"As for the difference between S-scheme and Z-scheme photocatalyst, the S-scheme photocatalyst is usually composed of two n-type semiconductors, while the Z-scheme is usually composed of n-type and p-type semiconductors. In addition, the construction of the Z-scheme photocatalyst is inspired by the natural photosynthesis process and the S-scheme photocatalyst is named for its staggered band structure."

FromArticle Advances in Z‐scheme semiconductor photocatalysts for the ph...

Dear Lekgowa Collen Makola

The S-scheme photocatalysts are developed after charge transfer due to the differences of Fermi energy levels of combined semiconductors (n-type/p-type), resulting in building internal electric field between the integrated semiconductors. This charge transfer helps to more separation of the photogenerated charges in the S-scheme photocatalysts, which is benefit for improving the photocatalytic activity. However, in the Z-scheme photocatalysts, there is not charge transfer between the Fermi levels. Hence, the separation efficiency of the photogenerated charges are not considerable.

Z-scheme and S-scheme photocatalysts are two types of photocatalysts used in the process of photocatalysis. The main difference between them is the mechanism by which they generate electron-hole pairs.

Z-scheme photocatalysts generate electron-hole pairs by sequential excitation of two different semiconductor materials, which are connected in series with a redox mediator. In this scheme, the first semiconductor absorbs light energy and generates electron-hole pairs, which are then transferred to the redox mediator. The second semiconductor, which has a lower energy bandgap than the first semiconductor, is then excited by the oxidized form of the redox mediator and generates electron-hole pairs that are used for photocatalysis.

S-scheme photocatalysts, on the other hand, generate electron-hole pairs by simultaneous excitation of two different semiconductor materials, which are connected in parallel. In this scheme, the two semiconductors have different energy bandgaps, and when light energy is absorbed, electron-hole pairs are generated in both materials simultaneously. The electrons and holes then migrate to the respective surfaces of the semiconductors, where they participate in photocatalytic reactions.

In summary, the main difference between Z-scheme and S-scheme photocatalysts is the mechanism by which they generate electron-hole pairs. Z-scheme photocatalysts generate electron-hole pairs sequentially through two different semiconductors connected in series, while S-scheme photocatalysts generate electron-hole pairs simultaneously through two different semiconductors connected in parallel.

Check those references. It will help you regarding all your doubts:

1-S-Scheme Photocatalytic Systems. "REVIEW"

2-Synergistic effect of cocatalyst and S-scheme heterojunction over 2D/2D g-C3N4/MoS2 heterostructure coupled Cu nanoparticles for selective photocatalytic CO2 reduction to CO under visible light irradiation.

Lekgowa Collen Makola .The Z-Scheme and S-Scheme photocatalysts differ mainly in their mechanisms of electron transfer and their ability to generate reactive oxygen species (ROS) for catalytic reactions.

In the Z-Scheme photocatalytic system, the electrons are transferred from photosystem II (PSII) to photosystem I (PSI) via an electron transport chain, and then to the final electron acceptor, which is usually an oxidizing agent such as oxygen. The electrons in the PSII are excited by light energy, then transferred to the electron transport chain, generating a proton gradient across the thylakoid membrane. This proton gradient generates ATP, which is used as energy for the catalytic reactions. Z-Scheme photocatalysts are known for their high efficiency in generating ROS, which are highly reactive species that can oxidize or reduce organic molecules.