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Page 14 of 20 Li et al. Microstructures 2023;3:2023024 https://dx.doi.org/10.20517/microstructures.2023.09

Figure 15. (A) S-scheme heterojunction. (B) The S-scheme SNO/CdSe-DET heterojunction charge migration and separation diagram
under light irradiation [102] . Copyright 2021, Wiley-VCH.

[106]
charge separation (as shown in Figure 16A and B) . Jiang et al. present a heterogeneous nucleation
strategy for stabilizing and dispersing ultrasmall Au NCs in an NHC-functionalized porous matrix (as
shown in Figure 16C) . The Au NCs are embedded in the MOF material to prevent cluster aggregation. It
[107]
gives the composite material a high degree of photostability and chemical stability. During the PCR process,
the Au-NC@MOF composite demonstrates outstanding and consistent activity (as shown in
[107]
Figure 16D) . Therefore, MOFs are ideally suited for photocatalysis design.

Noble MNCs-based catalysts improve PCR performance by photosynthetic biohybrid system
Noble MNCs exhibit excellent biocompatibility, minimizing interference with the inherent functions of
living organisms. This advantage allows noble MNCs to be used in the biological field. To link pre-
assembled biosynthetic pathways with inorganic light absorbers, a photosynthetic biohybrid system (PBS)
was developed. Both the high light-harvesting efficiency of solid-state semiconductors and the superior
[108]
catalytic performance of whole-cell microorganisms are inherited by this strategy . For instance,
Zhang et al. utilized Au NCs as biocompatible intracellular light absorbers in PBS . A biocompatible light
[109]
absorber circumvents slow electron transfer kinetics and functions of the existing PBS as an inhibitor of
reactive oxygen species to maintain high bacterial activity. With the dual advantages of light absorption and
biocompatibility, this PBS can efficiently absorb sunlight and transfer photogenerated electrons to cellular
[109]
metabolism, allowing for several days of continuous CO fixation (as shown in Figure 17) . The method of
2
constructing PBSs offers a novel concept for PCR.

To summarize, compared to noble MNCs-based catalysts, nonnoble MNCs-based catalysts have a lower
price, greater availability, a more comprehensive selection of materials, and better stability. The
disadvantage is that the catalytic effect of the PCR process is inferior to that of noble MNCs. Furthermore,
noble MNCs-based catalysts exhibit better biocompatibility. However, the scarcity of precious metals causes
them to be expensive. The high specific surface area of noble MNCs-based catalysts can cause aggregation.
Maintaining the long-term stability of the composites under in situ light conditions is challenging, a
bottleneck in developing noble MNCs-based catalysts for practical applications. Thus, adopting strategies to
prevent cluster aggregation on the carrier (such as Z/S-scheme heterojunction or MOF structure) is
essential for their photocatalytic performance.

SUMMARY AND PROSPECTS
Artificial carbon fixation has stimulated the development of PCR as a promising technology. MNCs are a
new potential photocatalyst with unique physical and chemical properties. To improve PCR performance,