Adsorption-Enhanced Sensitivity for Electrochemical Sensing of Diclofenac by Poly(ether sulfone)-Based Laser-Induced Graphene

Emerging contaminants are a matter of growing concern for environmental and human health and safety, requiring efficient and affordable sensing platforms. Laser-induced graphene (LIG) is a novel material with a 3D porous graphene structure that can be fabricated in a simple one-step fabrication process. However, most LIG-based works in electrochemical sensors are limited to polyimide (PI)-based platforms, thus limiting the purview of properties of LIG dependent on the substrate-laser interaction. Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is an emerging contaminant in water and wastewater that threatens aquatic and terrestrial life. Furthermore, LIG-based sensors have not been used to sense DCF. In this work, we demonstrate the spontaneous adsorption behavior of LIG toward DCF without applying any external potential. This spontaneous adsorption phenomenon can enhance the sensitivity per the characteristics of the tested water samples and permissible standards to be followed. Poly(ether sulfone)-based LIG (PES-LIG) is found to be more responsive to laser irradiation than PI-LIG due to its highly porous surface and fibrous nature, imparting more electrochemical sites and adsorption area for DCF. These characteristics lead to a higher sensitivity of 0.2774 μA μM-1 toward DCF sensing for PES-LIG with a limit of detection of 0.1 μM. The sensors were applied for DCF measurement in wastewater and tap water samples with appreciable selectivity. The specific adsorption behavior of LIG toward DCF could pave the way for new pathways in emerging contaminant sensing and removal as well as for other applications.

Lignocellulosic carbon sheets-based hybrid electrochemical sensor for ultra-sensitive detection of chloramphenicol

Efficient detection of chloramphenicol (CAP) in the environment and food products is crucial for addressing global health and environmental safety concerns. This study presents the development of a cost-effective hybrid electrocatalyst comprising lignocellulosic carbon sheets, graphene oxide, and manganese oxide (LCSs/GO@MnO2) for CAP detection using a simple electrochemical sensor fabricated on a glassy carbon electrode (GCE) substrate. The synergistic interaction between LCSs, GO, and MnO2 enhance the electroactive surface area of GCE, facilitating effective dispersion and electrode modification. This composite material significantly improves electrical conductivity and provides numerous electroactive sites for electrochemical CAP detection via voltammetric techniques. The developed sensor demonstrates a rapid electron transfer rate, enhancing electrode sensitivity for CAP detection at a low overpotential (-0.5717 V) and an optimal pH (7.0). The sensor exhibits a wide linear range (0.017-477.247 μM), excellent sensitivity (105.22 μA μM-1 cm-2), and a low limit of detection (1.2 nM) with enhanced charge carrier efficiency. Additionally, the sensor shows good cycle stability, reproducibility, selectivity, and trace-level CAP sensing applicability in food samples at a low cost. These features make the sensor a promising platform for monitoring antibiotics in various applications.

Bi-functional NiFe2O4/SrTiO3 S-scheme heterojunction for eminent performance photocatalytic treatment of sewage effluent and electrochemical hydrazine determination

Devising of materials that afforded dual applicability in decontamination and pollutant detection were still a towering challenge owing to the increasing flux of discharge toxic contaminants over the years. Herein, the NiFe2O4 nanoparticles-loaded on cube-like SrTiO3 (NiFe2O4/SrTiO3) composite was fabricated by a two-step hydrothermal approach providing remarkable photocatalytic treatment and electrochemical sensing of noxious pollutants in wastewater. The material traits of the fabricated composite were scrutinized by myriad characterization approaches. The NiFe2O4/SrTiO3 hybrid material demonstrated high surface area of 19.81 m2/g, adequate band gap energy of 2.75 eV, and prominent photoluminescence characteristics. In the presence of visible light, the NiFe2O4/SrTiO3 exhibited profound photocatalysis capability to eliminate sewage effluent-bearing chlortetracycline hydrochloride (CTCH) with 88.6% COD removal in 120 min, outperforming other pure materials. Meanwhile, the toxicity examination of effluent, the possible degradation pathway of CTCH and the proposed photocatalysis mechanism were also divulged. More importantly, the glassy carbon electrode was modified with synergized NiFe2O4/SrTiO3 (NiFe2O4/SrTiO3-GCE) was adopted for the precise quantification of Hydrazine (Hz). The NiFe2O4/SrTiO3-GCE obeyed first-order response for the Hz detection within the range of 1-10 mM: cyclic voltametric: limit of detection (LOD) of 0.119 μM with sensitivity of 18.9 μA μM-1 cm-2, and linear sweep voltametric: LOD of 0.222 μM with a sensitivity of 12.05 μA μM-1 cm-2. The stability and interference of modified electrode were also inspected. This work furnished valuable insights to yield a composite with the prominent S-scheme heterojunction system for quenching of charge carrier recombination and consequently contributing to the future realization into the domains of environmental clean-up and toxic chemical detection.

Heterojunction of branched benzopyrazine-based polymers coating on graphene for electrochemical sensing of vanillin

Vanillin finds widespread applications in various industries, such as food, pharmaceuticals, and cosmetics. However, excessive intake of vanillin could pose risks to human health. This study detailed the successful creation of a heterojunction of branched benzopyrazine-based polymers coating on graphene (CMP-rGO) through the Sonogashira-Hagihara coupling reaction. Utilizing the CMP-rGO, a novel electrochemical sensor for vanillin detection was developed. Besides, the synthesized materials were validated using standard characterization techniques. Both cyclic voltammetry and differential pulse voltammetry techniques were employed to investigate vanillin's electrochemical characteristics on this sensor. The findings indicated a significant enhancement in vanillin's electrochemical signal responsiveness with the application of CMP-rGO. Under optimal conditions, the sensor demonstrated a linear response to vanillin concentrations ranging from 0.08 to 33 μM and achieved a detection limit as low as 0.014 μM. Also, the constructed electrochemical sensor exhibited excellent selectivity, stability, and reproducibility. It has been effectively employed to detect vanillin in real samples such as human serum, human urine, and vanillin tablets, with a recovery rate of 99.13-103.6 % and an RSD of 3.46-1.26 %. Overall, this innovative sensor offers a novel approach to the efficient and convenient detection of vanillin.

Nanocomposites with ZrO2@S-Doped g-C3N4 as an Enhanced Binder-Free Sensor: Synthesis and Characterization

This study describes new electrocatalyst materials that can detect and reduce environmental pollutants. The synthesis and characterization of semiconductor nanocomposites (NCs) made from active ZrO₂@S-doped g-C₃N₄ is presented. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) measurements were used to examine electron transfer characteristics of the synthesized samples. Using X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HR-SEM) techniques, inclusion of monoclinic ZrO₂ on flower-shaped S-doped-g-C₃N₄ was visualized. High-resolution X-ray photoelectron spectroscopy (XPS) revealed successful doping of ZrO₂ into the lattice of S-doped g-C₃N₄. The electron transport mechanism between the electrolyte and the fluorine tin-oxide electrode (FTOE) was enhanced by the synergistic interaction between ZrO₂ and S-doped g-C₃N₄ as co-modifiers. Development of a platform with improved conductivity based on an FTOE modified with ZrO₂@S-doped g-C₃N₄ NCs resulted in an ideal platform for the detection of 4-nitrophenol (4-NP) in water. The electrocatalytic activity of the modified electrode was evaluated through determination of 4-NP by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions (pH 5). ZrO₂@S-doped g-C₃N₄ (20%)/FTOE exhibited good electrocatalytic activity with a linear range from 10 to 100 μM and a low limit of detection (LOD) of 6.65 μM. Typical p-type semiconductor ZrO₂@S-doped g-C₃N₄ NCs significantly impact the superior detection of 4-NP due to its size, shape, optical properties, specific surface area and effective separation of electron-hole pairs. We conclude that the superior electrochemical sensor behavior of the ZrO₂@S-doped g-C₃N₄ (20%)/FTOE surfaces results from the synergistic interaction between S-doped g-C₃N₄ and ZrO₂ surfaces that produce an active NC interface.

Sensitive Electrochemical Detection of 4-Nitrophenol with PEDOT:PSS Modified Pt NPs-Embedded PPy-CB@ZnO Nanocomposites

In this study, a selective 4-nitrophenol (4-NP) sensor was developed onto a glassy carbon electrode (GCE) as an electron-sensing substrate, which decorated with sol-gel, prepared Pt nanoparticles- (NPs) embedded polypyrole-carbon black (PPy-CB)/ZnO nanocomposites (NCs) using differential pulse voltammetry. Characterizations of the NCs were performed using Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), Ultraviolet-visible Spectroscopy (UV-vis), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Diffraction Analysis (XRD). The GCE modified by conducting coating binders [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; PEDOT:PSS] based on Pt NPs/PPy-CB/ZnO NCs functioned as the working electrode and showed selectivity toward 4-NP in a phosphate buffer medium at pH 7.0. Our analysis of 4-NP showed the linearity from 1.5 to 40.5 µM, which was identified as the linear detection range (LDR). A current versus concentration plot was formed and showed a regression co-efficient R² of 0.9917, which can be expressed by i_p(µA) = 0.2493C(µM) + 15.694. The 4-NP sensor sensitivity was calculated using the slope of the LDR, considering the surface area of the GCE (0.0316 cm²). The sensitivity was calculated as 7.8892 µAµM^-1cm^-2. The LOD (limit of detection) of the 4-NP was calculated as 1.25 ± 0.06 µM, which was calculated from 3xSD/σ (SD: Standard deviation of blank response; σ: Slope of the calibration curve). Limit of quantification (LOQ) is also calculated as 3.79 µM from LOQ = 10xLOD/3.3. Sensor parameters such as reproducibility, response time, and analyzing stability were outstanding. Therefore, this novel approach can be broadly used to safely fabricate selective 4-NP sensors based on nanoparticle-decorated nanocomposite materials in environmental measurement.

Synthesis and characterization of CuO@S-doped g-C3N4 based nanocomposites for binder-free sensor applications

This study presents the simultaneous exfoliation and modification of heterostructured copper oxide incorporated sulfur doped graphitic carbon nitride (CuO@S-doped g-C₃N₄) nanocomposites (NCs) synthesized via chemical precipitation and pyrolysis techniques. The results revealed that the approach is feasible and highly efficient in producing 2-dimensional CuO@S-doped g-C₃N₄ NCs. The findings also showed a promising technique for enhancing the optical and electrical properties of bulk g-C₃N₄ by combining CuO nanoparticles (NPs) with S-doped g-C₃N₄. The crystallite and the average size of the NCs were validated using X-ray diffraction (XRD) studies. Incorporation of the cubical structured CuO on flower shaped S-doped-g-C₃N₄ was visualized and characterized through XRD, HR-SEM/EDS/SED, FT-IR, BET, UV-Vis/DRS, PL, XPS and impedance spectroscopy. The agglomerated NCs had various pore sizes, shapes and nanosized crystals, while being photo-active in the UV-vis range. The synergistic effect of CuO and S-doped g-C₃N₄ as co-modifiers greatly facilitates the electron transfer process between the electrolyte and the bare glassy carbon electrode. Specific surface areas of the NCs clearly revealed modification of bulk S-doped g-C₃N₄ when CuO NPs are incorporated with S-doped g-C₃N₄, providing a suitable environment for the binder-free decorated electrode with sensing behavior for hazardous pollutants. This was tested for the preparation of a 4-nitrophenol sensor.

Structural and anionic effects of microcrystalline Zn-CPs on 4-nitrophenol sensing performances

Coordination polymers (CPs: [ZnL₃]_n(X)_2n, L = trans-1,4-bis(imidazolyl)-2-butene; X⁻ = BF₄⁻, ClO₄⁻, NO₃⁻) allow for detection of the 4-nitrophenol (4-NP) oxidation process by enhanced electrochemical signals. Electrochemical measurement is a highly sensitive method providing much evidence of chemical reactions on an electrode surface. In the present study, we designed and synthesized, with reference to X-ray diffraction data and by spectroscopic analyses, new 3D coordination structures containing imidazolyl donors and zinc(ii). The presence of microcrystals [ZnL₃]_n(BF₄)_2n on the working electrode enhanced the redox signals. Therefore, we propose a simple catalytic process that can explain these results and clarify the influence of anions that constitute CP materials used to improve electrochemical detection applications. The CP materials were characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (IR), thermogravimetric (TG) analyses, single crystal X-ray diffraction (SC-XRD), and electrochemical analyses.

To investigate structural and anionic effects of coordination polymers (CPs) on electrochemical sensors, Zn-CPs were synthesized and used for 4-nitrophenol oxidation sensors.

Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

The rational design and demonstration of a facile sequential template-mediated strategy to construct noble-metal-free efficient bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and electrocatalytic detection of hazardous environmental 4-nitrophenol (4-NP) have continued as a major challenging task. Herein, we construct a novel Ag@polymer/NiAl LDH (designated as APL) nanohybrid as an efficient bifunctional electrocatalyst by a simple hydrolysis method. The well-fabricated APL/GCE exhibited an extensive linear range from 0.1 to 100 μM in optimized conditions. It showed a detection limit (LOD) of 0.0096 μM (9.6 nM) (S/N = 3) for 4-NP in pH 6 by differential pulse voltammetry (DPV). Meanwhile, the newly fabricated APL exhibited outstanding OER activity with a very low overpotential of 259 mV to deliver 10 mA cm^-2 current density (J) at a scan rate of 5 mV/s. The Tafel plot value of APL is low (97 mV/dec) compared to that of the benchmark RuO₂ due to a fast kinetic reaction. Besides, the durability of the electrocatalyst was assessed by a chronoamperometry test (CA) for 36 h at 1.55 mV vs RHE, and the long-term cycling stability was analyzed by using cyclic voltammetry (CV); after 5000 cycles, the electrocatalyst was highly stable. These demonstrated results could lead to an alternative electrocatalyst construction for the bifunctionally efficient electrochemical sensing of 4-nitrophenol and oxygen evolution reaction.

Selective Electrochemical Sensing Platform Based on the Synergy between Carbon Black and Single-Crystalline Bismuth Sulfide for Rapid Analysis of Antipyretic Drugs

Nanomaterials are of significant interest in acetaminophen (APAP) detection in pharmaceutical samples. Herein, a carbon black/single-crystalline rodlike bismuth sulfide (CB/Bi₂S₃) composite prepared by an ultrasonic method is reported and utilized for the rapid analysis of APAP. The highly oriented edge reactive sites of the CB/Bi₂S₃ composite promoted synergy and good electrochemical sensing performance with a fast electron transfer rate and low overpotential (0.35 V). Therefore, a CB/Bi₂S₃ composite-modified glassy carbon electrode (GCE) was applied to the selective determination of APAP by the voltammetric technique. The CB/Bi₂S₃ composite-modified electrode showed the lowest limit of detection of APAP (1.9 nM) with excellent sensitivity. The proposed CB/Bi₂S₃/GCE platform exhibited high selectivity, excellent stability (87.15%), and reproducibility. Also, the CB/Bi₂S₃/GCE sensor was then successfully used to analyze an APAP pharmaceutical sample and exhibited satisfactory outcomes. Therefore, the CB/Bi₂S₃-modified GCE sensor platform would be a low-cost and robust GCE electrode material for APAP detection.

Simultaneous determination of nitrophenol isomers based on reduced graphene oxide modified with sulfobutylether-β-cyclodextrin

The present study reports the development of an electrochemical sensor based on sulfobutylether-β-cyclodextrin modified reduced graphene oxide hybrid (SBCD-rGO) for simultaneous detection of nitrophenol isomers. First, SBCD-rGO hybrid was synthesized and detailed characterized. Afterwards, a sensor was fabricated via the modification of glassy carbon electrode (GCE) with SBCD-rGO, and its electrochemical detection performances were also investigated. Then, the constructed electrochemical sensor was applied to detect nitrophenol isomers by voltammetry analysis. The results suggested that the sensitivities were 389.26, 280.88 and 217.19 μA/mM for p-nitrophenol (p-NP), m-nitrophenol (m-NP), and o-nitrophenol (o-NP), respectively, and their corresponding detection limits were all about 0.05 μM. Significantly, the combination of voltammetry analysis with the constructed sensor and data analysis by multiple linear regression realized the simultaneous detection of nitrophenol isomers.

Tailoring of bismuth vanadate impregnated on molybdenum/graphene oxide sheets for sensitive detection of environmental pollutants 2, 4, 6 trichlorophenol

In the present work, we reported a one pot simple colloidal-gel synthesis of molybdenum bismuth vanadate (MoBiVO₄). The charge transfer property of MoBiVO₄ was improved by developing a composite with graphene oxide (GO) through sonochemical technique. The optical and morphological analysis revealed that successful formation of GO-MoBiVO₄ composite without any other filth. As prepared composite was used to modify the superficial surface of glassy carbon electrode (GO-MoBiVO₄/GCE) and applied for the selective detection of environmental pollutant 2, 4, 6 trichrlorophenol (TCP). The electron channeling capability of GO with molybdenum bismuth vanadate possessed a superior electrochemical response in cyclic voltammetry (CV), whereas bare GCE and other modified electrodes provided an inferior response with lower current response. The differential pulse voltammetry (DPV) response of TCP at GO-MoBiVO₄/GCE outcomes with low level detection of 0.4 nM and higher sensitivity of 2.49 μA μM^-1 cm^-2 with wider linear response 0.199-17.83 μM. Furthermore, the proposed sensor applied in practicability analysis and the results indicates GO-MoBiVO₄/GCE prominent towards electrochemical detection of TCP.

Fabrication of Co3O4 nanoparticle-decorated porous activated carbon electrode for the electrochemical detection of 4-nitrophenol

Preparation of Co3O4@BVFC for the electrochemical detection of 4-NP.