Microwave-assisted hydrothermal synthesis of mesoporous three-dimensional hexagonal graphitic carbon nitride for selective CO2 photoreduction

• 3D hexagonal and mesoporous g-C 3 N 4 is prepared by using a microwave-assisted method. • Higher visible-light absorption, S BET and NH 2 groups cause the surpassing CO 2 photoreduction. • This could offer the potential applications in the selective CO 2 -to-CO photoconversions. The selective photocatalytic reduction of CO 2 to CO by using three-dimensional hexagonal and mesoporous graphitic carbon nitride (denoted as 3D H-g-C 3 N 4 -T) which are prepared via a microwave-assisted route is reported. The physicochemical and optical properties of prepared photocatalysts are characterized by various analytic tools and spectroscopies. Notably, the structure and morphology of 3D H-g-C 3 N 4 -T can be regulated by microwave-assisted hydrothermal temperatures (130-190 °C) in an ammonia solution. The obtained g-C 3 N 4 and 3D H-g-C 3 N 4 -T are used as photocatalysts in the CO 2 photoreduction under the visible-light irradiation. Among these photocatalysts, the 3D H-g-C 3 N 4 -130 shows the superior CO yield which is ca. 2.6-fold higher than the pristine g-C 3 N 4 . The formation of 3D hexagonal prisms with mesoporous structure observed for 3D H-g-C 3 N 4 -130 is responsible for the promoted visible-light absorption, greater surface area and abundant amino functional groups boosting the selective CO 2 -to-CO conversions. The present work demonstrates a time and energy-efficient route to prepare unique 3D g-C 3 N 4 which may offer the possible applications in the solar photoreduction of CO 2 .