*Article* **3D Nanoarchitecture of Polyaniline-MoS<sup>2</sup> Hybrid Material for Hg(II) Adsorption Properties**

#### **Hilal Ahmad 1,2, Ibtisam I. BinSharfan <sup>3</sup> , Rais Ahmad Khan <sup>3</sup> and Ali Alsalme 3,\***


Received: 25 October 2020; Accepted: 16 November 2020; Published: 17 November 2020

**Abstract:** We report the facile hydrothermal synthesis of polyaniline (PANI)-modified molybdenum disulfide (MoS2) nanosheets to fabricate a novel organic–inorganic hybrid material. The prepared 3D nanomaterial was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction studies. The results indicate the successful synthesis of PANI–MoS<sup>2</sup> hybrid material. The PANI–MoS<sup>2</sup> was used to study the extraction and preconcentration of trace mercury ions. The experimental conditions were optimized systematically, and the data shows a good Hg(II) adsorption capacity of 240.0 mg g−<sup>1</sup> of material. The adsorption of Hg(II) on PANI–MoS<sup>2</sup> hybrid material may be attributed to the selective complexation between the–S ion of PANI–MoS<sup>2</sup> with Hg(II). The proposed method shows a high preconcentration limit of 0.31 µg L−<sup>1</sup> with a preconcentration factor of 640. The lowest trace Hg(II) concentration, which was quantitatively analyzed by the proposed method, was 0.03 µg L−<sup>1</sup> . The standard reference material was analyzed to determine the concentration of Hg(II) to validate the proposed methodology. Good agreement between the certified and observed values indicates the applicability of the developed method for Hg(II) analysis in real samples. The study suggests that the PANI–MoS<sup>2</sup> hybrid material can be used for trace Hg(II) analyses for environmental water monitoring.

**Keywords:** toxicity; polyaniline; mercury; adsorption; MoS<sup>2</sup>

## **1. Introduction**

Mercury (Hg(II)) is one of the most toxic metal pollutants found in the environment and ranks third after arsenic and lead in the National Priorities List of the Agency for Toxic Substances and Disease Registry (ATSDR) [1–3]. The Hg(II) contamination of ground and surface water results from geochemical reactions and anthropogenic activities such as improper dumping of electronic waste, thermometer, barometer and mercury lamp waste. Human exposure to metal ions, including Hg(II), can occur during occupational activities, mainly through inhalation and dermal routes in mining and industry, and over a lifetime, from water and food consumption and exposure to soil, dust and air [4,5]. Long-term consumption of drinking water contaminated with Hg(II) can be associated with increased risk of cancers, reproductive problems, detrimental effects on the human brain, blood circulation, immune and reproductive systems and cardiovascular disease [2,6,7]. Therefore, to minimize these risks, the United States Environmental Protection Agency (USEPA) has set the maximum permissible limit of 2 µg L−<sup>1</sup> [8].

Modern analytical techniques such as X-ray fluorescence, atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, and inductively coupled plasma mass

spectrometry have been widely used for the analysis of Hg(II) [9–11]; however, direct determination of Hg(II) in real aqueous samples is challenging due to their low concentrations and complexity of sample matrices [12]. Therefore, preliminary extraction and preconcentration steps are often necessary before instrumental determination. Various separation methods such as solvent extraction, hydride generation, electro-coagulation, precipitation, cloud point extraction and solid-phase extraction (SPE) are employed to extract metal ions [13–17]. SPE is a preferred procedure because of its advantages such as easy operation, the negligible use of organic solvents, complete desorption of analytes, high preconcentration factor, and used in both batch and column modes [18,19]. Adsorption of the analyte onto nanomaterials in SPE is considered an efficient process based on factors like the high surface area of sorbent, efficient adsorption capacity, and easy functionalize activity [20–23]. Nanomaterial-based adsorbents have been extensively researched in the past two decades to find new solutions or to enhance the existing solutions in environmental water remediation [21,24–26]. In recent years, two-dimensional (2D) nanostructures such as metal chalcogenides, metal hydroxides, and double-layered metal hydroxides have attracted tremendous interest due to their high surface area and a porous structure with large surface active sites [27–32]. However, the critical drawback of directly employing these 2D materials in the SPE column is its small size and dispersion in aqueous media, leading to loss of adsorbent during a column operation. Moreover, for the effective deployment of 2D nanostructures, they must prevent stacking. The weak interlayer bonding and low free spacing cause the stacking of nanosheets in the SPE column.

In the present work, we fabricate a blend of 3D hybrid material (organic–inorganic composite) made from 2D MoS<sup>2</sup> and a 1D polymer polyaniline (PANI) via in situ oxidative polymerization of PANI with exfoliated MoS<sup>2</sup> nanosheets to overcome the limitations mentioned above. The integration of MoS<sup>2</sup> nanosheets with PANI restricts the nanosheets leaching from the column and provide stability in aqueous media. Wang et al. reported the polyaniline/zirconium composite to remove organic pollutants [33]. Similarly, Gao et al. reported the hybrid polyaniline/titanium phosphate composite to remove Re(VII) [34]. Moreover, there are no reports on Hg (II) extraction using PANI–MoS<sup>2</sup> hybrid material. The extensive and profound studies are carried out using PANI–MoS<sup>2</sup> hybrid nanomaterial to develop a column SPE method for the extraction of trace Hg(II). The accuracy and applicability of the developed method were validated by analyzing the certified reference material and by spiking of real environmental water samples.

#### **2. Experimental Details**
