Rice University researchers have developed a highly porous, Swiss cheese-like nanomaterial for treating industrial wastewater.
According to the researchers, the metal-organic framework’s (MOF) perfectly-sized defects helps it to soak up more perfluorooctanesulfonic acid (PFOS) in less time.
PFOS is an integral part of stain-resistant fabrics and is the best-known member of a family of toxic chemicals called ‘Per- and Polyfluoroalkyl Substances’ (PFAS).
The Environmental Protection Agency (EPA) has labelled these chemicals as “very persistent in the environment and in the human body – meaning they don’t break down and they can accumulate over time.”
Rice professor Michael Wong and his team believe they have taken the right step in developing materials that can effectively treat industrial wastewaters in the parts-per-billion and parts-per-million level of total PFAS contamination.
MOFs turned out to be ideal candidates for PFAS remediation because they are highly porous and have been used to absorb and hold significant amounts of specific target molecules in previous applications
Moreover, their structure, pore sizes and functions can all be varied by tinkering with the synthesis, or chemical recipe that produces them.
Chelsea Clark, a graduate student in Wong’s Catalysis and Nanomaterials Laboratory, began with a well-characterized MOF called UiO-66, and conducted dozens of experiments to see how various concentrations of hydrochloric acid changed the properties of the final product.
She found she could introduce structural defects of various sizes with the method – like making Swiss cheese with extra-big holes.
“The large-pore defects are essentially their own sites for PFOS adsorption via hydrophobic interactions,” Clark said. “They improve the adsorption behavior by increasing the space for the PFOS molecules.”
Clark tested variants of UiO-66 with different sizes and amounts of defects to determine which variety soaked up the most PFAS from heavily polluted water in the least amount of time.
“We believe that introducing random, large-pore defects while simultaneously maintaining the majority of the porous structure played a large role in improving the adsorption capacity of the MOF.”
“This also maintained the fast adsorption kinetics, which is very important for wastewater remediation applications where contact times are short.”
Image and content: Jeff Fitlow/Rice University