Arsenic contamination in natural water is a worldwide problem. Arsenic mostly exists in two different oxidation states, i.e., arsenate (AsO43- ) and arsenite (AsO33- ), in natural water, in which arsenite is fifty times more toxic than arsenate. Molybdenum disulfide (MoS2), a 2D material, has shown a wide range of mechanical, physicochemical, electrical, and adsorption applications, owning to its active sulfur functional groups. To accelerate the adsorption densities towards anionic pollutants, the highly stable MoS2 is modified as defective by the incorporation of oxygen atoms. In this study, we aimed to synthesize a metal (La) loaded O-rich MoS2 nanosheets through an in-situ hydrothermal reaction for the adsorption of toxic arsenite and arsenate ions from water and compared their efficiency with commercially obtained La(OH)3/MoS2 materials. The intercalation/surface loading of La at different equivalent ratios into a few layered O-rich MoS2 nanosheets were successfully synthesized and characterized through several spectro-analytical techniques. The PXRD patterns showed that the La-incorporation on the sheets was confirmed by the presence of LaMoO peaks and the existence of Mo d-space value as 0.60 nm. When increasing the concentration of La from 0.5 to 2.0 eq. Mo, the layered arrangements were altered. At 1.0 eq. Mo, the highly exfoliated sheets (~4-5 sheets) of MoOxS2-x were obtained, confirmed by micro-Raman data. From the FE-SEM and TEM images that obvious ripples and corrugations can be observed, revealing the ultrathin nature of the nanosheets, and the La-particles were decorated over it. The maximum removal of arsenite and arsenate were 1.566 and 2.278 mmol/g for La1.0MoOxS2-x and these values were found to have much higher than the existing materials in the literature and the studied materials. The La-ions tend to bind with the O-moiety in the MoOxS2-x, rather than S by well understood HSAB principle and the S atoms are free for the capture of arsenite ions. Loading La-ions in the defective structure intended to adsorb arsenate ions from water through multiple mechanisms. Reusability of the material after seven cycles is yet another merit of the developed material towards arsenic removal. The results indicated that La-incorporated O-rich MoS2-x has considerable potential candidates for the decontamination of arsenic from waters.

La-incorporation in oxygen-rich MoS2 nanosheets for arsenic removal

ACS Spring 2022

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