Effects of synthesis parameters on the properties and photocatalytic activity of the magnetic catalyst TiO2/CoFe2O4 applied to selenium photoreduction

intake to human health. Heterogeneous photocatalysis can be successfully applied to remove selenium ions from water, but the photocatalyst recovery in the end of the process still needs improvement. The application of a magnetic photocatalyst (TiO2/CoFe2O4) in the Se(IV) photoreduction was investigated, with emphasis in the catalyst magnetic separation. The photocatalyst was synthetized via a simple sol-gel method and a central composite design was considered to evaluate the effects of titanium isopropoxide mass ratio used in the synthesis, calcination temperature and pH on Se(IV) reduction. Calcination temperature showed a strong influence in the photocatalytic activity, and the catalyst calcined at 381 ◦C presented the best performance. In the bests test, at pH 2.61, it was possible to remove >99% selenium after 2 min of exposure to radiation. Photocatalysts containing great amounts of rutile phase produced the lowest removal results. The TiO2/CoFe2O4 photocatalyst was magnetically separable, however its saturation magnetization (2.7 emu g 1) was considerably smaller than pure CoFe2O4 (84.6 emu g 1) and the photocatalyst magnetic separation from the aqueous medium was about 11 times slower in comparison to pure cobalt ferrite. The synthetized photocatalyst was able to satisfactorily photoreduce Se(IV) (96.5%) even after five cycles of photocatalysis

Exact results for hydrogen recombination on dust grain surfaces

The recombination of hydrogen in the interstellar medium, taking place on surfaces of microscopic dust grains, is an essential process in the evolution of chemical complexity in interstellar clouds. The H_2 formation process has been studied theoretically, and in recent years also by laboratory experiments. The experimental results were analyzed using a rate equation model. The parameters of the surface, that are relevant to H_2 formation, were obtained and used in order to calculate the recombination rate under interstellar conditions. However, it turned out that due to the microscopic size of the dust grains and the low density of H atoms, the rate equations may not always apply. A master equation approach that provides a good description of the H_2 formation process was proposed. It takes into account both the discrete nature of the H atoms and the fluctuations in the number of atoms on a grain. In this paper we present a comprehensive analysis of the H_2 formation process, under steady state conditions, using an exact solution of the master equation. This solution provides an exact result for the hydrogen recombination rate and its dependence on the flux, the surface temperature and the grain size. The results are compared with those obtained from the rate equations. The relevant length scales in the problem are identified and the parameter space is divided into two domains. One domain, characterized by first order kinetics, exhibits high efficiency of H_2 formation. In the other domain, characterized by second order kinetics, the efficiency of H_2 formation is low. In each of these domains we identify the range of parameters in which, the rate equations do not account correctly for the recombination rate. and the master equation is needed.Comment: 23 pages + 8 figure

Optimizing outcomes for patients with severe haemophilia A

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73864/1/j.1365-2516.2007.01552.x.pd