Novel Z-scheme CuO@Ag/g-CN heterojunctions: integrating ultrasensitive SERS detection with superior visible-light photocatalysis for tetracycline elimination.

Tetracycline (TC), a widely used broad-spectrum antibiotic for treating bacterial infections, poses significant risks to human health and ecological environments caused by extensive abuse. Hence, sensitive detection and efficient degradation of TC are crucial for protecting both human health and ecological environment. In this work, a multifunctional Z-scheme CuO@Ag/g-CN heterojunction was designed and constructed in order to achieve both ultrasensitive surface-enhanced Raman scattering (SERS) detection and efficient photocatalytic degradation of TC. The influence of the Ag content on the SERS performance was investigated using the finite-difference time-domain (FDTD) method. The charge transfer (CT) mechanism was deduced by band gap and Fermi level calculations. The results showed that the synergistic effect of electromagnetic enhancement (EM) and chemical enhancement (CE) contributed to the excellent SERS sensitivity of CuO@Ag/g-CN nanocomposites (NCs). The limit of detection (LOD) for TC using CuO@Ag/g-CN NCs as SERS substrate was as low as 10 M, and the SERS substrate could also be used to TC detection in real milk samples. In addition, CuO@Ag/g-CN NCs could also act as the efficient photocatalyst to achieve the removal of TC with degradation rate of 94 % under visible light irradiation. Especially, the CuO@Ag/g-CN NCs maintained excellent photocatalytic performance even after six cycles. Possible degradation pathways and photocatalytic degradation mechanism of TC catalyzed by CuO@Ag/g-CN NCs were also proposed. This multifunctional Z-scheme CuO@Ag/g-CN NCs should thus have great potential for the integration of ultrasensitive SERS detection and efficient degradation of antibiotics.