TiO2 hollow microspheres: synthesis, photocatalytic activity, and selectivity for a mixture of organic dyes

The photocatalytic properties of TiO2 have been extensively studied. TiO2 hollow microspheres may be useful for removing organic pollutants from waste water, given their high photocatalytic activities and ease of reclamation. In the work described here, TiO2 hollow microspheres were synthesized by a facile solvothermal method and characterized by XRD, SEM, TEM, and N-2 adsorption-desorption isotherm measurements. Their optical properties were investigated using UV-Vis diffuse reflectance absorption spectroscopy. The photocatalytic activity of the as-prepared TiO2 hollow microspheres was evaluated by studying the microsphere-catalyzed photodegradation of an aqueous rhodamine B solution irradiated with simulated sunlight, and comparing the results with those obtained using commercial TiO2 (P25) as the catalyst instead. The selectivity of the catalytic microspheres was studied by applying them in the photodegradation of a mixed dye solution of rhodamine B and 4-(p-nitrophenylazo)resorcinol (Magneson I). The TiO2 hollow microspheres were found to exhibit enhanced photocatalytic activity compared to that of P25, and a much higher photodegradation percentage for rhodamine B than for Magneson I in the mixed solution. Interestingly, the photodegradation percentages of the TiO2 hollow microspheres for rhodamine B and Magneson I in the mixed solution were the same as those observed in a solution of rhodamine B and a solution of Magneson I. That is, the TiO2 microspheres degraded the two dyes simultaneously in the mixed solution with the same high efficiency as they did in separate solutions of each dye. This characteristic would be very useful in practical applications. Moreover, the TiO2 hollow microspheres rapidly settled under gravity and were therefore easy to reclaim. These results suggest that the microspheres represent a promising photocatalyst for use in waste water treatment.