# Innovative Vaporization of Wood Panel Waste into Activated Biochar for Efficient Phenol Adsorption
## 3 Results and Discussion
### Kinetics and Isotherms of Phenol Adsorption  
As shown in Figure 3, biochar (BWP) has a relatively modest phenol adsorption capacity, with increasing efficiency as a function of contact time and initial concentration up to a certain threshold. At low concentrations (5-20 mg/L), the maximum adsorption capacity after 48 h varies from 1.8 to 4.9 mg/g. At 100 mg/L, higher adsorption is observed (18.3 mg/g at 48 h), although a significant drop is recorded at 24 h, suggesting partial desorption or saturation of the active sites on its surface. At very high concentrations (200 mg/L), the efficiency becomes negligible or even zero. However, thermal activation of BWP at 750, 850, and 950 \({}^{\circ}\)C induces significant improvements in adsorption capacity, with an increasing trend as a function of activation temperature and contact time. The best-performing material, BWP950, shows 171.93 mg/g adsorption capacity after 48 h, followed by BWP850 (142.25 mg/g) and BWP750 (51.89 mg/g). These improvements correlate with significant increases in specific surface area, from 99 m\({}^{2}\)/g for raw BWP to 450, 682, and 866 m\({}^{2}\)/g for BWP750, BWP850, and BWP950, respectively, as well as increased total pore volume, including both micropores and mesopores. These significant improvements can be correlated with the higher specific surface area and pore volumes resulting from the increased volatilization of non-carbon organic constituents and the development of more microporous structures at high temperatures. Furthermore, the better adsorption yields as a function of time suggest that the process follows a dominant intraparticle diffusion  
Figure 2: Elemental composition of biochar and activated biochar. mechanism, where electrostatic interactions and \(\pi\)-\(\pi\) bonds with the aromatic rings of the phenol play a critical role [59; 60]. Figure 3: Adsorbed amounts of phenol from synthetic solutions at initial concentrations of (**a**) 5 mg/L, (**b**) 10 mg/L, (**c**) 20 mg/L, (**d**) 100 mg/L, and (**e**) 200 mg/L as a function of time for all biochars. Figure 3 highlights the critical influence of thermal activation on the phenol removal efficiency of biochars. At low initial concentrations (5-20 mg/L), adsorption efficiency significantly increases with increasing pyrolysis temperature. For instance, while the raw biochar (BWP) achieves only 16.4% phenol removal after 2 h of contact at 5 mg/L, the biochars thermally activated at 850 \({}^{\circ}\)C and 950 \({}^{\circ}\)C (BWP850 and BWP950) exhibit efficiencies exceeding 97%, reaching up to 99.2% after 48 h. Similar trends are observed at 10 and 20 mg/L, where the activated biochars demonstrate near-complete adsorption within 24 h (99.8%). At higher concentrations (100-200 mg/L), the performance of raw biochar remains limited. In contrast, the activated biochars maintain high adsorption capacities, with BWP950 achieving up to 93.3% at 100 mg/L and 86.3% at 200 mg/L after 48 h. These results underscore the pivotal role of activation temperature in enhancing porous structure, specific surface area, and active site availability, thereby improving affinity for aromatic compounds such as phenol. Increasing the biochar activation temperature leads to substantially greater phenol adsorption capacity, as evidenced by numerous recent studies [61; 62]. Thus, high-temperature activation promotes the development of optimal porous structures in biochar, thereby enhancing phenol adsorption. The kinetic modeling results (Table 2) reveal that the pseudo-second-order model best describes the phenol adsorption behavior for all biochars, as evidenced by the high correlation coefficients (R\({}^{2}\) > 0.99 for BWP850 and BWP950). This suggests that the adsorption mechanism is predominantly governed by chemisorption involving specific chemical interactions such as hydrogen bonding or \(\pi\)-\(\pi\) interactions between phenol molecules and the aromatic structures on the biochar surface.