Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 322

The solid-liquid extraction occurs at a weaker pH than in liquid-liquid extraction. A
theoretical model is used to determine the stoichiometries of the extracted complexes in
the doped silica. Some extracted complexes were found to be comparable to those
obtained in solvent extraction Cu(PMSP) 2 , Cu(L-10-L) and Eu(PMSP) 3 . The complex
formed in the doped silica between HL-10-LH and Eu is the same as the one formed in
micellar extraction. Sorption kinetics has also studied at 25 C. The best fit is obtained
with the pseudo-second order model. Extraction capacity of the doped materials is
determined and comparable to the extraction capacity of europium by HL-10-LH
solubilized in cetyltrimethylammonium bromide micelles (Bou-Maroun et al., 2006).
Jiang et al. (2004) studied enhanced infrared (IR) absorption of CO adsorbed on
Pd nanoparticles embedded in the mesoporous molecular sieve SBA-15. Palladium ions
were introduced into the mesoporous molecular sieve SBA-15 through impregnation of
the sieve into palladium chloride solution followed by calcinations. In situ Fourier
transform-infrared (FTIR) results revealed that IR absorption of CO adsorbed on Pd
nanoparticles embedded in the SBA-15 has been enhanced 11-fold, and the full-width at
half-maximum of the CO bands is significantly increased (Jiang et al., 2004). Nam and
Tavlarides (2005) prepared a high-capacity phosphonic acid functional adsorbent by co-
condensing oligomers of tetraethoxysilane (TEOS) and trimethoxysilylpropyl
diethylphosphonate (DEPPS). Hydrolysis/condensation reactions for both silanes were
monitored in the sol-state using 29 Si NMR spectroscopy, and the dependency of the
resulting physicochemical properties on these reaction times was investigated. The
adsorbent exhibits a ligand density of 10.0 mmol P/g, and maximum values of S BET of
437 m 2 /g, D p of 59 Å, and V p of 0.65 cm 3 /g. Further characterization shows an
equilibrium Cr(III) adsorption capacity of 82 mg/g at pH 3.6 and rapid adsorption
kinetics. Lin et al., (2001) investigated cesium sorption using copper ferrocyanide
immobilized on mesoporous silica. Chromate and arsenate were adsorbed using mono-,
di-, and triamino functionalized adsorbents through the ionic interactions between the
amine heads and the negatively charged oxyanion (Yoshitake et al., 2002; Lam et al.,
2007b). A new functionalized mesoporous silica (MCM-41) using salicylaldehyde was
utilized for the separation, preconcentration and determination of uranium in natural
water by inductively coupled plasma atomic emission spectrometry (ICP-AES) (Jamali
et al., 2006). The sorption of uranyl ions in mesoporous MCM-41 and MCM-48 was
accomplished with the help of a direct-template-exchange route, and the progress was
monitored as a function of pH in the precursor uranyl nitrate solution. Under identical
synthesis conditions, about 1.5 times larger amount of uranium was found to be sorbed
in MCM-48 (~12.5 wt.%) as compared to MCM-41 (~9.5 wt.%) (Vidya et al., 2004).
In summary, Silica is one of the most widely used adsorbent substrates to remove
pollutants during the sorption process. Molecular sieves comprising pure silica are
hydrophobic and can absorb organic components in water (Davis, 2002). The silicate
substrate has been used in combination with other metals as adsorbents to remove a