Development, testing, and molecular dynamics simulation of a membrane that resists fouling by gel pollutants for humidification–dehumidification–type seawater desalination

Abstract

Humidification-dehumidification-type seawater desalination is an effective technology for solving the ongoing water shortage issue. As organic acid-rich seawater contains many amphiphilic gel pollutants, it is necessary to develop a membrane with anti-gel-fouling characteristics. Most of the previous studies have focused on the hydrophobic functionalisation of the membrane surface or the introduction of certain anti-fouling components to remove contaminants, such as salts or proteins, from membranes. In contrast, the contamination of membranes with gels has rarely been investigated. In this study, a commercial membrane was modified with citric acid to overcome the contamination of the membrane surface with gel during organic acid-rich seawater desalination. A novel functional membrane was prepared by introducing citric acid into a polyvinylidene fluoride (PVDF) membrane. Then, SiO2 was loaded onto the membrane surface to form an electronegative layer and also improve its hydrophobicity by increasing the surface roughness. The SiO2-loaded membrane was further modified with low-surface-energy fluoroalkylsilane to render the membrane surface hydrophobic. During water treatment, citric acid combined with Ca2+ to form soluble complexes on the membrane surface, preventing the formation of gel. Preferential selection and steric hindrance prevented the aggregation of gelatinous particles on the membrane surface. The formation of the hydration layer prevents the partial adsorption of the hydrophobic gel on the membrane surface. Further, the highly electronegative layer on the membrane surface synergistically reduced the adsorption of the most electronegative gel. The so-modified PVDF membrane was used to treat brine with a high gel content, and the structural parameters, moisture permeability, and resistance to gel fouling of the new functional membrane were evaluated. In addition, molecular dynamics simulations were performed to clarify the mechanism through which the modified membrane resists gel fouling. The new functional membrane could satisfactorily prevent gel pollution during seawater desalination.