**3.1 Characterization of carbon black materials**

The results of FT-IR analysis (FT-IR spectra) of the carbon black and its activated carbons are shown in **Figure 4** (A-B carbon black-based activated carbons), (C Raw carbon black or tyre waste), and (D Saturated commercial carbon black). In **Figure 4A**, absorption bands around 1100 cm−1 with an overtone at 1430 cm−1 corresponding to Si-O-Si asymmetric stretch [6]. The C=C stretching vibration attributed to the lignocellulose aromatic structure appeared at 1657–2000 cm−1 in carbon black and in activated carbons [6, 7]. Another vibration bands at 2345 cm−1 appeared in both carbon black and activated carbons can be assigned to the alkyne groups [8]. However, it was also observed that the IR spectrum of raw carbon black showed less functional groups as compared to the sulfuric acid and hydrogen peroxide-based activated carbons [9]. The latter is due to the fact that, during/after activation, various functional groups are formed. The C-O-C stretching vibrations in ether, phenol and esters groups appeared around 1041–1248 cm−1. In their study, [7] also reported acyclic C-O-C groups around 1300–1000 cm−1 coupled with aromatic structures (C=C). The stretching vibration band at 1000 cm−1 attributed to C-O group is distinct in sulfuric acid-based activated carbon. It has been reported that chemical activation with hydrogen peroxide oxidant normally yield carbonaceous structures with oxygen-functionalities on the surface [7]. In this study, oxygen-functionalities were observed in the surface of the activated carbon and are believed to have participated in the activated carbon-Hg interaction, and subsequently influenced the Hg uptake and adsorption rate of Hg by activated carbons.

### **Figure 4.**

*The FT-IR spectra of carbonaceous materials. A, B: Sulfuric acid and hydrogen peroxide-based activated carbons, respectively. C-raw carbon black, and D-saturated commercial carbon black.*

BET analysis results revealed that activated carbon prepared via impregnation with hydrogen peroxide exhibits high surface area, high micropore volume, and average pore volume diameter. However, both activated carbons (CB-AC 1 and CB-AC 2) prepared via chemical activation in this study showed improved surface area and micropore volume. It is believed that the activating agents were good enough to percolates the interior of the waste tyre carbon black, breaks the lateral bonds in the cellulose molecules (increases Inter and Intra miscelle voids) and able to influence the surface properties [9]. The BET results obtained confirmed the successfulness of the chemical activation method and the influence of the chemical activating agents on the surface of carbon black. Based on the surface area and micropore volume results obtained, raw carbon black and the two as-prepared activated carbons were further used for the adsorption of Hg vapor. It has been reported that the uptake of an gaseous or liquid materials by an adsorbent normally rely on the BET surface area and pore volume, which all indicate the degree of microporosity in an carbonaceous material [7, 9].

Pyrolytic carbon black and as-prepared activated carbons were also studied under pXRD to check the crystalline arrangement of the carbonaceous materials. In the untreated carbon black (**Figure 5**), peaks at 2*θ* = 27 and 58° corresponds to the reflections from (111) and (222) planes for cubic ZnS. Additionally, peaks at 2*θ* = 51 and 64° corresponding to the reflections (102) and (110) planes, respectively, are of the wurtzite phase of ZnO (F.A. [10]). It has been reported that Zinc Oxides are normally added as vulcanization agents/catalysts during tire manufacturing and they decompose to different forms of ZnS during pyrolysis [6]. However, as shown in **Figure 5**, the diffraction patterns depict broad bands centered around 2*θ* = 24, 25 and 45°, associated or attributed to (002) and (100 and/or 101) planes, respectively [11]. These denote the stacking height Lc and the lateral size of the crystallites La in the carbonaceous material [12]. The presence of a predominantly porous structure, especially in H2O2-AC, is confirmed by the sharp peak around 2*θ* = 25° [12]. Naturally, carbon black is a lignocellulosic material (containing interlinked cellulose, hemicellulose, and lignin structures). However, the introduction/use of an

**Figure 5.** *Powder XRD patterns of pyrolytic carbon black and activated carbons.*

activant (i.e. H2O2) normally brings the breakdown and alteration of the 3D linkages between the chemical components of carbon black (cellulose, hemicellulose, lignin), thereby forming skeletons of fully disorganized carbonaceous materials (activated carbon). Furthermore, the X-ray diffraction patterns of saturated carbonaceous material (SATU-CB, **Figure 5C**) shows relatively broad, weak and low intensity peaks as compared to raw carbon black or H2O2-AC, confirming the interaction of carbonaceous material with adsorbate. In comparison, [6] also studied the crystallographic structure of activated carbon prepared via KOH activation. A broad hump peak was observed around 2*θ* = 22°, which was attributed to the amorphous nature of the carbon material before activation. After KOH treatment, sharp peaks around 2*θ* = 23° were observed and assigned to the turbostratic structure and corresponds to the (002) reflection.

The surface morphology and elemental content of the carbon black and asprepared activated carbons were determined using field emission scanning electron microscopy-coupled with energy-dispersive X-ray spectroscopy (FESEM/EDX). **Figure 6A** and **B** shows the SEM image and the EDX of carbon black used in this study, respectively. According to **Figure 6A**, carbon black exhibits a dense and rough porous structure with very limited pores. EDX confirms a highly carbon-dominated material (carbonaceous), having high carbon content and minimal presence of other elements such as sodium (Na), silicon (Si), and Sulfur (S). Upon activation with hydrogen peroxide and sulfuric acid, the as-prepared activated carbons were also analyzed with FESEM/EDX. **Figure 6A** and A1 shows the FESEM/EDX results of the activated carbon prepared by hydrogen peroxide activation before adsorption of Hg. As shown in the image (**Figure 6A**), the surface morphology of the resultant activated carbon is dominated by increased and improved irregular cracks and pores with many shapes and sizes [9]. This type of porous morphology confirms that activation with hydrogen peroxide was successful and has produced carbonaceous material with improved porous structure (as shown in the BET analysis). The advantage of field-emission scanning electron microscope (FESEM) is that, it studies the structures of carbonaceous materials to microporous level. After adsorption it was expected that some Hg will be spotted and noticed on the surface of the activated carbon. As shown in **Figure 7B** and **B1**, the surface of the activated carbon is covered by dense and light materials of Hg. To that effect, the light spots of Hg infused in the pores of the activated carbon were also deeply checked and focused with high resolution of the microscopy and EDX (**Figure 7**). **Figure 8** illustrates the round-ball like structure of Hg found inside the pores of the activated carbons. Furthermore, the backscatter electron technique was applied to further analyze the surface of the materials against Hg. Light and heavy Hg was seen and confirmed by EDX analysis (**Figure 7C** and **D**, respectively). Mercury is known to show dense and lighter spots when screened by the backscatter electrons (**Figure 9**). In the study by [13], it

**Figure 6.** *FESEM/EDX of pyrolytic carbon black.*

### **Figure 7.**

*FESEM/EDX of CB-AC 2 before and after adsorption of Hg.*

### **Figure 8.** *FESEM/EDX of Hg in the activated carbons prepared.*

was revealed through the SEM/EDX analysis that high elementary mercury vapor concentration was found in synchronicity with high sulfur content in a mercurysaturated carbon material as very white spots in the SEM images [13]. In this study, it can been concluded that the interactions between Hg and the activated carbons were influenced and facilitated by heterogeneous surface (oxygen-functionalities) of the adsorbent and its narrow micropores (**Figure 9**). Due to the heterogeneous surface nature of the activated carbons and variety of oxygen-functionalities, the adsorption of Hg is believed to have involved both the physisorption and chemisorption valence forces in both multilayer and monolayer fashion. Recently, reported the preparation and subsequent chemical activation of carbon black via pyrolysis of waste scrap tyres. In order to achieve complete activated material, they employed pyrolysis temperature of 600°C, and further KOH chemical activation at 800°C.

**Figure 9.** *FESEM/EDX of CB-AC 1 before and after adsorption of Hg.*

It was observed that KOH solution chemical activated predominantly affected the porous structure of the resultant activated material.
