Ultrasound assisted adsorption of malachite green dye onto ZnS:Cu-NP-AC: Equilibrium isotherms and kinetic studies - Response surface optimization

The present manuscript deals with the synthesis and application of zinc sulfide:copper nanoparticle loaded on activated carbon (ZnS:Cu-NP-AC) for the ultrasound-assisted removal of malachite green from water samples. ZnS:Cu nanoparticles were synthesized and characterized using FE-SEM and FTIR. The FE-SEM revealed the formation of nano-sized particles. Ultrasonic-assisted adsorption was optimized using response surface methodology (RSM) combined with UV-Vis spectrophotometry analysis. The important adsorption parameters viz. pH of MG solution, MG concentration, adsorbent and sonication time by Central Composite design (CCD) and Derringer's desirability function. The optimal conditions were as followed: pH of 6.0, adsorbent of 0.02, sonication time of 3 min and MG concentration of 20 mg L-1. The experimental checking in these optimal conditions confirmed good agreements RSM results. The results indicated that adsorption of MG on adsorbent was strongly dependent on adsorbent mass. The MG uptake by ZnS:Cu-NP-AC was quantitatively evaluated by using sorption isotherms such as Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models, out of which Langmuir isotherm (R2 = 0.992) gave better correlation and maximum adsorption capacity was found to be 168.1 mg g-1.