Paramagnetic properties of manganese chelated on glutathione-exfoliated MoS2

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Abstract

Generation of zero-dimensional molybdenum disulphide (MoS2) nanoparticles with effective chemical and physical properties have offered a widerange of applications. The advancement in two-dimensional (2D) MoS2 functionalization materials for the fabrication of biomedical applications has become a recent trend owing to their physicochemical properties such as high surface area, mechanical properties, and excellent electrical conductivity. In this study, the pristine bulk MoS2 was exfoliated by probe sonication with glutathione (GSH) as a capping ligand to form MoS2-GSH nanoparticles. Further, the as-prepared MoS2-GSH was coated with amino terminated ethyl polyethylene glycol (MoS2-GSH-AEPEG) through electrostatic interactions between GSH and AEPEG. Thereafter, both MoS2-GSH and MoS2-GSH-AEPEG nanoparticles (NPs) were chelated with manganese (Mn) metal ion to form magnetic MoS2-GSH-Mn and MoS2-GSH-AEPEG-Mn NPs. The obtained MoS2-GSH-Mn and MoS2-GSH-AEPEG-Mn nanoparticles exhibited a spherical in shape with sizes of 60.7 and 80.6 nm, respectively. The chelated Mn2+ in the prepared MoS2 NPs was confirmed by XPS and Raman spectroscopy. The paramagnetic properties of the MoS2-GSH-Mn and MoS2-GSH-AEPEG-Mn samples were investigated using a superconducting quantum interference device at 5 K temperature and the saturation magnetization was calculated to be 17.5 and 15 emu/g for MoS2-GSH-Mn and MoS2-GSH-AEPEG-Mn, respectively. The MoS2-GSH-Mn exhibited higher magnetic hysteresis loops than MoS2-GSH-AEPEG-Mn due to shielding effects of nonmagnetic nature of PEG coating.

Introduction

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) monolayers are considered to be potential graphene substitutes owing to their diverse and unique optical and electronic properties [[1], [2], [3], [4], [5]]. TMDCs have been demonstrated as having strong potential for a broad range of fields such as electronic devices, transistors, energy storage devices, and catalysis [[6], [7], [8], [9], [10]] Molybdenum disulphide (MoS2) is a common TMDCs composed of S-Mo-S triple layers that are weakly bonded by van der Waals forces. Particularly, monolayered MoS2 exhibits various attractive properties such as semiconductivity, photoluminescence emission, and so on [11]. Single or few-layered MoS2 sheets can be prepared either from bulk MoS2 through mechanical, intercalation-assisted, or stimulated exfoliation methods or via chemical vapor deposition methods [12,13]. By applying these synthetic approaches, fairly large MoS2 monolayers have been prepared corresponding to submicron-sized MoS2 layers [14].

McAdams and coworkers reported the synthesis of covalently functionalized, atomically thin 2H-MoS2 nanosheets concurrently with Eu (III) and Gd (III) complexes to form a novel 2D luminescent and paramagnetic multimodal material. Additionally, the 2D structure of the MoS2 nanosheets was supported by post-functionalization, and they established that the material exhibits sensitized luminescence from Eu3+ as well as paramagnetism from Gd3+ [15]. Later, Martinez et al. reported paramagnetic point defects in hydrothermally grown 2H-MoS2 Monocrystalline (NCs). X-band electron spin resonance (ESR) spectroscopy was applied to distinguish the defects, which have unpaired electron spins, in the as-synthesized and Ar-annealed MoS2 NCs. Seven minor ESR signals were identified as arising from four inequivalent paramagnetic defect sites of adsorbed oxygen species, sulphur vacancies, thiol, and oxo-Mo5+ [16]. Wang et al. demonstrated that transition-metal doping is also an effective approach to inducing robust ferromagnetism in MoS2 nanostructures, where a small percentage of Mn2+ ions could induce a dramatic magnetic enhancement [17]. Moreover, the magnetic properties obeyed Curie’s law, i.e., the magnetic property of MoS2 strongly depended on temperature, which is different from the defect-induced magnetism in MoS2 nanostructures.

Functionalized MoS2 nanomaterials with polymers have garnered much attention due to the various properties induced by a variety of modifications [18,19]. Particularly, polyethylene glycol (PEG) is a hydrophilic molecule, which is used to enhances the colloidal stability and crystal growth of magnetic nanoparticles (MNPs). Furthermore, PEG is an FDA-approved excipient in various pharmaceutical formulations owing to its biocompatibility [[20], [21], [22]]. Previously, Sabah et al. proposed that cellulose acetate (CA), cellulose acetate-polyethylene glycol (CA-PEG) functionalization processes change the surface magnetic state of the particles by producing a magnetic dead layer, and the strong covalent bonding between CA/CA-PEG and reactive groups on the iron oxide (Fe3O4) surface was suggested as the origin of the enhanced magnetic properties of the Fe3O4 MNPs upon functionalization. These conclusions are of importance because biomedical devices employing Fe3O4 MNPs are highly sensitive and effective by employing the high magnetization values, and Fe3O4 MNPs have biocompatible surfaces with regard to the PEG functional groups [23]. Later, Tai et al. proposed that MNPs coated with PEG exhibited a higher colloidal stability in a basic solution (pH = 10) including a Nitrile Butadiene Rubber (NBR) stain for up to 21 days than that of the unmodified MNPs during sedimentation tests [24]. Ehi-Eromosel and coworkers reported that the increased magnetization of PEG-coated MNPs could apparently be attributed to nanoparticle crystal growth after polymer coating compared with the uncoated PEG sample. Nanoparticles higher colloidal stability are advantageous because they provide higher sensitivity and efficacy in biomedical applications. For example, PEG coating enhances the colloidal stability and stability of nanoparticles which increases their applicability hyperthermia and biological applications [25].

Manganese-chelated 2D nanomaterials have been demonstrated as promising for MRI, CT scanning, and magnetic drug delivery applications in the last decade [26,27]. Herein, we report glutathione (GSH)-functionalized exfoliated MoS2 chelated with Mn and PEGylated to produce magnetic MoS2 nanomaterials (Scheme 1). The prepared magnetic MoS2 nanomaterials were characterized by infrared (IR), ultra-violet (UV)–vis, and Raman spectroscopy, dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The Mn2+-loaded PEGylated MoS2-GSH exhibited a higher magnetization than MoS2-GSH.

Section snippets

Materials

Molybdenum disulphide (MoS2), L-glutathione (l-GSH) reduced, dimethyl sulfoxide (DMSO), manganese (II) chloride tetrahydrate (MnCl2.4H2O), and O-2-amino ethyl polyethylene glycol (molecular weight 10 000 Da) were purchased from Sigma Aldrich. A cellulose dialysis membrane 6−8 K Da and 14 K Dawere purchased from Orange Scientific Dialysis. Other reagents and buffer solution components were of analytical grade.The deionized water was used in all over experiments in this study.

Synthesis of MoS2-GSH nanoparticles

MoS2 (800 mg) and l

Formation of MoS2-GSH-AEPEG-Mn

MoS2 with multifunctionality become an emerged as research material for the biomedical applications, and functionalized MoS2 can be attained upon the addition of various moieties through the sulphur vacancies on the MoS2 surface, that is considered to be a simple and easy process to produce functionalized MoS2. Thus, in this study GSH was utilized to modify the sulphur vacancy on the MoS2 and to replace them via Mo-S interactions. Preparation of MoS2-GSH-AEPEG-Mn nanoparticles entangled with

Conclusion

In this study, we prepared magnetic nanomaterials composed of GSH functionalized MoS2 with Mn2+ ions and were compared with AEPEG incorporation, which was demonstrated their magnetic behaviors. The prepared functionalized MoS2 nanoparticles possessed a spherical shape as confirmed by TEM with particle sizes of 57, 60.7, and 80.5 nm for MoS2-GSH, MoS2-GSH-Mn, and MoS2-GSH-AEPEG-Mn, respectively. Both functionalized MoS2 nanoparticles exhibited good optical properties with significant red shifts.

CRediT authorship contribution statement

Adhisankar Vadivelmurugan: Conceptualization, Methodology, Investigation, Writing - original draft. Rajeshkumar Anbazhagan: Investigation, Validation, Formal analysis. Juin-Yih Lai: Resources, Funding acquisition, Supervision. Hsieh-Chih Tsai: Resources, Supervision, Conceptualization, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors would like to thank Ministry of Science and Technology, Taiwan, for financial support (MOST -104-2221-E-011-154).

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