Simulation-Guided Engineering of Mg-Doped Silica Membranes via DFT and MATLAB: Toward High-Efficiency Desalination and Antibacterial Protection

Abstract

In this work, magnesium (Mg)-doped silica membranes were fabricated via a facile sol-gel method and systematically evaluated for multifunctional water purification applications with a specific focus on membrane distillation (MD). In this study, controlled incorporation of magnesium into the silica network effectively improves the membrane's hydrophobicity, structural compactness, and functional performance. This enhancement presents a novel and efficient strategy for developing high-performance membranes tailored to water desalination applications. Characterization using FTIR and SEM confirmed successful integration of Mg and trimethoxy-octyl-silane (C₈TMOS) into the silica matrix, leading to the formation of a dense, uniform surface with tunable hydrophobicity. Water contact angle measurements revealed superhydrophobic behavior at higher Mg loadings, ranging from 80° to 140°, indicating reduced wettability and improved liquid entry pressure. DCMD experiments using NaCl and Na₂SO₄ solutions (1000 ppm) showed significant enhancement in salt rejectionup to 98.3%and a stable permeate flux of 32 L/m²·h, especially for membranes doped with 15 wt % Mg. These improvements are attributed to densification and surface modification induced by Mg cross-linking, which inhibited pore wetting and maintained membrane stability during long-term operation. EDX and XRD confirmed elemental distribution and the amorphous structure of the membranes, respectively. Furthermore, density functional theory (DFT) simulations provided insight into the role of Mg in improving electronic structure, ion repulsion, and mechanical robustness at the molecular level. The membranes also exhibited strong antibacterial efficacy against and , suppressing over 90% bacterial regrowth. This multi-functionality, combining desalination efficiency, antifouling resistance, and antimicrobial activity, makes Mg-doped silica membranes a promising and scalable solution for sustainable water treatment, including high-salinity brines and industrial effluents.

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Schematic illustration for the method for the preparation of membrane.

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Ammonium citrate formation by sodium citrate.

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(A) Dynamic photograph of water droplet on Mg doped silica membrane at different times from 20 to 80 s. (B) Graph of time (s) vs contact angles (°) of Mg-doped silica membranes.

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Scanning electron microscopy (SEM) images comparing undoped and doped silica membranes. Subfigures (a) and (e) depict the surface and cross-sectional structures, respectively, of the undoped silica membrane, revealing a porous surface morphology. Subfigures (b, c, d, i) and (f, g, h, j) display surface and cross-sectional images under high magnification (5K×) respectively, of Mg-doped silica membranes exhibiting varying concentrations of dopant, characterized by porous structures and aggregation phenomena. Subfigure (k) provides energy-dispersive X-ray (EDX) analysis confirming the presence of Mg within the doped silica membranes.

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XRD diffraction pattern of Mg- doped SiO₂ membranes for 5, 10, 15 and 20% conc. shown the amorphous nature of Silica membranes.

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Comparison FTIR spectrum of samples with different concentrations of Mg doping.

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(A) UV–visible spectrum of silica membrane absorption with 10% Mg and 15% Mg and 20% Mg doping. (B) Comparison graph for band gap shows that upon increasing of dopant concentration band gap increases.

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(A) Graph of membrane composition versus the permeation flux used for the removal of salt. (B) Salt (Na₂SO₄ and NaCl) rejection from water.

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Zone of inhibition produced by undoped and Mg-doped silica membranes against (A) GPC and (B) GNC .

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(A) Membership functions for inputs (a) Mg doping concentration and (b) C₈TMOS concentration. (B) Membership functions for outputs (a) contact angle and (b) band gap.

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(A) 3D graph for input (C₈TMOS and Mg doping concentration along x and y axis, respectively) and its effect on the contact angle along the z axis. (B) 3D graph for input (C₈TMOS and Mg doping concentration along x and y axes, respectively) and its effect on the band gap along the z direction.

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Rule spectator for input and output of dopant concentration, silica source concentration, the contact angle, and band gap.

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(A) Structural model of Mg-doped silica membranes. (B) Ion size and density distribution from DFT simulations. (C) Geometry optimization trends linked to the density fields. (D) Relationship between the radius of gyration and perimeter (P).

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(A) Comparative evaluation of the elastic modulus, hardness, and thermal conductivity in magnesium-doped silica (Mg@SiO₂) membranes. (B) Ternary diagram illustrating the interplay among bond energy, potential energy, and magnesium content within the silica framework. (C) Correlative trends between membrane density, mechanical hardness, thermal conductivity, and elastic modulus. (D) Schematic depiction of how magnesium doping influences density distribution and pore size architecture.