M. Mokhtarifar, R. Kaveh, M. Bagherzadeh, M. Ormellese, M.P. Pedeferri, M.V. Diamanti
Politecnico di Milano,
Keywords: TiO2, photocatalysis, reduced graphene oxide, nanoparticles, sol-gel
Summary:Maghemite (ɤ-Fe2O3) is an outstanding metal-oxide semiconductor with a band gap (~2.2 eV), which possess better light harvesting and charge transport properties. The presence ɤ-Fe2O3 in TiO2 composites can favor the charge separation and improves the photocatalytic activity of the heterostructure dramatically [1,2]. Reduced graphene oxide (rGO) is considered a very promising material due to its superior electrical conductivity, chemical stability and high specific surface area. The increased photoactivity of semiconductor/graphene composites has been reported in many applications [3,4]. In our present investigations by applying the sol-gel technique we synthesized magnetically separable TiO2/SiO2/ɤ-Fe2O3/rGO (TSFG) nanocomposite with high photocatalytic activity on degradation of Methylene blue (MB). The synergistic effects of rGO, SiO2 and ɤ-Fe2O3 nanoparticles in TiO2 composites on the photocatalytic efficiency are investigated. The photocatalytic activities of the as-prepared samples were evaluated by the degradation of MB under visible light irradiation. Fig. 1 shows the photocatalytic discoloration of MB under simulated solar light with TiO2/SiO2 (TS), TiO2/SiO2/Fe2O3 (TSF) and TSFG powder photocatalysts. As expected, Methylene blue absorbance, measured with a Vis spectrophotometer, does not show any significant change under visible light irradiation even after 340 min (data not shown). While TS shows a low photoactivity (less than 30% overall degradation in 340 min), adding ɤ-Fe2O3 the degradation extent increases to about 51%. It can be seen that the MB degradation on the TSFG increases to more than 60% after a period of about 340 min. This is probably due to effect of rGO in decreasing the band gap of TiO2. Data on XRD, SEM and band gap support the actual obtaining of reduced graphene oxide and consequent decrease in the composite band gap, as well as the deposition of oxides nanoparticles on the rGO nanosheets.