One step synthesis of Co/Cr-codoped ZnO nanoparticle with superb adsorption properties for various anionic organic pollutants and its regeneration

Adsorption is an effective means to remove organic pollutant. However, it is challenging to prepare the adsorbents with high adsorption capacities and their regeneration. Herein, Co/Cr-codoped ZnO nanoparticles (NPs) with superb adsorption for dyes and antibiotics have been successfully synthesized by a mild solvothermal method. At the optimal Co:Cr:Zn doping moral ratio of 4:6:100, the maximum adsorption capacities of methyl orange (MO) and tetracycline hydrochloride (TC-HCl) on Co/Cr-codoped ZnO NPs is 1057.90 mg g−1 and 874.46 mg g−1, respectively. The adsorption process of the sample over MO and TC-HCl both agreed well with the pseudo-second-order kinetic model and Langmuir isotherm model. Adsorption thermodynamics proved that the adsorption of MO and TC-HCl on Co/Cr-codoped ZnO NPs was a spontaneous and endothermic process. The mechanism shows that the surface of Co/Cr-codoped ZnO NPs have more positive charges, larger specific surface area and more crystal defects due to Co3+ and Cr3+ substitutes Zn2+ in ZnO lattice, improving their adsorption property. In addition, Co/Cr-codoped ZnO NPs have also excellent adsorption capacity for Direct Red, Congo Red, Evans Blue and Methyl Blue. More importantly, the regeneration of adsorbents was studied to achieve the reuse of materials, and avoid secondary pollution. Co/Cr-codoped ZnO NPs will be a promising choice for wastewater treatment owing to its excellent adsorption capacity and relatively low cost.