In-situ “nitrogen-bidirectional migration”-induced g-C3N4-x/N-TiO2-x heterojunction serving as a high-stability and high-selectivity SERS platform for ultrasensitive detection of antibiotic residues in multiple scenes

Developing new-type semiconductor surface-enhanced Raman scattering (SERS) platform with synchronous enhancement of sensitivity and stability is an effective strategy for achieving ultra-sensitive detection of emerging pollutants in various pollution scenarios. In this work, a new g-C 3 N 4-x /N-doped TiO 2-x (g-C 3 N 4-x /N-TiO 2-x ) heterojunction SERS matrix was purposefully developed by a combined strategy of interface engineering and defect engineering. During the formation of heterojunction, “N-bidirectional migration” between two monomers can be achieved (that is, N vacancies and N doping can be generated simultaneously), which achieves a synchronous modulation of the atomic and electronic structures of the heterojunction. This endows g-C 3 N 4-x /N-TiO 2-x with excellent interfacial performance, abundant defect states, as well as ultra-high stability. The enhancement factor of the SERS matrix is as high as 10 9 . Theoretical calculations and experiments reveal the contribution of charge transfer (CT) mechanism to the SERS enhancement. The high-efficiency carrier separation induced by the strong interface coupling effect and the multi-channel CTs mediated by multiple defect states (vacancy defects and doping defects) are jointly responsible for the observed huge SERS enhancement. Benefiting from its high SERS sensitivity (selectivity) and excellent stability, g-C 3 N 4-x /N-TiO 2-x can be applied for ultrasensitive detection of antibiotic pollutants in multiple scenarios, including animal-derived foods such as milk, sour milk and beef, as well as natural water systems such as lake water and seawater. The detection limit of several typical antibiotic residues (enoxacin, ciprofloxacin, sulfamethoxazole and florfenicol) is as low as 1 × 10 −11 mol/L.