Electrospinning Device for Nanofibers| Engineered nickel-based metal - organic framework nanofiber membranewith fish-scale microstructure for enhanced photocatalytic CO, conversion

Professor Yi Chunhai's Team at Xi'an Jiaotong University: Nickel-Based Metal-Organic Framework Nanofiber Membranes with Fish-Scale Microstructure for Efficient Photocatalytic CO2 Reduction

Metal-organic frameworks (MOFs) have attracted significant attention due to their wide applications in heterogeneous catalysis. However, their limited separation efficiency and difficulty in recovery from reaction mixtures present practical challenges. Membrane-based catalysts offer a solution by preventing light scattering and aggregation while being easier to recover compared to powdered catalysts. Although MOF membranes have been extensively studied for photocatalytic pollutant degradation, their application in photocatalytic CO2 reduction remains underexplored.

Recently, Professor Yi Chunhai's team at Xi'an Jiaotong University published their latest research "Engineered nickel-based metal−organic framework nanofiber membrane with fish-scale microstructure for enhanced photocatalytic CO2 conversion" in Separation and Purification Technology. The corresponding author is Researcher Guo Jiaxin, with doctoral student Lin Pengfei as first author, and the School of Chemical Engineering and Technology at Xi'an Jiaotong University as the primary affiliation.

This study successfully immobilized defective Ni-MOF-74 (NMD) nanosheets containing more unsaturated Ni active sites onto electrospun polyacrylonitrile (PAN) nanofiber membranes (NFMs). The resulting composite catalyst, called NMD/PAN NFMs (NPNs) with uniform fish-scale structure, was evaluated for photocatalytic CO2 reduction under mild conditions. Results showed NPNs exhibited excellent photocatalytic performance and stability. The membrane achieved CO production of 1,641 μmol g-1 h-1 with 91% selectivity, even surpassing powdered NMD. Additionally, NPNs demonstrated easy recovery and reuse, further enhancing their practical applicability. This innovative approach for constructing high-performance MOF nanofiber membranes opens new possibilities for broader applications in photocatalytic CO2 conversion.

Figure 1: Schematic diagram of NPNs preparation

Figure 2: SEM images of NMD and NPNs at different magnifications

Fragmented NMD and NPNs were successfully synthesized using hydrothermal and hybrid electrospinning techniques. NMD incorporation significantly altered PAN fiber morphology, especially at higher NMD content. Figure 2e-j shows morphologies of different NPN percentages at various magnifications. Observations revealed 0.1g NMD created fish-scale patterns on PAN fiber surfaces. When NMD increased to 0.5g, partial aggregation occurred while maintaining relatively uniform dispersion overall.

Figure 3: CO2 catalytic performance of NPNs

Under mild conditions, CO2 photoreduction to CO was examined versus duration to study NPNs' photoreduction behavior in visible light. NPN-0.3 showed highest catalytic efficiency, producing 11.362 μmol CO and 1.093 μmol H2 - higher than NPN-0.1 (CO: 5.451 μmol; H2: 0.743 μmol) and NPN-0.5 (CO: 9.077 μmol; H2: 0.792 μmol). This suggests increased NMD content may cause particle aggregation, reducing CO2 adsorption and light utilization. All three NPNs maintained >88% CO selectivity (91% for NPN-0.3), highlighting their suitability as CO2 reduction catalysts.

Figure 4: (a) Recovery steps of NPNs and powder MOFs. (b) Yield after seven reaction cycles with NPN-0.3. (c) XRD spectrum of regenerated NPN-0.3 photocatalyst after seven reaction cycles. (d) Optical images of NPN-0.3 and NMD powders dispersed in solvent.

Reusability tests showed membrane catalysts significantly simplified recovery by eliminating centrifugation, reducing operational costs while maintaining 71% photocatalytic efficiency after 7 cycles. Activity decline was mainly attributed to NMD crystallinity loss rather than catalyst leakage. XRD analysis showed slightly reduced NMD characteristic peaks, indicating partial structural and crystallinity changes. NPN fibers retained fish-scale structure, demonstrating effective NMD encapsulation in PAN nanofiber membranes with good recyclability.NPNs' acetonitrile-philic and hydrophilic properties maintained suspension in solvents for optimal light absorption and reaction contact, whereas powdered NMD tended to aggregate and settle, reducing photocatalytic efficiency.

Figure 5: Mechanism of photocatalytic reaction

In CO2 photoreduction systems, NPNs significantly improved electron-hole pair mobility through efficient charge utilization. Advantages include: abundant ligand defects in NMD nanosheets exposing more active sites uniformly distributed on PAN nanofibers; free-standing structure enabling solvent suspension for optimal contact and light absorption; prevention of light scattering and aggregation issues in powder systems; and easy membrane catalyst recovery and reuse. Finally, the reaction mechanism for NPNs' photocatalytic CO2 reduction was proposed. This study provides new insights for preparing MOF NFMs with high-performance photocatalytic CO2 reduction, promoting MOF materials for more practical applications.