**Abstract**

A new inorganic hydrophobic porous membrane was prepared and applied in desalination with the air-gap membrane distillation process. Ceramic supports from lowcost natural Tunisian sand have been elaborated by the extrusion method. The microfiltration layer has been elaborated from ZrO2 powder by slip casting technical using a solution of water, sand powder, and polyvinyl alcohol solution. The hydrophobic surface of the active layer was elaborated by grafting 1H,1H,2H,2H-perfluorodecyltriethoxysilane on the ceramic microfiltration membrane surface (Tunisian Sand/Zirconia), to prepare a hydrophobic surface. The contact angle method allows showing the hydrophobic nature on the grafted membrane surface since it increases from 25° before grafting to values exceeding 140° after grafting. The efficiency of the grafting process was characterized by scanning electron microscopy (SEM). The membrane permeability varies from 700 l.h−1. m−2 before grafting to 10 l.h−1.m−2 after grafting. The new hydrophobic membrane seems to be promising in the field of membrane distillation. Salt retention higher than 98% was obtained using a modified microfiltration ceramic membrane.

**Keywords:** membrane, ceramic, hydrophobic, Tunisian sand, desalination

## **1. Introduction**

Currently, several searches are focusing on the different applications of ceramic membranes [1–3]. The major application fields for ceramic membranes are water purification, pharmaceutical industries, and biotechnology. In this research work, we have prepared a ceramic microfiltration membrane that used the mud of hydrocyclone laundries of phosphates as support, which has very interesting properties in terms of mechanics, chemical resistance, and thermal compared with commercial inorganic ceramic membranes based on pure oxide mineral material such as zirconia, titania, and alumina [4]. Because of the presence of surface hydroxyl groups, these ceramic materials originally have a hydrophilic appearance that can form bonds easily with water molecules [1, 5, 6]. Modifying the hydrophilic character into hydrophobic ceramic membrane is very interesting for several applications. The grafting process

can be performed by reaction between the -OH surface groups of the microfiltration layer and the ethoxy (O-Et) groups of the organosilane, leading to the increase of the hydrophobic properties [5, 7, 8]. Changing the hydrophobicity of the microfiltration layer surface would expand the potential applications of this material. The modification of the microfiltration layer surface allows forming a monomolecular layer of organosilane nature on the ceramic microfiltration layer [9, 10]. Fluoroalkylsilanes are organic groups used to modify the nature of different surfaces and create hydrophobic properties [11–13]. Several researchers have used the transplant process of different fluoroalkylsilanes on the surface of zirconia, silica, titania, and alumina membranes and their applications in different fields [5, 8, 14–16]. The modified inorganic ceramic membranes will be used, for example, in pervaporation and membrane distillation processes. Due to its hydrophobic character, the membrane will not be wet by the aqueous supply solution; then filling of the pores will occur due to capillary forces. The membrane distillation is a thermally driven separation process; in this case, only vapor is transported through a membrane. The membrane distillation technique allows potential applications in several fields of great scientific and industrial interest. It has been used in the treatment and purification of thermally sensitive industrial products such as the concentration of aqueous solution for wastewater treatment [17], water desalination [18–21], fruit juices [22] and in the pharmaceutical industry [23]. The technique of air-gap membrane distillation configuration was used in this work because it is simple to be performed in the laboratory, and it generally produces high water permeate flux. Inorganic ceramic membranes have several advantages in the application of oil-water separation, such as high mechanical strength, chemical inactivity, and thermal stability. Currently, a large amount of oily wastewater is discarded by food industries, petrochemical, and pharmaceutical, leading to further pollution of the environment. Widely used methods of purification of oily wastewater, such as air flotation, gravity separation, coagulation, skimming, and flocculation, have many disadvantages such as high operating costs, low efficiency, corrosion, and recontamination problems [24, 25]. The most widely used techniques are based on the membrane separation process such as dehydration of oil emulsion by pervaporation [26], by reverse osmosis [27], flocculation followed by microfiltration [28], microfiltration alone [29], membrane distillation [30], and ultrafiltration [31].

In this work, a microfiltration membrane prepared of sand/zirconia was surface modified with grafted perfluoroalkyl-silane. Ceramic membranes surface grafted with perfluoroalkyl-silane changed the hydrophilic character into a hydrophobic one. The prepared hydrophobic ceramic membrane was used for water desalination for the air-gap membrane distillation process. It is noted that fresh water can be produced from NaCl solutions as well as seawater.
