Fabrication of Ultrathin MoS2 Nanosheets and Application on Adsorption of Organic Pollutants and Heavy Metals

Abstract

Owing to their peculiar structural characteristics and potential applications in various fields, the ultrathin MoS2 nanosheets, a typical two-dimensional material, have attracted numerous attentions. In this paper, a hybrid strategy with combination of quenching process and liquid-based exfoliation was employed to fabricate the ultrathin MoS2 nanosheets (MoS2 NS). The obtained MoS2 NS still maintained hexagonal phase (2H-MoS2) and exhibited evident thin layer-structure (1–2 layers) with inconspicuous wrinkle. Besides, the MoS2 NS dispersion showed excellent stability (over 60 days) and high concentration (0.65 ± 0.04 mg mL−1). The MoS2 NS dispersion also displayed evident optical properties, with two characteristic peaks at 615 and 670 nm, and could be quantitatively analyzed with the absorbance at 615 nm in the range of 0.01–0.5 mg mL−1. The adsorption experiments showed that the as-prepared MoS2 NS also exhibited remarkable adsorption performance on the dyes (344.8 and 123.5 mg g−1 of qm for methylene blue and methyl orange, respectively) and heavy metals (185.2, 169.5, and 70.4 mg g−1 of qm for Cd2+, Cu2+, and Ag+). During the adsorption, the main adsorption mechanisms involved the synergism of physical hole-filling effects and electrostatic interactions. This work provided an effective way for the large-scale fabrication of the two-dimensional nanosheets of transition metal dichalcogenides (TMDs) by liquid exfoliation.

Aqueous Adsorption of Heavy Metals on Metal Sulfide Nanomaterials: Synthesis and Application

“…The adsorption capacity may also be affected by the HM ions' charge values related to the strength of the electrostatic activity between the adsorbate and the adsorbent. With MoS 2 NS, the adsorption capacity of Ag + was much lower than those of Cu 2+ and Cd 2+ [128].…”

“…For example, while rising pH amplifies the negative charges on the surface of MoS 2 , a strongly alkaline solution would engender the formation of HM-OH complexes [140,141], reducing the adsorption efficiency of the sorbent. As a result, HM ion adsorption's optimum pH on MoS 2 is found in the range of 4.5-7.5 (Table 4) [126][127][128]130,139]. Interestingly, the highest limit of around pH 8 may be general for MS-NMs because of the same reason.…”

“…Jia et al [121] confirmed multilayer adsorption of Hg 2+ from aqueous solution using MoS 2 besides the inner layer complexation that occurred, indicating an attraction of the positive ions to the negative surface of the adsorbent. The specific surface area of sorbents and the interaction between adsorbents and adsorbates affect the sorption capacity, while the rate of water-soluble ions and the degree of electrostatic interaction may be contingent on the strength/value of the surface charge of the sorbent [128]. Increasing the quantity of MoS 2 in the MoS 2 NC increases the adsorbent's negative surface charge and the adsorption capacity [138].…”

“…MoS 2 has a significant number of available adsorption sites due to its peculiar 2D structure and excess of exposed sulfur atoms and hence has an excellent HM ion removal capacity in water [9,121,123,126,128,130,137,139]. The same sorbent material having different synthetic techniques exhibits different sorption performance for the same adsorbate since the sorbent will have different characteristics such as structures, morphologies, adsorption sites, and thicknesses.…”

“…Another critical parameter, the time required for arriving at equilibrium (equilibrium contact time), depends on the adsorbent's nature and the adsorbate's concentration. With increasing contact time, the initial rapid increase in removal efficiency of HMs on MoS 2 NCs [84,121,122,124,128,130] can be attributed to abundant vacant adsorbent sites and high solute concentration gradient before equilibrium. The flattening shape of the removal efficiency curve with time could indicate reduced active sites just before equilibrium and a possible HM monolayer deposition on the outer surface with HM diffusion through this coating into the internal cavity of MoS 2 particles.…”