Modification of N-doped TiO2 photocatalysts using noble metals (Pt, Pd) - a combined XPS and DFT study.

Nitrogen-doped TiO2 (N-TiO2) is considered as one of the most promising materials for various photocatalytic applications, while noble metals Pd and Pt are known as good catalysts for hydrogen evolution. This work focuses on the determination of structural and electronic modifications of N-TiO2, achieved by noble metal deposition at the surface, as a starting indicator for potential applications. We focus on the properties of easily synthesized nanocrystalline nitrogen-doped anatase TiO2, modified by depositing small amounts of Pd (0.05 wt%) and Pt (0.10 wt%), aiming to demonstrate efficient enhancement of optical properties. The chemical states of dopants are studied in detail, using X-ray photoemission spectroscopy, to address the potential of N-TiO2 to act as a support for metallic nanoparticles. DFT calculations are used to resolve substitutional from interstitial nitrogen doping of anatase TiO2, as well as to study the combined effect of nitrogen doping and oxygen vacancy formation. Based on the binding energies calculated using Slater's transition state theory, dominant contribution to the N 1s binding energy at 399.8 eV is ascribed to interstitially doped nitrogen in anatase TiO2. Given that both structure and photocatalytic properties depend greatly on the synthesis procedure, this work contributes further to establishing correlation between the structure and optical properties of the noble metal modified N-TiO2 system.

The influence of silicon substitution on the properties of spherical- and whisker-like biphasic α-calcium-phosphate/hydroxyapatite particles.

In this work, the influence of the morphology of hydroxyapatite particles on silicon substitution through hydrothermal synthesis performed under the same conditions was investigated. Spherical- and whisker-like hydroxyapatite particles were obtained starting from calcium-nitrate, sodium dihydrogen phosphate, disodium-ethylenediaminetetraacetic acid and urea (used only for the synthesis of whisker-like particles) dissolved in aqueous solutions. Silicon was introduced into the solution using tetraethylorthosilicate. X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy indicate that silicon doping induce different phase compositions and bioactivity of spherical- and whisker-like hydroxyapatite particles obtained under the same hydrothermal conditions. Silicon-substituted, spherical hydroxyapatites particles showed greater phase transformation to silicon-substituted α- calcium-phosphate compared with whiskers-like hydroxyapatite particles synthesized with the same amount of added silicon. Metabolic activity assay performed with SaOs2 osteosarcoma cells showed better biocompatibility of annealed biphasic spherical-like particles compared with annealed whiskerlike particles while dried spherical-like particles induce high cytotoxicity effect.

Comparative study of differently treated animal bones for Co(2+) removal.

The objective of the present study was the evaluation of differently treated bovine bones for Co(2+) removal from aqueous media. Powdered bones (B), as well as samples prepared by H(2)O(2) oxidation (BH(2)O(2)) and annealing at 400-1000 degrees C (B400-B1000), were tested as sorbent materials. A combination of XRD, FTIR spectroscopies, DTA/TGA analyses, specific surface area (S(p)) and point of zero charge (pH(PZC)) measurements was utilized for physicochemical characterization of sorbents. Sorption of Co(2+) was studied in batch conditions as a function of pH, contact time and Co(2+) concentration. Initial pH values in the range 4-8 were found optimal for sorption experiments. Equilibrium time of 24h was required in all investigated systems. The maximum sorption capacities differ significantly from 0.078 to 0.495mmol/g, whereas the affinity towards Co(2+) decreased in the order: B400>BH(2)O(2)>B600>B>B800>B1000. The pseudo-second-order model and Langmuir theoretical equation were used for fitting the kinetic and equilibrium data, respectively. Ion-exchange with Ca(2+) and specific cation sorption were identified as main removal mechanisms. The amounts of Co(2+) desorbed from loaded bone sorbents increased with the decrease of pH as well as with the increase of Ca(2+) concentration. Heating at 400 degrees C was found to be an optimal treatment for the production of the Co(2+) removal agent.

Controlled assembly of poly(D,L-lactide-co-glycolide)/hydroxyapatite core-shell nanospheres under ultrasonic irradiation.

An ultrasound field was applied to obtain PLGA/HAp biocomposite nanospheres. Formulation of PLGA/HAp composite revealed significant dependence of the morphology of the obtained composite on synthesis parameters, like the intensity of applied ultrasonic field, polymeric and ceramic parts' wt.% ratio in the composite, temperature of the medium, type of surfactant, and the sequence of steps in the formation of PLGA/HAp. Optimal parameters for the formation of PLGA/HAp included a lower content of the ceramic phase (PLGA/HAp=90:10), higher power of ultrasonic field (P=142.4W), lower temperature of the medium during ultrasonic treatment (T=8 degrees C), dilute solution of PVP as surfactant and dispersion of hydroxyapatite in polymer solution in order to achieve required homogeneity before the formulation of the composite. The morphology of PLGA/HAp particles synthesized under these conditions was highly regular: sphere-like, with particles of very small dimensions (150-320nm), highly uniform particle size distribution and characteristic planar spatial self-organization. These characteristics indicate significant improvements in PLGA/HAp composite resulting from ultrasonic method.

Investigation of properties of electrochemically synthesized iron oxide nano-powders.

Nano-sized powders of iron oxides have been synthesized electrochemically at temperatures in the range of 295-361 K, and current densities in the range of 200-1000 mA dm(-2). The structure and morphology of the powders were investigated by X-ray diffraction and scanning electron and transmission electron microscopy techniques. Their infrared absorption spectra, specific heat C(p)(T) and magnetic susceptibility chi(T) temperature dependences are also determined. The obtained powders consist of two phases, each possessing distinguished characteristics: the one formed of large plates and the other of whiskers. By appropriate adjustment of the synthesis conditions, it is possible to change features and relative abundances of the two phases, and that way to control morphology and other powder properties. Relaxation and transformation of the phases under external influences was also investigated, and the optimal procedure for preparation and stabilization of iron oxide nano-sized powders with desired characteristics was established.

Factors influencing the removal of divalent cations by hydroxyapatite.

The effect of pH, contact time, initial metal concentration and presence of common competing cations, on hydroxyapatite (HAP) sorption properties towards Pb(2+), Cd(2+), Zn(2+), and Sr(2+) ions was studied and compared using a batch technique. The results strongly indicated the difference between the sorption mechanism of Pb(2+) and other investigated cations: the removal of Pb(2+) was pH-independent and almost complete in the entire pH range (3-12), while the sorption of Cd(2+), Zn(2+) and Sr(2+) generally increased with an increase of pH; the contact time required for attaining equilibrium was 30 min for Pb(2+) versus 24h needed for other cations; maximum sorption capacity of HAP sample was found to be an order of magnitude higher for Pb(2+) (3.263 mmol/g), than for Cd(2+) (0.601 mmol/g), Zn(2+) (0.574 mmol/g) and Sr(2+) (0.257 mmol/g); the selectivity of HAP was found to decrease in the order Pb(2+)>Cd(2+)>Zn(2+)>Sr(2+) while a decrease of pH(PZC), in respect to the value obtained in inert electrolyte, followed the order Cd(2+)>Zn(2+)>Pb(2+)>Sr(2+); neither of investigated competing cations (Ca(2+), Mg(2+), Na(+) and K(+)) influenced Pb(2+) immobilization whereas the sorption of other cations was reduced in the presence of Ca(2+), in the order Sr(2+)>Cd(2+)>or=Zn(2+). The pseudo-second order kinetic model and Langmuir isotherm have been proposed for modeling kinetic and equilibrium data, respectively. The sorption of all examined metals was followed by Ca(2+) release from the HAP crystal lattice and pH decrease. The ion exchange and specific cation sorption mechanisms were anticipated for Cd(2+), Zn(2+) and Sr(2+), while dissolution of HAP followed by precipitation of hydroxypyromorphite (Pb(10)(PO(4))(6)(OH)(2)) was found to be the main operating mechanism for Pb(2+) immobilization by HAP, with the contribution of specific cation sorption.

Ultrasonic de-agglomeration of barium titanate powder.

BaTiO3 (BT) powder, with average particle size of 1.4 microm, was synthesized by solid-state reaction. A high-intensity ultrasound irradiation (ultrasonication) was used to de-agglomerate micro-sized powder to nano-sized one. The crystal structure, crystallite size, morphology, particle size, particle size distribution, and specific surface area of the BT powder de-agglomerated for different ultrasonication times (0, 10, 60, and 180 min) were determined. It was found that the particles size of the BT powder was influenced by ultrasonic treatment, while its tetragonal structure was maintained. Therefore, ultrasonic irradiation can be proposed as an environmental-friendly, economical, and effective tool for the de-agglomeration of barium titanate powders.

Removal of Co2+ from aqueous solutions by hydroxyapatite.

A study on the removal of cobalt ions from aqueous solutions by synthetic hydroxyapatite was conducted in batch conditions. The influence of different sorption parameters, such as: initial metal concentration, equilibration time, solution pH and presence of EDTA on the amount of Co(2+) sorbed was studied and discussed. The sorption process followed pseudo-second-order kinetics with necessary time of 24 h to reach equilibrium. Cobalt uptake was quantitatively evaluated using the Langmuir and Dubinin-Kaganer-Radushkevich (DKR) model. The Langmuir adsorption isotherm constant corresponding to adsorption capacity, Xm, was found to be 20.92 mg/g. Sorption of Co(2+) is constant in the initial pH range 4-8, because HAP surface buffers these solutions to the constant final pH value of 5.1. In the presence of EDTA, sorption of Co(2+) decreases due to formation of complex with lower sorption affinities. Cobalt desorption depends on the composition of the extracting solution. The desorbed amount of cobalt decreased continuously with increasing pH, and increased with increasing Ca(2+) concentration in leaching solution.

Service quality in public and private pharmacies in the city of Kragujevac, fr Yugoslavia.

AIM: To compare the service quality in public and private pharmacies in the city of Kragujevac by measuring patient care and health facility indicators. METHODS: The patient care indicators and health facility indicators, established by the World Health Organization in 1995, were measured prospectively in 7 public and 7 private pharmacies in Kragujevac, Yugoslavia, during November and December 1999. A sample of 100 patient-visits was analyzed in each pharmacy. RESULTS: Our study showed that the average drug dispensing time ranged from 20.5 to 48.2 seconds, being significantly longer in private (21.1-48.2 s) than in public pharmacies (20.5-33.7 s) (F=13.12, p<0.001). The percentage of actually dispensed drugs ranged from 29% to 63%, and no significant difference was found between public and private pharmacies. Patients' knowledge of a correct dosage ranged from 30% to 74% and the availability of key drugs ranged from 67% to 93% with no significant difference between public and private pharmacies. There was serious negligence in labeling the dispensed drugs in both public and private pharmacies: not a single drug package was labeled according to the World Health Organization recommendations. Key drugs were highly available in both public and private pharmacies. CONCLUSION: The average drug dispensing time was too short for a proper interaction between a pharmacist and a patient in both public and private pharmacies. The results of our study suggest that there was no real difference in the service quality between the public and the private pharmacies.