Introduction Silicalite-1 zeolite membrane has a high separation performance due to its hydrophobic properties, which can preferentially permeate organic molecules and effectively block water molecules in aqueous-organic phase mixtures. However, the hydrophilic Si—OH on the surface of Silicalite-1 zeolite membrane is one of the most important reasons for the low hydrophobicity and selectivity of membrane, which preferentially adsorbs water molecules, and easily reacts with ethanol in the solution and generates Si—OC2H5 to block the zeolite pores. To solve the problems above, the n-octyltriethoxysilane (OTES) was grafted onto the surface of Silicalite-1 zeolite membrane to eliminate Si—OH, further improving hydrophobicity and separation ability of the membrane. The effects of mass fraction of OTES, reaction temperature and modification time on the membrane modification were investigated. The modification mechanism was analyzed, and the pervaporation stability of Silicalite-1 zeolite membrane before and after modification was compared.Methods A molar ratio of precursor solution was n(TEOS):n(TPAOH):n(H2O):n(NaOH) of 1.00:0.05:75.00:0.03. Silicalite-1 zeolite with a particle size of 400 nm was used as seeds to prepare Silicalite-1 zeolite membranes by a secondary growth method. The membranes were hydrothermally crystallized at 175 ℃ for 8 h. After washing, the membranes were calcined at 550 ℃ for 4 h to remove the template, obtaining silicalite-1 zeolite membranes.Silicalite-1 zeolite membranes were placed in a solution with OTES as a solute and toluene as a solvent at different mass fractions of 1%-5%, and modified at 20-100 ℃ for 5-20 h. The membranes were washed with anhydrous ethanol to remove the residual solvent, and finally dried at 80 ℃ for 12 h to obtain the OTES@Silicalite-1 zeolite membranes.The separation performance of OTES@Silicalite-1 zeolite membranes was tested by a laboratory homemade pervaporation device. The membrane flux was calculated via a weighing method, the separation factor was analyzed with the solution composition data on the feed-side and permeate-side. The physical phase composition of the membranes was determined by X-ray diffractometry. The chemical bonds and functional groups of the membranes were analyzed by Fourier transform infrared spectroscopy. The microscopic morphology and elemental distribution of the membranes were determined by scanning electron microscopy. The hydrophobicity of the membranes was analyzed via water contact angle measurement.Results and discussions The separation factor of OTES@Silicalite-1 zeolite membranes shows an upward trend with the increase of the mass fraction of OTES. A part of the Si—OH on the membrane surface are replaced by OTES, and the membrane surface becomes more hydrophobic, which favors the adsorption and diffusion of ethanol molecules. At the OTES mass fraction of 3%, the OTES@Silicalite-1 zeolite membrane has the maximum separation factor. However, the separation factor decreases as the mass fraction of OTES further increases. This is possibly due to the excess OTES covering the pores on the membrane surface and affecting the transportation of ethanol. As Si—OH eliminates, the amount of Si—OC2H5 decreases, so the membrane flux trenda upward initially. However, the hydrophobicity of OTES hinders the water molecule transportation, thus reducing the membrane flux.As the temperature increases, the grafting reaction is easier to accomplish, and the hydrophobicity of the OTES@Silicalite-1 zeolite membrane enhances. At 60 ℃, the membrane shows the maximum separation factor and membrane flux. However, the separation performance of the membrane decreases slightly as the temperature further increases, which is attributed to the excessive and promiscuous organic groups that block ethanol permeation, while reducing water flux.The hydrophobicity and selectivity of the membrane improve at 5-10 h as the modification time increases. At 10 h, the membrane has the maximum separation factor. However, the separation performance of the membrane decreases sharply as the modification time further increases possibly due to the OTES cross-link with each other to form polymers, which severely block the pores of the zeolite, resulting in a significant decrease in membrane flux. Also, the transport of ethanol is impeded, thus decreasing the separation factor.Conclusions The surface modification of OTES could not damage the framework and crystal structure of Silicalite-1 zeolite membrane. It could effectively eliminate the Si—OH on the membrane surface, improve the hydrophobicity and separation performance of the membrane. The Silicalite-1 zeolite membrane showed the membrane flux of 0.92 kg·m-2·h-1 and the separation factor of 30.4 at 70 ℃ for 3.5%±0.1% ethanol aqueous solution, which was modified at a mass fraction of OTES of 3% and 60 ℃ for 10 h. Meanwhile, this membrane could also maintain a great stability during the pervaporation test for 120 h. This study indicated that alkylsilane grafting could be an effective measure to substantially improve the hydrophobicity and separation performance of Silicalite-1 zeolite membrane, having promising application prospects in the field of organic component recovery by pervaporation.