# Application of Three-Dimensional Porous Aerogel as Adsorbent for Removal of Textile Dyes from Water
## 2 Materials and Methods
### Characterization  
Aerogel capsules were circular, 5 (+/ -0.5) cm in diameter and 1 cm in height (Figure 1). The density of the aerogel was 40.753 kg/m\({}^{3}\).  
The contact angle of the aerogel samples, which were based on cardboard and paper waste, was between 117 and 125\({}^{\circ}\) (Figure 2). The wettability of the aerogel surface, which was made from paper and cardboard waste, was investigated by measuring the water contact angle (\(\theta\)) by using the sessile drop method. In order to take a close-up picture, the high-resolution camera of a smartphone was used. The contact angle was calculated by using contact angle measurement software (protractor) based on the droplet shape image obtained. A few drops of distilled water were used for the test.  
Figure 1: Photo of aerogel surface, top view.  
Figure 2: Determination of contact angle of aerogel.  
If the angle is less than 90\({}^{\circ}\), the aerogel is hydrophilic, and if the angle is greater than 90\({}^{\circ}\), it is hydrophobic.  
After crushing the adsorbent to granules, the aerogel still retains its hydrophobicity properties. However, shredding should only be performed during the production stage, as even slightly incorrect shredding the aerogel during the cutting stage can damage its 3D structure. Aerogel crushing is a negative factor to the aerogel's porosity, low density and large specific surface area, properties that lead to higher adsorption capacity values.  
A SEM was employed to visualize the morphology of aerogel. The surface area of the aerogel before the adsorption process under static conditions can be seen in Figure 3 below.  
The unique internal structure of aerogel, made from paper and cardboard waste, is a major factor that is expected to improve its absorption properties under static conditions. As can be seen in Figure 3, the aerogel was composed of many fibers with angular edges. This high surface-area-to-volume ratio improves aerogels' adsorption properties.  
Further, Figure 4 shows that after the adsorption process, which took 24 h, dye particles settled on the surface of aerogel; the visible bubbles on the surface indicate dye particles.  
FTIR analysis is one of the efficient techniques used in the characterization of organic compounds. As described in [PERSON] et al. (2024) [20], FTIR was used in order to confirm the presence of functional groups. Functional groups of azo group for the dye Congo red were found from 1410 cm\({}^{-1}\) to 1440 cm\({}^{-1}\). Peaks around the 3200 cm\({}^{-1}\) and 3300 cm\({}^{-1}\) indicated the group of O-H. The peaks of Naphthol green B which were found between 1318 cm\({}^{-1}\) and 874 cm\({}^{-1}\) presented the characteristic bands of the sulfonate groups. The  
Figure 4: Surface area of aerogel captured after adsorption process with SEM Helios Nanolab 650: (a) 400 \(\upmu\)m; (b) 5 \(\upmu\)m.  
Figure 3: Surface area of aerogel captured before adsorption process with SEM Helios Nanolab 650: (a) 400 \(\upmu\)m; (b) 5 \(\upmu\)m.  
peaks of Rhodamine B at 1639 cm\({}^{-1}\) and 1423 cm\({}^{-1}\) were due to NH\({}_{2}\) bending vibration. The peak at 1333 cm\({}^{-1}\) corresponded to the stretching vibrations of the C-N-terminal saturated dimethylamine groups.