Lewis functional nanodiamonds for efficient metal-free photocatalytic CO₂ reduction

Artificial photosynthesis of fuels and valuable compounds from CO₂ and H₂O, as a flawless method, has aroused universal interest. Metal-free catalytic materials with balanced efficiency and stability have rarely been demonstrated. To date, emerging carbon-based photocatalysts promise to break the ordeal of extreme environments for catalysts, leading to practical industrial applications. Among them, surface functional group-modified nanodiamonds offer additional possibilities in terms of long-term stability and tunable catalytic activity. In this work, the nature of distinctions in photocatalytic efficacy induced by two varieties of NDs modified with distinct Lewis acid-base functional groups was also systematically investigated. Furthermore, by using a bottom-up approach, the three-dimensional g-C₃N₄ (3D CN) loaded with nanodiamond (ND) functionalized with amino and carboxyl groups, has been demonstrated as an impressive metal-free photocatalyst for photosynthetic production of CO. Combining in situ photoelectrochemical analysis and density functional theory, the mechanism of heterojunction formation between 3D CN and NDs modified with different functional groups was elucidated from kinetic and thermodynamic perspectives. The synergistic CO production rate of amino-modified NDs was found to be roughly 1.97 times higher than that of carboxyl-modified NDs. This pioneering work introduces promising sp³-hybridized ND materials into photoreduction CO₂ systems in terms of surface chemistry, helping to establish an improved understanding of this emerging carbon material.