Tunable titanium metal–organic frameworks with infinite 1D Ti–O rods for efficient visible-light-driven photocatalytic H₂ evolution

Infinite 1D Ti-O rod-based metal-organic frameworks (MOFs) are promising photocatalysts for water splitting due to their high optical response and favourable photo-redox properties and stability, but have not been explored yet. In this study, three isoreticular porous 1D rod-based Ti-MOFs <b>ZSTU-1</b>, <b>ZSTU-2</b> and <b>ZSTU-3</b> are successfully constructed from infinite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow><mml:mrow><mml:mo>[</mml:mo> <mml:mrow> <mml:msub><mml:mrow><mml:mtext>Ti</mml:mtext></mml:mrow> <mml:mn>6</mml:mn></mml:msub> <mml:msub> <mml:mrow><mml:mrow><mml:mo>(</mml:mo> <mml:mrow><mml:msub><mml:mi>μ</mml:mi> <mml:mn>3</mml:mn></mml:msub> <mml:mo>-</mml:mo> <mml:mtext>O</mml:mtext></mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:mrow> <mml:mn>6</mml:mn></mml:msub> <mml:msub> <mml:mrow><mml:mrow><mml:mo>(</mml:mo> <mml:mrow><mml:msub><mml:mi>μ</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mo>-</mml:mo> <mml:mtext>OH</mml:mtext></mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:mrow> <mml:mn>6</mml:mn></mml:msub> </mml:mrow> <mml:mo>]</mml:mo></mml:mrow> </mml:mrow> <mml:mi>n</mml:mi></mml:msub> </mml:mrow> </mml:math> secondary building units (SBUs) and tritopic carboxylate linkers 4,4',4″-nitrilotribenzoic acid (H₃TCA), 1,3,5-tris(4-carboxyphenyl) benzene (H₃BTB) and tris(4'-carboxybiphenyl)amine (H₃BTCA), respectively. Their porosities systematically increase with the larger and longer organic linkers. The two MOFs <b>ZSTU-1</b> and <b>ZSTU-3</b> built from the triphenylamino-based ligands can absorb visible light, exhibiting much better photocatalytic performance than <b>ZSTU-2</b> as shown by the H₂ production rate of <b>ZSTU-1</b> and <b>ZSTU-3</b> being 3-4 times higher than that of <b>ZSTU-2</b>. The photocatalytic H₂ production rates for <b>ZSTU-1</b>, <b>ZSTU-2</b>, and <b>ZSTU-3</b> are 1060 μmol g^-1 h^-1, 350 μmol g^-1 h^-1 and 1350 μmol g^-1 h^-1, respectively. The extraordinary photocatalytic activity of <b>ZSTU-3</b> is attributed to its visible light absorption, large surface area, and favorable charge separation.