Nanoparticles for Trace Analysis of Toxins: Present and Future Scenario - Advanced Materials for Agriculture, Food and Environmental Safety - page 187

Some pollutants are poorly adsorbed on nanoparticles. To overcome
this problem, physical or chemical modii cation of the surface of these
nanoparticles with certain functional groups containing some donor
atoms such as oxygen, nitrogen, sulfur and phosphorus is necessary. h e
most ot en used method is to load a kind of specii c chelating reagent
by physical or chemical procedure. h e formal method is simple but the
loaded reagent is prone to leaking out from the sorbent, while the chem-
ically bonded material is more stable and can be used repeatedly. h e
modii cation of nanometer-sized materials is usually required in order
to prevent a conglomeration of particles and to improve its consistency
in relation to other materials. Also, the modii cation of nanometer-sized
materials can improve their selectivity toward pollutants. Selectivity of
suitable specii c functional groups towards metal ions depends on cer-
tain factors such as: (1) size of the modii ers, (2) activity of loaded group,
and also on (3) the basis of the concept of hard-sot acids and bases.
Chemisorption of nanoparticles provides immobility, mechanical stabil-
ity and water insolubility, thereby increasing the ei ciency, sensitivity
and selectivity.
Chemical modii cation is a process that leads to a change in chemical
characteristics of the surface of nanoparticles. By the modii cation, the
adsorption properties are signii cantly af ected. Chemisorption of che-
lating molecules on nanoparticle surface provides immobility, mechani-
cal stability and water insolubility, thereby increasing the ei ciency,
sensitivity and selectivity of nanoparticles for the analytical application.
Chemical modii cation of nanoparticles by the silylation procedure
using dif erent silylating agents such as 3-aminopropyltriethoxysilane,
3-chloropropyltriethoxysilane and 3-mercaptopropyltriethoxysilane
provides immobility, mechanical stability and water insolubility. N-[3-
(trimethoxysilyl)propyl]ethylenediammine-modii ed SiO 2 nanoparti-
cles have been used for the preconcentration of some toxic heavy metal
ions such as Hg(II), Cu(II) and Zn(II) [55]. Modii ed silica nanopar-
ticles have also been used for the preconcentration of drugs and pes-
ticides. Silylation of silica nanoparticles followed by their chemical
modii cation using 4-(2-pyridylazo)-resorcinol [56] and these modii ed
SiO 2 nanoparticles have been used for the selective preconcentration of
Hg(II). h e SiO 2 nanoparticles have also been modii ed with acetylsali-
cylic acid, p-dimethylaminobenzaldehyde and 5-sulfonylsalicylic acid
for use in the preconcentration of Cr(III), Fe(III), Pb(II) and Cu(II)
[57-59]. Chemical modii cation of silica nanoparticles are shown in
Figure 7.4.