2.1 | Materials
Chemical reagents were commercially available and used without further purification. Co(NO3)2ยท6H2O (98%) was obtained from Sigma-Aldrich. Pyrazine (99%) and 2,5-dihydroxyterephthalic acid (97%) were provided by Shanghai Aladdin Bio-Chem Technology Co., LTD. N, N-dimethylformamide (DMF, AR), ethanol (AR) and methanol (AR) were obtained from Sinopharm Group Co., LTD.