Luisa M. Pastrana-Martínez

Design of graphene-based TiO2 photocatalysts—a review

There is a recent increase in the interest of designing high-performance photocatalysts using graphene-based materials. This review gathers some important aspects of graphene–TiO2, graphene oxide–TiO2, and reduced graphene oxide–TiO2 composites, which are of especial relevance as next generation photocatalysts. The methods used for the preparation of these materials, the associated mechanistic fundamentals, and the application of graphene-based composites on the photocatalytic degradation of pollutants are reviewed. Some structural, textural, and chemical properties of these materials and other photo-assisted applications, such as hydrogen production from water splitting and dye-sensitized solar cells, are also briefly included.

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

AbstractMagnetite (Fe3O4), a core-shell material (SiO2@Fe3O4), and reduced graphene oxide-Fe3O4 (referred as rGO-MN) were used as supports of a specific highly active TiO2 photocatalyst. Thermal treatments at 200 or 450xa0°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@Fe3O4 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 (1.61xa0mgxa0L−1, i.e., below the threshold for water reuse in irrigation) was found for the magnetic catalyst prepared with SiO2@Fe3O4, an intermediate TiO2:support ratio (1.5), and treated at 200xa0°C under N2 atmosphere (i.e., SiO2@Fe3O4-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 (3.53xa0mgxa0L−1), added H2O2 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.n Graphical abstract% Imazalil conversion using different magnetic catalysts and comparison with bare TiO2