Pressurized photo-reactor for the degradation of the scarcely biodegradable DPC cationic surfactant in water

• The photolytic and photocatalytic degradation of a surfactant in water was studied.
• A proper reactor was built on purpose to investigate the influence of O2 pressure.
• O2, He and Ar were used as pressurizing gases in the range 1–15 bar.
• Using O2, the mineralization degree is greatly enhanced with working pressure.
• The reaction mechanism does not change with increasing the operative pressure.

The photocatalytic processes studied for the water depollution can be influenced by the operating pressure, being this parameter strictly correlated, by the Henry law, with the solubility of gas in the liquid phase. A proper reactor was built on purpose to investigate the influence of pressure on both photolysis and photocatalysis processes by using commercial nano-TiO2 sample. The degradation of a cationic surfactant, dodecyl pyridinium chloride (DPC) was investigated in a pressure range between 1 and 15 bar and using three different gases (O2, He, Ar) in the headspace of the reactor. Oxygen is a reactant of the oxidizing process, while argon and helium are two inert gases (the first one with a solubility in water similar to oxygen and the second with a much lower solubility) used to verify the role of simple pressure action in the surfactants degradation. If oxygen is used as pressurizing gas, the mineralization degree of the pollutant is greatly enhanced with working pressure by both simple photolysis and also nanopowders assisted processes. The degradation mechanism appears to be fully comparable with the ones reported in the literature; the increased oxygen amount promotes only the rate and not the formation of reaction intermediates.

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