Nature-inspired self-powered reverse osmosis membranes for sustainable water purification

由于快速城市化、人口增长、严重滥用和气候变化，清洁饮用水的需求和短缺日益增加，已成为本世纪前所未有的紧迫问题。在全球范围内，每10人中就有近2人无法获得清洁饮用水，根据世界卫生组织的数据，每天有3900名儿童死于由不安全的水/糟糕的卫生条件传播的各种疾病。根据联合国世界水发展报告，到2050年，这一令人担忧的困境预计将大幅恶化，届时地球上至少四分之一的人将生活在一个遭受长期或经常性淡水短缺的国家。现有的淡水水体需要得到保护，必须通过新的净水方法产生新的清洁水源，以更低的成本和更少的能源来满足日益增长的需求。这就需要更好、更创新的水处理技术。基于膜的水过滤方法优于消毒、蒸馏或介质过滤方法，因为它的工艺更清洁，而且不需要热输入和废介质的再生。到目前为止，大多数分离和水过滤膜都是基于传统的聚合物材料，如纤维素、聚酰胺、聚砜、聚偏氟乙烯、聚丙烯腈等，这些膜过滤技术的限制因素包括：高能耗、低通量、截留妥协、高有机和生物污染；对高温、氧化剂、酸碱介质和有机溶剂的耐受性差，这为开展新的水处理工艺研究提供了重要的动力。在过去的十年里，纳米技术已经完全从学术研究转变为商业现实。人们试图用纳米材料、微凝胶、交联蛋白等来构建膜。然而，使用先进材料的新材料或基于设计的创新仍然不能解决传统膜过滤中的一个根本瓶颈--需要额外的外部压力来克服盐溶液的渗透压力，从而使纯水穿过半透膜。在没有外部驱动力的情况下，水分子在渗透压下的传输似乎违反了基本的热力学定律，但这种自然现象是存在的。耐盐树是自然界中最简单的例子之一，它通过利用红树林叶子中蒸发的毛细管力产生的高度负压，有效地将环境中的咸水转化为淡水。在这项提案中，申请人的目标是设计一种新型的膜，它模仿自然膜，从而能够实现自动驱动的水传输。

Increasing demand for and shortage of clean drinking water as a result of rapid urbanization, population growth, gross misuse, and climate change have become an unprecedented urgent issue in this century. Globally nearly 2 in every 10 people lack access to clean drinking water, and according to World Health Organization, 3,900 children die every day due to various diseases transmitted by unsafe water/poor hygiene. According to the U.N. World Water Development Report, this troubling predicament is projected to worsen substantially by 2050, when at least a quarter of the people on Earth will live in a country suffering from chronic or recurring freshwater shortages. The existing freshwater bodies need to be protected and new sources of clean water must be generated through new methods of purifying water at lower cost and with less energy to meet the growing demand. This requires better and innovative water treatment technology. Membrane-based water filtration is superior to the disinfection, distillation, or media filtration methods because of the cleaner process and requires no thermal inputs and regeneration of spent media. So far, the majority of separation and water filtration membranes are based on conventional polymeric materials, such as cellulose, polyamide, polysulfone, polyvinylidene fluoride, polyacrylonitrile, etc. The limiting factors for these membrane-based filtration technologies include, for example: high energy consumption, low flux, rejection compromise, high organic and biological fouling; poor tolerance to high temperature, oxidizing agents, acidic/alkaline medium, and organic solvents, impart significant impetus to deliver new research for novel water treatment process. Over the past decade, nanotechnology has totally transformed from academic research to commercial reality. Attempts have been made to construct membranes using nanomaterials, microgels, cross-linked proteins etc. The new materials or design-based innovations using advanced materials, however, are still deficient in tackling one of the fundamental bottlenecks in conventional membrane filtration - the requirement of surplus external pressure to overcome the osmotic pressure of the salt solution to drive pure water across a semipermeable membrane. Transport of water molecules against the osmotic pressure in the absence of an external driving force seems to break the fundamental thermodynamic laws, but such natural phenomena exist. Salt-tolerant trees are one of the simplest examples in nature that efficiently convert the salty water of its environment into freshwater by using highly negative pressure that is generated by evaporative capillary forces in mangrove leaves. In this proposal, the applicant aims to design a new type of membrane which mimics the natural membranes such that self-driven water transport can be achieved.