Emerging investigator series: Molybdenum disulfide-enabled activated carbon - A multifunctional adsorbent for practical water treatment applications

While molybdenum disulfide (MoS2) nanosheets have demonstrated selective and efficient adsorption potential toward heavy metals, there are still many barriers - such as nanomaterial practicality, safety, and sustainability - to nanomaterials' large-scale application in water treatment schemes. For example, nano-MoS2 has been shown to take part in redox reactions during heavy metal recovery (which deteriorates the active nanomaterial) and can release molybdenum to the treated water. This study addresses these barriers through the bottom-up hydrothermal synthetic growth of MoS2 onto granular activated carbon (AC) as an active adsorbing platform. Not only does this strategic design avoid redox reactions, but it also largely immobilizes MoS2 to a substrate, which mitigates nanomaterial loss to solution and enables facile recovery of the nanomaterial after use. The hybrid adsorbent (MoS2@AC) was extensively characterized, demonstrating high AC surface coverage by sulfurized and oxidized molybdenum moieties. The maximum removal capacity of mercury (heavy metal target pollutant) was 1280 mg mercury per g MoS2 (driven by adsorption rather than redox reactions), with no drop in Hg adsorption when simultaneously tested for methylene blue adsorption (organic target pollutant, 555.5 mg MB g-1 AC). Finally, we tested the potential use of the developed multifunctional adsorbent in the presence of background ions and natural groundwater samples, demonstrating removal of mercury to concentrations below the US-EPA maximum contamination level. Overall, this study suggests a sustainable design of a multifunctional MoS2-based adsorbent for simultaneous removal of organic and inorganic pollutants in environmentally relevant conditions, thus advancing the practical use of nanomaterials in water treatment streams.