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

Amine-functionalized graphitic carbon nitride (g-C 3 N 4 ) decorated with Au nanoparticles (CN/Au) was prepared by N 2 plasma treatment of g-C 3 N 4 powders impregnated with HAuCl 4 ·3H 2 O. Well-dispersed Au nanoparticles with a small particle size were deposited on g-C 3 N 4 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 CO 2 reduction under visible-light irradiation. CO and CH 4 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-C 3 N 4 (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 CO 2 ; (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 CO 2 ; (3) the Schottky junction between Au and g-C 3 N 4 promoted the migration of electrons from g-C 3 N 4 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 13 C nuclear magnetic resonance spectra provided a support for inferring the position of the amino group.