Speranta Tanasescu

Thermodynamic properties of the rock-salt entropy stabilized oxide (Co,Cu,Mg,Ni,Zn)O have been determined and the relevant functions suitable for evaluation of thermodynamic stability in particular temperature ranges associated with structural changes during heating have been measured. The energetic parameters obtained via several experimental methods under both the equilibrium and dynamic conditions (drop calorimetry, solid state electromotive force measurements, DSC/TG), together with the thermal expansion and electrical conductivity data, have been analyzed, and the relationship of the thermodynamic stability with changes in the defect structure has been revealed. Our results are consistent with a phase transition to a high entropy state around 1150 K and the large negative values of the free energy, observed in the 1173 to 1223 K temperature domain, highlight a more stable state in the sample with the rock-salt structure. The partial molar enthalpy and entropy values of oxygen dissolution in the crystalline phase increase with increasing temperature suggesting the decrease of the binding energy of oxygen and the decrease of order in the oxygen sublattice of the structure, respectively. Due to the significant increase in partial molar entropy in the temperature range of 1173–1273 K, it is likely that oxygen vacancies are not concentrated at specific oxygen sites but they are randomly distributed, supporting the previous findings related to an entropy-driven phase transformation. The experimental methods outlined in this report can be used to distinguish between the phase transitions associated with the formation of an entropy stabilized phase and highlight the correlative effects of temperature and defect structure on the thermodynamic behavior of the (Co,Cu,Mg,Ni,Zn)O compound.

Metal oxide (Me_xO_y) nanomaterials are used as catalysts and/or sorbents in processes taking place in supercritical water (scH₂O), which is the “green” solvent needed to obtain energy-relevant products. Their properties are significantly influenced by the synthesis method used to prepare active Me_xO_y. In addition, the use of supported Me_xO_y nanoparticles is more practical and cost-effective in terms of their performance maintenance. Within this context, the present study reports on the preparation of carbon-supported ZnO and CuO composites using an innovative scH₂O impregnation method. Metal oxides were impregnated on a carbon (C) support using a continuous-flow tubular reactor. The results show that impregnation in scH₂O is a promising approach for the preparation of ZnO/C and CuO/C composite materials. This one-step synthesis method, in a continuous flow, uses neither a seed layer nor a mineralizer, and it needs substantially lower preparation times than conventional impregnation methods.

Nanomaterials based on metal oxides (MexOy) are employed as catalysts and/or sorbents in processes undergoing conditions in supercritical water (scH2O), the “green” reaction medium used to obtain energy relevant products. Their properties are greatly affected by the synthesis method used to produce the active MexOy. Moreover, in order to maintain their performance, it is more practical and cost-effective to use supported MexOy nanoparticles. Within this context, the present work deals with the preparation of carbon-supported ZnO and CuO composites by an innovative method based on impregnation under scH2O conditions. Metal oxides were impregnated on a carbon (C) support using a continuous flow tubular reactor. The results show that impregnation in scH2O is a promising approach for the preparation of ZnO/C and CuO/C composite materials. This one-step synthesis method, in a continuous flow, uses neither seed layer nor mineralizer, and it needs substantially lower preparation times than the conventional impregnation methods.

The recent focus in the development of novel nanosystems for biomedical applications lays firmly on their interactions with biomolecules. Thermodynamic parameters driving the interaction between nanoparticles and proteins provide insights into complex processes at bio/nanointerface. The present work aims to investigate the binding mechanisms and the dominant contributions that determine the adsorption processes during the interactions of a model protein, that is, bovine serum albumin, with a new type of drug delivery systems, Vitamin E/sphingomyelin nanoemulsions, plain and coated with polyethylene glycol, and d‐ɑ‐tocopheryl polyethylene glycol succinate. The binding parameters (binding constant, binding stoichiometry, enthalpy, Gibbs energy, and entropy changes of binding) are evaluated by the isothermal titration calorimetry with a MicroCaliTC200 equipment. The effect of nanoemulsions on the protein stability is examined by measuring the thermodynamic parameters for the protein's unfolding (heat capacity; enthalpy, entropy, and free energy changes) with a NanoDSC (TA Instrument) apparatus. The thermodynamic profile shows for all compositions an entropy‐driven interaction dominated by hydrophobic forces due to the rearrangements/displacement of the surrounding water molecules, while maintaining the native conformation of the protein. All the information acquired by thermodynamic approach may significantly enhance the knowledge with special focus on PEGylated nanoemulsions used for biomedical applications.

In response to increasing energy demand, various types of organic wastes, including industrial and municipal wastewaters, or biomass wastes, are considered reliable energy sources. Wastes are now treated in supercritical water (SCW) for non-fossil fuel production and energy recovery. Considering that SCW technologies are green and energetically effective, to implement them on a large scale is a worldwide interest. However, issues related to the stability and functionality of materials used in the harsh conditions of SCW reactors still need to be addressed. Here we present an overview on materials used in the SCW technologies for energy harvesting from wastes. There are catalysts based on metals or metal oxides, and we discuss on these materials’ efficiency and selectivity in SCW conditions. We focus on processes relevant to the waste-to-energy field, such as supercritical water gasification (SCWG) and supercritical water oxidation (SCWO). We discuss the results reported, mainly in the last decades in connection to the current concept of supercritical pseudo-boiling (PB), a phenomenon occurring at the phase change from liquid-like (LL) to gas-like (GL) state of a fluid. This review aims to be a useful database that provides guidelines for the selection of the abovementioned functional materials (catalysts, catalyst supports, and sorbents) for the SCW process, starting from wastes and ending with energy-relevant products.

Open access peer-reviewed chapter

The mixed conducting perovskite-type oxides BaxSr1-xCo1-yFeyO3-δ (BSCF) are intensively studied as potential high-performance solid oxide fuel cell cathode materials. The effect of different compositional variables and oxygen stoichiometry on the structure and thermodynamic stability of the BaxSr1-xCo1-yFeyO3-δ (x = 0.2, 0.4, 0.5, 0.6, 0.8; y = 0.2, 0.4, 0.6, 0.8, 1) perovskite-type compositions were investigated by solid electrolyte electrochemical cells method and scanning electron microscopy (SEM). The thermodynamic quantities represented by the partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen were obtained in the temperature range of 823–1273 K. The in situ change of oxygen stoichiometry and the determination of thermodynamic parameters of the new oxygen-deficient BSCF compositions were studied via coulometric titration technique coupled with electromotive force (EMF) measurements. The effect of A- and B-site dopants concentration correlated to the variation of oxygen stoichiometry on the thermodynamic stability and morphology of the BSCF samples was evidenced.