Green synthesis of zirconia nanoparticles based on Euclea natalensis plant extract: Optimization of reaction conditions and evaluation of adsorptive properties

The development of nanomaterials has attracted increasing attention recently. The study of new technologies to obtain these materials becomes extremely important since the majority of the nanomaterials synthesized require reagents and solvents. These reagents and solvents are sometimes toxic and may generate harmful residues to the environment and the health of living beings. Therefore, green synthesis is a potential alternative to obtain nanoparticles, sustainably, using ecological sources. This study developed a method of synthesizing the green of zirconia (ZrO2) nanoparticles using Euclea natalensis (Natal gwarri or Natal ebony tree with African origin) plant extract. Moreover, the adsorptive properties against tetracycline were evaluated. A factorial design was applied in the synthesis process, and an optimization of the reaction parameters (plant extract concentration, precursor concentration, and calcination temperature) was also described for the first time in literature. The nanoparticles were characterized using the XRD, FTIR and TEM techniques, and then subjected to batch adsorption tests. The samples presented the zirconia monoclinic and tetragonal phases, according to the XRD analysis, yielding materials with minimum crystallite sizes equal to 5.25 nm. The FTIR spectra confirmed the results obtained by the XRD, presenting band characteristic of the zirconia monoclinic and tetragonal phases. The particles had a rounded morphology with a very low average diameter ranging from 5.90 to 8.54 nm. Moreover, the nanoparticles were applied to the adsorption of tetracycline. The samples were synthesized with vegetal extract and precursor concentration equal to 50 g L−1 and 0.03 mol L−1, respectively, and calcination temperature of 550 °C, presented in the best performance (loading of 30.45 mg g−1). The adsorption capacity of the zirconia synthesized in this study was significantly higher than other common materials applied to tetracycline removal. The green synthesis procedure, as well as the application of the zirconia nanoparticles to the adsorption of an emerging pollutant, were promising.