Enhanced photocatalytic bacterial inactivation of atomic-layer deposited anatase-TiO2 thin films on rutile-TiO2 nanotubes.

In this work, experimental conditions were established to fabricate self-ordered rutile-TiO2 nanotube arrays, coated with a conformal anatase-TiO2 thin layer using atomic layer deposition. E. coli inactivation tests showed a considerable increase in photocatalytic activity using rutile-TiO2 nanotubes coated with anatase-TiO2 compared to that using single rutile or anatase TiO2 nanotubes only. Photocatalytic hydroxyl radical generation rates (determined by pNDA bleaching) were also meaningfully enhanced for the combined anatase/rutile TiO2 nanostructures. Therefore, we show that it is possible to take advantage of the morphological properties of the materials and the synergic effect from the combination of both TiO2 polymorphs during the design of novel materials, which could be used as antibacterial agents to improve the quality of drinking water.

Degradation of 1-hydroxy-2,4-dinitrobenzene from aqueous solutions by electrochemical oxidation: role of anodic material.

Electrochemical oxidation (ECOx) of 1-hydroxy-2,4-dinitrobenzene (or 2,4-dinitrophenol: 2,4-DNP) in aqueous solutions by electrolysis under galvanostatic control was studied at Pb/PbO2, Ti/SnO2, Ti/IrxRuySnO2 and Si/BDD anodes as a function of current density applied. Oxidative degradation of 2,4-DNP has clearly shown that electrode material and the current density applied were important parameters to optimize the oxidation process. It was observed that 2,4-DNP was oxidized at few substrates to CO2 with different results, obtaining good removal efficiencies at Pb/PbO2, Ti/SnO2 and Si/BDD anodes. Trends in degradation way depend on the production of hydroxyl radicals (OH) on these anodic materials, as confirmed in this study. Furthermore, HPLC results suggested that two kinds of intermediates were generated, polyhydroxylated intermediates and carboxylic acids. The formation of these polyhydroxylated intermediates seems to be associated with the denitration step and substitution by OH radicals on aromatic rings, this being the first proposed step in the reaction mechanism. These compounds were successively oxidized, followed by the opening of aromatic rings and the formation of a series of carboxylic acids which were at the end oxidized into CO2 and H2O. On the basis of these information, a reaction scheme was proposed for each type of anode used for 2,4-D oxidation.