Metal organic framework are highly porous solids with many internal channels and holes that easily absorb gases or liquids which will quickly release them when heated. MOFs are currently being tested to put more gas into tanks of hydrogen fueled cars, and to absorb carbon dioxide from smokestacks and store methane; building on Omar Yaghi’s pioneered vision on technology as part of joint research with King Abdul Aziz City for Science and Technology in Riyadh with the Center of Excellence for Nanomaterial and Clean Energy research.
Successful field tests have proved the team’s predictions that the harvester could extract drinkable water every day/night cycle at very low humidity and at low cost, making the harvester an ideal water solution for people living in arid water starved areas.
Currently there is nothing else like this that operates at ambient temperatures with ambient sunlight using zero additional energy input to collect drinkable water in the desert; turning water harvesting from an interesting phenomenon to actual working science.
The trail took place in Scottsdale, Arizona where the relative humidity drops from a high of 40% at night to around 7% during the day, successfully demonstrating the harvester would be easy to scale up by adding more water absorber. It is anticipated the current MOF made from metal zirconium will be able to harvest 200 mm of water per kilogram of MOF-801, about 3 ounces of water per pound. A new MOF has been created using aluminum that is at least 150 times cheaper. This new MOF-303 has also captured twice as much water in lab tests, which could produce more than an estimated 400 ml in the harvester per day using a kilogram of MOF.
The harvester is a box within a box, with the inner box holding 2 square foot bed of MOF grains open to air to absorb moisture which is encased in a two foot plastic tube with transparent sides and top. During night time the top is left open to let in air flow to come in contact with the MOF and replaced again during the day to heat up the box like a greenhouse to drive water back out of the MOF, released water condenses on the insides of the outer box and falls to the bottom where it is collected with a pipette.
Extensive field tests serve to create a blueprint for engineers to configure the harvester for differing conditions in Arizona or other places such as the Mediterranean, Africa, disaster relief, areas with no access to clean water, or anywhere else given a specific MOF. Key to development is that it operates at low humidity using only solar energy, the harvester even collects water at sub-zero dew points.
Next field tests will be in Death Valley late summer when temperatures reach 110+ degrees Farenheit daytime and in the 70s at night with humidity around 25% using the newly developed aluminum based MOF.
