TiO-based (FeO, SiO, reduced graphene oxide) magnetically recoverable photocatalysts for imazalil degradation in a synthetic wastewater.

Magnetite (FeO), a core-shell material (SiO@FeO), and reduced graphene oxide-FeO (referred as rGO-MN) were used as supports of a specific highly active TiO photocatalyst. Thermal treatments at 200 or 450 °C, different atmospheres (air or N), and TiO:support weight ratios (1.0, 1.5, or 2.0) were investigated. X-ray diffractograms revealed that magnetite is not oxidized to hematite when the core-shell SiO@FeO material-or a N atmosphere (instead of air) in the thermal treatment-was employed to prepare the TiO-based catalysts (the magnetic properties being preserved). The materials treated with N were first tested for degradation of imazalil (a well-known fungicide) in deionized water. The best compromise between the photocatalytic activity, magnetic separation, and Fe leached (1.61 mg L, i.e., below the threshold for water reuse in irrigation) was found for the magnetic catalyst prepared with SiO@FeO, an intermediate TiO:support ratio (1.5), and treated at 200 °C under N atmosphere (i.e., SiO@FeO-EST-1.5-200-N). This material was then tested for the treatment of imazalil in a synthetic wastewater, SW (with a chemical composition simulating an effluent resulting from fruit postharvest activity). This SW has a pH of 4.2 and the experiments were carried out at this natural pH and at neutral conditions (keeping pH at 7 along the reaction). The magnetic catalyst was more active than bare TiO for the treatment of imazalil in SW at natural pH. Since Fe leaching was observed (3.53 mg L), added HO enhanced both imazalil degradation and mineralization. Conveniently, these catalysts can be readily recovered by using a conventional magnetic field, as demonstrated over three consecutive recycling runs. Graphical abstract % Imazalil conversion using different magnetic catalysts and comparison with bare TiO.