Adsorption behavior of rhamnolipid modified magnetic Co/Al layered double hydroxide for the removal of cationic and anionic dyes

In the present research, magnetic rhamnolipid-Co/Al layered double hydroxide (MR-LDH) was synthesized to uptake methylene blue (MB) and reactive orange 16 (RO16) from aqueous solution. The main parameters, including pH, adsorbent dosage, contact time, and initial analyte concentration, were optimized to achieve the best adsorption efficiency. Accordingly, the elimination of MB on MR-LDH is improved in the basic medium due to the electrostatic interactions between the negative charge of MR-LDH and the positive charge of MB dye. In contrast, the acidic medium (pH = 3) was favored for RO16 adsorption because of hydrogen bonding between the protonated form of azo dye and protonated hydroxyl groups at the surface of MR-LDH. The calculated maximum adsorption capacities for MB and RO16 were 54.01 and 53.04 mg/g at 313 K, respectively. The Langmuir model, which assumes monolayer adsorption on the adsorbent surface, provides the best explanation for the adsorption of both dyes (R-2 = 0.9991 for MB and R-2 = 0.9969 for RO16). Moreover, the pseudo-second-order kinetic model best described the adsorption process for MB (R-2 = 0.9970) and RO16 (R-2 = 0.9941). The proposed adsorbent maintains stable adsorption performance for four consecutive cycles. After each adsorption process, MR-LDH is easily separated by an external magnet. The findings show that MR-LDH was found to be an excellent adsorbent for the removal of both cationic and anionic organic dyes from aqueous solutions.

Automated summary

Magnetic rhamnolipid-Co/Al layered double hydroxide (MR-LDH) was synthesized and used for the adsorption of methylene blue (MB) and reactive orange 16 (RO16) from aqueous solution. MR-LDH displayed better removal efficiency for MB in alkaline medium and for RO16 in acidic medium. The Langmuir model and pseudo-second-order kinetic model provided the best fit for the adsorption of both dyes.