Quantitative Spectroscopic\nAnalysis of Surface-Reaching\nPhotoexcited Holes in g‑C<sub>3</sub>N<sub>4</sub>/TiO<sub>2</sub> Z‑Scheme Heterojunctions

The Z-scheme heterojunction has been demonstrated to\nbe effective\nin tuning the photocatalytic performance of photocatalysts. However,\nthere is still a lack of quantitative and in-depth research on how\nthe Z-scheme heterojunction affects the concentration of surface-reaching\nphotoexcited charges. Here, by combining time-resolved spectroscopies\nand kinetic analysis, the concentration of surface-reaching photoholes\n(<i>C</i><sub>h+(surf)</sub>) within g-C<sub>3</sub>N<sub>4</sub>/TiO<sub>2</sub> Z-scheme heterojunctions was quantitatively\nanalyzed for the first time. Quantitative measurements reveal that <i>C</i><sub>h+(surf)</sub> of the prepared Z-scheme photocatalysts\nis highly dependent on the g-C<sub>3</sub>N<sub>4</sub> content and\nthe induced Z-scheme heterojunctions at the g-C<sub>3</sub>N<sub>4</sub>/TiO<sub>2</sub> interface. Encouragingly, we found that a properly\nengineered Z-scheme heterojunction with close coupling of g-C<sub>3</sub>N<sub>4</sub> and TiO<sub>2</sub> can significantly increase\nthe <i>C</i><sub>h+(surf)</sub>, leading to nearly a 1.7-fold\nincrease compared with pristine TiO<sub>2</sub> samples. Furthermore,\na distinct hole trap state-mediated Z-scheme charge transfer mechanism\nwas uncovered in which the intrinsic interface defects at the g-C<sub>3</sub>N<sub>4</sub>/TiO<sub>2</sub> junction act as hole traps,\naccelerating interface electron–hole recombination, thereby\nboosting spatial charge separation and ultimately enriching the <i>C</i><sub>h+(surf)</sub>. This work provides insights into understanding\nand controlling electron pathways and <i>C</i><sub>h+(surf)</sub> in Z-scheme photocatalysis, with implications for the screening\nof different types of direct Z-scheme photocatalysts.