Ultrasound-assisted adsorption of Congo red from aqueous solution using Mg-Al-CO3 layered double hydroxide

Mg-Al-CO3 layered double hydroxide (LDH) was prepared via the hydrothermal method, and used to remove Congo red (CR) from the aqueous solution with the assist of ultrasound. The influence of ultrasonic power on the CR adsorption, together with adsorption kinetics and isotherms were investigated. The mechanism of ultrasound-assisted adsorption was elucidated. The results showed that compared with stirring and shaking, ultrasound-assisted adsorption resulted in a significantly shorter adsorption equilibrium time of 120 min under initial 0.2 g/L CR and 0.2 g/L LDH dosage. The optimal ultrasonic power was 180 W at which a maximum adsorption capacity of 934.43 mg/g was achieved. The adsorption kinetics fitted the pseudo-second order kinetic model well (R-2 = 0.9999), and the adsorption isotherms fitted the Langmuir isotherm model well (R-2 = 0.998). The adsorption rate remained above 60% after three cycles.