Bridging between NiAl-LDH and g-C₃N₄ by using carbon quantum dots for highly enhanced photoreduction of CO₂ into CO

A series of treble NiAl-LDH/g-C₃N₄/carbon quantum dots (LDH/CN/CQDs) photocatalysts is successfully prepared for the photoreduction of CO₂ to CO via a facile hydrothermal pathway. In the 3D flower-like LDH/CN/CQDs, CQDs not only achieve the efficient inhibition of charge recombination but also act as the unhindered "electronic bridges" to synergistically construct a classical type-Ⅱ charge transfer configuration, which synchronously permits the effluence of photogenerated electrons from CN to LDH and holes from LDH to CN, and promotes ultraviolet-visible irradiation respondence. The sample of LDH/CN/CQDs-6 is the optimal one amongst the LDH/CN/CQDs with a larger special surface area (98.43 m²g^-1) and an appropriate content of CQDs (66.9 wt%), exhibiting the highest CO evolution rate (5.2 μmol·g^-1·h^-1) under visible light irradiation without any sacrificial agent or photosensitizer in water. This is 26.8- and 20.9-fold higher than those of the pristine LDH, pure CN, and their binary counterparts, respectively, and also outperforms most reported LDH-based photocatalysts. As unhindered electron conduction bridges, the highly dispersed CQDs in the LDH/CN heterojunction significantly increase utilization efficiency of light energy and separation efficiency of photogenerated electron-hole pairs. This work provides a beneficial attempt to integrate CQDs with LDH/CN for the positive synergetic effect on both photoelectric properties and electron transfer to obtain highly enhanced photocatalytic activity of CO₂ into CO, and expected to be extended towards broader photocatalytic applications.