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. 2019 Aug 14;4(9):13922-13935.
doi: 10.1021/acsomega.9b01603. eCollection 2019 Aug 27.

Efficient Removal of Pb(II) and Cd(II) from Industrial Mine Water by a Hierarchical MoS2/SH-MWCNT Nanocomposite

Rashi Gusain  1   2 , Neeraj Kumar  1 , Elvis Fosso-Kankeu  3 , Suprakas Sinha Ray  1   2
Affiliations

Efficient Removal of Pb(II) and Cd(II) from Industrial Mine Water by a Hierarchical MoS2/SH-MWCNT Nanocomposite

Rashi Gusain et al. ACS Omega. .

Abstract

In this study, we investigate the adsorption capability of molybdenum sulfide (MoS2)/thiol-functionalized multiwalled carbon nanotube (SH-MWCNT) nanocomposite for rapid and efficient removal of heavy metals [Pb(II) and Cd(II)] from industrial mine water. The MoS2/SH-MWCNT nanocomposite was synthesized by acid treatment and sulfurization of MWCNTs followed by a facile hydrothermal reaction technique using sodium molybdate and diethyldithiocarbamate as MoS2 precursors. Morphological and chemical features of the nanocomposite material were studied using various characterization techniques. Furthermore, the effects of adsorbent (MoS2/SH-MWCNT nanocomposite) concentration, contact time, initial concentration of heavy-metal ions, and reaction temperature were examined to determine the efficiency of the adsorption process in batch adsorption experiments. Kinetics and isotherm studies showed that the adsorption process followed pseudo-second-order and Freundlich adsorption isotherm models, respectively. Thermodynamic parameters calculated using van't Hoff plots show the spontaneity and endothermic nature of adsorption. MoS2/SH-MWCNT nanocomposite demonstrates a high adsorption capacity for Pb(II) (90.0 mg g-1) and Cd(II) (66.6 mg g-1) following ion-exchange and electrostatic interactions. Metal-sulfur complex formation was identified as the key contributor for adsorption of heavy-metal ions followed by electrostatic interactions for multilayer adsorption. Transformation of adsorbent into PbMoO4-x S x and CdMoO4-x S x complex because of the adsorption process was confirmed by X-ray diffraction and scanning electron microscopy-energy-dispersive spectrometry. The spent adsorbent can further be used for photocatalytic and electrochemical applications; therefore, the generated secondary byproducts can also be employed for other purposes.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic presentation of the synthesis route of the MoS2/SH-MWCNT nanocomposite.
Figure 2
Figure 2
(a) XRD patterns and (b) Raman spectra of (i) MWCNT, (ii) O-MWCNT, and (iii) MoS2/SH-MWCNT nanocomposite.
Figure 3
Figure 3
(a) Full scan survey XPS spectrum and high-resolution (b) C 1s, (c) O 1s, (d) Mo 3d, (e) S 2p, and (f) Si 2p XPS images of MoS2/SH-MWCNT nanocomposite.
Figure 4
Figure 4
Field emission SEM images of (a) MWCNTs, (b) O-MWCNTs, and (c–f) MoS2/SH-MWCNT nanocomposite.
Figure 5
Figure 5
High-resolution TEM images of (a–c) MoS2/SH-MWCNT nanocomposite and (d) with (100) plane and defects. (e) Elemental mapping of MoS2/SH-MWCNT nanocomposite showing the presence of carbon (C), nitrogen (N), oxygen (O), molybdenum (Mo), and sulfur (S) in the nanocomposite.
Figure 6
Figure 6
(a) Nitrogen adsorption–desorption isotherms and (b) pore size distribution of MWCNT and MoS2/SH-MWCNT nanocomposite.
Figure 7
Figure 7
Effect of (a) MoS2/SH-MWCNT nanocomposite dosage and (b) pH on the adsorption of Pb(II) and Cd(II) from mine water. Adsorption conditions: heavy-metal concentration (Co): 100 mg L–1; temperature = 25 °C; and time = 60 min.
Figure 8
Figure 8
(a) Effect of contact time between adsorbate and adsorbent on the maximum uptake of Pb(II) and Cd(II) using MoS2/SH-MWCNT nanocomposite. (b) Pseudo-first-order, (c) pseudo-second-order, and (d) intraparticle diffusion kinetic models for the adsorption of [Pb(II) and Cd(II)] from mine water using MoS2/SH-MWCNT nanocomposite as adsorbent. Adsorption conditions: Co = 100 mg mL–1; temperature = 25 °C; and adsorbent dosage = 2 mg mL–1.
Figure 9
Figure 9
(a) Effect of initial concentrations of Pb(II) and Cd(II) in the solution on the adsorption behavior of MoS2/SH-MWCNT nanocomposite as an adsorbent in terms of % removal of heavy-metal ions. (b) Langmuir and (c) Freundlich adsorption isotherms for the adsorption of [Pb(II) and Cd(II)] from mine water using MoS2/SH-MWCNT nanocomposite as adsorbent. (d) Comparison of adsorption capacity of O-MWCNT and MoS2/SH-MWCNT nanocomposite for Pb(II) and Cd(II). Adsorption conditions: time = 60 min; temperature = 25 °C; and adsorbent dosage = 2 mg mL–1.
Figure 10
Figure 10
Effect of temperature of the solution on the % removal of heavy-metal ions [Pb(II) and Cd(II)] from mine water using MoS2/SH-MWCNT nanocomposite as the adsorbent and (b) linear thermodynamic plot of Ln Kd vs 1/T for the adsorption of heavy-metal ions onto the MoS2/SH-MWCNT nanocomposite. Adsorption conditions: Co = 100 mg mL–1; time = 60 min; and adsorbent dosage = 2 mg mL–1.
Figure 11
Figure 11
Diagrammatic illustration of Pb(II) and Cd(II) adsorption mechanism on MoS2/SH-MWCNTs.
Figure 12
Figure 12
SEM images of Cd(II) (a, b) and Pb(II) (c, d) adsorbed MoS2/SH-MWCNT nanocomposite, followed by EDS mapping.
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