored to suit a wide range of industrial applications. Many attempts have been made by researchers to produce porous ceramic membranes from specific materials, but their industrial applications remain very limited because of the high cost of the raw materials used. The use of ceramic materials for producing membranes has many advantages, such as high mechanical and chemical stability and excellent thermal resistivity. The evaluation of membrane performances, essentially their permeability and rejection, can assert their use in many industrial fields, namely beverage and food, pharmaceutical, biotechnology, petrochemical industries as well as water treatment and several other environmental problems. This article aims to make a thorough review of the different processes used in the synthesis of ceramic membranes using inexpensive raw materials as well as their intrinsic characteristics and industrial applications in several sensitive fields taking into account both economic and environmental aspects.
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Membrane fouling and resistance in drinking water treatment systems can be considerably reduced by precoating or predepositing the dynamic membrane (DM) filtration system using adsorbent particles on the membrane surface. The char...
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Membrane fouling and resistance in drinking water treatment systems can be considerably reduced by precoating or predepositing the dynamic membrane (DM) filtration system using adsorbent particles on the membrane surface. The characteristics and roles of heated aluminum oxide particles (HAOPs) for adsorbent size and surface loading according to membrane type (ceramic: Ce; polymeric: Po) were investigated using ahumic acid (HA) solution. DM filtrations precoated with Ce or Po membranes indicate that fouling occurs in both membranes at the cake layer. In the case of Ce membrane filtration, the effect of foulants was noticeably reduced and irreversible membrane fouling can be alleviated by pretreating the Ce membrane with HAOPs. Permeability is proportional to the adsorbent size and surface loading. The optimum surface loading and particle size of HAOPs on the Ce membrane filtration should be < 75 mu m and 0.05 Al g/cm(2), respectively. Using a DM with HAOPs, membrane performance is more enhanced when using the Ce membrane than when using the Po membrane. From these results, it could be concluded that DM filtration with a Ce membrane has potential as an operating system for alleviating membrane fouling.
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the paper attempts to summarize recent significant progress in synthesis of microporous and dense inorganic membranes with the help of the results obtaied in the author's laboratory or reported in the literature. The paper first r...
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the paper attempts to summarize recent significant progress in synthesis of microporous and dense inorganic membranes with the help of the results obtaied in the author's laboratory or reported in the literature. The paper first reviews several methods for synthesis of microporous amorphous and polycrystalline 9zeolite) inorgnaic membranes and their major characteristics. These microporous membranes exhibit fascinating gas permeation and separation properties. The paper also reviews equally impressive progress on oxygen semipermeable dense oxygen ionic-conducting ceramic membranes and hydrogen semipermeable metal membranes. Searching for better membrane materials, developing effective membrane synthesis methods, and improving chemical and structural stability of the current membrane materials will continue to be the focus of active research in these areas. Specific examples of the future research include synthesis of micro and mesoporous polycrystaline inorganic membranes with oriented pores and development of the more effective dense proto-conducting ceramic membranes for high temperature hydrogen separation and membrane reactor applications.
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