Photo–Fenton reaction in the presence of morphologically controlled hematite as iron source

• Hematite particles with controlled size and shape were produced and tested.
• Phenol degradation under photo–Fenton conditions with hematite was observed.
• There was no correlation between particle size and photoactivity.
• Hematite particles act as Fe reservoir, released in solution upon irradiation.
• The concentration of photo-leached Fe was safely far from wastewater limits.

Hematite particles with controlled size and shape (cubic, spherical and ovoidal, with size range from hundreds nm to μm) were produced by modulating the conditions of synthesis and were characterized by different techniques (XRD spectroscopy, scanning electron microscopy, BET analysis, dynamic light scattering, UV–vis spectroscopy). The photoactivity of the synthesized hematite particles was tested towards the degradation of phenol under photo–Fenton conditions, obtaining optimal results in the pH range 3–4. Although the smaller particles have a larger contact interface between the solid and the solution, no obvious relationship was found between size and photoactivity. A possible explanation is that the smallest particles tested showed an important radiation scattering, which would interfere with radiation absorption and, therefore, with photoactivity. In contrast, the most photoactive samples were those showing the highest concentrations of leached iron. This issue would imply that photoactivity may be related to partial dissolution of hematite with formation of Fe(II) and of photo-active Fe(III) species, which activate the classic photo–Fenton process. Anyway, leached Fe was limited to the μg L−1 range that is safely far from the mg L−1 limits for wastewater.

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