## 2 Materials and Methods
### Synthesis of the Adsorbents from Pyrolysis Char and Characterization of the Solids  
The char, namely \"C\", was obtained from the pyrolysis of a mixture of plastics from non-selective collecting from a local urban solid waste processing plant. The average composition was rigid polypropylene (56%), high impact polystyrene (9%), expanded polystyrene (10%), and polyethylene and polypropylene film (25%). The pyrolysis was conducted under an N\({}_{2}\) atmosphere (100 L-min\({}^{-1}\)) at 500 \({}^{\circ}\)C for 90 min, with a 10 \({}^{\circ}\)C-min\({}^{-1}\) heating rate. The resulting char was ground and sieved, size below 500 \(\upmu\)m. This char powder was stabilized by acid washing to remove ash and leachable components with an aqueous 1 M HCl solution (50 g\(\cdot\)L\({}^{-1}\) of char) [36], followed by ultrapure water washing and drying step at 120 \({}^{\circ}\)C for 24 h. This stabilized char was labeled as \"SC\".  
Different chemical activation procedures were considered to turn the char into a porous carbonaceous solid. First, the activation of the char was carried out under a CO2 atmosphere due to the good results provided by this technique in the literature [14]. Particularly, in the activation step, a gas flow rate of 100 mL\(\cdot\)min\({}^{-1}\), a temperature of 760 \({}^{\circ}\)C, a heating rate of 10 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\) and a hold time of 1 h were used. Then, the resulted material was stabilized with HCl, rinsed with water, and dried following the same procedure indicated above. This obtained material was named \"SC-CO2\". Alternatively, chemical activation under an N2 atmosphere (100 L\(\cdot\)min\({}^{-1}\)) with the addition of NaOH and KOH (char: alkali ratio, 2:1 [37]) was carried out. In this case, for activation, a two-step process was adopted, including (i) heating from room temperature to 300 \({}^{\circ}\)C at 10 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\) and holding at 300 \({}^{\circ}\)C for 1 h to ensure the melting of the alkali, and (ii) heating from 300 \({}^{\circ}\)C to 760 \({}^{\circ}\)C at 10 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\) and then holding at 760 \({}^{\circ}\)C for 1 h. After the activation process, the material was stabilized with HCl, rinsed with water, and dried following the same procedure indicated above. The resulting activated carbons were named \"SC-NaOH\" and \"SC-KOH\" depending on the chemical agent used. Finally, a blank activation test was performed under an N2 atmosphere under the same activation conditions as those used for SC-CO2 preparation to analyze the influence of the physical and chemical agent, excluding the effect of thermal treatment, on the properties of the final product. The resulting material from this test was called SC-N2. Table S1 of the Supplementary Materials provides a summary of different prepared activated carbons.  
The textural properties were assessed by N2 adsorption-desorption isotherms at 77 K in an ASAP 2020 apparatus of Micromeritis(r). The specific surface area was calculated by the BET method (SBET), the specific surface area of micropore (SMP) was estimated by the t-plot method, the total pore volume (V\({}_{\text{T}}\)) was calculated from the N2 uptake at p/p\({}_{0}\) = 0.99, and the volume micropore (V\({}_{\text{MP}}\)) from the t-plot method. The morphology of the particles was evaluated by Scanning Electron Microscopy in a FEG-ESEM QUEMSCAN 650F device of FEI QuantaTM. The presence of functional surface groups was studied by Fourier Transformed Infrared (FTIR) spectroscopy in a PerkinElmer(r) Spectrum 65 FT-IR device working within 550-4000 cm\({}^{-1}\).