Tuning Band Gap in Fe-Doped g-C₃N₄ by Zn for Enhanced Fenton-Like Catalytic Performance

Multiple oxidation states of first-row transition-metal cations were always doped in g-C₃N₄ to enhance the catalytic activity by the synergistic action between the cations in the Fenton-like reaction. It remains a challenge for the synergistic mechanism when the stable electronic centrifugation (3d¹⁰) of Zn²⁺ was used. In this work, Zn²⁺ was facilely introduced in Fe-doped g-C₃N₄ (named xFe/yZn-CN). Compared with Fe-CN, the rate constant of the tetracycline hydrochloride (TC) degradation increased from 0.0505 to 0.0662 min^-1 for 4Fe/1Zn-CN. The catalytic performance was more outstanding than those of similar catalysts reported. The catalytic mechanism was proposed. With the introduction of Zn²⁺ in 4Fe/1Zn-CN, the atomic percent of Fe (Fe²⁺ and Fe³⁺) and the molar ratio of Fe²⁺ to Fe³⁺ at the catalyst's surface increased, where Fe²⁺ and Fe³⁺ were the active sites for adsorption and degradation. In addition, the band gap of 4Fe/1Zn-CN decreased, leading to enhanced electron transfer and conversion from Fe³⁺ to Fe²⁺. These changes resulted in the excellent catalytic performance of 4Fe/1Zn-CN. Radicals •OH, •O₂^-, and ¹O₂ formed in the reaction and took different actions under various pH values. 4Fe/1Zn-CN exhibited excellent stability after five cycles under the same conditions. These results may give a strategy for synthesizing Fenton-like catalysts.