# Designing Dual-Function Nanostructures for Water Purification in Sunlight
## 3 Results and Discussion
### Water Purification by Dual Process: Adsorption and Photocatalysis  
According to the enhancement of surface texture and narrowing of the band gap energy of Zn-Al LDHs after introducing graphene oxide in its structure, the adsorption behavior and the photocatalytic  
Figure 11: Band gap energy of (**a**) Zn-Al LDH, and (**b**) Zn-Al-GO1. Figure 12: Band gap energy of (**a**) Zn-Al-GO2, and (**b**) Zn-Al-GO3. activity of Zn-Al-GO1, Zn-Al-GO2 and Zn-Al-GO3 were studied and compared with the pure Zn-Al LDH through removal of the colored pollutants. Therefore, the adsorption behavior of Zn-Al LDHs was determined by mixing the solid material with acid green 1 in the dark for 1 h and measuring the UV-Vis spectra two times for getting equilibrium state. Figure 13d showed 35% of dye removal by using the pure Zn-Al LDHs. After introducing the lower percentage of graphene oxide, the removal of dye increased to be 48% using Zn-Al-GO1 as shown in Figure 13e. However, by further increasing the content of graphene oxide, the dye removal decreased to be 32.7% and 11.2% in the case of using both Zn-Al-GO2 and Zn-Al-GO3; respectively as shown in Figure 13b,c. It means that graphene oxide has positive and negative role in the adsorption behavior of Zn-Al LDHs depending on the content of graphene oxide. In the case of using Zn-Al-GO1, the 1.3% of graphene oxide has positive role for improving the efficiency of water purification by increasing dye removal through adsorption process. These results can be explained according to the results of surface properties. Where, this percentage caused production for new micro- and meso-porous structure for Zn-Al LDHs accelerating the diffusion of dyes and trapping the organic molecules of dyes inside the structure. The photocatalytic activity of the prepared materials was examined through the degradation of green dye in presence of sunlight. The photocatalytic degradation of the dye was investigated by irradiating the aqueous solution of the green dye with the sunlight in presence of the prepared material. After the irradiation of sunlight for certain hours, the absorbance of the liquid portion is measured. The degradation of the dye was followed by the reduction of the absorption of the dye at \(\lambda_{\text{max}}=714\) nm, while the naphthyl rings, which produce from the degradation of acid green 1, can be followed through the absorption peaks lower than 400 nm as shown in Figure 13. A blank test was achieved without a photocatalyst. The green dye was found to be stable towards irradiation of light as shown in Figure 13a. The photocatalytic degradation of acid green 1 was studied as a function of the sunlight irradiation time in presence of the prepared material. The green dye removal efficiency with the pure Zn-Al LDHs was only 45.9% under irradiation with sun light for 3.5 h. This low removal efficiency was mainly attributed to the low excitement of the pure Zn-Al LDHs under irradiation with visible light. After introducing 1.3% of graphene oxide inside Zn-Al LDHs, we observed that the photocatalytic degradation of Zn-Al-GO1 improved to be  
Figure 13: Absorbance spectra of acid green dyes after 1 h in dark in presence of (**a**) standard sample, (**b**) Zn-Al-GO3, (**c**), Zn-Al-GO2, (**d**) Zn-Al LDH and (**e**) Zn-Al-GO1. 100% after 3.5 h of irradiation of sun light causing a complete decolorization and mineralization as shown in Figure 14. However, the green dye removal degradation for ZnAl-GO2 and Zn-Al-GO3 were 49.5% and 19.4%; respectively.