Dear Dr. Hamza El-Hosainy

The main difference between s-Scheme and Z-scheme photocatalysts is related to the electron transfer among the Fermi energy of semiconductors after heterojunction construction in S-scheme photocatalysts. This electron transfer leads to establishing internal electric field, which enforces charge separations in s-Scheme photocatalysts.

Regards

Aziz

Thanks Prof. Aziz for your reply !

Brother Hamza,

Please read Fig 8 in this paper and its explanation. You will get your answer: Chem 6, 1543–1559, 2020, Article S-Scheme Heterojunction Photocatalyst

Cheers,

Esmail

Ok, many Thanks brother Dr. Esmail. I’ll check on it. Esmail Doustkhah

Welcome my brother Dr. Hamza El-Hosainy! I highly recommend you read this paper, I also read it yesterday thanks to your question, haha

Article Emerging S‐Scheme Photocatalyst

This article has explained them: Emerging S‐Scheme Photocatalyst.

But I still think there is a room for a review describing in details the differences between the two mechanisms

Thank's so much dear Professor Aziz Habibi-Yangjeh

Recently, S-Scheme system is proposed as an attempt to correct the mechanism of the direct Z scheme [21]. In fact, S-scheme system is nothing but Z-scheme system after considering Fermi level alignment (work function), built-in electric field, and band bending. The need of replacing the name of Z-scheme system with S-scheme is not clear to the authors since the charge transfer mechanism is the same.

https://www.sciencedirect.com/science/article/pii/S245222362300038X

The difference between Z scheme and S scheme systems is the consideration of Fermi level alignment, band alignment, band bending, and the generated interfacial electric field (E).These aspects are considered only in S scheme systems leading to proposing a more accurate charge transfer pathway and are not considered in Z scheme systems resulting in proposing an ambiguous charge transfer pathway.

https://onlinelibrary.wiley.com/doi/full/10.1002/smtd.202201103

In agreement with what Dr. Hezam said, there is no difference between the two mechanisms and I also recommend to you these two latest reviews I wrote: https://doi.org/10.1021/acs.jpclett.2c03387

https://doi.org/10.1016/j.cej.2022.138894

Thank you for the shed light Dr. Abdo Hezam, I was also in the dark regarding the question raised by Hamza El-Hosainy. It makes a lot of sense since there are no mechanistic charge transfer variations between the two systems.

S-scheme is the more modified version of the Z-scheme mechanism, where the redox capability of the materials participating in the heterostructure can be understood more by introducing the internal electric field and Fermi level alignment in the junction interface,

The direct Z-scheme heterojunction system is identical to the S-scheme type. whereas, the two systems separate the photo-carriers without an electron mediator.

In general, the Z-scheme involves the use of two different photocatalysts, one for the oxidation reaction and one for the reduction reaction. The two photocatalysts are connected in series, with the electrons and holes generated by one photocatalyst being transferred to the other photocatalyst. Also the Z-scheme requires a suitable electron mediator to transfer electrons from one photocatalyst to the other. While The S-scheme, on the other hand, involves the use of a single photocatalyst that can perform both the oxidation and reduction reactions. In the S-scheme, the excited electrons and holes generated by the photocatalyst are used directly in the oxidation and reduction reactions.

To determine whether a photocatalytic mechanism is Z-scheme or S-scheme, several experimental methods can be used. For example, transient absorption spectroscopy can be used to observe the generation and transfer of excited electrons and holes between different materials in the Z-scheme. In the S-scheme, the photocatalyst can be studied under different conditions to determine whether it can perform both the oxidation and reduction reactions.

Overall, the determination of the photocatalytic mechanism requires a detailed analysis of the experimental data and the reaction intermediates involved.

There is no fundamental difference between S-scheme and Z-scheme photocatalysts. S-scheme photocatalyst is technically a Z-scheme photocatalyst whose charge transfer pathway is explained by using difference in the fermi levels of individual components, their respective band bending and establishment of internal electric field.

In reality, there is no fundamental difference between the charge transfer mechanisms of S-scheme and Z-scheme systems. However, the S-Scheme has been proposed to refine the mechanism of the conventional Z-scheme. Essentially, the S-Scheme is considered a refinement of the Z-scheme, incorporating factors such as Fermi level alignment, work function, built-in electric fields, and band bending.

S-Scheme and Z-scheme heterojunctions are two types of photocatalytic systems that can enhance the efficiency and stability of photocatalysts by spatially separating the photogenerated electron-hole pairs and improving their redox abilities. The main differences between them are:

1-S-Scheme heterojunctions consist of a reduction photocatalyst and an oxidation photocatalyst with staggered band structure, which can provide a large driving force for photocatalytic reactions. Z-Scheme heterojunctions consist of two photocatalysts with matched band structure, which can mimic natural photosynthesis and achieve overall water splitting.

2-S-Scheme heterojunctions require direct contact between the two photocatalysts for charge transfer, while Z-Scheme heterojunctions require a mediator (such as a redox couple or a solid-state conductor) to shuttle the charges between the two photocatalysts.

3-S-Scheme heterojunctions can effectively suppress the recombination of photogenerated charges in the bulk of the photocatalysts, while Z-Scheme heterojunctions can also suppress the recombination of charges on the surface of the photocatalysts.

I hope this helps you understand the differences between S-Scheme and Z-Scheme heterojunctions in Photocatalysis.