الملخص الإنجليزي
The science of well-designed surfaces for more selective pollution control is growing. In this
research study, using epichlorohydrin, silica gel was surface functionalized with α-, β-, γ- and
β-hydroxypropyl-cyclodextrin (CD), and chitosan (CS) to produce Si-aCD, Si-bCD, Si-gCD,
Si-hp-bCD, and Si-CS, respectively. The mass of silica gel to CD (g) was varied to be between
1:4 to 4:1 and the products were tested for the best-performing adsorbents towards the uptake
of Cu(II), Pb(II), iodine, and methylene blue from aqueous solution. The selected adsorbents
for Cu(II) adsorption, include Si-CD (1:4), Si-CD (1:4), Si-CD (1:4), Si-hp-CD (1:1), and
Si-CS (4:1), and for both Pb(II) and MB, include Si-CD (4:1), Si-CD (2:3), Si-CD (2:3),
Si-hp-CD (1:1), and Si-CS (4:1). For iodine adsorption, Si-CD (3:2), Si-CD (4:1), Si-CD
(4:1), Si-hp-CD (4:1), and Si-CS (4:1) were selected. The selected adsorbents have been
characterized physico-chemically including surface area and thermogravimetric analysis. The
surface area of silica gel (428.3 m2
/g) has tremendously decreased on functionalization (4.23-
21.7) m2
/g. TGA (Thermogravimetric analysis) showed a thermal degradation took place
around 400 oC indicating the covalent chemical bonding of immobilized CDs and CS.
Cu(II), and Pb(II) showed better adsorption at initial pH of 6. The kinetic experiments showed
fast adsorption following a pseudo-second-order kinetic model with the rate of adsorption
increasing as temperature rises. The activation energy, Ea, was found to be less than 42 kJ/mol
indicating physical adsorption. Equilibrium adsorption follows L-type isotherms with
increased adsorption as the temperature rises and the adsorption data were found to fit well the
Langmuir model. Pb(II) adsorption was slightly higher than Cu(II). The weak adsorption of
metal onto Si-CDs is because metal is only adsorbed onto the –OH groups on the peripheries
of the cyclodextrin cavities.
For iodine and MB, the adsorption performance was found optimum at initial pH of 6. The
kinetic experiments showed that the adsorption of both iodine and MB followed a pseudosecond-order kinetic model with an increased rate as the temperature rises. The activation
energy, Ea, was found to be less than 42 kJ/mol indicating physical adsorption. The equilibrium
adsorption data fit the Langmuir model more than the Freundlich model. The adsorption
capacity (q) of iodine was found to decrease on temperature rise for Si-CDs, however, increases
with Si-CS. This is because CD cavities do not expand on temperature rise. MB shows
enhanced adsorption at a high temperature on both SiCDs and Si-CS. MB molecule is large
and does not enter into the CD cavity showing an adsorption capacity of 6.0 mg/g while the
small iodine molecules can be adsorbed inside the hydrophobic cavities of CD showing
maximum adsorption of 714 mg/g. The selected adsorbents showed good recycle properties for
Cu(II) and iodine from aqueous solution.
