A novel molybdenum disulfide nanosheet self-assembled flower-like monolithic sorbent for solid-phase extraction with high efficiency and long service life

Use of transition metal dichalcogenides (TMDs) in analytical sample preparation applications

Since the discovery of graphene, nano-sized two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2, MoSe2, MoTe2, NbS2, NbSe2, WS2, WSe2, TaS2 and TaSe2, which have been classified as next-generation nanomaterials resembling graphene (G) have complementary basic properties with those of graphene in terms of their practical applications. TMDs are attracting great attention due to their attractive physical, chemical and electronic properties. Despite being overshadowed by graphene in terms of frequency of use, TMDs have been used frequently in many areas in recent years instead of carbon-based materials such as graphene (G), graphene oxide (GO), carbon nanotubes (CNTs) and nanodiamonds (NDs). It is seen that the first and frequent uses of TMDs, which are classified as new generation materials, are in the fields of catalysis, electronic applications, hydrogen production processes and energy storage, but it has been used as an adsorbent in sample preparation techniques in recent years. Similar to graphene, layers of TMDs are held together by weak van der Waals interactions. The sandwiched layers of TMDs provide sufficient and effective interlayer spaces so that foreign molecules, ions and atoms can easily enter these spaces between the layers. Intermolecular interactions increase with the entry of different materials into these spaces, and thus, high activity, adsorption capacity and efficiency are obtained in adsorption-based analytical sample preparation methods. Although there are about 35 research articles using TMDs, which are classified as promising materials in analytical sample preparation techniques, no review studies have been found. This review, which was designed with this awareness, contains important informations on the properties of metal dichalcogenides, their production methods and their use in analytical sample preparation techniques.

One-step fabrication of hydrophobic metal-organic framework@covalent organic framework hybrid as sorbent for high-performance solid-phase extraction of flavonoids

Metal-organic framework (MOF) and covalent organic framework (COF) exhibit excellent extraction performance in sample pretreatment, but their wider application is hindered by some inherent drawbacks. Herein, we successfully synthesized a novel MOF@COF hybrid material with large specific surface area, good chemical stability and reusability, which is suitable as a solid phase extraction (SPE) sorbent for the efficient extraction of flavonoids. Importantly, due to the synergistic effect, the obtained MOF@COF hybrid material showing a higher extraction efficiency than individual MOF and COF. This is mainly due to the obtained MOF@COF hybrid material combines the high specific surface area of MOF and multiple interactions (hydrophobic interaction, hydrogen bonding and π-π stacking interaction) with flavonoids conferred by the COF structure. Then, a sensitive analytical method for flavonoids with ideal linear range (1-500 ng mL^-1), low detection limit (0.15-0.41 ng mL^-1) and good repeatability (2.64-6.20%) was developed under optimized conditions. In addition, the MOF@COF hybrid sorbent has better selectivity for hydrophobic targets containing multiple hydrogen bond acceptors/donors. Finally, the established method was applied to the determination of flavonoids in different food samples, and satisfactory recoveries (81.4-102.1%) were obtained, which initially confirmed its applicability.

MIL-101(Fe)@TiO2 nanotube composite material is used for the solid phase extraction of non-steroidal anti-inflammatory drugs under the synergy of multiple interactions

Increasing the adsorption sites and effective interactions between sorbents and the targets can improve the solid-phase extraction (SPE) efficiency. Herein, based on the advantages of MOFs and TiO₂ nanotubes (TiO₂ NTs), an MIL-101(Fe)@TiO₂ NT composite was prepared and applied to extract non-steroidal anti-inflammatory drugs (NSAIDs) from water samples coupled with high performance liquid chromatography (HPLC). Through characterization, it was established that MIL-101(Fe) was effectively composited on the surface and inside the TiO₂ nanotubes, increasing effective adsorption sites. The obtained composite material well retains the structure and functional groups of the two original materials, and while retaining the original force with the target, it achieves a synergistic effect and produces more interactions with the target. Therefore, the extraction efficiency was greatly improved. The recovery efficiency reached 97.7-105.1% with an RSD of less than 6.71%, the detection limit was 0.1-0.2 μg L^-1, and the linear range was 1-200 μg L^-1 with a determination coefficient of 0.9972-0.9994. Owing to the stability of the two original materials, the composite material could be recycled and reused to extract NSAIDs up to 15 times without a loss of the recovery rate. Satisfactory results were obtained when it was used to extract NSAIDs from the Yellow River. These results indicate that the synthesized MIL-101(Fe)@TiO₂ NT material is a promising sorbent to extract NSAIDs at trace concentrations with high efficiency and long lifetimes.

Preparation of flower-like molybdenum disulfide for solid-phase extraction of N-nitrosoamines in environmental water samples

In this paper, a flower-like molybdenum disulfide material was prepared by hydrothermal method and was first used as adsorbents in the solid-phase extraction process for enriching N-nitrosoamines. Molybdenum disulfide exhibited three-dimensional petal-like microspheres with about 500 nm in diameter. The relevant analyte extraction and elution parameters (sample volumes, solution pH, washing solvents, elution solvents, and elution volumes) were optimized to improve the solid-phase extraction efficiency. The solid-phase extraction process coupled with high-performance liquid chromatography-tandem mass spectrometry for determining N-nitrosoamines in environmental water samples was established. The limits of detection were in the range of 0.01-0.05 ng/mL. The satisfactory recoveries (68.9-106.1%) were obtained at three different spiked concentrations (2, 5, and 8 ng/mL) in water samples, and the relative standard deviations were between 1.96 and 8.38%. This proposed method not only showed high sensitivity and good reusability but also provided a new adsorbent for enriching trace N-nitrosoamines in environmental water samples.

Electrochemical detection of hepcidin based on spiegelmer and MoS2NF-GNR@AuNPs as sensing platform

Spiegelmers, mirror image L- RNA oligonucleotides, possesses high plasma stability and non-immunogenicity. Herein, a novel spiegelmer based impedimetric biosensor grafted with Au nanoparticles and molybdenum disulfide nanoflowers/graphene nanoribbons nanocomposite has been designed to detect hepcidin in spiked-in human serum sample. Firstly, molybdenum disulfide nanoflowers/graphene nanoribbons (MoS₂NF-GNR) hybrid was drop-casted onto the FTO electrode followed by electro deposition of Au nanoparticles (AuNPs). Hepcidin specific thiolated spiegelmer was then immobilized on the MoS₂NF-GNR@AuNPs for hepcidin detection. Electrochemical impedance spectroscopy was used to assess the performance of the sensing platform based on the variation of charge transfer resistance (ΔR_ct) relative to the Fe(CN)₆^4-/3- electrochemical probe in the presence of hepcidin. The impedance signals were recorded at the frequency range of 10^-1 to 10⁵ Hz and potential was set as 0.18 V. Under optimized conditions, the limit of detection of spiegelmer based sensor for hepcidin was 0.173 pgmL^-1 within a wide linear range of 0.005-10 ngmL^-1. The biosensor possesses selectivity, acceptable reproducibility with RSD as 4.76% and stability for up to 20 days. The satisfactory recovery result (89.8-103.1 %) in human serum indicates that the sensor has applicability in clinical monitoring of hepcidin.

A magnetic MOF derivative with rich interactions formed under mild preparation conditions for the extraction of non-steroidal anti-inflammatory drugs from the Yellow River

For sorbents, good magnetic properties and rich interactions with targets are important ways to improve the efficiency of magnetic solid-phase extraction (MSPE). The magnetic MOF-101 derivative (MD) was obtained by heat-treating MOF-101 at different temperatures. After a series of characterizations, it was found that MD-350 had the best magnetic properties and retained more functional groups of the original MOF-101, and had better extraction efficiency as compared to MD obtained under other treatment temperatures for the MSPE of four non-steroidal anti-inflammatory drugs (NSAIDs) in water samples, coupled with high-performance liquid chromatography (HPLC). The remaining functional groups of MD-350 can produce more interactions with NSAIDs, such as hydrogen bonding, π-π conjugation, and coordination interactions; good magnetic properties facilitate the separation of the sorbent and the solution. These advantages indicate that the established extraction method demonstrated satisfactory extraction performance: an excellent recovery rate (96.73-100.61%) with a short extraction time (15 min), a wide linear range (4-400 μg L-1) with a determination coefficient of 0.9975-0.9993, a low LOD of 0.2-0.5 μg L-1 and up to 12 times service-life without the loss of the recovery rate. Satisfactory results were also obtained in extracting NSAIDs from Yellow River. All these results indicate that MD-350 prepared under mild conditions has potential as an MSPE sorbent to detect and remove NSAIDs from environmental waters with high efficiency and long service life.

Three-dimensional magnetic stannic disulfide composites for the solid-phase extraction of sulfonamide antibiotics

In the present work, three-dimensional (3D) and flower-like SnS₂ materials were coated on the surface of Fe₃O₄@nSiO₂ through an in-situ growth method. The 3D architecture could avoid the accumulation and reaggregation with better stability and was beneficial for the exposure of more active sites. The prepared magnetic SnS₂ composites were used for the enrichment of sulfonamide antibiotics (SAs), and various experimental parameters affecting the extraction efficiency were investigated. The results showed the equilibrium of extraction and desorption towards target SAs could be reached within 3 min by using the Fe₃O₄@nSiO₂-SnS₂ composites. Under optimized conditions, the proposed approach possessed good linearity in the range of 0.1-200 ng·mL^-1 with correlation coefficients r² above 0.9964 and low limits of detection (LODs) from 0.025 to 0.250 ng·mL^-1 for the five target SAs. Moreover, good repeatability was obtained with the intra-day and inter-day precision in terms of relative standard deviations (RSDs) within 1.1%-10.8% and 7.4%-13.1%, and the recoveries under three spiked concentrations were between 81.8% and 119.7% with adequate accuracy. Different samples including tap water, milk and honey were collected for magnetic solid-phase extraction and determination of target SAs by using the obtained Fe₃O₄@nSiO₂-SnS₂ composites to demonstrate the utility. All the results indicated that the proposed method had great potential for effective preconcentration and determination of SAs in complex samples.

Voltammetric detection of vitamin D employing Au-MoS2 hybrid as immunosensing platform

A voltammetric immunosensor based on molybdenum sulphide (MoS₂) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D₃ (25(OH)D₃) is reported. Anti-vit D (Ab-25(OH)D₃) was immobilized onto the cysteamine-modified MoS₂ and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS₂/FTO). The MoS₂ sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS₂/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS₂/FTO which acts as a linker to covalently bind Ab-25(OH)D₃. The Ab-25(OH)D₃-immobilized Cys/Au/MoS₂/FTO was used to detect 25(OH)D₃ using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D₃ and 25(OH)D₃. The immunosensor shows linear response from 1 pg mL^-1 to 100 ng mL^-1 25(OH)D₃ and a sensitivity of 189 μA [log (pg mL^-1)]^-1 cm^-2 along with a low limit of detection (LOD) of 0.38 pg mL^-1. The immunosensor is highly selective towards 25(OH)D₃ and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15-3.22%).

Three dimensional flower-like magnetic polyethyleneimine@MoS2 composites for highly efficient removal of Cr(VI) and Pb(II) ions

Magnetic Fe₃O₄ nanoparticles were coated by polyethyleneimine (PEI), and then Fe₃O₄@PEI was further modified with MoS₂ by the hydrothermal method to fabricate 3D flower-like structured magnetic polyethyleneimine@MoS₂ (MP@MoS₂) composites, and the composites were served as efficient adsorbents to capture Cr(VI) and Pb(II) from aqueous solution. The effects of temperature, pH, shaking time and environmental conditions on adsorption performance of MP@MoS₂ towards Cr(VI) and Pb(II) have been conducted by batch adsorption experiments. The prepared MP@MoS₂ exhibited high adsorption capacities (192.30 mg/g for Cr(VI) at pH 3.0 and 256.41 mg/g for Pb(II) at pH 6.0) and the adsorption equilibrium could be achieved in a short time. Moreover, MP@MoS₂ composites with high saturation magnetization could be simply separated under an external magnet. Combined experiments and spectral analysis, the underlying adsorption mechanism for Cr(VI) on MP@MoS₂ was mainly attributed to the reduction of Cr(VI) to Cr(III), and the removal of Pb(II) was due to the complexation with sulfur groups and amino-groups. Consequently, the prepared 3D flower-like structured MP@MoS₂ has a great potential for the practical application in removing Cr(VI) and Pb(II) from the aquatic environment.

Mechanical milling: a sustainable route to induce structural transformations in MoS2 for applications in the treatment of contaminated water

Two-dimensional (2D) nanomaterials have received much attention in recent years, because of their unusual properties associated with their ultra-thin thickness and 2D morphology. Besides graphene, a new 2D material, molybdenum disulfide (MoS₂), has attracted immense interest in various applications. On the other hand, ball-milling process provides an original strategy to modify materials at the nanometer scale. This methodology represents a smart solution for the fabrication of MoS₂ nanopowders extremely-efficient in adsorbing water contaminants in aqueous solution. This work reports a comprehensive morphological, structural, and physicochemical investigation of MoS₂ nanopowders treated with dry ball-milling. The adsorption performances of the produced nanopowders were tested using methylene blue (MB) dye and phenol in aqueous solution. The adsorption capacity as a function of ball-milling time was deeply studied and explained. Importantly, the ball-milled MoS₂ nanopowders can be easily and efficiently regenerated without compromising their adsorption capacity, so to be reusable for dye adsorption. The eventual toxic effects of the prepared materials on microcrustacean Artemia salina were also studied. The present results demonstrate that ball-milling of MoS₂ offers a valid method for large-scale production of extremely efficient adsorbent for the decontamination of wastewaters from several pollutants.