IIT Guwahati scientists use nature's techniques to harvest water from air

The team has developed novel materials inspired by plants such as lotus and nepenthes, and insects such as the beetle to design a water-harvesting technique from air

While India has made substantial improvements over the past decades in the availability and quality of potable water, the fact remains that its is facing a water crisis of gargantuan proportions. This is borne out by evidence and scientific estimates, one of which suggests that by 2030-- that's less than 10 year from now--the country will have only half the water it needs, if the current consumption practices persist. For starters, about four-fifths of the country's freshwater resources are consumed by agriculture, a sector devotes more than half its cultivable land to water-intensive crops such as sugarcane, rice and wheat. It also draws nearly a quarter of the planet's groundwater reserves, rendering a staggering 60 per cent of its districts critically depleted of this resource. 

The silver lining is that with increasing water scarcity, there have been attempts to collect and conserve water through non-traditional means, with some scientists turning towards nature to design innovative ways to harvest water.

A recent attempt in this area is one by researchers at the Indian Institute of Technology (IIT), Guwahati, who have developed novel materials that can efficiently draw water from atmospheric humidity. In regions of the world with scanty rainfall, plants and insects have devised ingenious strategies to pull and collect water right out of the air.

Mimicking this, scientists at IIT Guwahati are trying to build technologies that can pull out water from thin air, both literally and figuratively, says Uttam Manna, Associate Professor at the institute's Centre of Nanotechnology. Manna heads a team that is working on water-harvesting techniques using the concept of hydrophobicity or water-repelling nature of some materials. The team includes research scholars Kousik Maji, Avijit Das and Manideepa Dhar.

The concept of hydrophobicity can be understood by looking at the lotus leaf. The lotus leaf repels water due to the presence of a layer of air trapped between the leaf surface and the water droplet, which causes the droplet to slide off the leaf, says Manna.

A hydrophile, on the other hand, is a molecule that is attracted to water. In the natural world, the namib beetle survives by collecting condensation from the atmosphere on the hardened shell of its wings. The shell has miniscule bumps that are hydrophilic at the tip and hydrophobic on the sides. So while the hydrophilic surface attracts the water from the air the hydrophobic side repels it and allows the organism to collect and store it.

IIT Guwahati's experience 

The researchers used the concept of a chemically-patterned slippery liquid-infused porous surface (SLIPS) for the first time, to effectively harvest water from moist air.

Speaking about the design, Manna says the technology involves the introduction of a dual chemically-reactive porous polymeric surface, which is based on various bio-inspired interfaces. These are compared for their water-harvesting performances under identical experimental set-ups.

An improved water-harvesting performance, in which 1,100 mg of water per hour can be harvested using one sq cm of coating, was observed when an edible oil (olive oil)-infused hydrophilic slippery interface was used. In comparison a hydrophobic slippery liquid-infused porous surface yielded a water harvest of 800 mg an hour using one sq sm, while a superhydrophobic interface yielded 250 mg.

Both the growth and the shedding of condensed water droplets were accelerated using the synthesised hydrophilic slippery surface, indicating its superiority to both, superhydrophobic and hydrophobic surfaces. The shedding of the water droplets on a hydrophilic surface was observed right after 107 seconds of exposure to artificial fog, whereas more than twice that time (230 seconds) was required for shedding of water droplets on a hydrophobic slippery surface under identical experimental conditions. Further, the association of chemically-modulated hydrophilic patterns on hydrophilic slippery surface accelerated the shedding of condensed droplets.

Even the strategic physical confinement of the hydrophilic-slippery interface and the specific arrangement of chemically modulated hydrophilic patterns on a hydrophilic-slippery background accelerated the shedding of condensed water droplets from 107 seconds to only 15 seconds. Eventually, a physically confined hydrophilic SLIPS with chemically-modulated patterns yielded a highly efficient (4,400 mg water an hour from 190 sq cm) water-harvesting SLIPS. This current approach allowed to harvest water from fog, without demanding any external interventions.

“We have produced a highly efficient water harvesting interface where the fog collecting rate is really high,” said Manna.

The researchers have also compared the performance of pitcher plant (nepenthes)-inspired materials to other bio-inspired ideas and have found theirs to be superior in terms of efficiency of water harvesting.

To summarise, the researchers have tried to address two important issues through the current research studies. Firstly, a dual chemically-reactive and porous polymeric coating has been appropriately modulated for adopting different bio-inspired interfaces. Further, the water harvesting abilities of these interfaces were compared under identical experimental set-up.

Secondly, the current studies revealed that an appropriate arrangement of chemically modulated pattern and physical confinement of hydrophilic-SLIPS led to a rapid shedding (from 107 seconds to 15 seconds) of condensed water droplet, which helped achieve a highly efficient (4,400 mg per hour, on a 190 sq cm surface) water harvesting SLIPS.

An IIT Guwahati spokesperson says that while the technology is still being tested at the laboratory level, it is designed such a way that it should work in all around the country, including rural areas where access to electricity is limited.