Photocatalytic degradation of phenol in water on as-prepared and surface modified TiO2 nanoparticles

• TiO2 nanoparticles continuously produced the high concentration of hydroxyl radicals.
• Modify TiO2 surface only strongly enhanced the photocatalytic performance.
• The Ti3+ sites on the blue TiO2 contributed the high phenol degradation rate.

The TiO2 nanoparticles in the diameter of 10–23 nm prepared in this study offered high photocatalytic activity to continuously produce the higher concentration of hydroxyl radicals than that stoichiometric produced from the highly oxidizing agent H2O2 in the water. The initiate phenol degradation rate on the TiO2 nanocatalyst was ca. 6 times higher than that in the phenol degradation only derived by H2O2. The addition of H2O2 with TiO2 could enhance the initial concentration of hydroxyl radicals for the higher degradation rate. However, overloading H2O2 with TiO2 could only slightly increase the degradation rate of phenol, and overloading TiO2 decreased the phenol degradation rate immediately. Further enhancement for the phenol degradation rate has been realized by surface modification of TiO2 via liquid acid treatment or hydrogenation. It did not change the bulk structure and the morphology/size of TiO2, but strongly enhanced the photocatalytic performance for the phenol degradation. The formation of Lewis acid Ti3+ sites on the blue TiO2 surface via hydrogenation contributed the higher phenol degradation rate than Brønsted acid sites on acid-treated TiO2. The preparation and regeneration of blue TiO2 avoids the utilization of corrosive liquid acids but offers higher photocatalytivity, which is promising for the water treatment.

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