Decreased Electron Transfer Resistance Research Articles

Enhancing methane production and interspecies electron transfer of anaerobic granular sludge by the immobilization of magnetic biochar

Supplementation of conductive materials has been proved to be a promising approach for enhancing microbial interspecies electron transfer (IET) in anaerobic digestion systems. In this study, magnetic bamboo-based biochar was prepared at temperatures of 400–800 °C via a ball milling/carbonization method, and it immobilized in mature anaerobic granular sludge (AGS) aimed to enhance methane production by improving the IET process between syntrophic microbial communities in the AGS. Results showed that the AGS with magnetic biochar immobilization demonstrated increased glucotrophic and acetotrophic methane production by 69.54–77.56 % and 39.96–54.92 %, respectively. Magnetic biochar prepared at 800 °C with a relatively higher Fe content (0.37 g/g magnetic biochar) displayed a stronger electron charge/discharge capacity (36.66 F/g), and its immobilization into AGS promoted methane production most. The conductivity of AGS increased by 52.13–87.32 % after incorporating magnetic biochar. Furthermore, the extracellular polymeric substance (EPS) of AGS showed an increased capacitance and decreased electron transfer resistance possibly due to the binding of magnetic biochar and more riboflavin secretion in EPS, which could contribute to the accelerated IET process in the inner AGS. In addition, the immobilization of magnetic biochar could promote the production of volatile fatty acids by 15.36–22.50 %. All these improvements may jointly lead to the enhanced methane production capacity of AGS. This study provided a fundamental understanding of the role of incorporated magnetic biochar in AGS in promoting anaerobic digestion performance.

An electrochemical sensor based on a pencil graphite electrode modified with poly-riboflavin for 4-nitrophenol quantification

It is essential to develop a simple and disposable electrochemical sensor for monitoring organic pollutants in water systems. This work aims in the quantification of hazardous water pollutant 4-Nitrophenol (4-NP) by electropolymerizing vitamin B complex (Vitamin B2/Riboflavin) over pencil graphite electrode (PGE). By differential pulse voltametric technique, the anodic peak current increased appreciably for 4-NP oxidation on poly-riboflavin modified pencil graphite electrode (PRB/PGE) as compared to bare PGE. The adapted sensor was characterized using scanning electron microscopy (SEM), infrared spectrometry (IR), energy dispersive X-ray analysis (EDX) and electrochemical impedance spectroscopy (EIS). The increased electroactive surface area and decreased electron transfer resistance was achieved by electropolymerisation of the electrode. A well-defined anodic peak of 4-NP was observed on the adapted electrode at a potential of +0.864 V in phosphate buffer solution of pH 7.2. Factors affecting the current response were optimized. Scan rate and pH analysis were used to study the fabricated electrode and thereby determining transfer electron and proton number. The sensor spectacled a linearity of 5.0 μM–700.0 μM with lower detection of limit (LOD) of 1.78 μM and limit of quantification (LOQ) of 5.94 μM. By using a simple single-step fabrication method, the PRB/PGEs exhibit high stability, reproducibility and repeatability making them an ideal tool to detect 4-NP in real water samples. The developed disposable sensor exhibited a recovery between 97-103%. Hence it is found to be a favorable tool for the electroanalysis of the analyte with high reliability.

Quinones contained in wastewater as redox mediators for the synergistic removal of azo dye in microbial fuel cells

The present paper aimed to investigate the roles of quinones contained in wastewater and the enhanced effects on microbial fuel cells (MFCs) under different redox conditions. The feasibility of using wastewater rich in quinones to act as co-substrate and redox mediators (RMs) library to strengthen the synergistic removal of azo dye in MFCs was evaluated. The results demonstrated that quinones achieved enhanced effects on electricity generation and COD removal of MFC better at higher current intensity. The addition of pure quinone decreased electron transfer resistance (Rct) of MFCs from 4.76 Ω to 2.13 Ω under 1000 Ω resistance and 1.16 Ω–0.75 Ω under 50 Ω resistance. Meanwhile, higher coulombic efficiency was achieved. Compared with sodium acetate, using quinone-rich traditional Chinese medicine (TCM) wastewater as the co-substrate enhanced the synergistic removal of reactive red 2 (RR2) in MFCs from 79.58% to 92.45% during 24 h. RR2 was also degraded more thoroughly due to the accelerated electron transfer process mediated by RMs. Microbial community analysis demonstrated that the presence of quinone in TCM wastewater can enrich different exoelectrogens under varied redox conditions and thus influenced the enhanced effects on MFC. Metagenomic functional prediction results further indicated that the abundance of functional genes involved in carbohydrate metabolism, membrane transport metabolism, biofilm formation, and stress tolerance increased significantly in presence of RMs. Redundancy analyses revealed that RMs addition was the more important factor driving the variation of the microorganism community. This study revealed the potential effect of quinones as redox mediators on the bioelectrochemical system for pollutants removal.

Mesoporous sulfur-doped CoFe2O4 as a new Fenton catalyst for the highly efficient pollutants removal

Herein, mesoporous sulfurized CoFe2O4 (S-CoFe2O4) was developed and applied as a new Fenton catalyst. As a result, the sulfurization for CoFe2O4 could significantly improve the Fenton performance, compared with the non-sulfurized CoFe2O4. The enhanced removal efficiencies of pollutants in Fenton process catalyzed by S-CoFe2O4 was attributed to the elevated specific area and decreased electron transfer resistance of S-CoFe2O4. The DFT calculations further confirmed that the increased charge densities of FeS bond and CoS bond could contribute to the existences of species of Fe and Co in S-CoFe2O4 with the low valence, which were more favorable to the H2O2 activation. Furthermore, electron paramagnetic resonance (EPR) tests showed that the OH and O2− were the main generated radicals during the H2O2 activation process. This work provided a new strategy for the synthesis and application of an efficient non-precious metal Fenton catalyst.

Growth of uniform g-C3N4 shells on 1D TiO2 nanofibers via vapor deposition approach with enhanced visible light photocatalytic activity

In this work, uniform g-C3N4 shells have grown on the surface of electrospinning TiO2 nanofibers to form one dimensional core/shell structured TiO2/g-C3N4 nanofibers by a facial melamine-involved vapor deposition approach. During the heat treatment process in a simple setup, the TiO2 nanofibers served as supports to prevent the collapses and aggregations of g-C3N4 while forming heterojunctions with g-C3N4 at the interface. The as prepared heterogeneous TiO2/g-C3N4 photocatalyst exhibited remarkably enhanced visible light photocatalytic activity for RhB degradation by maxing heterojunctions at the core/shell interface. The photodegradation reaction rate constant of the obtained heterojunction is 0.064 min−1, which is 4.0 times that of pure g-C3N4 (0.016 min−1). To reach higher RhB degradation efficiency (>90%), TiO2/g-C3N4 shortened the irradiation time by 60 min compared with individual components (pure g-C3N4 or TiO2 nanofibers). The remarkably high photocatalytic performances are mainly ascribed to the synergetic effect of efficient photogenerated charge separation properties and decreased electron transfer resistance of the heterojunctions formed between g-C3N4 and TiO2. We believe the proposed simple method and setup is an attractive strategy for constructing one dimensional g–C3N4–based nano-heterojunctions with excellent photocatalytic properties.

Pt-decorated SnO2 nanotubes prepared directly on a conducting substrate and their application in solar energy conversion using a solid polymer electrolyte

We report the electrostatic decoration of Pt nanoparticles on SnO2 nanotubes (ST) directly prepared on a conducting substrate and high electrocatalytic activities of the resulting materials. A pre-coating of poly(vinyl acetate) (PVAc) is the key for the direct uniform deposition of the ST, which serves dual functions as a fast electron transport path as well as a physical support for Pt nanoparticles. The self-assembly of Pt nanoparticles on the ST is based on electrostatic interaction between the Pt cations and negatively charged ST surface. A dip-coating method leads to homogeneous decoration of well-connected Pt nanoparticles with a larger surface area. Solar energy conversion devices with a solid polymer electrolyte are fabricated using Pt on ST as the electrocatalyst for the reduction of I3− to I−. The Pt dip-coated ST shows a photovoltaic efficiency of 5.07%, which is higher than those of Pt spin-coated ST (4.88%) and Pt spin-coated on the substrate without ST (4.59%). An increase in the Pt concentration leads to further improvement in the efficiency up to 5.51%, which is a moderate value for solid electrolyte devices. The improved performance is attributed to the decreased electron transfer resistance and increased surface area of the electrode.

Synergetic Effect of Ti3+ and Oxygen Doping on Enhancing Photoelectrochemical and Photocatalytic Properties of TiO2/g-C3N4 Heterojunctions.

To improve the utilization of visible light and reduce photogenerated electron/hole recombination, Ti3+ self-doped TiO2/oxygen-doped graphitic carbon nitride (Ti3+-TiO2/O-g-C3N4) heterojunctions were prepared via hydrothermal treatment of a mixture of g-C3N4 and titanium oxohydride sol obtained from the reaction of TiH2 with H2O2. In this way, exfoliated O-g-C3N4 and Ti3+-TiO2 nanoparticles were obtained. Simultaneously, strong bonding was formed between Ti3+-TiO2 nanoparticles and exfoliated O-g-C3N4 during the hydrothermal process. Charge transfer and recombination processes were characterized by transient photocurrent responses, electrochemical impedance test, and photoluminescence spectroscopy. The photocatalytic performances were investigated through rhodamine B degradation test under an irradiation source based on 30 W cold visible-light-emitting diode. The highest visible-light photoelectrochemical and photocatalytic activities were observed from the heterojunction with 1:2 mass ratio of Ti3+-TiO2 to O-g-C3N4. The photodegradation reaction rate constant based on this heterojuction is 0.0356 min-1, which is 3.87 and 4.56 times higher than those of pristine Ti3+-TiO2 and pure g-C3N4, respectively. The remarkably high photoelectrochemical and photocatalytic performances of the heterojunctions are mainly attributed to the synergetic effect of efficient photogenerated electron-hole separation, decreased electron transfer resistance from interfacial chemical hydroxy residue bonds, and oxidizing groups originating from Ti3+-TiO2 and O-g-C3N4.

Shape Evolution of Hierarchical W18O49 Nanostructures: A Systematic Investigation of the Growth Mechanism, Properties and Morphology-Dependent Photocatalytic Activities.

Hierarchical tungsten oxide assemblies such as spindle-like structures, flowers with sharp petals, nanowires and regular hexagonal structures are successfully synthesized via a solvothermal reduction method by simply adjusting the reaction conditions. On the basis of the experimental results, it is determined that the reaction time significantly influences the phase transition, microstructure and photocatalytic activity of the prepared samples. The possible mechanisms for the morphology evolution process have been systematically proposed. Moreover, the as-prepared products exhibit significant morphology-dependent photocatalytic activity. The flower-like W18O49 prepared at 6 h possesses a large specific surface area (150.1 m2∙g−1), improved separation efficiency of electron-hole pairs and decreased electron-transfer resistance according to the photoelectrochemical measurements. As a result, the flower-like W18O49 prepared at 6 h exhibits the highest photocatalytic activity for the degradation of Methyl orange aqueous solution. The radical trap experiments showed that the degradation of MO was driven mainly by the participation of h+ and •O2− radicals.

Composition-tunable ternary CdS1−xSex/graphene composites with enhanced photocurrent response

CdS1−xSex/graphene composites were prepared by a solvothermal process using cadmium acetate as Cd precursors, sulfourea as S precursors and selenosulfate as Se precursors. The value of x could be adjusted by controlling the molar ratio of S and Se precursors, and the products were characterized by X-ray diffraction, scanning electron microscope and further evaluated by transient photocurrent responses and electrochemical impedance spectroscopy. Compared with pure CdS1−xSex, CdS1−xSex/graphene composites exhibit enhanced photocurrent response and decreased electron-transfer resistance due to the presence of graphene. The photocurrent of CdS1−xSex/graphene increases with the increase of the Se/S ratio and reaches the maximum at the Se/S ratio of 0.75:0.25. The effect of graphene on the photocurrent response was explored and a higher photocurrent density can be observed for 1 % CdS1−xSex/graphene.

PH-regulated template-free assembly of Sb4O5Cl2 hollow microsphere crystallites with self-narrowed bandgap and optimized photocatalytic performance.

Sb4O5Cl2 hollow microspheres with self-narrowed bandgap and optimized photocatalytic performances are synthesized via a facile template-free method. It is found that the crystal structure and morphology of Sb4O5Cl2 crystallites are strongly dependent on the pH values of precursors. Nano-sized irregular-cuboids assembled Sb4O5Cl2 micro-particles and hollow microspheres can be synthesized at pH 1 and 2, whereas individual Sb4O5Cl2 micro-belts become to form when the pH is higher than 3. The irregular-cuboids assembled Sb4O5Cl2 micro-particles and hollow microspheres exhibit self-narrowed bandgap and higher light absorption ability compared with individual Sb4O5Cl2 micro-belts. The photoelectrochemical measurements show that the assembled Sb4O5Cl2 hollow microsphere crystallites prepared at pH 2 exhibit enhanced carrier density, improved separation efficiency of electron-hole pairs and decreased electron-transfer resistance. As a result, the irregular-cuboids assembled Sb4O5Cl2 hollow microspheres prepared at pH = 2 exhibit the highest photocatalytic activity for the degradation of gaseous iso-propanol (IPA) and Rhodamine B (RhB) aqueous solution. The good photocatalytic activity of Sb4O5Cl2 sample prepared at pH = 2 may be caused by the synergistic effect of its higher light absorption, the decreased electron-transfer resistance, the suppressed recombination of photogenerated electrons and holes, and the increased surface area.

Enhanced photoelectric properties of CdSe/graphene composites with various contents of graphene

CdSe/graphene composites with different contents of graphene were prepared by the solvothermal method. The composites were characterized by X-ray diffraction, scanning electron microscope and further investigated by transient photocurrent responses and electrochemical impedance spectroscopy. Compared with pure CdSe particles, CdSe/graphene composites show improved photocurrent responses and decreased electron-transfer resistance due to the presence of graphene, which acts as an electron collector and transporter as well as the supporting matrix for CdSe particles. The composites were synthesized by varying the graphene content from 0.5wt% to 6wt%, which has been experienced to exert great influence on the photoelectric characteristics of CdSe/graphene composites. A higher photocurrent density and smaller arc radius can be observed for 0.5% CdSe/graphene composites.

Solid-state tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence sensor based on ionic liquid/sol–gel titania/Nafion composite film

The feasibility of being able to control the selectivity of solid-state tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) electrogenerated chemiluminescence (ECL) sensor is proposed by selecting ionic liquids with appropriate hydrophobicity in the sol–gel titania/Nafion composite film. Four different kinds of ionic liquids with different hydrophobicity such as 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMImPF6), 1-hexyl-3-methylimidazolium hexafluorophosphate (HMImPF6), 1-benzyl-3-methylimidazolium hexafluorophosphate (BnMImPF6) were incorporated in the sol–gel titania/Nafion composite films. The sequence of the observed ECL intensities for hydrophobic analytes is closely related to the sequence of the hydrophobicity of the ionic liquids used in the composite-based ECL sensor. In contrast, the observed ECL sequence for hydrophilic analytes such as ascorbic acid and oxalate is the opposite to the sequence of the hydrophobicity of the ionic liquids used in the composite film. Due to the decreased electron transfer resistance in the ionic liquid-based sol–gel titania/Nafion composite films, the present ECL sensor based on the BMImPF6/titania/Nafion composite film gave a remarkable detection limit (S/N=3) of 0.48nM for TPA.

A signal-on electrochemical biosensor for sensitive detection of silver ion based on alkanethiol–carbon nanotube-oligonucleotide modified electrodes

A simple, signal-on electrochemical biosensor for sensitive detection of Ag+ was developed based on the three components of alkanethiol, single-walled carbon nanotube (SWNT) and silver ion-specific oligonucleotide (SSO) layer-by-layer modified electrode where square wave voltammetry (SWV) response of K3[Fe(CN)6] at the modified electrode was used for signal transduction. A gold electrode was first assembled with 1-dodecanethiol (C12H25SH) monolayer to which SWNTs were attached. The SWNT surfaces were further noncovalently bound with SSO probes to obtain the sensor interface. The negatively charged SSO probe acts as a physical obstacle and electrostatic repulsion barrier to block the SWNT-mediated long-distance electron transfer of K3[Fe(CN)6] across the –SC12H25 monolayer. Upon Ag+ binding, the SWNT surface-bound SSO probe forms an unimolecular duplex through C–Ag+–C interaction-mediated intramolecular hybridization and departs from the SWNT surface, resulting in decreased electron transfer resistance and increased SWV current of K3[Fe(CN)6] at the modified electrode. This current enhancement effect provides a signal-on mechanism for sensitive transduction of Ag+ recognition and the resulted current increase is linear with the logarithmic concentration of Ag+ from 2.0nM to 100nM. The developed biosensor was highly selective and its practical applicability in tap water was also tested with a satisfactory result.

Evaluation of Magainin I interactions with lipid membranes: An optical and electrochemical study

Most antimicrobial peptides (AMPs) have shown clear activity related to the disruption of lipid bilayers. In order to improve knowledge of this subject, the interaction of Magainin I (MagI) with phospholipid layers (PLs), uncoated or coated with synperonic (Synp), was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) techniques. MagI peptide was immobilized on gold electrode via a self-assembling monolayer obtained from liposomes and liposomes covered by Synp. MagI induces pores in the supported lipid membranes, which are reflected in an increased amperometric-response and also a decreased electron-transfer resistance (RCT). In addition, MagI showed a significant interaction with the PL-Synp-modified gold electrode, but MagI showed a reliable contact with the PL-modified gold electrode, leading to a decrease in the relative resistance charge transfer value of −17.38%. Our results demonstrated that Synp acts as a membrane sealant after exposure of the lipid membrane to MagI. A parallel reaction model was proposed for the interaction of MagI and a hybrid layer that result in a complex bimolecular interaction. In short, the importance of triblock copolymer to stabilize liposomes for future applications as drug delivery systems for MagI was demonstrated.

High-Temperature Performance of Amorphous Nickel Hydroxide Coated with Y(OH)3/Co(OH)2

Y(OH)3/Co(OH)2 coated amorphous nickel hydroxide was prepared by chemical coprecipitation method. The microstructure, surface morphology, and chemical composition of the prepared sample were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Electrochemical performances of the sample were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The results demonstrated that the coating of Y(OH)3/Co(OH)2 dramatically decreased electron transfer resistance and increased oxygen evolution potential of amorphous nickel hydroxide. Moreover, the high-temperature performance of amorphous nickel hydroxide was significantly improved after the coating of Y(OH)3/Co(OH)2.

High-Temperature Performance of Amorphous Nickel Hydroxide Coated with La(OH)<sub>3</sub>

La(OH)3coated amorphous nickel hydroxide was prepared by chemical coprecipitation method. The microstructure, surface morphology and chemical composition of the prepared sample were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Electrochemical performances of the sample were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The results demonstrated that the coating of La(OH)3 dramatically decreased electron transfer resistance and increased oxygen evolution potential of amorphous nickel hydroxide. Moreover, the high-temperature performance of amorphous nickel hydroxide was significantly improved after the coating of La(OH)3.

Tris(2,2′‐bipyridyl)ruthenium(II) Electrogenerated Chemiluminescence Sensor Based on Platinized Carbon Nanotube–Zirconia–Nafion Composite Films

AbstractMesoporous films of platinized carbon nanotube–zirconia–Nafion composite have been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium (II) (Ru(bpy)32+) on an electrode surface to yield a solid‐state electrogenerated chemiluminescence (ECL) sensor. The composite films of Pt–CNT–zirconia–Nafion exhibit much larger pore diameter (3.55 nm) than that of Nafion (2.82 nm) and thus leading to much larger ECL response for tripropylamine (TPA) because of the fast diffusion of the analyte within the films. Due to the conducting and electrocatalytic features of CNTs and Pt nanoparticles, their incorporation into the zirconia–Nafion composite films resulted in the decreased electron transfer resistance within the films. The present ECL sensor based on the Pt–CNT–zirconia–Nafion gave a linear response (R2=0.999) for TPA concentration from 3.0 nM to 1.0 mM with a remarkable detection limit (S/N=3) of 1.0 nM, which is much lower compared to those obtained with the ECL sensors based on other types of sol‐gel ceramic–Nafion composite films such as silica–Nafion and titania–Nafion.