The sensitized photocatalytic degradation of colored aromatic pollutants using titanium dioxide

The sensitized photocatalytic degradation of 4-nitrophenol (4-NP), a model colored aromatic pollutant, was examined using a variety of methods, to determine the feasibility of using sensitized photocatalysis as a degradation method, to determine reaction pathways, and to explore the ability of sensitized photocatalysis to drive the degradation of non-colored aromatic pollutants.; Diffuse reflectance spectroscopic techniques were employed to probe the degradation process of nitrophenols and azo dyes in powder systems. The degradation of adsorbed nitrophenols was affected by surface type, surface coverage, the presence of oxygen, the presence of moisture on the surface, and the acid-base characteristics of the nitrophenol. 4-Nitrocatechol (4-NC) was identified by diffuse reflectance FTIR as the primary reaction intermediate of adsorbed 4-NP by sensitized photocatalysis.; 4-NP was photocatalytically degraded in aqueous TiO{dollar}sb2{dollar} slurries in the presence and absence of O{dollar}sb2.{dollar} Hydroquinone (HQ) and 4-nitrosophenol were identified as the primary oxidative and reductive intermediates of direct photocatalytic degradation of 4-NP; 4-NC and HQ were the major oxidative and reductive intermediates of sensitized photocatalytic degradation. Oxygen increased the ratio of oxidative products, and also decreased the amount of 4-NP adsorbed on TiO{dollar}sb2.{dollar} The production of nitrate, nitrite, and smaller amounts of ammonium ion indicate that denitration occurs rapidly in both direct and sensitized photocatalysis. Photo-induced adsorption of 4-NP and its intermediates greatly affected the degradation pathway.; Oxidation of 4-NP by {dollar}gamma{dollar}-radiolysis in conditions favoring {dollar}cdot{dollar}OH as the reactive species produced HQ and 4-NC as the primary intermediates. 4-Nitrosophenol was proposed to be the primary intermediate formed by reaction with hydrated electron. These results are consistent with observations and reaction pathways proposed for TiO{dollar}sb2{dollar} systems.; Laser flash photolysis techniques have determined that the reactive excited state in sensitized photocatalysis is most likely the triplet state. The lifetime of the triplet 4-NP is affected by solvent polarity and pH.; Mixed reactant systems of 4-NP and 4-CP usually show enhanced degradation when compared to single reactant systems under similar conditions. Pollutant concentration relative to catalyst surface area strongly affected the extent of degradation of the mixed system. In most systems, 4-NP was identified as the primary sensitizer, while 4-CP was the primary electron acceptor, indicating that 4-NP is capable of driving the degradation of noncolored pollutants.