Preparation of CTAB intercalated bentonite for ultrafast adsorption of anionic dyes and mechanism study

In this paper, organo-bentonite (CTAB-B) was prepared with cetyltrimethylammonium bromide (CTAB) as modifier, and systematically studied for its adsorption performance and mechanism as an effective adsorbent for anionic dyes (acid red (AR) and acid fuchsin (AF)). Natural bentonite and CTAB-B were characterized by XRD, FT-IR, TG, BET and Zeta potential. The influences of adsorbent amount and oscillation time on the removal for AR and AF were investigated. And the adsorption isotherms, kinetics and adsorbent recycling were also studied. The results suggested the bentonite modification by CTAB substantially expanded its galleries. Under same initial conditions, the adsorption of AF by CTAB-B required less adsorbent amount and equilibrium time and its removal efficiency of both AR and AF exceeded 94%. The Langmuir adsorption isotherm satisfactorily accounted for their adsorption characteristics as compared to the Freundlich model, which leaded to their saturated adsorption capacities of 79.29 mg/g and 281.14 mg/g at 30 ℃, respectively. The differences in their adsorption capacity were mainly affected by the molecular size of the dyes. And the second-order kinetic model yielded the highest fit to the experimental facts compared with first-order kinetic model and intraparticle diffusion model. Under three adsorption-desorption cycles, CTAB-B had good re-adsorption and desorption effects. Thus, CTAB-B can be an efficient and recyclable adsorbent for anionic dyes. [Display omitted] •CTAB-B exhibited ultrafast and efficient removal of acid red and acid fuchsine.•The adsorption mechanisms were described with isotherm and kinetics models.•Electrostatic interactions and hydrogen bonds governed adsorption of the two dyes.•Molecular size controlled their differences in adsorption effects.