Direct electrochemical reduction of graphene oxide thin film for aptamer-based selective and highly sensitive detection of matrix metalloproteinase 2

Simple and low-cost biosensing solutions are suitable for point-of-care applications aiming to overcome the gap between scientific concepts and technological production. To compete with sensitivity and selectivity of golden standards, such as liquid chromatography, the functionalization of biosensors is continuously optimized to enhance the signal and improve their performance, often leading to complex chemical assay development. In this research, the efforts are made on optimizing the methodology for electrochemical reduction of graphene oxide to produce thin film-modified gold electrodes. Under the employed specific conditions, 20 cycles of cyclic voltammetry (CV) are shown to be optimal for superior electrical activation of graphene oxide into electrochemically reduced graphene oxide (ERGO). This platform is further used to develop a matrix metalloproteinase 2 (MMP-2) biosensor, where specific anti-MMP2 aptamers are utilized as a biorecognition element. MMP-2 is a protein which is typically overexpressed in tumor tissues, with important roles in tumor invasion, metastasis as well as in tumor angiogenesis. Based on impedimetric measurements, we were able to detect as low as 3.32 pg mL-1 of MMP-2 in PBS with a dynamic range of 10 pg mL-1 - 10 ng mL-1. Further experiments with real blood samples revealed a promising potential of the developed sensor for direct measurement of MMP-2 in complex media. High specificity of detection is demonstrated - even to the closely related enzyme MMP-9. Finally, the potential of reuse was demonstrated by signal restoration after experimental detection of MMP-2.

Electrochemical oxidation diminished toxicity of zearalenone significantly, while reduction increased

Zearalenone (ZEN), one of the most common mycotoxins in cereals, poses a severe health risk to humans. In this study, electrochemical oxidation and reduction degraded ZEN in solution completely within 8 min and 20 min. The structure of ZEN products was elucidated by mass spectrometry (MS), and their toxicity was evaluated by ECOSAR software and cytotoxicity assay. From simulation, electrochemical oxidation products had lower acute and chronic toxicity, and the product at 9.0 V is not harmful (LC50/EC50 greater than 100 mg/L, ChV greater than 10 mg/L). CCK-8 assay further confirmed their less cytotoxicity. To our surprise, LC50, EC50, and ChVs of all electrochemical reduction products were lower than 1 mg/L, and cell viabilities were less than ZEN, meaning the higher toxicity of electrochemical reduction products. On this Basis, electrochemical oxidation was applied in ZEN contaminated wheat with a degradation rate of 92.32 ± 2.37%, indicating its potential to degrade ZEN practically.

A low-cost and efficient route for large-scale synthesis of NiCoSx nanosheets with abundant sulfur vacancies towards quasi-industrial electrocatalytic oxygen evolution

Transition-metal sulfides (TMS) have piqued a great deal of interest due to their unprecious nature and high intrinsic catalytic activity for water splitting. In this work, a low-cost and efficient route was developed, which included electrodeposition to prepare Ni-Co layered double hydroxide (NiCo-LDH) followed by ion exchange to form nickel cobalt sulfide (NiCoSx). Electrochemical reduction was used to modulate sulfur vacancies in order to produce sulfur vacancies-rich NiCoSx with nanosheet arrays on -three-dimensional nickel foam (NiCoSx-0.4/NF) with a large area of more than 250 cm2. Combining data from experiments and density functional theoretical (DFT) calculations reveals that engineered sulfur vacancies change the electronic structure, electron transfer property, and surface electron density of NiCoSx, significantly improving the free energy of water adsorption and boosting electrocatalytic activity. The developed NiCoSx-0.4/NF has long-term stability of more than 300 h at 500 mA cm-2 in 1 M KOH at ambient temperature and only needs a 289 mV overpotential at 100 mA cm-2. Remarkably, the synthesized electrocatalyst rich in sulfur vacancies, exhibits exceptional performance with a high current density of up to 1.9 A cm-2 and 1 A cm-2 in 6 M KOH and leads to overpotentials of 286 mV at 80 °C and 358 mV at 60 °C, respectively. The catalyst's practicability under quasi-industrial conditions (60 °C, 6 M KOH) is further demonstrated by its long-term stability for 220 h with only a 3.9 % potential increase at 500 mA cm-2.

Assess the formation of disinfection by-products from pyrogenic dissolved organic matter (pyDOM): impact of wildfire on the water quality of forest watershed

Wildfires can release pyrogenic dissolved organic matter (pyDOM) into the forest watershed, which may pose challenges for water treatment operations downstream due to the formation of disinfection by-products (DBPs). In this study, we systematically assessed the physio-chemical properties of pyDOM (e.g., electron-donating and -accepting capacities; EDC and EAC) and their contributions to DBP formation under different disinfection scenarios using (1) ten lab samples produced from various feedstocks and pyrolysis temperatures, and (2) pre- and post-fire field samples with different burning severities. A comprehensive suite of DBPs-four trihalomethanes (THMs), nine haloacetic acids (HAAs), and seven N-nitrosamines-were included. The formations of THM and HAA showed an up to 5.7- and 8.9-fold decrease as the pyrolysis temperature increased, while the formation of N-nitrosamines exhibited an up to 6.6-fold increase for the laboratory-derived pyDOM. These results were supported by field pyDOM samples, where the post-fire samples consistently showed a higher level of N-nitrosamine formation (i.e., up to 5.3-fold), but lower THMs and HAAs compared to the pre-fire samples. To mimic environmental reducing conditions, two field samples were further reduced electrochemically and compared with Suwannee River natural organic matter (SRNOM) to evaluate their DBP formation. We found increased DBP formation in pyDOM samples following electrochemical reduction but not for SRNOM, which showed increased N-nitrosamines but decreased THMs and HAAs post-electrochemical reduction. Furthermore, this study reported for the first time the formation of two previously overlooked N-nitrosamines (i.e., nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA)) in both laboratory and field pyDOM samples, raising concerns for drinking water safety given their higher toxicity as compared to the regulated counterparts. Results from this study provide new insights for DBP mitigation during post-fire recovery, which are particularly relevant to communities that rely on forest watersheds as their drinking water sources.

High efficiency electrochemical separation of uranium(VI) from uranium-containing wastewater by microbial fuel cells with different cathodes

As an emerging versatile technology for separating uranium from uranium-containing wastewater (UCW), microbial fuel cell (MFC) offers a novel approach to UCW treatment. Its cathode is essential for the treatment of UCW. To thoroughly investigate the efficacy of MFC in treating UCW, investigations were conducted using MFCs with five materials (containing iron sheet (IP), stainless steel mesh (SSM), carbon cloth (CC), carbon brush (CB), and nickel foam (NF)) as cathodes. The results revealed that each MFC system performed differently in terms of carbon source degradation, uranium removal, and electricity production. In terms of carbon source degradation, CB-MFC showed the best performance. The best uranium removal method was NF-MFC, and the best electricity production method was carbon-based cathode MFC. Five MFC systems demonstrated stable performance and consistent difference over five cycles, with CC-MFC outperforming the others. Furthermore, SEM and XPS characterization of the cathode materials before and after the experiment revealed that a significant amount of U(IV) was generated during the uranium removal process, indicating that uranium ions were primarily removed by electrochemical reduction precipitation. This study confirmed that abiotic cathode MFC had a high UCW removal potential and served as a good guideline for obtaining the best cathode for MFC.

Targeted electrochemical reduction of carcinogenic N-nitrosamines from emission control systems within CO2 capture plants

N-Nitrosamines are one of the environmentally significant byproducts from aqueous amine-based post-combustion carbon capture systems (CCS) due to their potential risk to human health. Safely mitigating nitrosamines before they are emitted from these CO₂ capture systems is therefore a key concern before widescale deployment of CCS can be used to address worldwide decarbonization goals. Electrochemical decomposition is one viable route to neutralize these harmful compounds. The circulating emission control waterwash system, commonly installed at the end of the flue gas treatment trains to minimize amine solvent emissions, plays an important role to capture N-nitrosamines and control their emission into the environment. The waterwash solution is the last point where these compounds can be properly neutralized before becoming an environmental hazard. In this study, the decomposition mechanisms of N-nitrosamines in a simulated CCS waterwash with residual alkanolamines was investigated using several laboratory-scale electrolyzers utilizing carbon xerogel (CX) electrodes. H-cell experiments revealed that N-nitrosamines were decomposed through a reduction reaction and are converted into their corresponding secondary amines thereby neutralizing their environmental impact. Batch-cell experiments statistically examined the kinetic models of N-nitrosamine removal by a combined adsorption and decomposition processes. The cathodic reduction of the N-nitrosamines statistically obeyed the first-order reaction model. Finally, a prototype flow-through reactor using an authentic waterwash was used to successfully target and decompose N-nitrosamines to below the detectable level without degrading the amine solvent compounds allowing them to be return to the CCS and lower the system operating costs. The developed electrolyzer was able to efficiently remove greater than 98% of N-nitrosamines from the waterwash solution without producing any additional environmentally harmful compounds and offers an effective and safe route to mitigate these compounds from CO₂ capture systems.

Evaluation of the effect of biofilm formation on the reductive transformation of triclosan in cathode-modified electrolytic systems

The performance of electrochemical reduction is often enhanced by electrode modification techniques. However, there is a risk of microbial colonization on the electrode surface to form biofilms in the treatment of actual wastewater with modified electrodes. In this work, the effects of biofilm formation on modified electrodes with reduced graphene oxide (rGO), platinum/carbon (Pt/C), and carbon nanotube (CNT) were investigated in triclosan (TCS) degradation. With biofilm formation, the TCS degradation efficiencies of carbon cloth (CC), rGO@CC, Pt/C@CC, and CNT@CC decayed to 54.53 %, 59.77 %, 69.19 %, and 53.97 %, respectively, compared to the raw electrodes. Confocal laser scanning microscopy and microbial community analysis revealed that the difference in biofilm thickness and activity were the major influencing factors on the discrepant TCS degradation rather than the microbial community structure. The electrochemical performance tests showed that the biofilm formation increased the ohmic resistance by an order of magnitude in rGO@CC, Pt/C@CC, and CNT@CC, and the charge transfer resistance was increased by 2.45, 3.78, and 7.75 times, respectively. The dechlorination and hydrolysis governed the TCS degradation pathway in all electrolysis systems, and the toxicity of electrochemical reductive products was significantly decreased according to the Toxicity Estimation Software Tool analysis. This study presented a systematic assessment of the biofilm formation on modified electrodes in TCS reduction, and the undisputed experimental outcomes were obtained to enrich the knowledge of implementing modified electrodes for practical applications.

Efficient removal of bromate from contaminated water using electrochemical membrane filtration with metal heteroatom interface

Efficient utilization of atomic hydrogen (H*) is of great importance for achieving efficient bromate reduction using electrochemical technologies. Herein, an electrochemical membrane with metal heteroatom interface of Ru and Ni was developed to enhance the utilization efficiency of H* via the membrane filtration process. The RuNi membrane demonstrated 91.3% of bromate removal at 5 mA cm^-2 under the flow-through operation (40 L m^-2 h^-1). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra elucidated that the bromate reduction was mainly attributed to H* -mediated reduction rather than the direct electron transfer between bromate and RuNi active layer. The quenching experiments revealed a significant contribution of adsorbed H* to the bromate removal during the membrane filtration. Based on X-ray photoelectron spectrometry and X-ray diffraction analyses, we found that the resultant Ru⁰Ni⁰ structure on the electrochemical membrane could facilitate the generation of H* during the bromate reduction reaction. Besides, the higher pH might suppress the formation of H* and increase the energy barrier for breaking the Br-O bond, resulting in dramatic increase of energy consumption for removing bromate. Our work highlights the potential of utilizing H* in electrochemical membrane for removing bromate in water treatment and remediation.

Low-nitrite generation Cu-Co/Ti cathode materials for electrochemical nitrate reduction

In order to reduce by-product nitrite, a more toxic compound than nitrate, and increase high value-added products ammonia in the electrochemical reduction nitrate process, the novel Cu-Co/Ti cathode material was applied in this process. In this paper, the electrochemical process was carried out in a single compartment electrolytic cell, and with Cu-Co/Ti electrode as cathode, identifying the effects of current density, pH, electrolytes in the nitrate reduction, and the distribution of products. The Cu-Co/Ti cathode exhibited 94.65% NO₃^--N (nitrate-N) removal, 0.18% NO₂^--N (nitrite-N) generation, and 40.86% NH₄^--N (ammonia-N) generation with the assistance of Na₂SO₄ electrolyte in 6 h at 10 mA cm^-2 and pH 6. Compared with the Cu/Ti cathode, the higher nitrate removal ratio and lower nitrite generation ratio were obtained on the Cu-Co/Ti cathode. The excellent performance of Cu-Co/Ti cathode is ascribed to the synergy of Cu and Co, which couples the facilitation of nitrate conversion to nitrite and the acceleration of nitrite reduction on the Cu-Co/Ti cathode. The LSV curves showed that nitrate and nitrite might undergo indirect and direct reduction reactions on Cu-Co/Ti cathode. The possible pathways of nitrate reduction on the Cu-Co/Ti cathodes were proposed. These results highlight the viability of using the Cu-Co/Ti cathode developed at this work for the nitrate removal from contaminated waters. This study achieved low-nitrite generation by Cu-Co/Ti cathode during electrochemical nitrate reduction.

Nano Pd doped Ni foam electrode stimulated electrochemical reduction of tetrabromobisphenol A: Optimization strategies and function mechanism

Tetrabromobisphenol A (TBBPA), a hazardous and persistent flame retardant, has been widely detected in the natural aquatic system. The acceleration of reductive debromination (rate-limiting process) is vital during the decomposition and detoxification of TBBPA. This study achieved superior TBBPA electrochemical reductive debromination performance by nano Pd doped Ni foam electrode (4.8 times higher than Ni foam electrode). The optimal TBBPA reductive debromination performance was obtained under -1.2 V of cathode potential, 1.2 wt% of Pd loading, 10 mg L^-1 of TBBPA and 100 mM of Na₂SO₄ as the electrolyte solution. UPLC-QTOF-MS verified that Br atoms in TBBPA were removed sequentially to form bisphenol A as the major product. Most TBBPA was reductively debrominated by atomic H* through indirect hydrodebromination, evidenced by the atomic H* quenching test. The higher solution conductivity and appropriate TBBPA concentration would contribute to the debromination efficiency. Excessive H₂ generation whether by over negative potential or H atom richness electrolyte largely disturbed the reaction process and restricted the debromination. The improved generation of reductant (H*)_adsPd was the most significant, while excessive Pd loading would make aggregation and limit the debromination efficiency. The study confirmed the optimization strategies of conditions for Pd/Ni foam electrode and revealed the related function mechanism for stimulating TBBPA electrochemical reduction, giving suggestions for the efficient removal of TBBPA in the aquatic environment.

Electrochemical determination of emodin in acidic media by high-performance liquid chromatography and its application to Polygoni Multiflori Radix samples

Electrochemical reduction of emodin under acidic media occurs at a less negative potential when compared with that under neutral media. When emodin is electrochemically detected at a less negative potential, a decrease in background noise and improvement in specificity benefit the development of high-performance liquid chromatography with electrochemical detection (HPLC-ECD) for its determination. HPLC-ECD was performed using an octadecyl silica column, acetonitrile-water (60:40, v/v) containing 5 mmol L^-1 hydrochloric acid and 10 mmol L^-1 lithium perchlorate, as a mobile phase, and an applied potential at - 0.4 V vs. Ag/AgCl. Under these optimal HPLC-ECD conditions, the detection limit (signal-to-noise ratio, S/N = 3) of emodin was 0.61 μg L^-1. When this HPLC-ECD system was applied to the determination of emodin in Polygoni Multiflori Radix (PMR) samples, other peaks did not appear close to the emodin peak on a chromatogram. The emodin contents in PMR samples were determined with relative standard deviations (RSDs, n = 6) of less than 3.9%, and their recoveries ranged from 92 to 106%. We have shown that our HPLC-ECD system performed an accurate, precise, and specific determination of emodin in PMR samples.

Stepwise dechlorination of chlorinated alkenes on an Fe-Ni/rGO/Ni foam cathode: Product control by one-electron-transfer reactions

Research on the stepwise hydrogenation dechlorination of chlorinated alkenes forms an important basis for eliminating toxic intermediate incomplete dechlorination products. The low-cost Fe-Ni/rGO/Ni foam cathode both supplied electrons and exhibited hydrogen conversion activity, and it was an excellent tool for the study of stepwise dechlorination. Electrochemical reduction experiments were carried out on homologous chlorinated alkenes. The conditions affecting the dechlorination efficiency and the repeatability of the catalytic electrode were analyzed. The trichloroethylene (TCE) removal rates were all above 78.0% over 8 cycles. The maximum EHDC efficiency was as high as 86.1%, and the faradaic efficiency was over 78.8%. Electrochemical methods combined with the calculation of the electron transfer number are proposed to verify the good hydrogenation ability of the electrode and the stepwise reduction ability at proper voltages. The stepwise dechlorination electroreduction characteristics of chlorinated alkenes were explained. The C-Cl bond dissociation enthalpies of chlorinated alkenes were calculated by density functional theory (DFT), and the 4-Cl and 5-Cl of TCE were expected to be removed first. The stepwise cleavage of chlorinated alkenes on Fe-Ni/rGO/Ni foam during dichlorination provided a reference for controlling the reduction products of chlorinated alkenes and preventing the pollution caused by toxic intermediate products formed during incomplete dechlorination.

Preparation of three dimensional bimetallic Cu-Ni/NiF electrodes for efficient electrochemical removal of nitrate nitrogen

It still remains a hotspot and great challenge to efficiently remove the nitrate nitrogen from high salt wastewater. Herein, a novel three dimensional porous bimetallic copper-nickel alloy electrode was fabricated with Ni foam (NiF) as substrate. The physicochemical and electrochemical characterization results showed Cu-Ni/NiF electrode possessed the smaller particle size (0.3-1.0 μm) and electrode film resistance comparing with Ni/NiF and Cu/NiF electrodes. Besides, higher double layer capacitance (C_dl) for Cu-Ni/NiF electrode indicated more electrochemical active sites could be used in the electrochemical nitrate nitrogen (NO₃^--N) removal. The electrochemical experiments showed the Cu-Ni/NiF electrode had the optimal NO₃^--N reduction ability and almost 100% NO₃^--N removal could be achieved with 30 min. All NO₃^--N removal processes were in accord with the pseudo-first-order reaction kinetics completely. The gaseous nitrogen selectivity for Cu-Ni/NiF electrode could reach 80.9% within 300 min. Stability assessment experiments indicated the Cu-Ni/NiF electrode all kept an excellent stability with Na₂SO₄ or NaCl electrolyte and the Cl^- addition could significantly improve the gaseous nitrogen selectivity. Finally, a possible removal mechanism of NO₃^--N was proposed. This work offered a direction for designing non-noble bimetallic electrodes for nitrate removal.

Removal behavior and mechanisms of cadmium and lead by coupled ethylenediaminetetraacetic acid washing and electrochemical reduction: influence of current conditions

Ethylenediaminetetraacetic acid (EDTA) washing has been used extensively to remediate heavy metal-contaminated soils. Electrochemical reduction treatment of spent washing solution is an effective method of EDTA regeneration. However, at present, these two technologies are usually regarded as two independent treatment processes. This research raised a new heavy metal-contaminated soil treatment strategy-a combination technique of coupled EDTA washing and electrochemical reduction. We speculated that the combination of EDTA washing and electroreduction treatment could improve the efficiency of Cd and Pb removal from contaminated soil. In this study, the removal performance and mechanisms of Cd and Pb under different current conditions were investigated based on a coupling of EDTA washing and electrochemical reduction. The combination technique can increase Cd and Pb removal efficiencies by 13.37-15.24% and 14.91-27.05%, respectively, compared with EDTA washing alone. Sequential extraction analysis showed that the reducible fraction improved metal removal efficiency. The percentage of metal removed increased with an increased current value and EDTA concentration. In addition, pulse current mode removed more Cd and Pb than continuous current, although the difference was not significant (p > 0.05). However, pulse current could effectively eliminate the cathodic hydrogen evolution reaction, resulting in a further heavy metal deposition at the cathode. The combination technique exhibited enhanced removal efficiency due to EDTA regeneration in the suspension and the cathodic reduction reaction. The most cost-effective treatment in 48 h was a pulse current mode of 32 min on/16 min off-32 mA-EDTA-10 mM, where 47.56% of Cd and 77.00% of Pb were removed from the soil with an electric energy consumption of 8.24 Wh.

Opportunities and challenges in CO2 utilization

CO₂ utilizations are essential to curbing the greenhouse gas effect and managing the environmental pollutant in an energy-efficient and economically-sound manner. This paper seeks to critically analyze these technologies in the context of each other and highlight the most important utilization avenues available thus far. This review will introduce and analyze each major pathway, and discuss the overall applicability, potential extent, and major limitations of each of these pathways to utilizing CO₂. This will include the analysis of some previously underreported utilization avenues, including CO₂ utilization in industrial filtration and the processing of raw industrial materials such as iron and alumina. The core theme of this paper is to seek to treat CO₂ as a commodity instead of a liability.

Electrochemical reduction of nitrate in a catalytic carbon membrane nano-reactor

Nitrate pollution is a critical environmental issue in need of urgent addressing. Electrochemical reduction is an attractive strategy for treating nitrate due to the environmental friendliness. However, it is still a challenge to achieve the simultaneous high activity and selectivity. Here we report the design of a porous tubular carbon membrane as the electrode deposited with catalysts, which provides a large triple-phase boundary area for nitrate removal reactions. The achieved nitrate removal rate is one order of magnitude higher than other literatures with high nitrate conversion and high selectivity of nitrogen. The carbon membrane itself had a limited catalytic property thus Cu-Pd bimetal catalysts were deposited inside the nano-pores to enhance the activity and selectivity. When Na₂SO₄ electrolyte was applied, the achieved single-pass removal of nitrate was increased from 55.15% (for blank membrane) to 97.12% by adding catalysts inside the membrane. In case of NaOH as the electrolyte, the single-pass nitrate removal efficiency, selectivity to nitrogen formation and nitrate removal rate was 90.66%, 96.40% and 1.47 × 10^-3 mmol min^-1 cm^-2, respectively. Density functional theory studies demonstrate that the loading of bimetal catalysts compared with single metal catalysts enhances the adsorption of *NO₃ on membrane surface favorable for N₂ formation than NH₃ on Cu-Pd surface. The application of catalytic carbon membrane nano-reactors can open new windows for nitrate removal due to the high reactor efficiency.

Electrochemical removal of NOx by La0.8Sr0.2Mn1-xNixO3 electrodes in solid electrolyte cells: Role of Ni substitution

Electrochemical removal of nitrogen oxides (NO_x) by solid electrolyte cells (SECs) is a promising technology due to no required reductant. Herein, a series of La_0.8Sr_0.2Mn_1-xNi_xO₃ (0 ≤ x ≤ 0.5) perovskites were first synthesized and utilized as the electrode materials of SECs. The role of Ni substitution in electrode performance and NO_x reduction mechanism were revealed by various experimental characterization and first-principle calculations. The results indicate that the moderate Ni substitution (x ≤ 0.3) increased the NO_x conversion of electrodes while reduced the polarization resistance. The further investigation shows that this improvement was attributed to the more surface oxygen vacancies, better reducibility and higher Mn⁴⁺ proportion of the Ni-substituted perovskites. The electrochemical impedance spectroscopy (EIS) shows that these changes facilitated the NO_x adsorption and dissociation processes on the electrode. According to first-principle calculations, the Ni-substituted perovskite had a lower formation energy of surface oxygen vacancy, while the NO molecule adsorbed on defect surface gained more electrons thus was easier to be reduced and dissociated. Finally, the electrode performance at different operating temperatures and the operational stability were verified.

Electrochemical nitrate reduction of brines: Improving selectivity to N2 by the use of Pd/activated carbon fiber catalyst

Contamination of water by nitrate has become a worldwide problem, being high levels of this ion detected in the surface, and groundwater, mainly due to the intensive use of fertilizers, and to the discharge of not properly treated effluents. This study aims to evaluate the electrocatalytic process, carried out in a cell divided into two compartments by a cation exchange membrane, and with a copper plate electrode as cathode, identifying the effects of current density, pH, the use of a catalyst in the nitrate reduction, and the production of gaseous compounds. The highest nitrate reduction was obtained with a current density of 2.0 mA cm^-2, without pH adjustment and, in this condition, nitrite ion was mainly formed. The application of activated carbon fibers with palladium (1% wt. and 3% wt.) in an alkaline medium presented an increase in gaseous compounds formation. With 2.0 mA cm^-2, pH adjustment, and applying 3% wt. Pd catalyst, the highest selectivity to gaseous compounds was obtained (95%) with no nitrite detection. These results highlight the viability of using the process developed at this work for the treatment of nitrate contaminated waters.

Highly stable branched cationic polymer-functionalized black phosphorus electrochemical sensor for fast and direct ultratrace detection of copper ion

Copper ions (Cu²⁺) is an indispensable trace element in the process of metabolism and intake of excessive Cu²⁺ may lead to fatal diseases such as Alzheimer's disease. It is highly demanding to develop a sensitive, selective and convenient method for Cu²⁺ detection. In this work, thin-layer structured polyethyleneimine (PEI) decorated black phosphorus (BP) nanocomposite is one-step synthesized for an electrochemical sensor toward direct detection of Cu²⁺. This sensor achieves a wide detection range of 0.25-177 μM, a low detection limit of 0.02 μM much below the Environmental Protection Agency (EPA) maximum contaminant levels for drinking water (20 μM for Cu²⁺), and much faster response (1.5 s response time) and simpler operation than the conventional tedious anodic stripping voltammetry, ranking one of the best among all reported Cu²⁺ sensor. The great sensing enhancement is mainly due to a synergistic effect of BP and PEI of the composite, of which the former offers the reactivity while the latter splits the thick BP to thin-layer structured PEI-BP composite for larger reaction area. Meanwhile, a flexible sensor has been successfully fabricated and applied in detecting of Cu²⁺ in real samples of river, confirming the application feasibility of PEI-BP sensor in water environment control.

Self-doping of Nb2O5NC by cathodic polarization for enhanced conductivity properties and photoelectrocatalytic performance

A simple novel electrochemical reduction approach was developed for the self-doping of Nb⁴⁺ in niobium oxide nanochannels (Nb₂O₅NC), changing the conductivity, optical properties, and photocatalytic properties of the material. Nb₂O₅NC was synthesized using different electrolytes: 0.4 wt% HF in 1 M H₂SO₄ (EI), 0.4 M NH₄F in glycerol (EII), and 0.25 g NH₄F with 4 vol% water in glycol at 50 °C (EIII). Field emission scanning electron microscopy (FEG-SEM) analysis showed well-organized arrays of Nb₂O₅ nanochannels produced on Nb foil, with varying tube diameters in the order EII < EI < EIII and film thickness in the order EI < EII < EIII, which drastically affected the photocurrent vs. potential curves. In order to self-dope the Nb₂O₅, the samples were electrochemically reduced in 0.1 M KH₂PO₄ buffer solution (pH 10) for 5 min, at -2.5 V vs. Ag/AgCl, resulting in the doped samples denoted P-EI, P-EII, and P-EIII. The results showed that reduction of Nb⁵⁺ to Nb⁴⁺ occurred for all the Nb₂O₅NC samples, leading to decreased surface charge transfer resistance between the Nb₂O₅NC and the electrolyte, as well as increases of the charge carrier density and photocurrent for all the self-doped samples, compared to undoped samples. Sample P-EI was also tested for the degradation of reactive red 120 (RR120) dye, achieving efficient photoelectrocatalytic degradation of a 10 mg L^-1 dye solution. These results reveal that the self-doping approach can enhance the photoelectrocatalytic properties of Nb₂O₅ photoanode, offering an alternative way for the removal of reactive dyes.

Electrochemical Fixation of Carbon Dioxide: Synthesis of Carboxylic Acids

In the past three decades, we have focused on the fixation of carbon dioxide by electrochemical method with a carbon-carbon bond forming reaction to yield carboxylic acid, so-called electrochemical carboxylation. Vinyl bromides and triflates, difluoroethylbenzenes, polyfluoroarenes, benzal diacetates, phenyl-substituted alkenes and enamides, and α-aminosulfones were found to be effective as substrates for electrochemical carboxylation. Phenylacetic acids and phenylpropanoic acids including non-steroidal anti-inflammatory agents and their fluorinated analogues, polyfluorobenzoic acids, mandel acetates, and α- and β-amino acids were successfully synthesized. Electrochemical double carboxylation of dibenzyl carbonates, reuse of carbon dioxide in benzyl carbonates for fixation of carbon dioxide (recycle-electrochemical carboxylation), sequential aryl/vinyl radical cyclization-electrochemical carboxylation, sacrificial anode-free electrochemical carboxylation, and the use of supercritical carbon dioxide both as a reaction media and a reagent were also developed. In this personal account, our efforts in and results of electrochemical fixation of carbon dioxide to organic compounds with carbon-carbon bond forming reactions yielding novel and useful carboxylic acids are introduced along with their applications and some new results.

Biotreatment for the spent lithium-ion battery in a three-module integrated microbial-fuel-cell recycling system

A bio-electrochemically (BE) recycling platform was assembled to recover Li and Co from the cathodic materials of spent LIBs in one integrated system. The BE platform consists of three microbial-fuel-cell (MFC) subsystems, including MFC-A, MFC-B, and MFC-C. Co and Li were smoothly recovered from the cathodic materials in the assembled platform. The initial pH and the loading ratios of LiCoO₂ both significantly influenced the leaching efficiencies of Li and Co in MFC-A. Approximately 45% Li and 93% Co were simultaneously released through the reduction of LiCoO₂ at the initial pH of 1 and the loading ratios of LiCoO₂ of 0.2 g/L. The (NH₄)₂C₂O₄-modified granular activated carbons (GAC) with a thickness of 1.5 cm was favorably stacked adjacent to the cathode of the MFC-B system. About 98% of removal efficiency (RE_Co1) and 96% of recovery efficiency (RE_Co2) of Co were achieved in MFC-B under optimum conditions. The dosing concentration of Li⁺ lower than 2 mg/L and the (NH₄)₂CO₃ of 0.01-0.02 M were conducive to enhancing the recovery of Li from raffinate and guaranteed the higher power output and coulombic efficiencies in MFC-C. The continuous release of CO₂ caused by exoelectrogenic microorganisms on the biofilm facilitated the precipitation of Li₂CO₃.

Nitrogen-doped porous carbon derived from digested sludge for electrochemical reduction of carbon dioxide to formate

Carbon-based materials have been applied as cost-effective electrocatalysts to reduce carbon dioxide (CO₂) into valuable chemicals. Here, an environment-friendly method is proposed to obtain nitrogen-doped porous carbons (NPCs) from digested sludge, which is an abundant waste product from sewage treatment plants. The materials were used as a metal-free electrocatalyst for electrochemical reduction of CO₂ to formate. The synthesized material (NPC-600) had a mesoporous and microporous structure with a specific surface area of 246.21 m² g^-1 and pore volume of 0.494 cm³ g^-1. Active sites based on nitrogen atoms accounted for 2.98 atom% of the content and included pyrrolic-, pyridinic-, and graphitic-N, which is useful for CO₂ adsorption and electron transfer in electrochemical reduction. The Faradaic efficiency for formate production from CO₂ in the presence of NPC-600 was 68% at the potential of -1.5 V vs. SCE. Tafel analysis indicated that the pathway of CO₂ conversion involved the reduction of CO₂ to CO₂*^- intermediate, which was then converted to HCOO*^- and finally formate.

Integrating microbial electrolysis cell based on electrochemical carbon dioxide reduction into anaerobic osmosis membrane reactor for biogas upgrading

It has been reported that anaerobic osmosis membrane bioreactors have the potential for energy recovery since dissolved methane was almost rejected by commercial forward osmosis membranes. Notwithstanding, upgraded biogas has to be achieved by removing as much carbon dioxide as possible. In this study, a novel anaerobic osmotic membrane bioreactor-microbial electrolysis cell (AnOMBR-MEC) system was developed for simultaneous biogas upgrading and wastewater treatment. The AnOMBR-MEC elicited an excellent and stable soluble chemical oxygen demand and phosphorus removal. As the experiment progressed, unwanted carbon dioxide produced from biogas was reduced to formate using a SnO₂ nanoparticles electrocatalytic cathode in an electrocatalytic-assisted MEC, with the highest faradic efficiency of formate being 85% at 1.2V. Compared to AnOMBR, the methane content increased from 55% to 90% at the end of operation and methane yield experienced a1.6-fold increment in the AnOMBR-MEC. Microbial community analysis revealed that hydrogenotrophic methanogens (e.g. Methanobacterium and Methanobrevibacter) converted the produced H₂ and formate to methane at saline conditions. These results have demonstrated an efficient strategy based on the integration of an electrocatalytic-assisted MEC into AnOMBR for upgrading biogas, enhancing methane yield and wastewater treatment.

Electrochemical simulation of metabolic reduction and conjugation reactions of unsymmetrical bisacridine antitumor agents, C-2028 and C-2053

Electrochemistry (EC) coupled with analysis techniques such as liquid chromatography (LC) and mass spectrometry (MS) has been developed as a powerful tool for drug metabolism simulation. The application of EC in metabolic studies is particularly favourable due to the low matrix contribution compared to in vitro or in vivo biological models. In this paper, the EC(/LC)/MS system was applied to simulate phase I metabolism of the representative two unsymmetrical bisacridines (UAs), named C-2028 and C-2053, which contain nitroaromatic group susceptible to reductive transformations. UAs are a novel potent class of antitumor agents of extraordinary structures that may be useful in the treatment of difficult for therapy human solid tumors such as breast, colon, prostate, and pancreatic tumors. It is considered that the biological action of these compounds may be due to the redox properties of the nitroaromatic group. At first, the relevant conditions for the electrochemical conversion and product identification process, including the electrode potential range, electrolyte composition, and working electrode material, were optimized with the application of 1-nitroacridine as a model compound. Electrochemical simulation of C-2028 and C-2053 reductive metabolism resulted in the generation of six and five products, respectively. The formation of hydroxylamine m/z [M+H-14]⁺, amine m/z [M+H-30]⁺, and novel N-oxide m/z [M+H-18]⁺ species from UAs was demonstrated. Furthermore, both studied compounds were shown to be stable, retaining their dimeric forms, during electrochemical experiments. The electrochemical method also indicated the susceptibility of C-2028 to phase II metabolic reactions. The respective glutathione and dithiothreitol adducts of C-2028 were identified as ions at m/z 873 and m/z 720. In conclusion, the electrochemical reductive transformations of antitumor UAs allowed for the synthesis of new reactive intermediate forms permitting the study of their interactions with biologically crucial molecules.

Rapid electrochemical reduction of a typical chlorinated organophosphorus flame retardant on copper foam: degradation kinetics and mechanisms

With the widespread use, chlorinated organophosphorus flame retardants (Cl-OPFRs) as a new emerging contaminant have been widely detected in water environments over the last few years. In this study, the degradation of a typical Cl-OPFR, TCEP (tris (2-chloroethyl) phosphate), by electrochemical reduction was investigated. It was found that copper (Cu) foam as the cathode showed more rapid and effective degradation for TCEP, compared to other cathodes. When TCEP was at the low concentrations (0.1 and 1 mg L^-1), its degradation by Cu foam could reach above 95% within 20 min, and the maximum rate constant was 0.127 min-1. TCEP reduction was little influenced by the co-existing humic substance and anions, except Cl^-. Compared with the reported oxidation methods, electrochemical reduction showed fast and stable degradation for TCEP. For other types of Cl-OPFRs, electrochemical reduction displayed a fast and effective removal for tris (1,3-dichloro-2-propyl) phosphate but lower removal for tris (2-cholroisopropyl) phosphate who possessed methyl units in the branched chains, influencing its reducibility. Based on the product analysis and Fukui function calculation, the bonds of TCEP molecule were found to be gradually broken, and the three oxygen-ethyl-chlorine arms were cleaved one by one. The products including C₆H₁₃Cl₂O₄P (MW = 249.99278 Da), C₄H₉Cl₂O₄P (MW = 221.96105 Da) and C₄H₁₀ClO₄P (MW = 188.0002 Da) were detected at 60 min reaction, and those intermediates showed much lower toxicities than TCEP according to the previous report. The findings may provide a promising treatment for Cl-OPFRs removal from aqueous environments and help understand their reductive fate.

Highly selective and active Cu-In2O3/C nanocomposite for electrocatalytic reduction of CO2 to CO

The Cu-In₂O₃/C nanocomposite was prepared by a simple solid-phase reduction method. The introduction of In₂O₃ into Cu/C to form the Cu-In₂O₃/C nanocomposite evidently enhances the electrocatalytic activity for the selective reduction of CO₂ to CO. Specifically, the Cu-In₂O₃/C nanocomposite exhibits higher Faraday efficiency (FE = 86.7%) at -0.48 V vs. the reversible hydrogen electrode (RHE) in the electrocatalytic reduction of CO₂ to CO and larger current densities (55 mA cm^-2) under a low overpotential (-1.08 V vs. RHE). These indicate its superior performance over many of the reported Cu-based catalysts [1-4]. It was also found that by rationally adjusting the applied potential, tunable syngas can be formed, which can be used to synthesize formic acid, methyl ether, methanol, synthetic fuels, or other bulk chemicals through appropriate industrial processes. Furthermore, the Cu-In₂O₃/C nanocomposite maintains good stability in the electrocatalytic reduction of CO₂. This work demonstrates a novel strategy to convert CO₂ into desired products with high energy efficiency and large current density under low overpotential by the rational designing of non-precious metal catalysts.

Carbon dioxide reduction to multicarbon hydrocarbons and oxygenates on plant moss-derived, metal-free, in situ nitrogen-doped biochar

Electrochemical reduction of carbon dioxide (CO₂) is considered a promising renewable energy conversion technology, but it remains challenging to find active, stable, low-cost, and highly efficient electrocatalysts for the CO₂ conversion. Here, we develop an in situ nitrogen-doped, metal-free, porous biochar from plant moss to catalyze the electrochemical reduction of CO₂ into methane (CH₄), methanol (CH₃OH) and ethanol (C₂H₅OH) at high current densities and low overpotentials. Using this metal-free biochar electrocatalyst, production rates of approximately 36.1, 32.1, and 18.1 μg h^-1 cm^-2 towards CH₄, C₂H₅OH, and CH₃OH are obtained with Faradaic efficiencies of 56.0%, 26.0% and 10.5%, respectively. In addition, the total faradaic efficiency reaches 92.6% at -1.2 V (vs. Ag/AgCl) with good stability. A favorable pathway for the electrochemical reduction of CO₂ over the metal-free biochar is also provided. This study presents a new approach to produce cost-effective, in situ nitrogen-doped porous biochars with excellent efficiency and durability for the electrochemical reduction of CO₂.

An acidic residue reactive and disulfide bond-containing cleavable cross-linker for probing protein 3D structures based on electrochemical mass spectrometry

Cross-linking mass spectrometry (XL-MS) has attracted broad attention because of the capability to probe three-dimensional structure of proteins. Up to now, several amine-reactive cross-linkers have been developed for characterization of proteins and protein complexes. However, spatial information retrieved by XL-MS is still limited, partly because the strategies using an acidic residue reactive cross-linker have been rarely reported. In this paper, an acidic residue (e.g. aspartic acid, glutamic acid)-specific, disulfide bond-containing, cleavable cross-linker with a length of 13.1 Å, named 3,3'-dithiobis(propanoic dihydrazide), was presented for the first time. In addition, a novel approach using the cross-linker was proposed for unambiguous characterization of peptides and proteins with disulfide bonds. After cross-linked, the peptides could be electrochemically reduced, then characterized by high performance liquid chromatography mass spectrometry. For demonstration, the approach has been adopted to characterize the emideltide, insulin, and myoglobin, of which four pairs of intrachain cross-links have been successfully identified in myoglobin. The results showed that the cross-links displayed predictable fragmentation pattern upon collision induced dissociation (CID), thus admitting simplifying data analysis. In summary, this work introduces a novel type of cross-linker utilized for cross-linking and a new strategy to XL-MS technology for comprehensively understanding the three-dimensional structure of proteins.

Extraction of Co and Li2CO3 from cathode materials of spent lithium-ion batteries through a combined acid-leaching and electro-deoxidation approach

Recycling of the spent LIBs to extract Li and Co not only offers raw materials for batteries but also lays a sustainable way for battery development. Herein, we adopt a route combining hydrometallurgical and pyro-electrochemical routes to extract Li₂CO₃ and Co powder from the spent LIBs of cell phones. The LiCoO₂-based cathode materials were firstly dissolved in H₂SO₄ solution containing H₂O₂ as the reductant, and the optimal conditions for attaining a high extraction rate of 99% were studied. After that, the precipitated Co(OH)₂ was calcinated in air under 500 °C to generate Co₃O₄ which was thereafter electrochemically converted into Co powder and oxygen in molten Na₂CO₃-K₂CO₃. Overall, the hybrid method employing both hydro- and pyro-route provides an effective pathway to recover both Li₂CO₃ and Co powder from spent LIBs.

Electrocatalytic synthesis of black tin oxide nanomaterial as photothermal agent for cancer therapy

Photothermal therapy (PTT) is among the popular approach for treating solid tumours. The rapid killing of cancer cells under the influence of infrared radiation by a rapid increase in the temperature of the remote area now demands external agents with high photothermal transduction efficiency (PTE). Despite their improved PTE, black nanomaterials such as black phosphorus and titanium oxide are unable to meet the challenges in the physiological conditions. To address this major concern, we have developed black tin oxide (bSnO) with enhanced capabilities to respond in the physiological milieu. To make the synthesis cost-effective and eco-friendly, we have used electrochemical oxidation at 5 V and 100 mA to achieve ∼15 nm nanoparticle of bSnO. The as-synthesized bSnO exhibited high NIR absorption as well as high photothermal transduction efficiency. To circumvent the low aqueous solubility and photostability, bSnO was functionalized with polyethyleneimine (PEI). Upon exposure to 808 nm laser for ∼8-10 min, the temperature of the bSnO@PEI solution reached ∼58.5 °C. PTE of bSnO@PEI was calculated to be 51.2%. Owing to its high biological compatibility, tin offers relatively better stability when exposed to cancer cells in vitro and in vivo. In comparison to other black nanomaterials, bSnO@PEI was found to exhibit better response under NIR irradiance for non-invasive photothermal therapy of cancer.

Looking Back and Looking Ahead in Electrochemical Reduction of CO2

Electrochemical reduction of carbon dioxide (CO₂ ) to valuable organic compounds is promising as to recycling of carbon source of CO₂ and technical compatibility with systems using renewable energy resources. In recent years, considerable efforts have been devoted to the research field of CO₂ conversion using electrocatalysis. This personal account particularly focuses on the recent progress that has been achieved by the Ertl Center and a number of groups in South Korea that becomes one of the larger CO₂ emitters. The research trends of catalyst development divided into different categories according to the primary products are presented first. Afterwards, several studies on theoretical calculations and electrolytic reactors are reviewed taking into account the fundamental understanding and feasibility of the CO₂ electroreduction. Finally, a perspective on the challenges and needs in achieving the advanced level of research and development is presented.

2,4-Dichlorophenol removal from water using an electrochemical method improved by a composite molecularly imprinted membrane/bipolar membrane

Low efficiency is often a problem in electrochemical reductive hydrodechlorination (ERHD) to remove chlorinated compounds such as 2,4-dichlorophenol (24DCP) from water. In this study, a composite molecularly imprinted membrane (MIM)/bipolar membrane (BPM) was introduced onto a palladium-coated titanium mesh electrode (BPM/MIM@Pd/Ti) to increase the concentration of 24DCP on the surface of electrode and ERHD efficiency. The efficiency of ERHD of 24DCP increased from 70 to 88% by introduction of the two membranes, from 71 to 89% by increasing current density from 5.0 to 30 mA/cm², and from 80 to 94% by increasing the electrolyte concentration from 0.25 to 1.00 mol/L. Treatment with Fenton's reagent after ERHD achieved 100% 24DCP removal, with chemical oxygen demand and total organic carbon reductions of 91 and 87%, respectively. Notably, these reductions were greater than obtained from the direct oxidation of the 24DCP solution by Fenton's reagent alone (i.e., 98, 84, and 72%, respectively). No products were detected in solution by GC-MS after treatment with the proposed combination technology. The mechanism of 24DCP removal and degradation involved adsorption, electrochemical hydrodechlorination via H_ads, and Fenton oxidation. Results show the process has high potential for removing 24DCP from aqueous solution.

Ti plate with TiO2 nanotube arrays as a novel cathode for nitrate reduction

The purpose of this research is to investigate the possibility of using a Ti plate with TiO₂ nanotube arrays as a novel cathode for nitrate reduction. TiO₂ nanotube arrays were grown on a Ti plate by anodization in a glycerol based electrolyte and annealed to change their crystallographic structure. Morphological and crystallographic structures of Ti plates with a TiO₂ nanotubular layer were analysed before and after anodization or annealing by using energy-dispersive spectroscopy, Brunauer-Emmett-Teller analysis and X-ray diffraction. Cyclic voltammetry and electrochemical impedance spectroscopy were also performed to test the electrochemical reactivity towards nitrate reduction. A lab-scale electrochemical reactor with a RuO₂/Ti anode and a Ti plate with a TiO₂ nanotubular layer as a cathode was operated to treat synthetic wastewater containing up to 600 mg L^-1 of NO₃-N. The Ti plate with a TiO₂ nanotubular layer was compared with other cathodes such as Ti, Cu, Ni, and Stainless Steel. The Ti plate with an anatase TiO₂ nanotubular layer with a layer thicknesses greater than 45 μm was able to show the most efficient nitrate reduction.

Disulfide linkage assignment based on reducing electrochemistry and mass spectrometry using a lead electrode

The study of disulfide linkage is a crucial part of the quality assessment of biopharmaceutical products because disulfide bonds stabilize the tertiary structure of proteins and maintain protein functions. Therefore, a suitable method is highly required for disulfide linkage assignment when nested disulfide bonds formed with closely spaced cysteine residues. A novel approach for disulfide linkage assignment of disulfide-rich peptides and proteins via electrochemical reduction on a lead electrode with mass spectrometry is presented in this paper. The method features partial electrochemical reduction and alkylation of peptides followed by alkylated peptide sequencing based on tandem mass spectrometry. Lead was chosen for the first time as an electrode material for disulfide bond reduction, because it has the advantages of maintenance free (only infrequent polishing needed), easy operation in DC mode, and reusability. Without any special sample preparation and any chemical reduction agents, disulfide bond in peptides can be cleaved rapidly. The new method was successfully tested with two peptides and one protein containing nested disulfide bonds.

Electrochemical removal of nitrate by Cu/Ti electrode coupled with copper-modified activated carbon particles at a low current density

Electrochemical reduction is currently one of promising methods for nitrate removal from water, yet most treatment approaches have problems of high cost and energy consumption. In this work, a low current density was applied in electrochemical reduction of nitrate. Copper-modified titanium (Cu/Ti) electrodes with optimal electrochemical activity and fastest kinetics were firstly screened. Thirty minutes of electrodeposition time and neutral pH were found to have the greatest nitrate reduction rate of 83.14%. To further improve the removal of nitrate, activated carbon (AC) and copper-modified activated carbon (Cu/AC) particles were applied to construct three-dimensional reaction systems, with removal rates of nitrate of 88.72% and 96.05%, respectively. The average conversion rates of nitrate to ammonia nitrogen increased from 15.28% to 42.68% and 62.64% in AC- and Cu/AC-based reaction systems, respectively. Oxidation of Cu(0) on surfaces of Cu/Ti cathode and Cu/AC particles to Cu(I) was revealed by X-ray photoelectron spectroscopy (XPS) and Cu LMM spectra analysis. Besides, results of water chemistry characteristics indicated the conversion of AC to carbonate ion. It could be concluded that enhanced nitrate reduction of Cu/Ti-based reaction system was attributed by Cu particle- and AC-mediated electron transfer. This study provided a reference for low-cost electrochemical reduction of nitrate.

Recent electrochemical methods in electrochemical degradation of halogenated organics: a review

Halogenated organics are widely used in modern industry, agriculture, and medicine, and their large-scale emissions have led to soil and water pollution. Electrochemical methods are attractive and promising techniques for wastewater treatment and have been developed for degradation of halogenated organic pollutants under mild conditions. Electrochemical techniques are classified according to main reaction pathways: (i) electrochemical reduction, in which cleavage of C-X (X = F, Cl, Br, I) bonds to release halide ions and produce non-halogenated and non-toxic organics and (ii) electrochemical oxidation, in which halogenated organics are degraded by electrogenerated oxidants. The electrode material is crucial to the degradation efficiency of an electrochemical process. Much research has therefore been devoted to developing appropriate electrode materials for practical applications. This paper reviews recent developments in electrode materials for electrochemical degradation of halogenated organics. And at the end of this paper, the characteristics of new combination methods, such as photocatalysis, nanofiltration, and the use of biochemical method, are discussed.

Reduced Graphene Oxide/Carbon Nanotube Composites as Electrochemical Energy Storage Electrode Applications

We demonstrate an electrochemical reduction method to reduce graphene oxide (GO) to electrochemically reduced graphene oxide (ERGO) with the assistance of carbon nanotubes (CNTs). The faster and more efficient reduction of GO can be achieved after proper addition of CNTs into GO during the reduction process. This nanotube/nanosheet composite was deposited on electrode as active material for electrochemical energy storage applications. It has been found that the specific capacitance of the composite film was strongly affected by the mass ratio of GO/CNTs and the scanning ratio of cyclic voltammetry. The obtained ERGO/CNT composite electrode exhibited a 279.4 F/g-specific capacitance and showed good cycle rate performance with the evidence that the specific capacitance maintained above 90% after 6000 cycles. The synergistic effect between ERGO and CNTs as well as crossing over of CNTs into ERGO is attributed to the high electrochemical performance of composite electrode.

Design and applications of Ti nano-electrode for denitrification of groundwater

In the present study, a Ti-nano-electrode was fabricated for electrochemical denitrification. Response surface methodology (RSM) was utilized for the optimization of the factors that influence the production of Ti nano-electrodes. Box-Behnken design was applied to develop mathematical models for predicting the best electrochemical nitrate removal geometry. Parameters interacting together can be identified in this typical electrochemical removal process. A correlation coefficient R² > 0.90 for the mathematical model was predicted to be a high correlation between observed and predicted values. The optimal NH₄F concentration, oxidation time and oxidation voltage for preparation of Ti nano-electrode in the present experiment are 0.03 wt%, 34.61 min and 6.31 V, respectively. In this case, the increase in the nitrate reduction efficiency was more d (105%) than that from an untreated electrode, and energy consumption was 4.45 × 10^-4 kWh.

Direct and indirect electrochemical reduction prior to a biological treatment for dimetridazole removal

Two different electrochemical reduction processes for the removal of dimetridazole, a nitroimidazole-based antibiotic, were examined in this work. A direct electrochemical reduction was first carried out in a home-made flow cell in acidic medium at potentials chosen to minimize the formation of amino derivatives and then the formation of azo dimer. Analysis of the electrolyzed solution showed a total degradation of dimetridazole and the BOD₅/COD ratio increased from 0.13 to 0.24. An indirect electrochemical reduction in the presence of titanocene dichloride ((C₅H₅)₂TiCl₂), which is used to reduce selectively nitro compounds, was then investigated to favour the formation of amino compounds over hydroxylamines and then to prevent the formation of azo and azoxy dimers. UPLC-MS/MS analyses showed a higher selectivity towards the formation of the amino compound for indirect electrolyses performed at pH 2. To confirm the effectiveness of the electrochemical reduction, a biological treatment involving activated sludge was then carried out after direct and indirect electrolyses at different pH. The enhancement of the biodegradability was clearly shown since mineralization yields of all electrolyzed solutions increased significantly.

The electrochemical selective reduction of NO using CoSe2@CNTs hybrid

Converting the NO from gaseous pollutant into NH₄⁺ through electrocatalytical reduction using cost-effective materials holds great promise for pollutant purifying and resources recycling. In this work, we developed a highly selective and stable catalyst CoSe₂ nanoparticle hybridized with carbon nanotubes (CoSe₂@CNTs). The CoSe₂@CNTs hybrid catalysts performed an extraordinary high selectivity for NH₄⁺ formation in NO electroreduction with minimal N₂O production and H₂ evolution. The specific spatial structure of CoSe₂ is conductive to the predominant formation of N-H bond between the N from adsorbed NO and H and inhibition of N-N formation from adjacent adsorbed NO. It was also the first time to convert the coordinated NO into NH₄⁺ using non-noble metal catalysis. Moreover, the original concept of employing CoSe₂ as eletrocatalyst for NO hydrogenation presented in this work can broaden horizons and provide new dimensions in the design of new highly efficient catalysts for NH₄⁺ synthesis in aqueous solution.

Technological advances in CO2 conversion electro-biorefinery: A step toward commercialization

The global atmospheric warming due to increased emissions of carbon dioxide (CO2) has attracted great attention in the last two decades. Although different CO2 capture and storage platforms have been proposed, the utilization of captured CO2 from industrial plants is progressively prevalent strategy due to concerns about the safety of terrestrial and aquatic CO2 storage. Two utilization forms were proposed, direct utilization of CO2 and conversion of CO2 to chemicals and energy products. The latter strategy includes the bioelectrochemical techniques in which electricity can be used as an energy source for the microbial catalytic production of fuels and other organic products from CO2. This approach is a potential technique in which CO2 emissions are not only reduced, but it also produce more value-added products. This review article highlights the different methodologies for the bioelectrochemical utilization of CO2, with distinctive focus on the potential opportunities for the commercialization of these techniques.

Highly sensitive interference-free electrochemical determination of pyridoxine at graphene modified electrode: Importance in Parkinson and Asthma treatments

To reduce the side effects in the medication of Parkinson and Asthma, pyridoxine (PY) is administered along with l-3,4-dihydroxyphenyl alanine (l-dopa) and theophylline (TP), respectively. However, excessive dosage of PY leads to nervous disorder. Thus, a sensitive and selective electrochemical method was developed for the determination of PY in the presence of major interferences including TP, l-dopa, ascorbic acid (AA) and riboflavin (RB) using electrochemically reduced graphene oxide (ERGO) film modified glassy carbon electrode (GCE) in this paper. The ERGO fabrication process involves the nucleophilic substitution of graphene oxide at basic pH on amine terminal of 1,6-hexadiamine which was pre-assembled on GCE followed by electrochemical reduction. The electrocatalytic activity of the ERGO modified electrode was examined towards the oxidation of PY. It greatly enhanced the oxidation current of PY in contrast to bare and GO modified GCEs due to facile electron transfer besides π-π interaction between ERGO film and PY. Since TP and l-dopa drugs antagonize the drug action of PY, ERGO modified GCE was also used for the simultaneous determination of PY and l-dopa and PY and TP. Further, the selective determination of PY in the presence of other water soluble vitamins such as ascorbic acid and riboflavin was also demonstrated. Using amperometry, detection of 100nM PY was achieved and the detection limit was found to be 5.6×10(-8)M (S/N=3). The practical application of the present method was demonstrated by determining the concentration of PY in human blood serum and commercial drugs.

Simultaneous removal of NOx and SO2 from flue gas using combined Na2SO3 assisted electrochemical reduction and direct electrochemical reduction

A method combining Na2SO3 assisted electrochemical reduction and direct electrochemical reduction using Fe(II)(EDTA) solution was proposed to simultaneously remove NOx and SO2 from flue gas. Activated carbon was used as catalyst to accelerate the process. This new system features (a) direct conversion of NOx and SO2 to harmless N2 and SO4(2-); (b) fast regeneration of Fe(II)(EDTA); (c) minimum use of chemical reagents; and (d) recovery of the reduction by-product (Na2SO4). Fe(II)(EDTA) solution was continuously recycled and reused during entire process, and no harmful waste was generated. Approximately 99% NOx and 98% SO2 were removed under the optimal condition. The stability test showed that the system operation was reliable.

Enhanced catalytic and dopamine sensing properties of electrochemically reduced conducting polymer nanocomposite doped with pure graphene oxide

Significantly enhanced catalytic activity of a nanocomposite composed of conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) doped with graphene oxide (GO) was achieved through a simple electrochemical reduction process. The nanocomposite (PEDOT/GO) was electrodeposited on an electrode and followed by electrochemical reduction, and the obtained reduced nanocomposite (PEDOT/RGO) modified electrode exhibited lowered electrochemical impedance and excellent electrocatalytic activity towards the oxidation of dopamine. Based on the excellent catalytic property of PEDOT/RGO, an electrochemical sensor capable of sensitive and selective detection of DA was developed. The fabricated sensor can detect DA in a wide linear range from 0.1 to 175μM, with a detection limit of 39nM, and it is free from common interferences such as uric acid and ascorbic acid.

Electrochemical behavior of N-methyl-N'-carboxydecyl-4,4'-bipyridinium probed by surface-enhanced Raman spectroscopy

Interfacial structure determines the activity and selectivity of a sensor and plays important roles in interfacial electrochemistry, electroanalysis, biosensing, etc. In situ electrochemical Raman spectroscopy appears to be a powerful tool to probe the electrochemical interface and surface process by providing the molecular fingerprint information. Herein, the electrochemical behaviors of N-methyl-N'-carboxydecyl-4,4'-bipyridinium (derivatives of methyl viologens, MV(2+)) with different alkyl chain lengths (n=2 and 10) on roughened Au electrodes were systematically investigated by the electrochemical surface-enhanced Raman spectroscopy (SERS). Three systems with different interfacial structures were constructed. One is to anchor the MV(2+) molecules via esterification with the 2-mercaptoethanol molecule pre-assembled on the Au surface. The second system is similar to the first one but without esterification. The third system is the direct adsorption of MV(2+) molecules on the bare roughened Au surfaces. The three systems gave different spectral response upon the change of the electrode potential. A drastically increased relative Raman intensity of 19a/8a modes of the MV(2+) molecules was observed at negative potentials. The phenomenon is attributed to the formation of the reduced form of MV(2+) molecules, which produces resonant Raman effect to enhanced the signal of 19a mode. The third system showed the highest electrochemical reduction activity towards the reduction of MV(2+) molecules, followed by the first and second systems. The result indicates that the interfacial structure can sensitively influence electrochemical activity of the electrode.

Voltammetric Behavior of o-Nitrophenol and Damage to DNA

The electrochemical behavior of o-nitrophenol was studied in detail with a glassy carbon electrode (GCE). The dependence of peak potential on pH indicated that equivalent electrons and protons were involved in the process of o-nitrophenol reduction. The interaction of o-nitrophenol with calf thymus DNA was investigated by adding DNA to the o-nitrophenol solution and by immobilizing DNA on GCE, respectively. The peak current decrement and peak potential shift in presence of DNA indicated that o-nitrophenol could interact with DNA. The result was demonstrated that the in situ DNA damage was detected by differential pulse voltammetry after the o-nitrophenol was electrochemically reduced.