TiO 2 -based (Fe 3 O 4 , SiO 2 , reduced graphene oxide) magnetically recoverable photocatalysts for imazalil degradation in a synthetic wastewater.

Magnetite (Fe3 O4 ), a core-shell material (SiO2 @Fe3 O4 ), and reduced graphene oxide-Fe3 O4 (referred as rGO-MN) were used as supports of a specific highly active TiO2 photocatalyst. Thermal treatments at 200 or 450 °C, different atmospheres (air or N2 ), and TiO2 :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 SiO2 @Fe3 O4 material-or a N2 atmosphere (instead of air) in the thermal treatment-was employed to prepare the TiO2 -based catalysts (the magnetic properties being preserved). The materials treated with N2 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-1 , i.e., below the threshold for water reuse in irrigation) was found for the magnetic catalyst prepared with SiO2 @Fe3 O4 , an intermediate TiO2 :support ratio (1.5), and treated at 200 °C under N2 atmosphere (i.e., SiO2 @Fe3 O4 -EST-1.5-200-N2 ). 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 pH0 and at neutral conditions (keeping pH at 7 along the reaction). The magnetic catalyst was more active than bare TiO2 for the treatment of imazalil in SW at natural pH. Since Fe leaching was observed (3.53 mg L-1 ), added H2 O2 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 TiO2 .