Quantitative Analysis and Efficient Surface Modification of Silica Nanoparticles

Abstract

Aminofunctional trialkoxysilanes such as aminopropyltrimethoxysilane (APTMS) and (3-trimethoxysilylpropyl)diethylenetriamine (DETAS) were employed as a surface modification molecule for generating monolayer modification on the surface of silica (SiO 2 ) nanoparticles. We were able to quantitatively analyze the number of amine functional groups on the modified SiO 2 nanoparticles by acid-base back titration method and determine the effective number of amine functional groups for the successive chemical reaction by absorption measurements after treating with fluorescent rhodamine B isothiocyanate (RITC) molecules. The numbers of amine sites measured by back titration were 2.7 and 7.7 ea/nm 2 for SiO 2 -APTMS and SiO 2 -DETAS, respectively, while the numbers of effective amine sites measured by absorption calibration were about one fifth of the total amine sites, namely, 0.44 and 1.3 ea/nm 2 for SiO 2 -APTMS(RITC) and SiO 2 -DETAS(RITC), respectively. Furthermore, it was confirmed that the reactivity of amino groups on the surface-modified silica nanoparticles could be maintained in ethanol for more than 1.5 months without showing any significant differences in the reactivity.

Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization

“…The co-precursors/TEOS molar ratio was chosen according to the method described by Brambilla et al [28]. The surface modification of the preformed SiO 2 particles was previously performed by other groups [29,30], but our preparation procedure is different from what was previously reported. Thus, Jung et al [29] obtained amino-functionalized silica particles only in ethanol medium and after the re-dispersion of the pristine SiO 2 particles.…”

Aerosol-synthesized siliceous nanoparticles: impact of morphology and functionalization on biodistribution

“…Thus, decreasing the ratio of surface amines to silanol groups should reduce particle aggregation and improve biocompatibility. Although not performed here, quantitative methods to determine the number of functional amine groups were reported 49 and could help to optimize the condition for surface modification and to further increase the particle dispersibility. Alternatively, adding other inert functional groups and/or negatively charged moieties (eg, methylphosphonate) can increase the overall solubility by preventing back-bonding 48 and might be a valuable strategy to improve the biocompatibility of our aerosol-synthesized NPs.…”

Functionalization of silica surface using Chan–Lam coupling

“…However, they can also undergo self-condensation to form gel or oily oligomers that precipitate within few hours in the presence of acid or base catalysts. 37 In spite of this, there is an issue as to whether to use the large excess amount of organotrialkoxysilane to maximize the coverage of silica surface or to use a minimum quantity to prevent the formation of any unwanted selfcondensed side products. 37 Repetition of centrifugation or redispersion process can help to remove the self-condensation by-product because the actual size of self-condensed products are very small in comparison to the size of SiO2 particle.…”

“…37 In spite of this, there is an issue as to whether to use the large excess amount of organotrialkoxysilane to maximize the coverage of silica surface or to use a minimum quantity to prevent the formation of any unwanted selfcondensed side products. 37 Repetition of centrifugation or redispersion process can help to remove the self-condensation by-product because the actual size of self-condensed products are very small in comparison to the size of SiO2 particle. 37 Therefore, there is a possibility that these self-condensed products further condense with silanol, Si-OH, groups on the silica surface, resulting in a thick coating layer instead of generating a monolayer.…”