In this work, N-doped carbon-coated ZnS with a sulfur-vacancy defect (ZnS@N-C) was performed for the visible-light-driven photodegradation of tetracycline hydrochloride (TCH). The obtained ZnS@N-C exhibited enhanced photocatalytic activity compared with ZnS for TCH removal. Among these ZnS@N-C composites, ZnS@N-C-3 with N-doped content of 3.01% (100 nm) presented the best visible-light photocatalytic activity and superior long-term photocatalytic stability after five cycle times for TCH removal in the visible light region. This may be ascribed to the interface between the N-doped carbon shell and ZnS with a sulfur-vacancy defect for efficient charge transfer and the restrained recombination of charge carriers. Electron spin resonance (ESR) results indicate that the ·O 2 radical plays a crucial role in the enhanced photocatalytic activity of ZnS@N-C-3. Nanomaterials 2019, 9, 1657 2 of 13 composites between carbon and semiconductors. To further enhance the electron transfer and extend the visible light harvesting region, carbon doped with N atoms can adjust the work function of carbon and induce charge delocalization [23-26]. Hsu et al. have reported that sandwich-like hydrogenated C-doped anatase TiO 2 nanocrystals/N-doped carbon dots@layer/rutile TiO 2 nanorod arrays have exhibited efficient photoelectron-chemical activity of water oxidation [27]. This may be attributed to the N-doped carbon dots being the photosensitizer of long wavelength light-harvesting and the N-doped carbon layer being the conductive layer of charge transport toward the current collector. Wang et al. have also confirmed that N-doped carbon dots/g-C 3 N 4 can enhance visible-light photo-degradation activity for indomethacin due to the efficient charge separation and band gap narrowing of N-doped carbon dots [28]. Core-shell structured ZnO@N-doped carbon can efficiently adsorb and photodegrade methylene blue in the visible light region [29]. Electrons generated from nitrogen are transferred from the N-doped carbon surface to adsorbed oxygen, forming reactive radicals in the photocatalytic system [30-34]. In addition, surface polarity of N-doped carbon can promote dispersion in aqueous solution. However, few works have focused on the enhanced photocatalytic activity of ZnS with sulfur-vacancy defects using N-doped carbon coating. This work focuses on the synthesis of ZnS with an N-doped carbon coating (ZnS@N-C) and its sulfur-vacancy effect on visible-light photocatalytic activity for the removal of tetracycline hydrochloride (TCH). Reported photocatalysts such as CuInS 2 /Mg(OH) 2 [35], ZnIn 2 S 4 /BiPO 4 [36], AgBr/Bi 2 WO 6 [37], BiOI/g-C 3 N 4 /CeO 2 [38], and TiO 2 / BiOCl [39] are efficient heterojunctions for the visible-light-driven degradation of TCH. Differently from these compositions, N-doped carbon serves as the electron capture, facilitating the separation of electron-hole pairs. In this strategy, N-doped carbon is generated from the decomposition of cyanamide and coated on the surface of ZnS nano-particles, which are further tr...