Nanoparticles membrane-passing

Properties of Micro- and Nanoparticles 9.3.1 Membrane-Passing Properties... 

Conventional filtration cannot be applied to the separation in purification of metal nanoparticles. If the metal nanoparticles are protected by polymer, however, the membrane filter, which can cut off the pol5mer with certain molecular weight, can be used to separate the polymer protected metal nanoparticles. Free metal nanoparticles which are not protected by polymer can pass through the membrane. Ion filter like cellulose can be used to separate ionic species from the reaction mixtures. 

Reszka et al. [168] used ultrahltration to separate free mitoxantrone from PBCA nanoparticles. The particle suspension was passed through a cellulose nitrate membrane with a pore size of 20 nm with magnetic stirring and pressurized nitrogen. The filtrate obtained was analyzed for free drug content. Recovery of the particles is not possible with... 

Nanoscale materials are known to have various shapes and structures such as spherical, needle-like, tubes, platelets, and so on. The effects of the shape on the toxicity of nanomaterials are unclear. The shape of nanomaterials may have effects on the kinetics of deposition and absorption to the body. Inhaled particles in the nanosize range can certainly deposit in all parts of the respiratory tract including the alveolar region of the lungs. Dependent upon the specific application, oral, dermal, and other routes of exposure are also possible for nanoparticles. Because of their small size, they may pass into cells directly through the cell membrane or penetrate the skin and distribute throughout the body once translocated to the blood circula-... 

An example of a possible system for photocatalytic water decomposition is shown in Fig. 6. The photocatalyst in Fig. 6 is a CdS nanoparticle, which is located, e.g., in the inner aqueous phase. A sacrificial electron, donor (D) is also located in the inner phase. In the presence of a suitable water oxidation catalyst, the role of the donor could be served by the molecules of water. The molecular carriers of electrons (C in the figure) are built into the lipid membrane by the principle of a cascade, providing a certain gradient of redox potentials. In the outer aqueous phase, an electron acceptor and a catalytic agent of water reduction to hydrogen are placed. Thus, at light quantum absorption by the semiconductor PhC, the charge separation derives an electron hole which passes to the catalyst of... 

Another interesting application explored for track-etched membranes is for the synthesis of nanoparticles by simply passing molecules from one side of the membrane and precipitating the molecules at the other side of membrane. Here, a PCTE was attached on an AAO nanoporous membrane as supporting substrate (Figure 20.26). Chitosan was... 

The next question is which of the above-discussed scenarios is most Kkely to be found at the catalyst/hydrated membrane interface. It is generally accepted that the proton conductivity of the membrane depends on the characteristics of ionic clusters formed surrounding the polymer hydrophilic sites, both within the bulk polymeric structure and at the interface with the catalyst [79]. The ionic clusters located at the membrane/catalyst interface are the ones that close the circuit of this electrochemical system. That is, these ionic clusters act as bridges through which protons and other hydrophilic reactants and products may pass from the membrane to the catalyst surface and vice versa during fuel cell operation. To get some insights into the possible formation of ionic clusters, we have analyzed the conformation of a hydrated model nation membrane over Pt nanoparticles deposited on a carbon substrate via classical MD simulations [80] at various degrees of hydration. 

Cationic nanocarriers are also promising carrier systems to cross biological membranes. Cationic cyclodextrin nanoparticles were studied for doxorubicin delivery across the blood/brain barrier (BBB). Nanopartieles of 65-85 nm diameter probably passed across the BBB with endoeytosis. Drug-loaded nanoparticles induced a cytotoxic effect on U87 human glioblastoma cells without toxicity on brain microvessel endothelial eells. ... 

This can be a very efficient and economical way of separating components that are suspended or dissolved in a liquid. The membrane is a physical barrier that allows certain compoimds to pass through, depending on their physical and/or chemical properties. Polymeric membrane materials are intrinsically limited by a tradeoff between their permeability and their selectivity. One approach to increase the selectivity is to include dispersions of inorganic nanoparticles, such as zeolites, carbon molecular sieves, or carbon nanotubes, into the polymeric membranes - these membranes are classified as mixed-matrix membranes. 

Figure 10.5 Density profiles for hydrophilic (H) and lipophilic (L) blocks of the membrane surfactant, as well as particles, along the line normal to the original membrane surface and passing through the nanoparticle center. Cases considered (a) Rp = 1.6 nm, Xm = 1 0 (b) Rp = 1.6 nm, Xph = -3.0 ...

There are three different categories of application for functionalized membranes separation, sorption and catalytic applications. For separation, the modified membranes must allow the selective permeation of the desired chemical species and can be prepared, for example, by layer-by-layer (LbL) assembling. In sorption applications, the modified membranes act as adsorbents, which can also lead to separation and capture. However, these membranes need to be regenerated before they can be reused. Finally, functionalized membranes for catalytic applications may include enzymes or immobilized nanoparticles that act as catalysts and convert the reactants into products as they pass through the membrane pore. Porous membrane supported catalytic applications not only provide a way for catalyst immobilization, avoiding the need for its subsequent removal from the reaction mixture, but also lead to improved mass-transport conditions, since this transport is mainly done through the pores. 

Forced-flow polymeric membrane reactors have also been successfully tested for the oxidation of benzene to phenol by Molinari and co-workers. Mixed-matrix membranes consisting of CuO powder or CuO nanoparti-cles dispersed in PVDF were prepared by the inversion phase method, by using dimethylacetamide (DMAc), dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) as solvents and water as non-solvent. The membranes were assembled in a ultraliltration unit to which a solution of acetonitrile/benzene and hydrogen peroxide (HjOj) was fed. The best results were obtained with a PVDF membrane hlled with CuO nanoparticles, with a phenol yield of 2.3% at 35°C and a contact time of 19.4 s in a single pass, in the presence of ascorbic acid. 

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