Silica based nanoparticles process

Endocytosis is essential for uptake of macromolecules and nanoparticles. Thereby, the physical and chemical characteristics of the cargo and transporter complex determine the nature of the cell uptake mechanism. Particles larger than 500 nm are typically phagocytosed or macropinocytosed, whereas smaller hydrophilic molecules are internalized by any of the various endocytotic processes [2,8]. Often, nanometersized transporter molecules or particles accomplish cell uptake simultaneously by several endocytotic mechanisms [9]. Clathrin-dependent endocytosis is the most widely understood pathway, which is present in nearly aU mammalian cells. The clathrin pathway is considered the most important uptake mechanism for several polymers such as poly(ethylene glycol)-polylactides, poly(lactide-c )-glycolide) (PLGA), silica-based nanoparticles, and chitosan nanoparticles [8, 10-12]. 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

The Stober method is also known as a sol-gel method [44, 45], It was named after Stober who first reported the sol-gel synthesis of colloid silica particles in 1968 [45]. In a typical Stober method, silicon alkoxide precursors such as tetramethylorthosili-cate (TMOS) and tetraethylorthosihcate (TEOS), are hydrolyzed in a mixture of water and ethanol. This hydrolysis can be catalyzed by either an acid or a base. In sol-gel processes, an acidic catalyst is preferred to prepare gel structure and a basic catalyst is widely used to synthesize discrete silica nanoparticles. Usually ammonium hydroxide is used as the catalyst in a Stober synthesis. With vigorous stirring, condensation of hydrolyzed monomers is carried out for a certain reaction time period. The resultant silica particles have a nanometer to micrometer size range. 

ArsenX"p is a sorbent that consists of porous (300-1200 pm diameter) polymeric beads that have been impregnated with iron (oxy)(hydr)oxide nanoparticles (Sylvester el al., 2007 Sarkar et al., 2007). The high porosity, surface area, and iron content of the beads allow them to reduce As(V) concentrations to below 10 pgL-1 in water (Tables 7.1 and 7.2). Sulfate, chloride, fluoride, and bicarbonate do not substantially interfere with the removal of As(V). However, like other iron-based sorbents, dissolved silica at pH > 7.5 and phosphate may interfere (Sylvester et al., 2007, 106). ArsenX7 is regenerated with a proprietary process, which involves rinsing the sorbent with a warm caustic solution and then neutralizing the surface charges on the beads (Sylvester et al., 2007, 109). 

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