Quantum-confinement induced enhancement in photocatalytic properties of iron oxide nanoparticles prepared by Ionic liquid

In this work, a cheap, low cost and environmental friendly microwave irradiation based solution method was used to prepare α-Fe2O3 nanostructures using ionic liquid for organic dye degradation. X-ray diffraction (XRD), Raman and high resolution transmission electron microscopy (HRTEM) results showed that the nanostructures were highly pure and well crystallized with rhombohedral structure. Field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) images confirmed the quantum dots with size ~10-13 nm and rodlike structures having length ~150 nm and diameter ~60 nm, respectively. Ultra violet- visible (UV-Vis) measurement of quantum dots showed an obvious blue-shift of the energy band gap due to the quantum size effect. The visible-light photo-degradation of methyl orange (MO) was evaluated using α-Fe2O3 nanostructures at ambient temperature. The efficiency in photo-degradation of organic dyes of prepared nanostructures was compared with the commercial α-Fe2O3 particles. The as-prepared α-Fe2O3 quantum dots showed higher activity than nanorods and commercial α-Fe2O3 in terms of degradation of MO within short time. Particularly, under visible light irradiation and the same experimental conditions, quantum dots exhibited superior photocatalytic performances of up to 96% for MO in the shorter time of 150 min. While, 89% and 68% of the MO could be degraded in the presence of α-Fe2O3 nanorods and commercial Fe2O3 particles, respectively. The apparent reaction rate constant for quantum dots was 1.64×10−2 min−1, while for nanorods and commercial particles the rate were 1.37×10−2 min−1 and 7.92×10−3 min−1. The smaller crystallite size in quantum regime of α-Fe2O3 quantum dots acted as active catalytic centers and played a key role in allowing effective interaction between organic dye and α-Fe2O3, in turn enhanced photocatalytic degradation performance.