# Designing Dual-Function Nanostructures for Water Purification in Sunlight
## 3 Results and Discussion
### Surface Properties  
The dual process of purification of water depends on the action of adsorption behavior and heterogeneous photocatalysis that happens at the interface of two phases. In order to increase the effectiveness of the dual process of purification water and get the optimum result, large specific surface areas can be obtained by developing the porous structures of the prepared materials. In addition, the other parameters of the texture of the materials are very important for purification of water; such as pore volume and pore size distribution. The porous structures have been described in different ways. They sometimes are networks built up of plane-parallel plates with spaces in-between running throughout the crystallite. In a different arrangement, they have uniform cylindrical small tubes and are randomly distributed in the substance. Other possible arrangements are a network consisting of globules with open spaces in-between being in contact with each other. Therefore, pore size distributions and surface area were measured through full nitrogen adsorption-desorption isotherms for the pure Zn-Al LDHs and their composites with graphene oxide Zn-Al-GO1, Zn-Al-GO2 and Zn-Al-GO3 and are shown in Figures 8 and 9. Figure 8: Nitrogen adsorption-desorption isotherm of: (**a**) Zn-Al LDH and (**b**) Zn-Al-GO1 (Inset-Pore size distribution of Zn-Al-GO1). The isotherm of Zn-Al-GO1 was convex to the high values of the relative pressure P/P\({}_{\rm o}\) while it was concave to the low values of P/P\({}_{\rm o}\) axis and in between, it was almost linear. It means that multilayers of the adsorbed nitrogen were formed by increasing relative pressure until P/P\({}_{\rm o}\) = 1. The knee of the isotherm was slightly sharp and the uptake of the adsorbed nitrogen at this point was used to estimate the surface area of the material. This isotherm is similar to type IV of [PERSON]'s classification [41], but, there was no plateau at the high relative pressure. Therefore, this isotherm belongs to pseudo-type II or sometimes calls type IIb [42]. In addition, it exhibited a hysteresis loop. According to the IUPAC classification, the shape of the loop allows us to assign this isotherm to H3 type. The hysteresis loop indicates that the material has micro- and/or meso-porous structures because the behavior of nitrogen adsorption during the filling of mesopores is different from the behavior of nitrogen desorption during the emptying of the mesopores because of capillary condensation. In addition, the isotherm has meniscus above P/P\({}_{\rm o}\) = 0.9. Many researchers [43] had discussed the mechanism of meniscus formation. They reported that when the meniscus formed at high P/P\({}_{\rm o}\), the pores have a slit shape. According to the IUPAC classification of hysteresis loops [44], type H3 loops are usually given by the aggregates of plate-like particles or adsorbents containing slit-shaped pores. These results agree with SEM images. The corresponding pore size distribution plot of Zn-Al-GO1 was shown in Figure 8 (inset). It could be seen that Zn-Al-GO1 had a broad mesopore size distribution in the range 20-500 A with maximum peaks at 50 A. These data agree with the results of the nitrogen adsorption-desorption isotherm which suggested that the mesopores were created from the aggregates of plate-like particles or slit shape of the aggregation of both the nanolayers of LDHs and the graphene oxide sheets. In Figure 8, the comparison between the isotherms of both the pure Zn-Al LDHs and Zn-Al-GO1 indicated that the texture and porous structure of Zn-Al--GO1 are highly improved because of creating new micro-and meso-pores. The isotherms of Zn-Al-GO2 and Zn-Al-GO3, which contain higher concentrations of graphene oxides, showed unclear hysteresis loop as shown in Figure 9. It means that the graphene oxide may cause blocking for the micropores and some mesopores.