Carbon nanotubes as base materials for water treatment processes

Chemical wastewater treatments are dependent on the addition of auxiliary oxidants, which may include molecular oxygen, ozone, and hydrogen peroxide, working on their own, or activated by means of a specialized catalyst or photocatalyst. Chemical treatments are by nature definitive processes, since they can lead to complete mineralization of the existing pollutants. However, this is seldom the case, when looking for a rational solution from the socio-economical point of view. In the case of industrial effluents, special treatments are often required, even when only a partial oxidative degradation is targeted, due to the complex nature of the pollutants (e.g. dyes, pharmaceuticals, oils, organics, inorganics and bio-compounds). Some compounds, like nitrophenols, are particularly refractory to aerobic biodegradation and in addition to that toxic, requiring strong oxidative solutions. Typical solutions are the thermal processes at elevated temperatures and pressures, or using metal supported catalysts. Alternatively, it is possible to use heterogeneous photocatalysis based on the efficient production of hydroxyl radicals. Somewhere between these two limits lies the catalytic wet peroxide oxidation (CWPO), an advanced oxidation process (AOP) involving the use of hydrogen peroxide (H2O2) as oxidation source and a suitable catalyst (typically iron based catalysts). The main role of the catalyst is to promote H2O2 decomposition through the formation of hydroxyl radicals (HO●) with high oxidizing potential, effective in the destruction of a huge range of pollutants [1,2]. This type of technology is especially attractive due to the use of mild conditions, simple equipment and the environmental safe oxidant H2O2.Work supported by project PTDC/AAC-AMB/110088/2009 and partially by project PEst–C/EQB/LA0020/2011, financed by FEDER through COMPETE - Programa Operacional Factores de Competitividade and by FCT - Fundação para a Ciência e a Tecnologia