2.3.2. Batch equilibrium experiments
Different lac dye concentrations were freshly prepared in
deionized water. The pH of the dye solution was adjusted to
3.0 with glacial acetic acid. The experiments were carried
out by shaking pretreated or untreated cotton with a 0.3%
(v/v) aqueous solution of chitosan (0.5 g) with different concentrations
of dye solution (50 mL) in a conical flask
(125 mL) at 10, 30 and 60 C in a thermostatted shaker bath
operated at 75 rpm. The amount of dye in the solution was
monitored by UVevisible absorption spectroscopy (Cary 1E
UVevisible spectrophotometer) until the absorbance values
at lmax 487 nm remained constant. The initial and equilibrium
dye concentrations were determined using a calibration curve
based on absorbance at lmax 487 nm versus dye concentration
in standard lac dye solutions. From Eq. (1), the amount of dye
adsorbed at equilibrium (qe) was calculated.
The influence of sodium chloride on the adsorption of lac
dye on cotton was investigated in a similar manner. The cotton
yarn (0.5 g) was dyed with different dye concentrations
(50 mL) in the presence of 0.5 M sodium chloride at 10 and
30 C. The pH of the dye solution before and after dyeing
was measured in each experiment. The absorbance of the
dye solution was measured at lmax 487 nm.