# Commercially Biochar Applied for Tartrazine Removal from Aqueous Solutions
## 3 Results and Discussion
### Kinetic Studies of the Adsorption Process  
In order to understand the rate of adsorption and mechanism, kinetic studies are conducted, pseudo-first-order, pseudo-second-order, and intra-particle-diffusion models being most widely used. The best-fitted model is selected considering the correlation coefficient R\({}^{2}\)[62]. Figure 6: Isotherms of tartrazine adsorption on biochar. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Adsorbent** & **q [mg g\({}^{-1}\)]** & **References** \\ \hline positively charged triethylenettermine biochar & 85.47 & [38] \\ octadecyltrimethylammonium & 43.20, 145.80, & [56] \\ bromide-modified bentonite & 175.80, and 201.00 & [10] \\ raw sawdust & 0.80 & [10] \\ activated sawdust & 127.00 & [10] \\ microcline & 37.96 & [57] \\ microcline/MWCNTs & 67.17 & [57] \\ chitosan/polyaniline & 584.00 & [58] \\ activated red mud & 136.98 & [59] \\ activated carbon derived from cassava sievate & 20.83 & [60] \\ activated carbon from Ziziphus Spina-Christi & 160.00 & [61] \\ commercial biochar & 3.28 & present study \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of several adsorbents’ adsorption capacities with charcoal for tartrazine removal. The investigation of tartrazine adsorption kinetics on biochar was carried out at 30 \({}^{\circ}\)C with an initial concentration of 3 mg mL\({}^{-1}\) brought to pH 2, for various durations, ranging from 3 to 30 min. The rate of adsorption and potential adsorption mechanism of tartrazine adsorption on biochar were examined using a number of kinetics models. The kinetic models applied in this study and their linearized form are presented in Table 4.  
The pseudo-first-order model ([PERSON] model) establishes the relationship between the change in time and the adsorption capacity with order of one, the pseudo-second-order kinetic model (Ho and Mckay model) shows the relationship of the adsorption capacity and concentration with second order, and the intraparticle diffusion model (Webber and Morris model) determines the rate-controlling factor for the adsorption process [66]. The kinetics parameters obtained for the adsorption of tartrazine on biochar are available in Table 5.  
By examining the appropriate values of R\({}^{2}\), it was discovered that the removal of tartrazine on biochar can be accomplished using the pseudo-second-order kinetic model. This suggests that the mechanism governing the rate of its adsorption was chemisorption. The pseudo-second-order model fit with the results obtained for adsorption of tartrazine on biochar-mediated ZrFe\({}_{2}\)O\({}_{5}\) nanocomposites [37] and on positively charged triethylenet-tramine biochar [38]. Additionally, Figure 7 shows that the plots are divided into two linear zones and were not linear across the whole time range. According to the literature, if the line passes through the origin point (0, 0), the adsorption is dominated by the intraparticle diffusion, while if not, it is a multiple adsorption process. Because the line does not pass through the origin, this indicates that the intraparticle diffusion is not the controlling stage of the adsorption rate of tartrazine on biochar and it is complex. \begin{table}
\begin{tabular}{c c c} \hline
**Kinetic Model** & **Linear Form** & **Reference** \\ \hline Pseudo-first-order kinetic & \(log(q_{e}-q_{t})=logq_{e}-\left(\frac{k_{i}}{2,303}\right)\) & [63] \\ Pseudo-second-order kinetic & \(\frac{1}{q_{e}}=\frac{1}{k_{2}q_{e}^{2}}+\frac{l}{q_{t}}\) & [64] \\ Intraparticle diffusion & \(q_{t}=k_{id}t^{0.5}+C\) & [65] \\ \hline \end{tabular}
\end{table} 
Table 4: The linearized forms of kinetic models.