Microscopic
nanodiamonds clump together when placed in water (shown above),
but dissociate
when in ethyl acetate to clean hot wastewater.
Courtesy: Adapted from ACS Applied
Materials & Interfaces 2020, DOI: 10.1021/acsami.0c15194.
Although
most of the planet is covered by water, only a fraction of it is clean enough
for humans to use. Therefore, it is important to recycle this resource whenever
possible. Current purification techniques cannot adequately handle the very hot
wastewater generated by some industries. But now, researchers reporting in ACS
Applied Materials & Interfaces have embedded amine-enhanced nanodiamond
particles into membranes to address this challenge.
Some oil recovery
methods and other industrial processes result in hot wastewater, which requires
energy-intensive cooling before it can be purified through traditional reverse
osmosis membranes. After purification, the water then needs to be heated before
it can be re-used. At such high temperatures, traditional reverse osmosis
membranes filter slowly, allowing more salts, solids and other contaminants to
get through. Researchers have embedded extremely tiny nanodiamonds—carbon
spheres produced by explosions in small, closed containers without oxygen
present—onto these membranes in previous studies. Although the membranes
effectively and quickly filtered large volumes of water and can protect against
fouling, they were not tested with very hot samples. To optimize the membranes
for use with hot wastewater, Khorshidi, Sadrzadeh and colleagues wanted to
modify the nanodiamond spheres and embed them in a new way.
The team
attached amines to nanodiamonds and bathed them in an ethyl acetate solution to
prevent the spheres from clumping. Then, a monomer was added that reacted with
the amines to create chemical links to the traditional membrane base.
Synergistic effects of the amine links and the ethyl acetate treatment resulted
in thicker, more temperature-stable membranes, contributing to improvements in
their performance. By increasing the amount of amine-enhanced nanodiamonds in
the membrane, the researchers obtained higher filtration rates with a greater
proportion of impurities being removed, even after 9 hours at 167 F, when
compared to membranes without nanodiamonds. The new method produced membranes
that could more effectively treat wastewater at high temperatures, the
researchers say.