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Hydrothermal synthesis of silver molybdate/reduced graphene oxide hybrid composite: An efficient electrode material for the electrochemical detection of tryptophan in food and biological samples
... A similar hydrothermal process has been employed for the synthesis of Ag 2 MoO 4 -rGO nanocomposite as a previously reported method with minor modifications. [28,31,33,34] First, the 0.2 M silver nitrate and 0.2 M sodium molybdate dihydrate were added to ChemistrySelect 2024, 9, e202403162 (2 of 11) Scheme 1. (A) Synthesis of the silver molybdate-reduced graphene oxide nanocomposite. (B) Steps involved in the fabrication of the "BSA/anti-MUC1/ Ag 2 MoO 4 -rGO/GCE" biosensor. ...
... Kokulnathan et al. fabricated an electrochemical sensor using Ag 2 MoO 4 -rGO nanocomposites for the sensitive detection of amino acid. [31] Still, there are limited works reported on Ag 2 MoO 4 -rGO nanocomposite-based electrochemical biosensors. Hence, there is huge potential to explore this nanocomposite as a biosensing material. ...
... However, similar peaks at 129, 320, 387, 784, and 872 cm À 1 correspond for the Ag 2 MoO 4 . [26,28,31] These results indicate the successful preparation of Ag 2 MoO 4 -rGO nanocomposite. ...
This work aims to detect the Mucin‐1 (MUC1) breast cancer biomarker using a label‐free impedimetric biosensor of silver molybdate anchored on reduced graphene oxide (Ag2MoO4‐rGO). A hydrothermal method has been employed to synthesize the Ag2MoO4‐rGO nanocomposite. Subsequently, they have been studied through analytical characterization techniques to study the electrocatalytic activity, electroactive surface area, surface functionalities, and morphologies to determine the suitability of the material for biosensor fabrication. Results reveal that the Ag2MoO4‐rGO nanocomposite possesses excellent electroconductivity and surface properties that have significant characteristics for the biosensor's performance. A biosensor has been fabricated by the immobilization of Ag2MoO4‐rGO nanocomposite and anti‐MUC1 antibody on a glassy carbon electrode. The electroanalytical studies revealed that the biosensor has excellent sensitivity and detection performance having a wide linearity of 100 fg mL⁻¹–5 ng mL⁻¹ and a low limit of detection of 2.70 fg mL⁻¹. Moreover, the remarkable selectivity, reproducibility, stability, and detection in serum samples determine the high performance of the biosensor. Therefore, the presented biosensor could be a promising diagnostic tool that shows the remarkable potential to efficiently detect the breast cancer MUC1 biomarker in patient's serum samples.
... [25][26][27][28] Due to their enormous surface area, remarkable selectivity for a variety of analytes, good conductivity, catalytic characteristics, long-term stability, and capacity for on-site detection, these materials tend to enhance the electrocatalytic activity. 29,30 In these applications, electrical conductivity, and the infiltration of CB within the matrix of the materials is critical, as they have an impact on the performance of the composites. [24][25][26][27][28][29][31][32][33][34] Because of its large surface area to volume ratio and amorphous carbon structure, CB is a common ingredient in the manufacture of inks and rubber. ...
... 29,30 In these applications, electrical conductivity, and the infiltration of CB within the matrix of the materials is critical, as they have an impact on the performance of the composites. [24][25][26][27][28][29][31][32][33][34] Because of its large surface area to volume ratio and amorphous carbon structure, CB is a common ingredient in the manufacture of inks and rubber. It is a useful material for electrode modification due to its affordable price in comparison to other carbon compounds, and superior conductivity. ...
In this study, a molybdenum-doped copper oxide (Mo–CuO) composite was synthesized via a hydrothermal method and combined with carbon black (CB) to form Mo–CuO@CB. This composite was used to modify a screen-printed carbon electrode (SPCE) for the detection of Metol (MT), an industrial pollutant harmful to both human health and the environment. Structural and surface characterization was performed using high-resolution transmission electron microscopy, field-effect scanning electron microscopy, energy-dispersive spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Electrochemical techniques, including differential pulse voltammetry and cyclic voltammetry, were used to assess the sensor’s performance. The Mo–CuO@CB@SPCE sensor exhibited a low detection limit of 2.7 nM, and limit of quantification is 82 nM, a broad linear range (5.0 × 10⁻⁹–170 mol L⁻¹), and high sensitivity (4.148 μA μM⁻¹ cm⁻²), benefiting from the catalytic activity of Mo–CuO and the large surface area of CB. With recovery rates ranging from 96% to 100.6% in pond, river, and tap water, the sensor effectively detects MT in environmental samples, ensuring reliable monitoring of this persistent pollutant.
... A thorough look at a number of studies reported in the literature shows that the standard techniques used for the detection of tryptophan include high-performance liquid chromatography with fluorescence [13], colorimetry [14], liquid chromatography mass spectrophotometry [15], and electroanalytical methods [16][17][18][19][20][21][22][23][24]. Among these techniques, electrochemical methods of analysis have recently attracted considerable attention among researchers due to their simplicity, low costs, and speed of analysis, apart from the fact that the application of these methods allows one to use portable devices for the conduct of analysis [25]. ...
... Among these techniques, electrochemical methods of analysis have recently attracted considerable attention among researchers due to their simplicity, low costs, and speed of analysis, apart from the fact that the application of these methods allows one to use portable devices for the conduct of analysis [25]. Previous studies published in the literature have reported the use of electrochemical sensors based on molecularly imprinted copolymer [26], perovskite-type SrTiO 3 nanocubes decorated reduced graphene oxide [24], Fe 3 O 4 /C composite [19], flower-like cerium vandate microstructures [16], gold nanoparticles [23,27], silver molybdate [22] and other materials [17,23] for tryptophan detection. It is worth noting that the use of graphene oxide-based electrodes for the electrochemical detection of tryptophan has resulted in promising responses in terms of selectivity and stability of the sensing devices [17]; in addition, the electron transfer reactions have been found to be typically slow in bare (unmodified) electrodes. ...
The present work reports the development of screen-printed electrode (SPE) using flexible polyester sheets modified with nanodiamond (ND), Au nanoparticles (AuNPs), and poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), and its application for the detection of tryptophan in synthetic urine, milk, and dark chocolate samples. The ND/AuNPs/PEDOT:PSS nanocomposite was characterized by cyclic voltammetry, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The proposed ND/AuNPs/PEDOT:PSS-based SPE was applied for the detection of tryptophan using square-wave voltammetry in a linear detection range of 0.8 µmol L⁻¹–18 µmol L⁻¹, with limits of detection (LOD) and quantification (LOQ) of 0.2 µmol L⁻¹ and 0.8 µmol L⁻¹, respectively. The sensor was successfully applied for tryptophan quantification in dark chocolate, milk and synthetic urine where good recovery percentages were obtained. The results obtained from the analysis of interference in the presence of dopamine and caffeine showed that the ND/AuNPs/PEDOT:PSS-based SPE exhibited excellent selectivity toward tryptophan. The findings of this study show that metallic nanoparticles, nanodiamonds and biocompatible conductive composites can be used as a suitable, affordable alternative tool for fast, simple, and low-cost detection of tryptophan in non-invasive testing and analysis of food products.
Graphical abstract
... L-Tryptophan (Trp) is an oxidizable amino acid that plays an important physiological role in the metabolism of protein synthesis and the nervous system for nitrogen equilibrium in adults and for normal growth in infants [1,2]. L-Trp cannot be produced by the human body and is not abundantly found in vegetables [3]; instead, it can generally be obtained from a diet including foods such as yogurt, dried dates, chocolates, milk, bananas, and pharmaceutical drugs. ...
... Additionally, apparent electron transfers constant (K s ) and the charge transfer coefficient (a) of the CNFeNiCoSe 4 composites electrodes were investigated using the Laviron equation (2) log K S ¼ a logð1 À aÞ þ ð1 À aÞloga À log RT nFn À ð1 À aÞanFDE p 2:3RT (2) where DEp, n, and n represent the peak potential separation, the number of electrons transferred in the rate-determining step, and the scan rate. From scan rate plots (Fig. 4d) and Eq. ...
In this study, a simple approach is established to fabricate NiCoSe4 nanorods grown onto carbon nanofiber (CNF) skeletons by combining electrospinning and a hydrothermal process. We achieved the rapid and ultrasensitive electrocatalytic sensing of tryptophan (Trp) in 0.1 M KOH by using intrinsically metallic NiCoSe4 anchored on CNFs as an alternative working electrode material. Benefiting from the large surface area due to rich defect active sites and the high electrocatalytic behavior of NiCoSe4 with CNF, the fabricated sensor exhibits a lower electron‐transfer resistance of Rct 92 Ω with respect to the CNF-NiCo and CNFs electrodes. The results of voltammetric technique confirmed that the CNF-NiCoSe4-GCE showed higher anodic peak intensity and a lower anodic potential for Trp detection than CNFs-GCE and CNF-NiCo-GCE electrodes since the integration of sp² carbon on the surface of the CNFs and bimetallic selenides improves the sensing performance. The amperometric I-t curve showed a linear response in the Trp concentration range of 5–95 nM and a detection limit of 0.68 nM at low potential of 0.4 V vs. Hg/HgO. The CNF-NiCoSe4-GCE was successfully utilized for the electrocatalytic monitoring of Trp from human serum, milk, and tomato juice samples with a recovery of 95.4–105.5%.
... Moreover, when Ag 2 MoO 4 was applied as an electrocatalyst for the detection of chemicals or in oxygen reduction reactions, their high electron transition proved favorable for these applications, having impressive activity [16,85,133,134]. However, no reports of its use as electro-based AOPs were found in the literature. ...
... However, no reports of its use as electro-based AOPs were found in the literature. This application would probably be very advantageous, once very efficient electrodes have been reported in previous results [16,85,134]. ...
Advanced oxidation processes can achieve high degradation levels for various recalcitrant contaminants but the cost of their use in water/wastewater treatment is high. In recent years, more effective catalysts have been developed (such as silver molybdate) to minimize this and other drawbacks, offering a lower band gap and larger operational pH range. Silver molybdate (Ag2MoO4) has attracted attention due to its intriguing electronic properties, diversity of morphologies, and physico-chemical characteristics. Even more recently, catalytic activity in photocatalysis, Fenton-like processes, electrocatalysis and disinfection has been reported, highlighting the potential for its use in a broad range of important fields of application, including water and wastewater treatment. This paper provides a brief history of this semiconductor, mainly focusing on the current state of knowledge and the remaining challenges in terms of its synthesis (particularly obtaining the metastable tetragonal α-phase), properties and characterization. The application of Ag2MoO4 as a catalyst for application in advanced oxidation processes is also addressed.
... The authors have cited additional references within the reference [45][46][47][48][49][50][51][52]. The Supporting Information includes the characterization and application of TPE-LL in latent fingerprints imaging. ...
Development of latent fingerprints (LFPs) at the scene played the important role in forensic investigations by reconstructing crime trajectory and individualizing suspect. In this work, the optical sensor named TPE‐LL with aggregation‐induced emission property was constructed and used in LFPs visualization. The sensor exhibited a satisfactory linear relationship to tryptophan (Trp) in the range of 1–20 nM with the low detection limit of 0.15 nM. The samples were collected from 60 volunteers, with a total of 7200 impressed samples and 160 natural samples. Significantly, the high‐resolution fingerprints images with high fidelity and contrast containing pore features were obtained from impressed samples left on porous object for 15 days. Meanwhile, the relative complete STR typing profiles of deposited DNA were obtained and the identification rate of DNA after the develop process was 76.5 %, suggesting that the method was low destructive to DNA. The results indicated that the sensor provided promising perspectives on solving the current technical problems in the field of forensic science and technology
... Moreover, the addition of semiconductor EuMoO 4 material to the carbon material may prevent agglomeration and boost catalytic active sites of composites. 42,43 However, the low electron transfer of EuMoO 4 hinders its further use in electrochemical sensors. In this study, the combination of conductive carbon materials with EuMoO 4 is shown to be an efficient strategy for enhancing electrochemical performance. ...
The widespread use of carbendazim insecticides has caused substantial concerns to human health due to their coexistence, high toxicity, and persistence. Therefore, it is crucial to develop a carbendazim detection more important for the protection of both humans and the environment safety. A graphitic carbon nitride/europium molybdate ( g -C 3 N 4 /EuMoO 4 ) composite was fabricated using a simple coprecipitation method and utilized for the selective detection of carbendazim. The glassy carbon electrode (GCE) was fabricated with g -C 3 N 4 /EuMoO 4 composite electrode (GCE/ g -C 3 N 4 /EuMoO 4 ) was simple, affordable, and offers an excellent platform for the detection of carbendazim. The structure formation was validated by suitable microscopic and spectroscopic techniques. Under optimal conditions, the GCE/ g -C 3 N 4 /EuMoO 4 electrode showed excellent electrochemical properties for the detection of carbendazim with a low detection limit (0.04 μ M) (S/N = 3), a large linear response range of 50–400 μ M, and high sensitivity (1.41 μ A μ M ⁻¹ cm ⁻² ). The findings demonstrated that the developed method can be used to analyze food samples. The g -C 3 N 4 /EuMoO 4 demonstrates greater sensitivity toward the electrochemical detection of carbendazim compared with the previous sensors. The GCE/ g -C 3 N 4 /EuMoO 4 electrode was utilized to detect carbendazim in real samples, and the results were satisfactory. Furthermore, the GCE/ g -C 3 N 4 /EuMoO 4 modified electrode offers several interesting properties, stability, reproducibility, repeatability, low cost, and practical applications.
... Our developing world of people face myriad problems that affect physical and mental health which can be treated with different kinds of drugs medically approved by physicians. 24,25 Among them, phenothiazine is an organic compound that is employed as a tranquilizer in medical applications under neuroleptics. 26 It is one of the widely used sedative agents which is also recognized as antipsychotic analgesics in several treatments of psychotic and varied physical and mental (personality disorder) related issues. ...
Transition metal dichalcogenides (TMC) are utilized in diverse applications due to their 2D structure and effective tendencies. Molybdenum disulfide (MoS2) based TMC is emphasized for its lamellar structure with enormous edges which afford faster transfer of electrons for detecting molecules. To promote the action of conductance of MoS2, metal oxide can be employed and cerium oxide (CeO2) with abundant distinguishable properties was embedded with MoS2. The nanocomposite MoS2/CeO2 was characterized for structural and functional analysis by X-ray diffraction, Raman, and Fourier infra-red spectroscopy, resulting in the pure presence of MoS2/CeO2 without additional constituent peaks. CeO2 nanorods embedded over MoS2 nanosheets were identified with field-emission scanning electron microscopy and their elemental presence identified with X-ray photoelectron spectroscopy and EDAX analysis. When fabricated over glassy carbon electrode (GCE) MoS2/CeO2 showed superior conductivity facilitated by the higher active sites provided by MoS2/CeO2 toward promethazine hydrochloride (PZC) oxidation. The resistance of the designed MoS2/CeO2 electrode, ∼61 Ω, is attributed to the synergetic conducting behavior. The stability of the electrode was consistent with the similar current response over 20 days. When used for real-time detection in biological samples, the MoS2/CeO2/GCE established excellent response and a detection limit at 3 nM for the linear range from 0.009-695 μM was obtained. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
... Carbon-based materials have attracted immense interest owing to their outstanding merits in the field of energy storage, field emission, pollutant degradation, energy conversion, and sensor applications [1,2]. Reduced graphene oxide (RGO) with one atom thick has been explored as the most promising candidate in the field of electrochemical sensors due to its advanced properties and the preparation of RGO from graphene oxide by ultrasonic method has utmost validation [3,4]. Compared to other methods, ultrasonic method is an eco-friendly and green method which upholds the metrics of green chemistry. ...
Rational design of different heteroarchitecture-based ultrasonic approaches offer great opportunities to improve the electrocatalytic properties in electrochemical reaction. Especially, zinc oxide (ZnO)-based carbon architecture has gained tremendous interest due its fascinating properties. Herein, we have synthesized flower-like ZnO superstructures on multiwalled carbon nanotubes (CNTs)/reduced graphene oxide (RGO) composite using an ultrasonic bath (100 W at 50 kHz). The structuro-chemical and crystalline properties of [email protected]/RGO composite are analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) analysis, and Raman spectroscopic analysis. Also, the as-synthesized [email protected]/RGO composite has been successfully applied towards the electrochemical detection of the nonsteroidal anti-inflammatory drug, flufenamic acid (FFA). As expected, [email protected]/RGO composite modified glassy carbon electrode (GCE) exhibits excellent electrocatalytic performance towards FFA detection, when compared to other modified and un-modified GCEs. The positive synergistic effect between ZnO, CNTs and RGO in the composite is highlighted by the advanced electrochemical sensing performance of the fabricated GCE which can be ascertained to more number of active sites and rapid electron transport. The proposed sensor establishes two response ranges with trace level detection limit and higher sensitivity towards FFA sensing. The feasibility of the sensor is also validated by its application towards the determination of FFA in bovine serum albumin and urine samples which offers satisfying recovery range. Thus the manipulation of the hierarchical architecture of ZnO together with the electronic conductivities of CNTs and RGO tailor the formation of a nanocomposite which can be utilized for real analysis of pollutants.
... 33 Similarly, the same group were worked on various carbon sources such as Sulphur doped graphene oxide, graphitic carbon nitrite, and carbon nano fibers for the various determination of molecular samples useful for environment. 34,35 Meanwhile Thangavelu et al. were also performed the determination of tryptophan using AgM@rGO. As per the expectation the fabricated catalyst with carbon sources found to be a good sensor. ...
In the present paper, a novel electrochemical sensor based on screen-printed carbon electrodes (SPCE) modified with self-assembled Praseodymium-Titanium Dioxide functionalized Carbon Nanotubes (Pr-TiO2/f-CNT) were reported. The sensor was applied for the detection of clinically important molecular marker-Tryptophan (Trp) a neurotransmitter. Synthesized nanocomposites were characterized by XRD and Raman spectra, optically confirming the material and composite formation. FE-SEM and TEM techniques were utilized to study and confirm the tube line structure formed with nanoparticles functionalized on the surface of CNT. Cyclic Voltammetry (CV) calculated the fabrication of the electrodes and the electrochemical activity. Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV) were utilized to know the electrocatalytic performance of the fabricated sensor. Activities of the fabricated new modified sensor to this analyte is pH dependent, which allowed to select the best working conditions as a function of the nanocomposite characteristics. The obtained linear ranges and Limits of Detection (LoD) were 0.49 to 10.93 and 15.95 to 89.59 μM and 0.024 μM respectively. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
... 32 The rGO can contribute good conductivity than graphene with a larger potential window, low charge transfer resistance with reduced oxygen species. 33,34 The accessibility of functional groups over its edge planes such as carboxyls, carbonyl, hydroxyls, epoxides groups makes its solubility in solvents and opting as an exceptional candidate. 35 Alongside this, it bears high carrier mobility, heterogeneous transfer of electrons, larger specific surface about (2630 m 2 g −1 ), and lots. ...
Sulfonamides are a broad assortment of drugs utilized in treating bacterial diseases in veterinary and human existence as anti-infection agents. The escalating usage of such medications requires explicit recognition. This work describes the electrochemical detection of sulfamethazine (SMZ) (a subgroup of sulfonamides) using strontium niobium combined with reduced graphene oxide (SN/rGO) as composite material. The structural and topological criteria illustrate the surface immaculateness and elemental presence of the crystalline material SN/rGO with XRD and FE-SEM analysis. Additional examinations of chemical states and the functional group were identified with XPS and FT-IR measurements. The feasibility of the sensor was inspected in the record of electrochemical studies. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) studies have demonstrated the effective implementation of the fabricated sensor with facilitating higher electroactive sites and enhanced conductance with SN/rGO. The amalgamation of SN and rGO has substantial influence with a lower limit of detection 6 nM with linearity from 0.009 μ M to 128 μ M. The limit of quantification was about 0.0224 μ M. The specific detection acquired over anti-interference studies and real-world actualize over milk, honey, and human blood serum tests mirror SN/rGO modified platform’s viable capability. The construction of SN/rGO is envisioned as a promising dais for improved SMZ sensing in real samples.
... Graphene is a 2D layered structure with sp 2 carbon sheet morphology with honeycomb lattice owing to peculiar properties in structural, physical, and chemical parameters [30]. Furthermore, reduced graphene oxide (rGO) is a carbon sourced nanosheet that serves as a superior catalyst in various applications like supercapacitors, lithium-ion batteries, photodegradation, biocompatibilities, cellular toxicology, and electrochemical studies [31,32]. This also increases the conductivity and stability of the composite compensating its synergistic effect [33]. ...
Prostate cancer is one of the major causes of death around the globe leading to cancer deaths in the US standing at a second position. Flutamide is one of the important drugs which is utilized in clinical diagnosis. Even though over usage and improper discharge leads to very serious harm to both living and environmental bodies. In this aspect developing a sensor for ultra-trace level detection of flutamide is very much indeed with selectivity, stability, and reproducibility. Herein, we report a facile synthesis of hexagonal Sn doped zinc oxide (Sn-ZnO) anchored on reduced graphene oxide (rGO) hybrid nanocomposite in discriminating reduction of flutamide. As per prepared Sn-ZnO/rGO nanocomposite has exhibited good catalytic performance when compared to bare and other modified electrodes. Resulting in inactive sites, large surface areas, synergic effects, and crystalline growths. Noticeable merits include the wide linear range of 0.01 to 170 µM and Limit of detection (LOD) of 7.3 nM with an excellent sensitivity of 14.10 µA µM⁻¹ cm⁻² and satisfying stability. The modified electrode was successfully applied as a real-time analysis in both biological and water bodies with promising recoveries.
... It is also used as a sleep aid, nutraceutical and antidepressant [7]. Tryptophan cannot be synthesised by the human body [8]. Therefore, this amino acid must be taken into the body through nutrition. ...
In this study, a quartz crystal microbalance (QCM) nanosensor was prepared to detect tryptophan. QCM nanosensor was prepared through the formation of tryptophan memories on the gold surface of QCM electrode using Methacryloylamidohistidine-Cu(II)-tryptophan ([MAH-Cu(II)]-tryptophan) pre-organised monomer system. The designed pre-organised monomer system was characterised by use of Fourier Transform Infrared (FTIR) and Atomic Force Microscope (AFM) was used to characterise the QCM nanosensors. After the characterisation studies, imprinted and non-imprinted sensors were connected to QCM system to determine the binding of the target molecule, selectivity and the detection of the amount of target molecule in real samples. The results showed that the imprinted QCM nanosensor had high selectivity for tryptophan.
The co‐precipitation approach was employed in this study to create Fe doped ZnO (Fe‐ZnO) nanoparticles (NPs). To characterize the synthesized NPs, Ultra violet‐Visible (UV‐Vis) spectroscopy, X‐ray diffraction (XRD), fourier transform infrared (FT‐IR), scanning electron microscopy (SEM), and Brunauer‐Emmett‐Teller (BET) were used. Here, a novel electrochemical approach for the detection of tryptophan (Trp) using a glassy carbon electrode modified with Fe‐ZnO NPs (Fe‐ZnO/GCE) is demonstrated. The research findings revealed that Fe‐ZnO/GCE enhanced the electron transfer rate of Trp oxidation. The sensitivity of Trp detection using Fe‐ZnO/GCE in phosphate buffer solution (PBS) at pH 64.0 was significantly improved compared to bare GCE due to the electrocatalytic activity of Fe‐ZnO NPs. Fe‐ZnO/GCE exhibited a linear response with Trp concentrations ranging from 0.1 to 150 μM with the limit of detection (LOD) is 0.089 μM (3σ /m ) and limit of quantification (LOQ) about 0.3 μM (10σ /m ) using linear sweep voltammetry (LSV). The Fe‐ZnO/GCE sensor was also effectively used to detect Trp in African catfish and multivitamin tablets. Trp analysis in real samples exhibited good recovery values of 89.60 to 99.15 %, demonstrating the accuracy and practicality of the method.
Here, a highly sensitive electrochemical sensor for detection of tryptophan (Trp) using a nitrogen defect graphitic carbon nitride-modified glassy carbon electrode (ND-CN/GCE) was introduced. ND-CN/GCE showed a higher oxidation current for Trp than the graphitic carbon nitride-modified glassy carbon electrode (g-CN/GCE) and bare glassy carbon electrode (BGCE). The synthesized nitrogen defect-rich graphitic carbon nitride (ND-CN) was characterized using X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical impedance spectros-copy and cyclic voltammetry were used to further analyze the electrochemical properties of BGCE, g-CN/GCE, and ND-CN/GCE. The oxidation of Trp at ND-CN/GCE is a diffusion-controlled process at pH 3.0. It was calculated that the transfer coefficient, rate constant, and diffusion coefficient of Trp were 0.53, 2.24 × 10 3 M −1 s −1 , and 8.3 × 10 −3 cm 2 s −1 , respectively, at ND-CN/GCE. Trp was detected using square wave voltammetry, which had a linear range from 0.01 to 40 μM at pH 3.0 and a limit of detection of about 0.0034 μM (3σ/m). Analyzing the presence of Trp in a milk and multivitamin tablet sample with a percentage recovery in the range of 97.0−108% satisfactorily demonstrated the practical usability of the electrochemical sensor. The ND-CN/GCE additionally displays good repeatability and reproducibility and satisfactory selectivity.
Sensors are significantly relevant to many aspects of life. The advancements in nanotechnology-based sensing systems are giving rise to exciting developments in sensor applications. Recently, nanocomposites have become highly promising candidates for the designing of new chemical sensing and biosensing platforms.
Graphene-based nanocomposites have been successfully employed in many sensing applications in view of their excellent physical properties including high surface area, electrical conductivity, flexibility and optical transparency. They provide remarkable advantages such as lower fabrication costs, improved biocompatibility, prominent sensitivity, stability and selectivity for effective real-world implementation.
The aim of the book is to give an overview on the properties and novel applications of graphene-based nanocomposites as chemical and biosensors. Chapters highlight various biosensing applications such as diabetes monitoring, cancer cell detection, virus, bacteria, DNA, protein and amino acid sensing, as well as hormone and cholesterol detection. Moreover, chemical sensing applications like gas, alcohol, and food toxin sensing, heavy metal ion detection, and H2O2 sensing are also covered. The book is ideal for postgraduates, analytical chemists, biomedical scientists and researchers in both academic and industrial settings working on materials science, chemical science and nanotechnology.
Novel silver/molybdenum bimetallic metal-organic framework (AgMo-MOF) was synthesized using the solvo-hydrothermal method and then converted to Ag2MoO4 nanoparticles by calcination process. The cubic spinel structure of Ag2MoO4 was confirmed by XRD. The valence states of Ag, and Mo are +1, and + 6, respectively, according to the XPS spectra. The specific surface area was evaluated to be 24.52 and 56.58 m2 g−1 for the AgMo-MOF and Ag2MoO4, respectively, using BET analysis. The optical band gap of Ag2MoO4 was estimated to be 3.38 eV. The GCD analysis revealed the superior specific capacitance of 652.5 and 1468.7 F g−1 at 1 A g−1 for AgMo-MOF/NF and Ag2MoO4/NF electrodes, respectively. The cyclic stability after 5000 cycles at 20 A g−1 revealed that the AgMo-MOF/NF and Ag2MoO4/NF electrodes are stable with capacitance retention of 86 % and 90 %, respectively. Furthermore, Ag2MoO4//AC asymmetric supercapacitor devices provide a terrific energy density of 72.1 Wh kg−1 at 1123.6 W kg−1 and capacitance retention of 88 % over 5000 cycles.
Emerging interest in developing multi-functional nanomaterials for industrial and clinical diagnosis creates novel and beneficial opportunities for the fabrication of new-generation sensing devices and their quantitative-purposed applications. Two-dimensional (2D) nanomaterials with outstanding chemical, physical and electronic properties no doubt hold great promise to construct analytical-based sensors for electrochemical applications. It is well-known that 2D-based electrochemical (bio)sensors present an excellent catalytic activity and superior analytical performance towards the target molecules. This review presents a first comprehensive overview of the current state-of-the-art progress in the design of electrochemical (bio)sensors including 2D nanostructures for only trace level detection of amino acids and pharmaceuticals. In this scope, we especially paid considerable attention to the design and fabrication of 2D electrochemical (bio)sensors and their analytical applications. This review concludes with a discussion about new possibilities/significant challenges for designing of 2D-based sensing devices, and future aspects of 2D-based new-generation sensors for clinical and industrial applications.
Herein, designing of sustainable flower-like novel Sr3(VO4)2/g-C3N4 (SrVO/CN) nanocatalyst was successfully fabricated by easier hydrothermal method and utilised as a visible-light-driven for the degradation of methylene blue (MB) dye and ciprofloxacin (CF) antibiotic for the first time. The physicochemical behaviour of the nanocomposite was confirmed by various analytical techniques. These results confirm the successive development of flower-like Sr3(VO4)2 anchored on the g-C3N4 layer. The SrVO/CN can serve as an excellent catalyst for the decomposition of MB dyes and CF drugs under visible light irradiation. The results from UV-Vis spectroscopy evidently showed that the catalytic efficiency of SrVO/CN nanocomposite is higher than pure Sr3(VO4)2 nano-flowers. The SrVO/CN nanocomposite explores degradation efficiency of about 88.20% and 92.50% for MB and CF drug respectively. Furthermore, the stability and recycle behaviour of the SrVO/CN nanocomposites exhibit excellent effects. Hence, as prepared SrVO/CN behave as an example of the ‘Killing of two birds with one arrow’ approach.
We developed a flexible electrode based on a bismuth molybdate/graphene (BiM/GR) nanocomposite for electrochemical detection of mercury (Hg2+). The formation of the BiM/GR nanocomposite was systematically examined with suitable characterization studies. The BiM/GR-modified electrodes exhibit a high electrocatalytic performance toward Hg2+ detection comparable to other electrodes. The excellent electrocatalytic activity of the BiM/GR nanocomposite can be attributed to its good conductivity, synergistic effect, and abundant active site. Notably, the BiM/GR sensor showed good sensing performance for Hg2+ in the wide detection range from 0.02 to 149 μM with a good sensitivity of 9.5 μA μM−1 cm2 and an ultralow detection limit of 5.0 nM, which is well below the threshold value set by the World Health Organization (30 nM) and the United States Environmental Protection Agency. More importantly, the BiM/GR nanocomposite-modified electrode was used successfully to detect Hg2+ in river water, corn, and fish samples with satisfactory recovery values
Herein, an electrochemical sensor based on samarium oxide anchored, reduced graphene oxide (Sm2O3/RGO) nanocomposite was developed for the rapid detection of carbendazim (CBZ). Different characterization methods were infused to deeply examine the morphology, composition, and elemental state of Sm2O3/RGO nanocomposite. The Sm2O3/RGO modified electrode exhibits an excellent electro-catalytic performance toward CBZ detection with a peak potential of +1.04 V in phosphate buffer solution, which is superior to the RGO–, Sm2O3– and bare– electrodes. This remarkable activity can be credited to the synergetic effect generated by the robust interaction between Sm2O3 and RGO, resulting in a well-enhanced electrochemical sensing ability. Impressively, the fabricated sensor shows improved electrochemical performance in terms of the wide working range, detection limit, and strong sensitivity. On a peculiar note, the electrochemical sensing performances of CBZ detection based on Sm2O3/RGO nanocomposite demonstrate an extraordinary behavior compared to the prior documented electro-catalyst. In addition, the fabricated Sm2O3/RGO sensor also displays good operational stability, reproducibility, and repeatability toward the detection of CBZ. Furthermore, it was successfully applied to the CBZ detection in food and environmental water samples with satisfactory recovery. In accordance with our research findings, the Sm2O3/RGO nanocomposite could be used as an electro-active material for effectual electrochemical sensing of food and environmental pollutants.
The modern development in the agricultural production has huge influential factors being highly beneficial and also includes some health hazards. Under the class of chlorophenols, 2,4,6-trichlorophenol is a widely used chemical which remains as a major pollutant in the environment. The detection of 2,4,6-trichlorophenol was initiated as a controlling measure to decrease the seriousness prevailing in the ecosystem. The electrochemical and UV–vis absorption sensing platform are simple and low-cost detection techniques with precise and sensitive analysis. Cadmium tin oxide integrated with the reduced graphene oxide was employed as a nanohybrid for the construction of the working electrode. The structural and morphological analysis confirmed the high degree of crystallinity of the nanocomposite with nanorod formation. The high surface area, with high charge carrier mobility, and increased electrical conductivity of the material boosted the 2,4,6-trichlorophenol detection. The active surface area was calculated to be 0.068 cm⁻¹, 0.089 cm⁻¹, 0.118 cm⁻¹ and 0.146cm⁻¹ for all the modified electrodes. The resistance of the electrodes was about 91.4 Ω, 72.9 Ω, 48.8 Ω and 41.6 Ω. The linear range of 2,4,6-trichlorophenol was 0.019 μM–0.299 μM and 1.299 μM–1678.97 μM in electrochemical sensing and 10.99 μM–24.84 μM in UV detection. The obtained limit of detection with the formulation 3σ/SD was about 3.05 nM and 80 nM with sensitivity about 14.01 μA μM⁻¹ cm⁻². The real sample detection in environmental real samples showed good recovery results. The specific selectivity, good repeatability, reproducibility and stability analysis proves the good sensing parameters. Thus, the fabricated electrode is highly sufficient of sensing 2,4,6-trichlorophenol. These excellent features of the material can be applied for several other applications which will provide good performances.
In recent decades, various rare-earth molybdate ceramic nanomaterials have been synthesized and applied in different fields. The rare-earth molybdate ceramic nanomaterials can be applied in pure or doped form depending on the field of application. The rare-earth elements give unique characteristics to these ceramic nanomaterials that distinguish rare-earth molybdate ceramic nanomaterials from other molybdate-based nanomaterials. Also, the nanometer size in these ceramic nanomaterials donates attractive properties such as high specific area and improved optical properties. The characteristics of rare-earth molybdate ceramic nanomaterials depend intensively on the shape and size, which is determined by the applied synthesis route. So far, various methods have been used to prepare these nanomaterials such as coprecipitation, hydrothermal, and sonochemical route. The rare-earth molybdate ceramic nanomaterials have been widely used in electrocatalysis, photocatalysis, light-emitting diode, and biosensors.
The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.
TiO2/RGO nanocomposites were synthesised via a simple one-pot hydrothermal method. The influence of different reducing agents on the composite preparation was systematically studied. Electrochemical sensors were developed using the synthesised TiO2/RGO nanocomposites as modifiers in a carbon paste electrode. The nanocomposite formed using sodium borohydride as the reducing agent exhibited superior electrochemical properties compared to other modified electrodes. The electrochemical sensing properties of the modified electrodes were studied using different electrochemical techniques, namely, cyclic voltammetry, differential pulse voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The electrochemical surface areas of all the modified electrodes were significantly improved, and their charge transfer resistance was substantially reduced by modification. Cyclic voltammetry studies revealed the quasi-reversible nature of dopamine and irreversible nature of serotonin (SER) and tryptophan (TRP) at neutral pH. Differential pulse voltammetric studies using the modified electrodes were utilised for ultra-trace level sensing of neurotransmitters. Detection limits as low as 0.18 nM, 0.32 nM and 0.4 nM for serotonin (SER), dopamine (DP) and tryptophan (TRP) were achieved. The modified electrodes exhibited a wide linear dynamic range, which allowed the simultaneous determination of the biomolecules SER, DP and TRP. Real sample analysis, stability measurements and reproducibility tests further demonstrated the practical applicability of the developed electrochemical sensor. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Highly toxic aromatic nitro compounds discharged from industries riskily pollute the environment. Graphene oxide/metal oxide modified electrodes have been used as electrochemical sensors for the detection of nitrobenzene (NBZ) in water samples from industrial effluents. This article reports the hydrothermal synthesis and characterization of magnesium oxide encapsulated on graphene oxide (GO/MgO) nanocomposite (NC) by X-ray diffraction, Raman spectroscopy, scanning electron microscope, and transmission electron microscopy analyses, fabrication of GO/MgO-NC glassy carbon electrode (GCE), and its application as electrochemical sensor for trace level NBZ detection in aqueous samples for environmental monitoring are explored. The electrochemical characteristics of GO/MgO-NC modified GCE are probed towards NBZ sensing using cyclic voltammetry and differential pulse voltammetry techniques at varying loads of GO/MgO-NC on GCE, concentrations and pH of NBZ solution, and scan rates. The GO/MgO-NC/GCE electrode displays significant electrocatalytic activities by promoting rapid electron transport and exhibits high sensitivity (11.6 µA μM⁻¹ cm²) in a wide range of NBZ concentrations (0.1-38.9 and 58.5-2333.5 µM) at neutral pH and low limit of detection (0.01 µM). The practicability of the proposed sensor is demonstrated in the determination of NBZ in water samples with satisfied recovery range. Hence, it is found to be a promising candidate for NBZ sensor.
With the development of protein imprinting technique, the certification about the existence of imprinted sites, the arrival of template molecules and target molecules into the same cavity, and the specific separation process based on imprinted sites have seldom been studied so far. To promote the development in the field of protein imprinting, a method for proving the existence of the imprinting sites based on the fluorescence signal changes of the fluorescent materials labeling at the imprinted sites is first proposed in this work. Simultaneously, a novel protein imprinted material with ability of binding signal transduction is developed. The core of the imprinted materials is that bovine serum albumin (BSA) modified by a designed and synthesized functional monomer containing a polymerizable double bond and a cleavable dynamic disulfide bond is selected as a template. And the imprinted polymers supported on the surface of the tubular carbon nanofibers are constructed by thermally initiated polymerization. Fluorescein 4-(N, N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) is used to label the sulfhydryl groups generated by the cleavage of disulfide bonds at the imprinting sites. The identification of the imprinting sites is achieved by the change in the fluorescent signal generated when BSA is recombined to the imprinting sites. The results of fluorescence detection and adsorption experiments show that the imprinting sites exhibit specific binding and excellent reusability for BSA. In addition, another fluorescein N-(9-acridinyl) maleimide is utilized to label the imprinting sites, which produced a similar fluorescence signal response. Therefore, the experimental results are verified.
Developing cost-effective approaches for the fabrication of electrochemical devices is instantly needed for transferring from basic research to point-care technology. Herein, we report an electrochemical sensing platform based on iron...
Transition metal chalcogenides (TMCs) have great potential in diverse electrochemical technologies owing to their unique characteristics. In the present work, we portray the design and synthesis of Vanadium selenide (V2Se9)/reduced graphene oxide (rGO) forming a two-dimensional (2D) hybrid nanocomposite via a simple hydrothermal method. The successfully synthesized nanocomposite underwent in-depth surface and morphological characterizations by XRD, Raman spectroscopy, XPS, TEM, STEM and its potential as an electro catalyst was investigated by using glassy carbon electrode (GCE) for the detection of 2,4,6-trichlorophenol (TCP). The structural features favored a high charge transfer ratio, high surface area as well as excellent conductivity and catalytic activity. The V2Se9/rGO/GCE modified electrode showed a low charge transfer resistance (Rct) of 54.057 Ω cm², a decent detection limit (LOD) of 35.07 nM and a very high sensitivity of 22 μA μM⁻¹ cm⁻² in a working range of 0.001 μM to 1150 μM. This is due to the active proton interaction, surface enhancement, and positive synergistic effect between rGO and V2Se9. The proposed sensor has good detection potential in agricultural soil, river water, fish, and beverage samples like wine and apple juice. The obtained results from our investigation would elucidate the application of the catalyst in electrochemical sensors.
Silver vanadate nanorods (β-AgVO3) with silver nanoparticles (Ag-NPs) decorated on the surface of the rods were synthesized by using simple hydrothermal technique and later anchored onto nitrogen-doped reduced graphene oxide (N-rGO) to make a novel nanocomposite. Experimental analyses were carried out to identify the electronic configuration by X-ray diffraction analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis, which revealed monoclinic patterns of the C12/m1 space group with Wulff construction forming beta silver vanadate (β-AgVO3) crystals with optical density and phase transformations. Ag nucleation showed consistent results with metallic formation and electronic changes occurring in [AgO5] and [AgO3] clusters. Transmission electron microscopy and field-emission scanning electron microscopy with elemental mapping and EDX analysis of the morphology reveals the nanorod structure for β-AgVO3 with AgNPs on the surface and sheets for N-rGO. Additionally, a novel electrochemical sensor is constructed by using Ag/AgVO3/N-rGO on screen-printed carbon paste electrodes for the detection of antiviral drug levofloxacin (LEV) which is used as a primary antibiotic in controlling COVID-19. Using differential pulse voltammetry, LEV is determined with a low detection limit of 0.00792 nm for a linear range of 0.09-671 μM with an ultrahigh sensitivity of 152.19 μA μM-1 cm-2. Furthermore, modified electrode performance is tested by real-time monitoring using biological and river samples.
In this paper, we demonstrate a combined theoretical and experimental study on the electronic structure, and the optical and electrochemical properties of β-Ag2MoO4 and Ag2O. These crystals were synthesized using the hydrothermal method and were characterized using X-ray diffraction (XRD), Rietveld refinement, and TEM techniques. XRD and Rietveld results confirmed that β-Ag2MoO4 has a spinel-type cubic structure. The optical properties were investigated by UV-Vis spectroscopy. DFT+U formalism, via on-site Coulomb corrections for the d orbital electrons of Ag and Mo atoms (Ud) and the 2p orbital electrons of O atoms (Up) provided an improved band gap for β-Ag2MoO4. Examination of the density of states revealed the energy states in the valence and conduction bands of the β-Ag2MoO4 and Ag2O. The theoretical band structure indicated an indirect band gap of approximately 3.41 eV. Furthermore, CO2 electroreduction, and hydrogen and oxygen evolution reactions on the surface of β-Ag2MoO4 and Ag2O were studied and a comparative investigation on molybdate-derived silver and oxide-derived silver was performed. The electrochemical results demonstrate that β-Ag2MoO4 and Ag2O can be good electrocatalysts for water splitting and CO2 reduction. The CO2 electroreduction results also indicate that CO2 reduction intermediates adsorbed strongly on the surface of Ag2O, which increased the overpotential for the hydrogen evolution reaction on the surface of Ag2O by as much as 0.68 V against the value of 0.6 V for Ag2MoO4, at a current density of -1.0 mA cm-2.
Scheme representing the electro-reduction of AZT at Mn 2 O 3 –rGO/SPCE.
Potentially hazardous chemical contaminants endanger the environment and human well-being, challenging the scientists and policy-makers to develop holistic alternative approaches for remediation. The addition or accumulation of these chemicals can have a series of far-reaching consequences and have direct and indirect effects at multiple levels of ecological organization. Therefore, the development of a sensitive tool for the comprehensive evaluation of chemical concentrations is highly relevant. Herein, we thus report the simultaneous electrochemical detection of highly toxic hydroquinone (HQ), Hg2+, and nitrite (NO2-) compounds using nanostructured metal molybdate (M=Mg, Fe and Mn) catalysts. These functional nanomaterials are synthesized using a deep eutectic solvent (DES) modified hydrothermal method that provides sustainable aspects and energy efficient synthesis strategies. Choline Chloride (ChCl)-urea DES used in this study exhibits an all-in-one behaviour by simultaneously acting as a template, reducing agent, and homogeneous means for stabilizing metal ions. This stimulates the fabrication of hierarchical structures of metal molybdates with high surface activities that cause their remarkable properties with minimal waste generation. The structural, morphological, catalytic, and electrochemical capacities of the as-synthesized MgMoO4, Fe2(MoO4)3, and MnMoO4 materials are explored through various techniques and comparatively, MnMoO4 presents superior characterization features such as reduced particle size, increased surface area and hierarchical architectures. Owing to their exceptional physicochemical attributes, MnMoO4 modified glassy carbon electrode (GCE) demonstrates superior electrochemical activities towards the individual and simultaneous detection of HQ, Hg2+, and NO2 -. Well-defined and separate peaks are observed for the simultaneous detection of HQ, Hg2+, and NO2- which is influenced by the binding
energies of these pollutants. Furthermore, the modified electrode exhibits a high sensitivity of 23.8, 17.7 and 10.2 μA μM−1 cm−2 with limit of detections (LOD) as 0.026, 0.05, and 0.01 μM for HQ, Hg2+, and NO2- respectively under ideal conditions. Also, the reproducibility and anti-interference ability reinforce the application potential of MnMoO4 modified electrode for the simultaneous electrochemical detection of HQ, Hg2+, and NO2
- in real samples with better recoveries thus assessing the effect of these hazardous chemicals on humanity.
The present work concentrates over the electrochemical sensing of hydroquinone (HQ) with modified Zirconium Molybdate Decorated Reduced Graphene Oxide (Zr(MoO4)2 @rGO/GCE). Zr(MoO4)2@rGO was synthesized by a facile hydrothermal method. Followed with the characterization of the as prepared material was examined with XRD, FTIR and FESEM along with their application was employed with cyclic voltammetry technique. Results obtained from XRD and FTIR clearly demonstrated that Zr(MoO4)2@rGO have been formed with good crystallinity and morphology. Differential pulsed voltammetry studies further declared the limit of detection and Linear range as 0.015 μM and 0.01-250 μM with the sensitivity about 0.02042 μA μM⁻¹ cm⁻². River water, waste water and tap water were implied for the real time applicability of the fabricated sensor. Interference studies as performed revealed that no other similar compounds have been interfered with HQ and along with this the repeatability, reproducibility and stability performances explains the excellent behavior of the as prepared sensors efficiency in repeated cycles and in numerous electrodes. Thus, the fabricated sensor could be a simple, effective and selective sensor for detection of HQ.
A silver zeolite (AgY) nanocomposite was prepared and applied for construction of a modified carbon paste electrode (AgY/CPE) for sensing tryptophan (Trp) in real samples by using differential pulse voltammetry (DPV). AgY nanocomposite was prepared with a simple method from nano-structured sodium zeolite (NaY) and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray analysis (EDX). Particle size of the prepared AgY was in the range between 17.8 and 44.7 nm. Fourier transform infrared (FTIR) and fluorescence spectra AgY and AgY/Trp nanocomposites reveals interaction between AgY and Trp. Cyclic voltammetry (CV) was used for evaluating the electrode behaviour. Effect of potential scan rate on the electrode response was also studied. The proposed electrode revealed a suitable current response at scan rate of 0.1 V.s−1. A descriptive mechanism was proposed for explaining the electrode response toward Trp based on the CV experiments. Effect of pH on the response of the electrode was also studied. The modified carbon paste electrode revealed a good response to Trp at pH of 6.9 in a phosphate buffer solution (PBS), in the range of Trp concentration between 10 nM and 1.2 µM. The detection limit of the electrode was 6.3 nM and it was successfully applied for the determination of Trp in milk and samples. The accuracy and precision of the results were evaluated with statistical methods.
Facile fabrication of advanced electrode material is highly desired for novel electrochemical sensor development. Herein, cerium oxide (CeO2) nanoparticles were successfully loaded on reduced graphene oxide (RGO) by one-step hydrothermal synthesis approach, and the as-prepared nanocomposite (CeO2/RGO) was used as novel electrode material for electrochemical detection of tryptophan. The structure and composition of CeO2/RGO nanocomposite were fully characterized by transmission electron microscope (TEM), X-ray powder diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The electrochemical properties were characterized by several techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). It was found that the CeO2/RGO nanocomposite electrode exhibits an enhanced peak current response compared with individual CeO2 or RGO material. The electrochemical sensor based CeO2/RGO material showed a selective and sensitive response toward tryptophan determination, and a linear range of 0.2–25 μM with a detection limit of 80 nM (S/N = 3) was achieved. The present electrochemical sensor displayed an excellent stability and reproducibility, and was successfully applied in the determination of tryptophan in real food and biological samples.
Two-dimensional (2D) MXene-based electrode materials have recently gained attention in the field of electrochemical sensors. Herein, we report the first titanium carbide (TiC)-based electrochemical sensor for the detection of 4-nitroquinoline N-oxide (4-NO). X-ray diffraction, field emission scanning electron microscopy, elemental mapping, and energy-dispersive X-ray spectroscopy were used to examine the structural and compositional properties of TiC. With the 2D MXene structure, the TiC-modified electrode provides excellent conductivity, an electron transfer boost, large surface area, and nanoscale effects, which improve the electrochemical activity for 4-NO detection. The fabricated electrochemical sensor shows a strong voltammetry performance at −0.32 V with a wide linear range (0.01–114 and 133–650 μM) and a low limit of detection (2 nM) for 4-NO detection. The real-time analysis of 4-NO content in biological samples was successfully conducted and afforded good recoveries. Our method of design produces an efficient electrode material for 4-NO detection with outstanding electrochemical performance.
Recently, two-dimensional nanomaterials have received great attention in the field of electrochemical applications due to their outstanding physicochemical properties. In this research, we developed vanadium carbide entrapped on graphitic carbon nitride nanosheets (VC/g-CN NSs) as a highly efficient electrocatalyst for determination of furazolidone (FZD) in biological samples. The VC/g-CN NSs nanocomposite was systematically characterized by various analytical and spectroscopic techniques. The performance of the VC/g-CN NSs modified glassy carbon electrode (GCE) for the FZD detection was studied by the cyclic voltammetry and amperometric methods. On the one hand, the fabricated electrode offers numerous active sites with the large electron transfer rate and the rapid mass transport ability to enhance the electrochemical activity towards the FZD detection. Under the optimization conditions, the modified electrode showed a wide detection range (0.004 to 141 µM), very low detection limit (0.5 nM), excellent selectivity and reproducibility. Compared to the previous studies in the literatures, the fabricated VC/g-CN NSs/GCE achieves the lowest LOD and the widest linear range until now towards the FZD detection. Furthermore, the fabricated sensor was successfully applied to determine FZD in the biological samples with satisfactory results.
A novel composite material, hybrid zeolitic imidazolate framework (HZIF)–conducting poly(3,4-ethylenedioxythiophene) (PEDOT) has been fabricated on carbon cloth electrode (CCE) by microwave-assisted crystallization, followed by drop-coating and vapor deposition procedures. Specifically, the HZIF inserted by molybdenum (HZIF-Mo) is entitled to intrinsic catalytic activity towards amine molecules, which is firstly integrated with the conductive and catalytic PEDOT as an enhanced electrochemical sensor for hydroxylamine. Detection is performed by amperometric method, and the composite sensor (HZIF-Mo/PEDOT/CCE) shows a low detection limit of 0.04 μM (S/N = 3) in the linear range of 0.1–692.2 μM, along with superior anti-interference ability, reproducibility (RSD = 4.43%) and outstanding performance in real samples. As noticed, the hydroxylamine catalytic process combines the advantages of the alkaline-stable HZIF-Mo containing ample catalytic sites and high surface area and the mesoporous PEDOT reining in outstanding conductivity and redox capability, thereby imparting amplified electrochemical signals. This work undertakes an opening to expand MOF-based composites for versatile sensing applications.
We report a novel electrochemical sensor for the determination of dihydroxybenzene isomers using a chitosan (CS) stabilized multiwalled carbon nanotubes (f-MWCNT) modified electrode. The CS/f-MWCNT composite was characterized by various physiochemical techniques. The CS/f-MWCNT modified electrode shows an excellent electrocatalytic activity towards the simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RC) due to the active amino and hydroxyl functional groups of CS and f-MWCNT. Besides, the CS/f-MWCNT modified electrode exhibits a wide linear response range for HQ, CC and RC concentrations from 0.09–171.4 µM, 0.09–155.43 µM and 0.3–174.82 µM, respectively. As well as, the CS/f-MWCNT modified electrode also achieved a lower detection limit (LOD) of 0.027 µM, 0.029 µM and 0.11 µM for HQ, CC and RC, respectively. Moreover, the practical applicability of CS/f-MWCNT modified electrode could be applied for the determination of HQ, CC and RC in different water samples, exhibits satisfactory recovery and RSD values.
In this present work, “killing two birds with one arrow” strategy was performed for the electrochemical trace level detection and photocatalytic degradation of antibiotic drug chloramphenicol (CAP) using Ce(MoO4)2 nanocubes/graphene oxide (CeM/GO) composite for the first time. The CeM/GO composite was synthesized via simple hydrothermal treatment followed by sonication process. The successful formation of CeM/GO composite was confirmed by several analytical and spectroscopic techniques. The CeM/GO composite modified GCE showed excellent electrocatalytic activity towards the reduction of CAP in terms of decrease the potential and increase the cathodic peak current in comparison with different modified and unmodified electrodes. The electrocatalytic reduction of CAP based on the CeM/GO modified GCE exhibited high selectivity, wide linear ranges, lower detection limit and good sensitivity of 0.012-20 & 26-272 µM, 2 nM and 1.8085 µAµM-1 cm-2, respectively. Besides, CeM/GO/GCE was used to analyze the CAP in real samples such as honey and milk, the satisfactory recovery results were obtained. On the other hand, the CeM/GO composite played excellent catalyst towards the photodegradation of CAP. The obtained results from the UV-Vis spectroscopy clearly suggested that CeM/GO composite had high photocatalytic activity compared than pristine Ce(MoO4)2 nanocubes. The degradation efficiency of CeM/GO toward CAP is observed about 99% within 50 min under visible irradiation and it shows a good stability by observing the reusability of the catalyst. The enhanced photocatalytic performance was attributed to the increased migration efficiency of photo-induced electrons and holes.
For the first time, a familiar metal-organic framework MIL-101(Fe) and silver nanoparticles composite (AgNPs/MIL-101) acted as a novel electrode modified material for the detection of tryptophan (Trp). The AgNPs/MIL-101 modified glassy carbon electrode (AgNPs/MIL-101/GCE) produces an increase in the oxidation current of Trp compared with the bare electrode. Additionally, the electrochemical behaviours of Trp on AgNPs/MIL-101/GCE were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimum experimental conditions, the oxidation peak currents are proportional to the concentrations of tryptophan over the ranges of 1μM to 50μM and 50μM to 150μM, respectively. The detection limit is 0.14μM (S/N=3). Moreover, the presented method was successfully applied to the determination of Trp in urine samples with good recovery.
In this work, a novel selective, sensitive and reversible copper (II) ion optical sensor was prepared based on the impregnation of N, N′-bis (2-hydroxynaphthaldehyde)-1, 3-phenylenediimine (HNPD) into plasticized poly vinyl chloride (PVC) film. The optimal values of pH and response time at which the maximum performance of prepared optical sensor is achieved were found to be 6 and 2 min, respectively. After the optimization of pH and response time, small central composite design (CCD) and desirability function (DF) were applied to evaluate the effects of variables including amount of dibuthylphthalate (DBP), anion excluder (sodium tetraphenylborate, NaTPB), PVC and HNPD content on the sensor as figures of merit. The possible interactions between the variables were also investigated using the CCD. Low detection limit and good selectivity in presence of other ions such as Fe3+, Ag2+, Cr3+, Zn2+, Hg2+, SO42- and etc. make it feasible to accurately and repeatedly monitor Cu2+ ions content in real samples with complicated matrices. The optode was successfully regenerated by its exposure in 0.1 mol L-1 of EDTA solution while its response was reversible with the relative standard deviation (RSD) lower than 1.5 %. This optode was stable and stored for at least 17 days without observing any change in its sensitivity.
A new selective and sensitive Lanthanum (La) ions optical sensor based on immobilization of -(2-aminoethyl)-salicylaldimine (AESI) on a triacetylcellulose membrane was prepared. The prepared optode exhibited a linear range of 30–150 part per billion (ppb) of the La (III) ion concentration with a detection limit of 14.38 ppb. The response time of the newly designed optode was derived within 30–60 s, depending on the La (III) ion concentration, however is independent to the pH of the solution in the range of 3–5. The proposed optode indicated a low detection limit, fast response time, and also remarkable selectivity regarding to the number of transition metals ions (i.e. Ce3+, Cu2+, Cd2+, Cr3+, Zn2+, Hg2+, and Fe2+). The optode was successfully regenerated with a thiourea solution, and its response which might be reversible and reproducible showed the relative standard deviation of less than 1.48%. This optode was applied for determining the La (III) ions in water samples.
A novel adsorbent was fabricated by covalently anchoring N-(3-nitro-benzylidene)-N′-trimethoxysilylpropyl-ethane-1,2-diamine onto multiwalled carbon nanotubes (NBATSPED-MWCNTs). This novel material was characterized by different techniques such as XRD, SEM, FT-IR and TGA-DTA. Subsequently, it was used for the ultrasound-assisted removal of aluminum(III) ions via its complexation with eriochrome cyanine R (ECR) indicator. The influences of variables such as initial ECR concentration (X1), initial Al3+ ion concentration (X2), adsorbent dosage (X3) and contact time (X4) on the efficiency of the removal process were investigated by small central composite design (CCD) under response surface methodology and genetic algorithm (GA). The process was empirically modeled to reveal the significant variables and their possible interactions. The optimization conditions were set as: 3 min, 20.238 mg, 20 mg L−1 and 15 mg L−1 for sonication time, adsorbent mass, initial Al3+ ions concentration and initial ECR concentration, respectively. Finally, it was found that the equilibrium and kinetics of the adsorption process follow the Langmuir isotherm and pseudo-second-order kinetic model, respectively. From the Langmuir isotherm, the maximum monolayer capacity (qmax) was found to be 46.74 mg g−1 at optimum conditions.
In this study, activated carbon engrafted with Ag nanoparticles (Ag-NPs–AC) was prepared and applied for ultrasonic assisted simultaneous removal of aluminum (Al3+) ions and Alizarin red S (ARS) dye from an aqueous medium. The physicochemical properties of Ag-NPs–AC were determined by different techniques such as SEM and FTIR. The effects of various operating parameters on the extent of adsorption were investigated. Optimum conditions were determined in order to achieve maximum removal percentage from the binary mixture. It was observed that the maximum performance for both the species was achieved at a pH of 6. The influence of different variables, such as the concentration of initial Al3+ (mg L−1) ions, ARS (mg L−1), adsorbent mass (mg) and sonication time (s), were studied using central composite design (CCD) combined with a desirability function approach (DFA) and genetic algorithm (GA). The isotherm models for the adsorption process were evaluated and the equilibrium data were accurately described by the Langmuir model with the maximum monolayer adsorption capacity for Al3+ ions and ARS as 222.2 and 232.6 mg g−1, respectively.
Metal molybdates nanostructures hold great promise as high-performance electrode materials for next-generation lithium-ion batteries. In this work, the facial design and synthesis of monodisperse FeMoO4 nanocubes with the edge lengths of about 100 nm have been successfully prepared and present as a novel anode material for highly efficient and reversible lithium storage. Well-defined single-crystalline FeMoO4 with high uniformity are first obtained as nanosheets and then self-aggregated into nanocubes. The morphology of the product is largely controlled by the experimental parameters, such as the reaction temperature and time, the ratio of reactant, the solution viscosity, etc. The molybdate nanostructure would effectively promote the insertion of lithium ions and withstand volume variation upon prolonged charge/discharge cycling. As a result, the FeMoO4 nanocubes exhibit high reversible capacities of 926 mAh g(-1) after 80 cycles at a current density of 100 mA g(-1) and remarkable rate performance, which indicate that the FeMoO4 nanocubes are promising materials for high-power lithium-ion battery applications.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The global usage of antibiotics drug chloramphenicol (CPL) in pharmaceuticals and food-producing animals may cause severe threats to both human health and animals. Therefore, the development of highly selective detection of chloramphenicol has turned the hottest issue to protect human health and another living organism. In this work, we have developed well dispersive palladium nanoparticles decorated with graphene oxide (Pd NPs/GO) nanocomposite, by facile ice bath method. Moreover, the successful formation of Pd NPs/GO nanocomposite was deep-rooted by various analytical and spectroscopic methods. The electrochemical comportment of the electrochemical sensor was investigated by cyclic voltammetry and amperometric method. The Pd NPs/GO nanocomposite shows an excellent electrocatalytic behavior in terms of higher cathodic peak current and lower peak potential than that of other modified and unmodified glassy carbon electrode (GCE). Furthermore, the Pd NPs/GO modified GCE displayed an excellent linear response range (0.007 to 102.68 μM), good sensitivity (3.0479 µA µM-1 cm2) and lower detection limit (0.001 µM), correspondingly. The Pd NPs/GO/GCE spectacles its excellent selectivity for the CPL sensing in the presence of other potentially interfering compounds. Additionally, the nanocomposite is efficaciously applied to the biological and food samples for the determination of CPL and the obtained good recoveries.
The removal of hazardous dyes is essential to supply safe drinking water. In this study, a new ferromagnetic composite based on Mn0.4Zn0.6Fe2O4 nanoparticles (NPs) supported on dead Yarrowia lipolytica ISF7 (D-YL-ISF7) was prepared. Dead Yarrowia lipolytica ISF7 was used to suppress the aggregation of the nanoparticles and to expose more number of active sites present in the nanoparticles. The Dead Yarrowia lipolytica ISF7-supported Mn0.4Zn0.6Fe2O4-NPs nanoparticles were characterized by FT-IR, XRD, FESEM, HRTEM, EDX, BET and VSM analysis and used as robust adsorbent/biosorbent for the simultaneous removal of tartrazine (TA) and ponceau 4R (P4R) azo food dyes in binary mixture. First order derivative spectrophotometric method was used for the simultaneous analysis of dyes in binary mixture. Central composite design (CCD) was employed to evaluate the influence of pH, sonication time, Mn0.4 Zn0.6Fe2O4-NPs-D-YL-ISF7 mass and initial TA and P4R concentration on the removal efficiency of understudy dyes. At optimum conditions (pH; 2.0, sonication time; 5 min, Mn0.4Zn0.6Fe2O4-NPs-D-YL-ISF7 mass; 0.015 g, TA concentration; 12 mg L-1 and P4R concentration; 16 mg L-1), high removal efficiencies (>99.0%) were obtained for TA and P4R dyes, reasonably well predicted by the model. The CCD allowed the optimization and the scale-up of the process, which presented a good correlation between large and small scales. Adsorption isotherm data fitted well to Langmuir model. Under ultrasound, the Langmuir adsorption capacity of Mn0.4Zn0.6Fe2O4-NPs-D-YL-ISF7 was obtained to be 90.827 mg g-1 for TA and 101.461 mg g-1 for P4R. Pseudo-second-order was chosen as a model reactant for a kinetic study.
In this paper, we report a highly selective and sensitive electrochemical determination of dopamine (DA) based on iron oxide nanoparticles (Fe2O3 NPs) capped graphene sheets (GRS) modified glassy carbon electrode (GCE). The Fe2O3 NPs was synthesized by pyrophoric technique and its nanocomposite with GRS was prepared by the simple sonochemical method. The as-prepared Fe2O3 NPs/GRS nanocomposite was characterized by using scanning electron microscopy, electron dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy. As expected, the proposed sensor exhibits a wide linear range from 0.01-195.18, low detection limit (LOD) of 0.004 µM for DPV technique and a broad linear range from 0.006 to 635 µM, the very low detection limit of 0.001 µM for amperometric technique, respectively. Moreover, it shows excellent selectivity of DA even in the presence of 20-fold higher concentration of potential interferences. The practical applicability of the reported sensor was recorded in human serum and urine sample. Finally, all electrochemical studies confirmed the excellent electrocatalytic activity of Fe2O3 NPs/GRS nanocomposite as a DA sensor.
Currently, metal molybdates compounds can be prepared by several methods and are considered as prospective electrode materials in many fields because the metal ions possess the ability to exist in several oxidation states. These multiple oxidation states contribute to prolonging the discharge time, improving the energy density, and increasing the cycling stability. The high electrochemical performance of metal molybdates as electrochemical energy storage devices are discussed in this review. According to recent publications and research progress on relevant materials, the investigation of metal molybdate compounds are discussed via three main aspects: synthetic methods, material properties and measured electrochemical performance of these compounds as electrode materials. The recent progress in general metal molybdate nanomaterials for LIBs and supercapacitors are carefully presented here.
Considering the crucial roles of superoxide anion (O2⁻) in pathological conditions, it is of great urgency to establish a reliable approach for real-time determination of O2⁻. Herein, a sensitive non-enzymatic sensor was constructed based on silver nanoparticles (AgNPs) and sodium dodecyl sulfate functionalized carbon nanotubes (SDS-MWCNTs) composites to measure the release of O2⁻ from living cells. As an analytical and sensing platform, the AgNPs/SDS-MWCNTs modified glassy carbon electrode exhibited excellent electrochemical performance toward O2⁻ with a determination limit as low as 0.0897 nM and wide linear range of 6 orders of magnitude, which was superior to other O2⁻ electrochemical sensors. The excellent performance was attributed to the SDS-MWCNTs composites being used as effective load matrix for the deposition of AgNPs. Importantly, this novel non-enzymatic sensor could be applied to determination of O2⁻ released from living cells, and the amount of flux of O2⁻ increased accordingly with the improving of the concentration of AA, which has the possibility of application in clinical diagnostics to assess oxidative stress of living cells.
A novel poly(β-cyclodextrin) (β-CD)/carbon quantum dots (CQDs) composite based sensor was successfully fabricated on glassy carbon electrode through electrochemical polymerization. As-prepared β-CD/CQDs modified electrode was used for the simultaneous determination of dopamine (DA), uric acid (UA) and tryptophan (Trp). Electrochemical responses of as-prepared electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. In co-existence system containing DA, UA and Trp, three oxidation peaks well separated from each other and the potential separations of oxidation peaks of DA-UA and UA-Trp were respectively large up to 150 and 420 mV, owing to the synergistic effect of β-CD and CQDs. The linear amperometric responses for DA, UA and Trp were obtained in the concentration range of 4 ∼ 220, 0.3 ∼ 200 and 5 ∼ 270 μM, respectively, with the limits of detection of 0.14, 0.01, 0.16 μM (S/N = 3) and the limits of quantification of 0.45, 0.04, 0.50 μM (S/N = 10). Moreover, as-prepared β-CD/CQDs modified electrode exhibited prominent selectivity, stability and reproducibility, which had promising application for the simultaneous determination of DA, UA and Trp.
An electrochemical chiral sensing platform based on amino-functionalized graphene quantum dots/β-cyclodextrin modified glassy carbon electrode (NH2-GQDs/β-CD/GCE) was developed for enantioselective detection of tryptophan (Trp) isomers. NH2-GQDs/β-CD/GCE showed high electrocatalytic activity and good analytical behavior toward the oxidation of Trp isomers. The oxidation peak potentials and oxidation peak currents of Trp isomers at NH2-GQDs/β-CD/GCE surface were observed by differential pulse voltammetry. NH2-GQDs/β-CD nanocomposite exhibited different binding ability for two Trp isomers and selectively bonded with d-Trp, resulting in the higher oxidation peak current of d-Trp at NH2-GQDs/β-CD/GCE surface. Trp isomers exhibited different oxidation peak potentials at NH2-GQDs/β-CD/GCE surface, and the peak potential separation between l-Trp and d-Trp was around 0.022 V, which was used for the enantioselective detection of Trp isomers. Under the optimum experimental conditions, the oxidation peak currents were linearly dependent on the concentrations of Trp isomers. The linear ranges of l-Trp and d-Trp were all from 1.0 to 30.0 μM with correlation coefficients of 0.9886 and 0.9800, respectively. The detection limits of l-Trp and d-Trp were 0.65 and 0.12 μM (3σ/K), respectively. Such NH2-GQDs/β-CD/GCE displayed high anti-interference against some physiological substances, good reproducibility and excellent long-term stability toward Trp isomers detection in biomedical applications.
In this study, a novel organic–inorganic hybrid adsorbent for single-step detection and removal of Pb(II) ions based on dithizone (DZ) anchored on mesoporous SBA-15 was fabricated. The designed solid optical sensor revealed rapid colorimetric responses and high selectivity. Central composite design (CCD) combined with desirability function (DF) was applied to evaluate the interactive effects and optimization of important variables such as pH value, mesoporous SBA-15 dosage, contact time and initial concentration of Pb(II) ions and optimum conditions for each of the factors were obtained 6.0, 25 mg, 30 min and 20 μg ml− 1, respectively. This adsorbent or solid optical chemo sensor exhibited a linear range of 1.0 to 100.0 μg ml−1 of Pb(II) ion concentration with a detection limit of 0.07 μg ml−1. This adsorbent was applied to determine and remove the Pb(II) in spiked samples. Various isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich were studied for fitting the experimental equilibrium data. Langmuir model was chosen as an efficient model. Various kinetic models such as pseudo-first, second order intraparticle, diffusion models were studied for analysis of experimental adsorption data and the pseudo second order model was chosen as an efficient model.
A cubic Pd and reduced graphene oxide modified glassy carbon electrode (Pd/RGO/GCE) was fabricated to simultaneously detect dopamine (DA) and uric acid (UA) by cyclic voltammetry (CV) and different pulse voltammetry (DPV) methods. Compared with Pd/GCE and RGO/GCE, the Pd/RGO/GCE exhibited excellent electrochemical activity in electrocatalytic behaviors. Performing the Pd/RGO/GCE in CV measurement, the well-defined oxidation peak potentials separation between DA and UA reached to 145 mV. By using the differential pulse voltammetry (DPV) technique, the calibration curves for DA and UA were found linear with the concentration range of 0.45 μM – 421 μM and 6 μM – 469.5 μM and the detection limit (S/N=3) were calculated to be 0.18 μM and 1.6 μM, respectively. Furthermore, the Pd/RGO/GCE displayed high selectivity when it was applied into the determination of DA and UA even though in presence of high concentration of interferents. Additionally, the prepared electrochemical sensor of Pd/RGO/GCE demonstrated a practical feasibility in rat urine and serum samples determination.
A selective adsorbent based on the modification of mesoprous SBA-15 with N,N′-bis(salicylidene)-1,3-ethylenediamine Schiff base and decorated with Fe3O4 nanoparticles (SBA-15-BSEA-Fe3O4-NPs) for Ce(III) ions removal was reported. The SBA-15-BSEA-Fe3O4-NPs was identified by XRD, FE-SEM, TEM, SEM, FT−IR, VSM, BET and BJH analysis. Central composite design (CCD) was applied to evaluate the main and interactive effects of adsorption variables and optimize the operational parameters. The important variable such as initial pH solution, SBA-15-BSEA-Fe3O4-NPs mass, shaking time and initial concentration of Ce3+ ions were studied under batch mode. In desirability concession of 1.0 as optimum value for R% Ce(III), the level of factors was as follows: shaking time 80 min, SBA-15-BSEA-Fe3O4-NPs mass 0.05 g, pH 5 and initial concentration of Ce(III) ions 40 mg L−1. The SBA-15-BSEA-Fe3O4-NPs exhibited high adsorption efficiency and very good selectivity through cerium removal even in the presence of other ions (La3+, Nb3+, Er3+, Cu2+, Cd2+, Cr3+, and Fe2+ ions). The SBA-15-BSEA-Fe3O4-NPs was successfully regenerated and the response was reversible. The R.S.D. of the adsorption process was less than 1.02%.
In the present research, we aimed to fabricate a novel electrochemical sensor based on Cu metal nanoparticles on the multiwall carbon nanotubes-reduced graphene oxide nanosheets (Cu/MWCNT/RGO) for individual and simultaneous determination of nitrite and nitrate ions. The morphology of the prepared nanocomposite on the surface of glassy carbon electrode (GCE) was characterized using various methods including scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy. Under optimal experimental conditions, the modified GCE showed excellent catalytic activity toward the electro-reduction of nitrite and nitrate ions (pH = 3.0) with a significant increase in cathodic peak currents in comparison with the unmodified GCE. By square wave voltammetry (SWV) the fabricated sensor demonstrated wide dynamic concentration ranges from 0.1 to 75 μM with detection limits (3Sb/m) of 30 nM and 20 nM method for nitrite and nitrate ions, respectively. Furthermore, the applicability of the proposed modified electrode was demonstrated by measuring the concentration of nitrite and nitrate ions in the tap and mineral waters, sausages, salami, and cheese samples.
In the present work, a novel optical chemical sensor (optode) was prepared based on impregnation of N, N´-bis (salicylidene)-1, 3-ethylenediamine (BESA) Schiff base into mesoprous SBA-15 paste for determination of trace amounts of Praseodymium (Pr) ion by UV/Vis spectrophotometry. The sensor was fabricated by dip-coating triacetylcellulose membrane into indicator solution. The proposed optical sensor was prepared through a routine procedure and characterized by various techniques such as ATR-FT-IR and SEM analyses. This optode exhibited a linear range of 10 to 190 ng mL-1 for Pr(III) ion concentration with a detection limit of 5.0 ng mL-1. The value of the response time for the newly synthesized optode was within 100 s while depending on the Pr(III) ion concentration. The proposed optode showed low detection limit, fast response time and high selectivity with respect to the group of transition metal ions (Ce3+, Nb3+, La3+, Cr3+, Zn2+, Hg2+, and Fe2+ ions). The optode was successfully regenerated with a mixture of thiourea and NaOH solution and the response was reversible with the relative standard deviation (R.S.D.) of 1.6%. The optode was stable and stored for at least 17 days without any considerable change in its sensitivity. Finally, the developed optode was applied to determine the Pr(III) ions in spiked samples.
This paper describes the beta silver molybdate (β-Ag2MoO4) samples with spinel-type cubic structures synthesized with various morphologies, including round tips coral-like, elongated coral-like and truncated cube, by the microwave-assisted solvo-/hydrothermal method. The crystal morphologies could be controlled by adjusting the solvent, surfactant, and pH of the precursor solution. X-ray diffraction, field-emission scanning electron microscopy, Fourier-transform Raman spectroscopy, and diffuse reflectance spectroscopy in the ultraviolet-visible (UV–Vis) region, were used to characterize the structures of the samples. The specific surface area was determined using the Brunauer–Emmett–Teller method. Furthermore, the photocatalytic/antibacterial properties of the particles were dependent on the β-Ag2MoO4 crystal morphogy and were evaluated by Rhodamine B dye photodegradation under UV–Vis light, and by determining their minimum inhibitory and bactericidal concentrations, using a broth microdilution assay for Escherichia coli bacteria.
A glassy carbon electrode (GCE) modified with electropun tricobalt tetroxide nanoparticles decorated carbon nanofibers (Co3O4-CNF) were first applied for the determination of L-tryptophan (L-Trp). The synthesized Co3O4-CNF were characterized by scanning electron microscopy, Raman, X-ray diffraction and electrochemical impedance spectroscopy. The electrochemical detection of L-try was successfully conducted in 0.1 M phosphate solution (pH 2). The linear relationship of L-Trp was in the range of 0.005–40 μM and the detection limit reached 0.002 μM (S/N = 3) with little interference from other amino acids.
A polymerized film of copper-2-amino-5-mercapto-1,3,4-thiadiazole (Cu(II)-AMT) complex (poly(Cu-AMT)) was successfully achieved via a simple and low-cost electrochemical methodology. Subsequently, a noncovalent nanohybrid of poly(Cu-AMT) with reduced graphene oxide (rGO) (rGO-poly(Cu-AMT)) was prepared through π–π stacking interaction as an efficient mimetic enzyme for the ultrasensitive and selective detection of dopamine (DA). The rGO-poly(Cu-AMT) nanocomposites showed considerable mimetic enzyme catalytic activity, which may be attributed to the significant promotion of the electron transfer between the substrate and graphene-based carbon materials, and also the synergistic electrocatalytic effect in mimetic enzyme between rGO sheet and poly(Cu-AMT). The electrocatalytic and sensing performances of the biomimetic sensor based on the rGO-poly(Cu-AMT) nanocomposites were evaluated in detail. The biomimetic sensor enables a reliable and sensitive determination of DA with a linear range of 0.01–40 μM and a detection limit of 3.48 nM at a signal-to-noise ratio of 3. In addition, we applied the proposed method to detect DA in real sample with satisfactory results. Accordingly, the rGO-poly(Cu-AMT) is one of the promising mimetic enzyme for electrocatalysis and biosensing.
Abstract
In the present work, potato-like silver molybdate (Ag2MoO4) microstructures were synthesized through a simple hydrothermal method. The microstructures of Ag2MoO4 were characterized by various analytical and spectroscopic techniques such as XRD, FTIR, Raman, SEM, EDX and XPS. Interestingly, the as-prepared Ag2MoO4 showed excellent photocatalytic and electrocatalytic activity for the degradation of ciprofloxacin (CIP) and electrochemical detection of hydrogen peroxide (H2O2), respectively. The ultraviolet-visible (UV-Vis) spectroscopy results revealed that the potato-like Ag2MoO4 microstructures could offer a high photocatalytic activity towards the degradation CIP under UV-light illumination, leads to rapid degradation within 40 min with a degradation rate of above 98%. In addition, the cyclic voltammetry (CV) and amperometry studies were realized that the electrochemical performance of Ag2MoO4 modified electrode on H2O2 detection. Our H2O2 sensor shows a wide linear range and lower detection limit of 0.04-240 µM and 0.03 µM, respectively. The Ag2MoO4 modified electrode exhibits a high selectivity towards the detection of H2O2 in the presence of different biological interferences. These results suggested that the development of potato-like Ag2MoO4 microstructure could be an efficient photocatalyst as well as electrocatalyst in the potential application of environmental, biomedical and pharmaceutical samples.
BiPO4/Bi2S3-HKUST-1-MOF as a novel blue light active photocatalyst was synthesized and characterized by X-ray XRD, SEM, PL, BET, BJH and DRS. This novel photocatalyst was applied in a new catalytic rotating packed bed reactor for intensification of simultaneous photocatalytic degradation of toluidine blue (TB) and auramine-O (AO). In this reactor, high gravity media generated by a high rotational speed in a porous domain leads to intensification of the external mass transfer rate and significantly increases the mixing and turbulency. The central composite design (CCD) following analysis of variance (ANOVA) was applied to optimize the operational parameters including irradiation time, pH, photocatalyst dosage, rotational speed, solution flow rate, aeration flow rate, and TB and AO concentration. The optimum values were found to be 65 min, 6, 0.25 g L-1, 1300 rpm, 0.40 L min-1, 35 L min-1, 25 and 25 mg L-1 for irradiation time, pH, photocatalyst dosage, rotational speed, solution flow rate, aeration rate and initial concentration of TB and AO, respectively. At these optimum conditions, the photocatalytic degradation percentages of TB and AO were found to be 99.37% and 98.44% respectively with an overall desirability of 1.0. Replication of all experiments at optimum conditions with a conventional photocatalytic reactor shows the requirement of more photocatalyst as well as more irradiation time for operation in comparison to the rotating packed bed reactor. Results showed that the rotating packed bed is more economical, has a higher efficiency and can operate at a higher flow rate. Kinetic studies are an essential step in designing and optimizing photocatalytic reactors during scale-up processes, a pseudo first order kinetics based on the Langmuir-Hinshelwood (L-H) model was able to successfully fit the data concerning the present photodegradation approach.
A 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) and reduced graphene oxide (rGO) based polymer nanocomposite (PNC) has been electrodeposited directly on the surface of glassy carbon electrode (GCE) using cyclic voltammertry. The electrochemical reduction of graphene oxide (GO) to rGO and the synthesis of PNC have been inspected using FE-SEM, TEM and Raman spectroscopy. The modified GCE was further used for the voltammetric quantification of Tryptophan (Trp) in the presence and absence of 5-hydroxytryptamine. The PNC modified sensor exhibited improved sensing and electrocatalytic properties in comparison to unmodified GCE, rGO modified GCE and AHNSA modified GCE. The fabricated sensor showed a linear calibration plot in the range of 0.5-200 μM with sensitivity and limit of detection (L.O.D.) of 0.0451 μA μM-1 and 316 nM (n = 3) respectively in comparison to 0.19 μA μM-1 and 2.54 μM (n = 3) respectively for unmodified GCE. The proposed method was also successfully applied for the determination of Trp in commercially available pharmaceutical formulations, human urine and plasma samples.
A novel nanorose-like metal organic system (MOS) based on Cu(ii) and biphenyl-4,4-dicarboxylic acid (Cu-BPDCA) was hydrothermally synthesized and characterized via EDS, FE-SEM, XRD, DRS and FT-IR analysis. This novel nanomaterial was found to be of narrow energy band gap (1.24 eV) and thus it was applied as a photocatalyst driven by visible light for the degradation of the rose bengal (RB) and eosin Y (EY) dyes. For further improvement in the photocatalytic performance of Cu-BPDCA, it was doped with a trace amount of Ce(iii) in a simple way followed by characterization. The achieved improvement is due to the formation of a large number of O2(-)˙ and ˙OH radicals compared to the case of undoped Cu-BPDCA. The influence of important variables such as initial dye concentration, photocatalyst dosage and time of irradiation on the photocatalytic degradation efficiency was studied and optimized using central composite design. The optimum condition for the photodegradation of RB was found to be 40 min, 4.0 mg L(-1) and 0.015 g, corresponding to the irradiation time, RB concentration and photocatalyst mass, respectively. The photodegradation of EY was optimized at 4.0, 76 min, 5.9 mg L(-1) and 0.015 g corresponding to the pH, irradiation time, EY concentration and photocatalyst mass, respectively. At these optimum conditions, the photocatalytic degradation percentages of RB and EY with a desirability of 0.95 and 1.0 were found to be 78.90% and 67.63%, respectively. Kinetics study showed that the Langmuir-Hinshelwood kinetics model suitably fits the experimental data. From the Langmuir-Hinshelwood kinetics model, a significantly high photodegradation to surface adsorption ratio was obtained which is the great advantage of this work in addition to applying visible light.
The electropolymerization of cetyltrimethylammonium bromide (CTAB) on glassy carbon electrode (GCE) was carried out when GCE was cycled in 0.1 M sulfuric acid containing CTAB from − 0.8 V to 1.2 V for several cycles. Scanning electron microscopy (SEM) study confirmed the formation of nanoporous poly(CTAB) thin film on GCE which is highly uniform and adhesive. Cyclic voltammetric (CV) shows that poly(CTAB)/GCE exhibited great catalytic capability for the oxidation of dopamine (DA), uric acid (UA), tryptophan (Trp) and theophylline (TP) by enhancing their oxidation currents. In pH 7.0 0.1 M PB solution containing DA, UA, Trp and TP, the linear calibration plots for DA, UA, Trp and TP were obtained over the range of 0.5–1000 μM, 1–1000 μM, 1–1000 μM and 0.5–1000 μM with detection limits of 0.11 μM, 0.33 μM, 0.44 μM and 0.11 μM, respectively. Satisfactory results were obtained when poly(CTAB)/GCE was applied to the simultaneous determination of DA, UA, Trp and TP in urine samples.
Activated carbon (AC) was magnetized with Fe3O4 nanoparticles (AC-Fe3O4-NPs) and loaded with Au nanoparticles (AC-Fe3O4-Au-NPs), while fully were characterized by different techniques such as XRD, XPS, VSM, TEM and SEM. 2-((2, 4-Dichloro-benzylidene)-amino)-benzenethiol (DBABT) as complexing agent was synthesized and characterized by 1H-NMR, ES-MS and FT-IR analysis. Subsequently, AC-Fe3O4-NPs was modified with DBABT and applied for the ultrasound-assisted removal of Cd2+, Pb2+, Cr3+ and Ni2+ ions via complexation with DBABT. The influence of variables like reaction time and adsorbent mass (equilibrium) was optimized simultaneously. The method at optimum condition set as 5 for pH, 5, 15, 25 and 25 mg L-1 for concentration of Cd2+, Pb2+, Cr3+ and Ni2+ ions, respectively, 0.02 g for adsorbent mass, 5 min for sonication time and 6 mg L-1 for concentration of DBABT has removal percentage of 80.59, 93.85, 68.52 and 81.68 for Cd2+, Pb2+, Cr3+ and Ni2+ ions, respectively. Analysis of real experimental equilibrium data at various concentration of analytes reveal the efficiency of Langmuir model for well representation of experimental data with maximum mono-layer adsorption capacity of 185.22, 135.14, 188.70 and 133.34 mg g-1 for Cd2+, Pb2+, Cr3+ and Ni2+ ions respectively. The experimental data at various real times reveal that at most situation the system reach equilibrium at contact time lower than 20 min, while the data well fitted by combination of pseudo second order kinetic model and intraparticle diffusion.