Tuning nanofiltration membrane performance: OH–MoS2 nanosheet engineering and divalent cation influence on fouling and organic removal

Natural organic matter (NOM) present in surface water causes severe organic fouling of nanofiltration (NF) membranes employed for the production of potable water. Calcium (Ca2+) and magnesium (Mg2+) are alkaline earth metals present in natural surface water and severely exacerbate organic fouling owing to their ability to cause charge neutralization, complexation, and bridging of NOM and the membrane surface. Hence, it is of practical significance to engineer membranes with properties suitable for addressing organic fouling in the presence of these cations. This study employed OH-functionalized molybdenum disulphide (OH–MoS2) nanosheets as nanofillers via the interfacial polymerization reaction to engineer NF membranes for enhanced removal of NOM and fouling mitigation performance. At an optimized concentration of 0.010 wt.% of OH–MoS2 nanosheet, the membrane was endowed with higher hydrophilicity, negative charge and rougher membrane morphology which enhanced the pure water permeance by 46.33% from 11.2 to 16.39 L m−2 h−1 bar−1 while bridging the trade-off between permeance and salt selectivity. The fouling performance was evaluated using humic acid (HA) and sodium alginate (SA), which represent the hydrophobic and hydrophilic components of NOM in the presence of 0, 0.5, and 1 mM Ca2+ and Mg2+, respectively, and the performance was benchmarked with control and commercial membranes. The modified membrane exhibited normalized fluxes of 95.09% and 93.26% for HA and SA, respectively, at the end of the 6 h filtration experiments, compared to the control membrane at 89.71% and 74.25%, respectively. This study also revealed that Ca2+ has a more detrimental effect than Mg2+ on organic fouling and NOM removal. The engineered membrane outperformed the commercial and the pristine membranes during fouling tests in the presence of 1 mM Ca2+ and Mg2+ in the feed solution. In summary, this study has shown that incorporating OH–MoS2 nanosheets into membranes is a promising strategy for producing potable water from alternative water sources with high salt and NOM contents

Functionalized MoS2 nanosheets enabled nanofiltration membrane with enhanced permeance and fouling resistance

In this study, a novel thin film nanocomposite (TFN) membrane incorporated with -OH functionalized molybdenum disulfide (OH-MoS2) nanosheets was fabricated through interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC) by addition of nanosheets in the aqueous phase. The physicochemical characterizations of the resultant TFN membrane confirmed the embedding of OH-MoS2 nanosheets and showed excellent compatibility with polypiperazine amide (PPA) matrix, as well as the nanosheets incorporation significantly increased the hydrophilicity, negative charge, surface roughness. In addition, the hydroxyl groups attached to the MoS2 nanosheets can be covalently bonded into the skin layer through its reaction with TMC, promoting excellent compatibility with the polymer matrix. At an optimum concentration of 0.010 wt% OH-MoS2, the TFN membrane exhibited 45.17% increase in pure water flux (84.14 L m−2 h−1) when compared to control membrane (57.96 L m−2 h−1) and maintained stable salt rejection for Na2SO4 (96.67%). This optimized TFN membrane exhibited high normalized flux of 96.92% when compared to 91.22% for control membrane and high flux recovery ratio of 98.88% was maintained as well as enhanced organic removal at 89.14% in terms of dissolved organic carbon (DOC) and 99.2% as ultraviolet absorbance at 254 nm (UV254) was recorded during 6 h filtration studies with humic acid containing feed water. 0.010 wt% OH-MoS2 incorporated membranes exhibited enhanced permeance, salt rejection and stability along with excellent fouling resistance and organic removal demonstrating the potential of OH-MoS2 nanosheets for engineering high performance and fouling resistant TFN NF membranes for water treatment

Removal of natural organic matter from surface water sources by nanofiltration and surface engineering membranes for fouling mitigation – a review

Given that surface water is the primary supply of drinking water worldwide, the presence of natural organic matter (NOM) in surface water presents difficulties for water treatment facilities. During the disinfection phase of the drinking water treatment process, NOM aids in the creation of toxic disinfection by-products (DBPs). This problem can be effectively solved using the nanofiltration (NF) membrane method, however NOM can significantly foul NF membranes, degrading separation performance and membrane integrity, necessitating the development of fouling-resistant membranes. This review offers a thorough analysis of the removal of NOM by NF along with insights into the operation, mechanisms, fouling, and its controlling variables. In light of engineering materials with distinctive features, the potential of surface-engineered NF membranes is here critically assessed for the impact on the membrane surface, separation, and antifouling qualities. Case studies on surface-engineered NF membranes are critically evaluated, and properties-to-performance connections are established, as well as challenges, trends, and predictions for the field's future. The effect of alteration on surface properties, interactions with solutes and foulants, and applications in water treatment are all examined in detail. Engineered NF membranes containing zwitterionic polymers have the greatest potential to improve membrane permeance, selectivity, stability, and antifouling performance. To support commercial applications, however, difficulties related to material production, modification techniques, and long-term stability must be solved promptly. Fouling resistant NF membrane development would be critical not only for the water treatment industry, but also for a wide range of developing applications in gas and liquid separations

2D nanosheet enabled thin film nanocomposite membranes for freshwater production – a review

Thin film composite (TFC) membranes are primarily used for commercial desalination and water purification applications by both reverse osmosis (RO) and nanofiltration (NF). The incorporation of 2D nanosheets across TFC membranes during interfacial polymerization generates a novel class of separation materials with higher permeability and selectivity, as well as greater chemical and thermal stabilities, supporting antifouling behaviours. Here, the potential of 2D nanosheet-based TFN to engineer materials of enhanced separation properties are critically discussed, in light of defect engineering approaches, types of unique properties of various nanosheets and Case studies on 2D nanosheet-based TFN membranes are critically compared, and properties-toperformance relationships are established to reveal trends and provide insights on the future of the field. The impact of the 2D nanosheets on the surface properties and interactions with solutes in water are extensively discussed. Challenges related to the TFN fabrication processes and leaching of nanosheets over time, which diminishes the scalability and long-term separation performance are also discussed. A vision for advanced and scalable manufacturing synthesis of nanosheets assemblies across or within TFN membranes is also evaluated alongside potential strategies to support the next generation of 2D-enabled separation membranes