Eleni Pachatouridou

Impact of the synthesis parameters on the solid state properties and the CO oxidation performance of ceria nanoparticles

Ceria-based materials have received considerable attention in catalysis field due to their unique physicochemical characteristics. Compared to bulk ceria, nanosized ceria received particular interest, due to its high surface to volume ratio, improved reducibility and optimal morphological features. Hence, the fine-tuning of ceria properties by means of advanced synthesis routes is of particular importance. In this regard, the present work aims at investigating the impact of synthesis parameters on the solid state properties of CeO2 materials. Four different time- and cost-effective preparation methods were followed, i.e. thermal decomposition, co-precipitation and hydrothermal method of low and high NaOH concentration, employing in all cases Ce(NO3)3·6H2O as cerium precursor. A complementary characterization study, involving N2 adsorption at −196 °C (BET method), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and scanning/transmission electron microscopy (SEM/TEM), was carried out to gain insight into the impact of synthesis route on the textural, structural, morphological and redox properties. The results revealed the superiority of the hydrothermal method towards the development of ceria nanoparticles of high specific surface area (>90 m2 g−1), well-defined geometry (nanorods) and improved redox properties. CO oxidation was employed as a probe reaction to gain insight into the structure–activity correlation. Ceria nanorods prepared by hydrothermal method of high NaOH concentration demonstrated the optimum CO oxidation performance. A direct quantitative correlation between the catalytic activity and the abundance of easily reduced, loosely bound oxygen species, was revealed. Hence, this particular reactivity descriptor can potentially be used for the rational design of ceria-based materials.

Preparation of novel CeO2-biochar nanocomposite for sonocatalytic degradation of a textile dye

The sonocatalytic performance of CeO2 nanoparticles synthesized by a hydrothermal method (CeO2-H) and CeO2@biochar (CeO2-H@BC) nanocomposite, were evaluated for the degradation of Reactive Red 84 (RR84) under ultrasonic irradiation. For comparison purposes the corresponding performance of bare biochar (BC) and commercial CeO2 (CeO2-C) samples were also assessed. A complementary characterization study, involving scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), N2 adsorption at -196°C (Brunauer-Emmett-Teller (BET) method) and Fourier transform infrared spectroscopy (FT-IR) was undertaken to gain insight into the structure-performance relationships. The effect of various parameters such as initial RR84 concentration, solution pH, catalyst amount and ultrasonic power on the sonodegradation of RR84 was studied in detail. The results indicated that the CeO2-H@BC nanocomposite exhibited the best RR84 degradation efficiency, which is enhanced with the increase of CeO2-H@BC amount and ultrasonic power but diminished with the increment in RR84 concentration and pH value. A 98.5% degradation was obtained with a CeO2-H@BC amount of 1g/L, ultrasonic power of 450 W, pH of 6.5 and initial RR84 concentration of 10mg/L. The quenching effects of various scavengers proposed that OH radical plays the key role in the process. Analyses of intermediates by Gas chromatography-Mass spectroscopy (GC-MS) identified several by-products and accordingly the main pathway was proposed.