Walnut shell-based biochar-assisted Fe sites anchored carbon-rich g-C3N4: Boosting photodegradation of 2-Mercaptobenzothiazole though synergistic enhancement of Fe sites and C substitution.

To expand the utilization of discarded walnut shells and enhance the photocatalytic activity of graphitic carbon nitride(g-C3N4), the carbon-rich graphitic carbon nitride anchored with Fe sites (FeW-CN) was synthesized via a walnut shell-based biochar-assisted strategy. Unlike the direct thermal copolymerization of melamine for g-C3N4, the iron-loaded walnut shell-based biochar (FeW) was first synthesized, followed by thermal copolymerization of melamine with FeW to form FeW-CN. The C substitution on the triazine ring enhanced the light absorption and electron migration for FeW-CN. And the Fe sites interacting with N-(C)3 further improved the migration and the utilization rate of photogenerated carriers. During the degradation of 2-Mercaptobenzothiazole, FeW-CN showed excellent photocatalytic performance and stability compared with g-C3N4. Moreover, FeW-CN maintained excellent photocatalytic performance in river water. Combination of electron paramagnetic resonance with active species quenching experiments, the synergistic mechanism of singlet oxygen, holes, and superoxide radicals was confirmed in the FeW-CN system. Compared to g-C3N4, the Fe sites and C substitution enhanced the production of singlet oxygen.