Oxygen In Reaction Mixture Research Articles

Diclofenac Degradation by New AOP System Zero-Valent Aluminium–Acid (ZVAl/H+) Process and its Modifications

Drugs and other pharmaceutical compounds are often used substances around the world. Diclofenac is one of the widely used anti-inflammatory drug for the treatment of acute and chronic pain, rheumatoid and osteoarthritis. In recent years diclofenac was considered as a new emerging environmental contaminant of water and soil ecosystems. In the present work the new AOP system based on the ZVAl/H+ and its modifications was applied to degrade diclofenac water solutions with its initial concentration of 25 mg L−1. The effects of initial pH, dosage of Al0 , addition of hydrogen peroxide, ferrous, ferric and aluminium ions were studied in the dark experiments. In addition, effects of irradiation with sunlight lamp were also investigated. Finally, environmental toxicity studies were conducted according to OECD tests with terrestrial plants. Degradation efficiency was measured by UV-VIS spectroscopy. After all experiments the degree of resulting TOC removal was determined. Concentration of dissolved oxygen in reaction mixture during and after reaction was also monitored. The results showed that all used systems are able efficiently remove diclofenac. The best diclofenac removal reached 98 % efficiency at pH of 3.0 in 4 hours, with Al0 dosage used of 2.0 g L−1 and with addition of 10 mg L−1 of aluminium ions (Al3+). The best TOC removal (83 %) was achieved under experimental condition of ZVAl/H+ with Al0 dosage of 4.0 g L−1 at pH of 3.0 after 4 hours. Negative results with the utilization of radical scavenger for hydroxyl radicals (methanol) led us to conclusion that degradation process in the first steps of reaction proceeds parallel by both two different mechanisms – reductive dehalogenation and hydrogenolysis. Finally, before and after treatment processes toxicity tests according to OECD Guideline 208 were performed. Resulted toxicity values showed that diclofenac solutions in concentration range from 5 to 25 mg L−1 and solutions after treatment processes had only a low toxic effect on terrestrial plants.

One pot synthesis of water-dispersible dehydroascorbic acid coated Fe3O4 nanoparticles under atmospheric air: Blood cell compatibility and enhanced magnetic resonance imaging

Water dispersible and biologically important molecule dehydroascorbic acid (DHA, capable to cross the blood brain barrier) coated Fe3O4 superparamagnetic nanoparticles having an average size of ∼6nm were synthesized through one pot aqueous coprecipitation method under atmospheric air. An antioxidant ascorbic acid (AA) used in the synthesis oxidized itself to dehydroascorbic acid (DHA) to consume dissolved or available oxygen in reaction mixture which died away the oxidative impact of atmospheric air and formed DHA encapsulated the Fe3O4 nanoparticles which stabilized the Fe3O4 nanoparticles and significantly enhanced their colloidal solubility in water. Fe3O4 phase, superparamagnetic property, DHA coating and stable colloidal solubility in water were confirmed by means of XPS, VSM, IR and zeta potential analysis respectively. T1, T2 and T2∗ weighted magnetic resonance imaging (MRI) and corresponding relaxivity (r1=0.416, r2=50.28 and r2∗=123.65mM−1 and r2/r1=120.86, r2∗r1=297.23) of colloidally dispersed DHA-coated nanoparticle water phantom revealed a strong contrast enhancement in T2 and T2∗ weighted images. The compatibility of DHA-coated Fe3O4 nanoparticles toward human blood cells was examined by means of cell counting and cell morphological analysis with the use of optical microscope and scanning electron microscope imaging.

Noble metal and sulfuric acid modified TiO2 photocatalysts: Mineralization of organophosphorous compounds

Photocatalytic oxidation by oxygen of air in water suspension of TiO2-based catalysts was carried out for dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP)—simulants of warfare agents. Active photocatalysts were prepared via surface modification of standard photocatalyst Degussa P25 with platinum and palladium. The developed catalysts were about three-fold more active than traditionally best photocatalyst Degussa P25. Kinetic curves of DMMP oxidation on TiO2 and Pt/TiO2 are well approximated by the Langmuir–Hinshelwood model with competitive adsorption of oxygen and organophosphorus compound. The increase of activity of Pt/TiO2 is linked with higher oxygen adsorption constant or reaction rate coefficient. Photocatalytic oxidation can be scaled up to a larger reactor with the same reaction rates expressed as mmoll−1min−1 in mineralization of DMMP. The batch recirculating reactor with total volume 3l utilizes photocatalyst deposited over porous support and demonstrated higher oxidation rate and catalyst stability compared to suspended photocatalyst. Main criteria for mass-transfer process in the batch recirculating reactor were calculated to understand how concentration cross gradient depends on flow rate. The concentration of oxygen in reaction mixture changed with the stirring or recirculation rate and exerts strong influence on the oxidation rate.

Very Thin Silicon Nitride Films Grown by Direct Thermal Reaction with Nitrogen

Very thin uniform silicon nitride films less than 100Å have been obtained on silicon wafers by direct thermal reaction with nitrogen at temperatures ranging from 1200° to 1300°C. Small amounts of water or oxygen in reaction mixture caused vapor etching which gave rise to local crystallization. By eliminating both from the reaction ambient to less than 1 ppm, amorphous silicon nitride films can be deposited. These films have been found to have properties similar to those of CVD by investigations of Auger electron spectroscopy, infrared spectroscopy, and ellipsometry. Remarkable masking effects of the films against oxidation and phosphorus diffusion have been found.