KTH’s material purifies water from heavy metals – time and time again

With a slow cooker in microwave ovens, researchers at KTH have created a gel that purifies water. It can absorb everything from heavy metals to textile dyes and antibiotics.

KTH is collaborating with Politecnico di Torino in Italy on the development of a hydrogel that efficiently absorbs water and traps pollutants. At the same time, it is so stable that it can be used several times, after a cleaning.

However, more research is needed before any known application areas exist.

The gel can be made from lignocellulose or other plant material – this includes cellulose rubber which is used, among other things, as a thickener in ice cream. The mixture also contains small dots in the form of carbon pieces made from biomass.

– We have worked with a hydrogel that has a negative charge and it can clear away both metals and organic substances that have opposite charges. Then the hydrogel can also remove some other neutral organic substances. Among other things, we have tested on textile paints, says Minna Hakkarainen, professor and head of the Department of Polymer Technology at KTH.

“A much more environmentally friendly process”

The carbon dots can also contribute to interactions with drugs, such as antibiotics, and other aromatic substances. Due to its absorbency, graphene oxide is often used in hydrogels, but at the expense of a significant environmental impact. KTH’s substitutes are carbon flakes created from a by-product from wood pulp.

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Lignosulfonate is placed in water and then heated to 240 degrees for two hours in a commercial microwave oven for laboratory work. The material is heated in closed vessels in the form of Teflon vials, and due to the pressure in the vials, water and other solvents can be heated to temperatures above their normal boiling points. There are temperature sensors in the vials and the researchers can program the oven so that it adjusts the power to keep the temperature.

– It is a much more environmentally friendly process to manufacture this product than both graphene and graphene oxide. The production in the traditional way includes very harsh chemicals and it is a long process. We use water and two strong acids, but in relatively dilute solutions compared to graphene oxide production, where, among other things, concentrated sulfuric acid and other strong chemicals are used, she says.

The big difference from ordinary graphene oxide is that KTH’s carbon flakes are in nanoscale on all joints, while spruce phenoxide can have a thickness that measures in nanometers but a “width” of several micrometers.

In addition to the hydrogel being made from bio-based raw materials, it is cured with UV light at room temperature. Chemically, it is a very mild process. It also allows for printing with 3D printers that use UV curing. The researchers have published an article about their work in Sustainable Materials and Technologies.


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