Direct Electron Transfer Process Research Articles

Modulating the adsorption orientation of methionine-rich laccase by tailoring the surface chemistry of single-walled carbon nanotubes

Achieving fast electron transfer process between oxidoreductase and electrodes is pivotal for the biocathode of enzymatic biofuel cells (EBFCs). However, in-depth understanding of the interplay mechanism between enzymes and electrode materials remains challenging when designing and constructing EBFCs. Herein, atomic-scale insight into the direct electron transfer (DET) behavior of Thermus thermophilus laccase (TtLac) with a special methionine-rich β-hairpin motif adsorbed on the carboxyl-functionalized carbon nanotube (COOH-CNT) and amino-functionalized carbon nanotube (NH2-CNT) surfaces were disclosed by multi-scale molecular simulations. Simulation results reveal that electrostatic modification is an effective way to tune the DET behavior for TtLac on the modified-CNTs electrode surface. Surprisingly, the positively charged TtLac can be attracted by both negatively charged COOH-CNT and positively charged NH2-CNT surfaces, yet only the latter is capable to trigger the DET process due to the ‘lying-on’ adsorption orientation. Specifically, the T1 copper site is near the methionine-rich β-hairpin motif, which is the key binding site for TtLac binding onto the NH2-CNT surface via electrostatic interaction, π−π stacking and cation−π interaction. Moreover, TtLac on the NH2-CNT surface undergoes less conformational changes than those on the COOH-CNT surface, which allows the laccase stability and catalytic efficiency to be well preserved. These findings provide a fundamental guidance for future design and fabrication of methionine-rich laccase-based EBFCs with high power output and long lifespan.

Enhanced electrochemical oxidation of tetracycline and atrazine on SnO2 reactive electrochemical membranes by low-toxic bismuth, cerium doping

SnO2-Sb electrodes are widely used in electrochemical advanced oxidation processes for water treatment; however, the release of highly toxic Sb3+/Sb5+ has aroused environmental concern. This study systematically investigated the potential of Bi and Ce elements as substitutes to fabricate doped-SnO2 reactive electrochemical membrane (REM) for water purification. Compared with the control (SnO2-Sb-REM), SnO2-Bi-REM showed a higher direct electron transfer (DET) rate and •OH yield due to its larger electroactive surface area. The higher oxygen evolution potential of SnO2-Ce-REM enhanced selectivity for •OH generation. Although both SnO2-Bi-REM and SnO2-Ce-REM exhibited higher electrooxidation of tetracycline hydrochloride (TCH) and atrazine (ATZ) than SnO2-Sb-REM, only the service lifespan of SnO2-Bi-REM can meet the requirements of practical applications. Mechanistic studies of the degradation pathways indicated that the rapid degradation of TCH on SnO2-Bi-REM was mainly contributed by the DET process, while the transformation of intermediates involved the reactions with •OH. In comparison, aqueous •OH played an important role in the degradation of refractory ATZ. Moreover, a SnO2-Bi-REM system demonstrated ∼99% removal of trace TCH and ATZ from wastewater effluent in single-pass operation at a low electrical efficiency per log order removal (EE/O, 0.71 kWh m−3). To this end, the SnO2-Bi-REM is demonstrated to be a promising electrode to replace SnO2-Sb-REM for efficient and sustainable water purification.

Synergistic effects between graphite nanosheets and OMS-2 to enhance the direct electron transfer process-based peroxymonosulfate activation for pollutants degradation

The abundant and low-cost manganese oxides have attracted increasing interest in peroxymonosulfate (PMS) activation. Nevertheless, the low zeta potentials and surface area of the catalysts lead to weak adsorptions of PMS and pollutants under neutral and basic conditions, and thus the low degradation efficiency. Herein, a promising hybrid from graphite nanosheets (GNs) and cryptomelane-type manganese octahedral molecular sieves (OMS-2) was developed by a simple redox method at room temperature. The catalysts possessed a high surface area and a great number of surface defects, which enhanced the adsorption of PMS; while the introduction of GNs increased the capacity of pollutants adsorption and the rate of electron transfer. Compared with pure OMS-2 and other catalysts, the hybrid catalyst showed a much higher performance for acid orange 7 degradation at pH 8.2 with a first-order rate constant of 0.414 min−1, due to the above synergistic effects between OMS-2 and GNs. Based on quenching experiments, PMS decomposition and degradation of pollutants with different oxidation potentials, a direct electron transfer process through Mn-O-PMS complexes was identified to contribute the degradation. Moreover, a galvanic oxidation system was set up to further confirm the occurrence of the mechanism. Overall, this work provides an important step in developing Mn-based hybrids for organic pollutants degradation.

Integrated flow anodic oxidation and ultrafiltration system for continuous defluorination of perfluorooctanoic acid (PFOA)

While flow anodic oxidation systems can efficiently generate hydroxyl radicals (·OH) and significantly enhance direct electron transfer (DET) processes that result in the oxidation of target contaminants via the charge percolating network of flow anode particles, challenges remain in constructing a flow anodic oxidation system that can be operated continuously with stable performance. Here we incorporate an ultrafiltration (UF) membrane module into the flow anodic oxidation system and achieve the continuous defluorination of perfluorooctanoic acid (PFOA) for 12 days with high efficiency (94.1%) and reasonable energy consumption (38.1 Wh mg–1) compared to other advanced oxidation processes by using a mixture of conducting TixO2x-1 and Pd/CNT particles as the flow anode. The results indicate that DET, ·OH mediated oxidation and adsorption processes play critical roles in the degradation of PFOA during the flow anodic oxidation processes. The synergistic effect of the TixO2x-1 and Pd/CNT particles enhances the defluorination efficiency by 3.2 times at 4.5 V vs Ag/AgCl compared to the control experiment (no flow anode particles present) and promotes the release of F– into solution while other intermediate products remain adsorbed to the surface of the Pd/CNT particles. Although the Pd/CNT particles were oxidized after the long-term operation, no obvious Pd ion leakage into solution was observed. Results of this study support the feasibility of continuous operation of a flow anode/UF system with stable performance and pave the way for the translation of this advanced oxidation technology to practical application.

Photoactive Manganese Ferrite-Modified Bacterial Anode to Simultaneously Boost Both Mediated and Direct Electron Transfer Processes in Microbial Fuel Cells

Photoactive Manganese Ferrite-Modified Bacterial Anode to Simultaneously Boost Both Mediated and Direct Electron Transfer Processes in Microbial Fuel Cells

Cellular electron transfer in anaerobic photo-assisted biocathode microbial electrosynthesis systems for acetate production from inorganic carbon (HCO3–)

The crucial role played by the cellular electron transfer in the production of acetate from aqueous inorganic carbon (HCO3–, bicarbonate) in anaerobic photo-assisted microbial electrosynthesis (MES) biocathodes incorporating a WO3/MoO3/g-C3N4 Z-scheme heterojunction and either Serratia marcescens Q1 or Stenotrophomonas sp. JY6 electrotrophs is disclosed. The electron transfer inhibitor 2,4-dinitrophenol (DNP) diffusing through the bacterial cell membrane was used to alter the ratio of indirect (via H2) and direct extracellular electron transfer processes, resulting in lower physiological release of extracellular polymeric substances (EPS) and lower acetate production rates under a transitional period. DNP effectively cancelled the synergistic effects on acetate production produced by the photo-irradiation of the WO3/MoO3/g-C3N4 heterojunction biocathode. The physiological release of EPS with either a compositional diversity (Q1) or varying composition percentages (Q1 or JY6), was correlated to photo-irradiation and to the electrotrophic species, whereas the total amount of EPS was closely related with the electrotrophic DNP-based cellular electron transfer processes. Interestingly, the microorganisms adapted and overcame the impact of DNP after only 4 days of continuous operation and restored their normal physiological metabolism after 7.5 d operation with periodical replenishment of bicarbonate. This study provides a detailed theoretical basis to understand the impact of direct and indirect extracellular electron transfer in hybrid photo-assisted MES biocathodes and elucidates the behavior of non-photosynthetic electrotrophic bacteria favoring high conversion of aqueous inorganic carbon (HCO3–) to acetate.

Peroxymonosulfate activation by brownmillerite-type oxide Ca2Co2O5 for efficient degradation of pollutants via direct electron transfer and radical pathways

• Ca 2 Co 2 O 5 catalyst with multiple Co oxidation states was prepared. • The catalyst showed high activity and stability via PMS activation. • Both radicals and direct electron transfer process contribute to the reaction. • The role of Co species with different oxidation states was discussed. The development of mixed metal oxides with excellent activity and stability for pollutants degradation via peroxymonosulfate (PMS) activation is highly desired in recent years. In this work, the brownmillerite-type oxide, Ca 2 Co 2 O 5 (CCO) with unique Ca 2 CoO 3 and CoO 2 layer structure and multiple oxidation states such as Co(II), Co(III) and Co(IV), was prepared and used to degrade organic pollutants with PMS as oxidant for the first time. It was found that CCO exhibited higher activity than other Co-based catalysts such as Co 2+ and Co 3 O 4 , and more than 93% of acid orange 7 (50 μM) was degraded after 7.5 min under mild reaction conditions. The catalysts were also stable during five successive runs. The easy oxidation of Co(II) species, the strong interactions among CCO, PMS and the pollutants, and the synergistic effect between Co and Ca were identified by several technologies and contributed to the high performance of the catalyst. Moreover, different from the conventional mechanism, radicals produced from low valent Co species oxidation by PMS, as well as the direct electron transfer process through the high valent Co species contributed the degradation reaction simultaneously. These findings provide an ideal bimetallic heterogeneous catalyst and a new mechanism for PMS-mediated reaction.

Direct electron transfer process-based peroxymonosulfate activation via surface labile oxygen over mullite oxide YMn2O5 for effective removal of bisphenol A

The development of efficient and eco-friendly Mn-based catalysts for peroxymonosulfate (PMS) activation and revealing the mechanism are highly desired for pollutants removal in wastewater. In this study, a ternary mullite oxide YMn2O5 (YMO) was synthesized for bisphenol A (BPA) degradation in the presence of PMS for the first time. Combined with XPS, EPR and TG, abundant surface labile oxygen species (Olab) with a ratio of 39.7% were identified in the mullite materials, which was higher than that for α-, β-, γ- and δ-MnO2. YMO also exhibited higher interfacial conductivity and stronger interactions among the catalyst, PMS and BPA than other MnO2. Superior performance in BPA degradation was observed with YMO, and Olab was suggested as the main active sites, for the normalized first-order rate constant was linearly dependent on the ratio of the oxygen species. Chemical quenching experiments, EPR and open circuit potential suggested that the degradation of BPA was mainly caused by the direct electron transfer process through the reactive Olab-PMS complexes. The influence of YMO concentration, PMS concentration, solution pH, different anions and reaction temperature was thoroughly studied. Moreover, the intermediates were identified and the possible degradation pathways were proposed. This work demonstrated that mullite oxide YMO with enriched Olab species can be used as eco-friendly catalysts for efficient PMS activation to remove recalcitrant organic compounds in wastewater.

Combining metal-microbe and microbe-microbe dual direct electron transfer on Fe(0)-cathode of bio-electrochemical system to enhance anaerobic digestion of cellulose wastewater

Considering that cathode of microbial electrochemical system (MES) is a good electrons source for methane production via direct/indirect electron transfer to electroactive microorganisms, and that Fe(0) is also a confirmed electron donor for some electroactive microorganisms through metal-microbe direct electron transfer (DET), Fe(0)-cathode was equipped into an MES digester to enhance cathodic methane production. The results of this study indicated that the potential DET participator, Clostridium possibly obtained electrons directly from Fe(0)-cathode via metal-microbe electrons transfer, then transferred electrons directly to the definite DET participators, Methanosarcina/Methanothrix via microbe-microbe electrons transfer for CH4 production. In addition, Methanobacterium is another specially enriched methanogen on Fe(0)-cathode, which might obtain electrons directly from Fe(0)-cathode to produce CH4via metal/electrode-microbe DET. The increment of conductivity of cathodic sludge in Fe(0)-cathode MES digester (R1) further confirmed the enrichment of electroactive microorganisms participating in DET process. As a consequence, a higher CH4 production (1205–1508 mL/d) and chemical oxygen demand (COD) removal (79.0%-93.8%) were achieved in R1 compared with graphite-cathode MES digester (R2, 720–1090 mL/d and 63.6%-85.6%) and the conventional anaerobic digester (R3, 384–428 mL/d and 35.2%-41.0%). In addition, energy efficiency calculated indicated that the output energy of CH4 production was 8.16 folds of electricity input in Fe(0)-cathode MES digester.

Direct electron transfer (DET) processes in a flow anode system–Energy-efficient electrochemical oxidation of phenol

In flow anode systems, surface-bound hydroxyl radicals (*OH) are generated at the solid-liquid interface of suspended particulate charge carriers at potentials well below that required for oxygen evolution as a result of water splitting. While these surface-bound radicals are powerful indiscriminant oxidants that often lead to complete mineralization of organic pollutants, the more selective process of direct electron transfer (DET) may also occur at the particle electrode interfaces and play a critical role in the degradation of some contaminants. In this study, we investigated DET processes in a flow anode system in which carbon black was utilized as the flow anode material and Pt, Ti, IrRu and IrTa meshes were used as the current collectors. The results indicate that the use of a carbon black flow anode enhanced the DET rate by 20 times at 1.0 V vs Ag/AgCl compared to the control experiment with no carbon black particles present. Low solution conductivity had a more obvious negative effect on the DET process (compared to *OH mediated oxidation) due to the high potential drop and inhibition of mass transfer processes at the solid-liquid interfaces of the anode particles. The DET rates were dependent on the particular anode current collector used (i.e., Ti, IrRu, IrTa or Pt mesh) with differences in rates ascribed to the electron transfer resistance of the current collectors in the flow anode system. Detailed investigation of the degradation of phenol in a flow anode system revealed that this widely studied contaminant could be degraded with an energy consumption of 3.08 kWh m−3, a value substantially lower than that required with other techniques. Results of this study provide a better understanding of the DET mechanism at the solid-solid and solid-liquid interfaces with these insights expected to benefit the design of flow anode materials and current collectors and lead to the improvement in performance of flow anode systems.

Anchoring CuFe2O4 nanoparticles into N-doped carbon nanosheets for peroxymonosulfate activation: Built-in electric field dominated radical and non-radical process

Radical and non-radical dominated PMS activation has been widely researched, but the driving force of this process is not well understood. Herein, CuFe2O4 nanoparticles anchored on nitrogen-doped carbon nanosheets (CFONC-2) was prepared for investigation. Experimental results and DFT calculations indicate that a built-in electric field (BIEF) is formed between CuFe2O4 and N-doped carbon nanosheets, which is proposed as the driving force to adjust the electron transfer for triggering radical and non-radical pathway. Specifically, Cu+/Cu2+ and Fe2+/Fe3+ redox cycles are regarded to be the dominant catalytic sites for radical generation (SO4•–, HO• and •O2–). Whereas graphitic N, sp2-hybridized structure, as well as C = O functional group are main active sites for non-radical production (1O2 and direct electron transfer process). Under the radical and non-radical processes dominated by BIEF, the CFONC-2/PMS system exhibits excellent removal performance of levofloxacin (LVFX), where 84.87% of LVFX is removed in 90 min. This work offers a feasible strategy for designing metallic oxides-carbon catalyst with strong electric field effect to satisfy the charge transfer in PMS catalytic reaction.

Enhanced mechanism of extracellular electron transfer between semiconducting minerals anatase and Pseudomonas aeruginosa PAO1 in euphotic zone

Focusing the marine euphotic zone, which is the pivotal region for interaction of solar light-mineral-microorganism and the elements cycle, we have conducted the research on the mechanism of semiconducting minerals promoting extracellular electron transfer with microorganisms in depth. Therein, anatase which is one of the most representative semiconducting minerals in marine euphotic zone was selected. The mineralogical characterization of anatase was identified by ESEM, AFM, EDS, Raman, XRD, and its semiconducting characteristics was determined by UV–Vis and Mott-Schottky plots. Determined by the electrochemical measurement of I-t curves, the photocurrent density of anatase was more prominent than dark current density. Pseudomonas aeruginosa PAO1 was widely distributed in the euphotic zone, and its mutants of operons deficient in biosynthesis pyocyanin (Δphz1Δphz2) and pili deficient (ΔpilA) were employed in this study. I-t curves indicated that both direct and indirect extracellular electron transfer processes occurred between anatase and PAO1. The indirect electron transfer depending on pyocyanin secreted by PAO1 was the main electron transfer mode. This work demonstrated the light-driven extracellular electron transfer and further revealed the photo-catalyzed mechanisms between anatase and PAO1 in marine euphotic zone.

Direct electron transfer process of pyrroloquinoline quinone–dependent and flavin adenine dinucleotide–dependent dehydrogenases: Fundamentals and applications

Pyrroloquinoline quinone–dependent and flavin adenine dinucleotide–dependent enzymes catalyze the oxidation of various compounds. These enzymes are large molecules, and the embedding of active sites in the insulating portion of the molecule generally make direct bioelectrocatalysis difficult. Dehydrogenases with a built-in electron transfer domain are capable of direct electron transfer (DET) to an electrode. Attempts have also been made to realize DET by artificially producing fusion proteins in which protein engineering is fully exploited to connect electron transfer domains. Furthermore, the reports of the DET of enzymes without an electron transfer domain to an electrode have started to appear. This review summarizes recent reports on fundamental findings on DET and applications using DET-enzyme electrodes.

Electrografted Interfaces on Metal Oxide Electrodes for Enzyme Immobilization and Bioelectrocatalysis

AbstractIn this work, we demonstrate that diazonium electrografting of biocompatible interfaces on transparent conducting oxide indium tin oxide (ITO) can be controlled and optimized to achieve low charge transfer resistance, allowing highly efficient electron transfer to an immobilized model enzyme, the oxygen‐tolerant [NiFe]‐hydrogenase from Ralstonia eutropha. The use of a radical scavenger enables control of the interface thickness, and thus facilitates maximization of direct electron transfer processes between the enzyme's active center and the electrode. Using this approach, amine and carboxylic acid functionalities were grafted on ITO, allowing enzyme immobilization both under moderate electrostatic control and covalently via amide bond formation. Despite an initial decrease in catalytic activity, covalent immobilization led to an improvement in current stability compared to just electrostatically immobilized enzyme. Given the superior stability of electrografted interfaces in comparison to adsorbed or self‐assembled interfaces, we propose electrografting as an alternative approach for the functional immobilization of redox‐active enzymes on transparent conducting oxide (TCO) electrodes in bioelectronic devices.

Proton-coupled electron transfer of catechin in tea wine: the enhanced mechanism of anti-oxidative capacity.

Tea wine is a Chinese traditional alcoholic drink made by cereal and tea leaves. It is rich in tea polyphenols, caffeine, amino acids, and protons and possesses various healthcare functions. In this work, electrochemical methods, as well as density functional theory (DFT) calculations, were adopted to reveal the proton-coupled electron-transfer process of catechin in tea wine. The electrochemical results showed that the catechin preferred hydrogen-bonding with ethanol and formed molecular clusters. Thus, the direct electron-transfer process of catechin changed to proton-coupled electron transfer. This procedure reduced the energy barrier of the redox reaction and enhanced the anti-oxidative capacity. Subsequently, DFT calculations were employed to explore the bond length, bond energy, and HOMO–LUMO energy gap of catechin, which confirmed the above-mentioned mechanism. Our work offers some positive value for the scientific promotion of traditional food and a greater understanding of the health mechanisms in terms of chemistry.

Production of bioelectricity may play an important role for the survival of Xanthomonas campestris pv. campestris (Xcc) under anaerobic conditions

The plant pathogen Xanthomonas is commonly found in biocontaminated bioreactors; however, few studies have evaluated the growth and impacts of this microorganism on bioreactors. In this study, we examined the characteristics of Xanthomonas campestris pv. campestris (Xcc). Our results showed that Xcc could reduce metal Fe (III) and decolorise methyl orange in vitro. Moreover, I-t and cyclic voltammetry curves showed that Xcc could generate bioelectricity and had two extracellular electron transfer pathways, similar to that of Shewanella. Based on the spectral analysis of intact cells and scanning electron microscopy analysis, one pathway was speculated to involve cytochrome C by direct contact with the pili or cell surface. The other pathway may involve indirect mediators, such as redox substrates, among extracellular polymeric substances. For the direct extracellular electron transfer process, the charge transfer coefficient α, electron number n, and the electron transfer rate constant ks were determined to be 0.49, 2.6, and 2.2 × 10−3 s−1, respectively. In the indirect extracellular electron transfer processes, the values of α, n, and ks were 0.52, 4, and 1.21 s−1, respectively. Of these two transfer methods, indirect electron transfer is dominant and faster than direct electron transfer. Moreover, after mutation of the dsbD gene, which is important for indirect electron transfer, the electrochemical parameters α, n, and ks decreased. Our findings reveal a new anaerobic mechanism mediating the survival of Xcc during wastewater treatment, and may help develop new strategies for preventing Xcc growth during wastewater treatment.

Molecularly wiring of Cytochrome c with carboxylic acid functionalized hydroquinone on MWCNT surface and its bioelectrocatalytic reduction of H2O2 relevance to biomimetic electron-transport and redox signalling

The electron-transport chain that involves a proton-coupled electron-transfer (ET) reaction between hydroquinone (H2Q) and Cytochrome c (Cyt c) in the acid pool is one of the key processes of the respiratory complex 1 in cytoplasmic membrane of the bacterium and mitochondrial complexes, complex III (cytochrome bc1 or ubiquinol:cytochrome c oxidoreductase) of photosynthesis systems. In the literature, several spectroscopic techniques in association with electron-transfer inhibitors have been reported for this purpose. Till now, there is no straight forward voltammetric proof to reveal the mechanistic feature of the direct ET process. In the electrochemistry point of view, it is a challenging task to prepare a chemically modified bio-electrode composed of H2Q and Cytc redox systems with proper ET channels between them and to probe the mixed-potential reaction by direct voltammetric technique. Herein, we report a carboxylic acid functionalized hydroquinone (2,5-dihydroxy benzoic acid; H2Q-COOH) immobilized multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT@H2Q-COOH), prepared by in-situ electrochemical oxidation of 2-hydroxy benzoic acid (Ph-COOH), as a molecular wiring system for unfolded Cytc protein and further to study the direct voltammetric ET reaction using H2O2 as a specific probe in pH 2 KCl-HCl medium. The formation of surface-confined H2Q-COOH was confirmed by physicochemical and spectroscopic characterization techniques including IR, Raman, UV-Vis, Thin-layer chromatography, NMR and GC-MS. The GCE/MWCNT@H2Q-COOH showed well-defined redox peaks corresponding to consecutive one-electron-transfer reactions of H2Q-COOH/•QH-COOH (Eo'= 0.410 V vs Ag/AgCl, A1/C1) and •QH-COOH/Q (Eo'= 0.750 V vs Ag/AgCl, A2/C2), similar to one occurs with a membrane-bound ubiquinone and plastoquinone systems in the biological systems. The unfolded Cytc modified electrode, GCE/MWCNT@H2Q-COOH@Cytc prepared by chemical modification technique, has exhibited a specific and selective bioelectrocatalytic reduction current signal in between the redox potentials of QH2/•QH and Cytc in pH 2 KCl-HCl biomimicking the biological electron-transport chain reaction. In further amperometric techniques have been used to successfully demonstrate the ET reaction.

Direct Electrochemical Enzyme Electron Transfer on Electrodes Modified by Self-Assembled Molecular Monolayers

Self-assembled molecular monolayers (SAMs) have long been recognized as crucial “bridges” between redox enzymes and solid electrode surfaces, on which the enzymes undergo direct electron transfer (DET)—for example, in enzymatic biofuel cells (EBFCs) and biosensors. SAMs possess a wide range of terminal groups that enable productive enzyme adsorption and fine-tuning in favorable orientations on the electrode. The tunneling distance and SAM chain length, and the contacting terminal SAM groups, are the most significant controlling factors in DET-type bioelectrocatalysis. In particular, SAM-modified nanostructured electrode materials have recently been extensively explored to improve the catalytic activity and stability of redox proteins immobilized on electrochemical surfaces. In this report, we present an overview of recent investigations of electrochemical enzyme DET processes on SAMs with a focus on single-crystal and nanoporous gold electrodes. Specifically, we consider the preparation and characterization methods of SAMs, as well as SAM applications in promoting interfacial electrochemical electron transfer of redox proteins and enzymes. The strategic selection of SAMs to accord with the properties of the core redox protein/enzymes is also highlighted.

Novel synthesis of carbon nanofiber aerogels from coconut matrix for the electrochemical detection of glucose

Bacterial cellulose aerogels (BCAs) were obtained from a delicious food grade coconut. Following with a simple process of carbonized calcination (700 °C~1100 °C). The obtained coconut matrix carbon nanofiber aerogels (CMCNFs) exhibit low density (≤3.47 mg/cm3), high surface area (≥1102 m2/g), and high porosity (≈99.6%), which are much higher than those of common BCAs owing to the removal of hydrogen, oxygen and other elements along with only small volume changes. Due to the flexibility of the nanofiber matrix of our presoma, the three-dimensional network micro-structure is preserved during high temperature carbonization process. The obtained CMCNFs show an excellent conductivity bearing a direct electron transfer process between glucose oxidase (GOx) and electrode surface in the electrochemical processes. It was discovered that CMCNFs can achieve a fast direct electron transfer (DET) of GOx to the rapid detection of glucose. This character should be related to the three-dimensional pore structure determined by carbonization temperature, which has been proved that the CMCNFs calcined at 1000 °C possesses the best capabilities. With merits above, a highly sensitive glucose sensor is successfully prepared by the simple carbonization of coconut cellulose matrix, which expands the application scope of bacterial cellulose aerogels. This work also offers insights for the future develop of protein-based electrochemical devices.

Plasmonic Enhancement Mechanism of Template‐Based Synthesized Au@TiO2 Nanodiscs

AbstractThe localized plasmon resonance enhancement mechanisms were investigated as a function to increase the shell thickness of the prepared hexagonal nanodiscs arrays of Au@TiO2 core‐shell. The bare Au hexagonal nanodiscs array exhibited multiple plasmon resonance modes in the ultraviolet (UV) to near‐infrared (NIR) region. Au@TiO2 nanodiscs configuration present three different enhancement mechanisms with increasing TiO2 shell thickness. First, a strengthened plasmon‐induced resonance energy transfer (PIRET) for higher plasmonic resonance mode in the UV region. Second, redshifted and broadened direct electron transfer (DET) processes for the plasmonic dipole resonance mode from the Vis to the NIR region. Third, an increased hybridization retardation effect for the higher plasmonic mode in the Vis region. By using a facile and cost‐effective technique (nonlithographic route) to fabricate highly ordered core‐shell nanodiscs arrays (Au@TiO2 hexagonal nanodiscs) on a large area of Si substrate (>cm2) via an ultrathin alumina membrane (UTAM), this technique provides a perfect shadow mask to fabricate Au nanodiscs arrays; furthermore, the shadow effect of UTAM pores offers enough space to cover Au nanodiscs by the TiO2. These plasmonic core‐shell nanodiscs reveal a highly promising pathway to discovering new enhancement phenomena that can be applied in diverse applications such as plasmon‐enhanced energy conversion, biosensing, and surface‐enhanced vibrational spectroscopy.