Facile one-pot synthesis of fluorinated graphene oxide for electrochemical sensing of heavy metal ions

Effects of Heteroatom Doping on the Electrochemical Hydrogen Uptake and Release of Pd-Decorated Reduced Graphene Oxide

Heteroatom doping has been widely recognized as a key strategy for improving the electrochemical properties of graphene-based materials for hydrogen storage. However, a precise understanding of how heteroatom doping influences catalytic performance, specifically regarding the intricate effects of doping-induced electron redistribution, has been lacking. Here, we report on a comprehensive exploration of the electrochemical performance enhancement in Pd-decorated reduced graphene oxide (rGO) nanocomposites through fluorine (F) or nitrogen (N) doping. Various analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were employed to thoroughly characterize the synthesized nanocomposites. The findings revealed that either F or N doping effectively addressed clustering issues of Pd nanoparticles formed on the rGO surface, resulting in improved homogeneity of Pd distribution. Electrochemical studies provided crucial insights into hydrogen adsorption-desorption behaviors. The heteroatom doped nanocomposites, Pd/N-rGO and Pd/F-rGO, exhibited superior electrochemical performance, which can be attributed to the increase of the active sites due to the N-/F-doping, respectively. The hydrogen discharge capacities of Pd/N-rGO (80.9 mAh g-1) and Pd/F-rGO (25.0 mAh g-1) nanocomposites were determined to be over 4.0 and 1.2 times higher than that of the Pd/rGO (20.1 mAh g-1), respectively. The distinctive electrochemical performances observed between the two types of heteroatom-containing nanocomposites highlight the subtle structural modifications of Pd nanoparticles as the key factor influencing performance. This research contributes essential knowledge to the evolving field of hydrogen storage materials, emphasizing the promising potential of heteroatom-doped Pd-decorated rGO nanocomposites for advancing clean and sustainable energy solutions.

Preparation magnetic graphene oxide/diethylenetriamine composite for removal of methylene blue from aqueous solutions

Graphene oxide (GO) and its derivatives have several applications in many areas such as environmental and energy materials, water treatment and biomedical technologies. Because of having various polar groups on its surface, GO is considered as an excellent adsorbent. However, for many applications such as adsorption of pollution from aqueous solutions, chemical functionalization of graphene oxide is often a necessary requirement. In the present study, a new composite from graphene oxide, diethylenetriamine (DETA) and silica coated MnFe2O4 nanoparticles (GO/DETA/MnFe2O4@SiO2) was prepared. The structure, thermal stability and magnetic properties of the composite were studied by FT-IR, XRD, SEM, EDS, VSM and TGA spectroscopic methods. The prepared composite showed magnetic property with a saturation magnetization of 3.0 emu/g. The adsorption properties of GO/DETA/MnFe2O4@SiO2 composite for methylene blue (MB) in aqueous solution were studied using batch method. The effects of important parameters on the surface adsorption process of MB, including pH, contact time, adsorbent dosage and initial dye concentration were investigated. The adsorption isotherm was in accordance with Langmuir model showing surface homogeneity of the adsorbent. According to the Langmuir analysis, the maximum adsorption capacity (qm) of GO/DETA/MnFe2O4@SiO2 composite for MB was found to be 243.91 mg/g. The kinetic studies showed that the adsorption was pseudo first-order process. In addition, the thermodynamic studies indicated the adsorption was spontaneous and endothermic process.

Recent advances and trends in innovative biosensor-based devices for heavy metal ion detection in food

Low-cost, reliable, and efficient biosensors are crucial in detecting residual heavy metal ions (HMIs) in food products. At present, based on distance-induced localized surface plasmon resonance of noble metal nanoparticles, enzyme-mimetic reaction of nanozymes, and chelation reaction of metal chelators, the constructed optical sensors have attracted wide attention in HMIs detection. Besides, based on the enrichment and signal amplification strategy of nanomaterials on HMIs and the construction of electrochemical aptamer sensing platforms, the developed electrochemical biosensors have overcome the plague of low sensitivity, poor selectivity, and the inability of multiplexed detection in the optical strategy. Moreover, along with an in-depth discussion of these different types of biosensors, a detailed overview of the design and application of innovative devices based on these sensing principles was provided, including microfluidic systems, hydrogel-based platforms, and test strip technologies. Finally, the challenges that hinder commercial application have also been mentioned. Overall, this review aims to establish a theoretical foundation for developing accurate and reliable sensing technologies and devices for HMIs, thereby promoting the widespread application of biosensors in the detection of HMIs in food.

Fluorinated photoreduced graphene oxide with semi-ionic C-F bonds: An effective carbon based photocatalyst for the removal of volatile organic compounds

There is much interest in developing metal-free halogenated graphene such as fluorinated graphene for various catalytic applications. In this work, a fluorine-doped graphene oxide photocatalyst was investigated for photocatalytic oxidation (PCO) of a volatile organic compound (VOC), namely gaseous methanol. The fluorination process of graphene oxide (GO) was carried out via a novel and facile solution-based photoirradiation method. The fluorine atoms were doped on the surface of the GO in a semi-ionic C-F bond configuration. This presence of the semi-ionic C-F bonds induced a dramatic 7-fold increment of the hole charge carrier density of the photocatalyst. The fluorinated GO photocatalyst exhibited excellent photodegradation up to 93.5% or 0.493 h-1 according pseudo-first order kinetics for methanol. In addition, 91.7% of methanol was mineralized into harmless carbon dioxide (CO2) under UV-A irradiation. Furthermore, the photocatalyst demonstrated good stability in five cycles of methanol PCO. Besides methanol, other VOCs such as acetone and formaldehyde were also photodegraded. This work reveals the potential of fluorination in producing effective graphene-based photocatalyst for VOC removal.

Development of in-situ electrochemical heavy metal ion sensor using integrated 1D/0D/1D hybrid by MWCNT and CQDs supported MnO2 nanomaterial

An integrated 1D/0D/1D hybrid nanomaterial was prepared from MWCNT supported carbon quantum dots @ MnO₂ nanomaterial for a sensitive and selective electrochemical heavy metal ion sensor by hydrothermal methods. The developed nanomaterials were characterized by various analytical methods such as FESEM, HRTEM, XRD, FTIR, EDX and elemental mapping study, and also its electrochemical properties of the prepared samples were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis. Differential pulse voltammetry (DPV) analysis has been used to investigate the quantitative detection of heavy metal ions such as cadmium and chromium on modified electrodes under optimal conditions. The in-situ electrochemical sensitivity and selectivity of the samples were determined by varying various parameters, such as the concentration of heavy metal ions, different electrolytes and electrolyte pH. The observed DPV results show that prepared MWCNT (0.05 wt%) and CQD (0.1 wt%) supported MnO₂ nanoparticles show effective detection response for chromium (IV) metal ion. In particular, 0D CQD, 1D MWCNT, and MnO₂ hybrid nanostructures produced a synergistic effect among them, resulting in strong electrochemical performance of the prepared samples against the target metal ions.

In-situ synthesized ZIF-67 graphene oxide (ZIF-67/GO) nanocomposite for efficient individual and simultaneous detection of heavy metal ions

Heavy metals are ubiquitous in water bodies as a result of anthropogenic activities and over time they accumulate in body thus posing serious health problems. Therefore, it is essential to improve sensing performance, for determination of heavy metal ions (HMIs), of electrochemical sensors. In this work, cobalt-derived MOF (ZIF-67) was in-situ synthesized and incorporated onto the surface of graphene oxide (GO) by simple sonication method. The prepared material (ZIF-67/GO) was characterized by FTIR, XRD, SEM, and Raman spectroscopy. Afterwards, a sensing platform was made by drop-casting synthesized composite onto glassy carbon electrode for individual and simultaneous detection of heavy metal ions pollutants (Hg²⁺, Zn²⁺, Pb²⁺, and Cr³⁺) with estimated detection limits of 2 nM, 1 nM, 5 nM, and 0.6 nM, respectively, when determined simultaneously, that are below the permissible limit by World Health Organization. To the best of our knowledge, this is first report of HMIs detection by ZIF-67 incorporated GO sensor which can successfully determine the Hg⁺², Zn⁺², Pb⁺², and Cr⁺³ ions simultaneously with lower detection limits.

Electrochemical Sensing of Lead in Drinking Water Using Copper Foil Bonded with Polymer

Levels of lead (Pb) in tap water that are well below established guidelines are now considered harmful, so the detection of sub-parts-per-billion (ppb) Pb levels is crucial. In this work, we developed a two-step, facile, and inexpensive fabrication approach that involves direct bonding of copper (Cu) and liquid crystal polymer (LCP) followed by polyester resin printing for masking onto Cu/LCP to fabricate Cu thin-film-based Pb sensors. The oxygen plasma-treated surfaces resulted in strongly bonded Cu/LCP with a high peel strength of 500 N/m due to the highly hydrophilic nature of both surfaces. The bonded specimen can withstand wet etching of the electrode and can address delamination of the electrode for prolonged use in application environments. The Cu-foil-based electrochemical sensor showed sensitivity of ~11 nA/ppb/cm² and a limit of detection (LOD) of 0.2 ppb (0.2 µg/L) Pb ions in water. The sensor required only 30 s and a 100 µL sample to detect Pb. To date, this is the most rapid detection of Pb performed using an all-Cu-based sensor. The selectivity test of Cu to Pb with interferences from cadmium and zinc showed that their peaks were separated by a few hundred millivolts. This approach has strong potential towards realizing low-cost, highly reliable integrated water quality monitoring systems.

Electrochemical Exfoliation of Graphite to Graphene-Based Nanomaterials

Here, we report on a new automated electrochemical process for the production of graphene oxide (GO) from graphite though electrochemical exfoliation. The effects of the electrolyte and applied voltage were investigated and optimized. The morphology, structure and composition of the electrochemically exfoliated GO (EGO) were probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy and Raman spectroscopy. Important metrics such as the oxygen content (25.3 at.%), defect density (I_D/I_G = 0.85) and number of layers of the formed EGO were determined. The EGO was also compared with the GO prepared using the traditional chemical method, demonstrating the effectiveness of the automated electrochemical process. The electrochemical properties of the EGO, CGO and other carbon-based materials were further investigated and compared. The automated electrochemical exfoliation of natural graphite powder demonstrated in the present study does not require any binders; it is facile, cost-effective and easy to scale up for a large-scale production of graphene-based nanomaterials for various applications.

Carbon Nanomaterials-Based Electrochemical Sensors for Heavy Metal Detection

Heavy metals are commonly found in a wide range of environmental settings metals, but the potential toxicity associated with heavy metal exposure represents a major threat to global public health. It is thus vital that approaches to efficiently, reliably, and effectively detecting heavy metals in a range of sample types be established. Carbon nanomaterials offer many advantageous properties that make them well-suited to the design of sensitive, selective, easy-to-operate electrochemical biosensors ideal for detecting heavy metal ions. The present review offers an overview of recent progress in the development of carbon nanomaterial-based electrochemical sensors used to detect heavy metals. In addition to providing a detailed discussion of certain carbon nanomaterials such as carbon nanotubes, graphene, carbon fibers, carbon quantum dots, carbon nanospheres, mesoporous carbon, and Graphdiyne, we survey the challenges and future directions for this field. Overall, the studies discussed herein suggest that the further development of carbon nanomaterial-modified electrochemical sensors will support the integration of increasingly advanced sensor platforms to aid in detecting heavy metals in foods, environmental samples, and other settings, thereby benefitting human health and society as a whole.

An optical and electrochemical sensor based on L-arginine functionalized reduced graphene oxide

The electrochemical and photochemical properties of graphene derivatives could be significantly improved by modifications in the chemical structure. Herein, reduced graphene oxide (RGO) was functionalized with L-arginine (L-Arg) by an amidation reaction between the support and amino acid. Deposition of a powerful ligand, L-Arg, on the optically active support generated an effective optical chemosensor for the determination of Cd(II), Co(II), Pb(II), and Cu(II). In addition, L-Arg-RGO was used as an electrode modifier to fabricate L-Arg-RGO modified glassy-carbon electrode (L-Arg-RGO/GCE) to be employed in the selective detection of Pb(II) ions by differential pulse anodic stripping voltammetry (DP-ASV). L-Arg-RGO/GCE afforded better results than the bare GCE, RGO/GCE, and L-Arg functionalized graphene quantum dot modified GCE. The nanostructure of RGO, modification by L-Arg, and homogeneous immobilization of resultant nanoparticles at the electrode surface are the reasons for outstanding results. The proposed electrochemical sensor has a wide linear range with a limit of detection equal to 0.06 nM, leading to the easy detection of Pb(II) in the presence of other cations. This research highlighted that RGO as a promising support of optical, and electrochemical sensors could be used in the selective, and sensitive determination of transition metals depends on the nature of the modifier. Moreover, L-Arg as an abundant amino acid deserves to perch on the support for optical, and electrochemical determination of transition metals.

General Strategies to Construct Highly Efficient Sensing Interfaces for Metal Ions Detection from the Perspective of Catalysis

Constructing high-effective electrode sensing interfaces has been considered an effective method for electrochemical detection toward heavy metal ions (HMIs). However, most research has been devoted to enhancing the stripping currents of HMIs by simply improving the adsorptive capacity and conductivity of the electrode modified materials, while lacking theoretical guidelines in fabricating catalytic sensing interfaces. Besides, the understanding of detection mechanisms is quite unscientific from the perspective of catalysis. This perspective summarizes five general strategies in designing highly efficient sensing interfaces in the recent five years, including modulating crystal phases, orientations and planes, defect engineering, ionic valence state cycle engineering, adsorption in situ catalysis strategy, and construction of atomic level catalytic active sites. What's more, the catalytic mechanisms for improving the signals of HMIs, such as boosting the electron transfer rates and conversion rates, lowering the energy barriers, etc., are introduced and emphasized. This study has a great significance in directionally controlling functionalized electrochemical sensors to achieve excellent sensitivity and selectivity in detecting environmental pollutants from the view of catalysis, and it also brings enlightenments and guidance to develop new electroanalytical methods.

Metal ion sensing with graphene quantum dots: detection of harmful contaminants and biorelevant species

Graphene quantum dots (GQDs) are attractive materials for use as highly selective and sensitive chemical sensors, owing to their simple preparation and affordability. GQDs have been successfully deployed as sensors for toxic metal ions, which is a significant issue due to the ever-increasing environmental contamination from agricultural and industrial activities. Despite the success of GQDs in this area, the mechanisms which underpin GQD-metal ion specificity are rarely explored. This lack of information can result in difficulties when attempting to replicate published procedures and can limit the judicious design of new highly selective GQD sensors. Furthermore, there is a dearth of GQD examples which selectively detect biologically relevant alkali and alkaline earth metals. This review will present the current state of GQDs as metal ion sensors for harmful contaminants, highlighting and discussing the discrepancies that exist in the proposed mechanisms regarding metal ion selectivity. The emerging field of GQD sensors for biorelevant metal ion species will also be reviewed, with a perspective to the future of this highly versatile material.

Sensitive electrochemical detection of metabisulphite in gastrointestinal fluids

Electrochemical detection of metabisulphite in simulated gastrointestinal fluids.

A Novel N-Doped Nanoporous Bio-Graphene Synthesized from Pistacia lentiscus Gum and Its Nanocomposite with WO3 Nanoparticles: Visible-Light-Driven Photocatalytic Activity

This paper reports the synthesis of a new nitrogen-doped porous bio-graphene (NPBG) with a specific biomorphic structure, using Pistacia lentiscus as a natural carbon source containing nitrogen that also acts as a bio-template. The obtained NPBG demonstrated the unique feature of doped nitrogen with a 3D nanoporous structure. Next, a WO₃/N-doped porous bio-graphene nanocomposite (WO₃/NPBG-NC) was synthesized, and the products were characterized using XPS, SEM, TEM, FT-IR, EDX, XRD, and Raman analyses. The presence of nitrogen doped in the structure of the bio-graphene (BG) was confirmed to be pyridinic-N and pyrrolic-N with N1 peaks at 398.3 eV and 400.5 eV, respectively. The photocatalytic degradation of the anionic azo dyes and drugs was investigated, and the results indicated that the obtained NPBG with a high surface area (151.98 m²/g), unique electronic properties, and modified surface improved the adsorption and photocatalytic properties in combination with WO₃ nanoparticles (WO₃-NPs) as an effective visible-light-driven photocatalyst. The synthesized WO₃/NPBG-NC with a surface area of 226.92 m²/g displayed lower bandgap and higher electron transfer compared with blank WO₃-NPs, leading to an increase in the photocatalytic performance through the enhancement of the separation of charge and a reduction in the recombination rate. At the optimum conditions of 0.015 g of the nanocomposite, a contact time of 15 min, and 100 mg/L of dyes, the removal percentages were 100%, 99.8%, and 98% for methyl red (MR), Congo red (CR), and methyl orange (MO), respectively. In the case of the drugs, 99% and 87% of tetracycline and acetaminophen, respectively, at a concentration of 10 mg/L, were removed after 20 min.

Recent Advancement in Disposable Electrode Modified with Nanomaterials for Electrochemical Heavy Metal Sensors

Heavy metal pollution has gained global attention due to its high toxicity and non-biodegradability, even at a low level of exposure. Therefore, the development of a disposable electrode that is sensitive, simple, portable, rapid, and cost-effective as the sensor platform in electrochemical heavy metal detection is vital. Disposable electrodes have been modified with nanomaterials so that excellent electrochemical properties can be obtained. This review highlights the recent progress in the development of numerous types of disposable electrodes modified with nanomaterials for electrochemical heavy metal detection. The disposable electrodes made from carbon-based, glass-based, and paper-based electrodes are reviewed. In particular, the analytical performance, fabrication technique, and integration design of disposable electrodes modified with metal (such as gold, tin and bismuth), carbon (such as carbon nanotube and graphene), and metal oxide (such as iron oxide and zinc oxide) nanomaterials are summarized. In addition, the role of the nanomaterials in improving the electrochemical performance of the modified disposable electrodes is discussed. Finally, the current challenges and future prospect of the disposable electrode modified with nanomaterials are summarized.

Preparation of Modified Fluorographene Oxide with Interlayer Supporting Structure

Fluorinated graphene (FGi) is easy to agglomerate, after which it turns into a curly and wavy shape, which results in a great decrease in the properties of the resultant composite materials and coatings. In this study, fluorinated graphene oxide (FGO) modified with p-phenylenediamine (PPD) was prepared, but with a view to avoid its agglomeration and retain a sheet-like structure. Through the reaction between PPD and the epoxy groups of FGO, the modified FGO with an amino group (N-PGO) had a larger interlayer d-spacing than FGO. The stability of N-PGO was also improved, and nitrogen, fluorine, oxygen, and carbon were evenly distributed in the N-PGO sheets. All the results indicate that PPD can act as an effective spacer to separate graphene sheets for good anti-agglomeration properties. This method produced modified graphene with fluorine, amino, and carbonyl groups. It shows potential in introducing N-PGO as a reactive modifier in composite materials and coatings for a variety of industrial applications including waterborne epoxy materials.

GaOOH-modified metal-organic frameworks UiO-66-NH2: Selective and sensitive sensing four heavy-metal ions in real wastewater by electrochemical method

Heavy metal pollution in the environment poses a serious threat to the ecosystem and human health, which has attracted widespread attention. In this study, an octahedral structure composite composed of UiO-66-NH₂ MOFs and semiconductor GaOOH materials has been prepared and used as electrode materials successfully. These composites can be used for the real-time and online determination of Cd²⁺, Cu²⁺, Hg²⁺, and Pb²⁺ in real water samples simultaneously or alone via an electrochemical method. Zr-MOF has a large and unique surface area that is beneficial to the adsorption and preconcentration of heavy metal ions. The experiment parameters such as pH, deposition potential, and deposition time were optimized. Under the optimized conditions, the electrochemical performances and practical applications of Zr-MOF composites modified electrode have been investigated, which shows excellent wider linear range and lower detection limit (LOD). The results demonstrated excellent selectivity, reproducibility, stability and applicability for the detection of four metal ions. These superior features stem from the synergistic reaction mechanism of UiO-66-NH₂ and GaOOH. In addition, it has been established a new detection strategy for heavy metal ions through the form of metal-organic framework (MOF) composite in this work. It may provide a novel platform for the quantitative determination of heavy metal ions in various environmental samples.

Halogen Functionalization in the 2D Material Flatland: Strategies, Properties, and Applications

Given the electronegativity and bonding environment of halogen elements, halogenation (i.e., fluorination, chlorination, bromination, and iodination) serves as a versatile strategy for chemical modifications of materials. The combination of halogens and 2D materials has triggered extensive interests since the first report on graphene fluorination in 2008. Subsequently, scholars consistently conduct pre-, in-process, or posthalogenation modifications of emerging 2D materials to achieve desired properties and broad device applications. They also continuously explore the role of halogens in 2D material functionalization. The multiple advantages introduced by halogen decoration make 2D materials outstanding from each subclass. In this review, an overall retrospect is provided on the research advances in the area of 2D material halogenation, including experimental halogenation strategies, halogen-triggered novel physics and properties, and advanced applications across the studied objects. Future research directions in this area are also proposed.

Anodic Stripping Voltammetry with the Hanging Mercury Drop Electrode for Trace Metal Detection in Soil Samples

The widely spread use of the hanging mercury drop electrode (HMDE) for multi-ion analysis is primarily ascribed to the following reasons: (i) excellent reproducibility owing to the easy renewal of the electrode surface avoiding any hysteresis effect (i.e., a new identical drop is generated for each measurement to be accomplished); (ii) a wide cathodic potential window originating from the passive hydrogen evolution and solvent electrolysis; (iii) the ability to form amalgams with many redox-active metal ions; and (iv) the achievement of (sub)nanomolar limits of detection. On the other hand, the main controversy of the HMDE usage is the high toxicity level of mercury, which has motivated the scientific community to question whether the HMDE deserves to continue being used despite its unique capability for multi-metal detection. In this work, the simultaneous determination of Zn2+, Cd2+, Pb2+, and Cu2+ using the HMDE is investigated as a model system to evaluate the main features of the technique. The analytical benefits of the HMDE in terms of linear range of response, reproducibility, limit of detection, proximity to ideal redox behavior of metal ions and analysis time are herein demonstrated and compared to other electrodes proposed in the literature as less-toxic alternatives to the HMDE. The results have revealed that the HMDE is largely superior to other reported methods in several aspects and, moreover, it displays excellent accuracy when simultaneously analyzing Zn2+, Cd2+, Pb2+, and Cu2+ in such a complex matrix as digested soils. Yet, more efforts are required towards the definitive replacement of the HMDE in the electroanalysis field, despite the elegant approaches already reported in the literature.

TMPyP-bound guanosine-borate supramolecular hydrogel as smart hemoperfusion device with real-time visualized/electrochemical bi-modal monitoring for selective blood lead elimination

Blood lead poisoning is a universal and severe health problem that greatly threatens human health in various industries. Elimination of blood lead relying on chelating agents and combination with hemoperfusion adsorbents has achieved considerable progress, but it is still suffering from the compromised selectivity of adsorbents as well as in absence of real time monitoring during treatment. Herein, we proposed a selective blood lead adsorbent integrated with real-time visualized/electrochemical bi-modal monitoring based on TMPyP-bound guanosine-borate (GB) supramolecular hydrogel as potential smart hemoperfusion device. The GB hydrogel possessed stability in physiological environment, self-healing ability resistant to fluid shear, blood compatibility, selective adsorption of lead ions superior to conventional adsorbents, anti-fouling performance to blood components and renewability. Benefiting from binding with TMPyP and the intrinsic conductivity, GB hydrogel was endowed with the ability to qualitatively diagnose the presence of blood lead via simple color change and quantitatively reflect the amount of adsorbed lead from blood accurately through electrochemical technique. This work puts forward an integrated treatment/monitoring hemoperfusion device with high selectivity, simple fabrication and low-cost, providing a paradigm for next generation design of intelligent, monitorable theranostic hemopurification system, which is also an extensible platform for the other research fields such as environmental monitoring and remediation.

Preparation and Applications of Fluorinated Graphenes

The present review focuses on the numerous routes for the preparation of fluorinated graphene (FG) according to the starting materials. Two strategies are considered: (i) addition of fluorine atoms on graphenes of various nature and quality and (ii) exfoliation of graphite fluoride. Chemical bonding in fluorinated graphene, related properties and a selection of applications for lubrication, energy storage, and gas sensing will then be discussed.

Radical sensitivity and selectivity in the electrochemical sensing of cadmium ions in water by polyaniline-derived nitrogen-doped graphene quantum dots

In the present work, the sensing capability of nitrogen-doped graphene quantum dots (N-GQDs) was explored for the first time toward hazardous heavy metal ions and they were found to be able to selectively detect cadmium ions (Cd(ii)).

Voltamperometric Sensors and Biosensors Based on Carbon Nanomaterials Used for Detecting Caffeic Acid-A Review

Caffeic acid is one of the most important hydroxycinnamic acids found in various foods and plant products. It has multiple beneficial effects in the human body such as antioxidant, antibacterial, anti-inflammatory, and antineoplastic. Since overdoses of caffeic acid may have negative effects, the quality and quantity of this acid in foods, pharmaceuticals, food supplements, etc., needs to be accurately determined. The present paper analyzes the most representative scientific papers published mostly in the last 10 years which describe the development and characterization of voltamperometric sensors or biosensors based on carbon nanomaterials and/or enzyme commonly used for detecting caffeic acid and a series of methods which may improve the performance characteristics of such sensors.

Graphene-Oxide-Based Electrochemical Sensors for the Sensitive Detection of Pharmaceutical Drug Naproxen

Here we report on a selective and sensitive graphene-oxide-based electrochemical sensor for the detection of naproxen. The effects of doping and oxygen content of various graphene oxide (GO)-based nanomaterials on their respective electrochemical behaviors were investigated and rationalized. The synthesized GO and GO-based nanomaterials were characterized using a field-emission scanning electron microscope, while the associated amounts of the dopant heteroatoms and oxygen were quantified using x-ray photoelectron spectroscopy. The electrochemical behaviors of the GO, fluorine-doped graphene oxide (F-GO), boron-doped partially reduced graphene oxide (B-rGO), nitrogen-doped partially reduced graphene oxide (N-rGO), and thermally reduced graphene oxide (TrGO) were studied and compared via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that GO exhibited the highest signal for the electrochemical detection of naproxen when compared with the other GO-based nanomaterials explored in the present study. This was primarily due to the presence of the additional oxygen content in the GO, which facilitated the catalytic oxidation of naproxen. The GO-based electrochemical sensor exhibited a wide linear range (10 µM–1 mM), a high sensitivity (0.60 µAµM⁻¹cm⁻²), high selectivity and a strong anti-interference capacity over potential interfering species that may exist in a biological system for the detection of naproxen. In addition, the proposed GO-based electrochemical sensor was tested using actual pharmaceutical naproxen tablets without pretreatments, further demonstrating excellent sensitivity and selectivity. Moreover, this study provided insights into the participatory catalytic roles of the oxygen functional groups of the GO-based nanomaterials toward the electrochemical oxidation and sensing of naproxen.

Efficient dye removal and separation based on graphene oxide nanomaterials

Different graphene-based nanomaterials were synthesized and tested for dye removal, showing that graphene oxide demonstrates high capability for the separation of cationic and anionic dyes.

Heteroatom-doped graphene as sensing materials: a mini review

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets. Graphene and its derivatives like graphene oxide and reduced graphene oxide have emerged as significant nanomaterials in the area of sensors. Furthermore, doping of graphene and its derivatives with heteroatoms (B, N, P, S, I, Br, Cl and F) alters their electronic and chemical properties which are best suited for the construction of economical sensors of practical utility. This review recapitulates the developments in graphene materials as emerging electrochemical, ultrasensitive explosive, gas, glucose and biological sensors for various molecules with greater sensitivity, selectivity and a low limit of detection. Apart from the most important turn of events, the properties and incipient utilization of the ever evolving family of heteroatom-doped graphene are also discussed. This review article encompasses a wide range of heteroatom-doped graphene materials as sensors for the detection of NH₃, NO₂, H₂O₂, heavy metal ions, dopamine, bleomycinsulphate, acetaminophen, caffeic acid, chloramphenicol and trinitrotoluene. In addition, heteroatom-doped graphene materials were also explored for sensitivity and selectivity with respect to interfering analytes present in the system. Finally, the review article concludes with future perspectives for the advancement of heteroatom-doped graphene materials.

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets.

Sensitive, selective and simultaneous electrochemical detection of multiple heavy metals in environment and food using a lowcost Fe3O4 nanoparticles/fluorinated multi-walled carbon nanotubes sensor

Multiple heavy metals pollution in environment and food has become an ever-increasing concern and poses a serious threat towards humans and animals. To broad the multiple heavy metals detection, Fe₃O₄ nanoparticles, Fe₃O₄/multi-walled carbon nanotubes (Fe₃O₄/MWCNTs) and Fe₃O₄/fluorinated multi-walled carbon nanotubes (Fe₃O₄/F-MWCNTs) nanocomposites were synthesized by hydrothermal method and constructed as a simultaneous electrochemical sensor, respectively. Compared the catalytic performances of the three electrochemical sensors for the simultaneous detection of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, the results showed that the Fe₃O₄/F-MWCNTs sensor demonstrated preponderant performance. It showed the sensitivity of 108.79, 125.91, 160.85, and 312.65 μA mM^-1 cm^-2 toward Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, which was obviously higher than that of Fe₃O₄/MWCNTs and Fe₃O₄. Additionally, the Fe₃O₄/F-MWCNTs sensor exhibited the wider linear detection ranges of 0.5-30.0, 0.5-30.0, 0.5-30.0, and 0.5-20.0 μM for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively. The limit of detections of the Fe₃O₄/F-MWCNTs sensor were 0.05, 0.08, 0.02, and 0.05 nM (signal to noise ratio of 3) for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, fulfilling the governmental requests of the World Health Organization, China and Indian. The excellent agreement was recorded between the lowcost Fe₃O₄/F-MWCNTs sensor and typical methods (inductively coupled plasma mass spectrometry or atomic fluorescence spectrometry) in river water and soybean samples. Additionally, the sensor also exhibited excellent performances in selectivity, recovery, stability, and reproducibility. This proposal sensor provides a promising strategy to monitor multiple targets in the environment and food.

Fluorinated Reduced Graphene Oxide-Encapsulated ZnO Hollow Sphere Composite as an Efficient Photocatalyst with Increased Charge-Carrier Mobility

Zinc oxide (ZnO) hollow spheres were prepared by the hydrothermal method and encapsulated with fluorinated reduced graphene oxide (FRGO) using a tetra- n-butylammonium bromide (TBAB) linker to give an FRGO/ZnO composite. X-ray diffraction and microscopic studies revealed their hexagonal-wurtzite structure, spherical morphology, and size of the crystallite to be 26.7 nm. Diffuse reflectance UV-visible spectroscopy showed an optical band gap and semiconductive nature of the composite. Atomic force microscopy images show the surface topography of FRGO-encapsulated ZnO hollow spheres. The photoluminescence spectra depicted the electron-hole pair recombination order to be ZnO > RGO/ZnO > FRGO/ZnO. The electrochemical impedance spectroscopy (EIS) demonstrates the increased charge-carrier mobility of the FRGO/ZnO composite; the R_ct values of ZnO, RGO/ZnO, and FRGO/ZnO were found to be 6.18 × 10³, 4.07 × 10³, and 3.45 × 10³ Ω, respectively. All the three materials were employed as photocatalysts in the degradation of methylene blue under UV-365 nm radiation and the results exposed the higher photocatalytic activity of reduced fluorinated graphene oxide/ZnO than RGO/ZnO and bare ZnO hollow spheres. The increased photocatalytic activity of the composite is due to the enhanced vectorial transport of charge carriers at the interface of the FRGO/ZnO composite and suppression of charge-carrier recombination. The presence of fluorine in the RGO sheet introduces additional defects and leverages heterogeneous electron transport. In turn, mobility of light-generated charge carriers is increased and results in suppression of their recombination, which facilitates the photocatalytic process.

Sensitive Electrochemical Detection of Caffeic Acid in Wine Based on Fluorine-Doped Graphene Oxide

We report here a novel electrochemical sensor developed using fluorine-doped graphene oxide (F-GO) for the detection of caffeic acid (CA). The synthesized graphene oxide (GO) and F-GO nanomaterials were systematically characterized with a scanning electron microscope (SEM), and the presence of semi-ionic bonds was confirmed in the F-GO using X-ray photoelectron spectroscopy. The electrochemical behaviours of bare glassy carbon electrode (GCE), F-GO/GCE, and GO/GCE toward the oxidation of CA were studied using cyclic voltammetry (CV), and the results obtained from the CV investigation revealed that F-GO/GCE exhibited the highest electrochemically active surface area and electrocatalytic activity in contrast to the other electrodes. Differential pulse voltammetry (DPV) was employed for the analytical quantitation of CA, and the F-GO/GCE produced a stable oxidation signal over the selected CA concentration range (0.5 to 100.0 μM) with a low limit of detection of 0.018 μM. Furthermore, the acquired results from the selectivity studies revealed a strong anti-interference capability of the F-GO/GCE in the presence of other hydroxycinnamic acids and ascorbic acid. Moreover, the F-GO/GCE offered a good sensitivity, long-term stability, and an excellent reproducibility. The practical application of the electrochemical F-GO sensor was verified using various brands of commercially available wine. The developed electrochemical sensor successfully displayed its ability to directly detect CA in wine samples without pretreatment, making it a promising candidate for food and beverage quality control.

Graphene-derived nanomaterials as recognition elements for electrochemical determination of heavy metal ions: a review

This review (with 155 refs.) summarizes the progress made in the past few years in the field of electrochemical sensors based on graphene-derived materials for the determination of heavy metal ions. Following an introduction of this field and a discussion of the various kinds of modified graphenes including graphene oxide and reduced graphene oxide, the review covers graphene based electrodes modified (or doped) with (a) heteroatoms, (b) metal nanoparticles, (c) metal oxides, (d) small organic molecules, (e) polymers, and (f) ternary nanocomposites. Tables are provided that afford an overview of representative methods and materials for fabricating electrochemical sensors. Furthermore, sensing mechanisms are discussed. A concluding section presents new perspectives, opportunities and current challenges. Graphical Abstract Schematic illustration of electrochemical sensor for heavy metal ion sensing based on heteroatom-doped graphene, metal-modified graphene, metal-oxide-modified graphene, organically modified graphene, polymer-modified graphene, and ternary graphene based nanocomposites.

Simultaneous voltammetric determination of cadmium(II), lead(II), mercury(II), zinc(II), and copper(II) using a glassy carbon electrode modified with magnetite (Fe3O4) nanoparticles and fluorinated multiwalled carbon nanotubes

A method is described for the simultaneous voltammetric determination of the heavy metal ions cadmium(II), lead(II), mercury(II), zinc(II), and copper(II) using a glassy carbon electrode (GCE) modified with magnetite (Fe3O4) nanoparticles and fluorinated multiwalled carbon nanotubes (Fe3O4/F-MWCNTs). The Fe3O4/F-MWCNT composite was synthesized by a hydrothermal method and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, elemental mapping, electrochemical impedance spectroscopy, and square wave stripping voltammetry. Under the optimum conditions, the electrode displays excellent response to the ions. Figures of merit for Cd(II), Pb(II), Hg(II), Zn(II), and Cu(II), respectively, include (a) high electrochemical sensitivity (29.88, 43.50, 120.86, 47.34 and 90.31 (μA μM-1 cm-2), (b) well separated peaks (at -0.70, -0.53, +0.37, -1.11 and + 0.01 V vs. Ag/AgCl); (c) low limits of detection (0.014, 0.0084, 0.0039, 0.012, and 0.0053 μM); and (d) wide linear ranges (0.048-30.0, 0.028-30.0, 0.013-32.5, 0.039-32.5, and 0.017-31.5 μM). The modified GCE displays satisfying selectivity in the presence of potentially interfering other metal ions, stability for 30 days, and reproducibility of electrodes (with a relative standard deviation between 1.2 and 4.8% for n = 6). The modified GCE was applied to the determination of several heavy metal ions in (spiked) water and rice samples, and the results agreed well with data obtained by atomic fluorescence spectrometry or inductively coupled plasma-mass spectrometry. The dramatic performance probably result from the semi-ionic C-F bond on F-MWCNTs surface with a strong negative charge, the good electrical conductivity of the F-MWCNTs and Fe3O4, the synergistic interaction between Fe3O4 and F-MWCNTs, and the nafion conductive membrane improving the stability of the modified layer and enhanced cation adsorption. Graphical abstract An environmentally-friendly, low-cost, high-throughput Fe3O4/fluorinated multi-walled carbon nanotube composite (Fe3O4/F-MWCNTs) modified glassy carbon electrode is described. It was applied to simultaneous electrochemical determination of Cd(II), Pb(II), Hg(II), Zn(II), and Cu(II) by square wave stripping voltammetry.

Defect-rich fluorographene nanosheets for artificial N2 fixation under ambient conditions

Defect-rich fluorographene behaves as a metal-free catalyst for the artificial conversion of N₂ to NH₃ at ambient conditions. In 0.1 M Na₂SO₄, it achieves a faradaic efficiency (FE) of 4.2% with an NH₃ formation rate (R_NH3) of 9.3 μg h⁻¹ mg_cat.⁻¹ at −0.7 V vs. RHE, with strong long-term electrochemical durability.