*Article* **Relationship between Cytotoxicity and Surface Oxidation of Artificial Black Carbon**

**Yen Thi-Hoang Le 1,2, Jong-Sang Youn 3, Hi-Gyu Moon 4, Xin-Yu Chen 4,5, Dong-Im Kim 4, Hyun-Wook Cho 1, Kyu-Hong Lee 4,5,\* and Ki-Joon Jeon 1,2,\***



 Daejeon 34113, Korea

**\*** Correspondence: khlee@kitox.re.kr (K.-H.L.); kjjeon@inha.ac.kr (K.-J.J.)

**Abstract:** The lacking of laboratory black carbon (BC) samples have long challenged the corresponding toxicological research; furthermore, the toxicity tests of engineered carbon nanoparticles were unable to reflect atmospheric BC. As a simplified approach, we have synthesized artificial BC (aBC) for the purpose of representing atmospheric BC. Surface chemical properties of aBC were controlled by thermal treatment, without transforming its physical characteristics; thus, we were able to examine the toxicological effects on A549 human lung cells arising from aBC with varying oxidation surface properties. X-ray photoelectron spectroscopy, as well as Raman and Fourier transform infrared spectroscopy, verified the presence of increased amounts of oxygenated functional groups on the surface of thermally-treated aBC, indicating aBC oxidization at elevated temperatures; aBC with increased oxygen functional group content displayed increased toxicity to A549 cells, specifically by decreasing cell viability to 45% and elevating reactive oxygen species levels up to 294% for samples treated at 800 ◦C.

**Keywords:** artificial black carbon (aBC); thermal treatment; cytotoxicity; reactive oxygen species (ROS)
