Double-sided modification of TiO2 spherical shell by graphene sheets with enhanced photocatalytic activity for CO2 reduction

[Display omitted] •TiO2 sphere shell with inner and outer of wall modified by graphene is prepared.•The modified effect caused by graphene on each wall is relatively independent.•The double-sided modified TiO2 possesses enhanced photocatalysis on CO2 reduction.•The optimal dosage of graphene on one side of wall isn’t affected by the other one. TiO2 spherical shells with both inner and outer surface modified by graphene have been successfully constructed through a stepwise loading method. This double-sided modification method greatly increases the contact area of the shell with graphene sheets, which is beneficial for graphene to separate more photoelectrons from both the inner and outer sides of the shell simultaneously. The results of photocatalytic reduction of CO2 into CO indicate that the modification effects of inner and outer wall of TiO2 shell by graphene seem to be relatively independent to each other. As a result, compared with the traditional single-sided modified samples, even these optimal ones, the loading of graphene on the other side of TiO2 shell can still improve the photocatalytic reduction performance. Moreover, the optimal dosage of graphene on one side of shell surface is always maintained, without being affected by the graphene usage on the other side. This work indicates that the unique heterojunction obtained by graphene double-sided modification is advantageous to enhance the photocatalytic CO2 reduction performance and expected to be extended to the construction of other photocatalysts.