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Biodiesel is a renewable energy source, which is produced through transesterification reactions. Despite great attention to develop enzymatic biodiesel production, there are serious obstacles to the industrial development of it such as its cost and slow reaction rate. Along with disadvantages, there are several advantages for enzymatic biodiesel production. Higher purity of fuel and glycerol is known as the most important achievement of enzymatic process. In this study, performance of four different fungi for lipase production was investigated and Aspergillus niger was selected as enzyme source. Lipase production were optimized using experimental design and the optimized factors were determined as pH 5, temperature 30 °C, Potato Dextrose Broth (PDB) 3 % w/v, olive oil 1.50 % v/v, with maximum lipase activity of 42.8±0.51 U/mg. In order to interfacial activation of the lipase, effect of surfactants was studied. Therefore, surfactant-enzyme aggregates were used as biocatalyst for transesterification reaction. Effects of factors on biodiesel yield were studied too. The yield was 96.41±1.20 % at the optimized conditions (methanol/oil molar ration 5.50:1, enzyme concentration 19 % v/ w, Tween 80 concentration 19 mg L–1, temperature 40 °C and reaction time 46 h).

In this work, we have successfully synthesized zinc-mesoporous metal–organic framework thin films (Zn-mMOFTFs) on the surface of a glassy carbon electrode (GCE) by self-assembly accumulation and electrochemical potentiostatic techniques. Then the electrodeposited Zn-MOFTFs were incorporated with Ni ions through the immersion of the obtained electrode in Ni(II) solution to form the final modified electrode, Ni/Zn-mMOFTFs/GCE, which was characterized utilizing the various instrumental techniques. In electrochemical studies, the obtained modified electrode, Ni/Zn-mMOFTFs/GCE, showed enhanced electrocatalytic activity toward the oxidation of methanol (CH3OH) in alkaline media. The values of catalytic rate constant (k) and the electron transfer coefficient (α) for the electrooxidation of CH3OH on the Ni/Zn-mMOFTFs/GCE were obtained to be 1.43 × 104 cm3 mol−1 s−1 and 0.56, respectively. The pseudo steady-state polarization method was employed for further investigation of the electrocatalytic oxidation of CH3OH on the Ni/Zn-mMOFTFs/GCE and the rate constant of the reaction k2Γ = 2.866 × 10−9 cm s−1 and the ratio of k0−1/k01 = 2.08 × 108 were determined. These results showed that the incorporation of the Ni(II) ions in the Zn-mMOFTFs produces a significant electrocatalytic activity toward the oxidation of CH3OH and consequently opens a new way to design a high-performance capable electrocatalyst for direct CH3OH fuel cell systems.

In this study, we introduced the synthesis of an innovative nanocomposite based on zeolitic imidazolate framework-67 (ZIF-67), bio-mobile crystalline material-41 (Bio-MCM-41) and carbon quantum dots (CQDs) for the fabrication of a simple, economic and novel electrochemical sensor on a glassy carbon electrode (GCE), namely, ZIF-67/Bio-MCM-41/CQD/GCE for the electrodetermination of thioridazine hydrochloride (TRZHC), for the first time. The prepared nanocomposite was characterized via relevant techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller, Barrett–Joyner–Halenda and electrochemical methods. The electrochemical behavior of TRZHC as an antipsychotic drug was studied at the ZIF-67/Bio-MCM-41/CQD/GCE and the obtained results indicate that the present modified electrode shows excellent electrocatalytic activity for the oxidation of TRZHC. Compared with the bare GCE, ZIF-67/GCE and Bio-MCM-41/CQDs/GCE, the ZIF-67/Bio-MCM-41/CQD/GCE exhibited excellent efficiency for the electrochemical oxidation of TRZHC due to the significant electrocatalytic properties of the nanocomposite, including high conductivity, large specific surface area and synergistic effect of its components. Under the optimized experimental conditions, the designed sensor showed a linear response in the range of 0.060–2.47 μM and 2.47–69.76 μM with a low detection limit (0.031 μM) and high sensitivity (1.5207 μA μM−1) for the determination of TRZHC, which are comparable or superior to some previously published studies. The designed sensor offers good reproducibility and repeatability with appropriate relative standard deviation (RSD) values. Further, the suggested sensor was successfully applied for the detection of TRZHC in pharmaceutical formulations and biological samples with satisfactory recovery values.

Here, the Ni-based metallic nano-particles (Ni, NiMo and NiMoP) were electrodeposited on/in the surface of ERGO/CE substrate from a citrate-based electrolyte and their catalytic activities investigated towards methanol and ethanol electro-oxidation. The physicochemical characterizations of all prepared electrocatalysts were investigated by different electrochemical and non-electrochemical techniques. The electrocatalytic activities of the modified electrodes towards the electro-oxidation of methanol and ethanol were studied in 0.1 M NaOH solution by conventional electrochemical methods such as cyclic voltammetry and chronoamperometry. In the optimized electrodeposition conditions, the obtained electrochemical results indicate that the NiMoP/ERGO/CE displays dramatically improved electrocatalytic activity [Jpf (mA.cm−2) = 263.14 for methanol and Jpf (mA.cm−2) = 253.35 for ethanol], stability and poisoning tolerance towards the electro-oxidation of these fuels in alkaline solution. Finally, for comparison, the Ni (alone) and NiMo (binary) electrodeposited on/in the ERGO/CE (without P) and also studying the influence of the ERGO layers on the surface of CE, the NiMoP/CE (without ERGO) were prepared and applied as electrocatalysts.

Electrochemical synthesis of poly 3-amino-5-hydroxypyrazole (PAHP) on copper electrode surface was carried out by cyclic voltammetry technique in 0.03 M 3-amino-5-hydroxypyrazole solution containing 0.3 M oxalic acid. The formation of dark brown PAHP on copper surface was characterized by cyclic voltammetry, FTIR and scanning electron microscopy techniques. The corrosion characteristics of copper/PAHP electrode were evaluated by electrochemical methods and electrochemical impedance spectroscopy in 3.5% NaCl solution. The obtained results indicated that PAHP thin film coating was an excellent inhibitor and controlled copper corrosion against corrosive agents in 3.5% NaCl solution.

In this study, hollow fiber supported liquid phase microextraction (HF-LPME) as a simple and efficient method was used for the preconcentration of Co(II), Fe(III) and Al(III) in water and dried tea leave samples prior to their liquid chromatographic determination as for their oxinate chelates. In the HF-LPME process, toluene was used as the acceptor phase, and 8-hydroxyquinoline (8-HQ) was used as a chelating agent. The effect of various experimental parameters on the extraction efficiency including acceptor solvent, stirring rate, ligand concentration, salting-out effect and extraction time were investigated and optimized. The calibration graphs were linear in the range of 1–300 µg L−1 and 0.8–250 µg L−1 for Co(II) and Al(III), respectively. The linear dynamic range for Fe(III) was 1–100 µg L−1 and 100–250 µg L−1 for low concentration and high concentration levels of Fe(III), respectively. Limits of detection (LOD) were in the range of 0.38–0.81 µg L−1. The relative standard deviations (RSD%) for three replicate determinations and the relative recoveries in different real samples were obtained 2.68%–4.58% and 88.0–104%, respectively.

Nowadays, fuel cells (FCs) attracted a great deal of attention due to their many applications and advantages: Higher efficiency than diesel or gas engines, less pollution than fossil fuels, no using fuels such as oil and gas and reducing economic dependence on fossil fuel producing countries and easy maintenance are the advantages of FCs. However, the obstacles encountered FCs commercialization’s are mainly expensive electrocatalyst materials such as platinum (Pt), it’s poisoning by intermediates like as CO and sluggish electrooxidation kinetics of fuels. For this reasons, in order to minimize the amount of Pt and accordingly total cost of FCs and also decreasing the poisoning effects, Pt particles are deposited on/in different conductive supports. Herein we investigated the effect of carbon nanoparticles (CNPs) and reduced graphene oxide (RGO) nanosheets on the carbon-ceramic electrode (CCE) as support for Pt nanoparticles (PtNPs) toward formic acid electro-oxidation. PtNPs were successfully deposited on the CNPs and RGO with electrochemical method. The fabricated nanocomposites were characterized by the field emission scanning electron microscopy, energy-dispersive X-ray and X-ray powder diffraction spectroscopy. The electrocatalytic activities of the prepared electrocatalysts for oxidation of formic acid were investigated in 0.1 M H2SO4 solution by electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA). The results of the experiments revealed that the PtNPs on the CNPs, PtNPs/CNPs/CCE, shows more electrocatalytic activity than the RGO nanosheets support. This high electrocatalytic efficiency of the PtNPs/CNPs/CCE can be attributed to large specific surface area and unique structure of CNPs that is being used as support. The influence of some experimental agents on the electrocatalytic activity of the PtNPs/CNPs/CCE was investigated and the optimal conditions were suggested. The present investigation reveals that the PtNPs/CNPs/CCE is a promising electrocatalyst for the formic acid electro-oxidation reaction in FCs. Preparation and electrocatalytic performance of carbon support and alone PtNPs toward oxidation of formic acid.

Ferulago angulata (Apiaceae), an important medicinal plant of Iran, has been considered to have different therapeutical effects and are widely used in the perfume and pharmacological industries. Considering capability of F. angulata essential oils, the present study was conducted to optimized microwave-assisted hydrodistillation (MAHD) method for F. angulata fruit in order to improve the yield and biological activities of essential oils. Optimization of the yield was done through central composite design (CCD) of the response surface methodology (RSM) using three variable factors (hydrodistillation time, irradiation power and plant/liquid ratio). Based on the RSM results, the maximum essential oil yield was obtained with the microwave power of 980 W and plant/liquid ratio of 2 (g/100 mL) at 72 min. The results revealed that MAHD of F. angulata produced the highest essential oil yield (6.50%) as compared with essential oil prepared with hydrodistillation (HD) (2.65%). The essential oils extracted by MAHD and HD were analyzed by gas chromatography–mass spectroscopy (GC–MS) and indicated the main constituents of them were limonene, α-Pinene, s-Phellandrene, α-Phellandrene, and Terpinolene. The antioxidant study revealed that MAHD essential oil had higher antioxidant activity than the HD essential oil. Furthermore, the essential oil obtained by MAHD demonstrated potent anti-proliferative activity against MCF-7 with IC50 8.51 μg/mL. This research revealed that MAHD could be an effective method for hydrodistillation of essential oil in F. angulata in terms of shortening hydrodistillation time, reduction of energy consumption and increasing biological activities compared with the HD method.

Herein, high performance peroxidase-like activity of zinc and cobalt bi-metal metal-organic framework (ZnCo MOF) is reported and applied for the sensitive measurement of atropine. ZnCo MOF was synthesized by the reaction of 2-methylimidazole with Zn and Co (II) cations in aqueous media. The colorimetric and fluorometric experiments were applied to investigate the catalytic activity of obtained MOF, using o-phenylenediamine (OPD) and terephthalic acid (TA) peroxidase substrates, respectively. The results demonstrated the more efficient mimetic behavior of ZnCo MOF compared with common Zn or Co MOFs. Besides, it was found that atropine hindered the catalytic action of ZnCo MOF and this effect was intensified by increasing the atropine concentration. So, it was considered to design a sensitive analytical assay for atropine detection. To assure a high specific recognition, molecularly imprinted polymer (MIP)-based extraction using magnetic graphene oxide supports was applied to extract atropine before its determination. The combination between the high specific extraction and great catalytic activity of ZnCo MOF led to the ultrasensitive and reliable determination of atropine. The best linear range of calibration graph was achieved using fluorometric detection system for 0.1–45 ng mL−1 atropine concentrations, and detection limit (3Sb/m) was 27 pg mL−1. The relative standard deviations (RSD %) for the determination of 1, and 10 ng mL−1 atropine (n = 5) were 2.13% and 3.08%, respectively. The explained fluorometric assay was examined for the measurement of atropine in biological fluids (Recoveries were in the range of 95.90–103.57%), and the results were validated by an official method.

In the present work, a nanocomposite of oxidized CoMnAl-layered double hydroxide (LDH) and graphene oxide (GO) was prepared by using the coprecipitation method. The obtained nanocomposite was characterized by X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) methods to get information about the structure, composition and morphology. After physicochemical characterization of the prepared sample, it was applied as an electro catalyst for the oxygen evolution reaction (OER). The obtained results show that the oxidized nanocomposite modified glassy carbon electrode exhibited higher electrocatalytic activity (with onset over potential of≈0.3 V in 0.1 M KOH and a Tafel slope of 36 mV dec−1) and excellent stability than that of the non-oxidized nanocomposite. On the other hand, in order to enhance the oxygen evolution reaction efficiency and achieve a higher electrocatalytic activity of the nanocomposite, the existence of higher oxidation numbers for the metal cations in LDH structure is indispensable. For this purpose, we utilized H2O2 as the oxidant agent to achieve the higher oxidation numbers of the LDH cations (Co3+, Mn4+).

Nonrenewable energy sources accounted for roughly 80% of total energy consumption [1]. Solar energy, wind energy, geothermal energy, hydropower, and fuel cells (FCs) have all recently been described as renewable energy sources. In commercial uses, renewable energy has experienced meteorological and logistical obstacles. Because of advantages such as simple fabrication/operation conditions, eco-friendly, high energy conversion efficiency, and long-term durability, FCs technologies are considered one of the most important renewable energy sources for many applications such as portable devices, cars, and electricity plants [2–5]. Methanol can be utilized in direct methanol fuel cells (DMFC) to produce clean energy that can be used in smart electronic gadgets or small automobiles in this regard [6]. However, before DMFC can be used commercially, the slow oxidation kinetics and catalyst toxicity [7] must be resolved. Therefore, the development of direct methanol fuel cells (DMFCs) is one of the most promising technologies for the applications of these devices in stationary power supplies and electric vehicles [8]. Apart from the future of mobile devices such as mobile chargers, phones, computers, and many other applications, this energy is environmentally benign because no gases are emitted and the waste is simply clean water. The biggest issue that this technique may encounter is its high cost due to the usage of noble metal catalysts (platinum (Pt) and ruthenium (Ru)) [9]. Methanol is oxidized via a multi-electron process and several products and/or intermediates can be formed, depending on the electrolyte and the nature of the electrode. Electrode materials are important parameters in the electrochemical oxidation of methanol, where high efficient electrocatalysts are needed. Several metal oxides such as Fe2O3, CeO2, MoOx, Co3O4, NiO, and CuO has been used in various applications, such as catalysis, water splitting photocatalysis, solar cells and gas sensing, besides their uses to enhance the electrocatalytic activity for methanol oxidation [10-11]. This paper describes the preparation of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite catalysts for investigating methanol oxidation in alkaline solutions. The electrode surface was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). After physicochemical characterizations of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite modified carbon ceramic electrode (Cu- MOF/GQDs-PAN/CCE), its electrocatalytic and stability characterizations toward methanol oxidation in alkaline media were investigated in detail by cyclic voltammetry and chronoamperometry. Results showed that, the electrocatalytic activity of the Cu- MOF/GQDs-PAN/CCE electrode is much higher than those of unmodified electrode under similar experimental conditions, showing the possibility of attaining good electrocatalytic anodes for fuel cells. Kinetic parameters such as the electron transfer coefficient (α) and the number of electrons involved in the rate determining step (nα) for the oxidation of methanol were determined utilizing cyclic voltammetry (CV). Keywords: Graphene quantum dot, Polyaniline, Metal-organic frameworks, electrocatalyst, Methanol References [1] S.K. Kamarudin, F. Ahmad, W.R.W. Daud, Overview on application of direct methanol fuel cell (DMFC) for portable electronic devices, Int. J. Hydrog. Energy 34 (2009) 6902–6916. [2] L. Carrette, K.A. Friedrich, U. Stimming, Fuel cells: principles, types, fuels and applications, ChemPhysChem 1 (2000) 162–193. [3] A.B. Stambouli, Fuel cells: The expectations for an environmental-friendly and sustainable source of energy, Renew. Sustain. Energy Rev. 15 (9) (2011) 4507– 4520. [4] P. Joghee, J.N. Malik, S. Pylypenko, R. O’Hayre, A review on direct methanol fuel cells – In the perspective of energy and sustainability, MRS Energy Sustain. 2 (2015), https://doi.org/10.1557/mre.2015.4. [5] D. Hassen, M.A. Shenashen, S.A. El-Safty, M.M. Selim, H. Isago, A. Elmarakbi, H. Yamaguchi, Nitrogen-doped carbon-embedded TiO2 nanofibers as promising oxygen reduction reaction electrocatalysts, J. Power Sources 330 (2016) 292– 303. [6] M. Mansor, S.N. Timmiati, K.L. Lim, W.Y. Wong, S.K. Kamarudin, N.H. Nazirah Kamarudin, Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction, Int. J. Hydrogen Energy 44 (29) (2019) 14744–14769, https://doi.org/10.1016/j.ijhydene.2019.04.100. [7] Z. Mousavi, A. Benvidi, S. Jahanbani, M. Mazloum-Ardakani, R. Vafazadeh, H. R. Zare, Investigation of electrochemical oxidation of methanol at a carbon paste electrode modified with Ni(II)-BS complex and reduced graphene oxide nano sheets, Electroanalysis 28 (12) (2016) 2985–2992, https://doi.org/10.1002/ elan.201501183. [8] S. Wasmus, A. Küver, Methanol oxidation and direct methanol fuel cells: a selective review, J. Electroanal. Chem. 461 (1-2) (1999) 14–31. [9] M. Liu, R. Zhang, W. Chen, Graphene-Supported Nanoelectrocatalysts for Fuel Cells: Synthesis, Properties, and Applications, Chem. Rev. 114 (2014) 5117– 5160. [10] N. Spinner, W.E. Mustain, Electrochim. Acta 56 (2011) 5656. [11] M.S. Risbud, S. Baxter, M. Skyllas-Kazacos, Open Fuels Energy Sci. J. 5 (2012) 9.

CA 125 is a Mucin glycoprotein and its concentration in human serum correlates with a woman's risk of developing ovarian cancer and also indicates response to therapy in diagnosed patients. Accurate detection of this large, complex protein in patient biofluids is of great clinical relevance. In this work, an innovative immunoassay for quantitation of CA 125 based on signal amplification strategy was proposed. In this work, Horseradish peroxidase (HRP) labeled CA 125-antibody (anti-CA 125) was immobilized onto a green and biocompatible nanocomposite containing poly cetyl trimethyl ammonium bromide (P (CTAB) as conductive matrix, chitosan (CS) as biocompatible agent and sliver nanoparticles (Ag NPs) as signal amplification element. Therefore, a novel nanocomposite film based P (CTAB-CS) and Ag NPs was exploited to develop a highly sensitive immunosensor for detection of CA 125 protein. Importantly, Ag NPs prepared by electrodeposition method which lead to compact morphology. Fully electrochemical methodology was used to prepare a new transducer on a glassy carbon surface which provided a high surface area to immobilize a high amount of the anti-CA 125. The surface morphology of electrode was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). The immunosensor was employed for the detection of CA 125 using cyclic voltammetry (CV) and differential pulse voltammetry (DPVs) techniques. Under optimized condition the calibration curve for CA 125 concentration by SWV and DPV was linear in 0.01–400 U/mL with lower limit of quantification of 0.001 U/mL. The method was successfully applied assay of the CA 125 in unprocessed human plasma samples.

In this study, ultrasonication, a facile and rapid process, was utilized for the preparation of ternary-component layered double hydroxides (LDHs), Ni3AlxFe1−x-LDHs, as the electrocatalyst material for the oxygen evolution reaction (OER) in a neutral solution. Despite the fact that bivalent metal ions, such as Ni2+, Co2+ and Zn2+, have been demonstrated to play a highly specialized role in water oxidation or OER, the role of trivalent metal ions in LDH structures within these areas requires a lot of research. Hence, herein, we demonstrated that Al3+ had a positive effect on the size and the bandgap energy of the as-synthesized LDHs, which led to the improvement in electrochemical performance. According to powder X-ray diffraction and field-emission scanning electron microscopy, it was found that Al3+ ions could regulate the crystallinity and the size of Ni3AlxFe1−x-LDHs nanoparticles. Ni3AlxFe1−x-LDHs were used as electrocatalyst materials in carbon paste electrodes (CPEs) for the OER in a neutral solution. The obtained results showed that the electrocatalytic activity of Ni3Al0.25Fe0.75-LDH was much better than the other binary-component LDHs. The Tafel slope of the OER in 0.1 M phosphate buffer (pH = 7) at the ternary-component Ni3Al0.25Fe0.75-LDH electrocatalyst (15 mV dec−1) was lower than that of Ni3Fe-LDH (61 mV dec−1) and Ni3Al-LDH (98 mV dec−1); also, it exhibited a low overpotential for this process. The high electrocatalytic activity of Ni3Al0.25Fe0.75-LDH may be attributed to the co-existence of Al3+ and Fe3+ active sites and also to its decreased bandgap in comparison to that of Ni3Fe-LDH and Ni3Al-LDH.

In this study, the ternary-component nickel-zinc-iron layered double hydroxides (NixZnyFez-LDHs) were synthesized by co-precipitation process and characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy and atomic absorption spectroscopy. The NixZnyFez-LDHs were then used as the efficient electrocatalyst materials to fabricate the modified carbon paste electrodes (CPEs) for water oxidation in neutral media. The effect of Zn2+ ions on the electrocatalytic activity of the ternary-component NixZnyFez-LDHs modified CPE was studied under suggested optimum condition. In this condition, the ternary-component Ni2Zn0.5Fe-LDH modified CPE displayed improved electrocatalytic activity in comparison with other ternary-component LDHs, and also binary-component LDHs, Ni2Fe-LDH and ZnFe-LDH modified CPEs due to high crystallinity and low band gap energy which enhanced the conductivity of the synthesized LDH. Furthermore, the ternary-component Ni2Zn0.5Fe-LDH modified CPE had good structural stability with no significant deactivation of the electrocatalytic properties in neutral media after 13 h oxygen evolution reaction at room temperature.

NiGa-LDH@X-NiWO4 (X: 3, 5 or 10 wt% NiWO4) nanocomposites were prepared at room temperature under mild conditions. The synthesized nanocomposites were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and field emission scanning electron microscopy (FESEM) techniques. Electrochemical tests of the nanocomposites were performed by using cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques. Application of the nanocomposites in a three-electrode cell revealed that the specific capacitance of the NiGa-LDH@10-NiWO4 nanocomposite, i.e. 275 F g−1 at 1 A g−1 current density in pseudocapacitors, is greater than those of the NiGa-LDH@3-NiWO4 and NiGa-LDH@5-NiWO4 nanocomposites and their pure NiGa-LDH and NiWO4 components. Moreover, the NiGa-LDH@10-NiWO4 nanocomposite exhibited a low resistance against ion diffusion and an outstanding capacitive behavior by retaining about 92% of its initial capacitance after performing 1000 cycles at 2 A g−1 current density. The improvement observed in the performance of the fabricated pseudocapacitor can be attributed to the synergistic effects of the NiWO4 and NiGa-LDH materials. Evaluation of the effect of electrolyte alkalinity and the presence of different cations indicated that highly alkaline electrolytes promote the electrochemical behaviour of nanocomposite coated electrodes. Application of the NiGa-LDH@10-NiWO4 electrode, along with an activated carbon electrode, for the fabrication of an asymmetric cell leads to the provision of an excellent cycle life, with 7.11 W h kg−1 energy density and 12 800 W kg−1 power density. Therefore, NiGa-LDH@10-NiWO4 can be considered as a suitable new electrode material used for the fabrication of portable electronics and electric vehicles that rely on high-performance asymmetric supercapacitors.

In this study, we have successfully synthesized the M@Pt (M = Fe3O4, Co and Ni) nanoparticles catalysts through the sodium borohydride reduction method for a comparative studies of their electrocatalytic performance towards ethanol oxidation in acidic media. After the structure, surface morphology and chemical composition characterization of the synthesized core–shell nanoparticles, their electrocatalytic activities towards oxidation of ethanol in acidic media were studied in detail. We investigated the effect of the core element (Fe3O4, Co and Ni) on the electrochemical behaviour as well as the enhancement of the electrocatalytic activity for ethanol oxidation reaction. Overall, the obtained results show that the all of these electrocatalysts exhibited an enhanced activity than Pt-alone nanoparticles towards ethanol oxidation reaction. On the other hand, the comparative studies of their electrocatalytic performance show that the Ni@Pt nanoparticles present the best performance with the maximum electrocatalytic activity and stability.

In the present work, a novel nanocomposite based on the graphene quantum dots and CoNiAl-layered double-hydroxide was successfully synthesized by co-precipitation method. To achieve the morphological, structural and compositional information, the resulted nanocomposite was characterized by scanning electron microscopy X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and photoluminescence. Then, the nanocomposite was used as a modifier to fabricate a modified carbon paste electrode as a non-enzymatic sensor for glucose determination. Electrochemical behavior and determination of glucose at the nanocomposite modified carbon paste electrode were investigated by cyclic voltammetry and chronoamperometry methods, respectively. The prepared sensor offered good electrocatalytic properties, fast response time, high reproducibility and stability. At the optimum conditions, the constructed sensor exhibits wide linear range; 0.01–14.0 mM with a detection limit of 6 μM (S/N = 3) and high sensitivity of 48.717 μAmM−1. Finally, the sensor was successfully applied to determine the glucose in real samples which demonstrated its applicability.

In the present study, a simple and highly sensitive electrochemical method was developed for the determination of hydrogen peroxide (H2O2) through a Ni–Al/layered double hydroxide/Ag nanoparticle composite modified carbon-paste electrode (Ni–Al/LDH/Ag NPs/CPE) as a renewable electrode in 0.1 M phosphate buffer solution (PBS, pH = 7.0). Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) were performed for the characterization of the Ni–Al/LDH/Ag NP composite. The electrocatalytic activity of the Ni–Al/LDH/Ag NPs/CPE for H2O2 reduction was studied by cyclic voltammetry and chronoamperometric (at an applied potential of −0.9 V) methods. The prepared renewable modified electrode as a H2O2 sensor shows good electrocatalytic activity, fast response time, good stability and reproducibility. The present sensor also displays a linear range from 10 μM to 10 mM concentration of H2O2 with a detection limit of 6 μM (S/N = 3) and sensitivity of 1.863 μA mM−1 cm−2. This sensor was employed successfully for the determination of H2O2 in real samples by the chronoamperometric method, which indicates its applicability in practical analysis.

In this study, a novel and sensitive nanocomposite of carboxylate-functionalized multiwalled carbon nanotube (COOH-fMWCNT) and silver nanoparticles (AgNPs) was fabricated and used to modify a glassy carbon electrode (GCE) by a simple drop casting method. Modified electrode was then applied for selective determination of emedastine difumarate (EDD). The COOH-fMWCNT/AgNPs nanocomposite was characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV). EDD showed two oxidation peaks at 0.634 and 1.2 V on the GCE surface. CV results of COOH-fMWCNT/AgNPs/GCE displayed superior electrocatalytic performance in terms of anodic peak current of EDD when compared to AgNPs/GCE, MWCNT/GCE, and COOH-fMWCNT/GCE. The experimental conditions such as effect of pH, supporting electrolyte, effect of accumulation time and potential, scan rate were optimized for getting intense current signals of the target analyte. Under optimized conditions, COOH-fMWCNT/AgNPs/GCE showed a linear current response for oxidation of EDD in the range of 1.0 × 10−7–1.0 × 10-4 M, with a limit of detection (LOD) and quantification (LOQ) of 5.25 nM, 15.9 nM, respectively, in 0.1 M phosphate buffer solution at pH 2.0 using differential pulse adsorptive stripping voltammetry technique. The proposed method was successfully applied for determination of EDD in pharmaceutical dosage form. Satisfactory recovery percentages were achieved from eye drop sample with acceptable RSD values (less than 2 %). Furthermore, the reproducibility, stability and repeatability of the modified electrode were studied.

In this work, nickel–cobalt alloy nanoparticles were electrodeposited on/in an electrochemically reduced nitrogen-doped graphene oxide (ErN-GO)/carbon-ceramic electrode (CCE) and the resulting nanocomposite (NiCo/ErN-GO/CCE) was evaluated as a low cost electrocatalyst for methanol and ethanol electrooxidation. Field-emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were used for the physical characterization of the electrocatalyst. To study the electrochemical behavior and electrocatalytic activity of the prepared electrocatalyst towards the oxidation of methanol and ethanol in alkaline media, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were utilized. Electrochemical investigation of the introduced electrocatalysts (NiCo alloy and Ni nanoparticles alone electrodeposited on/in different substrates) indicated that NiCo/ErN-GO/CCE has highest activity and stability towards methanol (Jp = 88.04 mA cm−2) and ethanol (Jp = 64.23 mA cm−2) electrooxidation, which highlights its potential use as an anodic material in direct alcohol fuel cells.

In this study, a mesoporous crystalline material including zinc metal–organic framework (Zn-mMOF) structure as a platform material synthesized by electrochemical method on glassy carbon electrode (GCE) and incorporated with copper ions by a simple chemical method, Cu/Zn-mMOF/GCE, was introduced for electrodetermination of the amoxicillin (AMOX). After physicochemical characterization of the modified electrode, it was used as an electrocatalyst toward oxidation of AMOX in 0.1 M NaOH solution. The Cu/Zn-mMOF/GCE showed high electrocatalytic activity for oxidation of AMOX with large catalytic rate constant; Kcat = 3.9 × 105 cm3 mol−1 s−1. The obtained results indicated that the incorporation of the Cu(II) ions plays an important role in the electrochemical and electrocatalytic activities of the Cu/Zn-mMOF/GCE for the oxidation of AMOX. The proposed modified electrode as a sensor exhibits excellent performances including a wide linear response range (1.0–205 µM), low detection limit (0.36 µM), high sensitivity (0.0256 µA µM−1 cm−2), high stability, short time response, and excellent reproducibility. The developed sensor was successfully applied for determination of AMOX in real samples.

In this study, a simple and innovative electrochemical method was utilized for the synthesis of the copper based metal-organic framework (Cu-MOF)/sulfur and nitrogen co-doped graphene (SNDGr) nanocomposite on the pencil graphite electrode (PGE) and developing of an electrochemical sensor for determination of sertraline hydrochloride (STLHC); an antidepressant drug. Firstly, the SNDGr was simply synthesized through the electrochemical exfoliation of PGE by using potentiostatic procedure in the mixture solution of melamine and ammonium sulfate. Thereafter, the Cu-MOF was also electrochemically deposited on/in SNDGr/PGE using chronoamperometry technique. The as-fabricated modified electrode (Cu-MOF/SNDGr/PGE) was characterized through relevant instrumental methods (scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, and electrochemical techniques). The designed modified electrode exhibited excellent electrocatalytic activity for the oxidation of STLHC compared with bare PGE, SNDGr/PGE and Cu-MOF/PGE due to its high specific surface area, high conductivity and fast charge transfer ability of the nanocomposite. The experimental results demonstrated that the present modified electrode has a promising potential as a stable and efficient electrochemical sensor for determination of STLHC. Under the optimized experimental condition, the designed sensor responds efficiently to STLHC over the concentration range of 0.05 to 2.67 µM with a low detection limit (0.038 μM), high selectivity, good sensitivity (0.4557 μA/μM cm2) and repeatability. Further, the suggested sensor was successfully employed for the determination of STLHC in real samples with suitable recovery values.

The authors describe a differential pulse voltammetric technique for the simultaneous determination of guanine (Gu) and adenine (Ad). A glassy carbon electrode (GCE) was modified with a chitosan film containing functionalized diamond nanoparticles (f-DNPs/CS) of 10–20 nm average size. The materials were characterized by field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry. The modified glassy carbon electrode (f-DNPs/CS/GCE) is shown to display high electrocatalytic activity toward the oxidation and determination of Gu and Ad, respectively, with oxidation peaks that are strongest at 0.72 ± 0.02 V for Gu and at 1.02 ± 0.02 V for Ad (both versus Ag/AgCl). Responses in differential pulse voltammetry are linear to Gu in the 0.05–30.0 μM concentration range, and to Ad in the 0.1–14.0 μM concentration range, and the detection limits (at an S/N ratio of 3) are 2 nM and 10 nM for Gu and Ad, respectively. The f-DNPs/CS/GCE was successfully applied to the simultaneous determination of Gu and Ad in fish sperm DNA and typically gave 97.5 and 98.8 % recoveries.

A glassy carbon electrode (GCE) modified with an ordered mesoporous carbon/Ag nanoparticle nanocomposite, namely an OMC/Ag-NP-modified GCE, was prepared by casting an OMC/Ag NP nanocomposite on a GCE. The morphological properties of the OMC/Ag NP nanocomposite was characterized by applying various techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), and the electrochemical properties of the modified electrode were investigated using cyclic voltammetry. The electrocatalytic reduction of iodate on the modified electrode was also studied using cyclic voltammetry as well as by using amperometric methods. The prepared modified electrode showed good electrocatalytic properties, fast response time, good stability and reproducibility. The performance of the sensor exhibited a linear range from 15.0 × 10−6 to 4.43 × 10−3 M with a limit of detection of 3.01 × 10−6 M (S/N = 3), and the sensitivity of the sensor was found to be 1.92 μA μM−1 cm−2. The modified electrode was applied successfully to the determination of iodate concentration in salt samples using the amperometric method, which demonstrated the applicability of the modified electrode.

Palladium nanoparticles/nanostructured carbon black composite (PdNPs/NCB), supported on the carbon–ceramic electrode (CCE), has been prepared by a chemical reduction method using sodium borohydride as a reducing agent. The synthesized composite was characterized by scanning electron microscopy, high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and electrochemical methods to delineate its surface morphology, nanostructure properties, composition, crystal phases and electrochemical properties. The obtained modified electrode, PdNPs/NCB/CCE, was used as an efficient electrocatalyst for the oxidation of formic acid. Electrochemical techniques including cyclic voltammetry and chronoamperometry were applied for electrocatalytic investigations and it was found that the PdNPs/NCB/CCE was catalytically more active than the Pd nanoparticles supported on the CCE without NCB (PdNPs/CCE). The effect of some experimental factors was studied and optimum conditions were suggested. The obtained results show that the PdNPs/NCB/CCE has satisfactory stability and reproducibility for electrooxidation of formic acid when stored in ambient conditions and improved electrocatalytic activity in continued cycling which make it more attractive for formic acid fuel cell applications.

In the present study, nickel (Ni) and Ni alloy (Ni–Cu and Ni–Co) nanoparticles modified carbon-ceramic electrodes (Ni/CCE, Ni–Cu/CCE and Ni–Co/CCE) were prepared by an electrochemical process for the oxidation of glycerol. In order to obtain the surface and physicochemical information, the Ni/CCE, Ni–Cu/CCE and Ni–Co/CCE were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and electrochemical techniques. Then, cyclic voltammetry and chronoamperometry were employed to characterize the electrocatalytic activity of the modified electrodes, Ni/CCE, Ni–Cu/CCE and Ni–Co/CCE, toward the oxidation of glycerol in 1.0 M NaOH solution. It was found that the Ni alloy nanoparticle modified electrodes are catalytically more active than the Ni/CCE, therefore, the alloying of the Ni with Cu and Co in the form of nanoparticles on the carbon-ceramic electrode, as a homemade substrate, greatly enhances the catalytic activity of the Ni-based electrocatalysts (as the non-platinum electrocatalysts) in glycerol oxidation.

In this research, a new and suitable electrochemical sensor for simultaneous determination of benzenediols (BD) isomers is fabricated by dripping well-dispersed graphene oxide nanosheets (GONs) and in situ plating of poly glycine (P-Gly)-metal copper nanoparticles at the glassy carbon electrode (GCE), Cu-NPs/P-Gly/GONs/GCE, successively. Besides, the as-prepared modified electrode was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), and electrochemical techniques. The proposed electrochemical sensor excellently enhanced the selectivity in the determination of BD isomers by differential pulse voltammetry (DPVs). Compared between the unmodified and modified electrode, unmodified electrode failure to dispel the voltammetric response of BD isomers in a mixture solution, Cu-NPs/P-Gly/GONs/GCE shows larger electrocatalytic activity for the oxidation of hydroquinone (HQ) and catechol (CC) with an enhancement in peak currents and a decrement in peak separation (ΔEp). Consequently, the two isomers can be determined simultaneously. Under the best response experimental, the linear response range was from 3 μM to 200 μM for CC with a detection limit of 1.015 μM and from 2 μM to 300 μM for HQ with a detection limit of 1.067 μM. Further, the suggested sensor was successfully applied for the detection of BD isomers in actual samples.

Mentha pulegium L. is an aromatic herb belonging to the Lamiaceae family, a wild plant which is distributed in different areas of Iran. In this research, we evaluated the variability of essential oil content and compositions of 12 M. pulegium populations. Essential oils were analyzed using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) methods. The essential oils content varied from 0.22 to 1.63% w/w within different populations. Twenty-nine compounds were identified which represent 83.4–98.7% of the total essential oil. The most significant essential oil compounds among the studied population were identified using the principal components analysis (PCA-biplot). According to the PCA-biplot, the major compounds were pulegone (2.5–51.7%), menthone (0.2–25.3%), limonene (0.0–35.4%), 1,8-cineol (0.0–33.4%), piperitenone oxide (0.2–55.2%), and trans-piperitone epoxide (0.0–28.5%). Besides, hierarchical cluster analysis indicated that the studied populations were classified into two main clusters based on the essential oil components. The canonical correspondence analysis (CCA) indicated that some environmental factors could influence the phytochemical constituents as well as the antioxidant activity. The temperature and altitude were effective environmental factors with regards to 1–8 cineol, limonene and menthone content, while average rainfall was the most effective factor with respect to trans-piperitone epoxide, piperitenone oxide, and pulegone content. Our results consequently showed that environmental factors had a significant effect on the essential oil content and its antioxidant activity in M. pulegium populations.

In the present study, the ternary CuNiPt alloy nanoparticles (CuNiPt-ANPs) were electrodeposited on the graphenized pencil lead electrode (GPLE) surface, and the obtained modified electrode (CuNiPt-ANPs/GPLE) was examined as a new electrocatalyst towards ethanol electro-oxidation reaction (EEOR). The GPLE was fabricated through the electrochemical exfoliation of pencil lead electrode (PLE) in acidic condition on a three-electrode electrochemical cell. The physicochemical and electrocatalytic characterizations of the prepared electrocatalyst were examined by means of various techniques: X-ray powder diffraction spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping analysis, cyclic voltammetry, and chronoamperometry. Comparison of the electrocatalytic activity of the introduced electrocatalysts (PtNPs/PLE, PtNPs/GPLE, CuPt-ANPs/GPLE, NiPt-ANPs/GPLE, and CuNiPt-ANPs/GPLE) showed that the CuNiPt-ANPs/GPLE has the highest and good electrocatalytic activity (first anodic peak current density = 101 mA cm−2) and outstanding stability for the EEOR in acidic media. This work offers not only an easy and efficient synthesis strategy but also opens new avenues for the design of high performance promising electrocatalyst for fuel cell systems.

Herein, a new ternary-component layered double hydroxide (LDH) consisting of Ca2+ was constructed using an inexpensive bio-waste; eggshell, through a facile hydrothermal method (NiCaFe-LDH-H). The prepared material, NiCaFe-LDH-H, was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption-desorption; Brunauer-Emmett-Teller (BET), difference thermogravimetry (DTG) and thermogravimetric analysis (TGA). Then, the NiCaFe-LDH-H was used as an electrocatalyst material to fabricate the modified carbon paste electrode (CPE) for water oxidation at neutral solutions (pH = 7.0). The electrochemical tests show that the NiCaFe-LDH-H modified CPE has efficient electrocatalytic activity towards the water oxidation reaction in a neutral solution. The effect of the LDH preparation method, presence of Ca2+ (as a low-cost material in comparison with transition metals), and its primary source was investigated on the electrocatalytic activity of the NiCaFe-LDH-H modified CPE and compared with binary-component LDHs (without Ca2+). The results of the electrochemical examinations indicate that the incorporation of Ca2+ from the eggshell source into the LDH by the hydrothermal method improve water oxidation performance of the NiCaFe-LDH-H modified CPE: lowering the onset potential to about 1.56 V vs. reversible hydrogen electrode (RHE) and overpotential to 373 mV in a neutral solution. The promoted electrocatalytic activity of the present modified CPE can be attributed to the high active surface area of the NiCaFe-LDH-H modified CPE due to the high crystallinity of LDH containing Ca2+.

Development of a sensitive detection method for the reliable screening of widely used organophosphorus (OP) toxins is a crucial request to control their side-effects. Herein, a novel fluorometric assay based on the acetylcholinesterase (AChE) inhibited enzymatic activity and the new peroxidase-like Fe3O4 nanoparticles@ZIF-8 composite (Fe3O4 NPs@ZIF-8) was developed for the determination of OPs. Magnetic Fe3O4 NPs were encapsulated into ZIF-8 and the high mimetic activity of produced composite was assessed on the oxidation of substrates. This observation was applied to the rapid detection of diazinon as a model OP compound. The sensing tool contains AChE and choline oxidase (CHO) enzymes, peroxidase colorimetric or fluorometric substrate, and Fe3O4 NPs@ZIF-8 as the catalyst. In the presence of mimic Fe3O4 NPs@ZIF-8, the generated H2O2 from the enzymatic reactions of acetylcholine is decomposed to hydroxyl radicals. The radicals oxidize the peroxidase substrates to generate a detectable signal. However, due to the inhibition effect of OPs on the enzymatic activity of AChE, lower H2O2 amounts are produced in the presence of diazinon. Using the fluorometric detection system, the generated signal is decreased proportionally by increasing diazinon concentration in the range of 0.5–500 nM. The limit of detection was obtained 0.2 nM. Consequently, the usage of high performance peroxidase-mimic Fe3O4 NPs@ZIF-8 provided a sensitive bio-assay with a potential to be applied as screening tool for toxic OP compounds. The developed assay was successfully applied for the determination of diazinon in water and fruit juices.

A nanocomposite for catalysis of methanol oxidation reaction was fabricated by carbon paste electrode modified with reduced graphene oxide supported bimetallic Ni–Co nanoparticles (Ni–Co/RGO/CPE). It was characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and cyclic voltammetry. The voltammetric results of the modified electrode showed a well redox activity for Ni nanoparticles which was improved by the presence of Co nanoparticles and reduced graphene oxide nanosheets. The electrochemical oxidation of methanol was investigated in alkaline media at Ni–Co/RGO/CPE. The obtained results showed that the presence of Ni–Co/RGO in the structure of electrocatalyst greatly enhance the electrocatalytic oxidation of methanol. The anodic peak potential of methanol oxidation was decreased to 0.65 V vs saturated calomel electrode and its current was greatly enhanced by Ni–Co/RGO/CPE. Also, the chronoamperometry technique was employed for obtaining the catalytic rate constant for the electrooxidation of methanol according to method of Galus as 1.05 M−1s−1.