Iron oxide functionalized graphene nano-composite for dispersive solid phase extraction of chemical warfare agents from aqueous samples

Magnetic activated carbon as an adsorbent for extraction of DMMP from aqueous samples followed by GC-IMS analysis

Micro-porous magnetic activated carbon was prepared under ultrasonic irradiation as an adsorbent for dispersed solid phase extraction of dimethyl methyl phosphonate from water samples, before analysis by gas chromatography-ion mobility spectrometry. The magnetic activated carbon was synthesized and characterized by using a vibrating sample magnetometer, Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction techniques. Then, the effects of the amount of sorbent, extraction time and pH of the sample in the dispersive solid phase extraction method were investigated and optimized by the response surface method. The dispersion of 20 mg adsorbent powder in a 50 mL water sample for 5 minutes with chloroform as the desorption solvent showed an average recovery value of 95% for dimethyl methyl phosphonate. Afterward, the method was used successfully for the determination of dimethyl methyl phosphonate in river and spring water. The linear range was obtained to be 0.05-1 μg mL-1. The limit of detection and the limit of quantification were obtained to be 0.02 μg mL-1 and 0.05 μg mL-1 respectively. The analysis also showed good reproducibility with a relative standard deviation value of 3.1%. This method was shown to be easy, fast, reliable, and inexpensive.

Magnetic tubular nickel@silica-graphene nanocomposites with high preconcentration capacity for organothiophosphate pesticide removal in environmental water: Fabrication, magnetic solid-phase extraction, and trace detection

Organothiophosphate pesticides (OPPs) are the most common water contaminants, significantly endangering human health and bringing serious public safety issues. Thus, developing effective technologies for the removal or trace detection of OPPs from water is urgent. Herein, a novel graphene-based silica-coated core-shell tubular magnetic nanocomposite (Ni@SiO₂-G) was fabricated for the first time and used for the efficient magnetic solid-phase extraction (MSPE) of the OPPs chlorpyrifos, diazinon, and fenitrothion from environmental water. The experimental factors affecting extraction efficiency such as adsorbent dosage, extraction time, desorption solvent, desorption mode, desorption time, and adsorbent type were evaluated. The synthesized Ni@SiO₂-G nanocomposites showed a higher preconcentration capacity than the Ni nanotubes, Ni@SiO₂ nanotubes, and graphene. Under the optimized conditions, 5 mg of tubular nano-adsorbent displayed good linearity within the range of 0.1-1 μg·mL^-1, low limits of detection (0.04-0.25 pg·mL^-1), low limits of quantification (0.132-0.834 pg·mL^-1), good reusability (n = 5; relative standard deviations between 1.46% and 9.65%), low dosage (5 mg), and low real detection concentration (< 3.0 ng·mL^-1). Moreover, the possible interaction mechanism was investigated by density functional theory calculation. Results showed that Ni@SiO₂-G was a potential magnetic material for the preconcentration and extraction of formed OPPs at ultra-trace levels from environmental water.

Carbon nanomaterial-based membranes in solid-phase extraction

Carbon nanomaterials (CNMs) have some excellent properties that make them ideal candidates as sorbents for solid-phase extraction (SPE). However, practical difficulties related to their handling (dispersion in the atmosphere, bundling phenomena, reduced adsorption capability, sorbent loss in cartridge/column format, etc.) have hindered their direct use for conventional SPE modes. Therefore, researchers working in the field of extraction science have looked for new solutions to avoid the above-mentioned problems. One of these is the design of CNM-based membranes. These devices can be of two different types: membranes that are exclusively composed of CNMs (i.e. buckypaper and graphene oxide paper) and polysaccharide membranes containing dispersed CNMs. A membrane can be used either as a filter, operating under flow-through mode, or as a rotating device, operating under the action of magnetic stirring. In both cases, the main advantages arising from the use of membranes are excellent results in terms of transport rates, adsorption capability, high throughput, and ease of employment. This review covers the preparation/synthesis procedures of such membranes and their potential in SPE applications, highlighting benefits and shortcomings in comparison with conventional SPE materials (especially, microparticles carbonaceous sorbents) and devices. Further challenges and expected improvements are addressed too.

Metal oxide decorated porous carbons from controlled calcination of a metal-organic framework

Thermal decomposition of an iron-based MOF was conducted under controlled gas environments to understand the resulting porous carbon structure. Different phases and crystallite sizes of iron oxide are produced based on the specific gas species. In particular, air resulted in iron(iii) oxide, and D2O and CO2 resulted in the mixed valent iron(ii,iii) oxide. Performing the carbonization under non-oxidative or reducing conditions (N2, He, H2) resulted in the formation of a mixture of both iron(ii,iii) oxide and iron(iii) oxide. Based on in situ and air-free handling experiments, it was observed that this is partially due to the formation of zero-valent iron metal that is rapidly oxidized when exposed to air. Neutron pair distribution function analysis provided insight into the effect of the gas environment on the local structure of the porous carbon, indicating a noticeable change in local order between the D2O and the N2 calcined samples.

Applications of Graphene and Its Derivatives in Chemical Analysis

In this review, the applications of graphene and its derivatives in the chemical analysis have been described. The properties of graphene materials which are essential for their use in chemical and biochemical analysis are characterized. The materials are used in sensors and biosensors, in electrochemistry, in chromatography and in the sample preparation techniques. Chemical and electrochemical sensors containing graphene materials are useful devices for detecting some chemical and biochemical compounds. Chromatographic columns for HPLC with graphene containing stationary phases may be used for separation of polar and nonpolar components of some specific mixtures. Graphene materials could be successfully employed during sample preparation for analysis with SPE, magnetic SPE, and SPME techniques. HighlightsThe review of the applications of graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), in chemical and biochemical analysis is proposed.The electron donor-acceptor and proton donor-acceptor interactions for the graphene based materials - analytes systems and their impact on the analysis results are discussed, particularly:    i) in electrochemistry,ii) in chromatography,iii) in modern sample preparation techniquesiv) in sensors of different types.The essence of the thermal stability and the nomenclature of the graphene based materials in their different applications in chemical systems of different classes was discussed (and suggested).The benefits of using SPME fibers with immobilized graphene materials have been presented in detail.

Chemical Vapour Deposition of MWCNT on Silica Coated Fe3O4 and Use of Response Surface Methodology for Optimizing the Extraction of Organophosphorus Pesticides from Water

Multiwalled carbon nanotube (MWCNT) was fixed onto the surface of a magnetic silica (Fe₃O₄@SiO₂) substrate via chemical vapour deposition (CVD). Acetylene gas was used as the carbon source and cobalt oxide as the catalyst. The chemical and physical characteristics of the materials were investigated by transmission electron microscopy (TEM), Raman spectroscopy (RS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen adsorption/desorption isotherm. The synthesized Fe₃O₄@SiO₂-MWCNT nanocomposite was used as a magnetic solid phase extraction (MSPE) adsorbent for the preconcentration of organophosphorus pesticides (OPPs), specifically, azinphos methyl, chlorpyrifos, parathion, and malathion. The factors influencing the extraction efficiency such as pH, contact time, and adsorbent dosage were investigated and optimized by response surface methodology (RSM) and desirability function. Linear response was obtained in the concentration range of 10–200 μg/L for the analytes with determination coefficients ranging between 0.9955 and 0.9977. The limits of detection (LODs) and quantification (LOQs) were in the range of 0.004-0.150 μg/L and 0.013-0.499 μg/L, respectively. Fe₃O₄@SiO₂-MWCNT was applied in the extraction and subsequent determination of OPPs in water samples from Vaal River and Vaal Dam with recoveries ranging from 84.0 to 101.4% (RSDs = 3.8–9.6%, n = 3) in Vaal River and 86.2 to 93.8% (RSDs = 2.9–10.4%, n = 3) in Vaal Dam. The obtained results showed that the newly synthesized Fe₃O₄@SiO₂-MWCNT nanocomposite can be an efficient adsorbent with good potential for the preconcentration and extraction of selected OPPs from aqueous media.

Development of α- and γ-Fe2O3 decorated graphene oxides for glyphosate removal from water

In this study, the proposed adsorbent composed of graphene oxide (GO) functionalized by magnetic nanoparticles of iron oxide (α-γ-Fe2O3) was obtained by a simple ultrasonication process. This new material was used for the removal of glyphosate in water. The nanoparticulated iron oxide used was synthesized by means of a modified sol-gel method, which does not use organic solvents. The adsorbent material (GO-α-γ-Fe2O3) obtained was characterized by magnetic measurements, and it can be proved that it has superparamagnetic properties, allowing fast and efficient magnetic separation. The equilibrium time for the adsorption of glyphosate when using GO-α-γ-Fe2O3 was 2 hours and the maximum removal was 92% at 15°C, with a maximum adsorption capacity of 46.8 mg g-1. Langmuir model and pseudo-second-order kinetic model correlated satisfactorily to the experimental data. The thermodynamic parameters showed that the adsorption of glyphosate on GO-α-γ-Fe2O3 was spontaneous, exothermic and thermodynamically favorable at temperature of 15-45°C. Thus the adsorbent material GO-α-γ-Fe2O3 proposed in this study is considered a good candidate to be used in the removal of glyphosate from aqueous solutions, presenting high adsorption capacity, low cost and magnetic properties that facilitate the separation of the adsorbent material.

Identification of G-nerve agents at picogram levels from complex organic samples containing hydrocarbon interferences by aqueous extraction, followed by derivatization and liquid chromatography-mass spectrometry analysis

The chromatograms obtained from the gas chromatography-electron ionization mass spectrometric (GC-EI-MS) analysis of extracts containing G-nerve agents in the presence of diesel, gasoline, etc., are dominated by hydrocarbon backgrounds that "mask" the G-nerve agents, leading to severe difficulties in identification. This paper presents a practical solution for this challenge by transferring the G-nerve agents from the organic phase into the aqueous phase using liquid-liquid extraction (LLE), followed by derivatization with 2-[(dimethylamino)methyl]phenol (2-DMAMP), allowing ultrasensitive LC-ESI-MS/MS analysis of the G-derivatives. The proposed approach enables rapid identification of trace amounts of G-nerve agents with limits of identification (LOIs) at the pg/mL scale.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Mitigation in Multiple Effects of Graphene Oxide Toxicity in Zebrafish Embryogenesis Driven by Humic Acid

Graphene oxide (GO) is a widely used carbonaceous nanomaterial. To date, the influence of natural organic matter (NOM) on GO toxicity in aquatic vertebrates has not been reported. During zebrafish embryogenesis, GO induced a significant hatching delay and cardiac edema. The intensive interactions of GO with the chorion induces damage to chorion protuberances, excessive generation of (•)OH, and changes in protein secondary structure. In contrast, humic acid (HA), a ubiquitous form of NOM, significantly relieved the above adverse effects. HA reduced the interactions between GO and the chorion and mitigated chorion damage by regulating the morphology, structures, and surface negative charges of GO. HA also altered the uptake and deposition of GO and decreased the aggregation of GO in embryonic yolk cells and deep layer cells. Furthermore, HA mitigated the mitochondrial damage and oxidative stress induced by GO. This work reveals a feasible antidotal mechanism for GO in the presence of NOM and avoids overestimating the risks of GO in the natural environment.