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BACKGROUND: Membrane distillation (MD) for desalination encounters significant hurdles as a result of pore wetting, leading to reduced permeate flux or deterioration in permeate quality over time. Therefore, membranes used in MD must be highly hydrophobic to prevent liquid from entering the pores and contaminating the permeate stream. In this study, a thin layer of MoS2‐TiO2 composite was coated using poly (DOPA) as an adhesive to enhance attachment. Two coating methods, interlinking and layering, were compared to determine the most effective method for forming a thin hydrophobic coating layer onto PVDF‐PES hollow fiber membrane. RESULTS: Interestingly, this study revealed that increasing the number of dipping cycles led to higher flux, defying conventional expectations. This unexpected outcome is likely to have resulted from the thicker coatings creating a more hydrophobic surface, reducing water molecule adhesion and preventing wetting. Consequently, the membrane demonstrated enhanced flux despite its increased thickness. Among the membranes tested, the MoS2‐TiO2/PVDF‐PES membrane coated using the layering method exhibited the best performance, leading to a flux of 2.06 kg m−2 h−1 and 99.99% salt rejection. This superior performance can also be attributed to the membrane's hydrophobic properties, evident in its water contact angle (WCA) of 99°. By contrast, the interlinking method resulted in lower performance, with a permeate flux of 1.70 kg m−2 h−1 and 99.96% salt rejection, which is likely to have resulted from its lower WCA of 86°. CONCLUSION: The findings from this study suggest that the coating method has the potential to greatly improve membrane distillation performance through wettability modification rather than altering membrane porosity. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Recently, a thermally-driven membrane process known as membrane distillation (MD) has emerged as an alternative to the high-pressure membrane process for contaminants removal from water. The driving force for MD is a vapor pressure gradient produced by a temperature differential across a hydrophobic porous membrane, which results in the transfer of water vapor from hot to cold side. However, the feasibility of MD for industry adoption is hampered by several issues such as temperature polarisation effects, low permeate flux, membrane wetting, and fouling. The membrane properties are known to have a significant role in controlling the final performances of MD. This review first looks into the feature of ideal MD membrane properties. Then, the use of graphenebased materials for the development of high performances MD membrane is discussed. Besides enhancing the water permeability and selectivity of MD, the incorporation of graphene offers additional properties such as anti-fouling, antibacterial, and photodegradation. The future direction of using graphene-based photothermal material in MD for heat generation under solar irradiation is also reviewed. It is found that the localised heating at membrane surfaces by photothermal material can minimise temperature polarisation effects and subsequently enhance the driving force for effective vapour transport. Thus, a more energy-efficient MD system can be developed. [ABSTRACT FROM AUTHOR]

This paper discusses the response surface methodology (RSM) study on a recent direct contact membrane distillation (DCMD) system. The DCMD system is reviewed due to its myriad attention on desalination process, especially on water treatment of high salinity and reclamation of industrial process water. The fundamental of DCMD, as well as the mass and heat transfer principles for modelling the system, are firstly explained and compared with previous studies. Then, the researcher highlighted the parameters involved in the modelling of DCMD process, such as feed temperature, velocity, and concentration, simultaneously with common membrane properties in mass and heat transfer models. The correlation of these frequently studied parameters with the conventional model was included and summarised. Subsequently, RSM was performed for the model development of the DCMD system, which included common design matrix applications, such as Box–Behnken, central composite design, and full factorial design. Finally, this work reviews the most recent application for the DCMD modelling of the model, comparing its experimental number runs, independent input number, model levels, and accuracy for optimising the DCMD process using RSM. [ABSTRACT FROM AUTHOR]

In this work, the surface of a PVDF-based hollow fiber membrane was modified by coating MoS 2 -TiO 2 to improve the performance of membrane distillation (MD). The MoS 2 -TiO 2 was first synthesized at different ratios using a one-step hydrothermal process. Then, the PVDF-based hollow fiber membrane was spun at various air gaps and PES was also added as an additive. As 5M5T (50 wt% MoS 2 and 50 wt% TiO 2) possessed better physicochemical properties and narrow band gap, the 5M5T was mixed with trichloro(octadecyl)silane in (OTS) at various loading to form a dip-coating solution. The PP20 membrane (PVDF + PES) spun at a 20 cm air gap was used as a support for MD due to its high porosity and low membrane thickness. It was observed that the contact angle of the MoS 2 -TiO 2 /PP20 membrane increased significantly to 136.8 ± 2.33° when the membrane was coated with 0.2% of 5M5T MoS 2 -TiO 2. The MD performances were investigated via an in-house MD system. The results revealed that the performances of MoS 2 -TiO 2 /PP20 membranes were much higher than previously reported membranes due to their enhanced hydrophobicity and porosity properties. It was observed that a higher operating temperature could elevate the permeate flux up to 23.3 kg·m−2·h−1, but less than 0.1% changes in the rejection rate. The results obtained in this work suggest that the MoS 2 -TiO 2 coated on the PVDF-based membrane can overcomes the typical permeability/rejection rate trade-off effect, which can play a significant role in enhancing MD performances. [Display omitted] • The surface of PVDF-based hollow fibre membrane was modified using various loading of MoS2-TiO2. • The coated PVDF-based membrane possesses a higher contact angle and better hydrophobicity. • The permeate flux of coated PVDF membranes was higher due to their enhanced hydrophobicity and porosity. • The permeate flux increased significantly with minimal changes in salt rejection rate at various operating temperature. [ABSTRACT FROM AUTHOR]

Tapping into solar energy seems to be a viable and sustainable solution for the ongoing global challenges of water scarcity and clean energy shortage. However, the natural mechanism of solar energy-driven water evaporation is often compromised by low evaporation rate and water and solar absorption spectrum mismatch. Therefore, localized heating on the water vapor-liquid interface by light-absorbing materials, known as photothermal materials, has been proposed. This allows the harvesting of energy from the full solar spectrum and high efficiency of light-to-heat conversion. With the emerging advances of photothermal nanomaterials and the urgent demand for a green transition of water treatment technology, the establishment of a photothermal-driven membrane distillation system has been reinvigorated, as seen by the number of publications recently. The efficiency of light absorption and light-to-heat conversion of photothermal materials are critical factors in determining the membrane performances. This review aims to assess the state-of-the-art photothermal materials, including innovative modifications that have been made. The second part is devoted to the emerging aspects and new directions of using these photothermal materials for the development of photothermal membranes. Lastly, the prospects of photothermal membrane for clean water production in the near future are also discussed. [Display omitted] • There is an urgent demand for a green transition of water treatment process. • The state-of-the-art of photothermal materials is discussed. • The utilization of photothermal membrane for various applications is highlighted. • Photothermal membranes for water-energy-environment nexus • Prospect of photothermal membrane for water reclamation and purification [ABSTRACT FROM AUTHOR]