Electrocatalytic Surface Area Research Articles

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

Green fabrication of ultrafine N-Mo x C/CoP hybrids for boosting electrocatalytic water reduction

Developing non-noble-metal electrocatalysts for hydrogen evolution reactions with high activity and stability is the key issue in green hydrogen generation based on electrolytic water splitting. It has been recognized that the stacking of large CoP particles limits the intrinsic activity of as-synthesized CoP catalyst for hydrogen evolution reaction. In the present study, N-Mo x C/CoP-0.5 with excellent electrocatalytic activity for hydrogen evolution reaction was prepared using N-Mo x C as decoration. A reasonable overpotential of 106 mV (at 10 mA cm−2) and a Tafel slope of 59 mV dec−1 in 1.0 M KOH solution was achieved with N-Mo x C/CoP-0.5 electrocatalyst, which exhibits superior activity even after working for 37 h. Uniformly distributed ultrafine nanoclusters of the N-Mo x C/CoP-0.5 hybrids could provide sufficient interfaces for enhanced charge transfer. The effective capacity of the hydrogen evolution reaction could be preserved in the complex, and the enlarged electrocatalytic surface area could be expected to offer more active sites for the reaction.

Aloe vera extract mediated hydrothermal synthesis of rose-like copper iron sulfide for efficient oxygen evolution reaction

BackgroundFabricating electrocatalysts with high surface area is salient to attain water splitting reaction with high efficiency. Conventionally, complexing agent assisted hydrothermal synthesis is often used to synthesize electrocatalyst with unique morphologies that could improve the electrocatalytic surface area. MethodIn this work, a novel approach of adopting aloe vera extract as green complexing agent was used to fabricate copper iron sulfide (CuFeSx)-based nanostructure on nickel foam. Different ratios of aloe vera extract and water were used to identify the effect of complexing agent on morphology of the material. Significantfindings FESEM micrographs verified the role of aloe vera extract as green complexing agent that formed nanorose-like morphology when 75% aloe vera was used. The optimized composition showed that only 234 mV overpotential was required upon iR-compensation to attain 100 mA cm−2 with a corresponding Tafel slope of 81 mV dec−1. Electrochemical surface area analysis (ECSA) revealed that high surface area exposure aided in lowering the overpotential to achieve high current density. The electrocatalyst exhibited good stability upon sustained exposure to alkaline medium for 48 h, retaining up to 84% of its initial current density. This study highlights the potential of using phytochemical-mediated synthesis to fabricate electrocatalysts for generation of sustainable hydrogen fuel via water splitting.

Packed OV-SnO2-Sb bead-electrodes for enhanced electrocatalytic oxidation of micropollutants in water

Electrocatalytic oxidation is an appealing treatment option for emerging micropollutants in wastewater, however, the limited reactive surface area and short service lifetime of planar electrodes hinder their industrial applications. This study introduces an innovative electrochemical wastewater treatment technology that employs packed bead-electrodes (PBE) as a dynamic electrocatalytic filter on a dimensionally stable anode (DSA) acting as a current collector. By using PBE, the electroactive volume is expanded beyond the vicinity of the common planar anode to the thick porous media of PBE with a vast electrocatalytic surface area. This greatly enhances the efficiency of electrochemical degradation of micropollutants. The OV-SnO2-Sb PBE filter achieved a nearly 100 % degradation of moxifloxacin (MOX) in under 2 min of single-pass filtration, with a degradation rate over an order of magnitude higher than the conventional electrochemical oxidation processes. The generation of abundant radical species (•OH) and non-radical species (1O2 and O3), along with the enhanced direct oxidation, led to the outstanding performance of the charged PBE system in MOX degradation. The OV-SnO2-Sb PBE was remarkably stable, and the separation between the electroactive PBE layer and the base Ti anode allows for easy renewal of the bead-electrode materials and scaling up of the system for practical applications. Overall, our study presents a dynamic electroactive PBE that advances the electrocatalytic oxidation technology for effective control of emerging pollutants in the water environment. This technology has the potential to revolutionize electrochemical wastewater treatment and contribute to a more sustainable future environment.

High phase purity of stable 1T-phase Co-doped WS2 for full pH hydrogen evolution reaction in water and seawater

Metallic 1T phase transition metal dichloride (TMDs) shows excellent catalytic activity for the hydrogen evolution reaction (HER), but stabilization of 1T phase TMDs is still challenging. Herein, the Finke-type POMs K10[Co4(H2O)2(PW9O34)2] [Co4(PW9)2] was used for the first time as a precursor to obtaining size ∼ 4 nm, highly dispersed 1T-WS2 in the hollow mesoporous carbon sphere (HMCS) by the effect of confinement, named 1T-CoWS/HMCS. 1T-WS2 was obtained based on the natural Co-W atomic interface of POMs and further enhanced dispersion at the molecular and nano scales. 1T-CoWS/HMCS only requires ultralow overpotential with high electrocatalytic surface area and robust stability in water and seawater. According to DFT calculations, the Co-S-edge site of 1T-CoWS significantly reduced the rate-limiting step of HER as the predominant active site. This work provides a worthy reference for the synthesis of high-quality metastable TMDs.

Highly-efficient removal of Rhodamine B using a flow-through electrocatalytic filtration system: Characteristics, efficiency and mechanism

The objective of this research is to develop an effective electrocatalytic filtration system using Ti/SnO2-Sb membrane anodes for eliminating Rhodamine B (RhB) from wasteater. Compared to Ti/SnO2-Sb plate anode, the prepared Ti/SnO2-Sb membrane anodes featured smaller particle size, bigger electrocatalytic active surface area, lower charge transfer resistance, and higher potential for oxygen evolution. The electrocatalytic filtration system obtained RhB removal of 90.29% with EE/O of 5.51 kWh m−3 after 90 min of electrolysis when initial pH value was 5, current density was 10 mA cm−2, initial RhB concentration was 50 mg L−1, and membrane flux was 2.17 m3 (m2·h)−1, respectively. The flow-through electrocatalytic filtration system was found to be limited by kinetics under a high membrane flux and dominated by an indirect radical oxidation. Finally, the possible RhB degradation pathways were proposed based on the detected intermediates and density functional theory calculations.

ZnO nanoparticles-copper metal-organic framework composite on 3D porous nickel foam: a novel electrochemical sensing platform to detect serotonin in blood serum

Herein, we report a simple non-enzymatic electrochemical sensor for the detection of serotonin (5-HT) in blood serum using ZnO oxide nanoparticles-copper metal-organic framework (MOF) composite on 3D porous nickel foam, namely, ZnO-Cu MOF/NF. The x-ray diffraction analysis reveals the crystalline nature of synthesized Cu MOF and Wurtzite structure of ZnO nanoparticles, whereas SEM characterization confirms the high surface area of the composite nanostructures. Differential pulse voltammetry analysis under optimal conditions yields a wide linear detection range of 1 ng ml−1 to 1 mg ml−1 to 5-HT concentrations and a LOD (signal to noise ratio = 3.3) of 0.49 ng ml−1, which is well below the lowest physiological concentration of 5-HT. The sensitivity of the fabricated sensor is found to be 0.0606 mA ng−1 ml−1.cm2, and it exhibited remarkable selectivity towards serotonin in the presence of various interferants, including dopamine and AA, which coexist in the real biological matrix. Further, successful determination of 5-HT is achieved in the simulated blood serum sample with a good recovery percentage from ∼102.5% to ∼99.25%. The synergistic combination of the excellent electrocatalytic properties and surface area of the constituent nanomaterials proves the overall efficacy of this novel platform and shows immense potential to be used in developing versatile electrochemical sensors.

Fine-tuning of Pd–CeO2/rGO nanocomposite: A facile synergetic strategy for effective electrochemical detection of dopamine in pharmaceutical and biological samples

A facile, sensitive, and rapid electrochemical sensor based on reduced graphene oxide (rGO) supported palladium–cerium oxide nanocomposite on the surface of a glassy carbon electrode (Pd–CeO2/rGO/GCE) was prepared by a two-step process. The Pd–CeO2/rGO nanocomposite was synthesized by the polyol method, and the as-synthesized nanocomposite was then drop-cast onto the surface of the electrode; Pd–CeO2/rGO/GCE. The microstructural and morphological properties of the as-prepared electrocatalysts were investigated using powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and electron microscopy techniques. These results show that rGO sheets are embellished with a face-centred cubic phase of Pd and a cubic fluorite structure of CeO2, resulting in an electrode material with a well-connected conducting network. The synergy of Pd–CeO2 composite with the support of rGO results in a significant increase in the electrocatalytic activity and active surface area of the electrode, which enables the excellent detection of dopamine (DA) with remaining paracetamol (PC), and tyrosine (TY). The optimized electrode demonstrated a good linear range of 5–240 µM, a low limit of detection (LOD) of 0.69 µM, and a sensitivity of 0.894 µM−1 cm−2. Additionally, the selectivity of the sensor was also successfully accomplished in the presence of several interfering substances. Some inherent properties of the produced sensor, such as reproducibility and stability, were also investigated. The developed sensor was also effectively used for DA sensing in human serum samples and pharmaceutical drug injection samples with satisfactory recoveries.

Theoretical and experimental approaches to the preparation, characterization and application of a newly synthesized mesoporous Zn-MOF as a selective ionophore for Ni(II) ion in carbon paste electrode matrix

A novel carbon paste electrode (CPE) chemically modified with a newly synthesized Zn-metal organic framework (Zn-MOF) was synthesized for Ni(II) ion determination with impressing enhancement in sensitivity and selectivity over the preceding studies. Due to their electrocatalytic and substantial surface area criteria, MOFs are a reasonably new category of fascinating materials for precise electrochemical detection. Under the sonication condition, a novel Zn-MOF depending on a Schiff base ligand in nano size was synthesized, and it was characterized using different characterization methods such as powdered X-ray diffraction (PXRD), FT-IR, BET surface area, contact angle and scanning electron microscope (SEM) combined with energy dispersive X-ray analyzer (EDX). The BET surface area and contact angle measurement techniques results were 2901.08 m2 g−1 and 143.49°, respectively, for the synthesized MOF. It was concluded that under the ideal experimental circumstances, the produced Zn-MOF can extract and sense nickel ions from aqueous solution selectively. Several crucial factors were optimized to gain the ultimate electrochemical response. Response mechanism was proved by the aid of study of morphological change and functional groups chemical shifts. Ultimately, a calibration with a Nernstian slope of 28.75 mV decade−1 over linear concentration limits from 5.0 × 10−8 to 1.0 × 10−1 mol L−1 (R2 = 0.9990) and detection limit of 5.0 × 10−8 mol L−1 was obtained. The relative standard deviations and recovery ranges of the proposed approach for determining the Ni(II) ion in various water and food tests (n = 5) were 0.94–2.35% and 97.0–104%, respectively.

Facile synthesis of CeSe2@CNs nanostructure for enhanced water oxidation

Using a hydrothermal technique, we created a composite of cerium selenide incorporated carbon nanospheres (CeSe2@CNs) nanocomposite. The carbon nanospheres and CeSe2 agglomerated nanorods were also created for comparison studies. X-rays diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption-desorption isotherm are all utilized to describe the produced samples. The CeSe2 nanorods were introduced into the microporous hollow carbon nanospheres to create amorphous textured integrated CeSe2@CNs. This increased the intrinsic activity of CeSe2@CNs for oxygen evolution reaction (OER) along with the active electrocatalytic surface area. OER in 1 M KOH alkaline solution can be initiated by the highly applied electrocatalyst CeSe2@CNs at 1.51V vs RHE, and 10 mAcm−2 was obtained at 298 mV overpotential. Additionally, at 315 mV and 335 mV overpotentials, it was able to attain greater current densities of 50 and 80 mAcm−2. As opposed to this, integrated composite CeSe2@CNs have amazing stability and durability and can continuously produce O2 gas bubbles for 10 h without any deterioration in current density for constant 1000 CV cycles.

Electronic Structure Engineering of Highly-Scalable Earth-Abundant Multi-Synergized Electrocatalyst for Exceptional Overall Water Splitting in Neutral Medium.

Efficient neutral water splitting may represent in future a sustainable solution to unconstrained energy requirements, but yet necessitates the development of innovative avenues for achieving the currently unmet required performances. Herein, a novel paradigm based on the combination of electronic structure engineering and surface morphology tuning of earth-abundant 3D-hierarchical binder-free electrocatalysts is demonstrated, via a scalable single-step thermal transformation of nickel substrates under sulfur environment. A temporal-evolution of the resulting 3D-nanostructured substrates is performed for the intentional enhancement of non-abundant highly-catalytic Ni3+ and pSn 2- species on the catalyst surface, concomitantly accompanied with densification of the hierarchical catalyst morphology. Remarkably, the finely engineered NiSx catalyst synthesized via thermal-evolution for 24h (NiSx -24h) exhibits an exceptionally low cell voltage of 1.59V (lower than Pt/C-IrO2 catalytic couple) for neutral water splitting, which represents the lowest value ever reported. The enhanced performance of NiSx -24h is a multi-synergized consequence of the simultaneous enrichment of oxygen and hydrogen evolution reaction catalyzing species, accompanied by an optimum electrocatalytic surface area and intrinsic high conductivity. Overall, this innovative work opens a route to engineering the active material's electronic structure/morphology, demonstrating novel Ni3+ /pSn 2- -enriched NiSx catalysts which surpass state-of-the-art materials for neutral water splitting.

Enhanced catalytic amplification of mesoporous bismuth-gold nano-electrocatalyst triggering efficient capture of tumor marker

A new sandwich-type electrochemical immunosensor for the sensitive detection of carcinoembryonic antigen (CEA) was originally developed using a unique bismuth (Bi)-gold (Au) nano-electrocatalyst triggering efficient capture of tumor marker, where the nano-electrocatalyst was obtained by implanting Au nanoparticles (Au NPs) inside the mesoporous NBiOF nanospheres (Au@NBOF NSs) for the purpose to marker secondary antibody (Ab2) and amplify the response signal through electrochemically catalyzing the reduction of hydrogen peroxide. The synergistic interaction between NBOF NSs and Au NPs endowed the as-received Au@NBOF nano-electrocatalyst with large electrocatalytic active surface area and powerful signal amplification function as upper sandwich layer to conjugate Ab2. The multi-walled carbon nanotubes sparkled with Au nanostars served as the lower sandwich layer to capture the primary antibody (Ab1), which enhanced the interfacial electron transport and the load capacity of Ab1 as a result of increasing the sensing response of the designed immunosensor based on the sandwich-type Ab1-CEA-Ab2 interaction. Such immunosensor proposed on the above double signal amplification strategy efficiently detected the target CEA in a wide concentration range from 100 fg mL−1 to 200 ng mL−1. The detection limit was as low as 9.57 fg mL−1 with excellent specificity and reproducibility. The satisfactory results in analyzing human serum samples indicate the potential application of this new immunosensor in early clinical diagnosis of cancer and the evaluation of treatment efficiency.

Interface modulation induced by the 1T Co-WS2 shell nanosheet layer at the metallic NiTe2/Ni core–nanoskeleton: Glib electrode-kinetics for HER, OER, and ORR

The metallic (1T) transition metal dichalcogenides (TMDCs) are known for their superior electrocatalytic performance, due to their high conductivity, active basal-planes, and exposed edges. Our novel approach of coupling a metallic-NiTe2/Ni nano-skeleton with 1T-Co-WS2 nanosheet in a core–shell arrangement to develop a hybrid heterostructure (1T Co-WS2/NiTe2/Ni) has helped to outperform the trifunctional-electrocatalytic activity (HER, OER, and ORR). 1T-Co-WS2/NiTe2/Ni only requires ultralow overpotential (ηHER = 88 mV@10, ηOER = 290 mV@30), higher half-wave potential for ORR (E1/2 = 0.781 V vs RHE), small Tafel slopes (HER = 68 mV dec-1, OER = 98 mV dec-1, and ORR = 63 mV dec-1) with high electrocatalytic surface area and robust stability in corresponding half-cell reactions. The designed heterostructured electrocatalyst (1T Co-WS2/NiTe2/Ni) presented exceptional total water-splitting performance, requiring a low voltage of 1.521 V to yield 10 mA cm−2 current with extensive structural and electrochemical durability. Such performance could be attributed towards improved nanochannel morphology with exposed active edge, fluent electrode-kinetics, facile adsorption–desorption of reaction intermediates owing to the intrinsically tuned 1T-WS2 by cobalt-doping, and hybridized NiTe2/Ni nano-skeleton. The DFT study confirmed that the incorporation of Co atoms in basal plane and the edge sites of WS2 lattice induces the redistribution and modulation of electronic structure for fast electron/charge transfer and the synergistic coupling of 1T NiTe2 heterostructures bolstered the electrocatalytic activity of the as-prepared catalysts. These outcomes provide a prospect towards the design and application of efficient 2D/2D heterostructured electrocatalyst for zero emission energy goal.

A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu5 Zn8 Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene.

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal-organic framework-derived copper-zinc hollow porous carbon nanocubes (Au@Cu5 Zn8 /HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu5 Zn8 /HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab2 ). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab1 ). Significantly, Cu5 Zn8 /HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H2 O2 using (i-t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu5 Zn8 /HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.

Three-dimensional hierarchical flowers-like cobalt-nickel sulfide constructed on graphitic carbon nitride: Bifunctional non-noble electrocatalyst for overall water splitting

Tailoring various micro-nano structured materials by employing different techniques to enhance their porosity and conductivity has captivated significant consideration, making their remarkable electrochemical properties accessible within the area of energy storage devices. Herein we report the impact of graphitic carbon nitride concentration (0.03 ∼ 0.1 g) on nickel-cobalt sulfide morphologies and performance in hydrogen production. Employing the facile hydrothermal method, a cubic crystalline nickel-cobalt sulfide was stabilized on defective layered graphitic carbon nitride nanosheets for overall water splitting. A performance peak was observed in a sample with a graphitic carbon nitride concentration of 50 mg, which not only prevented the agglomeration but also provided a porous structure for enhanced gas diffusivity and charge transfer rates owing to the synergistic Carbon and Nitrogen bonding with Cobalt and Nickel Sulfide. Optimized concentration of graphitic carbon nitride also increased the electrocatalytic active surface area threefold when compared with nickel-cobalt sulfide. The fabricated well-aligned flower-like pattern CoNi2S4/graphitic carbon nitride (50 mg) delivered a low overpotential of 310 mV and 160 mV for oxygen evolution reactions and hydrogen evolution reactions to reach a current density of 30 mA/cm2 and 10 mA/cm2 in alkaline media. The electrolyzer displayed an electrolysis potential of 1.58 V to reach 10 mA/cm2 current density with the long-term durability of 24 h. This strategy depicts a novel approach for utilizing this renowned nickel-cobalt sulfide with graphitic carbon nitride catalyst for the application of alkaline electrocatalytic water splitting.

Novel syntheses of modified black TiO2/C3N4 and their efficient behavior toward water splitting under neutral conditions

Black titania (BT) incorporated carbon nitride (C3N4) nanoparticles; synthesized with imidazole and titania P-25 for the first time, without washing steps, was then loaded with 3 wt% of Ag2O, Ag2S, and CuO nanoarchitecture through a deposition hydrothermal route. The obtained electrocatalyst CuO/BT offers abundant active sites composed of TiO2−x@TiO2 interfaced with C3N4; that has been emphasized via various physicochemical techniques, besides the Cu+/Cu++ moieties, thus providing an exceptional electrocatalytic performance (configured using CV, LSV, EIS, and ECSA) under both neutral (KCl, pH = 7) and dark conditions. The overall water electrolysis to produce 10 mA cm−2 requires a potential of 1.7 V. This electrode exhibits a superior efficiency due to lowering Tafel slope values for HER (−38.96 mV dec−1) and OER (102.2 mV dec−1), surface oxidation layers due to Cu2+/Cu1+, good conductivity, charge transfer facility, and high electrocatalytic surface area. This study provides a plausible route to construct the C3N4 heterostructure Ti2O3/Ti3O5 with multiple interfaces, which is considered a good candidate for water splitting.

Decoupled hydrogen evolution from water/seawater splitting by integrating ethylene glycol oxidation on PtRh0.02@Rh nanowires with Rh atom modification

PtRh nanowires with sub-monolayer of Rh atoms on the surface (PtRh0.02@Rh NWs) are fabricated and facilitate both hydrogen evolution reaction and ethylene glycol evolution reaction owing to the tensile strain and large electrocatalytic active surface area.

Enzymeless voltammetric sensor for simultaneous determination of parathion and paraoxon based on Nd-based metal-organic framework

The aim of this work is to fabricate a sensitive and novel enzymeless electrochemical sensor for the simultaneous determination of parathion and paraoxon using the Nd-UiO-66@MWCNT nanocomposite. For this purpose, Neodymium (Nd) was introduced into a Universitetet i Oslo (UiO-66) structure to construct Nd-UiO-66 and then, adding multi-walled carbon nanotubes to the Nd-UiO-66 to increase the electrocatalytic activity and surface area of the obtained composite. The Nd-UiO-66@MWCNT has numerous advantages like excellent conductivity, tunable texture, and large surface area and can be used as a distinctive structure for the construction of modified glassy carbon electrode (GCE) to enhance the charge-transfer and the efficiency of electrochemical sensors. This modified electrode showed sensitive and selective determination of paraoxon and parathion over the linear ranges of 0.7–100 and 1–120 nM, with detection limits of 0.04 and 0.07 nM, respectively. The proposed Nd-UiO-66@MWCNT/GCE sensor in this study can be applied in environmental and toxicological laboratories and field tests to detect parathion and paraoxon levels.

Laccase bioconjugate and multi-walled carbon nanotubes-based biosensor for bisphenol A analysis

Bisphenol A (BPA) is an endocrine disruptor compound that has been detected in aquatic ecosystems. In this work, the development of an electrochemical biosensor for BPA determination based on laccase from Trametes versicolor is reported. A bioconjugate was optimized to maximize the biosensor electrocatalytic activity and stability, which for the first time involved the synergistic effect of this specific enzyme (6.8 UmL−1), chitosan (5 mgmL−1) and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate in an optimum 5:5:2 (v/v/v) proportion. This bioconjugate was deposited onto a screen-printed carbon electrode previously modified with multi-walled carbon nanotubes (MWCNTs). Nanostructuration with MWCNTs enlarged the electrocatalytic activity and surface area, thus improving the biosensor performance. The BPA electrochemical reaction follows an EC mechanism at the optimum pH value of 5.0. Linearity up to 12 µM, a sensitivity of (6.59 ± 0.04) × 10-2 μAμM−1 and a detection limit of 8.4 ± 0.3 nM were obtained coupled with high reproducibility (relative standard deviations lower than 6%) and stability (87% of the initial response after one month). The developed biosensor was employed to the analysis of BPA in river water displaying appropriate accuracy (94.6–97.9%) and repeatability (3.1 to 6% relative standard deviations) proving its high potential applicability for in situ environmental analysis.

Enhancement of the electrocatalytic activity for the oxygen reduction reaction of boron-doped reduced graphene oxide via ultrasonic treatment

Commercial polymer electrolyte membrane fuel cells have relied on scares Platinum to catalyse the kinetically sluggish oxygen reduction reaction occurring at their anodes. Over the last decade organic materials, frequently based on graphitic structures have been demonstrated as promising alternative electrocatalysts to the noble metals. Researchers typically utilize ultrasonic treatment as part of the synthesis procedure to achieve homogeneous dispersion of graphitic carbon prior to. Herein we investigate the implications of the structural and compositional changes induced by the ultrasonication treatment on boron-doped reduced graphene oxide for oxygen reduction reaction. It is shown that ultrasonication pre-treatment prior to the boron doping and reduction of graphene oxide via hydrothermal process step leads to the increase of both substitutional B and electrocatalytic surface area, with associated reduction of average pore size diameter, leading to a significant improvement in the oxygen reduction reaction performance, with respect to the non-ultrasonicated material. It is proposed that the higher degree of substitutional doping of boron is a result of formation of the additional epoxy functionalities on graphitic planes, which act as a doping site for boric acid.