Gabriela Ciobanu

Tailoring the functional properties of PLZT-BaTiO3 composite ceramics by core-shell approach

In the present work, composite ceramics of BaTiO3 with La0.08Pb0.92Ti0.20Zr0.80O3 were prepared from powders synthesized by two different methods: (a) PLZT@BT ceramics from core-shell powders with PLZT-core and BaTiO3 shell and (b) PLZT-BT ceramic composites from mixed PLZT and BaTiO3 powders. In core-shell ceramics, a thin conductive layer of BaPbO3 was formed that resulted in an increased effective permittivity with relatively low losses (tanu2009δu2009<u20090.7 in kHz regions). The extrinsic contributions play an important role in both ceramics, but they are more evident in core-shell samples due to the large number of interfaces. These results show that novel functional properties can be tailored by the controlled chemical reaction at interfaces.

Studies on adsorption of oxytetracycline from aqueous solutions onto hydroxyapatite

The presence of antibiotics in the water and wastewater has raised problems due to potential impacts on the environment and consequently their removal is of great importance. For this reason, this article aims to perform a study on the possibility of oxytetracycline (OTC) adsorption from aqueous medium by using the hydroxyapatite (HA) nanopowders as adsorbent materials. The hydroxyapatite nanopowders were synthesized by wet precipitation method by using orthophosphoric acid and calcium hydroxide as raw materials and investigated by XRD, SEM-EDX, FTIR and BET methods. The uncalcined and calcined hydroxyapatite samples have hexagonal crystal structure with crystal sizes smaller than 100nm and a specific surface area of 316m2/g and 139m2/g, respectively. The adsorption behavior of oxytetracycline, a zwitterionic antibiotic, on nanohydroxyapatite was investigated as a function of pH, contact time, adsorbent dosage and drug concentration by means of batch adsorption experiments. High oxytetracycline removal rates of about 97.58% and 89.95% for the uncalcined and calcined nanohydroxyapatites, respectively, were obtained at pH8 and ambient temperature. The adsorption process of oxytetracycline onto nanohydroxyapatite samples was found to follow a pseudo-second order and intraparticle diffusion kinetic models. The maximum adsorption capacities of 291.32mg/g and 278.27mg/g for uncalcined and calcined nanohydroxyapatite samples, respectively, have been found. The adsorption mechanism of OTC on the hydroxyapatite surface at pH8 can be established via surface complexation. The obtained results are indicative of good hydroxyapatite adsorption ability towards oxytetracycline drug.