Surface basicity mediated rapid and selective adsorptive removal of Congo red over nanocrystalline mesoporous CeO₂

Herein we first report surface basicity mediated rapid and selective adsorptive removal of organic pollutants over nanocrystalline mesoporous CeO₂. The role of surface features in controlling the selectivity and efficiency of adsorption is well known. Nevertheless, the possibility of tuning the adsorption capacity and selectivity of adsorbents through their surface characteristics remains less explored. In this work, the surface basicity of mesoporous CeO₂ nanoparticles was improved by Er³⁺ doping under two different reaction conditions: via sol-gel and sol-hydrothermal methods. The nature and amount of surface basic sites were determined with the help of CO₂ temperature programmed desorption (TPD). The adsorption capacity and selectivity of four different CeO₂ samples were investigated using Congo red, methyl orange, and methylene blue as the model pollutants. From the adsorption studies, Er³⁺ doped CeO₂ synthesized by the sol-gel method, having the highest amount of surface basic sites, proved to be the most efficient and highly selective adsorbent among the four developed variants of CeO₂ towards Congo red. According to the proposed mechanism, surface basicity can be employed as a controlling parameter capable of tuning the adsorption capacity as well as the selectivity of CeO₂ towards organic pollutants.