This study demonstrates fast and efficient removal of ionic dyes using highly monodispersed crystalline hematite. Highly monodispersed crystalline hematite with similar cube-shape but different sizes were successfully fabricated via a series of facile template-free microwave (MW)/ultrasound (US) assisted hydrothermal (HT) techniques. The products were characterized by eight techniques including powder Xray diffraction, fourier transform infrared and ultraviolet – visible spectroscopies, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer– Emmett–Teller analysis, and dynamic light scattering analysis. Hematite microcubes with an average edge size of 1535 nm were prepared during a 12 h hydrothermal process at 180
C. Decreasing the time or temperature led to a goethite/hematite mixture. Nevertheless, applying 1 h of MW refluxing or US waves before 2 h of hydrothermal treatment, resulted in submicro hematite cubes with the average sizes of 640 or 236 nm in edge, respectively. The removal of three dyes using prepared hematite cubes was systematically investigated. The sample prepared by US + HT technique showed the best visible light photocatalytic activity towards reactive black 5 (RB5), an azo-dye, where almost all of the dye molecules were degraded in less than 40 min under a white LED-3W irradiation. In order to compare the photocatalytic activity of this sample with that of hematite structures in the literature, the removal of methylene blue (MB) and rhodamine B (RhB) was investigated. Our catalyst represented an enhanced photocatalytic activity against the photodegradation of 10 ppm MB (100% in 12.5 min) and 10 ppm RhB (96% in 25 min) with reaction rates constants of 0.641 and 0.127 min1.

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