Heterogeneous Electron Transfer Research Articles

Kraft-Based Femtosecond Laser-Induced Graphene for Electrochemical Dopamine Sensing.

In this work, laser-induced graphene from kraft paper (kraft paper-LIG) was employed for the nonenzymatic electrochemical sensing of dopamine (DA). We reported the fabrication and characterization of a disposable, cost-effective, kraft-based electrochemical dopamine sensor with the sensing electrode consisting of laser-induced graphene derived from kraft paper. Kraft paper-LIG was formed by the femtosecond laser modification of kraft paper into a three-dimensional (3D) graphene arrangement. Our study labeled that the electrochemical activity of kraft paper-LIG can be improved via a dual pass (defocused, followed by focused lasing). Kinetic analysis showed that the effective heterogeneous electron transfer rate constant of kraft paper-LIG was 2.8 × 10-3 cm s-1 using Fe(CN)63-/4- as a redox probe. The kraft paper-LIG electrodes successfully detected and quantified dopamine in phosphate-buffered solution (PBS) within the 1-100 μM range. A linear response (R2 = 0.9986) was observed, with a sensitivity of 37.381 μA cm-2 μM-1. Furthermore, the kraft paper-LIG electrodes denoted sufficient selectivity for DA in electrolytes containing ascorbic acid (AA) and uric acid (UA). Kraft paper-LIG electrodes also had good stability at ordinary temperature.

In Situ Ag-Seeded Lamellar Ti3C2 Nanosheets: An Electroactive Interface for Noninvasive Diagnosis of Oral Carcinoma via Salivary TNF-α Sensing.

In the fast-paced quest for early cancer detection, noninvasive screening techniques have emerged as game-changers, offering simple and accessible avenues for precession diagnostics. In line with this, our study highlights the potential of silver nanoparticle-decorated titanium carbide MXene nanosheets (Ti3C2_AgNPs) as an electroactive interface for the noninvasive diagnosis of oral carcinoma based on the prevalence of the salivary biomarker, tumor necrosis factor-α (TNF-α). An in situ reduction was utilized to synthesize the Ti3C2_AgNPs nanohybrid, wherein Ti3C2 acts as the reducing agent, and the resulting nanohybrid was subjected to various characterization techniques to examine the optical, structural, and morphological attributes. The results revealed that spherical AgNPs formed on the surface of Ti3C2 MXene nanosheets by virtue of the low-valent Ti species present in Ti3C2, which facilitated the reduction of AgNO3 to AgNPs. Furthermore, the electrochemical characterization of the nanohybrid-modified screen-printed electrode (Ti3C2_AgNPs/SPE) indicated enhanced heterogeneous electron transfer kinetics. With these encouraging results, the Ti3C2_AgNPs nanohybrid was employed as an immobilization matrix for TNF-α antibodies and applied for electrochemical sensing. Analytical studies of the fabricated immunosensor, conducted by differential pulse voltammetry (DPV), exhibited a broader linear range (1 to 180 pg mL-1), a low limit of detection (0.97 pg mL-1), and high sensitivity (1.214 μA mL pg-1 cm-2) and specificity, even in artificial saliva, indicating its reliability for oral carcinoma diagnosis. Therefore, the Ti3C2_AgNP nanohybrid seems a promising candidate for the effective sensing of TNF-α and could also be explored for other biomarkers.

Electric Field Distribution in Bipolar Electrochemical Cells: Effects on the Wirefree Electrodeposition of Conducting Polymer Films.

Wirefree, or bipolar electrochemistry, is advancing key fields, including (nano)materials, human health, and energy. Central to these applications is an understanding of the potential distribution induced in the bipolar electrode, BPE. Here, the impact of the electric field distribution is reported for the wirefree deposition of the conducting polymer, poly(3,4-ethylenedioxythiophene), PEDOT, in the absence of deliberately added electrolytes. PEDOT films with a gradient thickness are deposited, and the films formed at 10 V cm-1 for 20 min have an average film thickness of 350 nm. Significantly, the quantity of the polymer deposited increases proportionally to the deposition time up to approximately 20 min, suggesting that the presence of a thin PEDOT film does not change the interfacial potential distribution or driving force for heterogeneous electron transfer. For electric field strengths ≥5 V cm-1, PEDOT is deposited on regions of the BPE where the voltage is predicted to be insufficient to drive electropolymerization. This result demonstrates that local intensification of the field, e.g., at edges, and migration of the cationic radicals can significantly affect the electrodeposition profile. These results provide an enhanced understanding of the potential profiles for applications from multianalyte detection devices to wirefree electroceuticals.

Engineering a Binding Peptide for Oriented Immobilization and Efficient Bioelectrocatalytic Oxygen Reduction of Multicopper Oxidases.

Enzymatic fuel cells (EFCs) are emerging as promising technologies in renewable energy and biomedical applications, utilizing enzyme catalysts to convert the chemical energy of renewable biomass into electrical energy, known for their high energy conversion efficiency and excellent biocompatibility. Currently, EFCs face challenges of poor stability and catalytic efficiency at the cathodes, necessitating solutions to enhance the oriented immobilization of multicopper oxidases for improved heterogeneous electron transfer efficiency. This study successfully identified a surface-binding peptide (SBP, 13 amino acids) derived from a methionine-rich fragment (MetRich, 53 amino acids) in E. coli CueO through semirational design. The first phase of engineering focused on the structural characteristics of MetRich, pinpointing fragment N394-H406 (SBP 1.0, corresponding to variant CueO-M12) as the key region dominating the binding. Subsequent site-saturation mutagenesis, combined with electrochemical screening, yielded three variants, and among them, the variant CueO-M12-1 (CueO-M12 H398I) exhibited a more uniform favorable orientation with a 1.38-fold increase in current density. Further electrocatalytic kinetics analysis revealed a significant 21.2-fold improvement in kinetics current density (Jk) compared with that of CueO-WT, leading to the development of SBP 2.0. When SBPs were fused to laccase from Bacillus pumilus (BpL) and fungal bilirubin oxidase from Myrothecium verrucaria (MvBOD), respectively, they transformed a sluggish adsorption process into a rapid and oriented one. In addition, compared with SBP 1.0, SBP 2.0 endows BpL and MvBOD with enhanced electrocatalytic capabilities for oxygen reduction and glucose/O2 EFC performance. The engineered SBPs are promising for serving as a versatile "glue" to enable the immobilization of oxidoreductases in an oriented manner, which leads to a breakthrough in bioelectrocatalysis and thereby overcoming the current bottleneck of EFCs.

Decoupling Conductivity, Heterogeneous Electron Transfer Rate, and Diffusion in Organic Molecular Electrocatalysis: Oxygen Reduction Reaction on Poly(3,4-ethylenedioxythiophene).

The electrified production of hydrogen peroxide (H2O2) by oxygen reduction reaction (ORR) is attractive to increase the sustainability of chemical industry. Here the same chains of intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) are utilized, as ORR electrocatalyst, while varying polymeric primary dopants (PSS and Nafion) and the level of secondary doping with DMSO. These changes modulate various properties of the film, such as its microscale organization and electronic conductivity. The aim here is to clearly decouple the rate of the heterogeneous electron transfer (HET) of ORR from the diffusion affected by electronic conductivity and the electrochemically available surface area. It is found that the rate of HET and the double layer capacitance are significantly affected by primary dopant. On the contrary, secondary doping shows very little effect on the rate of HET. However, such secondary doping resulted in the increase of both electrochemically available surface area and the diffusion through the polymer film. This effect is attributed to a few orders increase of the electronic conductivity in the film improving availability of the polymer for electron transfer. The enhancement of diffusion upon the secondary doping of conducting polymer is utilized to improve direct conversion of air into H2O2 on gas diffusion electrode.

Heterogeneous electron transfer on single- and few-layer supported 2D materials

Heterogeneous electron transfer on single- and few-layer supported 2D materials

(Invited) Faradaic Electron Transfer in Inner Helmholtz Plane

Since the electrical double layer (EDL) is where heterogeneous electron transfer occurs, understanding the effects of the electrode-electrolyte interface structure on electrocatalysis is important. The strong electric field in the EDL offers unique environment for electrochemical reactions by altering the solvation structure and mass transport of redox species. Yet, it is challenging to evaluate the physicochemical properties of the matter within EDL, especially for the inner Helmholtz plane (IHP), where most electrochemical reactions occur. This is largely because of the lack of an appropriate model system for experiments. In this talk, the microscopic environment in the IHP of ionic liquids (ILs) is investigated through the reorganization energy reflecting the solvation structure. Exceptionally fast mass transport of Br2 in N-methyl-N-ethyl-pyrrolidinium polybromide allows to obtain bromine reduction voltammograms in which the current plateau is governed by electron-transfer kinetic and to evaluate the reorganization energy based on the Marcus-Hush-Chidsey model. This enables investigation of the microscopic environment in the IHP of the IL affecting electrocatalytic reactions through reorganization energy. As a demonstration, titanium oxide-modified Pt was employed to show pH-dependent reorganization energy, which suggests the switch of major ions at the IHP as a function of surface charges of electrodes. On the other hand, regulating the potential of zero charge (PZC) of electrodes by surface modification and preparation of alloys with various elemental compositions, the surface charge sensitive-ionic structure in ILs is introduced. References Kim, M.; Park, S.; Chung, T. D., Heterogeneous electron transfer reorganization energy at the inner Helmholtz plane in a polybromide redox-active ionic liquid. Chem. Sci. 2022, 13(30), 8821-8828. Kim, M.; Tetteh, E. B.; Savan, A.; Xiao, B.; Ludwig, A.; Schuhmann, W.; Chung, T. D., Reorganization energy in a polybromide ionic liquid measured by scanning electrochemical cell microscopy. J. Chem. Phys. 2023, 158(13), 134707. Kim, M.; Tetteh, E. B.; Krysiak, O. A.; Savan, A.; Xiao, B.; Piotrowiak, T. H.; Andronescu, C.; Ludwig, A.; Chung, T. D.; Schuhmann, W., Acidic Hydrogen Evolution Electrocatalysis at High-Entropy Alloys Correlates with its Composition-Dependent Potential of Zero Charge. Angew. Chem. Int. Ed. 2023, 62(39), e2023100.

Structural and Electrochemical Discussion on Direct Electron Transfer-Type Bioelectrocatalysis By Membrane-Bound Fructose Dehydrogenase from Gluconobacter Japonicus

Oxidoreductases have been utilized as bioelectrocatalysts to realize a variety of biotechnologies, such as biosensors, biofuel cells, solar fuel production, carbon dioxide capture and utilization, and cofactor-regeneration systems. These systems are based on bioelectrocatalysis which couples electrode and enzymatic reactions. Several metalloenzymes can communicate electronically with suitable electrodes without redox mediators. This phenomenon has been termed “direct electron transfer (DET)-type bioelectrocatalysis”. Owing to the mediator-less configuration, the reaction can offer the following benefits in future bioelectrochemical technologies: (i) minimized overvoltage, (ii) low cost, (iii) simple design, (iv) high degree of design freedom, and (v) nontoxic and environmentally friendly properties. However, there have been few reports of enzymes that can realize DET-type bioelectrocatalysis, thus the unique mechanism of the reaction has yet to be elucidated.We focused on a d-fructose dehydrogenase (FDH) from Gluconobacter japonicus NBRC3260, which is known as a model enzyme for DET-type reactions. FDH is a unique enzyme with intense DET-type bioelectrocatalytic activity and has been extensively investigated from electrochemistry, protein engineering, and spectroscopy perspectives. FDH is a heterotrimeric membrane-bound protein with a molecular mass of ca. 138 kDa and is comprised of subunits I (67 kDa), II (51 kDa), and III (20 kDa). Subunit I contains a covalently bound flavin adenine dinucleotide (FAD), and subunit II carries three heme c moieties from its N-terminus called hemes 1c, 2c, and 3c. The redox potentials of hemes c in FDH and several variants were investigated using bioelectrochemical and spectroscopic methods. The DET pathway of FDH was examined with site-directed mutagenesis to replace the axial ligand of heme c or to delete the heme c moiety. These studies have shown that the electron is transferred from the reduced FAD through heme 3c to heme 2c and then to the electrode; heme 1c does not seem to be involved in the reaction. However, the entire three-dimensional (3D) structure of FDH and other DET-type membrane-bound quinohemoproteins, flavohemoproteins, and metallohemoproteins, remained unknown. Therefore, a quantitative discussion of their DET-type reaction was difficult.In the present study, we clarified the 3D structure of FDH using cryo-electron microscopy and single-particle image analysis with a resolution of 2.5 Å (PDB ID: 8JEJ). This is the first study to report the entire structures of membrane-bound flavohemoproteins, quinohemoproteins, and metallohemoproteins capable of DET-type reactions. The structure has revealed the 3Fe-4S iron-sulfur cluster (3Fe4S) in subunit I. The electron transfer (ET) pathway during the catalytic oxidation of d-fructose through FAD, 3Fe4S, and hemes 3c, 2c, and 1c were examined based on Marcus’ theory. In addition, structural analysis has shown the localization of the electrostatic surface charges around heme 2c in subunit II, and experiments using functionalized electrodes with a controlled surface charge support the notion that heme 2c is the electrode-active site. Furthermore, two aromatic amino acid residues (Trp427 and Phe489) were located in a possible long-range ET pathway between heme 2c and the electrode. We constructed variants in which each of the corresponding residues was replaced with alanine (W427A and F489A) by site-directed mutagenesis, and their effects on DET-type activity were investigated by electrochemical measurements. Kinetic analysis of steady-state catalytic waves has revealed that Trp427 plays an essential role in accelerating long-range ET and triples the standard rate constant of heterogeneous ET between enzymes and an electrode.These groundbreaking findings provide vital information for searching for critical elements in DET-type reactions and a reasonable explanation for the outstanding DET-type activity of FDH. The appropriate mutation of aromatic residues to accelerate ET between an enzyme and an electrode will be a novel way to create new DET-type enzymes and innovative biomimetics. Figure 1

Effect of Direct Current and Periodic Polarization on Differential Electrolytic Potentiometric Signal Produced By Carbon Nanotube Electrode

In differential electrolytic potentiometry (DEP), a pair of identical indicator electrodes is polarized using either a very small, heavily stabilized direct current (DC) or a periodic square waveform (SW) of constant amplitude. The square wave can be biased or bias-free. In this study, carbon nanotube-modified silver electrodes, CNT-Ag, were used as the DEP indicating system with all types of polarization. This was done to investigate how the polarization mode affects the signal intensity, shape, position, and amplification. The method was applied to analyze various analytes including ascorbic acid, Fluoroquinolone, cyanide, and chloride using normal titrimetric and sequential injection analysis (SIA) methods. Many of the findings showed that raising the polarizing direct current density (µA/cm2) boosts the DEP peak until reaching a certain point, after which the peaks begin to widen and the position of the peak center shifts. Similar changes were observed when increasing the percentage bias of the square waveform used to polarize the CNT-Ag indicator electrodes. The free-biased square waveform led to the least improvement in peak intensity. As the percentage bias increased, the peak intensity improved up to a certain level. However, beyond that point, all peaks began to broaden without further enhancement in intensity. In all cases, periodic polarization of electrodes produced a much greater enhancement in peak intensities compared to direct current polarization. With square-wave polarization, the ongoing reversal of polarity prevents the accumulation of films on the electrodes, speeds up the response, and substantially reduces electrode fouling and deactivation.Furthermore, aside from the advantages of the periodic polarization, the CNT-Ag electrode, fabricated through chemical vapor deposition with aligned and well-structured CNTs, contributes to boosting the DEP peak intensity by promoting heterogeneous electron transfer. This process facilitates fast equilibrium, leading to precise and reproducible results. Figure 1

(Invited) Innovation in Heterogeneous Catalysis: Constructive Interference at the Interface

Reaction rates are increased by better catalysts and by introduction of energy as heat or pressure. In electrochemical systems, energy is introduced as electrical potential that drives electron transfer across the electrode solution interface. In sonochemical systems, energy is imparted to bulk solvents by ultrasound that generates cavitation bubbles; as cavitation bubbles collapses extremes of temperature (> 5000 C) and pressure (> 1000 atm) are induced in a narrow domain about the collapsed bubble.By coupling sonochemistry and electrochemistry, extremes of pressure are deposited at the electrode solution interface to increase electron transfer rates and to remove passivating layers such as oxides from the electrode surface.The system is built as a thin layer electrochemical cell where sonicator and electrode are separated by about the wavelength of the ultrasound, on the order of a 1 cm. When properly aligned, constructive interference builds pressure at the electrode solution interface at a rate of about 1 J (mole s)-1. The oscillators operate in the range of 40 kHz, with little parasitic loss.Constructive interference in thin layer sonoelectrochemical cells substantially increases rates of O2 reduction and alcohol electrolysis.The financial support of the National Science Foundation (NSF CHE-1309366) is acknowledged. References Chester G. Duda, Brenna Parke, and Johna Leddy, “Thin Layer Sonoelectrochemistry:Impact on Slow Heterogeneous Electron Transfer,” Electrochimica Acta (2023) 468 143118 https://doi.org/10.1016/j.electacta.2023.143118. Daniel L. Parr IV, Chester G. Duda, and Johna Leddy, “Why Sonochemistry in a Thin Layer? Constructive Interference," J. Physical Chemistry C (2023) 127(25) 12184-12193, https://doi.org/10.1021/acs.jpcc.3c00804.Daniel L. Parr IV and Johna Leddy, “To Configure Thin Layer Sonoelectrochemical Experiments,” Journal of the Electrochemical Society (2021) 168(6) 066524, https://iopscience.iop.org/article/10.1149/1945-7111/ac0861.J. Leddy, C. G. Duda, J. Lyon, and W. J. Leddy III, “Thin layer sonochemistry and sonoelectrochemistry devices and methods,” US Patent 10,300,453, May 2019, Assignee: Johna Leddy, https://patents.google.com/patent/US10300453.

Advanced 3D-Printed Flexible Composite Electrodes of Diamond, Carbon Nanotubes, and Thermoplastic Polyurethane.

In this work, we pioneered the preparation of diamond-containing flexible electrodes using 3D printing technology. The herein developed procedure involves a unique integration of boron-doped diamond (BDD) microparticles and multi-walled carbon nanotubes (CNTs) within a flexible polymer, thermoplastic polyurethane (TPU). Initially, the process for the preparation of homogeneous filaments with optimal printability was addressed, leading to the development of two TPU/CNT/BDD composite electrodes with different CNT:BDD weight ratios (1:1 and 1:2), which were benchmarked against a TPU/CNT electrode. Scanning electron microscopy revealed a uniform distribution of conductive fillers within the composite materials with no signs of clustering or aggregation. Notably, increasing the proportion of BDD particles led to a 10-fold improvement in conductivity, from 0.12 S m-1 for TPU/CNT to 1.2 S m-1 for TPU/CNT/BDD (1:2). Cyclic voltammetry of the inorganic redox markers, [Ru(NH3)6]3+/2+ and [Fe(CN)6]3-/4-, also revealed a reduction in peak-to-peak separation (ΔE p) with a higher BDD content, indicating enhanced electron transfer kinetics. This was further confirmed by the highest apparent heterogeneous electron transfer rate constants (k 0 app) of 1 × 10-3 cm s-1 obtained for both markers for the TPU/CNT/BDD (1:2) electrode. Additionally, the functionality of the flexible TPU/CNT/BDD electrodes was successfully validated by the electrochemical detection of dopamine, a complex organic molecule, at millimolar concentrations by using differential pulse voltammetry. This proof-of-concept may accelerate development of highly desirable diamond-based flexible devices with customizable geometries and dimensions and pave the way for various applications where flexibility is mandated, such as neuroscience, biomedical fields, health, and food monitoring.

Vertically Aligned Nanocrystalline Graphite Nanowalls for Flexible Electrodes as Electrochemical Sensors for Anthracene Detection.

Plasma-enhanced chemical vapor deposition (PECVD) was used to obtain several graphite nanowall (GNW)-type films at different deposition times on silicon and copper to achieve various thicknesses of carbonic films for the development of electrochemical sensors for the detection of anthracene. The PECVD growth time varied from 15 min to 30 min to 45 min, while scanning electron microscopy (SEM) confirmed the changes in the thickness of the GNW films, revealing a continuous increase in the series. X-ray diffraction (XRD) analysis revealed that the crystallinity of the GNW film samples increased with increasing crystallite size and decreasing dislocation density as the deposition time increased. Electrochemical characterization of the GNW-based electrodes indicated that the electroactive area and heterogeneous electron transfer rate constant were greater for the GNW 45 min film in the carbonic material series. We present the transfer of GNW films on flexible polyethylene substrates for achieving flexible electrochemical sensors for further use in anthracene determination. The flexible GNW-based electrodes were investigated using differential pulse voltammetry (DPV) in the presence of anthracene. The results showed that the highest sensitivity in anthracene detection was provided by the sensor with the GNW film obtained after 45 min of PECVD growth. The optimization of the GNW film thickness for the development of flexible electrochemical sensors on polyethylene substrates represents a successful approach for enhancing the electrochemical performance of carbonic materials.

Comparison of Au Nanoparticle/Poly(9-vinylcarbazole) Thin-Film Electrogeneration at 3 Distinct Liquid/Liquid Interfaces: Water/1,2-Dichloroethane, /α,α,α-Trifluorotoluene, Or/Ionic Liquid.

Metal nanoparticle (NP) incorporated conductive polymer films are attractive for their mechanical stability for biomedical applications and as heterogeneous electrocatalysis materials. Novel approaches to generate these materials with tunable properties are still being sought. Herein, the interface between two immiscible electrolyte solutions (ITIES) has been employed as a molecularly sharp and reproducible platform for simultaneous Au NP and poly(9-vinylcarbazole) generation. Three interfaces have been compared, including between water|1,2-dichloroethane (w|DCE), water|α,α,α-trifluorotoluene (w|TFT), and water|ionic liquid (w|IL). In this case the IL was P8888TB (tetraoctylphosphonium tetrakis(pentafluorophenyl)borate). 9-Vinylcarbazole (VC) can polymerize via two routes, either propagating through the vinyl substituent or the aryl rings. The former gives rise to a white semiconducting polymer with a wide bandgap, while the latter produces a green, conducting polymer. External potential control through voltammetric cycling was found to generate the film more rapidly favoring heterogeneous electron transfer with formation of the green poly(VC) variant at the ITIES. This was a free-standing film that could be easily removed from the interface. In the absence of external control, white polymer crystals formed within the oil phase spontaneously likely via AuCl4- w → o transfer followed by a homogeneous electron transfer reaction mechanism. Scanning electrochemical microscopy probe approach curve experiments were used to quantify the electroactivity of the film and are complemented by direct conductivity measurements.

A Constrained CASSCF(2,2) Approach to Study Electron Transfer between a Molecule and Metal Cluster.

We have implemented a constrained CASSCF(2,2) calculation so as to study thermal electron transfer between a chlorine ion and a cluster of lithium atoms of variable size (from 1 to 17). Our calculations illustrate how the geometry of the ground state-charge transfer state crossing point (as well as the strength of a diabatic coupling) can depend sensitively on the number of metal ions (i.e., the size of the cluster) and the relative positioning of the donor and acceptor. Thus, this set of calculations is an initial step toward understanding the transition from homogeneous to heterogeneous electron transfer. In the future, these constrained calculations should allow us to model still far larger systems, ideally opening up a pathway to study meaningful electrochemical phenomena.

Enhancing the electrochemical performance of graphite sheet electrodes for ketamine detection

Flexible graphite sheets (GS) have been a promising material for developing electrochemical sensors. In this work, we showed that the electrochemical activation protocol (+1.4 V followed by -1.0 V vs. Ag|AgCl|KCl(sat.) both at 200 s) in alkaline medium (0.5 mol l-1 NaOH) enhances the electrochemical activity of GS. Before the treatment, cyclic voltammetric profile of inner-sphere [Fe(CN)6]3-/4- redox couple at 50 mV s-1 exhibited an ill-defined voltammetric profile (ΔEp = 800 mV) while an increase in the reversibility was achieved (ΔEp = 225 mV) after the treatment. Additionally, the lower charge transfer resistance (Rct) measured by Electrochemical Impedance Spectroscopy (EIS) and a higher heterogeneous electron transfer constant (k0) corroborate with the enhancement in the electrochemical performance of treated GS electrodes. The SEM images revealed an irregular pattern with number of grooves, indicating a partially surface exfoliation and AFM analysis displayed an increase in the roughness. These findings agreed with the estimation of electroactive area which increased 3-times after the treatment. As proof of concept, ketamine (KET), an anesthetic often used as drug of abuse, was determined in synthetic saliva and veterinary pharmaceutical samples using treated GS electrodes and square wave voltammetric measurements. Linear range of 5.0–100.0 µmol l-1 with a limit of detection value of 2.1 µmol l-1 was obtained for KET. Appropriate recovery values (∼105 %) for the analysis of samples were achieved.

Parkinson biomarker determination with an Au microflower-enhanced electrochemical immunosensor using non-Faradaic capacitancemeasurements.

This work comprehends the development and characterization of a carbon black-based electrode modified with Au microflowers to increase its effect as a capacitance biosensor for the determination of PARK7/DJ-1. Due to its high surface-to-volume ratio and biocompatibility, Au particles are suitable for antibody binding, and by monitoring surface capacitance, it is possible to identify the immune-pair interaction. Au microflowers allowed the adequate immobilization of Parkinsonian-related proteins: PARK7/DJ-1 and its antibody. The protein is associated with several antioxidant mechanisms, but its abnormal concentrations or mutations can be the cause of the loss of dopaminergic neurons, leading to Parkinson's disease. The device was characterized by scanning electron microscopy and cyclic voltammetry, revealing the flower-like structures and the electrochemically-interest enhancements they provide, such as increased heterogeneous electron transfer rate coefficient and electroactive area. The self-assembled monolayers of different molecules were optimized with the aid of 22 central composite experiments and a linear calibration curve was obtained between 0.700 and 120ngmL-1 of PARK7/DJ-1, with a limit of detection of 0.207ngmL-1. The data confirms that the addition of Au microflowers enhanced the electrochemical signal of the device, as well as allowed for the determination of an early stage Parkinson's disease biomarker with appreciable analytical performance.

Activated carbon-mediated arsenopyrite oxidation and arsenic immobilization: ROS formation and its role

The oxidative dissolution of arsenopyrite (FeAsS) is a significant source of arsenic contamination in nature. Activated biochar (AC), a widely used environmental remediation agent, is prevalent in ecosystems and participated in various geochemical processes of arsenic and iron-containing sulfide minerals. However, the impact of AC-arsenopyrite association on reactive oxidation species (ROS) generation and its contribution to As transformation were rarely explored. Here, ROS formation and the redox conversion of As during the interaction between AC and arsenopyrite were investigated. AC-mediated arsenopyrite oxidation was a two-stage process. At stage I, the heterogeneous electron transfer from arsenopyrite facilitated O2 reduction on AC, enhancing arsenopyrite dissolution and ROS formation. TBA, PBQ and catalase inhibited 86.40 %, 79.39 % and 49.66 % of As(III) oxidation, respectively, indicating indicated that HO˙, (O2•)- and H2O2 were responsible for As(III) oxidation. However, at stage II, the mobility of As was highly restricted, especially increasing AC addition. Besides adsorption, AC retained appreciable As through catalyzing insoluble ferric arsenate formation and growth by promoting Fe(II) and As(III) oxidation and functioning as nuclei. These findings deepen our understanding of the coupling behavior of AC-arsenopyrite and its influence on geochemical cycling of arsenic in mined surroundings, which has important implications for mitigating arsenic pollution.

Unlocking Interfacial Interactions of In Situ Grown Multidimensional Bismuth‐Based Perovskite Heterostructures for Photocatalytic Hydrogen Evolution

AbstractTo combat the energy crisis and environmental pollution, developing renewable energy technology such as hydrogen (H2) production is necessary. The sulfur–iodine thermochemical cycle has high commercial potential in conducting hydrogen iodide (HI) splitting for H2 generation, but it requires high‐temperature conditions. In comparison, photocatalytic HI splitting of halide perovskites is non‐polluted and low‐cost for H2 production at room temperature. Herein, an in situ constructed multidimensional bismuth (Bi)‐based 3D/2D EDABiI5/MA3Bi2I9 perovskite heterojunction is developed first by synergistically integrating dimensionality control with heterostructure engineering. Accordingly, the optimal EDABiI5/MA3Bi2I9 without any co‐catalysts exhibits the H2 evolution rate of 213.63 µmol h−1g−1 under irradiation. Equally importantly, interfacial dynamics of solid/solid and solid/liquid interfaces play a crucial role in photocatalytic performance. Therefore, using temperature‐dependent transient photoluminescence and electrochemical voltammetric techniques, it is confirmed that the exciton transportation of EDABiI5/MA3Bi2I9 is accelerated by stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions. Moreover, the effective diffusion coefficient and electron transfer rate of EDABiI5/MA3Bi2I9 demonstrate efficient heterogeneous electron transfer, resulting in improved photocatalytic hydrogen production. Consequently, the in situ formation of perovskite heterostructures studied by a combination of photophysical and electrochemical techniques provides new insights into green hydrogen evolution and interfacial interaction dynamics for commercial applications of solar‐to‐fuel technology.

2D/1D VSe2/MWCNT hybrid-based electrochemical sensor for carbendazim quantification of environmental, food, and biological samples.

Forthe first time the sensitive determination of carbendatim (CRB) is reportedutilizing a well-designed sensing architecture based on vanadium diselenide-multiwalled carbon nanotube (VSMC). FTIR, XRD, FESEM, EDS, and EIS were employed to evaluate the sensor's structural integrity, and the results demonstrated the successful integration of nanomaterials, resulting in a robust and sensitive electrochemical sensor. Cyclic voltammetry (CV) and chronoamperometric (CA) investigations showed that the sensor best performed at pH 8.0 (BRB) with an excellent detection limit of 9.80nM with a wide linear range of 0.1 to 10.0µM. A more thermodynamically viable oxidation of CRB was observed at the VSMC/GCE, with a shift of 200mV in peak potential towards the less positive side compared with the unmodified GCE. In addition, the sensor demonstrated facile heterogeneous electron transfer, favorable anti-fouling traits in the presence of a wide range of interferents, good stability, and reproducible analytical performance. Finally, the developed sensor was validated for real-time quantification of CRB from spiked water, food, and bio-samples, which depicted acceptable recoveries (98.6 to 101.5%) with RSD values between 0.35 and 2.23%. Further, to derive the possible sensing mechanism, the valence orbitals projected density of states (PDOS) for C, H, and N atoms of an isolated CRB molecule, VSe2 + CNT and VSe2 + CNT + CRB were calculated using density functional theory (DFT) calculations. The dominant charge transfer from the valence 2p-orbitals of the C and N atoms of CRB to CNT is responsible for the electrochemical sensing of CRB molecules.

The Electrostatic Stimulation of Adsorbed Carbon Monoxide Oxidation on Pt in Aqueous Acidic Electrolytes

The oxidation of adsorbed carbon monoxide on Pt electrodes, CO(ads)|Pt, in aqueous electrolytes ranks among the most studied reactions in electrocatalysis both from theoretical[1]and experimental viewpoints.[2][3] Much of the interest in this electron transfer process stems from the role CO(ads) plays as an impurity that affects adversely the operation of H2|O2 fuel cells. Consensus appears to have been reached regarding the role of adsorbed hydroxyl, OH.(ads) in controlling the activation and ultimate oxidation of CO(ads). The present contribution illustrates the use of electrochemical stimulation techniques developed in our laboratory[4] to explore new aspects of this process not as yet unveiled by the use of more conventional methods. As described in our earlier publications,[4,5] electrode stimulation refers to changes in the rates of heterogeneous electron transfer processes involving adsorbed species induced by modifications in the electrostatic potential in the solution immediately adjacent to the electrode generated by the passage of current between an electrode placed very close to the working electrode, WE, polarized at constant potential, and a second electrode far away from it. The electrochemical cell used for these experiments consisted of a glass tube covered at each end with custom-made Teflon caps and, thus, similar in design to that described by Qi et al.[4] Experiments were performed in Ar-purged 0.1 M H2SO4 involving CO adsorbed at saturation coverages on polycrystalline Pt, polarized at EWE = 0.8 V, a potential very close to the onset of CO(ads) oxidation with a Au disk electrode placed directly above it working as a stimulating electrode, SE, i.e. face to face configuration. Shown in Fig. 1 are plots of the current flowing through the SE (red), iSE and iWE (black) (see Left Panel) and their expanded views during stimulation (Middle Panel) and CO full oxidation (Right Panel), respectively. As shown in the middle panel in this figure. the passage of a negative iSE, elicits a positive iWE ascribed to CO oxidation, which persists even when iSE turns positive, until the end of the stimulation process (see Right Panel), which takes several seconds. In brief, a single stimulation lasting 140 ms can trigger the full oxidation of the entire adsorbed CO layer in CO|Pt over a subsequent period of ca. 4 s. The most likely explanation for this unique effect may be found in the formation of adsorbed OH. on sites previously covered with CO, as the CV of bare Pt would strongly suggest, which will promote the subsequent oxidation of CO(ads), a process that will propagate through the entire Pt surface. Further support for this mechanism was provided by an experiment in which the WE potential was stepped down to 0.4 V immediately after the stimulation was applied, which stopped virtually instantaneously the further oxidation of CO(ads). Experiments are now in progress to image the surface of the CO|Pt electrode during and after the stimulation to monitor in real time the rates of propagation and to provide a more details theoretical model to account for this phenomenon. References 1 Gao, W.; Mueller, J.E.; Jiang, Q.; Jacob, T. Angew. Chem. Int. Ed. 2012, 51, 9448 –94522 Scott, S.B.; Kibsgaarda, J.; Vesborga, P.C.K.; Chorkendorff, I. Electrochim. Acta 2021, 374, 1378423 Scott, S.B.; Kibsgaarda, J.; Vesborga, P.C.K.; Chorkendorff, I. Electrochim. Acta 2021, 374, 1378444 Han, Q.; Georgescu, N. S.; Gibbons, J.; Scherson, D. Electrochim. Acta 2019, 325, 1349575 Heer, A.S.; Mantelli, H; Han, Q.; Georgescu, N. S.; Scherson, D. in preparation. Acknowledgement Support for this work provided by NSF, CHE-1808592.Fig. 1. Plots of iWE and iSE recorded for EWE = 0.8 V prior, during and following WE stimulation (see text for details) (Left Panel). The middle and right panels show expanded views of the data in the left panel during stimulation and CO full oxidation, respectively. Figure 1