## 3 Results and Discussion
### Characterization of the Adsorbents
On the other hand, the PZC values indicate that all adsorbents have a net negative charge on the particle surface and thus, they are able to interact with the positively charged molecules of CV in several degrees. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Element** & **SW** & **CM** & **AC1** & **AC2** & **CAC** \\ \hline \multirow{8}{*}{**Elemental**} & C & 59.6 & 53.1 & 59.4 & 69.8 & 84.0 \\  & O & 32.7 & 34.6 & 29.7 & 23.5 & 15.3 \\  & Ca & 16.7 & 19.9 & 10.4 & 10.3 & 0.3 \\  & P & 1.5 & 1.9 & 7.3 & 3.3 & 0.8 \\  & N & 15.9 & 0.00 & 0.00 & 0.00 & 0.00 \\  & Si & 0.00 & 0.5 & 0.10 & 0.00 & 0.2 \\
**analysis** & K & 0.00 & 0.00 & 0.94 & 1.03 & 0.05 \\  & Cl & 0.23 & 0.20 & 0.00 & 0.00 & 0.04 \\  & Mg & 0.35 & 0.56 & 0.12 & 0.09 & 0.00 \\  & Al & 0.00 & 0.32 & 0.06 & 0.04 & 0.06 \\  & Na & 0.00 & 0.26 & 0.00 & 0.00 & 0.00 \\  & Sn & 0.99 & 0.00 & 0.00 & 0.00 & 0.00 \\ \hline \multirow{8}{*}{**Physical**} & Moisture (\%) & 8.0 & 3.2 & 8.2 & 8.8 & 15.7 \\  & Porosity (\%) & 75.9 & 81.8 & 81.9 & 77.0 & 80.0 \\  & Yield (\%) & 81.7 & 53.6 & 73.3 & 73.2 & N/A \\ \cline{1-1}  & \(\rho_{\text{bulk}}\) & & & & & \\ \cline{1-1}  & (g/cm\({}^{3}\)) & \(0.43\pm 0.02\) & \(0.47\pm 0.02\) & \(0.42\pm 0.02\) & \(0.49\pm 0.01\) & \(0.32\pm 0.02\) \\ \cline{1-1}  & \(\rho_{\text{true}}\) & & & & & \\ \cline{1-1}  & (g/cm\({}^{3}\)) & \(1.79\pm 0.00\) & \(2.58\pm 0.00\) & \(2.32\pm 0.00\) & \(2.13\pm 0.01\) & \(1.59\pm 0.03\) \\ \cline{1-1}  & \(\text{n}=3\) & & & & & \\ \cline{1-1}  & Total pore volume & & & & & \\ \cline{1-1}  & (cm\({}^{3}\)/g) & \(0.55\pm 0.00\) & \(0.34\pm 0.00\) & \(0.36\pm 0.00\) & \(0.39\pm 0.00\) & \(0.61\pm 0.01\) \\ \hline \hline \end{tabular} SW, raw shrimp waste; CM, charred material; AC1, activated charcoal with H\({}_{3}\)PO\({}_{4}\) using SW as precursor; AC2, activated charcoal with H\({}_{3}\)PO\({}_{4}\) using CM as precursor; CAC, commercial activated charcoal; \(\rho_{\text{bulk}}\), bulk density; and \(\rho_{\text{true}}\), true density.  
\end{table} 
Table 2: Physical properties and elemental analysis of the adsorbents. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Functional Moieties (imm/g)**} & & & & & & & & \\ \cline{2-10}  & \multicolumn{2}{c}{**Total Acidity**} & & & & & & & & \\ \multirow{2}{*}{**Adsorbent**} & (**Carboxylic,** & **Phenol** & **Lactones** & **Carboxylic** & **Total** & **PZC** & **pH** & **Conductivity** & **SigT** & **Cv** \\  & **Phosphoric,** & **and** & **Lactones** & **Carboxylic** & **Alkalinity** & & & & (**s/cm)** & **(cm\({}^{3}\)/g)** & **Adseorption** \\  & **Lactones and** & **Phosphoric** & & & & & & & (**s/cm)** & **(cm\({}^{3}\) * n = 3 \\  & **Phenols)** & & & & & & & & \\ \hline
**SW** & 3960 & 0 & 0 & 5850 & 2.5 & 8.0 & 69.5 & 97.6 & 95.3 * n = 0.0 \\
**CM** & 2040 & 2040 & 0 & 0 & 9350 & 2.0 & 8.4 & 68.8 & 44.4 & 84.8 * c = 0.2 \\
**AC1** & 4760 & 4600 & 0 & 160 & 0 & 1.3 & 6.0 & 80.3 & 146.9 & 100.5 * a = 0.0 \\
**AC2** & 4880 & 4880 & 0 & 0 & 0 & 1.1 & 7.2 & 85.5 & 83.3 & 100.6 * a = 0.4 \\
**CAC** & 4320 & 4320 & 0 & 0 & 950 & 3.8 & 6.9 & 44.5 & 597.9 & 100.5 * a = 0.0 \\ \hline \hline \end{tabular} SW, raw shrimp waste; CM, charred material; AC1, activated charcoal with H\({}_{3}\)PO\({}_{4}\) using SW as precursor; AC2, activated charcoal with H\({}_{3}\)PO\({}_{4}\) using CM as precursor; CAC, commercial activated charcoal, PZC, point of zero charge; SpInt, specific surface area; * data corresponds to equilibrium experiments at 25 °C for 1 h; and pH taken on a 5% adsorbent dispersion; values within a column having the same letter indicate no significant differences according to the Tukey test.  
\end{table} 
Table 3: Relationship between moieties, physical properties and CV adsorption. SW had an innate high surface area due to the roughly surface composed by proteins, chitin, and minerals. Pyrolysis of SW destroyed this structure once volatile gases such as NO\({}_{2}\) were formed resulting in a product with a complete absence of N and a low surface area.