Effect of natural organic matter (NOM) on the removal efficiency of Hg(ii) by MoS2: dependence on the Hg/MoS2 ratio and NOM properties

Abstract

Mercury (Hg) contamination in groundwater poses significant environmental and health risks, necessitating effective remediation strategies. Recently, molybdenum disulfide (MoS₂) nanosheets have emerged as a promising nanomaterial for the remediation of Hg-associated contaminated groundwater. However, the complex interactions between ubiquitous natural organic matter (NOM) and MoS₂ may play a significant role in controlling the removal of Hg from groundwater. In this study, we investigated the mechanisms underlying the role of NOM in Hg(II) removal by MoS₂. Our findings demonstrated that NOM inhibited the Hg(II) removal by MoS₂ from groundwater at a high molar ratio of Hg/MoS₂. However, at a low molar ratio of Hg/MoS₂, NOM hardly affected the removal performance of MoS₂ on Hg(II) because NOM was unable to compete with sufficient MoS₂ to complex with Hg(II). The inhibitory effect of NOM on Hg(II) removal was found to be determined by both the molecular weight (MW) and functional groups of NOM: the NOM fraction with higher MW exhibited a higher degree of inhibition, and the –SH groups displayed preferential binding of Hg(II) rather than the –COOH group. It was concluded that the reduction of MoS₂ to Hg(II) gradually decreased with increasing addition of NOM, attributed to NOM complexation with Hg(II). Overall, this study provides insights into the significance of NOM characteristics in controlling the removal of Hg(II) from groundwater.