Catalytic effect of γ-Al(OH)₃, α-FeOOH, and α-Fe₂O₃ on the ozonation-based decomposition of diethyl phthalate adsorbed on sand and soil

Diethyl phthalate (DEP) is a pollutant which can be found on soils as a result of its widespread application in plastic industry. Soil contaminated with DEP requires the application of different chemical methods to attain its remediation. Among these methods, ozonation has proven to be effective against toxic soil pollutants. The presence of metal oxides in soil is a possible source of catalytic effect. In this study, it was analyzed the catalytic effect of goethite (α-FeOOH), hematite (α-Fe₂O₃), and gibbsite (γ-Al(OH)₃) in combination with O₃ to achieve DEP decomposition. The DEP elimination efficiency by ozonation on the sand increased according to the following order: without catalyst < γ-Al(OH)₃ < α-Fe₂O₃ < α-FeOOH. Among these three oxides, goethite has the highest OH groups density. The reaction of OH groups and O₃ favors the formation of oxidant species, such as O₂•⁻ and OH•. The effect of the moisture content, the catalyst concentration, and the type of soil (sand and calcined soil) were also studied. The latter had a significant influence on the total organic carbon (TOC) removal. The mineralization degree was 84% in the O₃–soil system, while only 40% was obtained with O₃–sand (α-FeOOH) in dry sand after 8 h of treatment. Calcined soil promoted the increase of TOC removal due to the presence of different metal oxides, which were active centers for O₃ decomposition. The toxicity tests of the three reaction systems (O₃–sand, O₃–sand (α-FeOOH), and O₃–soil) were evaluated on lettuce seed germination before and after DEP ozonation.