g-CN/TiO Mesocrystals Composite for H Evolution under Visible-Light Irradiation and Its Charge Carrier Dynamics.

The photocatalytic performance of graphitic carbon nitride (g-CN) has been limited to low efficiency due to fast charge recombination. Here, we constructed g-CN nanosheets/TiO mesocrystals metal-free composite (g-CN NS/TMC) to promote the efficiency of charge separation. The photocatalytic H evolution experiments indicate that coupling g-CN NS with TMC increases photogenerated charge carriers in g-CN NS/TMC composite due to efficient charge separation. g-CN NS (31 wt %)/TMC shows the highest photocatalytic activity and the corresponding H evolution rate is 3.6 μ mol h. This value is 20 times larger than that of g-CN NS without any noble metal cocatalyst under visible-light irradiation (λ > 420 nm). The photocatalytic activity of g-CN NS/TMC (3.6 μmol h) is 7 times higher than that of g-CN NS/P25 (0.5 μ mol h), confirming the importance of strong interface interaction between two-dimensional g-CN NS and plate-shape TMC. Femtosecond time-resolved diffuse reflectance (fs-TDR) was employed to study the fundamental photophysical processes of bulk g-CN, g-CN NS, and g-CN/TMC composite which are essential to explain the photocatalytic activity. Using fs-TDR, we demonstrate that the photocatalytic activity depends on the increased driving force for photoinduced electron transfer and a higher percentage of photogenerated charges.