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APTS-modified silicon dioxide in an aqueous solvent is a commonly used method of modifying the aqueous solvents used include: water, a mixed solvent of water and an alcohol and acetone, which most commonly is water, ethanol, a mixed solvent. The silica to be modified is placed a certain percentage of water mixed solvent of alcohol with ammonia as a catalyst, an excess of APTS. APTS hydrolysis of Si-OH in the reaction system, the mechanism according to (1) react with the silica to form a Si) O) Si-bonded on the silica surface. This modification method is very simple, is widely used in research and industry. Molecular layer APTS condensation reaction but due to reaction in an aqueous system, usually generate multiple molecular layer at the silica surface irregularities, and hydrolysis of APTS APTS silica surface and between molecules hydrolyzed difficult to control, so the resulting the thickness and surface density amino difficult to control, poor response reproducibility. Furthermore, when the silica nanoparticles of silica gel or micrometer scale may be modified due to the reaction system is prone to form three-dimensional cross-linked aggregates between excess APTS, particles and particles in the solution precipitated.

Halas, Graf et al., For the issue of this method is improved. They Stêber method was used to prepare monodispersed spherical silica nanoparticles, according to the reaction system, the amount of TEOS added, the system calculates the total surface area of the spherical silica particle concentration and silica particles. According to APTS molecule cross-sectional area (0169nm2), you can determine the theoretical value of APTS to generate a specific amount of layers required, which can be approximated to control the silica surface modification APTS layers. And then added to the reaction system in an amount of usually less APTS, can effectively prevent the occurrence of crosslinking between silica particles, the silicon dioxide particles modified with good colloidal stability.


 

 

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