# Effective Adsorption of Phenoxyacetic Herbicides by Tomato Stem-Derived Activated Carbons
## 2 Experimental Section
### Synthesis and Characterization of Activated Carbons from Tomato Stems (TS-AC)  
Tomato stems were cleaned and dried to a constant weight at 105 \({}^{\circ}\)C. The dried stems underwent carbonization in a muffle furnace (Czylok, Jastrzebie-Zdroj, Poland) under an oxygen-free atmosphere with controlled process conditions. Carbonization was performed at 400 \({}^{\circ}\)C, 500 \({}^{\circ}\)C, and 600 \({}^{\circ}\)C, employing a heating rate of 3 \({}^{\circ}\)C/min and a 1 h dwell time at the target temperature. After completing the process, the chars were ground using an SM100 mill (Retsch GmbH, Haan, Germany) and then fractionated on sieves. A fraction of 0.5-1.0 mm of the chars prepared in this way was activated chemically using KOH or NaOH as activators (weight ratio of char to activator 1:4) in an argon atmosphere in a tube furnace (Czylok, Jastrzebie-Zdroj, Poland). The activation temperatures were 150 \({}^{\circ}\)C higher than the carbonization temperatures and were 550 \({}^{\circ}\)C, 650 \({}^{\circ}\)C, and 750 \({}^{\circ}\)C, respectively. Activation was performed for 15 min (time measured from the moment of reaching the target activation temperature), and the volume flow of argon was 20 dm\({}^{3}\)/h. The chemically activated carbon materials were extracted with 2% aqueous HCl for 8 h, then rinsed with distilled water until a neutral pH was achieved (approximately 12 h). The obtained material was then dried with a laboratory dryer at 105 \({}^{\circ}\)C to constant weight. TS-AC obtained in this way was abbreviated in the text by specifying the activating agent and the activation temperature in their name, e.g., AC-KOH-550 means TS-AC activated at 550 \({}^{\circ}\)C with potassium hydroxide, AC-NaOH-750 means TS-AC activated at 750 \({}^{\circ}\)C with sodium hydroxide, etc. The yield was defined as the final weight of the product after the processing stages of activation, washing, and drying. The percent yield was calculated from Equation (1):  
\[Yield=\frac{w_{AC}}{w_{B}}\cdot 100\% \tag{1}\]  
where  
\(w_{AC}\)--dry activated carbon weight (g);  
\(w_{B}\)--dry carbonate weight (g). The surface chemistry of six activated carbons derived from tomato stems (TS-AC), produced by KOH and NaOH activation, was characterized. To determine the content of surface functional groups, the method of selective neutralization, employing standard solutions of NaOH, NaHCO\({}_{3}\), Na\({}_{2}\)CO\({}_{3}\), and HCl, was utilized according to the Boehm method [22]. The procedure was as follows: approximately 0.25 g of TS-AC was equilibrated with 25 mL of 0.01 mol/L NaOH or HCl solution by shaking for 24 h. Following degassing and filtration, the amount of bound neutralizing agent was determined by titration with 0.1 mol/L NaOH or HCl using the Tashiro index. Three replicate measurements were performed, and the average value was calculated. Equation (2) was used to quantify the surface functional group content:  
\[G_{X}=(V_{0}-V_{X})\cdot c\cdot\frac{25}{M_{AC}} \tag{2}\]  
where  
\(G_{X}\)--content of selected oxygen surface groups (mmol/g);  
\(V_{0}\), \(V_{X}\)--amount of the HCl/NaOH solution used for titration of the supernatant sample (\(V_{X}\)) and the blank sample (\(V_{0}\)) (mL);\(c\)--concentration of hydrochloric acid or sodium hydroxide (mol/L);  
\(M_{\rm AC}\)--a mass of tomato stem-derived activated carbon (TS-AC) (g). The point of zero charge (pH\({}_{\rm pzc}\)) of TS-AC was determined using the drift method. A series of Erlenmeyer flasks containing 20 mL of 0.01 mol/L NaCl solution was prepared, with initial pH values ranging from 2 to 12. These initial pH values were adjusted using 0.1 mol/L NaOH or HCl. Subsequently, 0.05 g of TS-AC was added to each flask, and the mixtures were shaken for 24 h. Following filtration, the final pH of each solution was measured. A plot of the final pH versus the initial pH was generated, and the pH\({}_{\rm pzc}\) was determined as the intersection point of the resulting curve.