**3. Result and discussion**

### **3.1 Functional group analysis**

Vibrational spectroscopy in the infrared region was used to perform the characterization of the molecular structure of the adsorbent from the vibrational modes related to functional groups present in the sample. ATR FTIR spectroscopy provides evidence for specific functional groups on the surface of the TiO2-modified mesoporous carbon (TiO2-MMC). Several characteristics bands were observed in the ATR FTIR spectrum (**Figure 1**). Many existing groups in carbon derived from agriculture waste (CDAW) (blank) [18] are also present in the TiO2-MMC, showing that modified material exhibits many of the same functional groups of CDAW (blank).

It was observed that the infrared spectra of TiO2-MMC which overlapping with CDAW (source material) so that there are new peaks as observed in 3832.20–3425.4, 1632.21, 1570, 1046.50, 600.23, 500.30 cm−1. The broad and strong bands at 3832.20–3425.4 cm−1 have been assigned because of bonded hydroxyl (-OH) or amine (-NH2) groups. The band 1632.21 can be ascribed to –C=O stretching. The band around 1570 cm−1 can be ascribed to –C=C. The band at 1046.50 cm−1 is due to the C-O of carbonyl groups. The stretching band corresponding to Ti-O-Ti is clearly in the region of 509 cm−1 [18]. The band around 620.23 cm−1 is attributed to the Ti-O-C vibration which indicates that TiO2 (Dugasa P25) were chemically bonded with carbonized carbon in TiO2-MMC [16, 17].

#### **3.2 Microstructural and elemental composition analysis**

The SEM images of CDAW (**Figure 2a**) [16] and TiO2-MMC are shown in **Figure 2b**, which demonstrate the porosity and texture of TiO2-MMC. It has been observed that TiO2-MMC retain the surface characteristics of its precursor (CDAW

**Figure 1.** *FTIR spectra of (1a). CDAW and (1b) TiO2-MMC.*

*Application of Titanium Dioxide in the Synthesis of Mesoporous Activated Carbon Derived… DOI: http://dx.doi.org/10.5772/intechopen.98395*

**Figure 2.** *SEM micrographs of (2a). CDAW (blank) and (2b) TiO2-MMC.*

and TiO2) as shown in **Figure 2**. However, with some remarkable modifications, the results (**Figure 2b**) obtained showed that there was displacement as the temperature of thermal decomposition of the modified adsorbent suggesting that the modification caused a difference in structure. The SEM micrographs (**Figure 2b**) show a spongy aspect, fibrous surface with irregular and heterogeneous structure with many pits and fissures through the surface prominent possibly due to powerful oxidizing agent H2O2, which caused some changes in the surface of TiO2-MMC.

### **3.3 Specific surface area, particle size measurement**

The most applicable and accessed procedure for evaluating the surface area of porous and finely-divided material is the Brunauer–Emmett–Teller method [6]. Given the specific controlled conditions, the BET-area of a nonporous, macroporous or mesoporous solid can be referred to as the 'probe accessible area' (which is the

**Figure 3.**

*BET analysis for CDAW and TiO2-MMC, (3a). N2 adsorption and desorption, (3b). BET, (3c). BJH and (3d). T-plot respectively.*

effective area available for the adsorption of the specified adsorptive). There are two particular stages involved in the application of the BET method. It is important to transform a physisorption isotherm into the 'BET plot'. The calculated value of the BET area is dependent on (i). The adsorptive and operational temperature and (ii). The procedure used to locate the pressure range in applying the BET equation.

The N2 adsorption–desorption of both CDAW and TiO2-MMC was conducted (**Figure 3a**). BET analysis (**Figure 3**) confirms that TiO2-MMC falls on the mesoporous domain. The typical specific surface area of TiO2-MMC was found as SBET = 18.845 m2 g−1 whereas the surface area of the CDAW was typically SBET = 10.251 m<sup>2</sup> g−1 (**Figure 3b**). In the case of fine and especially, free-floating powdered samples can present an additional difficulty to the during BET analysis. Particles may also be deposited on valve seats causing problematical leaks. This loss of powder from the confinement of the sample bulb, known as elutriation, should be controlled and eliminated as far as is reasonably practicable.

The adsorption/desorption isotherm (**Figure 3a**) shows the relationship between the amount of adsorbed/desorbed gas (y-axis) and the pressure of adsorptive (x-axis) at the constant temperature. Nitrogen (at the boiling temperature of 77 K) was the conventional and usual choice for the adsorptive to obtain (BET), with σm(N2) assumed to be 0.162 nm2 and being a close-packed monolayer. Moreover, liquid nitrogen was readily available and also nitrogen isotherms on many adsorbents were found to exhibit a well-defined Point B. Though, present studies have shown that due to its quadrupole moment, the orientation of a nitrogen molecule is dependent on the surface chemistry of the adsorbent. And, this could lead to the tentative reading of the value of σm (N2) – possibly ∼ 20% for some surfaces [7].

A more suitable alternative adsorptive for surface area analysis could be Argon. Argon does not have a quadrupole moment and is less reactive than the diatomic nitrogen molecule. Argon, though, at 77 K is, possibly, less reliable than Nitrogen. Argon adsorption at 87 K (liquid argon temperature) is the possible alternative. At 87 K, a cross-sectional area, σm(Ar), of 0.142 nm2 is assumed. Due to the absence of a quadrupole moment and the higher temperature, σm (Ar) is less prone to the differences in the structure of the adsorbent surface. Argon adsorption at 87 K facilitates the micropore analysis. Analysis at 87 K can be done by using either liquid argon (replacing liquid nitrogen) or a cryostat (or cryocooler) [1, 7]. Manometric adsorption equipment of maximum accuracy can effectively assess the surface areas as low as (∼ 0.5–1) m2 with nitrogen or argon as the adsorptive. For lower surface areas, krypton adsorption at 77 K is the preferred adsorptive. Though krypton at 77 K is similar to argon at 77 K. Hence, the standard thermodynamic state of the adsorbed layer is not accurately gauged.

These methods (**Figure 3**) used to calculate the micropore radius (cylindrical shape), micropore diameter (cylindrical shape), area distribution, volume distribution, Integral curve, pore specific surface area and pore volume. Methods for mesopore size analysis have been proposed by Barrett, Joyner, and Hlenda (BJH) (**Figure 3c**) [19, 20]. The preadsorbed multilayer film can be accounted for with the integration of the Kelvin equation with a standard isotherm (the t-curve) to analyze the specific nonporous solids. Still, for analyzing the accurate size of narrow mesopores, the standard t-curve is not a convincing procedure (**Figure 3d**), the validity of the Kelvin equation also provides an approximation only because the mesopore width is reduced in the procedure. Studies have proven that the Kelvin equationbased procedures, such as the BJH method, underestimate the pore size for narrow mesopores.

The IUPAC classification, where pores are classified in macro-, meso-, and micropores, is mostly based on the different mechanisms that occur in these pores *Application of Titanium Dioxide in the Synthesis of Mesoporous Activated Carbon Derived… DOI: http://dx.doi.org/10.5772/intechopen.98395*

#### **Figure 4.**

*IUPAC classification of pores. Figure adapted from reference [1]. © 2015 IUPAC & De Gruyter.*

during 77 K and 1 atm isothermal adsorption of N2 Pressure (**Figure 4**). Multilayer adsorption, capillary condensation, and microporous filling, respectively, are processes related to macropores, mesopores, and micropores. Depending on the different relative pressures p/p° ratio, the pore width classes correspond to the application of the capillary condensation theory. The 50 nm pore width is associated with 0.96 relative pressures. Above this value, isothermic adsorption experiments are quite difficult to interpret and the capillary condensation theory of applicability has not been adequately tested [21–25].

#### **3.4 Phase determination**

The pXRD spectra shown in **Figure 5** illustrates that the treated CDAW and modified with TiO2 under optimum preparation condition is crystalline in structure. There are seven broad peaks centred on a 2θ value of 250, 300, 370, 470, 520, 540 and 630. 2θ = 68° is not clearly described [21–25].

**Figure 5.** *XRD spectra of CDAW and TiO2-MMC.*

**Figure 6.** *XPS survey AlK*α *PES of CDAW and spectra CDAW.*
