These centrifuge tubes were capped and placed on an orbital shaker at 170 rpm to ensure equilibrium, and then centrifuged at 2500 rpm for 20 min. The residual concentration of dyes AB25, AB93, ATBA and AGYG in the supernatant was determined by a UV2450 spectrophotometer (Shimadzu, Japan) at wavelength of 560 nm, 663 nm,637 nm and 440 nm, respectively. Each experiment was duplicated under uniform condition. The adsorbed dyes were measured by the differences between the initial and final dye concentrations in the equilibrium solutions. Removal efficiencyR(%)(Eq.(1))andadsorption capacity q(mg/g) (Eq. (2)) were calculated using the following
formulas: