Carbon paste electrode modified with fern leave-like MIL-47(as) for electrochemical simultaneous detection of Pb(II), Cu(II) and Hg(II)

Determination of diethylstilbestrol in environmental water based on electrochemical senser modified with vanadium based metal organic framework material composite

In this research, the MIL-47/ACET/Nafion/GCE electrochemical senser for the determination of diethylstilbestrol (DES) was prepared with vanadyl sulfate (VOSO4·nH2O) and terephthalic acid (H2BDC) as the main raw materials, compounded with acetylene black (ACET) and perfluorosulfonic acid polymer (Nafion). The compound DES belongs to the category of estrogens, and prolonged exposure to the environment can have detrimental effects on the physiological functioning of both humans and animals. Due to the strong DES enrichment performance of MIL-47(V-MOFs) with large specific surface area, in addition to the excellent conductivity and electrocatalysis of composite materials, this modified senser had good electrochemical response to DES. With differential pulse voltammetry, in optimum condition of 0.1 M NaH2PO4-Na2HPO4at pH = 7.0, potential interval of -1.0 to 1.0 V, enrichment time of 120 s and enrichment potential of 0.2 V, there was a good linear relationship between peak current and the concentration of DES over the range of 0.1 and 50μM, and the limit of detection was 0.008μM. The sensor accurately detected DES in actual water samples, with recovery rates ranging from 89.21% to 105.3%. The electrochemical sensor was simple to prepare and had practical significance for the detection of DES in water. The research results of the sensor provide another alternative analytical means for the sensitive detection of DES in the environment, which is important for maintaining public health.

Recent advances in the modification of electrodes for trace metal analysis: a review

This review paper summarizes the research published in the last five years on using different compounds and/or materials as modifiers for electrodes employed in trace heavy metal analysis. The main groups of modifiers are identified, and their single or combined application on the surface of the electrodes is discussed. Nanomaterials, film-forming substances, and polymers are among the most used compounds employed mainly in the modification of glassy carbon, screen-printed, and carbon paste electrodes. Composites composed of several compounds and/or materials have also found growing interest in the development of modified electrodes. Environmentally friendly substances and natural products (mainly biopolymers and plant extracts) have continued to be included in the modification of electrodes for trace heavy metal analysis. The main analytical performance parameters of the modified electrodes as well as possible interferences affecting the determination of the target analytes, are discussed. Finally, a critical evaluation of the main findings from these studies and an outlook discussing possible improvements in this area of research are presented.

Recent progress and perspectives of metal organic frameworks (MOFs) for the detection of food contaminants

Over the past decades, increasing research in metal-organic frameworks (MOFs) being a large family of highly tunable porous materials with intrinsic physical properties, show propitious results for a wide range of applications in adsorption, separation, electrocatalysis, and electrochemical sensors. MOFs have received substantial attention in electrochemical sensors owing to their large surface area, active metal sites, high chemical and thermal stability, and tunable structure with adjustable pore diameters. Benefiting from the superior properties, MOFs and MOF-derived carbon materials act as promising electrode material for the detection of food contaminants. Although several reviews have been reported based on MOF and its nanocomposites for the detection of food contaminants using various analytical methods such as spectrometric, chromatographic, and capillary electrophoresis. But there no significant review has been devoted to MOF/and its derived carbon-based electrodes using electrochemical detection of food contaminants. Here we review and classify MOF-based electrodes over the period between 2017 and 2022, concerning synthetic procedures, electrode fabrication process, and the possible mechanism for detection of the food contaminants which include: heavy metals, antibiotics, mycotoxins, and pesticide residues. The merits and demerits of MOF as electrode material and the need for the fabrication of MOF and its composites/derivatives for the determination of food contaminants are discussed in detail. At last, the current opportunities, key challenges, and prospects in MOF for the development of smart sensing devices for future research in this field are envisioned.

Voltammetric determination of tryptophan at graphitic carbon nitride modified carbon paste electrode

Herein, we reported carbon paste electrode modified with graphitic carbon nitride (g-C3N4-CPE) to determine of tryptophan (Trp) using voltametric techniques. Various spectroscopic and electrochemical techniques were used to characterize the as-synthesized g-C3N4 and the assembled electrodes. The transfer coefficient, rate constant and the diffusion coefficient of Trp in this system were found to be 0.28, 1.9 × 104 M-1s-1 and 3.2 × 10-5 cm2s-1, respectively. The linear range was obtained for the detection of Trp using LSV is from 0.1 μM to 120 μM at pH 5. The limit of detection (LOD) (3σ/m) was 0.085 μM. The demonstrated modified CPE was also effectively used for the detection of Trp in milk with percentage recovery of 98 %-105.2 %. Furthermore, the modified CPE exhibited good repeatability, reproducibility and appropriate selectivity.

Adsorption of Pb2+ and Cu2+ in wastewater by lignosulfonate adsorbent prepared from corn straw

The heavy metal ions contained in industrial wastewater are a great threat to human health. Exploring a adsorbent which have low-cost, green environmental friendly, high adsorption capacity, good recycle is key to solve heavy metal ions pollution. Lignin sulfonate was obtained by treating corn stover, and then modified lignin sulfonate was obtained by hydrothermal method. The porous structure makes heavy metal ions occupy more internal adsorption sites. Modified lignosulfonate adsorbent efficiency removes heavy metals in wastewater especially Cu2+ and Pb2+. The adsorption capacity of Cu2+ on modified lignosulfonate is 450.3 mg g-1, Pb2+ is 475.4 mg g-1. In addition, for 40 mg L-1 Cu2+ and Pb2+ using 0.4 g L-1, the adsorption equilibrium is only reached within 60 min. Meanwhile, the removal ratio of Pb is 83 %, Cd is 72 %, Cu is 87 %, Zn is 36 %, Mn is 25 %, Cr is 95 %, and Fe is 99 % in wastewater using 0.4 g L-1 adsorbent in 2 h. This research develops a practical adsorbent to remove heavy metals from actual wastewater.

Green synthesis of copper oxide nanoparticles using Ficus elastica extract for the electrochemical simultaneous detection of Cd2+, Pb2+, and Hg2

In this paper, for the first time, we report the use of a new carbon paste electrode based on a low-cost pencil graphite powder modified with polyaniline (PANI) and green synthesized copper oxide nanoparticles using Ficus elastica extract as a sensor for Cd²⁺, Pb²⁺, and Hg²⁺. The elaborated electrode was characterized by FT-IR spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and simultaneous thermal analysis (TGA/DSC). The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy techniques. According to CV, as well as square wave voltammetry (SWV) results, it was found that the CuONPs/PANI-CPE sensor was able to determine very low concentrations of Cd²⁺, Pb²⁺, and Hg²⁺ in HCl (0.01 M) either in single metal or in multi-metal solutions with a high sensitivity. Furthermore, Cd²⁺, Pb²⁺, and Hg²⁺ simultaneous detection on CuONPs/PANI-CPE achieved very low limits of detection (0.11, 0.16, and 0.07 μg L^-1, respectively). Besides, the designed sensor displayed a good selectivity, reproducibility, and stability. Moreover, CuONPs/PANI-CPE enabled us to determine with high accuracy Cd²⁺, Pb²⁺, and Hg²⁺ traces in environmental matrices.

An ultrasensitive electrochemical sensor based on antimonene simultaneously detect multiple heavy metal ions in food samples

Here, we constructed a novel ultra-sensitive electrochemical sensor based on ZIF-67@antimonene (AMNFs) nanocomposites which are based on the first-principles density functional theory the adsorption properties of antimonene on heavy metal ions were studied for simultaneous determination of Cu²⁺, Pb²⁺ and Hg²⁺. The ZIF-67@AMNFs was prepared by using ZIF-67 MOF surface loaded with a large amount of antimonene sheet. Its morphology and crystal structure were characterized by Transmission electron microscope (TEM), Energy Dispersive Spectroscopy (EDS), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Functional ZIF-67@AMNFs due to its unique layered structure, large active surface area, strong adsorption capacity and good electrical conductivity. In addition, the adsorption capacity of the sensor electrode for Cu²⁺, Pb²⁺ and Hg²⁺ was effectively enhanced. The detection limits of Cu²⁺, Pb²⁺ and Hg²⁺ were 0.01 pM, 0.042 pM and 0.031 pM, respectively. The determination mechanism of Cu²⁺, Pb²⁺ and Hg²⁺ was further clarified based on the adsorption properties and electrochemical accumulation of antimonene on metal atoms. It has been successfully applied to the simultaneous determination of Cu²⁺, Pb²⁺ and Hg²⁺ in rice, sorghum, corn, milk, honey and tea samples, and has good practicability.

Vein-Like Ni-BTC@Ni3S4 with Sulfur Vacancy and Ni3+ Fabricated In Situ Etching Vulcanization Strategy for an Electrochemical Sensor of Dopamine

In this study, a novel Ni-BTC@Ni₃S₄ composite was fabricated by solvothermal reaction using an in situ etching vulcanization strategy and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and Brunauer-Emmett-Teller (BET) analyses. The existence of a sulfur vacancy and Ni³⁺ in the as-prepared vein-like Ni-BTC@Ni₃S₄ greatly promoted the electrochemical sensing activity of the materials. Herein, a simple electrochemical sensor (Ni-BTC@Ni₃S₄/CPE) has been fabricated and used for the detection of dopamine (DA). The current signal of the Ni-BTC@Ni₃S₄/CPE-modified electrode was linear with the concentration of DA in the range of 0.05-750 μM (R² = 0.9995) with a sensitivity of 560.27 μA·mM^-1·cm^-2 and a detection limit of 0.016 μM. At the same time, the sensor has good stability and anti-interference ability. This study could provide a new idea and strategy for the structural regulation of composite electrode-modified materials and sensitive sensing detection of small biological molecules.

A novel gallium oxide nanoparticles-based sensor for the simultaneous electrochemical detection of Pb2+, Cd2+ and Hg2+ ions in real water samples

Differential pulse voltammetry (DPV) using gallium oxide nanoparticles/carbon paste electrode (Ga₂O₃/CPE) was utilized for the simultaneous detection of Pb²⁺, Cd²⁺ and Hg²⁺ ions. Ga₂O₃NPs were chemically synthesized and fully characterized by Fourier-transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Through the assay optimization, electrochemical screening of different nanomaterials was carried out using the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in order to determine the best electrode modifier that will be implemented for the present assay. Consequently, various parameters such as electrode matrix composition, electrolyte, deposition potential, and deposition time were optimized and discussed. Accordingly, the newly developed sensing platform showed a wide dynamic linear range of 0.3-80 µM with detection limits (LODs) of 84, 88 and 130 nM for Pb²⁺, Cd²⁺ and Hg²⁺ ions, respectively. While the corresponding limit of quantification (LOQ) values were 280, 320 and 450 nM. Sensors selectivity was investigated towards different non-targeting metal ions, whereas no obvious cross-reactivity was obtained. Eventually, applications on real samples were performed, while excellent recoveries for the multiple metal ions were successfully achieved.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Facile solvothermal synthesis of a MIL-47(V) metal-organic framework for a high-performance Epoxy/MOF coating with improved anticorrosion properties

The vanadium-based metal–organic framework MIL-47 distinguishes itself among other MOFs for its distinctive structure and unique properties (e.g., flexible structure, high thermal stability, and high surface area). The synthesis of MIL-47 has been reported from various metal precursors, including vanadium(iii) chloride (VCl₃) as a rich source of metal ions. Attempts have been made to include other starting materials, a step forward towards large-scale production. Synthesis from various solid materials is encouraged, seeking an economic and greener approach. In this study, vanadium pentoxide (V₂O₅), a readily abundant low-cost and thermodynamically stable metal source, was used to synthesize the MIL-47(V) framework via a facile solvothermal route. This precursor provides a controllable rate of metal ion production depending on the applied reaction conditions. In our method, the synthesis took place at a low temperature and reaction time (180 °C for 20 h, instead of 220 °C for 72 h), yielding MIL-47 microrods. Moreover, among its unique properties, the metal centers of MIL-47 oxidize under the influence of thermal or chemical treatments, preserving the framework structure. This unusual character is not commonly witnessed in comparable MOF structures. This property can be leveraged in anti-corrosion applications, whereby a redox reaction would sacrifice the framework components, protecting the metal in contact. However, the chemical stability of MIL-47 is doubted against a corrosive medium. Thus, an epoxy coating with 10 wt% MOF loading was incorporated in our investigation to extend the aluminum alloy (AA2024) surface protection for prolonged exposure duration. The uniformity of distribution of the prepared MOF within the epoxy matrix was confirmed using SEM/EDX. Electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion performance of the coated samples. The results showed that the inclusion of V-MOF offers extended corrosion prevention, over 60 days, for the AA2024 alloy against artificial seawater. The neat epoxy coating could not prevent the corrosion of AA2024 over two weeks of immersion, whereby pitting corrosion was clearly observed. The V-MOF could induce a series of redox reactions leading to the precipitation of vanadium on the cathodic sites of metal surfaces.

The well-known MIL-47(V) metal–organic framework was synthesized solvothermally with high quality using V₂O₅ as a precursor. Applying the MOF particles in an epoxy coating resulted in an improved anticorrosion protective barrier for the AA2024 substrate against a chloride-rich environment.

N and P co-doped MXenes nanoribbons for electrodeposition-free stripping analysis of Cu(II) and Hg(II)

The present electrochemical stripping analysis (ESA) for multiple heavy metal ions (HMI) generally requires an electrodeposition process at a very low potential below -1.0 V, which inevitably makes the sensing procedures more complex, inefficient and power-wasting. Meanwhile, the emerging MXenes rising-star materials have been studied in various fields recently. While there are only few reports focusing on the heteroatom doping of MXenes, especially no doping-MXenes for electroanalysis. Based on these issues, a novel multifunctional heteroatoms-doped MXenes nanomaterial, N and P co-doped Ti₃C₂T_x MXenes nanoribbons (N,P-Ti₃C₂T_xR), was prepared herein for the first time, and then N,P-Ti₃C₂T_xR was used as electrode material to propose an electrodeposition-free ESA strategy for multiple HMI (Cu²⁺, Hg²⁺). Owing to the unique spontaneous adsorption and reducing capacities of N,P-Ti₃C₂T_xR towards Cu²⁺ and Hg²⁺ coupled with the excellent sensing performances, Cu²⁺ and Hg²⁺ can undergo self-reduction to be preconcentrated on N,P-Ti₃C₂T_xR surface with the form of Cu⁰ and Hg⁰, thus a simple and ultrasensitive electrodeposition-free ESA platform was developed successfully for the simultaneous detection of Cu²⁺and Hg²⁺. This work opened a new pathway for the detection for multiple HMI and the preparation/application of heteroatoms doping MXenes.

Construction of a Carbon/Lignosulfonate Adsorbent to Remove Pb2+ and Cu2

Removing heavy metal ions from water is an important issue to improve water quality. However, using cost-effective and more environmentally friendly adsorbents to achieve efficient adsorption capacity remains a challenge. Carbon spheres were prepared by the hydrothermal method and then combined with sodium lignosulfonate to form a lignosulfonate carbon (C/SL) adsorbent. C/SL achieved the adsorption of Pb²⁺ and Cu²⁺ after 60 min (the adsorption capacity was 281 mg g^-1 for Pb²⁺ and 276mg g^-1 for Cu²⁺) and had good selectivity and reusability (5 cycles). The simulated experimental data show that the pseudo-second-order kinetics and Langmuir isotherm are closer to the actual adsorption. Thermodynamic studies show that the adsorption of Pb²⁺ and Cu²⁺ is enhanced by the spontaneous process at higher temperature. This study also shows that functional groups such as hydroxyl and amino groups play an important role in the adsorption process.

Study of an adsorption method for trace mercury based on Bacillus subtilis

In order to decrease the difficulty in trace mercury determination, an adsorption method for trace mercury based on Bacillus subtilis cells was proposed in this article. The adsorption process was characterized by optical microscopy and SEM. The adsorption mechanism was analyzed by IR. The adsorption performance was studied by measuring the concentration of supernate and calculating the adsorption efficiency. When adsorbing Hg2+, Bacillus subtilis cells gathered and their structure turned coarse. The IR results illustrated that functional groups bound with Hg for complexation during adsorption. Bacillus subtilis completed adsorption for trace Hg2+ in 15 min. The adsorption efficiency was maintained above 80% under low Hg2+ concentrations (<200 µg/L). The proposed study illustrates that Bacillus subtilis cells are highly efficient and easily obtained material for the adsorption of trace mercury, which shows potential to be further used in the pretreatment of trace Hg2+ detection.