Linkage Unit Modulation\nof Triazine-Based Conjugated\nPorous Polymers/g‑C<sub>3</sub>N<sub>4</sub> Heterostructures\nTo Boost Cocatalyst-Free Photocatalytic Water Splitting

Rational design of heterostructures is a promising approach\nto\npromote the solar-to-chemical energy conversion; thus, the design\nof individual units in heterostructures via a molecular engineering\nstrategy is particularly important for unleashing the superior performance\nof heterojunction materials. In this paper, two organic polymers TrTB\nand TrBB with two different linking units were designed and synthesized\nfrom 2,4,6-tris(5-bromothiophen-2-yl)-1,3,5-triazine (M1), 2,4,6-tris(4-bromophenyl)-1,3,5-triazine\n(M2), and 1,4-phenylene diboronic acid bis(pinacol) ester (M3), serving\nas candidates for the composite with carbon nitride (g-C<sub>3</sub>N<sub>4</sub>, CN). The obtained TrTB/CN and TrBB/CN heterojunctions\nprepared by physical ball milling methods showed efficient photocatalytic\nhydrogen evolution activity. TrTB/CN and TrBB/CN with a 20% feeding\nratio showed the best hydrogen production rate, in which TrTB/CN-20\nand TrBB/CN-20 produced hydrogen at rates of 41.60 and 4.46 mmol g<sup>–1</sup> h<sup>–1</sup> under full light conditions\nwithout any cocatalyst, respectively. Additionally, the hydrogen evolution\nreaction (HER) rates of TrTB/CN-20 and TrBB/CN-20 bare catalysts under\nvisible light illumination (λ > 420 nm) were 26.83 and 1.74\nmmol g<sup>–1</sup> h<sup>–1</sup>, respectively. The\nlarge difference in the HER rates of the two heterojunctions arises\nfrom the small changes in the linking units of the two polymers, and\nthe excellent photocatalytic performance of TrTB/CN is mainly attributed\nto the enhanced light absorption ability of the thiophene unit and\nthe suppressed recombination of photogenerated charge carriers by\nthe formation of a type II heterojunction. In addition, TrTB/CN-20\nhas a good photocatalytic stability with an apparent quantum yield\nof 3.43% at 420 nm. This study provided an idea for the rational design\nof efficient metal-free-based heterojunction photocatalysts in the\ncocatalyst-free hydrogen evolution systems.