Unveiling the influence of MTMS:TEOS ratios in silica layer membranes enhanced by cetyltrimethylammonium bromide

Silica-based thin-layer membranes, meticulously coated on alumina tubes, were synthesized from methyltrimethoxysilane (MTMS) and tetraethylorthosilicate (TEOS), which were further modified with cetyltrimethylammonium bromide (CTAB) and subsequently deployed for the brine desalination. Comprehensive characterization of the membrane materials was conducted employing Fourier Transform Infrared (FTIR) spectrophotometry, Gas Sorption Analysis (GSA), Thermogravimetric Analysis combined with Differential Scanning Calorimetry (TGA-DSC), Scanning Electron Microscopy (SEM), and an optical tensiometer. A detailed investigation was executed on the effects of varying MTMS:TEOS mole ratios, 10:90 (STL-1), 25:75 (STL-2), 50:50 (STL-3), 75:25 (STL-4), and 90:10 (STL-5), elucidating their impact on the structural attributes and functionalities of silica. These parameters were subsequently correlated with their respective desalination efficacies. The FTIR analysis underscored an evident association between the escalation in cyclic siloxane and methyl groups vis-à-vis increasing MTMS concentrations. An elevated MTMS content conferred the silica matrix with diminished porosity, augmented thermal resilience, a more refined surface, and pronounced hydrophobicity, albeit at the cost of reduced surface area and pore volume. Remarkably, the STL-5 silica membrane manifested optimum desalination metrics, boasting a salt rejection percentage of 99.99 % and a water flux rate of 5.61 kg m−2 h−1, thereby accentuating the intrinsic trade-off existing between salt rejection and water flux.