# Easy Fabrication of Ultrafiltration Membrane via Polyethersulfone-Fumed Silica
## 1 Introduction  
The current global water crisis is an urgent issue that requires immediate attention. The UN World Water Development Report 2020 highlights an imminent global water crisis resulting from water overuse, uncontrolled water contamination, and climate change. These factors contribute to clean water shortages, posing severe risks to livelihoods [1]. Surface water and groundwater contamination, especially in developing and Global South countries, poses challenges for people seeking access to clean water that meets WHO standards [2]. Water filtration plays a crucial role in removing impurities and contaminants from water using various media such as sand, charcoal, ion exchange media, distillation, and membrane filtration [3]. The growing concern over water scarcity and the need for easy clean water access have driven significant advancements in polymeric membranes for water and wastewater filtration [4]. Polyethersulfone (PES) is commonly employed for membrane application at different levels, from microfiltration to nanofiltration. This vast range of applications is partly attributed to its strong mechanical properties and chemical stability in acidic/alkaline states [5]. Despite these advantages, the hydrophobic characteristic of PES membranes makes them prone to fouling, which subsequently reduces water flux over time [6]. Toimprove the anti-fouling properties of PES membranes, several additives have been investigated. [PERSON] et al. explored phospholipid biomimetic PES membranes by blending hydrophilic polymer and chloromethyl functional polyetheresulfone [7]. While in vitro blood circulation confirmed its excellent anti-coagulant properties, its low protein retention did not meet the standards for hemodialysis membranes. [PERSON] et al. studied the fouling behavior of mixed-matrix hollow fiber membranes PES/PVP/TiO\({}_{2}\) and observed an improved humic acid rejection compared to neat PES membranes, attributed to the higher surface hydrophilicity of TiO\({}_{2}\)-blended membranes [8]. Another study integrated Ti\({}_{3}\)AlC\({}_{2}\) MXene nanomaterials into a PES matrix to enhance membrane performance, demonstrating superior porosity and homogeneous pore size distribution due to the intrinsic properties of Ti\({}_{3}\)AlC\({}_{2}\)[9]. [PERSON] et al. used hydroxyapatite to enhance the PES membranes' anti-fouling properties, with the negative charge groups on hydroxyapatite enhancing wettability and reducing irreversible fouling [10]. Silica stands out as a highly favorable inorganic additive owing to its low cost, ease of synthesis, and easy surface modification, hence enabling tailored properties for specific purposes. In the context of polymeric membranes, silica nanoparticles are often synthesized and incorporated into polymer structures as additives to achieve better performances. Researchers have explored functionalizing silica with various other materials into ultrafiltration membranes to enhance their performance, such as PVDF/Silica/Psf composite [11], zwitterionic functionalized silica nanogel [12], high-porosity silica sodalite [13], tetraethyl orthosilicate [14], and pyrazole-modified mesoporous silica [15]. Fumed silica nanoparticles are a promising membrane modifier candidate. Fumed silica is manufactured by the combustion of volatile silanes in an oxygen-hydrogen flame, hence offering a variety of fascinating properties, exhibiting a smooth and nonporous particle surface [16]. [PERSON] et al. analyzed the impact of fumed silica particles as an inorganic additive on a polyvinylidenefluoride (PVDF) membrane, a microfiltration-range membrane, using dimethyl acetamide (DMAAc) as a solvent. They revealed that while the PVDF-FS blend membrane exhibited significantly higher flux, it also had a high fouling tendency because its hydrophobicity increased [17]. [PERSON] et al. synthesized non-fluorinated coatings for high-performance superhydrophobic coatings.