Palygorskite-TiO₂ nanocomposites: Part 2. photocatalytic activities in decomposing air and organic pollutants

In this paper we measure the photocatalytic activities of small-sized TiO₂ particles supported on palygorskite in five different proportions (TiO₂:Pal ratios of 90:10, 80:20, 70:30, 60:40 and 50:50) in decomposing NO gas and a volatile organic compound (VOC, toluene). The prepared Pal-TiO₂ nanocomposites showed significantly higher photocatalytic activity in decomposing NO gas under visible-light irradiation up to 2.6 times, and under UV light irradiation (λ>290nm) up to 1.17 times, than that of the commercial titania, P25. The best photocatalytic activities were measured for 30% palygorskite with 70% TiO₂, which could be attributed to a combination of good dispersion, relatively low agglomeration and relatively high amount of TiO₂.The photocatalytic efficiency of the prepared Pal-TiO₂ samples in decomposing toluene was also tested. Under UV irradiation, all palygorskite-supported TiO₂ samples showed larger catalytic activity compared to the commercial titania, P25. The reaction rates of toluene photo-oxidation were found to be 1.37-1.74 times greater than that of P25. The higher reaction rates corresponded to the samples containing 20-30% palygorskite. Under artificial solar-light irradiation all palygorskite-supported TiO₂ catalysts showed higher toluene photo-oxidation rates compared to P25. The catalytic activity increased by 2.7-3.34 times under artificial solar-light irradiation. An increase in catalytic activity was observed with increasing TiO₂ content up to 70%. The sample with 30% palygorskite and 70% TiO₂ gave the highest reaction rates. Further decrease of palygorskite (increase of TiO₂) content resulted in a decrease of the reaction rate.