porosity

We have occasionally talked about metal-organic frameworks, which are organic-inorganic hybrid crystalline structures that have a microscopic cage-like structure. MOFs have been under development for a diverse set of applications including gas storage and separation, liquid purification, energy storage, catalysis, and sensing.

For the first time, an international research team, led by researchers from Monash University in Australia, has created an ultrathin porous membrane based on MOF technology that can completely separate potentially harmful ions, such as lead and mercury, from water.

This innovation could enhance water desalination and transform even the dirtiest water into something potable for millions of people around the world. The new membrane performed steadily in tests for more than 750 hours using only limited energy.

The technology uses water-stable monolayer aluminum-based MOFs just a millionth of a millimeter in thickness. These are essentially two-dimensional structures. The ultrathin membrane is permeable to water – it achieves maximum porosity – but rejects nearly 100 percent of ions. It has been a daunting challenge to fabricate ultra-thin MOFs for water-based processing. Most previous membranes were too thick and unstable in water.

Most existing ion separation membrane technologies are based on polymers and have the limitation that they have limited selectivity. They don’t reject all unwanted ions.

The new membrane technology has great potential based on its precise and fast ion separation and could be ideal for a variety of filtration applications such as gas separation and separation of organic solvents such as paint. Such membranes might also be used to remove harmful carcinogens from the atmosphere.

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Ultrathin nanosheets separate ions from water

Photo courtesy of Monash University.

Earth Wise is a production of WAMC Northeast Public Radio.

Coal burning is still one of the primary means of generating electricity in the United States, but its use is diminishing and doing so fairly rapidly. The coal burning process produces residual, incombustible materials. One of them is fly ash, which is composed of fine, glassy, rounded particles rich in silicon, aluminum, calcium, and iron oxides. Fly ash is captured from coal plant flue gas by precipitators and bag filters. It turns out that two-thirds of this fly ash is not dumped into landfills or impoundments, but rather is put to use.

Because of its chemical and physical characteristics, fly ash can substitute for a portion of portland cement in concrete. Using this byproduct material in making cement actually reduces its cost. Beyond cost, the addition of fly ash as a so-called supplementary cementitious material or SCM improves concrete’s long-term strength and reduces porosity and permeability. It reduces the risk of thermal cracking and provides good long-term mechanical properties.

The amount of fly ash used in concrete products increased by 5% between 2011 and 2017 while the amount produced dropped by 36%. Concrete production continues to increase steadily while fly ash production is steadily dropping.

Therefore, the concrete industry is looking for alternative sources of SCM. The most obvious is the approximately 1/3 of fly ash that hasn’t been used to make concrete. Much of that is landfilled or ponded onsite at power plants. So, opportunities exist for excavating or dredging and recovering these materials.

As coal burning goes away, concrete manufacturing needs to make some changes.

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What Does the Changing Face of Electricity Production Mean for Concrete?

Photo, posted February 16, 2017, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Nanotech Water Purification | Earth Wise

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Concrete Production And Diminishing Coal Burning | Earth Wise

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