**4. Photocatalytic activity**

#### **4.1 Dye removal procedure**

The photocatalytic activity of the as-prepared samples was investigated under UV-Vis light irradiation. The aqueous MB solution (20 mg L�<sup>1</sup> ) was prepared and kept in dark for 60 min to attain equilibrium. Later, 10 mg of the as-prepared photocatalyst was added to 10 ml MB solution and it was placed in a water jacketed photocatalytic reactor for the photocatalytic degradation process. A 250 W Hg lamp was used as the illumination source to excite the photocatalysts. In the whole reaction, the photocatalytic container was maintained at room temperature by circulating water. At 15 min time interval, 3 ml of solution was taken and centrifuged to remove the photocatalyst particles. The supernatant was examined by a Shimadzu UV3000 UV-Vis spectrophotometer and the dye absorption band maximum was observed at �664 nm. The percentage of degradation was calculated using the Beer-Lambert relation [48]:

$$\mathbf{A}(\lambda) = \log \left( \mathbf{I}(\lambda) / \mathbf{I}\_0(\lambda) \right) = -\text{el}[\mathbf{B}\mathbf{M}] \tag{1}$$

where

A – absorbance at a given wavelength λ,

I0 (λ) – incident light intensity,

I (λ) – light intensity transmitted through the MB solution,

ε – Molar attenuation coefficient of MB.

l – Path length of the beam of light.

The degradation efficiency was calculated by

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior… DOI: http://dx.doi.org/10.5772/intechopen.89325*

$$\text{Degradiation } (\%) = (\text{C}\_0 - \text{C}) \langle \text{C}\_0 \ast \text{100} \tag{2}$$

where,

**3.5 Surface area investigation**

*Assorted Dimensional Reconfigurable Materials*

**4. Photocatalytic activity**

**4.1 Dye removal procedure**

using the Beer-Lambert relation [48]:

I0 (λ) – incident light intensity,

A – absorbance at a given wavelength λ,

ε – Molar attenuation coefficient of MB. l – Path length of the beam of light.

The degradation efficiency was calculated by

I (λ) – light intensity transmitted through the MB solution,

�37 m<sup>2</sup> <sup>g</sup>�<sup>1</sup>

where

**114**

reaction.

**Figure 8.**

The specific surface area of the photocatalyst was determined by Brunauer-Emmett-Teller (BET) analysis through N2 adsorption/desorption measurements at 25°C (**Figure 8**). The measured surface area of the ternary nanocomposite was

absorbed on its surface, which might proficiently help the kinetics of photo catalytic

The photocatalytic activity of the as-prepared samples was investigated under

kept in dark for 60 min to attain equilibrium. Later, 10 mg of the as-prepared photocatalyst was added to 10 ml MB solution and it was placed in a water jacketed photocatalytic reactor for the photocatalytic degradation process. A 250 W Hg lamp was used as the illumination source to excite the photocatalysts. In the whole reaction, the photocatalytic container was maintained at room temperature by circulating water. At 15 min time interval, 3 ml of solution was taken and

centrifuged to remove the photocatalyst particles. The supernatant was examined by a Shimadzu UV3000 UV-Vis spectrophotometer and the dye absorption band maximum was observed at �664 nm. The percentage of degradation was calculated

Að Þ¼ λ log Ið Þ¼� ð Þλ *=*I0ð Þλ εl BM½ � (1)

) was prepared and

UV-Vis light irradiation. The aqueous MB solution (20 mg L�<sup>1</sup>

*BET surface area analysis of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

. The high surface area support more active species and reactants to be

C0 is the initial dye concentration and C is the dye concentration at time t from the start of the photocatalytic reaction.

For the reusability purpose, the as-prepared photocatalyst collected after the photocatalytic reaction by centrifuging, washed with DDW and then dried at 60°C.

#### **4.2 Radical trapping experiment**

To elucidate the reaction mechanism of the photocatalytic MB dye degradation, the radical trapping investigation was performed. In the scavenging activity, h<sup>+</sup> , OH and O2 � radicals are trapped by EDTA, 2-propanol and benzoquinone, respectively. The trapping experiments were carried out with the accumulation of different scavengers into the catalytic reaction. The reaction samples were taken from the photocatalytic reactor to record their UV-Vis absorption spectra.

#### **4.3 Reaction mechanism of dye degradation**

The photocatalytic activities of the Mg-Al LDH, g-C3N4, and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite were assessed under UV-Vis light illumination. In this work, MB dye was utilized as an objective contamination so as to decide the photocatalytic action of the impetuses under obvious light illumination. The MB dye solutions were prepared and the photocatalytic reactions were performed by adding the as-prepared samples to the MB dye solutions. The pure MB dye fragment shows a strong visible light absorption around 664 nm. The MB dye with prepared photocatalyst is subjecting under the visible light irradiation, corresponding absorption peak intensity was decreased, and the decreasing MB dye intensity is attributed to the degradation of MB dye through the photocatalytic activity. When increases the irradiation time, absorption intensity of MB dye molecules was decreased (i.e.) once increase the irradiation/reaction time, the large number of dye molecules can be degraded. In this process, a photocatalyst is irradiated by light with energy equal to or higher than the bandgap energy of the photocatalyst. This results in the excitation of an electron (e�) from the valence band to the conduction band, leaving a hole (h<sup>+</sup> ) in the valence band. Before the recombination takes place, the photogenerated electrons (e�) and holes (h+ ) should be transferred to the surface of the photocatalyst in order to take part in the redox reactions with the adsorbed species. The redox reactions of electrons (e�) and holes (h<sup>+</sup> ) with adsorbed oxygen and water molecules lead to the formation of superoxide radical anion (<sup>∙</sup> O2 �) and hydroxyl radical (<sup>∙</sup> OH), respectively.

Among all the as-prepared photocatalyst samples, g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite sample exhibit better photocatalytic activity. This could be attributed to a large number of electrons and holes generated by the as-prepared photocatalyst system, caused by the favorable visible light absorption. On the other hand, ZnO, a wide bandgap material, provides intermediate states to delay the electron–hole recombination, which could also contribute to the high photocatalytic activity. The morphological arrangements of the nanocomposite and its resultant electronic structure, (i.e.) the even distribution of ZnO intercalated LDH over the surface of g-C3N4 [49], collectively contribute to the effective separation of the photogenerated charge carriers. The observed photocatalytic degradation efficiencies of the as-prepared photocatalysts are 32%, 30%, 49% and 96.5% for ZnO, LDH, g-C3N4, and g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite, respectively.

It has to be noted that the photocatalytic efficiency reported in the present study, betters our previous research work, in which ZnS QDs-LDH [49] exhibited a photocatalytic degradation efficiency of 95%. The enhanced photocatalytic efficiency is originated from the photocatalytic activity of N-rich g-C3N4, (i.e.,) the improved photocatalytic mechanism could be ascribed to the synergetic effect of graphitic N rich surface which offers more reactive sites for photocatalytic reaction. This in turn increases the utilization of the photo-separated charges towards the radical formation and corresponding degradation. Parallelly, the N-carbon acted as a co-catalyst to improve surface reaction kinetics and the nitrogen species directly contributed to the outstanding photocatalytic activity under visible light irradiation. Especially the nitrogen rich surface can achieve essential optical absorbance under visible light due to the mixing of O 2p states with p states. And also the nitrogen rich surface 2D/2D offers more active surface for the e� transfer. The reaction kinetics of the MB dye degradation of the prepared photocatalysts is investigated by fitting the pseudo-first-order kinetic curve [50].

The plots of ln (C0\C) against illumination time are appeared in **Figure 9**. From the kinetic graph, the ternary nanocomposite fits well and the outcome is in concurrence with the pseudo-first-order model. The impact of different scavengers on the photodegradation of MB dye solution was studied in order to recognize the role of receptive oxidative species in the photodegradation process. The role of H<sup>+</sup> , OH and O2 radicals were done individually, utilizing EDTA, 2-propanol, and BQ respectively. During the addition of EDTA and BQ, there were conspicuous variations in the photocatalytic process, which shows that H+ and O2 radicals are influences in MB dye degradation. But after the addition of 2-Proponal (scavenger for the OH radical), the degradation of MB is highly suppressed than other reactions, indicating the major of \*OH in MB dye degradation. From this result, it is clear that the photocatalytic degradation process is led by the contribution of hydroxyl radical (\*OH). After the addition of the as-prepared photocatalyst into the reaction and irradiating with visible light, the electrons were photoexcited from the valence band (VB) to the conduction band (CB). Once electrons are excited, the hole act as an oxidizing agent and oxidize the aquatic or the dye directly to form \*OH radicals.

These OH reactive species are responsible for the efficient degradation of organic pollutants in water. The following equation represent the possible photocatalytic reaction mechanism of MB dye degradation under visible light irradiation.

$$\begin{aligned} &\text{g}-\text{C}\_{3}\text{N}\_{4}/\text{ZnO}\text{(MBH)}+\text{h}\nu \rightarrow \text{g}-\text{C}\_{3}\text{N}\_{4}/\text{MgAlLDH}(\text{h}^{+}+\text{e}^{-})\text{ZnO} \\ &\text{g}-\text{C}\_{3}\text{N}\_{4}/\text{MgAl}(\text{LDH})+\text{(h}^{+}) \rightarrow (\text{e}^{-})(\text{free}-\text{electrons}) \\ &\text{e}^{-}+\text{O}\_{2} \rightarrow \text{O}\_{2}^{\*} \\ &\text{h}^{+}+\text{OH}^{-} \rightarrow \text{OH} \\ &\text{h}^{+}+\text{H}\_{2}\text{O} \rightarrow \text{OH}+\text{H}^{+} \\ &\text{O}\_{2}^{\*}+\text{MB} \rightarrow \text{CO}\_{2} + \text{H}\_{2}\text{O} (\text{By}-\text{product}) \\ &\text{OH}^{\*}+\text{MB} \rightarrow \text{CO}\_{2} + \text{H}\_{2}\text{O} (\text{By}-\text{product}) \\ &\text{h}^{+}+\text{MB} \rightarrow \text{CO}\_{2} + \text{H}\_{2}\text{O} (\text{By}-\text{product}) \end{aligned} \tag{3}$$

The **Figure 10** shows the schematic illustration of possible photocatalytic degradation of MB dye under visible light irradiation. The reusability of the prepared photocatalyst was studied by performing continual tests under same reaction conditions (shown in **Figure 11b**). The fresh MB solution was utilized for resulting cycles. Subsequently in each cycle, the prepared catalyst was isolated from the photocatalytic reactor through centrifugation. After 4 cycles, the degradation ability of the prepared catalyst was slightly reduced and it might be because of the loss

of catalyst during the recycling process. The photocatalytic dye degradation activity of the prepared sample was compared to the previously reported nanomaterials,

*(a) Radical trapping experiments of active species over g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and (b) reusability of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite in the photodegradation of MB [34].*

*(A) Photocatalytic degradation and (B) pseudo-first-order kinetics for the degradation of MB over (a) ZnO*

*(b) LDH(c) g-C3N4 (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior…*

*DOI: http://dx.doi.org/10.5772/intechopen.89325*

which is given in **Table 1**.

**Figure 10.**

**Figure 9.**

**Figure 11.**

**117**

*Schematic illustration of proposed photocatalytic reaction mechanism.*

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior… DOI: http://dx.doi.org/10.5772/intechopen.89325*

**Figure 9.**

It has to be noted that the photocatalytic efficiency reported in the present study, betters our previous research work, in which ZnS QDs-LDH [49] exhibited a photocatalytic degradation efficiency of 95%. The enhanced photocatalytic efficiency is originated from the photocatalytic activity of N-rich g-C3N4, (i.e.,) the improved photocatalytic mechanism could be ascribed to the synergetic effect of graphitic N rich surface which offers more reactive sites for photocatalytic reaction. This in turn increases the utilization of the photo-separated charges towards the radical formation and corresponding degradation. Parallelly, the N-carbon acted as a co-catalyst to improve surface reaction kinetics and the nitrogen species directly contributed to the outstanding photocatalytic activity under visible light irradiation. Especially the nitrogen rich surface can achieve essential optical absorbance under visible light due to the mixing of O 2p states with p states. And also the nitrogen rich surface 2D/2D offers more active surface for the e� transfer. The reaction kinetics of the MB dye degradation of the prepared photocatalysts is investigated by fitting

The plots of ln (C0\C) against illumination time are appeared in **Figure 9**. From the kinetic graph, the ternary nanocomposite fits well and the outcome is in concurrence with the pseudo-first-order model. The impact of different scavengers on the photodegradation of MB dye solution was studied in order to recognize the role of receptive oxidative species in the photodegradation process. The role of H<sup>+</sup>

and O2 radicals were done individually, utilizing EDTA, 2-propanol, and BQ respectively. During the addition of EDTA and BQ, there were conspicuous variations in the photocatalytic process, which shows that H+ and O2 radicals are influences in MB dye degradation. But after the addition of 2-Proponal (scavenger for the OH radical), the degradation of MB is highly suppressed than other reactions, indicating the major of \*OH in MB dye degradation. From this result, it is clear that the photocatalytic degradation process is led by the contribution of hydroxyl radical (\*OH). After the addition of the as-prepared photocatalyst into the reaction and irradiating with visible light, the electrons were photoexcited from the valence band (VB) to the conduction band (CB). Once electrons are excited, the hole act as an oxidizing agent and oxidize the aquatic or the dye directly to form \*OH radicals. These OH reactive species are responsible for the efficient degradation of organic pollutants in water. The following equation represent the possible photocatalytic reaction mechanism of MB dye degradation under visible light irradiation.

<sup>g</sup> � C3N4*=*ZnO*=*MgAl LDH ð Þþ <sup>h</sup><sup>ν</sup> ! <sup>g</sup> � C3N4*=*MgAlLDH h<sup>þ</sup> <sup>þ</sup> <sup>e</sup>� ZnO

The **Figure 10** shows the schematic illustration of possible photocatalytic degradation of MB dye under visible light irradiation. The reusability of the prepared photocatalyst was studied by performing continual tests under same reaction conditions (shown in **Figure 11b**). The fresh MB solution was utilized for resulting cycles. Subsequently in each cycle, the prepared catalyst was isolated from the photocatalytic reactor through centrifugation. After 4 cycles, the degradation ability of the prepared catalyst was slightly reduced and it might be because of the loss

<sup>g</sup> � C3N4*=*MgAl LDH ð Þþ <sup>h</sup><sup>þ</sup> ! <sup>e</sup>� ð Þð Þ free � electrons

<sup>e</sup>� <sup>þ</sup> O2 ! <sup>O</sup>•

O•

**116**

h<sup>þ</sup> þ OH� ! OH h<sup>þ</sup> þ H2O ! OH þ H<sup>þ</sup>

2

<sup>2</sup> <sup>þ</sup> MB ! CO2 <sup>þ</sup> H2O By � product OH• <sup>þ</sup> MB ! CO2 <sup>þ</sup> H2O By � product <sup>h</sup><sup>þ</sup> <sup>þ</sup> MB ! CO2 <sup>þ</sup> H2O By � product

, OH

(3)

the pseudo-first-order kinetic curve [50].

*Assorted Dimensional Reconfigurable Materials*

*(A) Photocatalytic degradation and (B) pseudo-first-order kinetics for the degradation of MB over (a) ZnO (b) LDH(c) g-C3N4 (d) g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite [34].*

**Figure 10.** *Schematic illustration of proposed photocatalytic reaction mechanism.*

#### **Figure 11.**

*(a) Radical trapping experiments of active species over g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite and (b) reusability of g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite in the photodegradation of MB [34].*

of catalyst during the recycling process. The photocatalytic dye degradation activity of the prepared sample was compared to the previously reported nanomaterials, which is given in **Table 1**.


#### **Table 1.**

*Comparison table of MB dye degradation using different photocatalyst with degradation (%) of previously reported nanomaterials.*

Form the experimental results, it was confirmed that the as-prepared ternary nanocomposite exhibits remarkable photocatalytic activity and reusability under visible light to photo-degrade MB dye.

### **5. Conclusion**

In summary, the hydrothermally prepared 2D\2D ternary nanocomposite was used as an efficient photocatalyst for the photodegradation of MB dye. The nitrogenrich 2D\2D (g-C3N4 and Mg-Al LDH) surface significantly enhanced the photocatalytic efficiency under the visible light irradiation due to the improved photo active surfaces. Especially, in ternary nanocomposite Mg-Al LDH 2D nanoplates are vertically well aligned on the surface of the g-C3N4 2D nanosheets. This 2D/2D arrangement results effectively enhances the photocatlytic activity due to the efficient separation of photo-induced charge carriers and transfer by the incorporation of ZnO into LDH brucite layers. In addition, the g-C3N4 surface contributed to the efficient charge injection in the photocatalytic reaction. The novel g-C3N4\ZnO\Mg-Al LDH ternary nanocomposite can be used as a proficient material for the photocatalytic degradation of MB dyes under visible light irradiation.

**Author details**

**119**

Kandasamy Bhuvaneswari<sup>1</sup>

and Ganapathi Bharathi<sup>2</sup>

Salem, Tamilnadu, India

Guangdong Province, P.R. China

provided the original work is properly cited.

, Thangavelu Pazhanivel<sup>1</sup>

*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior…*

*DOI: http://dx.doi.org/10.5772/intechopen.89325*

1 Smart Materials Interface Laboratory, Department of Physics, Periyar University,

2 Key Laboratory of Optoelectronic Devices and Systems of Guangdong Province,

© 2020 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,

College of Optoelectronic Engineering, Shenzhen University, Shenzhen,

\*Address all correspondence to: pazhanit@gmail.com

\*, Govindasamy Palanisamy<sup>1</sup>

#### **6. Future aspects/prospective**


*LDH Ternary Nanocomposites: g-C3N4 Intercalated ZnO\Mg-Al for Superior… DOI: http://dx.doi.org/10.5772/intechopen.89325*
