*2.1. Materials*

Sodium alginate, ethanol, styrene, potassium persulfate (K2S2O8), nitric acid (HNO3), GO suspension (in water), sodium chloride (NaCl), and other metal salts were bought from Shanghai Aladdin Biochemical Technology Co. Ltd. (Shanghai, China). Certain reagents such as styrene, potassium persulfate, and sodium chloride, were used with further purification. High concentration GO suspension was diluted with deionized (DI) water, and DI water was used throughout this study.
