## 3 Results and Discussion  
### Effects of Pyrolysis Temperatures on Biochar Yield and Characteristics  
Figure 1 shows the yield in volatiles and biochar at different pyrolysis temperatures. The results indicate that the yield in biochar decreased from 37.10 wt% to 33.89 wt% when the pyrolysis temperature was increased from 500 to 700 \({}^{\circ}\)C. In fact, the biochar still contained residual volatile matter, as shown in Table 1, because pyrolysis was not complete in any of the conditions tested. The thermal treatment was indeed sufficient to accomplish the loss of moisture and hydroxyl groups [22; 23], but only the partial degradation of the lignocellulosic components, most likely of the holocellulosic ones [24]. Figure 1: Influence of pyrolysis temperature on biochar yield distribution. The physicochemical characteristics of the produced biochars (CCB500, CCB600, and CCB700) are listed in Table 1. Compared to the initial feedstock (Table S1), the data on the proximate analysis reveal higher ash and FC contents with increasing pyrolysis temperature, ranging from 37.97 to 45.44 wt% and from 24.74 to 26.58 wt%, respectively. The VM content varies in inverse order and decreases from 35.29 to 26.07 wt%. The increase in ash content from 500 to 700 \({}^{\circ}\)C is a consequence of the increased degree of volatilization of the lignocellulosic components at higher temperatures [25]. During pyrolysis, VM is lost as bio-oil and gas. Even though the FC content increases along with increasing temperature [26], the elemental analysis results indicate a decline in C content with the rising pyrolysis temperature. Also, the O and H content decrease along with the pyrolysis temperature: CCB700 has the lowest C (37.93 wt%), H (0.93 wt%), and O (14.61 wt%) contents. These findings concur with the results obtained by the FTIR spectra, which show the degradation of oxygenated functional groups with increasing temperature  
\begin{table}
\begin{tabular}{c c c c} \hline  & **CCB500** & **CCB600** & **CCB700** \\ \hline \multicolumn{4}{c}{Proximate analysis (wt\%)} \\ \hline Moisture & 2.01 & 1.35 & 1.91 \\ \hline VM & 35.29 & 30.01 & 26.07 \\ \hline FC & 24.74 & 25.11 & 26.58 \\ \hline Ash & 37.97 & 43.52 & 45.44 \\ \hline \multicolumn{4}{c}{Ultimate analysis (wt\%)} \\ \hline C & 41.55 & 38.07 & 37.91 \\ \hline H & 1.33 & 1.16 & 0.93 \\ \hline N & 1.61 & 1.13 & 1.09 \\ \hline S & - & - & - \\ \hline O \({}^{\star}\) & 17.53 & 16.12 & 14.61 \\ \hline \multicolumn{4}{c}{Morphological properties} \\ \hline Surface area (m\({}^{2}\)/g) & 95.80 & 143.56 & 209.64 \\ \hline Total pore volume (cm\({}^{3}\)/g) & 0.013 & 0.03 & 0.033 \\ \hline \multicolumn{4}{c}{Physicochemical properties} \\ \hline pH & 10.26 & 11.12 & 12.45 \\ \hline pH\({}_{\text{PZC}}\) & 11.00 & 11.35 & 12.53 \\ \hline \multicolumn{4}{c}{Mineral content (wt\%)} \\ \hline CaO & 53.88 & 56.12 & 60.90 \\ \hline K\({}_{2}\)O & 16.13 & 13.57 & 8.16 \\ \hline MgO & 9.40 & 9.57 & 10.75 \\ \hline P\({}_{2}\)O\({}_{5}\) & 1.24 & 1.11 & 1.30 \\ \hline Fe\({}_{2}\)O\({}_{3}\) & 0.09 & 0.05 & 0.10 \\ \hline Na\({}_{2}\)O & 0.72 & 0.13 & 0.27 \\ \hline SO\({}_{3}\) & 1.73 & 1.68 & 1.98 \\ \hline Cl & 8.75 & 6.34 &The pH values of the different biochars are given in Table 1. It can be observed that the pH increases from 10.26 to 12.45 with the temperature of the biochar preparation. Typically, the pH values of biochar change with the biomass nature and production process [27]. The high pH value (12.45) of CCB700 could be the result of the loss of acidic functional groups and the release of alkaline minerals [28]. At higher temperatures (above 600 \({}^{\circ}\)C), the biochar ash content is more crucial in determining the pH [29]. The results obtained in the present work are in line with the literature on biochar of its alkaline nature [23; 27].