Bimetallic Ag-Cu Supported on Graphitic Carbon Nitride Nanotubes for Improved Visible-Light Photocatalytic Hydrogen Production.

This work, for the first time, reports visible-light active bare graphitic carbon nitride nanotubes (C3N4 NTs) for photocatalytic hydrogen generation, even in the absence of any cocatalyst. Upon uniform dispersion of the cocatalysts, Ag-Cu nanoparticles, on the well-ordered bare C3N4 NTs, they exhibit twice the H2 evolution rate of the bare C3N4 NTs. The improved activity is attributed to their unique tubular nanostructure, strong metal-support interaction, and efficient photoinduced electron-hole separation compared to their bare and monometallic counterparts, evidenced by complementary characterization techniques. This work reveals that the H2 production rates correlate well with the oxidation potentials of the sacrificial reagents used. Triethylamine (TEA) outperforms other sacrificial reagents, including triethanolamine (TEOA) and methanol. Mechanistic studies on the role of various sacrificial reagents in photocatalytic H2 generation demonstrate that irreversible photodegradation of TEA into diethylamine and acetaldehyde via monoelectronic oxidation contributes to the improved H2 yield. Similarly, TEOA is oxidized to diethanolamine and glycolaldehyde, whereas methanol is unable to quickly capture the photoinduced holes and remains intact due to the low oxidation potential.