Challenges of Z-scheme photocatalytic mechanisms

Z-scheme photocatalytic systems have been extensively studied since they are supposed to promote carrier separation while boosting redox abilities. Herein, we analyze the challenges of photocatalytic mechanisms in liquid-phase and all-solid-state Z-scheme systems from various perspectives, including thermodynamics, charge-transfer dynamics, applicability, and practical synthesis. Notably, in this opinion, we analyze the challenges for electron transfer in liquid-phase Z-scheme systems, where photocatalyst nanoparticles (NPs) and redox couples are constantly under dynamic motion and the transfer of free electrons via water media is prohibited. These problems ultimately led to the flourishing of step-scheme (S-scheme) heterojunctions.