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

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.