Functional PAN-based monoliths with hierarchical structure for heavy metal removal

With the ever-rising development of manufacturing, water pollution by heavy metals such as lead has become a bottle-neck problem with regards to public health and environmental concerns. It has been reported that excess lead intake may damage the liver, kidney, and reduce hemoglobin formation. Because of this, the World Health Organization (WHO) has stipulated a tolerable weekly intake of 0.025mg/kg of body weight. As such, the efficient removal of heavy metals from aqueous solution is vital for better environment and better life in the end.

Several techniques have been adopted for lead removal including chemical precipitation, liquid extraction, adsorption, and capacitive deionization. Of these methods, adsorption has attracted more attention owing to its low cost, reusability, and high efficiency. Some traditional adsorbents including zeolites, clays, and activated carbon have been used for heavy metal removal, however, which are far from the satisfactory in terms of the functionality, removal efficiency, and the operation cost.

Researchers led by professor Jieshan Qiu from Dalian University of Technology in China developed functional polyacrylonitrile (PAN) based monoliths with hierarchical structure for the efficient removal of heavy metals. The PAN monolith has a continuous connected network with well-developed macropores and mesopores, and high surface areas, which provided more active sites for adsorption and fast transportation of ions. Their work is recently published in Chemical Engineering Journal.

The authors successfully prepared three PAN-based monolith adsorbents grafted with different functional groups by reacting with diethylenetriamine, hydroxylamine hydrochloride, and sodium hydroxide, respectively. They evaluated the potential of these PAN-based monoliths for removal of lead(II) in solution in terms of kinetic adsorption, and the impact of ionic strength, initial pH, initial lead(II) concentration, and the adsorption time, and the regeneration capability.

It has been found that the functionalized PAN-based monoliths has a superior capability to remove lead (II) from the aqueous solution. Under the optimized conditions, the adsorption capacity for lead (II) of the PAN-based monolith modified by diethylenetriamine, sodium hydroxide, and hydroxylamine hydrochloride, is 144, 206, and 242 mg g-1, respectively. The functionalized PAN-based monoliths can be easily regenerated, and re-cycled, with the adsorption ability remaining over 70% after 4 cycles.

From the outcomes of this study, one can conclude that functionalized monoliths hold promise as adsorbent for the removal of heavy metal ions from aqueous solution.