Synergistic Effects of Boron and Sulfur Co-doping into Graphitic Carbon Nitride Framework for Enhanced Photocatalytic Activity in Visible Light Driven Hydrogen Generation

During in situ thermal co-polymerization of melamine using boric acid and thiourea as the dopant, graphitic carbon nitride (g-C3N4) co-doped with boron and sulfur has been successfully synthesized. The crystallographic, morphological, and spectroscopic data of synthesized materials were characterized through powder X-ray diffraction, transmission electron microsopy, elemental mapping, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, photoluminescence (PL), time-resolved PL (TRPL), and UV–vis diffuse reflectance spectroscopy techniques. The boron and sulfur doping in carbon nitride lattice enhance light absorption, charge separation, and migration and increase the effective surface area, constructing it to be the best photocatalyst among the bulk g-C3N4 as well as singly doped C3N4 counterparts for the generation of hydrogen. The introduction of dopants into the g-C3N4 framework could tune the electronic property, suppress the recombination of photogenerated charge carriers, and trap photoinduced electrons by the defects created by the dopants. The bielemental doped C3N4 shows excellent photocurrent response and a decrease in carrier recombination as suggested by linear sweep voltammetry, electrochemical impedance spectroscopy, and TRPL studies. The photocatalyst shows 11- and 8.5-fold current enhancement in cathodic and anodic directions, respectively, as compared to the bulk g-C3N4 which indicates both p and n type character in a single material. The synergistic effect contributed by boron and sulfur is responsible for achieving a high hydrogen evolution rate of about 53.2 μmol h–1 that is 8 times higher than that of bulk g-C3N4 (6.6 μmol h–1). Density functional theory calculations have been performed to explore the HOMO–LUMO gap of synthesized materials.