Electrochemical multiwalled carbon nanotube filter for viral and bacterial removal and inactivation

Nanotechnology has potential to offer solutions to problems facing the developing world. Here, we demonstrate the efficacy of an anodic multiwalled carbon nanotube (MWNT) microfilter toward the removal and inactivation of viruses (MS2) and bacteria (E. coli). In the absence of electrolysis, the MWNT filter is effective for complete removal of bacteria by sieving and multilog removal of viruses by depth-filtration. Concomitant electrolysis during filtration results in significantly increased inactivation of influent bacteria and viruses. At applied potentials of 2 and 3 V, the electrochemical MWNT filter reduced the number of bacteria and viruses in the effluent to below the limit of detection. Application of 2 and 3 V for 30 s postfiltration inactivated >75% of the sieved bacteria and >99.6% of the adsorbed viruses. Electrolyte concentration and composition had no correlation to electrochemical inactivation consistent with a direct oxidation mechanism at the MWNT filter surface. Potential dependent dye oxidation and E. coli morphological changes also support a direct oxidation mechanism. Advantages of the electrochemical MWNT filter for pathogen removal and inactivation and potential for point-of-use drinking water treatment are discussed.     

Efficient electrochemical oxidation of perfluorooctanoate using a Ti/SnO2-Sb-Bi anode

The electrochemical decomposition of persistent perfluorooctanoate (PFOA) with a Ti/SnO2-Sb-Bi electrode was demonstrated in this study. After 2 h electrolysis, over 99% of PFOA (25 mL of 50 mg·L(-1)) was degraded with a first-order kinetic constant of 1.93 h(-1). The intermediate products including short-chain perfluorocarboxyl anions (CF3COO-, C2F5COO-, C3F7COO-, C4F9COO-, C5F11COO-, and C6F13COO-) and F- were detected in the aqueous solution. The electrochemical oxidation mechanism was revealed, that PFOA decomposition first occurred through a direct one electron transfer from the carboxyl group in PFOA to the anode at the potential of 3.37 V (vs saturated calomel electrode, SCE). After that, the PFOA radical was decarboxylated to form perfluoroheptyl radical which allowed a defluorination reaction between perfluoroheptyl radical and hydroxyl radical/O2. Electrospray ionization (ESI) mass spectrum further confirmed that the oxidation of PFOA on the Ti/SnO2-Sb-Bi electrode proceeded from the carboxyl group in PFOA rather than C-C cleavage, and the decomposition processes followed the CF2 unzipping cycle. The electrochemical technique with the Ti/SnO2-Sb-Bi electrode provided a potential method for PFOA degradation in the aqueous solution.     

Synergetic degradation of rhodamine B at a porous ZnWO4 film electrode by combined electro-oxidation and photocatalysis

Synergetic degradation of rhodamine B (RhB) was investigated by combining electro-oxidation and photocatalysis using porous ZnWO4 film at various bias potentials. The applied bias potential below 0.8 V enhanced the photocatalytic degradation of RhB by promoting the separation and transfer of photogenerated holes and electrons. At the potential between 0.8 and 1.0 V, the degradation of RhB was further enhanced, which is induced by direct electro-oxidation and photocatalysis. At the potential greater than 1.3 V, indirect electro-oxidation of RhB occurred with the largest synergetic effect. The synergetic effect can also increase the mineralization degree of the RhB. On the basis of the X-ray photoelectron spectra (XPS) analysis of the surface of the electrode after electrochemical reaction, the electropolymerization occurred which blocked the electrode and slowed the electro-oxidation of RhB. Active species generated via the photocatalytic process can activate the passivated electrode and promote the electro-oxidation of RhB. The O2 electrochemically generated at the anode promoted the photocatalysis by capturing the photogenerated electrons and may induce the formation of H2O2. Thus, more active species could be formed through new reactive routines in the photoelectrocatalytic (PEC) process. RhB degradation was mainlythrough decomposition of the conjugated chromophore structure with slight occurrence of de-ethylation. The stability of the electrode in the PEC process was confirmed based on the XPS and Raman analysis.     

漂白废水中氯化木素的电氧化处理

用二氧化铅作阳极,不锈钢网为阴极,通过电氧化法处理多段漂白废水中的氯化木素。研究发现,废水中氯化木素的浓度及电导率均是随时间先增加后减少;而废水的COD和色度在整个过程中一直减少;废水的pH在电氧化初期不变,在中后期下降。木素的芳香环在电氧化过程中,会发生开环反应。不同的电解电压对电氧化处理效果有不同的影响。     

Electrochemical oxidation characteristics of p-substituted phenols using a boron-doped diamond electrode

Electrochemical oxidation of some p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) with electron-donating and -withdrawing substituents was studied to reveal the relationship between the structure and the electrochemical reactivity of p-substituted phenols using a boron-doped diamond electrode by voltammetry and bulk electrolysis. Voltammetric study shows that the oxidation peak potentials of p-substituted phenols become more positive with an increase of Hammett's constants, that is, the direct electrochemical oxidation of p-substituted phenol with an electron-withdrawing group is more difficult than that of p-substituted phenol with an electron-donating group. However,the p-substituted phenols with electron-withdrawing groups are degraded faster than those with electron-donating groups in bulk electrolysis, which is opposite to the result obtained on the Pt electrode. These results indicate that the p-substituted phenols are mainly degraded by indirect electrochemical oxidation with hydroxyl radicals on a boron-doped diamond electrode. Under the attack of hydroxyl radicals, the release of p-substituted groups from the aromatic ring is the rate-limiting step. Since electron-withdrawing groups are easy to be released, the p-substituted phenols with these groups are degraded faster than those with electron-donating groups. Therefore, the degradation rates of the p-substituted phenols rise with an increase of Hammett's constants.     

Electricity-assisted biological hydrogen production from acetate by Geobacter sulfurreducens

Geobacter sulfurreducens is a well-known current-producing microorganism in microbial fuel cells, and is able to use acetate and hydrogen as electron donor. We studied the functionality of G. sulfurreducens as biocatalyst for hydrogen formation at the cathode of a microbial electrolysis cell (MEC). Geobacter sulfurreducens was grown in the bioelectrode compartment of a MFC with acetate as the substrate and reduction of complexed Fe(III) at the counter electrode. After depletion of the acetate the electrode potential of the bioelectrode was decreased stepwise to -1.0 V vs Ag/AgCl reference. Production of negative current was observed, which increased in time, indicating that the bioelectrode was now acting as biocathode. Headspace analyses carried out at electrode potentials ranging from -0.8 to -1.0 V showed that hydrogen was produced, with higher rates at more negative cathode potentials. Subsequently, the metabolic properties of G. sulfurreducens for acetate oxidation at the anode and hydrogen production at the cathode were combined in one-compartment membraneless MECs operated at applied voltages of 0.8 and 0.65 V. After two days, current densities were 0.44 A m(-2) at 0.8 V applied voltage and 0.22 A m(-2) at 0.65 V, using flat-surface carbon electrodes for both anode and cathode. The cathodic hydrogen recovery ranged from 23% at 0.5 V applied voltage to 43% at 0.9 V.     

Mechanism of perchlorate formation on boron-doped diamond film anodes

This research investigated the mechanism of perchlorate (ClO(4)(-)) formation from chlorate (ClO(3)(-)) on boron-doped diamond (BDD) film anodes by use of a rotating disk electrode reactor. Rates of ClO(4)(-) formation were determined as functions of the electrode potential (2.29-2.70 V/standard hydrogen electrode, SHE) and temperature (10-40 °C). At all applied potentials and a ClO(3)(-) concentration of 1 mM, ClO(4)(-) production rates were zeroth-order with respect to ClO(4)(-) concentration. Experimental and density functional theory (DFT) results indicate that ClO(3)(-) oxidation proceeds via a combination of direct electron transfer and hydroxyl radical oxidation with a measured apparent activation energy of 6.9 ± 1.8 kJ·mol(-1) at a potential of 2.60 V/SHE. DFT simulations indicate that the ClO(4)(-) formation mechanism involves direct oxidation of ClO(3)(-) at the BDD surface to form ClO(3)(?), which becomes activationless at potentials > 0.76 V/SHE. Perchloric acid is then formed via the activationless homogeneous reaction between ClO(3)(?) and OH(?) in the diffuse layer next to the BDD surface. DFT simulations also indicate that the reduction of ClO(3)(?) can occur at radical sites on the BDD surface to form ClO(3)(-) and ClO(2), which limits the overall rate of ClO(4)(-) formation.     

Preparation of titania nanotubes and their environmental applications as electrode

Titanium oxide nanotubes were successfully grown from a titanium plate by direct anodic oxidation with 0.2 wt % hydrofluoric acid being the supporting electrolyte. These nanotubes are of uniform size and are well-aligned into high-density arrays. They look like honeywell with the structure similar to that of porous alumina obtained by the same technique. TiO2 anatase phase was identified by X-ray diffraction. Significant blue-shift in the spectrum of UV- vis absorption was observed. The mechanism of the novel, simple, and direct growth of the nanotubes was postulated. To investigate their potentials in environmental applications, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photoelectrocatalytic (PEC) processes, comparing with electrochemical process (EP) and photocatalytic (PC). A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using TiO2 nanotubes electrode was 86.5% higher than that using TiO2 film electrode. In degrading PCP, 70% of TOC was removed using the TiO2 nanotubes electrode against 50% removed using TiO2 film electrode formed by sol-gel method in 4 h under similar conditions.     

Development of an E-H2O2/TiO2 photoelectrocatalytic oxidation system for water and wastewater treatment

In this study, an innovative E-H2O2/TiO2 (E-H2O2 = electrogenerated hydrogen peroxide) photoelectrocatalytic (PEC) oxidation system was successfully developed for water and wastewater treatment. A TiO2/Ti mesh electrode was applied in this photoreactor as the anode to conduct PEC oxidation, and a reticulated vitreous carbon (RVC) electrode was used as the cathode to electrogenerate hydrogen peroxide simultaneously. The TiO2/Ti mesh electrode was prepared with a modified anodic oxidation process in a quadrielectrolyte (H2SO4-H3PO4-H2O2-HF) solution. The crystal structure, surface morphology, and film thickness of the TiO2/Ti mesh electrode were characterized by X-ray diffraction and scanning electron microscopy. The analytical results showed that a honeycomb-type anatase film with a thickness of 5 microm was formed. Photocatalytic oxidation (PC) and PEC oxidation of 2,4,6-trichlorophenol (TCP) in an aqueous solution were performed under various experimental conditions. Experimental results showed that the TiO2/Ti electrode, anodized in the H2SO4-H3PO4-H2O2-HF solution, had higher photocatalytic activity than the TiO2/Ti electrode anodized in the H2SO4 solution. It was found that the maximum applied potential would be around 2.5 V, corresponding to an optimum applied current density of 50 microA cm(-2) under UV-A illumination. The experiments confirmed that the E-H2O2 on the RVC electrode can significantly enhance the PEC oxidation of TCP in aqueous solution. The rate of TCP degradation in such an E-H2O2-assisted TiO2 PEC reaction was 5.0 times that of the TiO2 PC reaction and 2.3 times that of the TiO2 PEC reaction. The variation of pH during the E-H2O2-assisted TiO2 PEC reaction, affected by individual reactions, was also investigated. It was found that pH was well maintained during the TCP degradation in such an E-H2O2/TiO2 reaction system. This is beneficial to TCP degradation in an aqueous solution.     

快速电化学法检测牛乳中的过氧化氢

目的 建立一种快速电化学法检测牛乳中的过氧化氢(H2O2)。方法 设计简单的三电极电化学反应池,制备普鲁士蓝(PB)修饰的石墨粉电极, 研究制得电极对H2O2的电化学响应, 用于牛乳中H2O2的快速电化学检测。结果 在?0.1 V处, 对0.2~1.4 mmol/L的H2O2具有线性响应。该电化学方法用于实际牛乳样品中H2O2的检测, 检测的回收率在91%~106%之间。结论 该H2O2电化学检测方法简单、快速、灵敏、价格低廉。     

Electrochemical oxidation for low concentration of aniline in neutral pH medium: application to the removal of aniline based on the electrochemical polymerization on a carbon fiber

Aniline, which causes serious environmental problems, was electrochemically treated and thereby removed from aqueous solution. This method demonstrated herein is based on the formation of polyaniline at an electrode surface by electrochemical oxidation. Initially, the electrode behavior of aniline at several conditions was investigated on a platinum, glassy carbon (GC), and carbon fiber (CF) electrode using voltammetric techniques. On the platinum electrode, aniline did not polymerize at low concentrations. However, electropolymerization of aniline was observed on both the GC and CF electrodes even at low concentrations in neutral pH solutions. The removal of aniline was carried out using a CF bundle with a large surface area. High removal efficiency for aniline was obtained by applying potentials greater than 0.8 V. Although generation of p-benzoquinone as a byproduct was observed during electrochemical treatment, its generation was suppressed by applying a potential lower than 0.9 V. The cyclic voltammograms and X-ray photoelectron spectra of the CF after the treatment for aniline solution showed that polymeric aniline existed on the CF surface. The maximum surface coverage of electropolymerized aniline was estimated to be about 1.49 x 10(-8) mol/cm2. Furthermore, the continuous treatment of aniline was demonstrated using a flow system.     

Electrochemistry of free chlorine and monochloramine and its relevance to the presence of Pb in drinking water

The commonly used disinfectants in drinking water are free chlorine (in the form of HOCl/OCl-) and monochloramine (NH2Cl). While free chlorine reacts with natural organic matter in water to produce chlorinated hydrocarbon byproducts, there is also concern that NH2Cl may react with Pbto produce soluble Pb(II) products--leading to elevated Pb levels in drinking water. In this study, electrochemical methods are used to compare the thermodynamics and kinetics of the reduction of these two disinfectants. The standard reduction potential for NH2Cl/Cl- was estimated to be +1.45 V in acidic media and +0.74 V in alkaline media versus NHE using thermodynamic cycles. The kinetics of electroreduction of the two disinfectants was studied using an Au rotating disk electrode. The exchange current densities estimated from Koutecky-Levich plots were 8.2 x 10(-5) and 4.1 x 10(-5) A/cm2, and by low overpotential experiments were 7.5 +/- 0.3 x 10(-5) and 3.7 +/- 0.4 x 10(-5) A/cm2 for free chlorine and NH2Cl, respectively. The rate constantforthe electrochemical reduction of free chlorine at equilibrium is approximately twice as large as that for the reduction of NH2Cl. Equilibrium potential measurements show that free chlorine will oxidize Pb to PbO2 above pH 1.7, whereas NH2Cl will oxidize Pb to PbO2 only above about pH 9.5, if the total dissolved inorganic carbon (DIC) is 18 ppm. Hence, NH2Cl is not capable of producing a passivating PbO2 layer on Pb, and could lead to elevated levels of dissolved Pb in drinking water.     

活性艳蓝B-RV的电化学无盐染色

探讨了活性艳蓝B-RV的电化学无盐染色工艺,分析了电极材料、外加电压、通电时间、初染温度等因素对染色效果的影响。试验结果表明,活性艳蓝B-RV上染棉织物的最佳染色工艺条件为:外加电压5 V(阳极为银-氯化银电极,阴极为铂电极),初染温度为60℃,上染阶段通电时间25 min,固色阶段通电时间35 min。活性艳蓝在电化学条件下无盐染色比传统染色织物的K/S值高,其匀染性、染色牢度与传统染色基本一致。     

番红花红O修饰铅笔芯电极测定水果酸度

在含番红花红O的磷酸盐缓冲溶液(phosphate buffered salines,PBS)中,采用循环伏安法在预处理过的铅笔芯电极表面生成聚番红花红O薄膜,考察溶液的pH值、扫描电位范围对修饰过程的影响。在－1.0～0.0V(vs SCE)的扫描电位范围和酸性介质中形成的薄膜,在空白PBS中具有较高电活性和稳定性,并且在pH1.5～7.5之间,阳极伏安峰电位与pH值有良好的线性关系。利用这种关系测定橙子和西红柿活体及果汁的酸度取得满意结果。     

CTMP模拟废水在铂电极上循环伏安特性的研究

为探索电化学法脱除桉木CTMP废水色度的机理，以鞣酸模拟CTMP废水作为研究对象，自行设计组装了循环伏安系统，考察了鞣酸在铂电极上的循环伏安特性。结果表明：在pH=4．0的柠檬酸钠-盐酸缓冲溶液中出现-灵敏的氧化峰，峰电位为-1．1V左右；随着鞣酸浓度的增加，峰电位开始逐渐增大，到一定浓度后略有下降，最后基本达到稳定值，而对于峰电流密度，则是随着鞣酸浓度的增加而不断增大；在铂电极上进行的鞣酸缓冲溶液体系的电化学氧化，同时涉及扩散和吸附两种过程；在鞣酸的结构式中，苯环上的取代基为-OH，其Hammet常数为负值，根据Hammet常数理论，推测鞣酸发生的是电化学氧化反应，与实验结果相一致。     

Dual electrodes oxidation of dye wastewater with gas diffusion cathode

The high energy cost of an electrochemical method is the fatal drawback that hinders its large scale application in wastewater treatment. In traditional single-chamber electrolysis cell, only direct oxidation at an anode exists. Although a small amount of hydrogen peroxide is produced at the cathode by reduction, it is transferred to the anode and destroyed there without adding much benefit to organic decomposition. A two-chamber electrolytic cell, connected with an electrolyte bridge, was developed in this work. In this new reactor, direct oxidation at anode and indirect oxidation by hydrogen peroxide at cathode can occur simultaneously. Therefore "dual electrodes oxidation" in one electrochemical reactor was achieved successfully. Compared to a traditional one cell reactor, this reactor cuts the energy cost by 50%, and thus might lead to reconsideration of the electrochemical role in wastewater treatment. A Pt/C gas diffusion electrode (GDE) is fabricated and used as a cathode fed with oxygen-containing gases to produce hydrogen peroxide. When purified air diffuses through the active layer on the GDE, oxygen is reduced to hydrogen peroxide with a high yield to decompose organics. It has been found that the direct oxidation process at an anodic zone is slightly affected by factors such as pH variation, Fe(II) existence and aeration, while indirect oxidation at the cathodic zone is strongly affected. Dye used as a model pollutant was oxidized into small organic acids in both anode and cathode regions in this electrolytic reactor. GC-MS and IR spectrum were employed to analyze the intermediates formed during the degradation. Twenty intermediates have been detected, including 14 esters, 3 acids and 3 compounds with NO2 or N-OH groups. Thereafter, the degradation pathways of dye Acid Red B are proposed.     

Determination of chlorine ions in raw milk by pulsed amperometric detection in a flow injection system

Chloride ion concentration in milk was determined by pulsed amperometric detection in a flow injection system. Results showed that the Au electrode lost 3 electrons at 1.10 V and formed chloroaurate ions (AuCl₄^?) by combining with chloride ions, after which AuCl₄^? was partly reduced to Au at 0.6 V. Based on the electrochemical process, a triple waveform with detection potential of 1.15 V, detection time of 150 ms, oxidation potential of 1.4 V, oxidation time of 550 ms, reduction potential of 0 V, and reduction time of 400 ms was applied to the Au electrode for detecting chloride ion concentration in milk. The approach is rapid and automatic and features a detection limit of 0.005 g/L. The relative standard deviation obtained by 60 repetitive injections reached 1.48% at 2 g/L of NaCl. The method developed using the Au electrode without modification was used to analyze the chloride ion concentration in raw milk without preprocessing. The method showed good agreement with potentiometric titration.     

Oxidative transformation of triclosan and chlorophene by manganese oxides

The antibacterial agents triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) and chlorophene (4-chloro-2-(phenylmethyl)phenol) show similar susceptibility to rapid oxidation by manganese oxides (delta-MnO2 and MnOOH) yielding Mn(II) ions. Both the initial reaction rate and adsorption of triclosan to oxide surfaces increase as pH decreases. The reactions are first-order with respect to the antibacterial agent and MnO2. The apparent reaction orders to H+ were determined to be 0.46 +/- 0.03 and 0.50 +/- 0.03 for triclosan and chlorophene, respectively. Dissolved metal ions (Mn(II), Zn(II), and Ca(II)) and natural organic matter decrease the reaction rate by competitively adsorbing and reacting with MnO2. Product identification indicates that triclosan and chlorophene oxidation occurs at their phenol moieties and yields primarily coupling and p-(hydro)quinone products. A trace amount of 2,4-dichlorophenol is also produced in triclosan oxidation, suggesting bond-breaking of the ether linkage. The experimental results support the mechanism that after formation of a surface precursor complex of the antibacterial agent and the surface-bound Mn(IV), triclosan and chlorophene are oxidized to phenoxy radicals followed by radical coupling and further oxidation to form the end products. Compared to several structurally related substituted phenols (i.e., 2-methyl-4-chlorophenol, 2,4-dichlorophenol, 3-chlorophenol, and phenol), triclosan and chlorophene exhibit comparable or higher reactivities toward oxidation by manganese oxides. The higher reactivities are likely affected by factors including electronic and steric effects of substituents and compound hydrophobicity. Once released into the environment, partitioning of triclosan and chlorophene to soils and sediments is expected because of their relatively hydrophobic nature. Results of this study indicate that manganese oxides in soils will facilitate transformation of these antibacterial agents.     

Electrochemical treatment of 2,4,6-trinitrotoluene and related compounds

This work involves electrolysis of nitrotoluene congeners, which are persistent pollutants that enter the environment as a consequence of their manufacture and use as explosives. Reduction to aminotoluenes occurred with high current efficiency at a variety of cathodes, at potentials -0.5 to -1 V vs SCE. The products were formed in high chemical yield and with excellent mass balance. Preliminary experiments were also carried out to find methods of removing the electrolysis products from solution by oxidative oligomerization. The most satisfactory method was partial reoxidation at a Ti/IrO2 anode, suggesting an overall remediation technology in which reduction is followed by reoxidation of the spent catholyte in the anode compartment of the same electrolytic cell.     

Removal of the pesticide methamidophos from aqueous solutions by electrooxidation using Pb/PbO2, Ti/SnO2, and Si/BDD electrodes

The anodic oxidation of methamidophos (MMD), a highly toxic pesticide used worldwide, was studied in a sodium sulfate aqueous solution on Pb/PbO2, Ti/SnO2, and Si/BDD (boron doped diamond) electrodes at 30 degrees C. Under galvanostatic conditions, it was observed thatthe performance of the electrode material is influenced by pH and current density as shown by HPLC and ATR-FTIR analysis of MMD and its oxidation products along the electrolysis. It was found that MMD degradation using Pb/PbO2 in acid media (pH 2.0 and 5.6) generates formaldehyde asthe main product of the reaction giving evidence of an indirect mineralization mechanism. Under the same conditions, Ti/SnO2 showed poor formaldehyde production compared to the Pb/PbO2 electrode. On Si/BDD electrodes formaldehyde production was not observed, instead the ATR-FTIR results showed the formation of phosphate as the reaction progressed suggesting a complete MMD mineralization on this electrode. In addition, HPLC results showed that the electrode efficiency is also dependent on the applied current density. This current density influence is remarkably clear on the Si/BDD electrodes where it was evident that the most efficient current density toward a complete MMD mineralization was reached with the application of 50 mA/cm2.