Integrating carbon vacancy modified carbon quantum dots with carbon nitride for efficient photocatalytic CO₂ reduction to syngas with tunable hydrogen to carbon monoxide ratio

Converting CO₂ to value-added syngas is an effective approach to relieve environmental problems and energy crisis simultaneously. However, it's still a challenge to establish long-wavelength irradiation technology in association with tuning H₂: CO proportion. Therefore, carbon vacancy modified carbon quantum dots were integrated with g-C₃N₄ to form VCQDs/C₃N₄ heterojunctions, which exhibited superior performance for CO₂ photoreduction in the presence of sacrificial agent and electron mediator under visible light irradiation. This was attributed to the strong interaction between g-C₃N₄ and VCQDs and carbon vacancy in VCQDs, which can facilitate the migration of photo-generated electrons and broaden the absorbance range of heterojunctions. Besides, the H₂: CO ratio of produced syngas can be tuned by adjusting the VCQD dosage in VCQDs/C₃N₄, and a 3 : 1 ratio is obtained over VCQD(25 μL)/C₃N₄ in conjunction with Co(bpy)₃Cl₂·6H₂O cocatalyst. This is significant for industrial application of syngas and for relieving the greenhouse effect brought by CO₂.