First, ZIF-67 was synthesized by the chemical method [29 (link)]. Briefly, 520 mg CoCl2 was dissolved in 40 mL methanol. Separately, a solution of 600 mg PVP and 2.63 g of 2-methylimidazole in methanol (40 mL) was prepared. The solutions were mixed under stirring and aged for 2 days at room temperature. The precipitate was sequentially washed thoroughly with methanol and deionized water three times and then lyophilized at −50 °C and 29 mTorr for 48 h (CHRIST, Alpha 2-4 LDplus, Osterode am Harz, Germany). Almost 400 mg of the synthesized ZIF-67 was obtained with a yield of ~13%.
Au/Ag modification of ZIF-67 was carried out by two-step electrodeposition after forming a thin layer on a screen-printed carbon electrode (SPCE with the surface area of 0.126 cm2, DRP-C110, DropSens, Netherlands) by drop-casting 10 µL of ZIF-67 in methanol with a concentration of 10 mg mL−1. To carry out electrodeposition, a mixture of 1 mM HAuCl4 and 1 mM AgNO3 with 100 mM KNO3 as a supporting electrolyte was used. Au-Ag nuclei were formed on ZIF-67/SPCE at a constant potential −1.3 V for 5 s. Afterward, cyclic voltammetry (CV) was employed in a potential window of −1.1 to 0.3 V with a scan rate of 200 mV s−1 for 15 cycles (Figure S1 in Supplementary Materials ). A similar procedure was used for electrodeposition of Au and Ag NPs on ZIF-67/SPCE.
Au/Ag modification of ZIF-67 was carried out by two-step electrodeposition after forming a thin layer on a screen-printed carbon electrode (SPCE with the surface area of 0.126 cm2, DRP-C110, DropSens, Netherlands) by drop-casting 10 µL of ZIF-67 in methanol with a concentration of 10 mg mL−1. To carry out electrodeposition, a mixture of 1 mM HAuCl4 and 1 mM AgNO3 with 100 mM KNO3 as a supporting electrolyte was used. Au-Ag nuclei were formed on ZIF-67/SPCE at a constant potential −1.3 V for 5 s. Afterward, cyclic voltammetry (CV) was employed in a potential window of −1.1 to 0.3 V with a scan rate of 200 mV s−1 for 15 cycles (