In the pH effect experiment, a 40 mL solution containing
0.1 mM tetracycline and 0.01 M NaCl was added into a 50 mL polypropylene
tube containing 0.04 g of sorbent. The pH of the solution
was adjusted by HCl or NaOH solution. The mixtures were shaken
at 293 K for 3 h. The samples were then collected for the analysis of
tetracycline concentration by the UV/Visible spectroscopy.
In the adsorption isotherm experiments, 40 mL tetracycline
solutions with different concentrations were added into 50 mL
polypropylene tubes containing 0.04 g of sorbent. The solution
pH was maintained at 5.0. Other procedures were the same as
those in the above pH effect experiments.