## 2 Materials and Methods
### Experiment Design and Methods  
#### 2.2.1 Single-Factor Experiment on CO\({}_{2}\) MNB Water Preparation  
In this experiment, the CO\({}_{2}\) MNB water was prepared using the dissolved gas release method. The effects of the gas-liquid ratio (_v/v_, %), generator running time (min), and inlet water temperature (\({}^{\circ}\)C) on the content of the CO\({}_{2}\) gas in the MNB water were found to determine the optimal MNB water preparation technique.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Specification** & **Manufacturer** \\ \hline Carbon dioxide gas & Purity of 99.9\% & Beijing Aokang Shuangquan Energy Technologies \\ Co., Ltd. (Beijing, China) & Beijing Kefeng Zhengye Business Center \\ Deionized water & Analytical reagent & (Beijing, China) \\ NaCl & Analytical reagent & Shanghai Maclin Biochemical Technology Co., Ltd. (Shanghai, China) \\ NaHCO\({}_{3}\) & Analytical reagent & Shanghai Maclin Biochemical Technology Co., Ltd. \\ H\({}_{3}\)PO\({}_{4}\) & Analytical reagent & Shanghai Maclin Biochemical Technology Co., Ltd. \\ NaOH & Analytical reagent & Shanghai Maclin Biochemical Technology Co., Ltd. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Materials and reagents.  
Figure 1: Schematic illustration of the MNB generator, where 1 represents the gas supply (CO\({}_{2}\) cylinders); 2 represents the gas flow meter; 3 represents the diaphragm pump; 4 represents the dissolved gas tank; 5 represents the hydraulic pressure gauge; 6 represents the throttling nozzle for the released gas.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Instrument Name and Model** & **Manufacturer** \\ \hline Carbon dioxide meter (multifunctional & Beijing Zhongxihuada Technology Co., Ltd. \\ analytical FC-100 model + pCO\({}_{2}\)-1 & (Beijing, China) \\ carbon dioxide gas sending electrode) & Mettler Toledo International Trading (Shanghai) Co., Ltd. \\ pH meter & (Shanghai, China) \\ Magnetic stirrer & \
\begin{tabular}{c} Scilogex (Connecticut, CT, USA) \\ \end{tabular} \\ Electronic balance &
\begin{tabular}{c} Ohaus Instrument (Shanghai) Co., Ltd. \\ (Shanghai, China) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: Major instruments and devices.  
(1) Impact of Gas-liquid Ratio on CO\({}_{2}\) Content  
When preparing the CO\({}_{2}\) MNB water, the MNB generator running time (30 min) and inlet water temperature (25 \({}^{\circ}\)C) were made constant. At the same time, the gas-liquid ratio (\(\gamma\)/\(\gamma\), \(\gamma\)) was adjusted to values of 1.3%, 2%, 2.7%, 3.4%, and 4.1%. The best CO\({}_{2}\) gas-liquid ratio was determined based on the CO\({}_{2}\) content measured by the carbon dioxide meter.  
(2) Impact of Equipment Running Time on CO\({}_{2}\) Content  
By fixing the gas-liquid ratio (2.7%) of the MNB generator and inlet water temperature (25 \({}^{\circ}\)C), the CO\({}_{2}\) contents of the MNB water were measured for generator running times of 10, 20, 30, 40, and 50 min, and used to define the optimal range of generator running times.  
(3) Impact of Inlet Temperature of Water on CO\({}_{2}\) Content  
By fixing the generator running time and gas-liquid ratio at 30 min and 2.7%, respectively, the CO\({}_{2}\) contents of the MNB water with different inlet temperatures (25, 30, 35, 40, and 45 \({}^{\circ}\)C) were measured to define the optimal range of inlet water temperatures.