Silica-graphene porous nanocomposites for environmental remediation: A critical review

With the increase of industrialization, there is an urgent need for developing technologies to detect and remove toxic pollutants from water bodies. The pollutants are often released to the environment due to the consumption of raw materials that are necessary for the production of technological goods (such as chemical and pharmaceutical compounds, metals, and alloys or foods). Amongst all the remediation techniques, adsorption is considered as one of the preferred techniques, due to its fast and efficient removal of contaminants. Novel materials, which are engineered for selective and responsive water remediation, have also recently revealed a strong potential in the detection of pollutants. Here, current trends of silica-graphene (SG) porous composites for the removal of oils, organic solvents, heavy metals, and dyes are reviewed in detail. Insights on the modifications of composites to enhance their sorption performance have been highlighted. In addition, the detection of pollutants using porous SG nanocomposites is also critically reviewed. Overall, SG composites reveal a strong potential as nanostructure materials with improved efficiency for environmental-based applications.

Microextraction Techniques with Deep Eutectic Solvents

In this review, the ever-increasing use of deep eutectic solvents (DES) in microextraction techniques will be discussed, focusing on the reasons needed to replace conventional extraction techniques with greener approaches that follow the principles of green analytical chemistry. The properties of DES will be discussed, pinpointing their exceptional performance and analytical parameters, justifying their current extensive scientific interest. Finally, a variety of applications for commonly used microextraction techniques will be reported.

The Current Role of Graphene-Based Nanomaterials in the Sample Preparation Arena

Since its discovery in 2004 by Novoselov et al., graphene has attracted increasing attention in the scientific community due to its excellent physical and chemical properties, such as thermal/mechanical resistance, electronic stability, high Young's modulus, and fast mobility of charged atoms. In addition, other remarkable characteristics support its use in analytical chemistry, especially as sorbent. For these reasons, graphene-based materials (GBMs) have been used as a promising material in sample preparation. Graphene and graphene oxide, owing to their excellent physical and chemical properties as a large surface area, good mechanical strength, thermal stability, and delocalized π-electrons, are ideal sorbents, especially for molecules containing aromatic rings. They have been used in several sample preparation techniques such as solid-phase extraction (SPE), stir bar sorptive extraction (SBSE), magnetic solid-phase extraction (MSPE), as well as in miniaturized modes as solid-phase microextraction (SPME) in their different configurations. However, the reduced size and weight of graphene sheets can limit their use since they commonly aggregate to each other, causing clogging in high-pressure extractive devices. One way to overcome it and other drawbacks consists of covalently attaching the graphene sheets to support materials (e.g., silica, polymers, and magnetically modified supports). Also, graphene-based materials can be further chemically modified to favor some interactions with specific analytes, resulting in more efficient hybrid sorbents with higher selectivity for specific chemical classes. As a result of this wide variety of graphene-based sorbents, several studies have shown the current potential of applying GBMs in different fields such as food, biological, pharmaceutical, and environmental applications. Within such a context, this review will focus on the last five years of achievements in graphene-based materials for sample preparation techniques highlighting their synthesis, chemical structure, and potential application for the extraction of target analytes in different complex matrices.

Role of Ionic Liquids in Composites in Analytical Sample Preparation

Ionic liquids (ILs) are a group of non-conventional salts with melting points below 100 °C. Apart from their negligible vapor pressure at room temperature, high thermal stability, and impressive solvation properties, ILs are characterized by their tunability. Given such nearly infinite combinations of cations and anions, and the easy modification of their structures, ILs with specific properties can be synthesized. These characteristics have attracted attention regarding their use as extraction phases in analytical sample preparation methods, particularly in liquid-phase extraction methods. Given the liquid nature of most common ILs, their incorporation in analytical sample preparation methods using solid sorbents requires the preparation of solid derivatives, such as polymeric ILs, or the combination of ILs with other materials to prepare solid IL-based composites. In this sense, many solid composites based on ILs have been prepared with improved features, including magnetic particles, carbonaceous materials, polymers, silica materials, and metal-organic frameworks, as additional materials forming the composites. This review aims to give an overview on the preparation and applications of IL-based composites in analytical sample preparation in the period 2017–2020, paying attention to the role of the IL material in those composites to understand the effect of the individual components in the sorbent.

Deep eutectic solvent functionalized graphene oxide composite adsorbent for miniaturized pipette-tip solid-phase extraction of toluene and xylene exposure biomarkers in urine prior to their determination with HPLC-UV

A deep eutectic solvent functionalized graphene oxide composite adsorbent (DFG) was synthesized through reversible-addition fragmentation chain-transfer polymerization. The synthesized DFG had multiple adsorption interactions after covalent modification with a deep eutectic solvent (allyltriethylammonium bromide/ethylene glycol). Adsorption isotherms and kinetics studies of DFG indicate that the adsorption of hippuric acid (HA) and methylhippuric acid (MHA) was monolayer chemical adsorption. The comparison of DFG with commercial adsorbents demonstrates that the adsorption ability of DFG was superior. This was due to the multiple adsorption interactions of DFG for the three analytes (mainly π-interaction, hydrogen bonding, electrostatic adsorption, and hydrophobic interaction). The DFG adsorbent was applied to miniaturized pipette-tip solid-phase extraction (MPT-SPE), followed by high-performance liquid chromatography (HPLC) to determine biomarkers in urine for toluene and xylene exposure. The DFG-MPT-SPE-HPLC method required only 2.00 mg of DFG as adsorbent, 0.50 mL of washing solvent, and 0.40 mL of elution solvent to achieve a wide linear range (0.200-200 μg mL^-1), high recoveries (90.9-99.1%), and high precision (RSD ≤ 6.3%). The proposed method was applied to determine HA and MHA in urine samples from occupational workers. Graphical abstract Deep eutectic solvent functionalized graphene oxide composite adsorbent for miniaturized pipette-tip solid-phase extraction of toluene and xylene exposure biomarkers in urine prior to their determination with HPLC-UV.

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.

Dispersion of magnetic graphene oxide nanoparticles coated with a deep eutectic solvent using ultrasound assistance for preconcentration of methadone in biological and water samples followed by GC-FID and GC-MS

Magnetic graphene nanoparticles coated with a new deep eutectic solvent (Fe₃O₄@GO-DES) were developed for efficient preconcentration of methadone. The extracted methadone was then analyzed by gas chromatography-flame ionization detection (GC-FID) or gas chromatography-mass spectrometry (GC-MS). Fe₃O₄@GO-DES were characterized by Fourier transform IR and X-ray diffraction techniques. Ultrasound was used to enhance the dispersion of the sorbent, with a high extraction recovery. Some parameters affecting the extraction recovery, such as pH, type of deep eutectic solvent, sample volume, amount of sorbent, extraction time, and type of eluent, were investigated. Under optimum conditions, the method developed was linear in the concentration range from 3 to 45,000 μg L^-1 for GC-FID and from 0.1 to 500 μg L^-1 for GC-MS, with a detection limit of 0.8 μg L^-1 for GC-FID and 0.03 μg L^-1 for GC-MS. The relative standard deviations (n = 6) as the intraday and interday precisions of the methadone spike at a concentration of 100 μg L^-1 were 5.8% and 8.4% respectively for GC-FID. The preconcentration factor was 250. Relative recoveries from spiked plasma, urine, and water samples ranged from 95.1% to 101.5%.

Elucidating the Properties of Graphene-Deep Eutectic Solvents Interface

The properties of five deep eutectic solvents prepared based on the selection of choline chloride ionic liquid as hydrogen bond acceptor, which are mixed with several hydrogen bond donors with selected molecular features, were studied theoretically at graphene interfaces via both density functional theory and classical molecular dynamics methods. Molecular structuring at the interfaces, angular orientation, densification, and dynamic properties were analyzed upon adsorption on the graphene surface and when the deep eutectic solvents were confined between two graphene sheets and analyzed in terms of the role of the type of hydrogen bond donor for each solvent. Likewise, the behavior of deep eutectic solvent nanodroplets on graphene was simulated leading to the calculation of contact angles and nanowetting with further studies considering the effect of an external electric field on nanodroplet properties.

Deep eutectic liquid organic salt as a new solvent for carrier-mediated hollow fiber liquid phase microextraction of lead from whole blood followed by electrothermal atomic absorption spectrometry

In the present work, for the first time, a new carrier-mediated hollow fiber liquid phase microextraction (CM-HFLPME) technique was applied for the determination of lead in whole blood samples by means of ETAAS.