Stock solutions 300mgL−1 of RB21 and RR195 were used in this
study. These stock solutions were diluted to give standard solutions
from 10 to 250mgL−1. 0.1 g ZEC and 10mL single-component
solution were shaken using a shaker with a water bath to control
temperature at 25.0 ◦C. The liquid and solid phases were separated
by centrifuging at 3950rpm for 5min. The change of adsorbate
concentration in each of the solutions was determined spectrophotometrically.
All the spectrophotometric measurements weremade
with a CHE-BIOS Optimum UV–vis spectrophotometer. The maximum
absorbance value of RB21 and RR195 was measured at 660
and 540 nm, respectively as shown in Fig. 1. The calibration graph
of absorbance versus concentration obeyed a linear Lambert–Beer
relationship [16].