CaO-doped tetragonal ZrO2 nanoparticles as an effective adsorbent for the removal of organic dye waste

Abstract

In this work, we show the promise and potential of CaO-doped tetragonal ZrO2 nanoparticles as a brilliant adsorbent for toxic azo dye (e.g., Congo red). Contrary to past works, where zirconia has mostly been used as a member to form composite for such adsorption experiments, we show that the system (i.e., doped-ZrO2) alone is capable to portray maximum adsorption capacity up to 186 mg/g for Congo red. High surface area (113 m2/gm) of the synthesized zirconia nanoparticles ensured a rapid removal of the dyes (>85% in just five minutes). The adsorption followed a pseudo-second order kinetic model and fitted closely with the Langmuir isotherm model. Adsorption mechanism reveals the efficacy of the dopant (i.e., CaO) which enabled a chemical interaction (via ion-exchange between the Ca2+ ion of dopant and Na+ ions in the dye molecules) that eventually holds all the success for the adsorption phenomena. To prove the environmental remediation of CaO-ZrO2 as a dye adsorbent in a more practical way, these dye adsorption studies were also carried out in real water. The popular market composition (i.e., yttria-stabilized ZrO2) was also compared and showed modest/little adsorption.