Membrane distillation properties of TiO2 ceramic membranes modified by perfluoroalkylsilanes

Abstract

The tubular and planar TiO2 ceramic membranes were modified by grafting with perfluoroalkylsilanes (PFAS) molecules. Two types of PFAS were used for grafting process: 1H,1H,2H,2H-perfluorooctyltriethoxysilane (C6) and 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (C12). Studies showed that hydrophilic surface of titania ceramic membranes can be efficiently modified as a results of the proposed grafting method. Grafting efficiency of the tubular membranes was determined by measurement of liquid water entry pressure (LEPw), whereas grafting efficiency of planar membranes was verified by contact angle measurement. The contact angle values of the planar membranes are 130 and 140° for grafting with C6 and C12, respectively. The LEPw of the tubular membranes increased from 2 bar to 10 bar after modification by C12, whereas the LEPw values were constant at 2 bar when TiO2 membrane was modified by C6 molecules. It was found that water contact angle, LEPw, and water flux in the membrane distillation (MD) process essentially depend on the time of grafting and the type of PFAS used. Retention coefficients for both membranes are very high, close to unity. The results were additionally analyzed using chemometric simplex method, this resulted in determining the optimum time of grafting. For the membrane grafted by C6, the optimum time according to simplex method was equal to 26 h (flux 4055 [g h-1 m-2]), whereas for a membrane grafted by C12 was 17 h (flux 4535 [g h-1 m-2]). The highest fluxes of permeate in MD were observed for the optimum times of grafting.