# The Removal of Crystal Violet from Textile Wastewater Using Palm Kernel Shell-Derived Biochar
## 3 Results and Discussion
### Thermodynamics  
The influence of thermal temperatures on CV removal by BC-PKS was examined using 30 mL of solution with a 400 mg/L initial concentration, and 0.5 g of BC-PKS at temperatures of 15, 25, and 35 \({}^{\circ}\)C. The thermodynamic parameters (Table 4) show negative values for Gibb's free energy change (\(\Delta G^{\circlearrowright}\)), indicating that CV adsorption onto BC-PKS is feasibly spontaneous. The decrease in the negative values of \(\Delta G^{\circlearrowright}\) with increasing temperature implies a favorable CV adsorption at higher temperatures. This is primarily due to the increased mobility of the CV molecules in solution [87].  
The values of \(\Delta H^{\circlearrowright}\) and \(\Delta S^{\circlearrowright}\) are estimated from the slope and intercept of the plot of In\(K_{e}\) versus 1/\(T\) for CV adsorption onto BC-PKS (Table 4). The positive values of \(\Delta H^{\circlearrowright}\) confirm that the adsorption reactions of CV onto BC-PKS are endothermic, suggesting the adsorption of CV was more favorable with increasing temperature [10; 88]. In addition, \(\Delta H^{0}\) was 60.5 kJ/mol, indicating that CV adsorption onto BC-PKS was achieved via chemisorption, which occurs when \(\Delta H^{0}>40\) kJ/mol [89; 90]. The positive values of \(\Delta S^{\circlearrowright}\) for BC-PKS signify an increase in the disorder at the interfaces between CV and BC-PKS during the CV adsorption on BC-PKS that is accompanied with changes in the CV and BC-PKS structures [10; 91].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature (K)** & \(\Delta H^{\circlearrowright}\) **(k/mol)** & \(\Delta S^{\circlearrow}\) **(k/mol\(\cdot\)K)** & \(\Delta G^{\circlearrow}\) **(k/mol)** \\ \hline
288 & 60.5 & 0.214 & \(-\)1.20 \\
298 & - & - & \(-\)2.71 \\
308 & - & - & \(-\)5.50 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Thermodynamic parameters for adsorption of CV on BC-PKS (initial concentration: 400 mg/L; volume: 30 mL; adsorbent dosage: 0.5 g; reaction time: 24 h; temperature: 15, 25, 35 \({}^{\circ}\)C).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**adsorbent** & **Adsorption** & **Particle Size** & **pH** & **Temperature** & **Reference** \\  & **Capacity (mg/g)** & & **pH** & (\({}^{\circ}\)C) & **Reference** \\ \hline Sugar cane bagasse & 692.1 & 0.075–0.149 mm & 7.0 & 45 & [76] \\ Graprefruit peel & 254.16 & 0.85–1.0 mm & 6.0 & 30 \(\pm\) 2 & [64] \\ Bamboo leaf & 229.35 & 0.125 mm & 7.36 & 32 & [77] \\ Tea dust & 175.4 & 315–500 μm & 7.00 & 25 & [78] \\ Coffee waste & 125 & \(<\)250 μm & 6.00 & 20 \(\pm\) 2 & [79] \\ Palm kernel fiber & 78.9 & 50–80 μm & 7.20 & 25 \(\pm\) 1 & [80] \\ Pineapple leaf powder & 78.22 & 100–125 μm & 8.00 & 20 & [81] \\ Wheat bran & 69.15 & 150–250 μm & 10.0 & 20 & [82] \\ Coir pith & 65.53 & \(>\)600 μm & 6.65 & 30 & [8] \\ Kaolin & 47.27 & 2.37 mm & 7.00 & 22 & [83] \\ NaOH-modified rice husk & 44.87 & NA & 8.00 & 20 & [9] \\ Jackrruit leaf powder & 43.40 & 100–125 μm & 7.00 & 20 & [84] \\ Rice bran & 41.68 & 150–250 μm & 10.0 & 20 & [82] \\ Himalayan long-leaf pine bark & 32.78 & 0.063–0.355 mm & 8.00 & 30 & [1] \\ BC-PKS & 24.45 & 0.85–1.16 mm & 7.00 & 25 & This study \\ Rubber seed shell & 23.81 & 0.425–2.8 mm & 7.00 & 30 \(\pm\) 2 & [31] \\ Sugarcane fiber-based & 10.44 & \(>\)600 μm & 4.80 & 30 & [8] \\ Saganu sawdust & 3.50 & 180 μm & 7.50 & 30 \(\pm\) 1 & [85] \\ Neem sawdust & 4.44–3.99 & 0.180 mm & 7.20 & 25–45 & [86] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of CV adsorption capacity to various adsorbents.