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，对清洁饮用水的需求不断增加和短缺已成为本世纪前所未有的紧迫问题。从全球来看，几乎每10个人中就有2个人无法获得清洁饮用水，据世界卫生组织称，每天有3 900名儿童死于由不安全的水/卫生条件差传播的各种疾病。根据联合国《世界水资源发展报告》，这一令人不安的困境预计将在2050年大幅恶化，届时地球上至少四分之一的人口将生活在长期或反复遭受淡水短缺的国家。现有的淡水水体需要得到保护，必须通过成本更低、能源更少的新的净水方法来产生新的清洁水源，以满足日益增长的需求。这需要更好和创新的水处理技术。膜基水过滤优于消毒、蒸馏或介质过滤方法，因为过程更清洁，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常规的高分子材料，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，例如：高能耗、低通量、拒绝妥协、高有机和生物污染；由于对高温、氧化剂、酸性/碱性介质和有机溶剂的耐受性较差，因此对新型水处理工艺的研究具有重要的推动作用。在过去的十年中，纳米技术已经完全从学术研究转变为商业现实。人们已经尝试使用纳米材料、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在解决传统膜过滤的一个基本瓶颈方面仍然存在缺陷——需要多余的外部压力来克服盐溶液的渗透压，以驱动纯水通过半透膜。在没有外力的情况下，水分子在渗透压下的运输似乎违反了基本的热力学定律，但这样的自然现象确实存在。耐盐树是自然界中最简单的例子之一，它们利用红树林叶片蒸发毛细力产生的高度负压，有效地将环境中的盐水转化为淡水。在这个提案中，申请人的目标是设计一种新型的膜，它模仿天然膜，从而实现自驱动的水输送。

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.