Reduced graphene oxide/TiO2 nanotube composites for formic acid photodegradation

[Display omitted] •Composites formed of TiO2 nanotubes and graphene oxide (GO) successfully prepared.•Positive influence of the GO addition on the formic acid photocatalytic degradation.•Partial reduction of GO favors the transfer of photogenerated electrons from TiO2.•Optimum GO loading observed at 1.0–1.5wt%.•Above a threshold GO loading of 2.0wt%, shielding effect by graphene oxide. The influence on the photocatalytic performance of TiO2 nanotubes (NT) resulting from the addition of graphene oxide (GO) was studied. TiO2 nanotubes (NT) were prepared using alkaline hydrothermal treatment of TiO2 P25 followed by calcination at 400°C under air. GO-NT composites were then obtained by wet impregnation of the as-prepared TiO2 nanotubes onto graphene oxide before reduction under H2 at 200°C. In a first step, the influence of the reduction treatment was evaluated on GO alone to determine its role towards the nature of the oxygen-containing functional groups present. GO-NT composites were also characterized considering both the effect of the reduction treatment and of the GO weight loading on textural, structural, electronic, and optical properties of TiO2 nanotubes. The resulting GO-NT composites were finally evaluated for the photocatalytic degradation of formic acid and compared to TiO2 nanotubes alone and to P25. Results emphasize a strong increase of the electron affinity and conductivity of the GO-NT composites if graphene oxide is reduced at 200°C. These enhanced properties lead to an easier separation of photogenerated charges and to a limitation of the recombination of electron-hole pairs. A dramatic gain in photocatalytic response is observed. Maximum in photocatalytic efficiency is reached at a GO loading of 1.0wt% while further increase of GO weight loading blocks light penetration and depletes the photocatalytic response.