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Li et al. Microstructures 2023;3:2023024 https://dx.doi.org/10.20517/microstructures.2023.09 Page 7 of 20

PROGRESS OF MNCS-BASED CATALYSTS IN PCR
MNCs have garnered attention for their potential to improve PCR performance due to their unique and
desirable properties. Several reasons contribute to the focus on MNCs for PCR, including:

(1) High catalytic activity: The small size and high surface area-to-volume ratio of MNCs result in a high
catalytic activity, which can enhance the efficiency of the PCR.

(2) Improved charge transfer: MNCs have been shown to improve the charge separation and transfer
processes in photocatalytic systems, leading to higher photocatalytic activity.

(3) Tailor-made properties: The properties of MNCs can be easily tuned or customized by controlling the
size, shape, and composition, allowing for better control of their catalytic activity.

Overall, MNCs have shown great potential for enhancing PCR performance. Continued research on MNCs
can contribute to the development of sustainable and efficient CO reduction systems. Many strategies have
2
been proposed to use MNCs as catalysts for improving PCR performance. This section reviews the recent
advances in MNCs-based catalysts for enhancing PCR performance. We classify the MNCs-based catalysts
[56]
[55]
[54]
[57]
into two subsections, nonnoble (e.g., Cu , CdS , Fe, Co , Ni, Cu) and noble MNCs-based (e.g., Au ,
[59]
[58]
Ag , Pt) catalysts . Then, we describe their respective roles as catalysts for improving the PCR process.
The photocatalytic performance of various MNCs-based catalysts under visible-light irradiation is presented
in Table 1.
Nonnoble MNCs-based catalysts in PCR
Nonnoble MNCs offer a wide range of material selection options, and commonly available and inexpensive
metals such as Fe, Ni, Cu, and Al can be used to prepare MNCs. Additionally, they are generally less costly
compared to noble MNCs, resulting in lower preparation costs. In addition, semiconductor materials with
wide energy gaps, such as TiO , SrTiO , BiVO , Ta N , g-C N , CdS, and MoS , are the most widely used
3
3
3
5
2
4
4
2
[60]
photocatalysts . However, most required light sources are in the ultraviolet spectrum, with low solar
utilization and high electron-hole complexation rates, resulting in low photocatalytic reaction
efficiency [61-63] . Consequently, using nonnoble MNCs as co-catalysts is suitable for overcoming these
[64]
disadvantages . Due to the advantages mentioned above, nonnoble MNCs-based catalysts are primarily
employed for surface modification of semiconductor materials to enhance PCR performance. The reaction
process for nonnoble MNCs-based catalysts to improve PCR performance by surface modification
techniques has two steps, namely visible-light-induced interfacial charge transfer (IFCT) between the MNCs
and semiconductor materials and the multielectron reduction of oxygen molecules mediated by the co-
catalytic promoter effect of the MNCs .
[65]
Preparation of nonnoble MNCs-based catalysts by impregnation to enhance PCR performance
Photocatalysts composed of nonnoble MNCs and semiconducting materials are typically fabricated by the
impregnation method . Impregnation is a method of incorporating one material into another by soaking
[66]
or spraying the material onto the surface of the other. Impregnation involves the following steps: The
prepared semiconducting material is soaked or sprayed with the MNCs’ solvent, which contains a
suspension of MNCs, and allowed to dry. The MNCs are then deposited onto the surface of the
semiconducting material. The impregnated semiconducting material is then calcined at high temperatures
to remove the solvent and stabilize the MNCs on the surface of the semiconducting material. The
impregnation method allows for the controlled deposition of MNCs onto the surface of semiconducting
materials, thereby preparing materials with good photocatalytic activity.