Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant and an industrial chemical still used in chrome plating applications and semiconductor manufacturing facilities. Activated carbon and other conventional treatment options are not effective in removing this toxic component of industrial wastewaters. However, a new metal-oxide-framework (MOF) material developed at Rice University has proven to be a superior adsorbent for PFOS.

These porous materials have found a niche in removing low levels of pollutants from industrial effluents and Researchers increased the amount of toxic pollutants adsorbed by introducing defects into the structure of an MOF. Source: Chelsea Clark, Rice Universitydrinking water. The researchers’ application of MOF technology to the removal of industrially relevant concentrations of PFOS proved successful, largely due to a defect in the parent material.

Zirconium-based MOFs were synthesized with nanometer-sized pore defects, using hydrochloric acid as a modulator, which served to speed the pollutant removal process by providing more area for PFOS retention. The defective MOF adsorbed PFOS two orders of magnitude faster than an ion-exchange resin, and sorption isotherms indicated that the material had a maximum Langmuir sorption capacity of 1.24 millimole per gram (mmol/g), double that of powdered activated carbon.

With engineered defects, the material combines high-capacity and fast-adsorption kinetics and is also applicable to the adsorption of both long- and short-chain perfluoroalkyl sulfonates. Commercial-scale production makes the material economically competitive with relatively inexpensive carbon-based options for filtration.