Rational Surface Oxidation Promoted Long-Term Cd(II) Removal Performance of Mackinawite (FeS)

Mackinawite (FeS) is an excellent Cd(II) removal material but suffers from rapid reactivity loss. Herein, we demonstrate that rational surface preoxidation could enhance the single maximum adsorption capacity of mackinawite from 625.0 to 666.7 mg g^–1 and also promote its air stability and reusability for long-term application. The Cd(II) removal processes were carefully characterized with a multifunctional in situ electrochemical device, theoretical calculation, and extended X-ray absorption fine structure (EXAFS) spectroscopy. Characterization results revealed that surface preoxidation treatment changed the Cd(II) removal mechanism from ion exchange to ion-exchange coupled surface adsorption because surface preoxidized FeS possessed abundant surface −OH sites. This extra surface adsorption process offered surface preoxidized FeS a superior long-term Cd(II) removal performance of 1290.5 mg g^–1 in 5 successive cycles, much higher than that of pristine FeS (842.4 mg g^–1). This study highlights the importance of surface oxidation on the Cd(II) removal performance of mackinawite and also opens a new strategy to design and produce high-performance mackinawite nanocrystals for pollutant control and environmental remediation.