TiO2/reduced graphene oxide composites for photocatalytic degradation in aqueous and gaseous medium

•0.5-4 wt.% of reduced graphene oxide (rGO) was suscessfully prepared through a combined sol-gel method and solvothermal treatment.•The optimal amount of rGO on the hybrid photocatalyst is 1.0%.•Excessive amount of rGO can act as recombination center.•Gaseous (NO) or liquid pollutants (methylene blue) are degraded using TiO2-rGO-1% under UV light.

A series of TiO2 composites loaded with 0.5-4 wt.% of reduced graphene oxide (rGO) was prepared through a combined sol-gel method and solvothermal treatment. The composites were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), the Brunauer-Emmett-Teller (BET) method and diffuse reflectance spectroscopy (DRS). The photocatalytic performance of the prepared materials was evaluated by methylene blue discoloration in aqueous medium. The TiO2-rGO 1% composite led to an increase of ca. 11% in the pseudo-first-order rate constant, however, further increasing in rGO contents led to a decrease in the photocatalytic activity. When present in a high content, reduced graphene oxide can act as a recombination center, rather than providing a pathway for charge transfer and preventing recombination of electron-hole pairs. Subsequently, the TiO2-rGO 1% was immobilized in a vinyl-base paint and evaluated for the purification of air containing 1 ppmv of nitrogen oxide (NO). The results showed that the NO conversion was 25% and the selectivity for the transformation of NO into nitrates and nitrites was 50%. The same paint containing bare TiO2 presented an NO conversion of 35% and selectivity of 40%. Although, the abatement of NO by the composite was lower, the selectivity for ionic compounds was higher, indicating that the presence of rGO is important for the decomposition of NO under more oxidized compounds.

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