Alkyl chain regulation of charge separation efficiency in edge-grafted g-C3N4 with carboxyl-alkyl substituted polythiophene for enhanced 2-mercaptobenzothiazole photodegradation

Abstract

To investigate the effect of alkyl chain on the charge separation of photocatalyst, three mono-component edge-grafted g-C3N4 with carboxyl-substituted polythiophenes (CN-CSPs) were designed and synthesized, which chemically anchored polythiophenes to the edge of g-C3N4 framework by amide bond. Theoretical calculations reveal that the donor-acceptor (D-A) structure of the CN-CSPs positions the HOMO at the CSP donor and the LUMO at the heptazine ring acceptor, effectively enhancing intramolecular charge separation. Moreover, the alkyl chain connecting thiophene units to carboxyl groups significantly alters the electronegativity of the carboxyl groups, thereby influencing the dipole moment (DM). An increase in DM correlates with stronger intramolecular charge separation. The DM values of the CN-CSPs rank in the following order: CN-Me(5) (without alkyl) < CN-Et(3) (linear alkyl) < CN-Ma(3) (branched alkyl), consistent with the increasing order of their photocatalytic performance. This modification led to a 17-fold increase in the photocatalytic degradation of 2-mercaptobenzothiazole by the modified CN-Ma(3) compared to pure CN, demonstrating significant cyclic stability and overall enhanced performance of the photocatalytic system. The insights from this study offer valuable guidance for the chemical modification of g-C3N4 to boost photocatalytic efficiency.