Highly stable honeycomb structured 2D/2D vanadium aluminum carbide MAX coupled g-C₃N₄ composite for stimulating photocatalytic CO₂ reduction to CO and CH₄ in a monolith photoreactor

Developing efficient materials for photocatalytic conversion of CO₂ to value added chemicals and fuels has gained significant attractions in the recent years. However, this is still a difficult task. In this work, a well-designed vanadium aluminum carbide (V₂AlC) MAX coupled with porous graphitic carbon nitride (g-CN) to construct a nanocomposite for photocatalytic CO₂ reduction has been investigated. 2D/2D V₂AlC/g-CN performance was conducted in a fixed-bed and monolith photoreactor under UV and visible light. The V₂AlC/g-CN exhibited photoactivity of 1747 and 67 µmol g⁻¹ h⁻¹ for CO and CH₄ evolution, which were 4.13 and 1.94 folds more than their production compared to using pristine g-CN, respectively. More importantly, among the sacrificial reagents such as H₂O, CH₃OH, and H₂, the highest productivity was obtained using CO₂-CH₃OH due to more attachment of methanol over g-C₃N₄ with more proton generation. Similarly, performance of V₂AlC/g-CN under UV-light was promising due to the ability of long pathways to penetrate light inside the fixed bed reactor. In addition to photocatalysts, the performance comparison of reactors confirms that the monolith photoreactor has higher productivity for CO₂ reduction to CO and CH₄. This was evidently due to the large illuminated active surface area, and more light utilization, and proficient mass transfer inside the monolithic microchannels. The stability examination further confirms the unceasing evolution of CO and CH₄ in the consecutive four cycles. Thus, V₂AlC MAX is a promising layered material and can be coupled with semiconductors as a support or cocatalyst to achieve both photoactivity and stability for continuous fuel production.