Ethylene glycol (EG), ethanol absolute, ferric chloride (FeCl3·6H2O), cobalt chloride (CoCl2·6H2O), anhydrous sodium acetate (CH3COONa), polyethylene glycol (molecular weight 4000), and ammonia water (25% NH3 H2O) were purchased from Macklin Reagent (Shanghai, China). All other reagents were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China) and were of analytical grade or better unless otherwise stated. Ultrapure water (Millipore, Milli-Q) was used for reagent water throughout the studies.