1.1 Reagents and instruments
1.1.1 Reagent
Tetracycline (Mclean Reagent Co., LTD., purity 99.9%), doxycycline (McLean Reagent Co., LTD., purity 99.9%); 98% sulfuric acid (H2SO4, Aladdin Reagent (Shanghai) Co., LTD.), hydrogen peroxide (H2O2) (Aladdin Reagent (Shanghai) Co., LTD.); Malonic acid (MA, Analytically pure), potassium iodate (KIO3, Sinopharm Chemical Reagent Co., LTD.); Catalyst [NiL](ClO4)2 of macrocyclic nickel was synthesized and characterized according to the literature method [11-12] (FIG. 2).
1.1.2 Instrument
Platinum electrode (model: 213, Shanghai LeiCi Company); Calomel electrode (Model 217, Shanghai LeiCi Company); Temperature /PH comprehensive tester/potential (Model: ZHFX-595, Jiaxing Disheng Electronic Technology Co., LTD.); Magnetic heating agitator (Type 79-3, Jintan Baota Electronics Factory); Electronic analytical balance (RS232C, Shanghai Wujiu Automation Equipment Co., LTD.); Iodide ion electrode (PI-1-01, Shanghai LeiCi).
1.3 Experimental Procedure
1.3.1 Preparation of solution
Firstly, a dilute sulfuric acid solution with a concentration of 0.025mol/L was prepared with 98% concentrated sulfuric acid and distilled water as the reserve solution. Then 0.14mol/L KIO3 solution, 0.0173mol/L [NiL](ClO4)2 solution, 2mol/L MA solution and 4mol/L H2O2 solution were prepared with 0.025mol/L dilute H2SO4 solution. Add 14.7mL 0.025mol/L H2SO4 solution, 3mL 2mol/L MA solution, 2.0mL 0.0173mol/L [NiL](ClO4)2 solution, 5.3mL 0.14mol/L KIO3 solution, and 15.0Ml 4mol/L H2O2 to a 50mL small beaker respectively. To ensure that the concentration of each component in the chemical oscillation system are 0.025mol/L H2SO4, 0.15mol/L MA, 8.65×10-4mol/L [NiL](ClO4)2, 0.01855mol/L KIO3, 1.5mol/L H2O2;
At the same time, 0.0045mol/L tetracycline solution and doxycycline solution were prepared with ethanol as solvent.
1.3.2 Connecting Devices
The iodine ion electrode is connected with the positive electrode of channel 1 of the comprehensive tester, the platinum electrode is connected with the positive electrode of channel 2, and the calomel electrode is connected with the negative electrode of channel 1 and channel 2 at the same time. The comprehensive tester is connected to the computer through the USB interface. Open the computer installed with chemical signal acquisition software, find and click the "Experimental Parameter Setting" window in the "Settings" column, select "Channel 1" and "Channel 2" in the pop-up window, and set the total sampling time to 150.0 minutes and the sampling interval to 0.5s. Find the "Time-based Collection" window and click. In the pop-up window, select "Start Collection" to collect data.
1.3.3 Start the experiment
Take a 50ml small beaker and measure the following solution into the small beaker with a pipette: 13ml 0.025mol/L H2SO4, 3ml 2mol/L MA solution, 7ml 0.14mol/L KIO3 solution, 2ml 2mol/L catalytic [NiL](ClO4)2 solution, The final concentrations of each component in the system were 8.125×10-3 mol/L H2SO4, 0.0245 mol/L KIO3, 0.1 mol/L [NiL](ClO4)2 and 0.15mol/L MA. Then, put the small breaker containing 25.5ml mixture on the magnetic heating agitator, set the temperature at 40.5℃, and adjust the magneton speed to 500r/min. After 10min, we use a pipette to measure 14.5ml 3.5mol/L H2O2 into the 25.5ml mixture. Then click "Start", at the potential lowest point of the fifth oscillation, add a certain amount of objects to be measured respectively, using a pipette in the range of 0-200uL, and record the change of potential over time.