Amine-functionalized graphitic carbon nitride decorated with small-sized Au nanoparticles for photocatalytic CO₂...

Amine-functionalized graphitic carbon nitride (g-C₃N₄) decorated with Au nanoparticles (CN/Au) was prepared by N₂ plasma treatment of g-C₃N₄ powders impregnated with HAuCl₄·3H₂O. Well-dispersed Au nanoparticles with a small particle size were deposited on g-C₃N₄ nanosheets. In addition, the amino group was introduced into the CN/Au system. Without the addition of cocatalyst and sacrificial agent, CN/Au exhibited enhanced photocatalytic activity for CO₂ reduction under visible-light irradiation. CO and CH₄ evolution rates of CN/Au reached 28.3 and 1.3 μmol·h^-1·g^-1, which were 7.6 and 2.6 times higher than those of pristine g-C₃N₄ (CN-0), respectively. The enhanced activity can be explained by these factors. (1) The introduced amino group improved the adsorption capacity of CN/Au for CO₂; (2) the hot electrons generated by Au nanoparticles activated the surrounding electrons through energy transfer and caused local temperature to rise, increasing the efficiency of the photoreduction reaction of CO₂; (3) the Schottky junction between Au and g-C₃N₄ promoted the migration of electrons from g-C₃N₄ to Au nanoparticles, suppressing the recombination of the carriers. Time-of-flight secondary ion mass spectrometry confirmed the introduction of amino groups, and solid-state ¹³C nuclear magnetic resonance spectra provided a support for inferring the position of the amino group.