Oxidized SWCNT and MWCNT as co-catalysts of polymeric carbon nitride for photocatalytic hydrogen evolution

•Oxidized CNT as co-catalysts of polymeric carbon nitride for H2 evolution.•SWCNT superior co-catalyst compared to MWCNT.•Enhanced photocurrent response of SWCNT-PCN compared to MWCNT-PCN. Polymeric carbon nitride (PCN) has been found as a promising photocatalyst for hydrogen evolution from water splitting. However, disadvantages limit its commercial applications. Therefore, modification of PCN in order to increase the hydrogen evolution rate and stability of the photocatalyst are extensively studied. In this contribution, we compare the influence of oxidation and the number of walls in carbon nanotubes (SWCNT and MWCNT) on the photocatalytic performance of PCN. It was found that oxidation of both types of CNT enhanced a photocurrent response, interfacial charge transfer and separation properties leading to the enhanced hydrogen evolution rate. Interestingly, MWCNT were found to enhance the charge transfer and separation properties more significantly. However, this material affected inferior co-catalytic behavior. We suggest it was related to the lower number of reactive electrons migrating to the surface reaction sites because of transferring to the inner tubes. SWCNT influence ~12-fold increase in H2 evolution rate, while MWCNT influenced ~8-fold enhancement in comparison to pristine PCN.