# Application of Three-Dimensional Porous Aerogel as Adsorbent for Removal of Textile Dyes from Water
## 3 Results  
### Adsorption Results  
The most important initial parameter of adsorbent functionality is adsorption capacity. The capacity of the adsorbent, the aerogel, to adsorb Congo red, Naphthol green B, Rhodamine B and Methylene blue from monocomponent solutions was assessed by performing adsorption tests with an adsorbent dose of 0.8 g. The values of adsorption capacity are given in Table 1.  
The Congo red dye was characterized by the highest adsorption capacity values. On the other hand, the lowest values of adsorption capacity were obtained for Naphthol green B and Rhodamine B. Methylene blue, which belongs to the group of basic dyes, showed better adsorption efficiency than Naphthol green B or Rhodamine B. It is assumed that the functional groups of the aerogel interact with the functional groups of the dyes; therefore, water purification occurs.  
It was demonstrated that cellulose was not only an important component to construct the aerogel structure but also a functional material to improve adsorption performance. The adsorption capacity of the adsorbent increases rapidly with the passage of time and reaches equilibrium after about 60 min.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Dye**} & \multicolumn{8}{c}{**Concentration of Dye, mg/L**} \\ \cline{2-10}  & **0.1** & **0.5** & **1.0** & **2.0** & **5.0** & **10.0** & **50.0** & **100.0** & **200.0** \\ \cline{2-10}  & \multicolumn{8}{c}{**q\({}_{e}\), mg/g**} \\ \hline Congo red & 0.028 & 0.133 & 0.262 & 0.490 & 1.173 & 2.139 & 8.793 & 8.621 & 14.483 \\ \hline Naphthol green B & 0.013 & 0.059 & 0.101 & 0.195 & 0.449 & 0.874 & 3.591 & 4.869 & 7.698 \\ \hline Rhodamine B & 0.020 & 0.096 & 0.176 & 0.334 & 0.811 & 1.228 & 4.603 & 6.576 & 8.768 \\ \hline Methylene blue & 0.024 & 0.123 & 0.229 & 0.435 & 0.940 & 1.838 & 7.364 & 10.127 & 13.538 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Values of adsorption capacity for textile dyes.  
The results show that the adsorption between the cellulose aerogel and the molecules of the dyes was mainly electrostatic attraction. As displayed in Figure 4, the dye particles settled on the aerogel surface, forming small dye bubbles. By removing the dye particles from the surface of the aerogel, the adsorbent could be reused. This type of research is planned in the future.  
According to the analysis of the adsorption experiments, the adsorption mechanism of dyes on cellulose aerogel can be summarized as follows: The cellulose in the aerogel contained a large amount of carboxyl and hydroxyl groups. Cellulose increased the specific surface area of the aerogel, which was beneficial for the adsorption of the dyes.  
The adsorption capacity was higher for the solutions of dyes with a 0.1-10.0 mg/L initial concentration. As the initial concentration of textile dye increased from 10.0 mg/L to 200.0 mg/L, the adsorption capacity of Congo dye decreased from 62.02% to 21.00%, that of Naphthol green B from 34.02% to 15.00%, that of Rhodamine B from 28.00% to 10.00% and that of Methylene blue from 48.01% to 18.00%.  
The color of the dyes was not removed in any case; the intensity of the color decreased, but the color did not disappear. The color intensity decreased significantly in the solution with concentration of 0.1 mg/L to 10.0 mg/L. As the dye concentration increased from 10.0 mg/L to 200.0 mg/L, the color remained bright. It can be assumed that the amount of adsorbent used was insufficient to remove the color of the dye.  
A comparative table with references from the literature with adsorption capacity (Table 2) can be found below. It can be noted that in recent years, aerogel has attracted a lot of attention among scientists due to it being a cheap, non-toxic, light and highly porous material.  
Since the amount of dyes in wastewater is not regulated, researchers conduct studies with various initial study parameters, so the concentration of the dye can vary over a wide range. It is also important to emphasize that aerogels of very different compositions can be used in studies.