# Immobilised Humic Substances as Low-Cost Sorbents for Emerging Contaminants
## 3 Results and Discussion
### Characterization of Immobilized Humic Substances  
Characterization of the immobilized HSs allowed for better understanding of their structure, including the elemental (C, H, N, O), phenolic and carboxylic group content and the specific surface area (BET) data. Some characteristics of the sorbents of the immobilized HSs are given in Table 1. Furthermore, the thermogravimetric (TG) data were used to characterize the structure elements of the studied samples. The SEM analysis was used to characterize the surface area of the immobilized HS samples. The elemental content (C, H, N, O) of the immobilized HSs (see Table 1) indicated that the content of carbon was similar in the HS samples that had been immobilized with organic substances (phenol and resorcinol), reaching 65.9% and 61.1%, respectively, while the carbon content was lower in the HS sample immobilized with iron compounds. The ash content of the immobilized HS samples determined by TG were 9.5%, 11.4% and 11.7% for HSph, HSrz and HSFe, respectively. The obtained results were as expected and could indicate that the immobilization process had been effective. The iron content of the original HSs was 10.7 mg/g. By comparison, when immobilized by a polycondensation reaction with phenol, the determined iron content in the product was 4.1 mg/g. When immobilizing the HSs with iron compounds, the iron content in the product increased to 133.3 mg/g. The highest surface area was characteristic of the HSs immobilized with phenol, while the Fe-modified sample had the lowest surface area. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Imobilized** & \multicolumn{3}{c}{**Elemental Content (wt.\%)**} & \multicolumn{3}{c}{**Phenolic**} & **Carboxylic** & **Total** & **Content** & **Surface** \\
**Humic** & \multicolumn{3}{c}{**C**} & **H** & **N** & **O** & **(meq/g)** & **(meq/g)** & **(meq/g)** & **(mg/g)** & **(m\({}^{2}\)/g)** \\ \hline HSph & 65.92 & 5.15 & 0.47 & 28.46 & 8.8 & 2.2 & 11 & 4.1 & 0.550 \\ \hline HSrz & 61.13 & 4.60 & 0.43 & 33.84 & - & - & - & - & 0.120 \\ \hline HSFe & 41.42 & 3.60 & 0.99 & 53.99 & 3.9 & 1 & 4.9 & 133.3 & 0.035 \\ \hline \end{tabular}
\end{table} 
Table 1: Characterization of the immobilized humic substances (HSs). The scanning electron microscope (SEM) images demonstrated the surface morphologies of the immobilized HSs. By comparing the surface morphology of the immobilized HSs with that of raw HS material, differences are observable. More heterogeneous, wrinkled surface areas were characteristic for the HSrz and HSph samples (Figure 2). Thermogravimetric analysis (TGA) could be used to characterize the physicochemical transformations of HS molecules in the pyrolytic degradation process. The weight loss in the heating process (TG, %) and mass loss rate (DTG - derivative TG, m%/\({}^{\circ}\)C) were determined as part of the study. Decomposition of the carbohydrates and degradation and transformation of the aliphatic structures and HA functional groups (methoxy, methylene and carboxyl) are typical in the temperature range of 250-340 \({}^{\circ}\)C. In turn the carbonyl, alkyl and phenyl groups decompose at 300 \({}^{\circ}\)C [26]. Such decomposition of an immobilized HS sample was well represented by the peak at 250-340 \({}^{\circ}\)C for the HSph and HSFe samples, while an increasing trend of the DTG curve was also observed for the HSrz sample (Figure 3). The HSs immobilized with phenol compounds (HSph) typically had a well-defined peak at a temperature range of 390-530 \({}^{\circ}\)C, which corresponded to the degradation of condensed, polyaromatic and polyheterocyclic compounds in the structure of HSs [27]. The less-defined peak was also observed for the HS immobilized with iron compounds (HSFe), and a wide shoulder in the DTG curve could also be observed for the HS immobilized with resorcinol (HSrz) (see Figure 3). Figure 2: Scanning electron microscope (SEM) images of the immobilized humic substances (**a**) humic substances immobilized with phenol (HSph) and (**b**) humic substances immobilized with resorcinol (HSrz).