This work was supported by the State Scholar Fund of China Scholarship Council (CSC, no. 201802505006). The authors thank Dr. Atsushi Sasaki of Yamagata University for his assistance with the ICP-MS measurements, Prof. Mitsumasa Kimata and Mr. Takumi Miyashita of Yamagata University for their assistance with the surface area measurement, and Mr. Wujiu Jiang of Hengyang Normal University for his assistance with the TGA measurement.