Construction of efficient active sites through cyano-modified graphitic carbon nitride for photocatalytic CO2 reduction

Abstract

The active site amount of photocatalysts, being the key factors in photocatalytic reactions, directly affects the photocatalytic performance of the photocatalyst. Pristine graphitic carbon nitride (g-C3N4) exhibits moderate photocatalytic activity due to insufficient active sites. In this study, cyano-modified porous g-C3N4 nanosheets (MCN-0.5) were synthesized through molecular self-assembly and alkali-assisted strategies. The cyano group acted as the active site of the photocatalytic reaction, because the good electron-withdrawing property of the cyano group promoted carrier separation. Benefiting from the effect of the active sites, MCN-0.5 exhibited significantly enhanced photocatalytic activity for CO2 reduction under visible light irradiation. Notably, the photocatalytic activity of MCN-0.5 was significantly reduced when the cyano groups were removed by hydrochloric acid (HCl) treatment, further verifying the role of cyano groups as active sites. The photoreduction of Pt nanoparticles provided an intuitive indication that the introduction of cyano groups provided more active sites for the photocatalytic reaction. Furthermore, the controlled experiments showed that g-C3N4 grafted with cyano groups using melamine as the precursor exhibited enhanced photocatalytic activity, which proved the versatility of the strategy for enhancing the activity of g-C3N4 via cyano group modification. In situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculations were used to investigate the mechanism of enhanced photocatalytic activity for CO2 reduction by cyano-modified g-C3N4. This work provides a promising route for promoting efficient solar energy conversion by designing active sites in photocatalysts.

Sodium doping in brookite TiO2 enhances its photocatalytic activity

“…However, the differences in the ionic radius and the electronegativity between Na and Ti can destroy the local atomic arrangement of the brookite phase and produce many microstructures such as the core–shell structure, the lattice distortion, interstitial atoms, and atomic vacancies. These interstitial atoms, surface vacancies, and the incomplete structure are considered as photocatalytic active sites that can enhance the photocatalytic activity [ 33 – 34 ]. However, the high temperature can improve the atomic migration rate which makes the atomic arrangement more ordered.…”

Molecular engineering of g-C3N4 with spatial charge separation for enhancing photocatalytic performances

“…Thus, many strategies have been developed to accelerate charge separation and increase light absorption with the goal of enhancing photocatalytic redox reaction. [7][8][9][10][11][12][13][14][15][16] Charge migration in CN nanosheets is anisotropic due to the sp 2 (p) p-conjugation structure, confining charge transfer to the nanosheet plane. 17 To induce rapid charge transfer carrier and separation, methods such as the creation of carbon/nitrogen vacancies 15,18 and intramolecular doping have been employed to narrow the bandgap of CN, generate active sites, and change the charge density of CN.…”

“…[7][8][9][10][11][12][13][14][15][16] Charge migration in CN nanosheets is anisotropic due to the sp 2 (p) p-conjugation structure, confining charge transfer to the nanosheet plane. 17 To induce rapid charge transfer carrier and separation, methods such as the creation of carbon/nitrogen vacancies 15,18 and intramolecular doping have been employed to narrow the bandgap of CN, generate active sites, and change the charge density of CN. 16,[19][20][21] Due to their similar aromatic structures and sizes, benzene derivatives have been introduced into CN backbones through sp 2 -hybridized C-N bonds to induce charge redistribution and extend the p-conjugated system of CN.…”

Construction of the Sn-doped defect pyrochlore oxide KNbMoO6·H2O/g-C3N4 composite and its photocatalytic reduction of CO2

“…[16][17][18] Composition and modification are important factors for designing photocatalysts with high active sites and a large specific surface area, which can reduce the recombination of electron-hole pairs and improve the photocatalytic activity. [19][20][21] Pyrochlore is an important mineral raw material and has been widely studied in the field of photocatalysis in recent years. 22,23 The general formula of pyrochlore oxide is A 2 B 2 O 6 O 0 (A 2 B 2 O 7 ).…”