# Adsorption of Hexavalent Chromium Ions Using Pine Sawdust Cellulose Fibres
## 3 Results and Discussion
### SEM-EDS Analysis  
Figure 6 displays SEM images, while Figure 7 presents EDX analyses of (a) untreated pine sawdust, (b) cellulose fibres before adsorption and (c) cellulose fibres after adsorption for examining the chemical composition of the adsorbent. The SEM examination of untreated pine sawdust (Figure 6a) reveals a rough surface with distinct crystalline patterns resulting from the regular arrangement and boundaries of cells like tracheids in pinewood. The roughness was caused by the irregular shape and size of the wood particles formed during cutting. The presence of lignin, cellulose, and hemicellulose in pine wood further contributes to the observed crystalline patterns on the surface. Lignin, an amorphous polymer, forms crystalline regions within the cell walls of wood fibres, becoming visible when the wood is converted to sawdust. In Figure 6b, acid hydrolysis effects on cellulose fibres are evident, resulting in significant changes such as reduced length, increased irregularity, and a higher aspect ratio than untreated fibres. The rinsing process following hydrolysis uncovers gaps between crystallites that were previously filled with dissolved sugars, further leading to morphological changes in the cellulose fibres. In Figure 6c, cellulose fibres display surface modifications resulting from their interaction with chromium ions. These alterations may involve chromium species binding or forming a chromium oxide layer on the fibre surface. These surface-level changes have the potential to reduce the carbon content, as evidenced by the observations in Table 1, SEM images, and EDS graphs. Table 4 and Figure 7 present the elemental composition percentages of carbon (C), oxygen (O), and chromium (Cr) in untreated pine sawdust (UPSD) and cellulosic fibres. The results for untreated pine sawdust (UPSD) (Figure 7a) indicate that carbon (C) constitutes approximately 54.31% of the weight and 61.29% of the atoms. Carbon is a significant component of organic materials, such as wood. Oxygen (O) is approximately 45.69% of the weight and 38.71% of the atoms. Oxygen can be found in organic and inorganic compounds and is a common element in biomass. Table 4 and Figure 7 display the elemental composition percentages of carbon (C), oxygen (O), and chromium (Cr) in both untreated pine sawdust (UPSD) and cellulosic fibres. The results for untreated pine sawdust (UPSD) (Figure 7a) show that carbon (C), being a significant component of organic materials like wood, makes up around 54.31% of the weight and 61.29% of the atoms. Oxygen (O), a common element in organic and inorganic compounds, including biomass, constitutes approximately 45.69% of the weight and 38.71% of the atoms. Prior to adsorption, cellulose fibres (Figure 7b) have a similar elemental composition to UPSD (untreated pine sawdust), with carbon (C) accounting \begin{table}
\begin{tabular}{c c c c c c} \hline  & **Untreated Pine Sawdust** & \multicolumn{2}{c}{**CF Before**} & \multicolumn{2}{c}{**CF After**} \\ \hline
**Element** & **W (\%)** & **A (\%)** & **W (\%)** & **A (\%)** & **W (\%)** & **A (\%)** \\ \hline C & 54.31 & 61.29 & 54.33 & 63.10 & - & - \\ O & 45.69 & 38.71 & 39.57 & 34.50 & 51.67 & 72.44 \\ Cr & & & & 12.02 & 5.19 \\ \hline \end{tabular}
\end{table} 
Table 4: SEM–EDS elemental composition analysis. for approximately 54.33% of the weight and 63.10% of the atoms. Oxygen (O) constitutes 39.57% of the weight and 34.50% of the atomic percentage. Notably, the carbon content remains relatively constant before adsorption, but its presence is no longer observed after absorption. The reduction in carbon (C) content in cellulose fibres after chromium (Cr) adsorption in Figure 7c could be attributed to several factors, one of which may be the modifications induced by Cr ions' adsorption on the fibre surface [37]. These modifications could involve the formation of new chemical bonds, crosslinking, or the deposition of Cr ions' compounds on the fibre surface. Consequently, new non-carbon components may remove or replace carbon-containing functional groups.