## 2 Materials and Methods
### Characterisation of Adsorbent  
Surface morphology and activated carbon composition were analysed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray microanalysis (EDX), using a JEOL JSM-IT500 HR scanning electron microscope.  
The porous structure of both carbons was characterised by exploiting the adsorption of iodine and methylene blue. The iodine number (IN) is a fast test that gives an indication of the micropore content [44]. This determination is based on ASTM D4607-94 [45; 46]. This method is based on a three-point isotherm. A standard iodine solution is treated with three different masses of adsorbent. The experiment consisted of washing the sample beforehand with 5.0 mL of 5 wt% HCl. Then, this sample was introduced into 50.0 mL of 0.05 mol/L iodine solution and the mixture was stirred vigorously for 30 s. The resulting solution was filtered and 25.0 mL of the filtrate was titrated with 0.05 mol/L sodium thiosulphate, using starch as a colour indicator. The iodine value was the value of the adsorbed amount when the residual concentration was 0.01 mol/L. The IN was calculated by the following Equation (1):  
\[\mathrm{IN}=\frac{\mathrm{C_{1}V_{1}M-\left(\frac{V_{1}+V_{\mathrm{HCl}}}{2V_{ \mathrm{F}}}\right)C_{2}V^{\prime}M}}{\mathrm{m}} \tag{1}\]  
Figure 1: Reactor and furnace used to produce activated carbon.  
where C\({}_{1}\) is the initial concentration of the I\({}_{2}\) solution (in mol/L); C\({}_{2}\) is the concentration of Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\) (in mol/L); V\({}^{\prime}\) is volume of Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\) at the equivalence (in mL); V\({}_{\rm F}\) is the volume of filtrate dosed (in mL); M is the molar mass of I\({}_{2}\) (in g/mol); V\({}_{1}\) is the adsorption volume (in mL); V\({}_{\rm HCl}\) is the volume of HCl (in mL); m is mass of adsorbent used (in g).  
The methylene blue number (MBN) was used to evaluate the mesoporous and macropovosity of an adsorbent, based on the European Chemical Industry Council (CEFIC) standard [46]. The MBN is defined as the maximum amount of methylene blue adsorbed on 1 g of adsorbent. In this test, 100 mg of ACSCGs was brought into contact with 100 mL of a methylene blue solution at different concentrations (0-1000 mg/L) and at room temperature. The remaining concentration after 24 h was determined by UV-Vis spectroscopy at 660 nm. The MBN was determined using the Langmuir model.  
The characterisation of the chemical functional groups present on the surface was carried out by Fourier transform infrared spectroscopy (FTIR), using an infrared spectrometer (Shimadzu. JASCO 4100). The samples were analysed as very well-dried pellets, prepared by diluting 4 mg of the sample in 96 mg of KBr. The spectra were recorded from 4000 to 400 cm\({}^{-1}\), with a resolution of 4 cm\({}^{-1}\) and 16 scans per sample.  
The quantification of the acidic and basic surface functions was performed using the Boehm method [47; 48]. Samples of the adsorbent (0.5 g) were brought into contact with 50 mL of different basic solutions (NaHCO\({}_{3}\), Na\({}_{2}\)CO\({}_{3}\), NaOH), of concentration 0.1 mol/L, with an acidic solution (HCl) of the same concentration, respectively. The excess of base or acid after 48 h of stirring was titrated back on 20 mL of filtrate by means of an HCl or NaOH solution of concentration 0.1 mol/L.  
The point zero charge (pH\({}_{\rm ZC}\)) was determined by the salt addition technique [49]. In a series of beakers containing 40 mL of NaCl solution (0.1 mol/L) each, a mass of 0.2 g of sample was added. The pH was adjusted by a solution of HCl (0.1 mol/L) or NaOH (0.1 mol/L) to values noted as pH\({}_{\rm i}\), between 2 and 12. The pH\({}_{\rm f}\) values were measured after 24 h of stirring at 200 rpm. The pH\({}_{\rm ZC}\) was obtained from the plot of \(\Delta\)pH (= pH\({}_{\rm f}\) - pH\({}_{\rm i}\)) versus pH\({}_{\rm i}\) at \(\Delta\)pH = 0.