A flexible, scalable and completely biodegradable photothermal evaporator for highly efficient solar steam generation is fabricatedvia in situloading polydopamine particles in bacterial nanocellulose matrix during its growth.

To alleviate the scarcity of clean water, solar steam generation, which utilizes the green and abundant resources of Earth, has attracted considerable attention and been recognized as a sustainable technology to purify seawater and wastewater.

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Herein, the recent advances in realizing highly efficient cellulose-based solar evaporators for alleviating the global water crisis are summarized. Fresh water scarcity is one of most threatening issues for sustainable development. Solar steam generation, which harnesses the abundant sunlight, has been recognized as a sustainable approach to harvest fresh water. In contrast to synthetic polymeric materials that can pose serious negative environmental impacts, cellulose-based materials, owing to their biocompatibility, renewability, and sustainability, are highly attractive for realizing solar steam generators. The molecular and macromolecular features of cellulose and the physicochemical properties of extracted cellulose nanoparticles (cellulose nanocrystals and cellulose nanofibrils) and natural cellulose materials (wood and bacterial nanocellulose) that make them attractive as supporting substrate materials in solar steam generators are briefly discussed. Recent progress in designing highly efficient cellulose-based solar evaporators, including utilizing the extracted cellulose nanoparticles via bottom-up assembly (cellulose nanofibrils), natural cellulose materials with intrinsic hierarchical structure (wood and bacterial nanocellulose), and commercial planar cellulose substrates (air-laid paper, cellulose paper and cotton fabric) is reviewed. The outstanding challenges that need to be addressed for these materials and devices to be utilized in the real-world and in overcoming global water crisis are also briefly highlighted.

This study demonstrates a simple, stable, and scalable polydopamine (PDA) coated PVDF membrane for highly efficient solar-driven membrane distillation.

Conspectus In meeting the increasing need for clean water in both developing and developed countries and in rural and urban communities, photothermal membrane water treatment technologies provide outstanding advantages: For developing countries and rural communities, by utilizing sunlight, photothermal membrane water treatment provides inexpensive, convenient, modular, decentralized, and accessible ways to clean water, which can reduce the consumption of conventional energy (e.g., electricity, natural gas) and the cost of clean water production. In developed countries and urban communities, photothermal membrane water treatment can improve the energy efficiency during water purification. In these water purification processes, the light absorption and light-to-heat conversion of photothermal materials are important factors in determining the membrane efficacy. Nanomaterials with well-controlled structure and optical properties can increase the light absorption and photothermal conversion of newly developed membranes. This Account introduces our recent work on developing scalable, cost-effective, and highly efficient photothermal membranes for four water purification applications: reverse osmosis (RO), ultrafiltration (UF), solar steam generation (SSG), and photothermal membrane distillation (PMD). By utilizing photothermal materials, first, we have demonstrated how sunlight can be used to improve the membrane’s resistance to biofouling in RO and UF processes by photothermally induced inactivation of microorganisms. Second, we have developed novel SSG membranes (i.e., interfacial evaporators) that can harvest solar energy, convert it to localized heat, and generate clean water by evaporation. This desalination approach is particularly useful and promising for treatment of highly saline water. These new interfacial evaporators utilized graphene oxide (GO), reduced graphene oxide (RGO), molybdenum disulfide (MoS2), and polydopamine (PDA). The solar conversion efficiency and environmental sustainability of the interfacial evaporators were optimized via (i) novel and versatile bottom-up biofabrication (e.g., incorporation of photothermal materials during bacterial nanocellulose (BNC) growth) and (ii) easy and cost-effective top-down preparation (e.g., modification of natural wood with photothermal materials). Third, we have developed membranes for PMD that incorporate photothermal materials to generate heat under solar irradiation, thus providing a higher transmembrane temperature difference and higher driving force for effective vapor transport, making the membrane distillation process more energy-efficient. Lastly, this Account compares the photothermal membrane applications, summarizes current challenges for photothermal membrane applications, and offers future directions to facilitate the translation of photothermal membranes from the laboratory to large engineered systems by improving their scalability, stability, and sustainability.

Biofouling poses one of the most serious challenges to membrane technologies by severely decreasing water flux and driving up operational costs. Here, we introduce a novel anti-biofouling ultrafiltration membrane based on reduced graphene oxide (RGO) and bacterial nanocellulose (BNC), which incoporates GO flakes into BNC in situ during its growth. In contrast to previously reported GO-based membranes for water treatment, the RGO/BNC membrane exhibited excellent aqueous stability under environmentally relevant pH conditions, vigorous mechanical agitation/sonication, and even high pressure. Importantly, due to its excellent photothermal property, under light illumination, the membrane exhibited effective bactericidal activity, obviating the need for any treatment of the feedwater or external energy. The novel design and in situ incorporation of the membranes developed in this study present a proof-of-concept for realizing new, highly efficient, and environmental-friendly anti-biofouling membranes for water purification.

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