**1. Introduction**

Water pollution is a concern for the European population, and the quality objectives for the water protection are set through the EU Water Framework Directive. Also, one of the targets of the Clean Water and Sanitation Goal within the Millennium Sustainable Development

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Goals of the 2030 Agenda is to achieve universal and equitable access to safe and affordable drinking water for all by 2030 [1].

Taking into account that the catalyst represents the key of the performance of the photocatalytic application, the catalyst-based composite should exhibit various effects related to the components and the obtaining methods [14], such as simple supporting effect, stabilizing the microstructure or active components, formation of new compounds which act as active components or stabilizers, having two or more functions, controlling of redox performances, and

In this chapter, two types of composites obtained by two different methods and applied in the

), namely, *supported TiO2*

nents were selected taking into account their utility as sorbent for natural organic matter [20–24].

**-based composites obtaining and morphostructural properties**

The granular, powdered activated carbon and natural zeolite were functionalized with TiO2

, GAC-TiO<sup>2</sup>

, and Z-TiO<sup>2</sup>

.


and multiwall carbon nanotubes and carbon nanofibers dispersed within epoxy matrix

.

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

), granular activated carbon

http://dx.doi.org/10.5772/intechopen.80803

101

 *composite*. The carbon and zeolite compo-

precursors by sol-gel method (**Figure 1**).

influencing the kinetics of adsorption/desorption and diffusion of molecules.

supported on powdered activated carbon (PAC-TiO<sup>2</sup>

drinking water treatment are presented:

), and zeolite (Z-TiO<sup>2</sup>

using titanium tetraisopropoxide (TTIP) as TiO<sup>2</sup>

**Figure 1.** Schematic diagram of obtaining PAC-TiO<sup>2</sup>


• TiO2

• TiO2

**2. TiO2**

(GAC-TiO<sup>2</sup>

(CNT-TiO<sup>2</sup>

The challenges in treating drinking water are dependent on the water sources, mainly consisted of surface and groundwater. Problematic substances in the drinking water sources can include organic matter and/or different inorganic contaminants, e.g., nitrite, nitrate, and ammonium.

One of the common and advanced unitary processes used in drinking water technology is sorption designed as activated carbon- or zeolite-based filtering. Due to more hydrophobic nature of the activated carbon, it has been recognized for elimination of a broad range of hazardous materials belong to the organic class from aqueous solutions. Activated carbon is less efficiently applied for removal of simple inorganic metallic ions or small-size anions [2].

Zeolite is also a known filtering material that exhibits a high sorption capacity [3] characterized by a selectivity degree in relation with the type of zeolite based on its specific properties of molecular sieve and ionic exchanger [4–6]. The main disadvantage is represented by the fouling of the filtering material surface.

Photocatalysis process is considered very promising for advanced water treatment based on the oxidation and reduction reaction for in situ generation of highly reactive transitory species (i.e., H<sup>2</sup> O2 , OH, O<sup>2</sup> , O<sup>3</sup> ) for mineralization of organic compounds and disinfection by-products [7–8], through the electron-hole pair formation under UV or solar irradiation.

Among various semiconductors that have been investigated in photocatalysis application, titanium dioxide (TiO<sup>2</sup> ) has attracted much attention due to its physical and chemical stability, negligible toxicity, the resistance to corrosion, redox selectivity, high photostability, and easy preparation [3, 9–10]. By UV irradiation onto TiO2 surface, under conditions of photon energy (hv) greater than or equal to the bandgap energy of TiO<sup>2</sup> , the electron will be photoexcited from the valence band to the empty conduction band leading to an empty unfilled valence band that corresponded to the hole and thus creating the electron-hole pair. The electron-hole pair is involved within various oxidative/reductive reactions including the degradation of organics.

For the drinking water treatment, the main disadvantage of TiO<sup>2</sup> -based photocatalysis is given by the necessity of the further separation phase to remove TiO2 from water, in order to avoid the loss of catalyst particles and introduction of the new pollutant of contamination of TiO2 in the treated water [11]. A solution to avoid the introduction of a new separation phase includes catalyst fixation onto various supports, e.g., activated carbon [12] and mesoporous clays [13]. The catalyst immobilization on different supports allows getting catalyst composites, which are considered a new generation of catalyst with different properties in relation with those of solely TiO2 . According to the obtaining methods, there are a large variety of composites [14], from which in this chapter will be discussed:


Taking into account that the catalyst represents the key of the performance of the photocatalytic application, the catalyst-based composite should exhibit various effects related to the components and the obtaining methods [14], such as simple supporting effect, stabilizing the microstructure or active components, formation of new compounds which act as active components or stabilizers, having two or more functions, controlling of redox performances, and influencing the kinetics of adsorption/desorption and diffusion of molecules.

Goals of the 2030 Agenda is to achieve universal and equitable access to safe and affordable

The challenges in treating drinking water are dependent on the water sources, mainly consisted of surface and groundwater. Problematic substances in the drinking water sources can include organic matter and/or different inorganic contaminants, e.g., nitrite, nitrate, and ammonium.

One of the common and advanced unitary processes used in drinking water technology is sorption designed as activated carbon- or zeolite-based filtering. Due to more hydrophobic nature of the activated carbon, it has been recognized for elimination of a broad range of hazardous materials belong to the organic class from aqueous solutions. Activated carbon is less efficiently applied for removal of simple inorganic metallic ions or small-size anions [2].

Zeolite is also a known filtering material that exhibits a high sorption capacity [3] characterized by a selectivity degree in relation with the type of zeolite based on its specific properties of molecular sieve and ionic exchanger [4–6]. The main disadvantage is represented by the

Photocatalysis process is considered very promising for advanced water treatment based on the oxidation and reduction reaction for in situ generation of highly reactive transitory species

Among various semiconductors that have been investigated in photocatalysis application,

negligible toxicity, the resistance to corrosion, redox selectivity, high photostability, and easy

the valence band to the empty conduction band leading to an empty unfilled valence band that corresponded to the hole and thus creating the electron-hole pair. The electron-hole pair is involved within various oxidative/reductive reactions including the degradation of organics.

the loss of catalyst particles and introduction of the new pollutant of contamination of TiO2

the treated water [11]. A solution to avoid the introduction of a new separation phase includes catalyst fixation onto various supports, e.g., activated carbon [12] and mesoporous clays [13]. The catalyst immobilization on different supports allows getting catalyst composites, which are considered a new generation of catalyst with different properties in relation with those of

• Hybrid composites, which comprise a matrix material of polymer (epoxy) in which TiO<sup>2</sup>

and the support of carbon nanotubes or nanofibers are dispersed [22–24]

. According to the obtaining methods, there are a large variety of composites [14],

coated (supported) on the support of activated carbon by the type of

[7–8], through the electron-hole pair formation under UV or solar irradiation.

) for mineralization of organic compounds and disinfection by-products

) has attracted much attention due to its physical and chemical stability,

surface, under conditions of photon energy

, the electron will be photoexcited from


from water, in order to avoid

in

drinking water for all by 2030 [1].

100 Photocatalysts - Applications and Attributes

fouling of the filtering material surface.

, O<sup>3</sup>

preparation [3, 9–10]. By UV irradiation onto TiO2

from which in this chapter will be discussed:

powder and granular and zeolite [15–21]

(hv) greater than or equal to the bandgap energy of TiO<sup>2</sup>

For the drinking water treatment, the main disadvantage of TiO<sup>2</sup>

by the necessity of the further separation phase to remove TiO2

(i.e., H<sup>2</sup>

solely TiO2

• Composites with TiO<sup>2</sup>

O2

, OH, O<sup>2</sup>

titanium dioxide (TiO<sup>2</sup>

In this chapter, two types of composites obtained by two different methods and applied in the drinking water treatment are presented:


#### **2. TiO2 -based composites obtaining and morphostructural properties**

The granular, powdered activated carbon and natural zeolite were functionalized with TiO2 using titanium tetraisopropoxide (TTIP) as TiO<sup>2</sup> precursors by sol-gel method (**Figure 1**).

**Figure 1.** Schematic diagram of obtaining PAC-TiO<sup>2</sup> , GAC-TiO<sup>2</sup> , and Z-TiO<sup>2</sup> .

**Figure 2.** Schematic diagram of obtaining CNT-TiO<sup>2</sup> -Epoxy and CNF-TiO<sup>2</sup> -Epoxy.

The morphology of all synthesized materials was observed by a scanning electronic microscope (SEM, Inspect S PANalytical model) coupled with the energy-dispersive X-ray analy-

, (inset: GAC), and (c) Z-TiO<sup>2</sup>

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

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103

which show the layered structure of activated carbon and a nonuniform distribution and

also, the presence of Ti on the natural zeolite (**Figure 4**). Small amounts of Al, Si, and S were identified within the activated carbon as both powdered and granular as impurities and the

were attached on the nanostructured carbon surface, and, also, a well dispersion of carbon

nanoparticles within epoxy matrix is noticed (**Figure 5a,b**). A slight more uniform

nanoparticles seems to be for CNF in comparison with CNT [22]. The

particles in composite materials was confirmed by EDX spectra (**Figure 6**).

only adhered to the surface of zeolite without the insight of the inside of the zeolite pores. The results of semiquantitative elemental analysis of the synthesized material surface were

, GAC-TiO<sup>2</sup>

(inset: zeolite).

and GAC-TiO<sup>2</sup>

nanoparticles onto the surface. It can be also seen that TiO2

, and Z-TiO<sup>2</sup>

nanoparticles

,

and,

sis detector (EDX). **Figure 3a**–**c** presents SEM images for PAC-TiO<sup>2</sup>

, (b) GAC-TiO<sup>2</sup>

presented by EDX spectra indicating Ti and C presence for PAC-TiO<sup>2</sup>

For composite materials that used epoxy as matrix, it can be noticed that TiO<sup>2</sup>

presence of K and Ca within the zeolite composition were found.

more or less agglomeration of TiO2

**Figure 4.** EDX spectra for (a) PAC-TiO<sup>2</sup>

and TiO2

distribution of TiO2

presence of TiO2

**Figure 3.** SEM images for (a) PAC-TiO<sup>2</sup> , (b) GAC-TiO<sup>2</sup> , and (c) Z-TiO<sup>2</sup> .

For the synthesis process of the composite materials consisting of carbon nanotubes or carbon nanofibers mixed with TiO<sup>2</sup> particles within epoxy matrix, the two-roll mill technique was applied (**Figure 2**).

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment http://dx.doi.org/10.5772/intechopen.80803 103

**Figure 4.** EDX spectra for (a) PAC-TiO<sup>2</sup> , (b) GAC-TiO<sup>2</sup> , (inset: GAC), and (c) Z-TiO<sup>2</sup> (inset: zeolite).

The morphology of all synthesized materials was observed by a scanning electronic microscope (SEM, Inspect S PANalytical model) coupled with the energy-dispersive X-ray analysis detector (EDX). **Figure 3a**–**c** presents SEM images for PAC-TiO<sup>2</sup> , GAC-TiO<sup>2</sup> , and Z-TiO<sup>2</sup> , which show the layered structure of activated carbon and a nonuniform distribution and more or less agglomeration of TiO2 nanoparticles onto the surface. It can be also seen that TiO2 only adhered to the surface of zeolite without the insight of the inside of the zeolite pores.

The results of semiquantitative elemental analysis of the synthesized material surface were presented by EDX spectra indicating Ti and C presence for PAC-TiO<sup>2</sup> and GAC-TiO<sup>2</sup> and, also, the presence of Ti on the natural zeolite (**Figure 4**). Small amounts of Al, Si, and S were identified within the activated carbon as both powdered and granular as impurities and the presence of K and Ca within the zeolite composition were found.

For composite materials that used epoxy as matrix, it can be noticed that TiO<sup>2</sup> nanoparticles were attached on the nanostructured carbon surface, and, also, a well dispersion of carbon and TiO2 nanoparticles within epoxy matrix is noticed (**Figure 5a,b**). A slight more uniform distribution of TiO2 nanoparticles seems to be for CNF in comparison with CNT [22]. The presence of TiO2 particles in composite materials was confirmed by EDX spectra (**Figure 6**).

For the synthesis process of the composite materials consisting of carbon nanotubes or carbon

, and (c) Z-TiO<sup>2</sup>



.

, (b) GAC-TiO<sup>2</sup>

particles within epoxy matrix, the two-roll mill technique was

nanofibers mixed with TiO<sup>2</sup>

**Figure 3.** SEM images for (a) PAC-TiO<sup>2</sup>

**Figure 2.** Schematic diagram of obtaining CNT-TiO<sup>2</sup>

102 Photocatalysts - Applications and Attributes

applied (**Figure 2**).

**Figure 5.** SEM images for (a) CNF-TiO<sup>2</sup> -Epoxy and (b) CNT-TiO<sup>2</sup> -Epoxy.

X-ray diffraction measurements were carried out to determine the crystal phase composition using a PANalytical X'PertPRO MPD diffractometer. **Figure 7** presents the XRD patterns of GAC-

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

diffraction lines at 2θ of 25.3, 38.6, 48, 54, and 62.97° [25]. Also, the XRD results revealed that the major component of natural zeolite used in this study is clinoptilolite (2θ ~ 10°; 12°; 22.5°; 30°) [26]. **Figure 8** presents the XRD patterns of composite materials based on nanostructured carbon.

**-based composite application for sorption and photocatalysis-**

Various types of carbon and zeolite are reported as good sorbents for various types of pollutants from water [2, 15–24]. The easy separation of these materials from water and their good sorption capacity that is important in the first stage of the overall photocatalysis process make

Humic acids (HAs) represent a main component of natural organic matter that gives the organic loading of drinking water sources, which must be removed or destroyed because of water quality regulations. Also, the presence of HAs before the chlorination step as disinfection could lead to trihalomethane and other toxic by-product generation. The efficiency of

immobilization.

materials for the sorption and the photocatalysis of HA from water, expressed

is the predominant phase, identified by

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105

as predominant phase, with the intensity

loading within the composite composition in

. The anatase form of TiO2

.

and CNF-TiO<sup>2</sup>

.

TiO2

**3. TiO2**

*supported TiO2*

, PAC-TiO<sup>2</sup>

**Figure 8.** XRD pattern for CNT-TiO<sup>2</sup>

, and Z-TiO<sup>2</sup>

It is obviously the presence of anatase form of TiO2

**unitary processes in drinking water treatment**

as HA removal efficiency, is presented comparatively in **Figure 9**.

of diffraction lines higher due to the higher TiO<sup>2</sup>

them very promising as support for the TiO2

comparison with the supported TiO2

**Figure 6.** EDX spectra for (a) CNF-TiO<sup>2</sup> -epoxy and (b) CNT-TiO<sup>2</sup> -epoxy.

**Figure 7.** XRD pattern for PAC-TiO<sup>2</sup> , GAC-TiO<sup>2</sup> , and Z-TiO<sup>2</sup> .

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment http://dx.doi.org/10.5772/intechopen.80803 105

**Figure 8.** XRD pattern for CNT-TiO<sup>2</sup> and CNF-TiO<sup>2</sup> .

**Figure 5.** SEM images for (a) CNF-TiO<sup>2</sup>

104 Photocatalysts - Applications and Attributes

**Figure 6.** EDX spectra for (a) CNF-TiO<sup>2</sup>

**Figure 7.** XRD pattern for PAC-TiO<sup>2</sup>

, GAC-TiO<sup>2</sup>

, and Z-TiO<sup>2</sup>

.





X-ray diffraction measurements were carried out to determine the crystal phase composition using a PANalytical X'PertPRO MPD diffractometer. **Figure 7** presents the XRD patterns of GAC-TiO2 , PAC-TiO<sup>2</sup> , and Z-TiO<sup>2</sup> . The anatase form of TiO2 is the predominant phase, identified by diffraction lines at 2θ of 25.3, 38.6, 48, 54, and 62.97° [25]. Also, the XRD results revealed that the major component of natural zeolite used in this study is clinoptilolite (2θ ~ 10°; 12°; 22.5°; 30°) [26].

**Figure 8** presents the XRD patterns of composite materials based on nanostructured carbon. It is obviously the presence of anatase form of TiO2 as predominant phase, with the intensity of diffraction lines higher due to the higher TiO<sup>2</sup> loading within the composite composition in comparison with the supported TiO2 .

#### **3. TiO2 -based composite application for sorption and photocatalysisunitary processes in drinking water treatment**

Various types of carbon and zeolite are reported as good sorbents for various types of pollutants from water [2, 15–24]. The easy separation of these materials from water and their good sorption capacity that is important in the first stage of the overall photocatalysis process make them very promising as support for the TiO2 immobilization.

Humic acids (HAs) represent a main component of natural organic matter that gives the organic loading of drinking water sources, which must be removed or destroyed because of water quality regulations. Also, the presence of HAs before the chlorination step as disinfection could lead to trihalomethane and other toxic by-product generation. The efficiency of *supported TiO2* materials for the sorption and the photocatalysis of HA from water, expressed as HA removal efficiency, is presented comparatively in **Figure 9**.

**Figure 9.** Evolution of HA removal efficiency by sorption and photocatalysis for 50 mg·L−<sup>1</sup> HA onto (a) GAC-TiO<sup>2</sup> , (b) Z-TiO<sup>2</sup> , and (c) PAC-TiO<sup>2</sup> .

The HA removal efficiency was calculated using the following equation:

$$\text{Removal efficiency} = \frac{c\_o - c\_i}{c\_o} \times 100 \text{ (\%)}\tag{1}$$

The evaluation of photocatalytic activity after the sorption step showed an increasing order:

HA using CNT-TiO<sup>2</sup>

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

These behaviors should be explained by the available sites of the carbon in the sorption pro-

Also, epoxy resin hindered the available sites, which decreased both sorption capacity and

In order to determine some mechanism aspects regarding the sorption and photocatalysis processes, several kinetic models must be checked to find the optimum one. Two different kinetic models are used to fit the experimental data, i.e., pseudo-first-order and pseudo-

The pseudo-first-order kinetic adsorption was suggested by Lagergren (1898) for the adsorption of solid/liquid systems. It can be expressed in integrated form as shown in Eq. (2):

*ln*(*qe* − *qt*) = *ln*(*qe*) − *k*<sup>1</sup> *t* (2)

) and q<sup>t</sup>

 *composite materials*.

in the photocatalysis process, which are in direct relations

, carbon, and zeolite support.


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107

is the adsorption loading of dye

GAC − TiO2 > Z − TiO2 > PAC − TiO2 > CNT − TiO2 − Epoxy > CNF − TiO2 − Epoxy

with the morphology, size, and the bonding type between TiO2

is the rate constant of adsorption (min−<sup>1</sup>

cess and the available sites of TiO2

**Figure 10.** Evolution of removal efficiency of 25 mg·L−<sup>1</sup>


photocatalytic activity of *TiO2*

second-order kinetic models [27].

) at time t (min).

where, k1

(mg·g−<sup>1</sup>

CNF-TiO<sup>2</sup>

**3.1. Pseudo-first-order kinetic model**

where C0 and C<sup>t</sup> are the concentrations of HA in aqueous solution in terms of A254 at initial time and at any time t, respectively (mg·L−<sup>1</sup> ).

The sorption was assessed as the preliminary and compulsory step of the overall photocatalysis process taking into consideration also the possibility to use the supports as simple sorbents and only for self-cleaning to apply the photocatalysis. The sorption capacity for HA is better for PAC-TiO<sup>2</sup> , while the photocatalytic activity is better for GAC-TiO<sup>2</sup> . This should explain the morphological structure and the sizes of the particles. The lower particle size leads to the higher sorption capacity, while for the photocatalysis application the size of support decreased the photocatalytic activity may be due to the finer suspension should hinder the UV irradiation penetration to the TiO2 surface.The sorption and the photocatalysis capacities of *TiO2 composite materials* assessed in terms of HA removal efficiency showed the superiority of CNT-TiO<sup>2</sup> - Epoxy versus CNF-TiO<sup>2</sup> -Epoxy. It can be noticed that a slight photocatalytic activity was found for both materials (**Figure 10**).

For HA removal, the sorption capacity of tested materials increased in order:

$$\text{PAC} - \text{TiO}\_2 > \text{Z} - \text{TiO}\_2 > \text{GAC} - \text{TiO}\_2 > \text{CNT} - \text{TiO}\_2 - \text{Epoxy} > \text{CNF} - \text{TiO}\_2 - \text{Epoxy}$$

**Figure 10.** Evolution of removal efficiency of 25 mg·L−<sup>1</sup> HA using CNT-TiO<sup>2</sup> -epoxy by photocatalysis (a), sorption (b), CNF-TiO<sup>2</sup> -epoxy by photocatalysis (c), and sorption (d).

The evaluation of photocatalytic activity after the sorption step showed an increasing order:

$$\text{GAC} - \text{TiO}\_2 > \text{Z} - \text{TiO}\_2 > \text{PAC} - \text{TiO}\_2 > \text{CNT} - \text{TiO}\_2 - \text{Epoxy} > \text{CNF} - \text{TiO}\_2 - \text{Epopy}$$

These behaviors should be explained by the available sites of the carbon in the sorption process and the available sites of TiO2 in the photocatalysis process, which are in direct relations with the morphology, size, and the bonding type between TiO2 , carbon, and zeolite support. Also, epoxy resin hindered the available sites, which decreased both sorption capacity and photocatalytic activity of *TiO2 composite materials*.

In order to determine some mechanism aspects regarding the sorption and photocatalysis processes, several kinetic models must be checked to find the optimum one. Two different kinetic models are used to fit the experimental data, i.e., pseudo-first-order and pseudosecond-order kinetic models [27].

#### **3.1. Pseudo-first-order kinetic model**

**Figure 9.** Evolution of HA removal efficiency by sorption and photocatalysis for 50 mg·L−<sup>1</sup>

The HA removal efficiency was calculated using the following equation:

*c*0

surface.The sorption and the photocatalysis capacities of *TiO2*


).

, while the photocatalytic activity is better for GAC-TiO<sup>2</sup>

For HA removal, the sorption capacity of tested materials increased in order:

The sorption was assessed as the preliminary and compulsory step of the overall photocatalysis process taking into consideration also the possibility to use the supports as simple sorbents and only for self-cleaning to apply the photocatalysis. The sorption capacity for HA is better

morphological structure and the sizes of the particles. The lower particle size leads to the higher sorption capacity, while for the photocatalysis application the size of support decreased the photocatalytic activity may be due to the finer suspension should hinder the UV irradiation

*materials* assessed in terms of HA removal efficiency showed the superiority of CNT-TiO<sup>2</sup>

PAC − TiO2 > Z − TiO2 > GAC − TiO2 > CNT − TiO2 − Epoxy > CNF − TiO2 − Epoxy

are the concentrations of HA in aqueous solution in terms of A254 at initial

Removal efficiency <sup>=</sup> *<sup>c</sup>*<sup>0</sup> <sup>−</sup> *<sup>c</sup>* \_\_\_\_*<sup>t</sup>*

Z-TiO<sup>2</sup>

where C0

for PAC-TiO<sup>2</sup>

penetration to the TiO2

Epoxy versus CNF-TiO<sup>2</sup>

found for both materials (**Figure 10**).

, and (c) PAC-TiO<sup>2</sup>

106 Photocatalysts - Applications and Attributes

and C<sup>t</sup>

.

time and at any time t, respectively (mg·L−<sup>1</sup>

HA onto (a) GAC-TiO<sup>2</sup>

. This should explain the

 *composite* 


× 100 (%) (1)

, (b)

The pseudo-first-order kinetic adsorption was suggested by Lagergren (1898) for the adsorption of solid/liquid systems. It can be expressed in integrated form as shown in Eq. (2):

$$
\ln \langle q\_\epsilon - q\_\iota \rangle = \ln \langle q\_\iota \rangle - k\_\iota t \tag{2}
$$

where, k1 is the rate constant of adsorption (min−<sup>1</sup> ) and q<sup>t</sup> is the adsorption loading of dye (mg·g−<sup>1</sup> ) at time t (min).

#### **3.2. Pseudo-second-order kinetic model**

The pseudo-second-order kinetics, proposed by Ho and Mckay [28], is expressed in Eq. (3):

$$\frac{t}{\overline{q}\_{\epsilon}} = \frac{1}{k\_{\!\_{2}} \cdot q\_{\epsilon}^{2}} + \frac{t}{\overline{q}\_{\epsilon}} \tag{3}$$

**Catalyst Parameters Value**

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

k1 (min−<sup>1</sup>

k1 (min−<sup>1</sup>

k1 (min−<sup>1</sup>

k1 (min−<sup>1</sup>

k1 (min−<sup>1</sup>

Based on the results presented in **Table 1**, it can be seen that the PAC-TiO<sup>2</sup>

sorption capacity and the best kinetics for HA removal and the GAC-TiO<sup>2</sup>

these types of material, the photocatalytic activity was better also for CNT-TiO<sup>2</sup>

PAC-TiO<sup>2</sup> qe

GAC-TiO<sup>2</sup> qe

Z-TiO<sup>2</sup> qe



**Table 2.** Pseudo-first-order kinetic parameters for HA photocatalysis.

CNT-TiO<sup>2</sup>

CNF-TiO<sup>2</sup>

were achieved for *TiO2*

ference was found between CNT-TiO<sup>2</sup>

**HA concentration (50 mg**·**L−<sup>1</sup>**

**HA concentration (25 mg**·**L−<sup>1</sup>**

higher than 0.90. However, there is a significant difference between calculated and experimental qe using the pseudo-first-order kinetic model that limits its interpretation (**Table 2**), and, thus, it means that the pseudo-second-order kinetic model is most appropriate. Besides the kinetic parameter, the pseudo-second-order kinetic model informed about the significance of the sorption step within the overall photocatalysis process. It is well known that the reaction rate and kinetics are influenced by many experimental parameters, *e.g*., HA concentration, catalyst dose, and pH [22].

photocatalytic kinetics, which are in accordance with the efficiency results. The worse results

matrix that reduced the active sites for the sorption and the photocatalysis. Also, the main dif-

sizes of the nanostructured carbon component, better for CNT in comparison with CNF. For

Arsenic is a common contaminant in drinking water supplies especially for groundwater sources. Inorganic arsenic speciation in water consists of arsenite (AsIII) and arsenate (AsV), but As(III) is more problematic because of its high toxicity and the difficulty to be removed from


**)**

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

R<sup>2</sup> 0.955

R<sup>2</sup> 0.913

R<sup>2</sup> 0.943

R<sup>2</sup> 0.995

R<sup>2</sup> 0.956

 *composite* materials, which can be explained by the presence of epoxy

**)**

) 9.95

http://dx.doi.org/10.5772/intechopen.80803

109

) 0.0073

) 1.64

) 0.0494

) 2.92

) 0.0142

) 0.33

) 0.085

) 1.66

) 0.0019

exhibited higher

exhibited the best



where, k2 is the rate constant of the pseudo-second-order adsorption kinetics (g·mg−<sup>1</sup> ·min−<sup>1</sup> ) and qe is the equilibrium adsorption capacity (mg·g−<sup>1</sup> ).

Pseudo-first- and pseudo-second-order kinetic models were tested for fitting the sorption and photocatalysis experimental data (**Tables 1** and **2**). The linear plots of *t/qt* vs. *t* show that the experimental data agree with the pseudo-second-order kinetic model for the HA adsorption. The calculated *qe* values agree very well with the experimental data, and the correlation coefficients for the pseudo-second-order kinetic model are higher than 0.90 in almost all cases. These indicate that the adsorption of HA from water onto materials obeys the pseudo-second-order kinetic model that predicts an exponential decay of concentrations as a function of time. The pseudo-first-order kinetic model was not appropriate for fitting the sorption experimental data, while the photocatalysis experimental data were fitted well with both kinetic models with the correlation coefficient


**Table 1.** Pseudo-second-order kinetic parameters for HA sorption and photocatalysis.



**Table 2.** Pseudo-first-order kinetic parameters for HA photocatalysis.

**3.2. Pseudo-second-order kinetic model**

108 Photocatalysts - Applications and Attributes

\_\_*<sup>t</sup>*

is the equilibrium adsorption capacity (mg·g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(mg\*g−<sup>1</sup>

(g·mg−1·min−<sup>1</sup>

·min−<sup>1</sup>

·min−<sup>1</sup>

·min−<sup>1</sup>

·min−<sup>1</sup>

**Table 1.** Pseudo-second-order kinetic parameters for HA sorption and photocatalysis.

k2 (g·mg−<sup>1</sup>

k2

k2 (g·mg−<sup>1</sup>

k2 (g·mg−<sup>1</sup>

k2 (g·mg−<sup>1</sup>

where, k2

PAC-TiO<sup>2</sup> qe

GAC-TiO<sup>2</sup> qe

Z-TiO<sup>2</sup> qe



CNT-TiO<sup>2</sup>

CNF-TiO<sup>2</sup>

qe

The pseudo-second-order kinetics, proposed by Ho and Mckay [28], is expressed in Eq. (3):

= \_\_\_\_\_ <sup>1</sup> *k*<sup>2</sup> ⋅ *qe* <sup>2</sup> <sup>+</sup> \_\_*<sup>t</sup> qe*

is the rate constant of the pseudo-second-order adsorption kinetics (g·mg−<sup>1</sup>

**Catalyst Parameters Adsorption Photocatalysis**

**HA concentration (50 mg**·**L−<sup>1</sup>**

R<sup>2</sup> 0.915 0.996

R<sup>2</sup> 0.966 0.998

R<sup>2</sup> 0.976 0.985 **HA concentration (25 mg**·**L−<sup>1</sup>**

R<sup>2</sup> 0.986 0.996

R<sup>2</sup> 0.996 0.943

) 38.34 44.25

) 25.59 49.78

) 28.65 42.32

) 20.68 19.98

) 13.06 12.37

) 0.0067 0.0031

) 0.00381 0.0170

) 0.0059 0.0025

) 0.0024 0.0015

) 0.0045 0.0001

**)**

**)**

). Pseudo-first- and pseudo-second-order kinetic models were tested for fitting the sorption and photocatalysis experimental data (**Tables 1** and **2**). The linear plots of *t/qt* vs. *t* show that the experimental data agree with the pseudo-second-order kinetic model for the HA adsorption. The calculated *qe* values agree very well with the experimental data, and the correlation coefficients for the pseudo-second-order kinetic model are higher than 0.90 in almost all cases. These indicate that the adsorption of HA from water onto materials obeys the pseudo-second-order kinetic model that predicts an exponential decay of concentrations as a function of time. The pseudo-first-order kinetic model was not appropriate for fitting the sorption experimental data, while the photocatalysis experimental data were fitted well with both kinetic models with the correlation coefficient

(3)

) and

·min−<sup>1</sup>

*qt*

higher than 0.90. However, there is a significant difference between calculated and experimental qe using the pseudo-first-order kinetic model that limits its interpretation (**Table 2**), and, thus, it means that the pseudo-second-order kinetic model is most appropriate. Besides the kinetic parameter, the pseudo-second-order kinetic model informed about the significance of the sorption step within the overall photocatalysis process. It is well known that the reaction rate and kinetics are influenced by many experimental parameters, *e.g*., HA concentration, catalyst dose, and pH [22].

Based on the results presented in **Table 1**, it can be seen that the PAC-TiO<sup>2</sup> exhibited higher sorption capacity and the best kinetics for HA removal and the GAC-TiO<sup>2</sup> exhibited the best photocatalytic kinetics, which are in accordance with the efficiency results. The worse results were achieved for *TiO2 composite* materials, which can be explained by the presence of epoxy matrix that reduced the active sites for the sorption and the photocatalysis. Also, the main difference was found between CNT-TiO<sup>2</sup> -Epoxy and CNF-TiO<sup>2</sup> -Epoxy due to the morphology and sizes of the nanostructured carbon component, better for CNT in comparison with CNF. For these types of material, the photocatalytic activity was better also for CNT-TiO<sup>2</sup> -Epoxy.

Arsenic is a common contaminant in drinking water supplies especially for groundwater sources. Inorganic arsenic speciation in water consists of arsenite (AsIII) and arsenate (AsV), but As(III) is more problematic because of its high toxicity and the difficulty to be removed from

The results showed that ammonium is removed by sorption on the zeolite based on ionic exchange, which is proven by comparison with natural zeolite, while the nitrite removal is based on its oxidation process during UV irradiation, which is enhanced by the presence of

Carbon-/Zeolite-Supported TiO2 for Sorption/Photocatalysis Applications in Water Treatment

Since activated carbon is a versatile sorbent class for the retention of a wide spectrum of organic compounds and arsenic(III) and the zeolite exhibited an adsorption/ion-exchange capacity for ammonium, nitrite, and heavy metals, their common presence as mixed materials

In this chapter, two types of composites obtained by two different methods and applied in the

), namely, *supported TiO2*

and multiwall carbon nanotubes and carbon nanofibers dispersed within epoxy

The sorption and photocatalysis studies showed that for HA removal, the sorption capacity of

The removal of pollutants/impurities dissolved in water is based, on the one hand, on the sorption capacity of activated carbon and/or zeolite, which exhibited selectivity for certain impurities dissolved under the lamp-off conditions. On the other hand, but taking into

the zeolite acted by photocatalytic activity generating oxidation and reduction processes that cause the degradation and mineralization of the dissolved organic compounds and the transformation of the inorganic contaminants into the compounds that can be retained on the surface material or compounds that do not affect the quality of the water. Also, the oxidation and reduction processes under irradiation conditions allow the destruction of the contaminants and, implicitly, the cleaning of the sorbent surface. A mixture of zeolite and

features. Thus, for low loading of water with contaminants that can be adsorbed on the filter material, the lamp is not switched on during system operation but only in the washing/ regeneration stage, and for a water loaded with contaminants that cannot be adsorbed on the filter material, the system works with the lamp on, ensuring water decontamination and


tested materials increased in order, PAC-TiO<sup>2</sup> > Z-TiO<sup>2</sup> > GAC-TiO<sup>2</sup> > CNT-TiO<sup>2</sup>


), granular activated carbon

http://dx.doi.org/10.5772/intechopen.80803

, obtained through sol-gel

 *composite*, obtained through

on the active carbon surface and

could exhibit bifunctionality, depending on the water



111

broadens the spectrum of contaminants that can be removed from the water.

supported on powdered activated carbon (PAC-TiO<sup>2</sup>

the Z-TiO<sup>2</sup>

**4. Conclusions**

(GAC-TiO<sup>2</sup>

Epoxy> CNF-TiO<sup>2</sup>

matrix (CNT-TiO<sup>2</sup>

the two-roll mill method.


activated carbon as support for TiO2

self-cleaning during operation.

method.

**a.** TiO2

**b.** TiO2

TiO2

photocatalyst.

drinking water treatment were studied:

), and zeolite (Z-TiO<sup>2</sup>


account the sorption phase, by starting the lamp, TiO2

**Figure 11.** Time evolution of As(III) concentration during sorption and photocatalysis using PAC-TiO<sup>2</sup> and GAC-TiO<sup>2</sup> .

**Figure 12.** Time evolution of NO<sup>2</sup> <sup>−</sup> concentration during photolysis (a), photocatalysis using Z-TiO<sup>2</sup> (b), of NH<sup>4</sup> + concentration during photocatalysis using Z-TiO<sup>2</sup> (c), and natural zeolite (d).

water [29]. The comparative results regarding As(III) removal in the presence of HA showed a good efficiency for both sorption and photocatalysis using *supported TiO2* material (**Figure 11**).

Another common problem of groundwater source used for drinking water supply is given by the presence of ammonium, nitrite, and nitrate. Nitrate could not be removed from water on these tested materials, while ammonium and nitrate were removed from Z-TiO<sup>2</sup> (**Figure 12**).

The results showed that ammonium is removed by sorption on the zeolite based on ionic exchange, which is proven by comparison with natural zeolite, while the nitrite removal is based on its oxidation process during UV irradiation, which is enhanced by the presence of the Z-TiO<sup>2</sup> photocatalyst.

Since activated carbon is a versatile sorbent class for the retention of a wide spectrum of organic compounds and arsenic(III) and the zeolite exhibited an adsorption/ion-exchange capacity for ammonium, nitrite, and heavy metals, their common presence as mixed materials broadens the spectrum of contaminants that can be removed from the water.
