Zhang, Y., H. Chi, W. Zhang, Y. Sun, Q. Liang, Y. Gu, and R. Jing. “Highly Efficient Adsorption of Copper Ions by a PVP-Reduced Graphene Oxide Based On a New Adsorptions Mechanism”. Nano-Micro Letters, vol. 6, no. 1, Jan. 2014, pp. 80-87, doi:10.1007/BF03353772.