Graphitic C<sub>2</sub>N<sub>3</sub>: An Allotrope of <i>g</i>-C<sub>3</sub>N<sub>4</sub> Containing Active Azide Pentagons as Metal-Free Photocatalyst for Abundant H<sub>2</sub> Bubble Evolution.

Tang, Dongmei; Shao, Chengtian; Jiang, Shujuan; Sun, Chuanzhi; Song, Shaoqing · ACS Nano · 2021

basic_science · Level V

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Abstract

A <i>g</i>-C<sub>3</sub>N<sub>4</sub> allotrope, a curved leaf-like graphitic C<sub>2</sub>N<sub>3</sub> (<i>g</i>-C<sub>2</sub>N<sub>3</sub>) with an intrinsic spontaneous polarization electric field (ISPEF), has been constructed for efficient solar energy conversion into H<sub>2</sub> energy <i>via</i> photocatalytic H<sub>2</sub>O splitting. The curved leaf-like π-delocalization <i>g</i>-C<sub>2</sub>N<sub>3</sub> was composed of aromatic azide pentagons and normal triazine hexagons obtained by cycloaddition between -C≡N groups from dicyandiamide polymerization and azide from the heat-treated polypyrrole fibers. Under light irradiation (λ > 420 nm), photo-generated charges are driven to separate efficiently and transfer from bulk to active sites of the surface under ISPEF that is opposite to the Coulomb field. Consequently, without any cocatalyst, <i>g</i>-C<sub>3</sub>N<sub>4</sub> allotrope demonstrates a very high H<sub>2</sub>-production activity of 14.9 mmol g<sup>-1</sup> h<sup>-1</sup> accompanied by a lot of H<sub>2</sub> bubbles, which is 2.6 times of <i>g</i>-C<sub>3</sub>N<sub>4</sub> loading with Pt. In comparison with the reported metal-free photocatalysts or those supported with noble metals, <i>g</i>-C<sub>3</sub>N<sub>4</sub> allotrope (<i>i.e.</i>, leaf-like <i>g</i>-C<sub>2</sub>N<sub>3</sub>) is confirmed to be the best metal-free photocatalyst for H<sub>2</sub>O splitting into H<sub>2</sub> fuel so far. The contructed leaf-like <i>g</i>-C<sub>2</sub>N<sub>3</sub> with SPEF supplies a suitable platform for solar energy conversion into H<sub>2</sub> fuel, which actively contributes to clean energy production.