**3. Experimental**

### **3.1 Reagents**

A composite microfiltration membrane mud of Tunisian sand/zirconia with pore diameters in the range of 0.2 μm entirely prepared in our laboratory [35] was used. Every grafting process was performed using 10−2 mol.l−1 solution of 1H,1H,2H,2Hperfluorodecyltriethoxysilane (97%) supplied from Sigma-Aldrich, it was dissolved in ethanol with an analytical grade of 95% purchased from Chemi-Pharma.

### **3.2 Preparation and characterizations of hydrophobic membranes**

Hydrophobic membranes were prepared by grafting C8 onto the sand/zirconia ceramic membrane. Grafting is performed with several condensation reactions

between the OH groups found on the membrane surface and the silane functional group. Samples of flat membranes and tubular membranes are fully immersed in fluoroalkylsilanes solutions for 1 h at room temperature. After drying the samplers at 90°C for 1 h, the grafted ceramic membranes were rinsed successively in ethanol and acetone and finally placed in a 100°C oven for 1 h. The contact angles were measured at room temperature (23°C) using a Dataphysics OCA 15 camera with a resolution of 752 to 582 square pixels. The camera is equipped with a CCD camera and operates at an acquisition rate of four frames per second. The surfaces of the samples before and after grafting were characterized by scanning electron microscopy (SEM) (Hitachi S-4500). The pore diameter of the modified microfiltration layer was determined through the nitrogen adsorption/desorption isotherm using the 2010 Asap Micro Metrics Gas Analyzer, the exact diameter of the pores was determined using the BJH (Barret–Joyner–Halenda) method [36]. The permeability was obtained for membranes grafted by a home-made pilot plant.

## **3.3 Membrane distillation**

The setup scheme in **Figure 1** was used for the application of grafted membranes in the air-gap membrane distillation process. In this work, the solution to be treated was heated in a stainless steel feed tank and then distributed in the filtration module. The working temperature on the power side ranged from 75 to 95°C, while on the cooling side was kept constant at 5°C. Permeate vapor will be condensed on a surface of cooled stainless steel near the membrane (**Figure 1**). The temperatures were measured with two thermometers located at the feed cell frame and at the cooling plates. It is noted that each analysis was performed at least twice. The water permeates flux was determined by measuring the volume of distilled water permeate as a function of time.

### **3.4 Saline water**

Both kinds of saline water were used: NaCl solutions prepared by using deionized water and pure NaCl (ProLabo) in the concentrations range of 0.5–3 mol NaCl.L−1 and seawater from SIDI MANSOUR Sea located in the city of Sfax (Tunisia) with salt concentration at about 0.5 mol.L−1. The saline water was heated in a feed tank and then circulated through the membrane module in the air-gap membrane distillation configuration process. The feed velocity of the used circulation water is 2.6 m.s−1. The feed pan temperature ranges from 75 to 95°C, while keeping the cooling system side temperature constant at 5°C.
