Hybrid nanosheets composed of molybdenum disulfide and reduced graphene oxide for enhanced solid phase extraction of Pb(II) and Ni(II)

An L-cysteine based sensor for Cu2+ detection applicable for both environmental water and human plasma

A flexible electrochemical sensor with high sensitivity and specificity is developed using gold nanoparticles (AuNPs) and a reduced graphene oxide/molybdenum disulfide (rGo-MoS2) composite modified screen printed carbon electrode (SPCE), with L-cysteine (L-Cys) as a probe for Cu2+ target recognition. Owing to the AuNPs/rGo-MoS2, the electron transference ability is improved by increasing the specific surface area of the working electrode, and a high sensitivity is achieved. Meanwhile, the bidentate chelation of L-Cys to Cu2+ contributes to a good selectivity. Using differential pulse voltammetry (DPV) for spiked standard Cu2+, the test results show a dynamic range from 0.1 μM to 100 μM, a detection limit of 0.020 μM, and a high sensitivity of 1.190 μA μM-1. Furthermore, detection in both environmental water and human plasma samples demonstrates a wide applicability of this sensor in various matrices, and an excellent feasibility for environmental and clinical applications.

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.

A magnetic solid phase extraction procedure for Pb(II) at trace levels on magnetic Luffa@TiO2 in food and water samples

A novel magnetic Luffa@TiO₂ sorbent was synthesized and characterized by using XRD, FTIR and SEM techniques. Magnetic Luffa@TiO₂ was used for solid phase extraction of Pb(II) in food and water samples prior to its flame atomic absorption spectrometric (FAAS) detection. The analytical parameters such as pH, adsorbent quantity, type and volume of eluent, and foreign ions were optimized. Analytical features such as the limit of detection (LOD) and the limit of quantification (LOQ) of Pb(II) are 0.04 μg L^-1 and 0.13 μg L^-1 for liquid samples and 0.159 ng/g and 0.529 ng/g for solid samples, respectively. The preconcentration factor (PF) and relative standard deviation (RSD%) were found 50, and 4 % respectively. The method was validated by using three certified reference materials (NIST SRM 1577b bovine liver, TMDA-53.3 and TMDA-64.3fortified water). The presented method was applied to lead contents of some food and natural water samples.

Dispersive Micro-Solid Phase Extraction Using a Graphene Oxide Nanosheet with Neocuproine and Batocuproine for the Preconcentration of Traces of Metal Ions in Food Samples

A dispersive micro-solid phase extraction (Dµ-SPE) method for the preconcentration of trace metal ions (Pb, Cd, Cr, Mn, Fe, Co, Ni, Cu, Zn) on graphene oxide with the complexing reagents neocuproine or batocuproine is presented here. Metal ions form cationic complexes with neocuproine and batocuproine. These compounds are adsorbed on the GO surface via electrostatic interactions. The factors affecting the separation and preconcentration of analytes such as pH, eluent (concentration, type, volume), amount of neocuproine, batocuproine and GO, mixing time, and sample volume were optimized. The optimal sorption pH was 8. The adsorbed ions were effectively eluted with 5 mL 0.5 mol L^-1 HNO₃ solution and determined by the ICP-OES technique. The preconcentration factor for the GO/neocuproine and GO/batocuproine in the range 10-100 and 40-200 was obtained for the analytes, with detection limits of 0.035-0.84 ng mL^-1 and 0.047-0.54 ng mL^-1, respectively. The method was validated by the analysis of the three certified reference materials: M-3 HerTis, M-4 CormTis, and M-5 CodTis. The procedure was applied to determine metal levels in food samples.

Flower-like molybdenum disulfide/cobalt ferrite composite for the extraction of benzotriazole UV stabilizers in environmental samples

Benzotriazole UV stabilizers (BUVSs) are a class of emerging contaminants of concern; the development of rapid and convenient monitoring method for these trace-level pollutants in waters is of crucial significance in environmental science. Here, a novel magnetic flower-like molybdenum disulfide/cobalt ferrite nanocomposite (MoS₂/CoFe₂O₄) was synthesized by hydrothermal reaction. Compared with the conventional Fe₃O₄-based magnetic composites, the proposed material just required a minimum consumption of Co/Fe towards the equivalent of MoS₂ while providing superior magnetization performance. Taking advantages of high adsorption capacity, extraordinary stability, and repeatability in construction, MoS₂/CoFe₂O₄ was applied to the extraction to BUVSs. The enrichment factors of three BUVSs were in the range 164-193 when 20 mL of environmental water sample was loaded on 40 mg of the adsorbent. MoS₂/CoFe₂O₄ could be regenerated and recycled at least 10 cycles of adsorption/desorption with recoveries of 80.1-111%. The method of MoS₂/CoFe₂O₄-based extraction coupled with high-performance liquid chromatography-variable wavelength detector was applied to the monitoring of BUVSs in seawater, lake water, and wastewater, which gave detection limits (S/N = 3) of 0.023-0.030 ng·mL^-1 and recoveries of 80.1-110%. The intra-day and inter-day precisions (relative standard deviation, RSDs, n = 3) were in the range 1.6-7.5% and 3.2-11.5%, respectively. The approach is an alternative for efficient and sensitive extraction and determination of trace-level environmental pollutants in waters.

Facile Synthesis and Environmental Applications of Noble Metal-Based Catalytic Membrane Reactors

Noble metal nanoparticle-loaded catalytic membrane reactors (CMRs) have emerged as a promising method for water decontamination. In this study, we proposed a convenient and green strategy to prepare gold nanoparticle (Au NPs)-loaded CMRs. First, the redox-active substrate membrane (CNT-MoS2) composed of carbon nanotube (CNT) and molybdenum disulfide (MoS2) was prepared by an impregnation method. Water-diluted Au(III) precursor (HAuCl4) was then spontaneously adsorbed on the CNT-MoS2 membrane only through filtration and reduced into Au(0) nanoparticles in situ, which involved a “adsorption–reduction” process between Au(III) and MoS2. The constructed CNT-MoS2@Au membrane demonstrated excellent catalytic activity and stability, where a complete 4-nitrophenol transformation can be obtained within a hydraulic residence time of <3.0 s. In addition, thanks to the electroactivity of CNT networks, the as-designed CMR could also be applied to the electrocatalytic reduction of bromate (>90%) at an applied voltage of −1 V. More importantly, by changing the precursors, one could further obtain the other noble metal-based CMR (e.g., CNT-MoS2@Pd) with superior (electro)catalytic activity. This study provided new insights for the rational design of high-performance CMRs toward various environmental applications.

Mechanism of novel MoS2-modified biochar composites for removal of cadmium (II) from aqueous solutions

The purpose of this study was to develop a MoS₂-impregnated biochar (MoS₂@BC) via hydrothermal reaction for adsorption of cadmium (Cd) from an aqueous solution. The prepared adsorbents were characterized, and their abilities to remove Cd(II) were evaluated. The Langmuir and pseudo-second-order models better described the removal of Cd(II) by MoS₂@BC. The prepared MoS₂@BC exhibited excellent monolayer adsorption capacity. The S-containing functional groups on MoS₂@BC enhanced the adsorption of Cd(II). Multiple Cd(II) sorption mechanisms were identified; including Cd(II)-π interactions, ion exchange, electrostatic interaction, and complexation. The dominant mechanism involved Cd-O (38.3%) bonds and Cd-S complexation (61.7%) on MoS₂@BC. The as-prepared MoS₂@BC is both economical and efficient, making it an excellent material for environmental Cd(II) remediation.

Facile preparation of MoS2@Kaolin composite by one-step hydrothermal method for efficient removal of Pb(II)

MoS₂@Kaolin was prepared by facile one-step hydrothermal method for the efficient adsorption of Pb(II) from aqueous solution. XRD, TG, SEM, BET, XPS and FTIR were used to characterize the phase and structure of composite before and after the adsorption of Pb(II). The results showed that MoS₂ nanosheets were successfully assembled on kaolinite surface to form MoS₂@Kaolin, and the adsorption capacity of the MoS₂@Kaolin is 1.74 and 16.95 times than that of single MoS₂ and kaolinite, respectively. MoS₂@Kaolin composite exhibited a fast adsorption rate for Pb(II) and an excellent adsorption efficiency for Pb(II) in a wide pH range (2-5.5). The adsorption process followed the Langmuir isotherm model and maximum adsorption capacity was 280.39 mg/g. The adsorption kinetics of MoS₂@Kaolin composite to Pb(II) fitted well with the pseudo-second-order kinetics models, which showed that the adsorption process was controlled by chemical sorption. MoS₂@Kaolin showed excellent regeneration and maintained high selectivity adsorption with co-existence metal ions. The adsorption mechanism was that the Pb(II) reacted with the S atoms on surface of MoS₂@Kaolin under oxidation conditions provided by molybdenum disulfide to form the insoluble compound β-Pb₃O₂SO₄ in aqueous solution. MoS₂@Kaolin was an adsorbent for Pb(II) in aqueous solution with excellent adsorption properties and application potential.

Ultrasound-assisted dispersive micro-solid phase extraction using molybdenum disulfide supported on reduced graphene oxide for energy dispersive X-ray fluorescence spectrometric determination of chromium species in water

Molybdenum disulfide (MoS2) was supported on graphene oxide (GO) by hydrothermal method. The resulting nanocomposite (MoS2-rGO) was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The experiments show that at pH 2, MoS2-rGO has a great affinity for adsorption of hexavalent chromium ions while Cr(III) ions remain in aqueous sample. In the adsorption process, the dominant role plays chemisorption. The determined adsorption capacity is 583.5 mg g-1. Parameters affecting the extraction process, namely sample pH, sample volume, contact time, and matrix ions, were investigated by sequential batch tests. Under optimal conditions (pH 2, sample volume 50 mL, sonication time 10 min, adsorbent mass 1 mg), the calibration curve covers the 1-200 ng mL-1 range with a correlation coefficient (R2) of 0.998. The recovery of the method is 97 ± 3%. Other data of merit include a relative standard deviation of < 3.5%, enrichment factor of 3350, and detection limit of 0.050 ng mL-1. The accuracy of the method was confirmed by analysis of the reference materials QC1453 (chromium VI in drinking water) and QC3015 (chromium VI in seawater). The method was successfully applied to chromium speciation in water samples, including high salinity ones. The concentration of Cr(III) was calculated as the difference between the total concentration of chromium (after oxidation of Cr(III) to Cr(VI) with potassium permanganate) and the initial Cr(VI) content.Graphical abstract Schematic presentation of a method for determination of chromium species by energy dispersive X-ray fluorescence spectrometry after preconcentration on molybdenum disulfide supported on reduced graphene oxide.

Recent Advances in Nanomaterials for Analysis of Trace Heavy Metals

In an effort to achieve high sensitivity analysis methods for ultra-trace levels of heavy metals, numerous new nanomaterials are explored for the application in preconcentration processes and sensing systems. Nanomaterial-based methods have proven to be effective for selective analysis and speciation of heavy metals in combination with spectrometric techniques. This review outlined the different types of nanomaterials applied in the field of heavy metal analysis, and concentrated on the latest developments in various new materials. In particular, the functionalization of traditional materials and the exploitation of bio-functional materials could increase the specificity to target metals. The hybridization of multiple materials could improve material properties, to build novel sensor system or achieve detection-removal integration. Finally, we discussed the future perspectives of nanomaterials in the heavy metal preconcentration and sensor design, as well as their respective advantages and challenges. Despite impressive progress and widespread attention, the development of new nanomaterials and nanotechnology is still hampered by numerous challenges, particularly in the specificity to the target and the anti-interference performance in complex matrices.

A magnetic graphene-like MoS2 nanocomposite for simultaneous preconcentration of multi-residue herbicides prior to UHPLC with ion trap mass spectrometric detection

A magnetic graphene-like molybdenum disulfide nanocomposite was prepared by liquid-phase exfoliation and hydrothermal synthesis. The morphology, structure, and magnetic behavior of the nanocomposite were characterized by X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, scanning electron microscopy and transmission electron microscopy. The nanocomposite was employed as a sorbent for magnetic solid-phase extraction (MSPE) of eight triazine and ten sulfonylurea herbicides from environmental water and corn samples. Specifically, this was studied with cyanazine, simetryn, atrazine, methoprotryne, ametryn, prometryn, terbutryn, dipropetryn, metsulfuron-methyl, sulfometuron-methyl, amidosulfuron, rimsulfuron, nicosulfuron, bensulfuron-methyl, halosulfuron-methyl, pyrazosulfuron-ethyl, chlorimuron-ethyl, and cyclosulfamuron. The parameters affecting extraction efficiency (sorbent amount, pH value of the sample, extraction and elution conditions) were studied and optimized. Following MSPE, the multi-residue herbicides were quantified by ultra-high performance liquid chromatography combined with ion trap mass spectrometry and electrospray ionization. The limits of detection range between 20 and 170 ng·L^-1. The extraction recoveries of eighteen herbicides from corn samples were in the range between of 64.7% and 103.1%, with RSDs of <17.6%. Graphical abstract Schematic presentation of magnetic graphene-like MoS₂ nanocomposite as an absorbent for simultaneous preconcentration of eight triazine and ten sulfonylurea herbicides in corn and water prior to ultra-high performance liquid chromatography (UHPLC) with ion trap mass spectrometry detection.

Novel porous magnetic nanospheres functionalized by β-cyclodextrin polymer and its application in organic pollutants from aqueous solution

Magnetic β-cyclodextrin (β-CD) porous polymer nanospheres (P-MCD) was fabricated by one-pot solvent thermal method using β-CD immobilized Fe₃O₄ magnetic nanoparticles with tetrafluoroterephthalonitrile as the monomer. Compared with the β-CD polymerization method reported in the literature,_ENREF_1 the synthetic route is effective and simple, thereby overcoming the harsh conditions that require nitrogen protection and always maintain anhydrous and oxygen-free. Moreover, the immobilization of β-CD on magnetic nanoparticles is combined with the cross-linking polymerization of the cross-linker, leading to a good synergistic effect on the removal of contaminants. Meanwhile, the dispersibility of the magnetic carrier enhances the dispersion of the β-CD porous polymer in the aqueous phase, and improves the inclusion adsorption performance and the adsorption process. P-MCD exhibited superior adsorption capacity and fast kinetics to MB. The maximum adsorption capacity of MB for P-MCD was 305.8 mg g ^-1, which is more than β-CD modified Fe₃O₄ magnetic nanoparticles (Fe₃O₄@β-CD). Moreover, the material had a short equilibrium time (5 min) for MB, high recovery and good recyclability (the adsorption efficiency was still above 86% after five repeated uses).

Achieving Controllable MoS2 Nanostructures with Increased Interlayer Spacing for Efficient Removal of Pb(II) from Aquatic Systems

The development of new synthesis approaches for MoS₂ is necessary to achieve controlled morphologies and unique physicochemical properties that can improve its efficiency in particular applications. Herein, a facile one-step hydrothermal route is proposed to prepare controllable MoS₂ micro/nanostructures with an increased interlayer using sodium diethyldithiocarbamate trihydrate as the new S source at different pH values. To investigate the morphology, chemical composition, and structure of the MoS₂ micro/nanostructures, various characterization techniques were used. The obtained microrods, microspheres, and microrods with hairlike structures (denoted as MoS₂-N-H) were composed of MoS₂ nanosheets with increased interlayer spacing (∼1.0 nm) and utilized for the removal of Pb(II) from aquatic systems. Among the structures, MoS₂-N-H demonstrated the highest adsorption capacity (303.04 mg/g) for Pb(II) due to the existence of -S/-C/-N/-O-comprised functional groups on its surface, which led to strong Pb-S complexation and electrostatic attractions. The uptake of Pb(II) onto MoS₂-N-H followed pseudo-second-order kinetics and Freundlich isotherm. To evaluate its practical applicability, the adsorbent was employed in real mine water analysis; it was found that MoS₂-N-H could adsorb almost 100% of the Pb(II) ions in the presence of various coexisting ions. Additionally, after Pb(II) adsorption, MoS₂-N-H was transformed into PbMoO_{4- x}S _x spindlelike nanostructures, which were further used for photodegradation of an antibiotic, viz., ciprofloxacin (CIP), to avoid secondary environment waste. Thus, this investigation provides an effective one-pot approach to fabricate controllable MoS₂ micro/nanostructures with increased interlayer spacing for water treatment. The utility of these nanostructures in related supercapacitor/battery applications may also be envisaged because of their unique structural properties.

Applications of three-dimensional graphenes for preconcentration, extraction, and sorption of chemical species: a review

This review (with 115 refs) summarizes applications of 3-dimensional graphene (3DGs) and its derivatives in the fields of preconcentration, extraction, and sorption. Following an introduction into the field (including a definition of the materials treated here), the properties and synthetic strategies for 3DGs are described. The next section covers applications of 3DG-based adsorbents in solid phase extraction of organic species including drugs, phthalate esters, chlorophenols, aflatoxins, insecticides, and pesticides. Another section treats applications of 3DGs in solid phase microextraction of species such as polycyclic aromatic hydrocarbons, alcohols, and pesticides. We also describe how the efficiency of assays may be improved by using these materials as a sorbent. A final section covers conclusions and perspectives. Graphical abstract Graphical abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.Tiff file of graphical abstract was attached. Schematic presentation of synthesis of three-dimensional graphene (3DG) from two-dimensional graphene (2DG) with self-assembly, template-assisted and direct deposition methods. Application of 3DG-based nanoadsorbents in direct immersion-solid phase microextraction (DI-SPME), headspace-SPME (HS-SPME), magnetic-solid phase extraction (Magnetic-SPE), dispersive-SPE, and magnetic sheet-SPE.

Graphene oxide chemically modified with 5-amino-1,10-phenanthroline as sorbent for separation and preconcentration of trace amount of lead(II)

Graphene oxide (GO) was chemically functionalized with 5-amino-1,10-phenanthroline. The resulting conjugate (phen-GO) was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The experiments show that phen-GO has a high affinity for extraction of Pb(II) ions. Isotherms and kinetics fit the Langmuir model and pseudo-second-order equations. By using phen-GO as a sorbent, Pb(II) ions can be quantitatively adsorbed at pH 6.0. The adsorption capacity is 548 mg g^-1. Following desorption with 2 mol L^-1 HNO₃, Pb(II) was quantified by inductively coupled plasma optical emission spectrometry. The effects of pH value, eluent type, sorption time, sample volume, and matrix ions were optimized. The accuracy of the method was validated by analysis of the reference materials DOLT-3 (dogfish liver) and SRM 1640a (natural water). Under optimal conditions, the calibration plots cover the 0.25 to 500 ng mL^-1 Pb(II) concentration range. The method was successfully applied to the analysis of spiked water and biological samples. Other figures of merit include a preconcentration factor of 250, a detection limit of 46 ng L^-1, and a relative standard deviation of <5%. Graphical abstract Schematic presentation of the dispersive solid-phase extraction of lead(II) ions using graphene oxide modified with 5-amino-1,10-phenanthroline, followed by their determination by inductively coupled plasma optical emission spectrometry (ICP OES).

Removal and Recovery of Heavy Metal Ions by Two-dimensional MoS2 Nanosheets: Performance and Mechanisms

We investigated the removal of heavy metals from water by two-dimensional MoS₂ nanosheets suspended in aqueous solution, and restacked as thin film membranes, respectively. From these studies we elucidated a new heavy metal ion removal mechanism that involves a reduction-oxidation (redox) reaction between heavy metal ions and MoS₂ nanosheets. Ag⁺ was used as a model species and MoS₂ nanosheets were prepared via chemical exfoliation of bulk powder. We found that the Ag⁺ removal capacity of suspended MoS₂ nanosheets was as high as ∼4000 mg/g and adsorption accounted for less than 20% of removal, suggesting the reduction of Ag⁺ to metallic silver as a dominant removal mechanism. Furthermore, we demonstrated that MoS₂ membranes were able to retain a similar high removal capacity, and attribute this capability to the formation of a conductive, permeable multilayer MoS₂ structure, which enables a corrosion-type reaction involving electron transfer from a MoS₂ site inside the membrane (anode) to another site on membrane surface (cathode) where heavy metal ions are reduced to metallic particles. The membrane surface remains active to efficiently recover metallic particles, because the primary oxidation products are soluble, nontoxic molybdate and sulfur species, which do not form an insulating oxide layer to passivate the membrane surface. Therefore, MoS₂ membranes can be used effectively to remove and recover precious heavy metals from wastewater.

Determination of sulfonamides in milk by capillary electrophoresis with PEG@MoS2 as a dispersive solid-phase extraction sorbent

A synthetic polyethylene glycol-molybdenum disulfide (PEG@MoS₂) composite was prepared using a simple method, and the application of this material in dispersive solid-phase extraction (DSPE) was investigated for the enrichment of eight sulfonamides (SAs) in milk samples. The composite was characterized by energy dispersive spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller measurements. The results showed that the MoS₂ synthesized in the presence of PEG has the advantage of a larger surface area and that the adsorption effect of this MoS₂ was enhanced. After extraction, the eight SAs were separated by capillary zone electrophoresis with a good linear relationship (R² > 0.9902) in the range of 0.3-30 µg ml^-1 and good precision (between 0.32% and 9.83%). Additionally, good recoveries (between 60.52% and 110.91%) were obtained for the SAs in the milk samples. The developed PEG@MoS₂-based DSPE method could be applied for the enrichment of SAs in real milk samples.

Structure-enhanced removal of Cr(vi) in aqueous solutions using MoS2 ultrathin nanosheets

Molybdenum disulfide (MoS₂) ultrathin nanosheets with enlarged interlayer spacing and defects enables the structure-enhanced removal of Cr(vi), in which the synergistic effects of adsorption and reduction not only captured Cr(vi) from aqueous solutions, but also alleviated the toxicity of chromium to some degree.