| Summary: | Synthesis of positively-charged 2-methoxyphenylcalix[4]resorcinarene
triphenylphosphonium chloride has been conducted. The synthesis was carried out from
salicylaldehyde via methylation, aromatic electrophilic substitution-cyclization,
chloromethylation and bimolecular nucleophilic substitution reactions. Structural elucidation of
products was performed using FT-IR spectrophotometer, NMR, GC-MS and MS
spectrometers. The synthesized calix[4]resorcinarene was then immobilized on the alginate
matrix. The immobilized material was characterized using FT-IR spectrophotometer. The three
adsorbents of positively-charged calix[4]resorcinarene C, alginate A, and calix[4]resorcinarenealginate
CA 1% were then applied in the removal of hexavalent chromium. Adsorption
parameters including pH, kinetic and equilibrium parameters were also determined.
Reaction of salicylaldehyde with dimethyl sulphate (DMS) catalyzed by NaOH was
performed by refluxing the mixture for 4 hours and gave 2-methoxybenzaldehyde in 93%
yield. The aromatic electrophilic substitution-cyclization of methylation product and resorcinol
in the presence of HCl gave 2-methoxyphenylcalix[4]resorcinarene in 86% yield.
Chloromethylation of calix[4]resorcinarene using paraformaldehyde, ZnCl2, HCl in N,Ndimethylformamide
(DMF) produced chloromethylated calix[4]resorcinarene (88% yield),
which was then reacted with triphenylphosphine to give positively-charged 2-
methoxyphenylcalix[4]resorcinarene triphenylphosphonium chloride in 88% yield.
Preparation of alginate and calix[4]resorcinarene-alginate gel beads was performed
using calcium chloride solution and produced transparent (diameter of 2.2 mm/bead) and
orange (2.4 mm) beads, respectively. The IR analysis showed that immobilized
calix[4]resorcinarene had similar functional group with free calix[4]resorcinarene. Adsorption
of Cr(VI) on calix[4]resorcinarene, alginate and immobilized calix[4]resorcinarene on alginate
was optimum at pH 3 and reached the equilibrium time at 8, 2 and 8 hours, respectively.
Furthermore, the pseudo second-order kinetic model of Ho could satisfactorily describe the
adsorption process, where the intraparticle and liquid film diffusions might govern the
adsorption mechanism. Adsorption of Cr(VI) on calix[4]resorcinarene, and immobilized
calix[4]resorcinarene on alginate with the capacities of 81.301 and 21.739 mg/g, could be
classified as chemisorption and correlated well with the Langmuir model, while that on alginate
with the capacity of 12.870 mg/g, could be considered as physical adsorption and fitted with
Freundlich model. The immobilization of calix[4]resorcinarene on alginate matrix might
reduce capacity of calix[4]resorcinarene and increase the capacity of alginate. The material
seemed to be more applicable in the industrial and environmental applications as it was easily
collected and had adequate particle size.
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