Desalination systems play a very important role in improving freshwater supplies, but some natural resources are too salty to be treated by current solutions. The salt content in this high-salinity water may be as much as 10 times that of salt water, and now scientists have developed a solar desalination system that relies on a special coating to fight the super-salt water.
High salinity water may be produced in industrial production, including oil and gas, and existing desalination systems produce strong saline water while separating fresh water. Therefore, these high-salinity water can not be treated by the common desalination technology, because it requires too much pressure, so it is very expensive and energy-consuming. At the same time, dealing with high-salinity water is often an expensive task.
A team of researchers from Columbia University developed the next generation of desalination systems last year, demonstrating how solvents can be added to high-salt salt water to extract salt at low cost and efficiency. And now a team of researchers from Rice University has found a breakthrough solution, also considered low-cost and efficient, using two-dimensional forms of boron nitride for desalination.
Boron nitride comes in a variety of shapes and sizes, but it has some very useful properties when forming a 2D hexa-shaped pattern (only a single atomic thickness). Sometimes referred to as “white graphene”, this material has great potential in the development of ultra-thin electronic devices and advanced solar cells. Now Rice University’s team has found that it can play a crucial role in treating salt water.
The team found that boron nitride in this form allowed larger temperature differences to be produced on both sides of the middle membrane of the desalination system. In one case, when salt water flows through one side of these porous membranes, it is heated by a special coating, which creates a temperature difference with cold fresh water on the other side. This, in turn, creates a pressure gradient that forces water vapor through the membrane to filter out salts and other contaminants.
The problem is that high-salinity water is more corrosive when heated, which immediately destroys the heating element in the device and makes it useless. Boron nitride, on the other hand, can grow a hexosphere layer on top of a stainless steel mesh, which is used as a heating element and is included in a commercial film.
This can be applied to solar desalination plants. In the device, the photo-active nanoparticles fixed to the membrane collect all the energy needed from the sun. In tests, the researchers found that the design was capable of desalination of high-salinity water, and that the film could produce 42 kg (92 lb) of fresh water per square meter (11 square feet), which they claim is 10 times thicker than current ambient solar film technology can provide.
This is because the voltage of the heating element operates at the same 50 Hz frequency as the home AC power supply and has a power density of up to 50 kW per square meter. Thanks to the special coating, the material reportedly maintains excellent stability and shows high thermal conductivity, water vapor permeability and corrosion resistance. Notably, the team was able to integrate technology into the helix membrane system, which foreshadowed a compact solution that could be transported and deployed as needed. Researchers are now looking for industry partners to help develop larger versions for field testing.
The study was published in the journal Nature Nanotechnology.
Source: Rice University