One of the most anticipated uses of nanomaterials for industrial applications is in the area of water management, which is central to heating, ventilation, and air conditioning; catalysis; natural gas production; bio-oil separation; and energy storage. But current approaches to synthesize these materials struggle to control their physical and chemical properties and typically require harsh reaction conditions, expensive templates, and solvents and surfactants that are a danger to the environment. The large amount of energy required by these conventional approaches also makes them cost-prohibitive.

Researchers at Pacific Northwest National Laboratory have developed a first-of-its-kind practical process for creating carbon-based nano-rods that address all these challenges while providing useful water adsorption and desorption properties. The patented process includes an approach to create rods, the created rods themselves, and an approach to recover water from rods at higher relative humidity.

To create rods, a growth medium comprising a switchable ionic liquid (SWIL) including an amidine- or guanidine-containing base (cation+), an alkyl xanthate (anion-), and an added iron (III) salt is incubated at 180 to 275 degrees centigrade for up to 16 hours or more. The dimensions of the completed nano-rods vary based on synthesis conditions and selected reagents. Incorporating components of the SWIL, these nano-rods are connected by a nexus or junction that dynamically adsorbs and desorbs moisture as a function of relative humidity or moisture content in the surrounding atmosphere.

When kept to a constant temperature and pressure, nano-rods adsorb a quantity of water when exposed to a certain relative humidity. They then spontaneously release water as mist when exposed to a second higher relative humidity. The process works at temperatures ranging from 1 to 99 degrees centigrade. Like a sponge, these nano-rods wring themselves out before they are fully saturated with water, giving them unique water management properties. This water recovery approach can be repeated, allowing continuous adsorption and desorption cycles.

APPLICABILITY

These nano-rods could be used for

• Water collection, purification, and separation
• Creation of water-selective and water-responsive membranes
• Dehumidification and desiccation
• Water pumping
• Heating, ventilation, and air conditioning
• Humidity selection and control
• Creation of humidity-responsive devices
• Energy storage
• Catalysis and oxidation of hydrocarbons.

For example, they could be used for low-energy water harvesting and purification for the developing world and fabric that automatically pulls sweat away from the body and releases it as a vapor.