Multifunctional Nano-enabled Membranes Toward Sustainable Seawater Desalination and Energy Production

Abstract

The growing concerns over global water scarcity, energy depletion, and environmental degradation have catalyzed the emergence of the water-energy-environment (WEE) nexus as a pivotal concept. Deciphering the intricate relationship among water, energy, and the environment is essential for achieving sustainable development goals. In this regard, membrane-based technology has garnered growing interest as an eco-friendly approach for addressing the water scarcity issue. However, challenges such as inefficient energy consumption, inadequate mass transfer, and membrane instability pose significant obstacles to its wider implementation. Nanomaterials have been employed to engineer membranes that excel in desalination efficiency with remarkable durability under challenging conditions. These innovations extend beyond mere water treatment, aiming to produce beneficial environmental effects by harnessing solar energy.

In the realm of water, thin-film composite (TFC) membranes have been widely utilized for their superior water permeability. However, the polyamide layer is vulnerable, especially under high chlorine concentration. To mitigate this issue, the first study of this dissertation presents a thin-film nanocomposite (TFN) membrane incorporated with amino-embedded carbon quantum dots (ACQDs). ACQDs were synthesized via hydrothermal method and subsequently incorporated into the polyamide layer of the membrane. The resultant ACQD-TFN membranes showed improved water permeability and maintained high salt rejection even under conditions of high chlorine exposure, showcasing their exceptional chlorine resistance and antifouling characteristics.

The second study introduces a novel photothermal-catalytic (PTC) membrane fabricated by incorporating MXene, a two-dimensional material with remarkable solar-to-heat capabilities. The MXene-PVA-TiO₂@PVDF membrane was fabricated through self-assembly and applied to a photothermal-catalytic membrane distillation (PMD) system. Driven by solar power, this system demonstrates simultaneously high desalination rates and photodegradation efficiency toward organic contaminated salt water. Furthermore, the chemical and mechanical stability of MXene was enhanced by the formation of MXene-PVA-TiO₂ 2D/3D network. This synergistic strategy not only promotes efficient solar energy utilization but also strengthen the membranes against environmental stressors, marking a significant step forward in the development of multi-functional membrane systems.

Shifting the focusing to energy, the third study integrates photocatalytic water splitting into photothermal MD. The innovative CdS/MXene hydrogel membrane, paired with the specialized PVMD system, enabled the concurrent production of water and hydrogen. This hydrogel membrane not only delivered substantial rates of freshwater flux and hydrogen generation but also demonstrated remarkable structural stability throughout extended periods of operation. The results confirm the effectiveness of the integrated PTC distillation system and underscore MXene-based membranes’ promising prospects for solar-driven applications, particularly its capability to co-produce water and green hydrogen.

The integration of cutting-edge nanomaterials into membrane technology heralds a transformative advancement in water treatment, addressing critical challenges such as wetting and fouling, and significantly enhancing water productivity and membrane stability. These nanomaterials, with their unique properties, not only improve the efficiency and longevity of membranes but also open innovative pathways for green energy production, thereby contributing to a sustainable WEE nexus. By mitigating common issues that have long plagued membrane technologies and facilitating energy recovery from water processes, this development promises a more efficient, sustainable, and environmentally friendly approach to managing the world’s water resources, aligning with the urgent need for solutions that support both our planet’s health and human prosperity.

Date of Award	19 Aug 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kyoung Jin Alicia AN (Supervisor)