Nanocomposites and nanomaterials

Catalysis of Wastewater Pollutants by Ruthenium Nanooxide in Porous Glass 
Doycho I.K., Gevelyuk S.A., Filevska L.M., Grinevych V.S.
Odessa I.I. Mechnikov National University, Dvoryanska str., 2, Odesa 65082, Ukraine.  E-mail: lfilevska@gmail.com  
Phenol is one of the main wastewater pollutants in industry and in everyday life. Wastewater purification from it is usually done by catalytic oxidation, which makes it possible the transition to closed waste-free technologies.
The redistribution of charge in the benzene ring during phenol oxidation leads to the formation of no less harmful hydroquinone. Its oxidation leads to a rearrangement of the benzene ring π-bonds. The resulting oxide is insoluble in water and, after a short settling the waste water may be considered as a clean one. These oxidative reactions are possible in the presence of certain transition metals with two incomplete shells in their electronic configuration as catalysts. Such substances are noble metals of the platinum group, the cheapest of which is ruthenium. The configuration of its outer electron shell 4d75s1 corresponds to high electronegativity (in comparison, for example, with iron), which makes ruthenium to be a good catalyst. For the highest efficiency of catalysis, the catalyst surface should be developed as much as possible. These substances are to be chemically inert in the aggressive environment of wastewater, and their morphology must remove intra-diffusion restrictions during the reaction. Optimal in this sense, according to many researchers, are catalysts based on nanodispersed RuO2.
The creation of a corresponding nanoparticles’ ensemble, needs a selection of a suitable matrix, in which it will be formed. Since ruthenium dioxide, like hydroquinone oxide, is insoluble in water, then its high adhesion to the matrix walls is very important. This will prevent the catalyst from leaching out and precipitating along with the hydroquinone oxide. The attempts of using organosilicate rods as matrices give a fairly high catalyst leakage (over 5% in 8 hours). The use of finely porous silicate glass with residual silica gel inside the pores can reduce the leaching of the catalyst to hundredths of a percent, and therefore is preferable. Secondary silica gel, preventing the aggregation of nanoparticles, additionally increases the efficiency of catalysis.
An ensemble of insoluble oxide nanoparticles in the pores was created by a corresponding reaction directly in the pores of the matrix after its impregnation by a precursor solution using RuCl3. Phenol (similar to some types of dyes) is capable of quite intense luminescence due to inter electronic-vibration sublevels transitions. In hydroquinone oxide such levels are practically not preserved, and therefore the end of the reaction can be detected by a sharp drop in the luminescence intensity.