Combining ZVI reduction with photo-Fenton process for the removal of persistent pollutants

•An integrated process combining reductive and oxidative stages has been developed.•Variation of experimental conditions allows favoring reductive or oxidative stages.•This methodology might be useful to deal pollutants reluctant to oxidation.

An iron-based photochemical process able to act via reductive and oxidative stages by tuning experimental conditions has been explored. In a first step, zero-valent iron (ZVI), added as steel wool, was used to reduce those pollutants reluctant to oxidative processes. Then, the iron released in the solution was employed, upon addition of hydrogen peroxide, to drive a photo-Fenton process. This procedure has been checked with a mixture of five chemicals, namely p-toluenesulfonic acid, benzoic acid, p-nitrobenzoic acid, acetaminophen and caffeic. p-Nitrobenzoic acid resulted to be the most reluctant against oxidation but it was reduced in the absence of H2O2 to form 4-aminobenzoic acid; the presence of salts (e.g. tap water) was required and best results were reached at neutral pH. As p-aminobenzoic acid can be more easily oxidized than p-nitrobenzoic, combination of both stages is meaningful: a ZVI-based reduction followed by a photo-Fenton like-oxidation was employed to remove this pollutant from tested solutions.

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